MXenes, a class of two-dimensional transition metal carbides and nitrides, have garnered significant attention in recent years as promising materials for energy-related applications. Their unique combination of properties, including exceptional electronic conductivity, impressive ionic conductivity, a large specific surface area, and highly tunable surface chemistries, make them highly versatile for a wide range of advanced energy technologies. These properties not only enhance energy storage and conversion efficiency but also allow for precise control over their performance characteristics by tailoring their preparation and material characteristics.

In this presentation, I will highlight the latest advancements from our group that leverage the exceptional properties of MXenes to develop innovative energy harvesting and storage devices. Our research explores a broad spectrum of applications, demonstrating the versatility of MXenes in addressing challenges across various domains of energy technology.

Specifically, I will discuss the integration of MXenes into commercial-scale silicon heterojunction solar cells, where we show they can replace expensive silver back contacts. I will also present our work on MXene use in salinity gradient energy harvesters, which exploit ionic conductivity and surface functionality for efficient energy extraction from saltwater gradients. Furthermore, our work in thermoelectric nanogenerators showcases how MXenes contribute to converting waste heat into electrical energy by optimizing thermal and electronic transport properties.

Additionally, MXenes have been demonstrator in triboelectric nanogenerators, where their mechanical robustness and electronic conductivity enable efficient energy harvesting from mechanical motion. Their role in ultrasound energy devices will also be highlighted, with a focus on their unique ability to convert acoustic energy into usable electrical energy.

Finally, I will present our advancements in integrating MXenes into microsupercapacitors, which combine high energy density and power density for next-generation compact energy storage solutions. These integrated devices demonstrate the ability to pair energy harvesting with storage, paving the way for self-powered electronic systems.

This comprehensive exploration underscores the transformative potential of MXenes in energy applications and highlights their role as key enablers of sustainable and efficient energy technologies. Through the examples presented, I aim to showcase the versatility and impact of MXenes in shaping the future of energy harvesting and storage devices.

The field of battery research continually seeks to improve energy storage capabilities while addressing sustainability concerns. This applies in particular to the exploration and development of novel materials, such as the promising material group of MXenes. MXenes, known for their two-dimensional morphology, vast chemical composition range, and excellent electrical conductivity, require the synergistic integration of conversion or alloying materials to achieve high charge storage capacities.

The presentation highlights the development of high-performance sodium-ion batteries using MXene / antimony hybrid electrodes. By carefully optimizing synthesis parameters and material design strategies, researchers achieved an optimized electrode composition. This hybrid material exhibited a high reversible capacity of 450 mAh/g at 0.1 A/g, along with excellent cycling stability and rate capability. We also explore the combination of MXenes and SnO₂, a conversion material, for enhanced lithium-ion battery performance of over 500 mAh/g for 700 cycles at 0.1 A/g. The researchers synthesized a nanocomposite consisting of a 50/50 mixture of SnO₂ and MXene. The resulting nanocomposite demonstrated high-capacity retention over numerous cycles and excellent rate capability.

Additionally, we demonstrate MXene electrode recycling and upcycling. With binder- and additive-free MXene paper electrodes, we show the significance of finding sustainable and efficient approaches to recycle spent batteries. Researchers investigated the use of annealed delaminated MXene electrodes, obtained through vacuum-assisted filtration and annealing processes, in lithium-ion and sodium-ion batteries. The electrodes exhibited good electrochemical performance and were easily recovered through direct recycling processes, achieving high capacity recovery rates. Moreover, the cycled MXene electrodes could be transformed into TiO₂/C hybrids with adjustable carbon content, providing opportunities for their utilization in various battery and electrocatalysis applications.

Collectively, we emphasize the potential of MXenes and MXene hybrid materials for enhancing charge storage capabilities in batteries. They also underline the significance of developing sustainable recycling and upcycling approaches for MXene electrodes, contributing to the overall advancement of battery technology.

The oxygen evolution reaction (OER) is critical for water electrolysis, a key technology for the production of green hydrogen. While non-noble metal oxides show promise as OER catalysts, their application is limited by poor conductivity and stability.[1] This study demonstrates the functionalization of CuCo based hydroxides with V₂CT_x MXene to address these challenges, resulting in significantly improved OER performance in alkaline media.[2]
The CuCo@V₂CT_x composites were synthesized via a hydrothermal process, with varying MXene content (1%, 10%, 25%, 50%). The optimized CC50 catalyst achieved a lower overpotential and superior stability, outperforming the pure Co and CuCo hydroxides. Post-mortem analyses, including XPS and ICP-OES, revealed that the MXene not only enhanced hydrophilicity and charge transfer properties but also reduced Cu leaching during OER, improving the overall stability.
Characterization using SEM/TEM/EDX, XRD, and XPS confirmed that MXene mitigates aggregation and stabilizes CuCo on the electrode surface. Furthermore, the preferential leaching of V₂CT_x over Cu during stability tests preserved a higher concentration of active CuCo species, contributing to long-term catalytic performance. This work highlights the potential of MXene based hybrids as high-performance electrocatalysts for sustainable energy applications.

The future of electronics, wearables, healthcare, and smart environments is being shaped by the integration of IoT (Internet of Things) with flexible technologies. A plethora of printed electronic components, including OLED displays, OPVs, TFTs, antennas, and diodes, among others, have already been developed [1], [2], [3]. These can then be integrated into technological platforms with a multitude of applications. When building such platforms, it is essential to address the question of energy autonomy. For flexible electronics, energy is normally harvested from the environment (solar energy, heat, movement, etc.) and stored in supercapacitors (SC) [4] ⁴. These energy storage devices are the optimal choice for printed and wearable electronics. They offer a long shelf life, seamless integration, and rapid charge and discharge capabilities. From many available options, MXenes have been regarded a good choice for SC manufacturing thanks to their optimal chemical properties. MXenes have a hydrophilic surface due to the presence of hydroxyl, oxygen, or fluorine functional groups (-OH, =O, -F), high electrical conductivity up to ~10,000 S/cm, especially for Ti₃C₂Tx, high flexibility, high capacitance (~1500 F/cm³ for Ti₃C₂Tx), fast ion transport, chemical stability, and more. As such, for the last couple of years, there has been a tremendous focus on MXene synthesis and implementation as SC electrodes [5], [6], [7].

This presentation will prove the vital importance of MXenes in the fabrication of SC electrodes for printed and flexible electronics. It will also show how they compare to other promising technologies and highlight their advantages and shortcomings. [8], [9]. It will also be discussed some strategies for MXene-based SC development to meet different applications requirements, such as voltage window, usable area and stability. However, the full potential of MXenes will only be exploited once the significant hurdles that currently stand in the way have been overcome, namely long-term stability and green synthesis. Nevertheless, due to their rich chemistry and optimal properties for electrochemical energy storage, MXenes are poised to play a significant role on powering up future and printed and flexible electronics.

Previous attempts to make monolayer gold has to date been limited to a few atomic layers stabilized on or inside another material. Challenges originate from the metal bonding, which is the reason for gold’s tendency to form 3D shapes by vapor-phase synthesis or precipitation from solutions.

This presentation will show the exfoliation of single-atom-thick 2D gold (named goldene) by wet-chemically etching away Ti₃C₂ layers from Ti₃AuC₂. The latter is a nano-laminated MAX-phase, formed by substituting the Si layer in Ti₃SiC₂ with Au, and the exchange substitution is an example of non-van der Waals intercalation. The process is also shown to be tunable, facilitating formation of both double and triple layers of Au inside the MAX phase, confirmed by theoretical predictions of phase stability. Evidence for corresponding few-layer goldene is also presented.

Goldene comprising one layer of gold display roughly 3% in-plane (111) lattice contraction compared to bulk gold, shown by scanning transmission electron microscopy. A tendency for curling and agglomeration of goldene is also observed, but surfactants are used to hinder the goldene sheets from coalescing with each other. Notably, ab initio molecular dynamics simulations suggest that flat atomic layers are inherently stable. Prospects for preparing goldene from a series of MAX phases - both carbides and nitrides – in thin film as well as powder form, will be presented. Proposed applications for goldene include sensors and catalyst for water splitting during solar energy harvesting.

Single-molecule detection represents the highest sensitivity in analytical techniques, enabling precise studies of individual molecular events. Methods based on single-molecule fluorescence energy transfer offer nanoscale distance measurements with significant implications for structural biology, biophysics, and material-biomolecule interfaces. Förster Resonance Energy Transfer (FRET) operates in the 3–10 nm range, typically involving two organic fluorophores as energy donor and acceptor. Graphene-based energy transfer (GET) extends this range to 10–40 nm, with a fluorophore as the energy donor and graphene acting as a broadband, unbleachable energy acceptor. FRET has been used predominantly to study protein conformational changes, but its measurements are often qualitative due to challenges in resolving nanometer-scale distances accurately. GET is a more straightforward quantitative method that enables precise z-localization of fluorophores. Notably, it has recently enabled real-time monitoring of DNA-protein interactions at the structural level [1]. However, graphene's hydrophobic nature and the strong influence of thickness on fluorescence lifetime measurements limit its biocompatibility to non-DNA systems and overall reproducibility.

Our research focuses on titanium carbide (Ti₃C₂Tₓ) MXene as a complementary, powerful energy transfer tool. MXenes possess unique advantages for studying biological assemblies that require hydrophilic surfaces, combining FRET-like short-distance sensitivity (1–10 nm) with GET's quantitative protocol, while offering unique material advantages such as hydrophilicity, biocompatibility, and thickness-independent energy transfer efficiencies.

This research line began by exploring MXene-DNA interactions with ensemble fluorescence spectroscopy measurements and molecular dynamics simulations. The interaction between MXene and DNA was found to be driven by salt bridges, coinciding with prior reports [2], with ssDNA and dsDNA lying horizontally on the surface while maintaining their native structure, approximately 1 and 1.3 nm away from the surface, respectively. In real-time hybridization experiments, we observed a fluorescence increase as ssDNA converted to dsDNA on the surface, suggesting that MXenes possess nanoscale sensitivity to sub-nanometer changes in the fluorophore position [3].

Next, we investigated MXenes’ fluorescence quenching mechanism and distance dependency of the energy transfer with single-molecule fluorescence microscopy and DNA origami nanopositioners using MXene thin films on glass. We positioned a single dye (ATTO 542) at defined distances from the surface (1–8 nm) via glycine-immobilized DNA origami nanostructures on MXene surfaces. Fluorescence quenching was observed between 1 to 8 nm, following a cubic distance dependence, consistent with the Förster mechanism observed in transparent conductors at the bulk level. These findings not only supported the hypothesis of MXenes' sub-nanometer sensitivity but also established them as hydrophilic, short-distance spectroscopic nanorulers uniquely positioned to operate in a distance regime inaccessible to GET. Additionally, the energy transfer efficiency was nearly independent of material thickness, enhancing robustness for sensing applications. 

Finally, we demonstrated the utility of MXene's sensitivity, robustness and hydrophilic, salt-driven interactions for leaflet-resolved, single-molecule biosensing of fluorescently-labeled, 5-nm thick supported lipid bilayers (SLBs) as model cell membranes, directly fused on the MXene surface [4]. Similar to typical SLBs formed on mica surfaces—where a thin hydration layer separates the bilayer from the surface to maintain biomimetic fluidity—MXenes also supported biomimetic SLBs, offering an advantage over other metallic surfaces and graphene. At the single-molecule level, we determined the SLB thickness by independently resolving each leaflet of the bilayer and the hydration layer separating it from the MXene surface. This capability to discern such fine structures highlights MXene substrates as uniquely suited to studying lipid-protein interactions, membrane organization, and dynamic hydration phenomena, potentially offering new insights into lipid biology and biomembrane research.

The surface chemistry, structure, and morphology of MXenes play a critical role in their applications. Various methods of covalent functionalization have been reported, demonstrating significant improvements over pristine MXenes terminated with hydroxyl and fluorine functional groups. Furthermore, the direct conversion of MXenes into various chalcogenides, while retaining their original structure, can significantly enhance properties such as hydrogen and oxygen evolution overpotentials, as well as the capacitance of the material for electrochemical energy storage. Chemical functionalization, such as the introduction of charged zwitterionic compounds and defect engineering, has been shown to significantly improve the performance of MXenes in energy storage applications. Treating MXenes with different reagents, such as elemental chalcogens or pnictogens, effectively modifies their surface functionalization and can lead to the formation of composite materials. These composites, consisting of functionalized MXenes and transition metal dichalcogenides, exhibit significant enhancements in capacitance for supercapacitors and lithium-ion batteries. By leveraging specific chemical transformations, MXenes containing vanadium, niobium, and molybdenum can be converted into chalcogenides or vanadates/niobates. These processes pave the way for the development of advanced materials with promising applications in photocatalysis, supercapacitors, and batteries.

MXenes dots as photocatalysts

Ruben Ramirez Grau¹, María Cabrero-Antonino¹, Hermenegildo García¹*, Ana Primo¹*¹Instituto de Tecnología Química, Consejo Superior de Investigaciones científicas-Universitat Politècnica de Valencia, Avda. de los Naranjos s/n, 46022, Valencia, Spain

Introduction

MXenes are 2D nanomaterials constituted by alternating one-atom thick layers of an early transition metal of the 3, 4, 5 or 6 groups of the Periodic Table (denoted as “M”) and a carbide, nitride or carbonitride layer (denoted as “X”) and have a general formula of M_n+1X_n.¹ We recently reported that MXene dots (MDs) prepared by liquid-phase laser ablation of the corresponding MAX phase exhibit intrinsic photocatalytic hydrogen generation activity in the absence of any other photoresponsive component.² Decrease of lateral size of MXenes to a few nanometers results in the operation of quantum confinement effects reflected in optical absorption and photoluminescence of MDs, these MDs exhibiting photocatalytic activity. Theoretical DFT calculations for Ti₃C₂ models indicates that the bandgap depends on the diameter of the MDs and on the nature of the surface functional groups. The compositional and structural versatility of MXenes will allow band engineering to align the energy values of the valence and conduction band to the values required to promote a given chemical reaction.

Continuing with this line of research, it is of interest to further explore the photocatalytic activity of these MDs. Specifically, it would be important to determine whether or not MDs promote the photocatalytic CO₂ reduction, the efficiency of the process and the products formed. Herein it is reported that MDs are active in the photocatalytic CO₂ reduction using H₂ as electron and proton donor.

Materials and Methods

3 mg of MAX phase were suspended in 3 ml of MilliQ water and the suspension was submitted to ultrasounds in order to prepare a homogenous dispersion. Then, the system was irradiated for 3 h using the second harmonic of a Q switched Nd:YAG laser (Quantel Brilliant, 532 nm, 5 mJ/pulse, 5 ns fwhm) operating at 1 Hz. Finally, the resultant material was centrifuged for 4 h at 4000 rpm and, then, 1 h more at 13 000 rpm to isolate from the bulk MAX and other phases that sediment in the process the small MXene QD that remains in the supernatant.

Results and Discussion

Four MDs, namely Ti₃C₂, Ti₂C, V₂C and Nb₂C were prepared from the corresponding Al MAX phases by 522 nm laser ablation in aqueous suspension, as previously reported.² After preparation, the four MD samples were characterized by different techniques, including AFM and transmission optical microscopy. Table 1 lists the corresponding average thickness and average particle lateral size values for each sample. The activity of the four MD samples was evaluated for the photocatalytic CO₂ hydrogenation under UV-Vis irradiation at 200 ^oC at 1 bar pressure, using a H₂/CO₂ ratio of 1/3. For the four samples, evolution of CO and methane as the only products was observed in different proportions. Fig. 1 shows the temporal product evolution upon irradiation of each MD, while Table 1 indicates the CO and methane production rates determined from these plots.

Significance

Photocatalytic CO₂ reduction is a clean technology that converts CO₂ into high-value-added products. The interest of the present study is to show that, MXenes by themselves, can exhibit an intrinsic photocatalytic activity that can be modulated depending on the composition. Since MXenes allow a wide range of compositions, including bimetallic solid solutions and a wide range of surface functional groups, there is still much room for improvement in the intrinsic photocatalytic efficiency by adjusting these parameters and also to achieve photocatalytic stability.

The pseudocapacitive behavior of Ti₃C₂T_x MXenes promises high power and energy densities thanks to redox reactions occurring during the (de-)protonation of the MXene surface in acidic electrolyte. Nevertheless, local electrochemical processes occurring at the MXene-electrolyte interface and the associated changes of the MXene surface chemistry are currently largely unexplored. To this aim, soft X-ray spectroscopies are particularly relevant as they enable the selective characterization of either the electrolyte or the material of interest thanks to their element specificity.¹ Furthermore, the high spatial resolution (<30 nm) offered by X-ray Microscopy can provide precious information about local inhomogeneities at the nanoscale,^2,3 enabling the characterization of single MXene flakes.

In this talk, I will introduce X-ray spectromicroscopy for monitoring the surface chemistry of Ti₃C₂T_x MXenes as well as intercalated species at the single flake level. In situ cells for the characterization of MXenes at controlled temperature or in liquid will be introduced. The effect of proton and alkali cations intercalation on the electronic structure of Ti and O atoms in the MXene will be discussed, as well as the electronic signature of water confined in the MXene interlayer. Perspectives towards correlative optical spectromicroscopy techniques will also be discussed.

MXenes are highly conductive materials with a high surface area, offering potential as promising catalyst supports in proton exchange membrane fuel cells (PEMFCs), a technology recognized for sustainable energy conversion. This study centers on a comparative analysis of various platinum (Pt) loadings uniformly distributed across MXene sheets to enhance catalytic performance. The synthesized materials were comprehensively characterized using X-ray diffraction (XRD), X-Ray Photoelectron Spectrscopy, scanning electron microscopy (SEM) and Raman spectroscopy to investigate their structural attributes and morphology and functional groups, providing insights into their stability and interaction with Pt particles. Electrochemical tests were conducted in rotating disc electrode (RDE) and half-cell setup to assess the efficiency of the catalysts in oxygen reduction reaction (ORR), a crucial step in PEMFC performance due to its role in limiting cell output. Results reveal that Pt particles on MXenes not only function effectively as ORR electrocatalysts but also improve reaction kinetics, positioning MXene-supported Pt catalysts as a promising alternative for PEMFC applications.

MXenes – transition metal-based carbides and (carbo)nitrides with the general chemical composition M_n+1X_nT_x (M = early-to-mid transition metals, X = C and/or N, T_x = surface groups, n = 1-4) are an incredibly fascinating class of 2D materials that have left almost no potential application area untouched. As much research as is dedicated to exploring their unique properties, for example in the context of biomedicine, catalysis and energy storage, especially of Ti-MXenes, as little focus is dedicated to non-Ti-MXenes as well as their synthesis science.

In this talk, I will discuss the synthesis of different V-MXenes derived from their MAX phase siblings. The preparation of the precursor MAX phases is not trivial as shown for MAX phase examples V₄AlC₃ and (V/Mo)₅AlC₄. MAX phases with minimal amounts of side phases as well as knowledge of their chemical composition are key to obtaining high-quality MXenes that allow for meaningful discussions of their properties. These aspects will be covered during my discussion of the “higher n” MXenes V₄C₃T_x and (V/Mo)₅C₄T_x including discussion of their electrocatalytic performance in the hydrogen evolution reaction (HER). Besides, I will highlight key synthetic chemistries during the exfoliation of V₂AlC as well as its Mo-substituted analogs and show how the catalytic properties depend on the V/Mo ratio.

We take advantage of diverse synthesis and exfoliation tools ranging from conventional to microwave heating and aqueous acid as well as Lewis acid (molten salt) etching. All materials are carefully characterized by diffraction (synchrotron and lab X-ray), microscopy and spectroscopy (lab and hard-X-ray photoelectron spectroscopy) techniques.

Producing hydrogen (H₂) through electrocatalytic water splitting in an electrolyzer offers a clean and sustainable pathway to generate an eco-friendly fuel and energy carrier. The oxygen evolution reaction (OER) plays a critical role in this process, though its efficiency is bottlenecked by sluggish kinetics [1-3]. Noble-metal-based catalysts, particularly IrO₂ and RuO₂, are the state-of-the-art OER electrocatalysts available today due to their excellent activity but are hindered by high costs and instability issues. In particular, a major obstacle to the large-scale application of Ru lies in its tendency to leach in alkaline media [4, 5].

To address these limitations, extensive research has focused on improving the stability of noble-metal-based catalysts, reducing noble metal usage while retaining high performance, and exploring non-noble metal alternatives with strong OER activity. Transition-metal-based catalysts are promising, affordable alternatives as they are stable in alkaline conditions and have low OER potentials [6, 7]. However, their limited conductivity restricts their catalytic performance in OER applications. To overcome both the instability issues and the OER activity, we propose using MXenes, a rapidly advancing family of 2D transition metal carbides and nitrides, as conductive supports to form NiRu@Ti₃C₂T_x hybrids [8-12]. While many studies have explored MXene-based materials for applications in water splitting, OER remains relatively less-explored compared to the hydrogen evolution reaction (HER). Moreover, there is limited information on how MXenes influence the stability of metal/oxide during alkaline OER.

In this study, the potential of MXenes to enhance the stability of Ru-based catalysts, which are known for their substantial dissolution in alkaline media during OER, was investigated. Here, a bimetallic NiRu compound was synthesized and incorporated onto the Ti₃C₂T_x MXene surface at varying concentrations (1%-25%) using a facile hydrothermal method. The resulting NiRu@Ti₃C₂T_x composites were tested for OER activity in 1 M KOH to examine the impact of Ti₃C₂T_x content on Ru dissolution and overall catalytic performance. After incorporating Ru into a stable Ni-based environment and functionalizing Ti₃C₂ with NiRu, the composites showed reduced Ru leaching and increased OER activity compared to pure Ru. Higher Ti₃C₂T_x content further stabilized Ru. These results highlight the positive impact of Ti₃C₂T_x functionalization on the stability and efficiency of Ru-based OER catalysts.

Two-dimensional (2D) materials have attracted significant attention for their high surface area, mechanical flexibility, and tunable electronic properties, enabling applications in energy storage, flexible electronics, optoelectronics, and biomedicine. The discovery of graphene's exceptional properties spurred interest in exfoliating other 2D materials from bulk crystals, uncovering diverse chemical structures and functionalities. Electrochemical exfoliation (ECE) offers a promising approach for mass-producing graphene and other 2D materials due to its mild conditions, fast processing, simplicity, and high yield. While ECE of layered van der Waals (L-vdW) crystals has advanced, research on layered non-van der Waals (L-NvdW) materials is still in its infancy. This work investigates ECE for producing 2D nanoplatelets from L-NvdW crystals, comparing exfoliation techniques for L-vdW and L-NvdW materials and reviewing recent progress in ECE methods for L-NvdW crystals. Key topics include selective extraction of 'M' and 'A' layers from MAX phases, decalcification of Zintl phases, and oxide delocalization from metal oxides. We also present our latest research on the electrochemical exfoliation of layered TM2SC-type MAX phases.

The growing global demand for sustainable energy has heightened the need to develop efficient electrocatalysts for energy conversion processes, particularly the oxygen evolution reaction (OER), which is a key part of water splitting for green hydrogen production. Although a wide range of catalysts has been investigated for use in electrolyser devices, challenges such as cost, conductivity, and stability continue to drive ongoing research in this area.[1]

Transition metal oxide (TMO) materials, despite their great potential as OER catalysts, suffer from limited conductivity, which hampers effective charge transfer during electrochemical processes, and can lead to deactivation due to structural transformations during the OER.MXenes, with their exceptional surface area and conductivity, are promising supports for enhancing the electrocatalytic performance of TMO-based OER catalysts.[2] However, MXenes are susceptible to oxidation under applied potentials, which can alter their structure and properties. By synergistic combination of TMOs with MXenes, a highly efficient OER catalyst could be developed, combining the enhanced conductivity, hydrophilicity, and increased surface area of MXenes with the active OER sites of TMOs.[3] While there have been numerous successful attempts in producing highly performing TMO/MXene composites, the overwhelming number of such reported catalysts is based on the first found and best known Ti₃C₂T_x MXene.[4] This leaves a wide range of potentially highly performing OER catalysts based on MXenes other than Ti₃C₂T_x yet to explore.

In our recent investigations we found that coprecipitation of CoFe layered double hydroxides (LDH) with V₂CT_x MXene at various weight percentages resulted in CoFe/ V₂CT_x composites that outperformed the separate components and physically mixed components as OER catalysts. Furthermore, we could show that the presence of V₂CT_x during the synthesis promotes the formation of a highly active CoFe-LDH phase as opposed to the pure CoFe sample. We further investigated the materials’ oxidation states under OER conditions via synchrotron based in-situ XAS to detect the catalytically active species for the OER.

These findings demonstrate the great potential of TMO/ V₂CT_x composites as OER electrocatalysts and are a step towards understanding the reasons for their improved catalytic activity.

As the world increasingly turns towards sustainable energy solutions, the efficient storage and transport of hydrogen has become critical. Ti₃C₂ MXenes, with their unique 2D structure and exceptional properties, are at the forefront of this technological revolution. For Ti₃C₂ MXene as energy storage material using hydrogen it is crucial to understand hydrogen bonding and diffusion, since unexpected properties may arise in terms of interaction with lattice atoms.

In this paper, it is shown that the chemical bonding of hydrogen atoms and molecules extends far beyond the simple picture of covalent, ionic and multicenter bonds. Density functional theory was used for the calculations. The Ti₃C₂ layers and surfaces were modelled in a slab geometry. The properties of H and H₂ were further analyzed by calculating the vibrational eigenmodes and their intensities by employing density-functional perturbation theory.

The results clearly show that in Ti₃C₂ hydrogen atoms and H₂ molecules form multicenter bonds. On the surface and between two Ti₃C₂ sheets, this bonding is restricted to the formation of Ti−H bonds. However, at interstitial sites, both H and H₂ form multicenter bonds. This includes the nearest neighbor Ti atoms and also C atoms. Notably, C−H bonds involve the formation of s−p hybrid orbitals. For H₂ molecules the formation of multicenter bonds results in an increase in bond length to 2.07 Å on the surface and to 1.85 Å at the interstitial site. When H₂ is accommodated between two Ti₃C₂ sheets the molecule dissociates. The vibrational eigenmodes for all complexes have been calculated and vibrational frequencies ranging from 890 to 1610 cm⁻¹ were obtained. This indicates that the hydrogen multicenter bonds are stable.

For efficient hydrogen storage and release the understanding of H transport in MXenes is vital for optimizing their performance in applications. Hence, the diffusion properties of H in Ti₃C₂ MXene were determined from ab-initio calculations. For this purpose, migration barriers, hopping frequencies, vacancy formation enthalpies, and the vibrational entropy were calculated to determine the temperature dependent diffusion coefficients. The data reveal that hydrogen diffusion predominantly occurs via interstitial sites, while vacancy-mediated diffusion plays a negligible role.

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MXenes having Metal-surface functional groups as well as structural defects offer much potential as solid catalysts, similarly as it happens with other metal carbides/nitrides and metal oxides. In addition, MXenes are also suitable supports for single atom and small metal clusters. The presentation will show that NH₃-thermoprogrammed desorption and pyridine adsorption/desorption monitored by IR spectroscopy are suitable techniques to measure the acidity of these materials. It has been found that the actual density of Brönsted and Lewis acid sites and their strength depends on the MXene type, preparation procedure and post-synthetic treatments. MXenes have been found to catalyze a series of organic reactions, including hydrocarbon oxidation, electrophilic additions to C-C triple and double bonds and guanylation reactions among other. In many of these cases, the turnover frequencies achieved by MXenes are among the highest reported for these reactions using solid catalysts. This is the case of 1-butanamine addition to 1-hexyne for which turnover frequencies over 10⁴ h^-1 have been measured. This illustrates the potential that MXenes can offer in the field.

Electrolytic water splitting is a clean and sustainable way of producing hydrogen gas, which has huge potential as a fuel source. There is a vast range of materials that can replace expensive state-of-the-art catalysts, and Transition metal oxides (TMOs)-based catalysts are currently under consideration due to their cost-efficient nature and abundance. However, their poor conductivity presents a major challenge. To address this issue, MXenes have emerged as a promising option to be integrated with TMOs thanks to numerous beneficial properties, such as high conductivity, hydrophilicity, and tunneling capacity, which makes them an excellent choice as a mechanically stable and conductive material [1]. To enhance the electrochemical activity and stability of Ti₃C₂T_x MXenes, the control of surface functionalization and area is paramount. In this regard, this study utilizes HF in situ generation to remove Al-elements for the direct production of delaminated Ti₃C₂T_x, and, consequently, exposing their high surface area. In this study, Ni-based MXene composites were fabricated with varying MXene content to investigate the effect of the MXene on the OER. The findings of this study provide a comprehensive understanding of the Ti3C2Tx MXenes influence on OER activity in terms of Ni dissolution, and electro-mechanic-chemical-stability, thus providing valuable insights for their implementation and the importance of MXenes content optimization in hybrid electrocatalysts for OER.

Renewable energy production is inherently intermittent, necessitating large-scale implementation to enhance energy storage capacity, which presently accounts for less than 1% of global electrical energy production. The pursuit of greener, more affordable, and safer rechargeable batteries is currently recognized as strategically important in advancing electrochemical energy storage technology, addressing environmental concerns and establishing a sustainable energy economy. Li-ion batteries (LIBs) and Na-ion batteries (NIBs) play a crucial role as energy storage devices for electric vehicles and smart grids. It is widely recognized that a detailed analysis of an electrode reveals that each component (active material, conductive carbon, current collector, and binder) contributes to the overall battery performance. It has been demonstrated that the binder, despite its relatively low content, typically a few percent of the total composition, plays a decisive role in determining the electrode performance, which is noteworthy considering its chemical and electrochemical inactivity. In addition, the transformation from liquid- to gel-/quasi-solid or fully solid-state architectures is expected to improve safety by using low-volatile, non-flammable materials and energy density of energy storage devices by enabling the use of lithium metal anodes, particularly if constraints of low ionic conductivity, low cation transport properties and stringent processing conditions are overcome [1].

In this context, here an overview is offered of the recent developments in our laboratories on the development of innovative solutions including recycled or biosourced polymer binders/electrolytes towards the development of sustainable, safe, high-performing post-lithium batteries. These include the possibility of repurposing in batteries the recycled polyvinyl butyral (PVB) from post-consume laminated glasses (from automotive and construction) that cannot be reused in glasses because of degraded optical properties. Two strategies were pursued: either using recycled PVB as binder in the electrodes composition or transforming it into a membrane to be used as electrolyte separator [2]. In the case of PVB as binder, we investigated the electrochemical and structural properties of polymer blends of PVB with standard binders, as polyacrylic acid (PAA) and poly(vinylidene fluoride) (PVDF), demonstrating its effective use in the development of various electrodes, including hard carbon (HC) anodes, and high-energy cathodes (NMC and NVP) showing full capacities even at high C-rates and stable long-term operation at ambient temperature, which pave the way to the development of more sustainable binders/separators from waste products for next-generation, sustainable energy storage. In addition, the strategy to develop an Electrically Rechargeable Zn-Air Battery (ERZAB) ideal for mid-term storage (days/weeks) to be coupled with renewable power sources and electrolysers will be discussed. Particularly, the focus will be on the acidic side of an aqueous Gel Polymer Electrolyte (GPE) that, coupled with the basic one, will increase the battery operating potential from 1.65 V in alkaline-based electrolytes to 2.55 V and, hence, the overall device energy density from ≈ 1353 to 2091 Wh/kg. The electrolyte preparation is based on the use of natural bio-polymers, such as cellulose derivatives and low-cost, sustainable chemicals, with also the exploration of the use of redox mediators to modulate the kinetic of OER and ORR processes. Particular attention is also paid to the regulation of Zn ion conduction/transport across the interfaces by adjusting the amount of water and the polymer crosslinking density coupled with mechanistic understanding.

Overall, in all cases, preliminary results are highly encouraging and pave the way to the development of more sustainable separators and binders from waste products for safe, low-cost energy storage devices.

Rechargeable aqueous Zinc (Zn) batteries are one of the emerging beyond lithium-ion batteries that could fulfil the requirements of cost-effective, safe, and reliable large-scale storage systems. Zn metal is abundant, globally available, and non-toxic, with a promising theoretical capacity of 820 mA h/g.^[1],[2] However, the current state of separator technology for aqueous batteries presents a significant obstacle, with no efficient commercially available options. Consequently, in research laboratories, the commonly used separators include glass-fibre filters and, in some instances, cellulose filters.^[3] However, these separators are not optimized for battery applications – leading to poor compatibility with Zn anode.^[4] Thus, the development of high-performing electrolytes and separators is imperative to unlock the full potential of aqueous Zn batteries.

In this study, we successfully developed two separators based on nano-chitin and nano-cellulose fibres. These separators, with a thickness of less than 70 µm, exhibit excellent mechanical properties and strong compatibility with Zn anodes. Notably, these separators significantly enhance Zn cycling stability, demonstrating a remarkable increase from a mere 100 hours with conventional glass-fibre and cellulose filters to 1000 hours. This combined approach presents a compelling strategy for the advancement of high-voltage aqueous Zn metal batteries, marking a significant step forward in battery technology.

The rapid progress in energy storage technologies demands innovative solutions to challenges related to sustainability, cost, and performance. Aqueous zinc-based energy storage systems, such as zinc metal batteries (AZMBs) and zinc-hybrid capacitors (ZHCs), offer promising possibilities due to their inherent safety, cost-effectiveness, and scalability.[1] Nonetheless, complications like hydrogen evolution reactions, dendritic growth, and water-induced parasitic reactions are major obstacles to be overcome before these technologies can be practically employed on a large scale. The following abstract summarizes findings from three new central studies that place MCEs at the forefront in driving a new generation of research breakthroughs to overcome these challenges and improve performance in aqueous zinc systems.

The first study investigates an advanced MCE containing a combination of Zn(TFSI)₂, LiTFSI, and polyethylene glycol (PEG400) to improve the performance of Zn//LFP hybrid batteries.[2] By confining water molecules and reducing free water activity, the optimized MCE enhances the reversibility of Zn plating/stripping and significantly improves long-term cyclability. The Zn//LFP battery, in turn, showed quite high capacities of 120 mAh g⁻¹ with excellent stability-65% capacity retention after 200 cycles-whereas the self-discharge rate is reduced and parasitic reactions are suppressed compared to conventional electrolytes. These confirm the effectiveness of MCEs for solutions of major anode and cathode problems in AZMBs.

The second investigation is concerned with a Zn//V₂O₅ battery, which works out a newly developed MCE, using Zn(TFSI)₂ as the main salt.[3] The electrolyte formulation in this work enhances ionic conductivity, hence boosting ion transport properties to further ensure superior rate capability and decent cycle stability. It obtains excellent performance metrics of the Zn//V₂O₅ system, such as 78% capacity retention after 1000 cycles and an impressive reduction in self-discharge. Mitigation of free water activity hence improved the stability window, which assured reversible Zn plating/stripping and placed the MCE as a versatile strategy toward the advancement of AZMBs for practical applications.

Another study investigates the use of PEGDME-based MCE in ZHCs as means to solve such Zn anode problems but without sacrificing its practicability.[4] The advanced MCE obtained had a widened electrochemical stability window of up to 2.7 V, which reduced the water activity and hence improved anti-corrosion properties that enabled superior performance in Zn//Cu and Zn//Zn symmetric cells. The hybrid system of Zn/MCE/AC achieved energy density at 138 Wh/kg, perfect capacitance of 281 F/g, and superlative cyclability, with capacity retained up to 100% after 19,100 cycles. These results really underline the big capability of MCEs in providing high-power, long-life energy storage solutions.

Collectively, these works highlight how MCEs will be game-changing in overcoming fundamental challenges in aqueous-based zinc energy storage systems. By taking advantage of novel electrolyte chemistries to suppress parasitic reactions, enhance ionic transport, and stabilize electrode interfaces, MCEs will provide a route toward safe, efficient, and sustainable energy storage systems. This work presents an important milestone toward successful practice application of AZMBs and ZHCs and in particular provides for impactful solutions to global challenges in energy storage.

Metal-air batteries are considered a viable alternative to conventional Li-ion batteries as their air-breathing electrode configuration results in higher theoretical capacity and energy density. Moreover, zinc-air batteries (ZABs) take advantage of low cost, environmental-friendliness and safety, since they work in aqueous electrolyte [1].

However, the main issue with ZABs is the limited performance due to sluggish kinetics of oxygen reduction reaction (ORR) and oxygen evolution reaction (OER), resulting in high overpotentials and low round-trip efficiency. The implementation of electrocatalysts helps to accelerate reaction kinetics and make ZABs more competitive for electrochemical storage applications.

Among a variety of electro-catalytical materials (transition metal oxides, heteroatom-doped carbon, metal organic frameworks, etc.) manganese dioxide (MnO₂) is one of the most promising for ORR/OER [2].

In this scenario, we optimized nanostructured MnO₂-based Gas Diffusion Electrodes (MnO₂-GDEs) using different types of MnO₂ micro/nanocrystals obtained by hydrothermal synthesis varying precursors and additives (such as CTAB or ionic liquids, e.g. BMIM-BF₄). The use of additives allowed us to show a transformation in MnO₂ morphology and crystallographic structure passing from beta-MnO₂ nanorods (with a diameter of 200 nm) to alpha-MnO₂ nanowires (with a diameter of 20 nm) by exploiting the capping agent capacity of additives during chemical synthesis [3].

In the end, we implemented MnO₂-GDEs in laboratory-scale Zn-air batteries to investigate the relationship between MnO₂ micro-nanostructure and their electrochemical performance in galvanostatic discharge/charge cycles and with electrochemical impedance spectroscopy in a full-device configuration.

Multivalent (Mg, Ca, Al) metal anodes offer promising gravimetric and volumetric capacities and are a promising option for future high energy density batteries based on sustainable materials. However, their practical application is severely limited by the difficulty of ion insertion, slow diffusion and the presence of side reactions during electrochemical operation. Organic cathodes, with their relatively soft and adaptable structures, offer an alternative to overcome the limitations of inorganic hosts.[1]

In our work we combine organic compounds with different multivalent non-nucleophilic electrolytes. We started our work with polymers from anthraquinone class, which fit well into the electrochemical stability window of multivalent electrolytes due to their moderate working potential. The long-term cycling stability in combination with insoluble organic polymers and suitable non-nucleophilic electrolytes reaches several hundred cycles. However, there are still some challenges in terms of capacity utilisation and cycling stability that need to be addressed. We aim to improve our understanding of these challenges by analysing the electrochemical mechanism in detail using electrochemical impedance analysis and ex-situ electron microscopy, which reveal limitations in the transport of multivalent ions within the active materials.[2] At the same time, we also focus on the development of active compounds with higher energy density, either through increased capacity or redox potential.[3]

The organic electrode materials (OEM) are emerging as a promising alternative to develop greener and sustainable battery technologies. However, significant improvements are still required in their cycling stability, rate capability and energy density. This can only be achieved through a fundamental understanding of the electrochemistry at molecular level establishing the structure-properties relationships. To contribute to this end, we are developing methodologies based on evolutionary algorithms (EA) and artificial neural networks (ANN) at interplay with density functional theory (DFT) based calculations. The EA has initially been employed to predict the structure and electrochemistry of a set of dicarboxylates. In a second stage, we have developed a wider database of organic materials for energy applications that contains information about molecular geometries and high-level features extracted from DFT calculations. Based on this database, we have developed a machine learning approach to predict the redox potentials by giving only chemical species and molecular structures, completely by-passing the computer-demanding DFT calculations. A number of learning algorithms based on ANN have been investigated along with different molecular representations. Here we have also included a layer to predict redox-stable compounds. This machinery has been employed to screen a large organic materials library leading to the discovery of novel cathode materials [1,2], which is actually one of the bottlenecks on the development of organic batteries. The computational materials design platform developed here has the potential of significantly contribute to accelerate the discovery of organic electrode materials with superior properties.

Nowadays, lithium-ion batteries (LIBs) remain the most widely used and manufactured energy storage technology due to their high energy density, long cycle life, and versatility across various applications, including consumer electronics, electric vehicles, and renewable energy systems. However, LIBs face challenges due to limited lithium reserves, toxic cathode materials like cobalt, and unethical mining practices in developing countries, causing environmental and social concerns. Sodium-ion batteries (SIBs) are considered highly promising to replace lithium in storing electrochemical energy from renewable sources and enabling long-range electric vehicles, as sodium is more abundant and widely available. Indeed, sodium-ion batteries face challenges due to the limited availability of suitable cathode materials capable of efficiently hosting sodium ions. Among the promising candidates, covalent organic frameworks (COFs), a class of crystalline porous organic polymers, stand out for their tunable structure, high surface area, and potential to enable reversible sodium-ion storage through redox-active sites.[1] COFs are suitable as electrodes for SIBs due to their insolubility in electrolyte, the possibility to introduce numerous redox-active sites and tunable porosity to facilitate ion diffusion.[2],[3] Herein, we will present the electrochemical performance of an anthraquinone-based COF cathode material in sodium batteries, encompassing cyclic voltammetry, long cycling stability, and analysis of the sodium-ion diffusion mechanism within the material.

Keywords: Sodium-ion batteries, covalent organic framework, organic batteries, electroactive porous materials.

Developing high-performance electrochemical energy storage systems is one of the most prominent pathways to reach the “net zero emission” goal. For that reason, the demand on batteries has increased exponentially in recent years. Indeed, the conventional batteries based on inorganic materials successfully replied to this request so far. On the other hand, since the R&D efforts have been very intense on such compounds either in academic or industrial level, theoretical limits are almost reached for those conventional systems. Moreover, it is predicted that the increased requirement on such inorganic materials (mostly based on lithium derivatives) may lead scarcity of their raw compounds. It is equally important to mention here that most of these inorganic materials are toxic, unsafe, and unsustainable.[1] Therefore, moving out of the comfort zone to discover novel abundant battery components, which can easily be reached without any geographical limitations, is intriguing. In this context, organic electrode materials (OEMs) are interesting alternatives.

Appearance of OEMs was nearly at the same time with their inorganic competitors. Recently, discovery of molecules carrying redox active side groups (e.g., carbonyls) made OEMs highly interesting in the field.[2] Although their leaching during operations due to their high solubility is always highlighted as a major drawback, forming their polymers neutralized this short-coming.[1] Additionally, going one step further from the traditional 1D polymers to high dimensional (hyper)crosslinked (porous) polymeric backbones make the functional moieties more reachable by the counter ions thanks to the high accessible surface area provided by the empty voids (i.e. pores).[3]

Here we present phenothiazine (PTz)-based hypercrosslinked polymers as high performance and low-cost p-type OEMs, which are rare[4] when compared to the n-types. The syntheses were carried out via a facile method, Friedel-Crafts alkylation (i.e. knitting polymerization),[5,6] in between the low-cost commercially available compounds either to form homopolymer of PTz or its random co-polymers with benzene. The increased benzene portion in the reaction resulted in higher crosslinking, therefore, higher accessible surface areas (BET surface areas from 29 to 586 m² g^-1). Although introduction of the redox inactive benzene reduced the theoretical capacity (from 112 to 77 mAh/g), such addition yielded OEMs with enhanced practicability, including increased durability, operationality in higher C-rates, propensity to increase both polymer content and its mass loading in the electrode. In conclusion, the possibility of such trade-off via macromolecular engineering can be a guide to produce advanced materials with high performance and practicability not only for application in batteries but also in complementary electrochemical techniques.

The stability of electrode materials in aqueous electrolytes is crucial for the longevity and efficiency of energy storage systems, especially under conditions that promote water electrolysis. This study examines the self-discharge characteristics of polyimide (PI)-based electrodes in aqueous environments. By systematically examining key factors such as electrolyte type, concentration, operational parameters, and environmental conditions, we aim to identify the underlying causes and elucidate the mechanisms driving self-discharge in organic polymer electrodes. Our findings reveal that water reduction at the electrode not only contributes to reversible self-discharge but also significantly influences irreversible capacity loss. Comparison with nonaqueous systems highlight the pronounced sensitivity of organic electrodes to even minimal water content, which exacerbates degradation. These observations underscore the urgent need for strategies to mitigate both reversible and irreversible degradation processes in aqueous battery systems. Our presentation will discuss these phenomena and potential mitigation strategies in detail, offering new perspectives on enhancing the stability and performance of organic electrodes in aqueous conditions.

In the first part of the talk, I will introduce recently developed methodology for elucidation of the most important electrochemical performance parameters for high energy density battery materials, including electrode/electrolyte interphase conducitivity and cationic transference numbers from electrochemical impedance spectroscopy, and bulk ion diffusion coefficients in electrolytes and electrodes from galvanostatic polarization. Here, detailed elucidation of spectra and equivalent circuit developement allows for extraction of charge transfer resistances and compext time/temperature behavior. In the second part of the talk, I will focus on application of such methodology on most promissing materials, such as Li/Na/K/Mg/Al metals in contact with contemporary liquid electrolytes, concentrated liquid (e.g. containing triple ions) and polymer electrolytes (above 40 wt% of salt), sustainable sodium cathodes and hard carbon anodes. In the case of metals, the findings show diversity of materials chemistry, with relevance of existence and potential corrosion of native oxide films, as well as dendrites.  Finally, I will give an outlook on how to potentially develop future sustainable high performance battery materials.

Lithium-sulfur (Li-S) batteries are among the most promising of the ‘beyond Li-ion’ battery technologies, due to their high theoretical gravimetric capacity (1675 mAh g^-1_S) and energy density (2500 Wh kg^-1_S), which far exceed those of Li-ion batteries (LIBs). Li-S batteries benefit from the use of sulfur as an earth-abundant, low-cost and geographically widespread positive-electrode material. These systems exploit the reversible 16-electron interconversion of S₈ and Li₂S at the positive electrode, coupled with the plating and stripping of Li at the negative electrode.

Despite the promise of the Li-S battery, practical cell performance is often limited due to poor interconversion of S₈ and Li₂S, which is exacerbated at higher rates of discharge and charge. While there are many reasons for this performance limitation, it is generally accepted the battery requires a catalyst at the positive electrode to achieve high energy efficiency and rates. Despite this, the exact role of the catalyst in the Li-S battery remains elusive and the nature of the rate limiting steps is unknown. Here we will discuss the fundamental reaction routes within the lithium sulphur battery. Using a combination of analytical electrochemical techniques we have identify those steps which are rate limiting during discharge of the cell. In addition, we will discuss the development of molecular catalysts able to drive the interconversion of S₈ and Li₂S. Two types of molecular catalysts will be described; 1) simple redox shuttles and 2) homogeneous catalysts able to trigger disproportionation reactions. A variety of electrochemical and analytical techniques have been utilised to assess the role of the molecular catalysts in sulfur redox chemistry. Using galvanostatic cycling,  we are able to demonstrate the impact of these molecular catalysts in cells, which display enhanced cycling performance. Finally, we present an alternative statistical approach to cell data analysis.

Ammonium-ion batteries have emerged as a promising energy storage technology for certain applications, offering advantages such as environmental friendliness, cost efficiency, and abundant resource availability. However, the side reactions originating from electrolytes, such as the water decomposition, and host material dissolution preclude their practical applications. Unlike the traditional metal-based aqueous batteries, the idea of “ultrahigh concentrated electrolyte” is not feasible due to the strong hydrolysis reactions of ammonium ions at high concentration.

Our group has been developing innovative strategies including hydrogen bond engineering, electrolyte engineering, and electrode engineering to overcome the challenges faced by aqueous ammonium-ion batteries. The role of hydrogen bond chemistry in stabilizing ammonium ions and improving ionic transport is particularly important, as it affects both electrode–electrolyte interfaces and bulk electrolyte performance.

In this work, we introduce sucrose molecules as electrolyte additive into the ammonium trifluoromethanesulfonate electrolyte. The quaternary hydrogen bond network is formed among cations (NH₄⁺), anions (OTf-), solvents (H₂O) and additives (C₁₂H₂₂O₁₁). Such unique hydrogen bond network can inhibit the water decomposition. More interesting, we found that the weak hydrogen bond coordination of NH₄⁺ ions and sucrose molecules allows faster ion diffusion in the bulk electrolytes. This is a new discovery which is very different from  metallic charger carriers used in aqueous batteries.

Utilizing such designed electrolytes, the assembled ammonium full battery shows remarkable cycling stability of 2000 cycles at 20 °C and 10000 cycles at −20 °C, respectively.

We believe this work presents a new electrolyte modulating strategy for advancing the practical potential of aqueous ammonium ion batteries. 

The growing demand for portable devices and electric vehicles has significantly accelerated the development of lithium-ion batteries, driving innovation towards achieving higher energy density, greater power output, and enhanced safety.[1] Currently, graphite anodes, with a theoretical capacity of 372 mAh g⁻¹, are widely used but remain a limiting factor. In contrast, lithium metal anodes offer a much higher theoretical capacity of 3860 mAh g⁻¹, making them promising candidates for next-generation lithium batteries that prioritize high energy density and extended cycle life.[2] However, challenges such as the irreversible loss of lithium due to dendrite formation, whisker growth, and the generation of "dead lithium" pose significant safety risks.

To address these issues, anode-less lithium battery design has emerged as a promising alternative, offered the highest achievable energy density while mitigating safety concerns.

In this study, an ultrathin layer was deposited onto a copper foil using physic-chemical methods, enabling its use as negative electrode in a quasi-anode-less lithium metal battery configuration. Electrochemical testing in a coin cell setup demonstrated notable performance improvements compared to traditional anode-less systems. Detailed morphological and compositional analyses of the thin layer, functioning as a solid electrolyte interphase, were conducted using SEM and XPS techniques. These findings lay a robust foundation for further research, aiming to enhance stability and extend the lifespan of lithium metal batteries through practical design optimizations.[3]

The role of binders is crucial to achieve high performance and long cycle lifes in next generation electrodes for lithium batteries. Poly(vinylidene difluoride) (PVDF) and its copolymers are the most commonly used binders for the processing of cathodes in Li-ion batteries, due to their good electrochemical stability. However, PVDF requires the usage of toxic and expensive organic solvent N-methyl-2-pyrrolidone (NMP) for the electrode processing and elevated temperatures for drying step, making the cathode manufacturing process environmentally unfriendly. In order to overcome these issues, it is necessary to develop cost effective and eco-friendly binders as alternatives to PVDF.

For this reason, the use of bio-polymers and water-processable polymeric binders is increasingly investigated. In this talk, we will present the development of water processable polymeric binders, such as  carrageenan biopolymers [1] and fluorine-free poly(ionic liquids) [2], together with their application as binder in  high-voltage NMC811 cathodes. Moreover, polymer binders that can provide additional functionalities, such as lithium mobility and/or electronic conductivity, are important for both lithium-ion and lithium-metal batteries. Here, organic mixed ionic-electronic conducting (OMIEC) binders will be presented based on the conducting polymer PEDOT and ionically conductive poly(ionic liquids) [3] and organic ionic plastic crystals [4], which improve the rate capability and cycling stability of Li-ion batteries.

The European Union has established a policy to achieve climate neutrality by 2050. Therefore, one of the strategies is to increase renewable energy sources drastically and, in turn, develop efficient energy storage devices and batteries of particular interest. For large-scale stationary applications, sustainability and cost-effective batteries are more attractive. In this context, lithium-ion batteries (LIBs) are not the most interesting battery chemistry due to their mass production comes with environmental and social challenges, which will even increase more as the market expands. Indeed, lithium-based technology production involves several critical raw materials, where suppliers concentrate in third countries and conflict zones, and expensive elements (i.e., natural graphite, cobalt, lithium, nickel, etc.) [1,2]. In this scenario, the development of alternative energy storage devices based on sustainable and cost-effective materials is crucial [3].

Sodium-ion batteries (NIBs) are postulated as a complementary technology to lithium-ion batteries (LIBs) for stationary applications and light electromobility due to their lower cost and sustainability, as they are made of non-critical raw materials [3]. Recently, several companies have been presented with potential applications of SIB to bolster their commercialization. For example, CATL, one of the biggest battery manufacturers in the world, recently announced on production of SIBs. Potassium-ion batteries (KIBs) might be another attractive alternative due to they keep the sustainability and cost aspects, with several advantages over NIBs. Potassium, as sodium, is abundant and widely distributed on the Earth’s crust and ocean, while it exhibits lower reduction potential than Na (i.e., -2.71 V and −2.93 V vs. SHE for Na and K, respectively). Moreover, K ions diffuse faster in liquid than Na ions -and Li ions, leading to higher energy density and higher power density than NIBs. The Group 1 start-up has recently released a KIB prototype, and they announced a large-scale production of KIBs by 2027, demonstrating that KIBs could be a reality. Unfortunately, the current performance of KIBs is inferior to that of both LIBs and NIBs. Therefore, further advances are necessary to enhance the viability of KIBs [4]. Thus, this work will be focused on the comparison of Na- and K-based electroactive materials (electrode and/or electrolyte) and identify the key parameters affecting the electrochemical properties to achieve high-performing NIBs and KIBs.

Na-ion battery technology, developed as a cost-efficient and sustainable alternative to the widely deployed Li-ion batteries (LIBs), has experienced unprecedented growth over the past years. Such rapid development greatly benefited from the earlier advancements in materials chemistry for LIBs, and, therefore, the general understanding of materials could be easily adopted by Na-ion chemistry. However, the use of conventional anode materials from LIBs is challenging, as the most common examples from LIBs (graphite and silicon) do not perform well in Na-ion batteries (NIBs). For that reason, hard carbon was adopted as state-of-the-art and the most common anode material for NIBs. Further improvement of Na storage capacity of anodes required alternative materials, such as alloying materials; however, their cycling stability represents a major drawback for their efficient implementation in NIBs.

The materials operating under conversion/alloying mechanism (where the alloying reaction is triggered by the conversion occurring during the first sodiation) represent a promising class of materials, which can deliver high Na storage capacities without sacrifice of cycling stability. However, the complexity of their operating mechanism(s) severely impedes their development. This presentation will be focused on development and implementation of operando methodologies for characterization of the operation mechanism of these materials and correlating the mechanisms with the electrochemical performances. The challenges associated with the design and characterization of these anode materials will be highlighted.

The global demand for electrochemical energy storage has been drastically growing and the projections are a challenge for the entire value-chain of lithium ionlithium-ion batteries.^[1] The related challenges in feedstock supply and cost fluctuations waswere driving the research and development on sodium-ion batteries, a drop-in technology using much more abundant raw materials.^[2] First commercial SIB cells from HAKADI® Shenzhen Zhonghuajia Technology Co.,Ltd. were available in September 2023 for private users in Europe. The objective of this study is to safely disassemble commercially available sodium-ion batteries (SIBs) and analyse the cell components—cathode, anode, separator, and electrolyte—in terms of their material composition. In this work, two types of SIB cells from different manufacturers were disassembled, examined, and compared. Similar approaches have been pursued by Waldman et al. and Sauer et al.^[3,4] However, different cell types are investigated in the current study.

Given the varied nature of the cell components, a comprehensive characterisation requires multiple analytical techniques. After successfully opening the cells, the electrodes were initially measured for dimensions, weight, and thickness. Scanning Electron Microscopy (SEM) was employed to investigate the particle morphology and size of both the cathode and anode. Additionally, Energy Dispersive X-Ray Spectroscopy (EDX) was used to determine the elemental composition of the active materials of anode and cathode. The specific surface area of the active material powders was also analysed.

Thermogravimetric Analysis (TGA) and Differential Scanning Calorimetry (DSC) enabled the determination of the thermal properties of the components. TGA allows for the assignment of characteristic weight losses to specific components, thereby enabling quantitative statements on material composition. DSC, in turn, allows for the identification of characteristic phase transitions associated with specific materials.

The analysis revealed very similar compositions at the material level for both cell types. Only in the electrolyte a difference was observed: one cell type contained three organic carbonates, while the other contained four organic carbonates. Intriguingly, the SEM data for the cathode demonstrated notable differences in particle size and morphology, despite both cathode active materials being composed of the same transition metal oxide, i.e., NaNi_0.33Fe_0.33Mn_0.33O₂.

The two cell types (SIB_A and SIB_B) displayed significant differences in cycling stability. SIB_B could be charged and discharged stably over several hundred cycles, while SIB_A lost nearly 10% of its initial capacity after approximately 20 cycles. These differences may stem from cell design, such as insufficient electrode contact or uneven coatings. Alternatively, the discrepancies in cycle stability could arise from material-level differences, such as electrolyte composition. The data obtained so far suggest that the differing cell performance observed may be linked to variations in particle size and morphology of the cathode active materials. These findings provide important insights into which material compositions, particle sizes, and morphologies may be advantageous for the further development of specific SIB cell components.

Due to abundant raw materials, low costs and promising high reversible specific capacities, hard carbons (HCs) are a common choice for commercially manufactured anodes in sodium-ion batteries (SIBs). Despite their potential and extensive use, the storage mechanism is still under debate. The non-stoichiometric adsorption mechanism also means that the search for an upper limit for the reversible capacity is ongoing. There is a strong requirement for synthetic anodes that enable a better understanding of the theoretical capacity associated with HC-anodes. We have developed core-shell carbon anodes consisting of a highly porous carbon core and (almost) non-porous shell. Thus, the reversible capacity can be deconvoluted from irreversible capacity losses, arising from the formation of the solid electrolyte interphase (SEI). Moreover, the porosity of the carbon-core can be linked to the reversible capacities gained.

A range of microporous activated carbons were coated via an optimized  chemical vapour deposition technique.[1][2] These materials were characterised using a range of techniques including powder x-ray diffraction, small angle x-ray diffraction (SAXS), gas physisorption (N₂, CO₂) measurements and electrochemical characterisation at coin cell level.  

After coating, the material showed a significant reduction in detectable surface area (up to a factor of 192x) by N₂-physisorption. The tailor-made shell allows the stable cycling of a carbon anode vs metallic Na-electrode in coin cells at room temperature. For the best performing material, the reversible capacity increased from 139 ± 2 mAhg^-1 to 396 ± 2 mAhg^-1 while irreversible capacity is decreased from 636 ± 3 mAhg^-1 to 89 ± 3 mAhg^-1 (see Figure 1). After initial stabilization, a CE of 99% was achieved. The coating technique was usefully applied to a range of materials.

The successful formation of core-shell structures with high capacities enables separation of the storage mechanism from SEI-formation. In turn a proposed calculation to rank the contributions of surface adsorption and pore filling capacity can be confirmed. The materials also create the opportunity to conduct a range of operando experiments (e.g., SAXS) that can shed further light on the sodium storage mechanism.

Potassium-ion batteries (KIBs) are emerging as a promising option for large-scale energy storage. Compared to Li-ion batteries, KIBs offer advantages such as the abundance of potassium resources and the potential for cobalt-free cathode materials, leading to lower costs. The fast diffusion kinetics of K⁺ ions in liquid electrolytes may also enable faster charge and discharge processes. Key electrode materials for KIBs include Prussian blue analogues (PBAs), vanadium fluorophosphates such as KVPO₄F, and transition metal oxides at the cathode, while graphite and hard carbon are the
most promising anode materials.
This study highlights the use of electrochemical characterization, along with a range of experimental techniques such as X-ray diffraction, Mössbauer spectroscopy, and Raman spectroscopy, supported by density functional theory (DFT) calculations, to analyze the electronic structure and electrochemical mechanisms of these materials for KIBs.
On the anode side, research shows that the mechanism of K⁺ intercalation into graphite in glyme-based electrolytes changes from co-intercalation to intercalation with increased electrolyte salt concentration, influenced primarily by K⁺ ion solvation rather than solid electrolyte interphase (SEI) formation. Graphite experiences a significant volume expansion (around 60%) during K⁺ intercalation, while hard carbon shows limited volume change, leading to superior performance in terms of initial coulombic efficiencies (ICEs) and specific capacities. This can be attributed to the uniform morphology and
higher interplanar distance of hard carbon structures.
On the cathode side, systems such as Mn-Fe PBAs and potassium manganese oxides like K₃MnO₄ were tested. While these materials are cost-effective and non-toxic, they suffer from Mn dissolution at extreme oxidation states, limiting stable cycling. Similarly, the instability at high potentials of KVPO₄F restricts its electrochemical capacity.
These insights, enabled by advanced characterization techniques, especially under operando conditions, underscore the need for a detailed understanding of electrochemical properties and cycling mechanisms to develop new, effective materials for KIBs

The concept of concentrated aqueous solutions, referred as water-in-salt electrolytes (WISEs),¹ brought back recently the interest in aqueous batteries. These electrolytes can be described as few water molecules surrounded by cations and anions. The limited amount of free water molecules, the particular interfaces created,² as well as the change of the solvation structure strongly modify the solutions behavior. Consequently, the electrochemical stability window is largely extended up to more than 3 V. Multiple strategies have been implemented to extend further the stability window by occupying the water molecules, with the addition of a co-salt (bi-salt electrolyte)³ or the presence of a molecular crowding agent such as a polymer.⁴ These strategies strongly impact the organization of the water molecules in solution. Similarly, the kosmotropic or chaotropic character of the salt anion⁵ affects the water network, with the chaotropic anions being more efficient in disturbing the water molecules. Yet, the importance of such strategies on the long-term reactivity of aqueous batteries,⁶ particularly on the challenging limitation of the hydrogen evolution reaction (HER) at the cathodic side, has yet to be fully demonstrated.

In this context, we performed a screening of the gas production in full magnesium cells as a function of the electrolyte’s nature: imide,⁷ acetate or perchlorate-based electrolytes, bi-salt electrolytes and polymer-based electrolytes. In particular, we focused on H₂ production, used as a universal criterion to assess the relevance of the solutions considered.

At low molalities, we found that the production of H₂ follows the kosmo/chaotropic classification of the anions. However, at the highest molalities (or lowest water-to-anion ratios), a similar trend for the production of H₂ is observed, whatever the electrolyte considered. While the nature of the anion has a major influence on the solution’s organization, ultimately the H₂ production and reactivity seems only guided by the quantity of water in solution.

As society moves toward a more sustainable energy future, there is a constant and ongoing demand to develop low-cost energy storage systems for large-scale applications. Classical lithium (Li) layered transition metal oxides have shown great promise and have been the most popular cathode material class for conventional Li-ion batteries. However, the Li layered transition metal oxides require expensive Co and Ni to stabilize their ordered layered structure to be properly functional. In addition, the practical energy density of layered transition metal oxides in Na- and K-ion batteries is restricted by their intrinsic sloped voltage profiles. In this respect, it is a priority to develop cathode materials beyond the classical layered transition metal oxide materials for Li- and post-Li-ion batteries. In this presentation, I will discuss materials design principles to overcome the limitations of the classical layered structures for Li-, Na-, and K-ion batteries and showcase Co- and Ni-free cathode materials.

Global population growth and the expansion of electric vehicles have led to a surge in energy demand, stimulating the search for alternatives to fossil fuels and accelerating the transition to renewable energy sources. In this context, metal-sulfur batteries (Li-S or Na-S) have become a promising area of research. Sodium batteries are characterized by their lower cost and abundance compared to lithium, making them an attractive candidate for large-scale applications. However, Na-S batteries face significant hurdles, including sluggish reaction kinetics, the insulating nature of sulfur, and the dissolution of polysulfides resulting in the well-documented "shuttle effect" [1].
To overcome these obstacles, advanced materials for Na-S batteries are being investigated, with sulfurized polyacrylonitrile (SPAN) showing remarkable potential. This carbon-based polymer has favorable electrochemical properties. Through simple and efficient synthesis methods, sulfur is covalently bonded to the polyacrylonitrile (PAN) backbone, eliminating the formation of long-chain polysulfides. This innovation largely mitigates or even eliminates the shuttle effect, resulting in improved stability and capacity in Na-S cells [2,3].
In this study, the textural and morphological properties of SPAN were extensively analyzed after a facile synthesis. Its electrochemical performance was tested using CR2032-type Na-S button cells, and it demonstrated exceptional long-term stability over more than a thousand charge-discharge cycles. Furthermore, it achieved impressive specific capacity values at high charge and discharge rates, surpassing many conventional materials.
This work introduces SPAN as a promising cathode material for Na-S batteries. Its combination of low cost, high sustainability, and scalability positions it as a strong candidate for next-generation energy storage solutions, addressing global energy demands while contributing to environmentally friendly technologies

Unlocking the secrets of electrochemical interfaces is key to advancing energy storage materials, yet these processes remain a complex and critical challenge. Among the tools for probing these elusive regions, X-ray photoelectron spectroscopy (XPS) stands out for its ability to analyze electronic structures and characterize the solid-electrolyte interphase (SEI) formed between electrodes and electrolytes. Traditional ex-situ studies (conducted postmortem on electrodes cycled in liquid electrolytes) have showcased XPS as the go-to technique for SEI analysis, thanks to its probing depth (up to 10 nm) matching typical SEI thicknesses [1, 2]. However, these methods often miss transient or intermediate species, crucial for unraveling charge transfer dynamics.

For solid-state batteries, the challenge deepens: the SEI formed between lithium metal anodes and solid electrolytes is buried, inaccessible to direct analysis. Preparing ex-situ samples without disrupting the SEI [3] further complicates the picture. Understanding this buried interphase demands alternative approaches that can monitor its formation and evolution in real time.

Herein, a virtual charging operando XPS (OpXPS) technique was deployed to electrodeposit lithium directly on a halide-based solid electrolyte within the XPS chamber, enabling real-time tracking of SEI formation. Halide solid electrolytes are promising for next-generation all-solid-state batteries, thanks to their outstanding properties such as high ionic conductivity, oxidative stability and ductility. However, their reactivity with lithium metal remains a major challenge [4].

OpXPS revealed the formation of a dynamic mixed ionic-electronic conductive (MIEC) interphase between the halide electrolyte and lithium metal anode. Complementary Electrochemical Impedance Spectroscopy (EIS) and Distribution of Relaxation Times (DRT) analyses provided critical correlations between interfacial resistance and evolving chemical composition. These techniques demonstrate the powerful capabilities of OpXPS in decoding the complex dynamics of buried interfaces, paving the way for designing stable and efficient solid-state battery systems.

Zinc metal batteries (ZMBs) are promising candidates for low-cost, intrinsically safe, and environmentally friendly energy storage systems. However, the anode is plagued with problems such as the parasitic hydrogen evolution reaction, surface passivation, corrosion, and a rough metal electrode morphology that is prone to short circuits. One strategy to overcome these issues is understanding surface processes to facilitate more homogeneous electrodeposition of zinc by guiding the alignment of electrodeposited zinc. Using Scanning Electrochemical Microscopy (SECM), the charge transport rate on zinc metal anodes was mapped, demonstrating that manipulating electrolyte concentration can influence competing surface reactions and solid electrolyte interphase (SEI) formation in ZMBs. This work show that more extended high-rate cycling can be achieved using a 1 M ZnSO₄ electrolyte, and that these systems have a reduced tendency for soft shorts. Using XPS and Raman spectroscopy, it is demonstrated that an SEI is formed on zinc electrodes at neutral pHs, composed primarily of a Zn₄(OH)₆SO₄.xH₂O species attributed to local pH increases at the interface.  This experimental methodology studying metal battery electrodes is transferable to lithium metal and anode-free batteries, and other sustainable battery chemistries such as sodium, magnesium, and calcium.

      Understanding the electrolyte-electrode interface under realistic operating conditions is critical to designing new-generation battery materials. The past few decades of research have focused on developing a range of spectroscopic and imagining tools to enable the study of the chemical and structural changes at the electrolyte-electrode interface. Here, we introduce operando surface-enhanced infrared absorption spectroscopy (SEIRAS), a promising lab-based tool for gaining a molecular-level understanding of interfacial electrochemical processes.

      This talk will bring the most recent understanding of the electrochemical interface during the operation of energy storage applications using operando SEIRAS. We will highlight how the holistic information about the nature of the electrolyte-electrode interface can provide additional knobs to tune the battery performance, leading to further improvements in efficiency and stability for energy applications. Furthermore, fundamentals and experimental tips for operando SEIRAS will also be explained, which is essential for those interested in introducing operandoSEIRAS to probe your electrochemical system, especially battery applications.

In many applications device performance can be significantly influenced by defects, surfaces, and interfaces, all of which may evolve during operation. Alkali metal ion batteries are no exception, and understanding of how individual atomic scale motifs affect their performance is crucial for development of next generation battery materials. For this, atomic scale modelling play an important part, linking the experimentally observed behaviour to atomic scale mechanisms. In this talk, I will present how we can use the atomic scale modelling toolbox, and discuss the latest results from our group on tackling these challenges, with examples taken from our work on lithium, sodium and potassium ion batteries. Focusing on hard carbon anodes materials, and their interfaces with electrolyte, we will see how surface defects can lead to irreversible capacity and dendrite formation, the effect of pore structure on metal intercalation, and then extend this treatment to investigate the initial stages of the solid electrolyte interphase (SEI) formation. Finally, we will assess how changing the alkali metal ion affects the electrochemical behaviour, what this means for future battery design, and how atomic scale modelling can play an important role in battery manufacturing.

Batteries are expected to play a pivotal role in the electrification of a range of sectors, including transport, aerospace and grid-scale storage. Of the next generation battery chemistries, Li-S batteries are a particularly attractive option due to their projected high energy density, low cost, and operating temperature range. However, the chemistry of such systems is complex, involving the electrochemical conversion between two insulating species (S and Li₂S), dissolution and shuttling of soluble intermediates, uncontrolled deposition of cathode and anode species, and large volume expansion; if not carefully regulated, these processes can lead to gradual capacity fade at best, explosive cell failure at worst. Here, we discuss the development of free-standing carbon fibre electrodes that are conductive, lightweight and mechanically robust, and their role in addressing degradation mechanisms arising from volume expansion, polysulfide shuttling, dendrite formation and inventory loss. The fibres were prepared via electrospinning of biomass precursors followed by further heat treatment. The porosity, functionality and conductivity can be tailored by varying the precursor and carefully tuning the treatment conditions, to enable free-standing cathodes with high sulfur loadings, improved redox kinetics and enhanced polysulfide interactions to suppress shuttling and sulfur inventory loss. As anode supports, the carbon fibres provide a lithiophilic substrate for a homogeneous lithium-ion flux and low deposition overpotential, which favours large, uniform and low surface area lithium deposits. Employing UV/vis spectroscopy and optical microscopy to observe operando cell processes, we correlate the surface and structural properties of the carbon fibre electrodes with the ability to suppress polysulfide shuttling and control Li deposition and plating, to allow us to further tune the fibre properties to optimise cycling performance. The assembled cell demonstrates greater capacity retention over long-term cycling than conventional Li-S cathode and anode substrates; additionally, the free-standing configuration allows significant gains in energy density by dispensing with traditional electrode components including the binder, conductive additive and metallic current collector, making this process a promising route to achieving new high-energy-density electrode materials for Li‑S technologies.

The structural accommodations, essential to the processes of insertion of the Li-ion inside the materials of the battery, are strongly dependent on the kinetics of the electrochemical reaction. Thus, the quantification of these structural inhomogeneities, their interfaces and their evolutions according to the state of charge and the electrochemical cycling regime is the key to better understand the processes at the origin of the degradation of the retentions in capacity for the Li-ion batteries. For example, knowledge of the spatial distribution of phase, orientation, grain boundary, and strain is crucial to obtain a complete picture of the phenomena occurring during material operation.

Recently, new in situ/operando analytical tools have been developed to monitor structural and chemical transformations, which have allowed important advances in the knowledge of dynamical processors. Liquid cell TEM is a developing technique that allows us to apply the powerful capabilities of the electron microscope to image and analyze materials immersed in liquid. The liquid/bias cell (Protochips) consists of silicon nitride windows on silicon support called E-chip, which separates the liquid from the vacuum of the microscope and confines it in a thin enough layer for TEM imaging. The importance of liquid cell microscopy in electrochemistry is that liquid cell experiments allow direct imaging of key phenomena during battery operation and relate structural and compositional changes to electrochemical behaviors. Different interesting results on monitoring dynamical processes occurring in a wide variety of electrochemical systems, such as LiFePO4, NMC811, LMNO and solid state will be presented here.

4D-STEM techniques yielding structure and strain maps were used to locally probe the crystallographic information of active material crystals and correlate it to the spatial occupancy of Li-ion during the electrochemical cycle. Liquid mass spectrometry analysis was also used to monitor the evolution of the liquid electrolyte during the formation of SEI on the surface of the negative electrode. Structural refinement of an individual cathode grain was achieved using 3DED (electron diffraction tomography) techniques revealing changes in lattice parameters after an in situ electrochemical delithiation process. The ability to couple emerging analytical techniques with liquid electrochemical cell TEM paves new way in energy material characterization, in particular in the study of the dynamic phenomena occurring during the operation which are until now inaccessible to the primary particle scale.

In this talk I will present our research on  developing susianable anode free  Na  and Li batteries. I will present fundamentals of Li/Na nucleatrion on various curent collectors along with  SEI characterisation in different electrolytes and full cells at coin and pouch level. In particular several characterisation techniques such as in operando optical  microscopy, solid state NMR, ToF-SIMS, Hard ray XPS will be discussed. The impact of the chathode choice and SEI and full cell performance will also be discussed. In particular for Li we will discuss pairing  anode Free Li with a Li2S8/carbon composite and full cell performance.

If time allows will also doscuss our reseacher on K ion batteries snd the inetrcalation into graphite with new insights provided into thickness change, SEI, intercalation mechanism and stage compounds. Characterisation methods such as in operando XRD, Rama and surafec characterisation via ToF-SIMS will be presented along with DFT calculations to back up the Raman results on intercalation compounds with geaphite.

Na-ion batteries have entered the energy storage field to confront the problems posed by the exponential demand of Li-ion batteries, i.e., price rise, materials scarcity, geopolitical dependence, and mining and extraction environmental impact. Luckily, Na-ion batteries commercialization has just begun. However, they still have a long way ahead of them for further improvements in energy and power density, as well as cycling stability, in order to shorten the performance gap with Li-ion batteries. Similar to their Li-counterparts, carbon is the star material in the anodes. In this case, hard carbon is the material showing the best performance, although still allowing for optimization in terms of capacity, stability and synthesis sustainability. Indeed, innovations in materials design and performance advances should go hand in hand with technical feasibility, as well as health and environmental protection. Accordingly, to ensure their potential commercial viability and comply with growing requirements on sustainable manufacturing and use of resources, research must focus on the development of greener, simple synthetic approaches that exploit abundant and renewable carbon sources, as well as benign or low-toxicity chemicals.

In this communication, we show several sustainable synthesis strategies towards S-doped disordered carbons with a high-rate performance in sodium storage [1-3]. S-doping has been selected as a tool to boost the pseudocapacitive storage of Na and coupled with nanostructuring to minimize the solid-state Na diffusion distances. As carbon precursor, renewable biomass or biomass-based substances have been used, such as glucose, tannic acid, cork or pistachio shells. As S dopant, environmentally benign sulfur or magnesium sulfate have been selected, while nanostructuring has been achieved by using benign and water-removable templates such as sodium salts (carbonate or chloride) or harnessing the intrinsic structure of the biomass. It is shown that S-doping promotes not only the redox activity at high potentials, but also the low potential capacity exploitable in Na-based technologies.

Sodium-ion batteries (SIBs), as one of the alternatives to lithium-ion batteries (LIBs), have developed fast in the last ten years, and some companies have started commercialising SIBs. To achieve ecological sustainability, it is necessary to recycle spent SIBs. However, there are limited studies about the direct recovery of SIB’s anode and cathode active materials. For anode materials, hard carbon (HC), has comparable capacity with graphite in LIBs, and is widely used in commercial SIBs. However, due to its low yield and high energy consumption, HC is expensive than graphite and produces CO₂ during its manufacture. It is, therefore, useful to recover HC from end-of-life (EOL) cells and reduce CO₂ emissions.^[1] In this work, HC was reclaimed from scrap coatings and EOL cells and recovered by low temperature annealing with N₂ protect. The HC structure was evaluated by Wide Angle X-rays Scattering and the results confirmed the effect of heating temperature on the graphene layers in the HCs. The electrochemical measurements confirmed that the recovered HC from the scrap after 300°C annealing retained a similar capacity level with pristine HC after 50 cycles at 100 mAg^-1. HC recovered from EOL cells showed a reversible 218 mAhg^-1 capacity after 50 cycles. In full-cell configurations, HC reclaimed from scrap and EOL cells retained 86% and 89% of their initial discharge capacity after 200 cycles, respectively, and exhibited better cyclability than pristine HC. This research demonstrates a simple and effective single-step direct recovery method for HC recycling.

Titanium dioxide (TiO₂) surfaces are extensively utilized in various applications, including dye-sensitized solar cells (DSSCs)¹, biomaterials², and photocatalysis³ due to their cost-effectiveness, stability, and suitable electronic properties⁴. Anatase TiO₂, synthesized via electrochemical anodization in organic electrolytes, is a promising candidate for photocatalytic hydrogen (H₂) evolution. However, the wide optical bandgap and low intrinsic catalytic activity of TiO₂ limit its overall performance. To address the limitations of TiO₂, we investigate a surface engineering method to enhance photocatalytic properties by introducing a bi-metal-phosphate layer as a surface modifier and co-catalyst simultaneously. As a comprehensive surface modification strategy, this phosphate layer increases⁴ the stability of the co-catalyst (Cu) and minimize co-catalyst agglomeration, which typically results in a reduction in surface area and catalytic efficiency. Among various co-catalysts, we have selected Cu due to its strong affinity for forming copper-phosphate bilayers, which provide additional active sites and stable co-catalyst integration within the TiO₂ structure, thereby enhancing the efficiency of H₂ production. The successful formation of copper-phosphate bilayers was confirmed through comprehensive characterization techniques, including Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS) and Cyclic Voltammetry/Electrochemical Impedance Spectroscopy (CV/EIS), demonstrating the effectiveness of the copper-phosphate bilayer as a modifier on the TiO₂. The hydrogen production rate for unmodified and modified TiO₂ was measured via gas chromatography (GC). The findings offer valuable insights into the development of material surfaces with potential applications in energy conversion, particularly enhancing photocatalytic hydrogen evolution (HER).

Keywords: Anatase TiO₂, Copper, TOF-SIMS, bi-phosphate layer, reactivity, hydrogen evolution (HER)

Among the anode materials for sodium-ion batteries (NIBs), hard carbon (HC) is attracting particular attention thanks to its advantages: low cost, availability, sustainability and theoretical capacity close to graphite (in lithium-ion batteries, LIBs) [1]. HCs are generally synthesised from eco-friendly precursors, such as bio-polymers and biomasses, ensuring local resources' utilisation. For electrode manufacturing, HC is usually mixed with a polymer binder to be cast onto the current collector and to improve its mechanical stability. The binder plays an essential role in the formation of the electrode/electrolyte interface (known as the SEI), which affects the efficiency, capacity and cycle life of the battery. However, the binder can also cause inconveniences related to its weight, stability and inactive electrochemical storage, reducing sometimes performance. In addition, most of the binders currently used contain fluorine, i.e. polyvinylidene fluoride (PVDF), which is not only difficult to recycle, but also requires toxic and volatile solvents (N-methyl-2-pyrrolidone, NMP) to dissolve it, raising environmental concerns. To overcome this problem, sustainable and green binders/solvents are explored in this work to obtain environmentally responsible and biodegradable electrodes, that can be recycled [2]. The results obtained show that significant optimisation of the electrode formulation is required for each individual binder and that the performance vs. Na/Na⁺ is strongly dependent on the binder used. In addition, the formation of SEI and its chemical composition is also influenced by the binder [3]. Furthermore, binder-free self-supporting electrodes (SSE) are proposed as a promising alternative to avoid the use of binder/solvent while reducing the price, toxicity and weight of the electrodes [4]. The synthesis of such SSE is quite challenging and, in particular, their performance is closely linked to their properties and the electrolyte used.

The development of carbon capture, storage, and utilization (CCS&U) technologies is critical for mitigating climate change and reducing reliance on fossil-based feedstocks. To ensure these technologies deliver sustainable solutions, it is essential to adopt sustainability assessment tools early in the design process, enabling timely identification of improvement opportunities and potential unintended consequences. Innovation efforts have focused on alternative solvents for CO₂ capture and novel catalysts and reactive systems for CO₂ utilization, addressing key technical and sustainability challenges in CCU.

This presentation highlights examples where life cycle assessment (LCA) was applied in early design stages to guide the sustainable development of carbon capture sorbents and CO₂ utilization systems. The first case study evaluates the environmental impacts of 1-butyl-3-methylimidazolium acetate, an ionic liquid (IL), used as a post-combustion CO₂ capture solvent in a power plant with CCS. Key impact contributors and design parameters that could enhance IL performance in CCS processes were identified, revealing molecular-level weaknesses and opportunities for improvement. While the findings focus on a specific IL, the approach is broadly applicable to other ILs if process design data is available.

The second case study demonstrates the use of LCA to guide the design of a non-thermal plasma (NTP) reactor for CO₂ hydrogenation to methanol. By integrating climate impact metrics with reactor design parameters, product selectivity and CO₂ conversion, optimal operating conditions were determined from a sustainability perspective. The reactor, packed with a novel copper-zinc catalyst on a zeolite support, was tested under various voltages. Results showed that methanol selectivity had the greatest influence on the reactor’s environmental performance.

These case studies illustrate that addressing trade-offs early when designing solvents and catalysts applied to CCS&U technologies, can significantly enhance their environmental sustainability performance and drive innovation.

The global increase in solar panel production has outpaced the development of effective recycling processes for end-of-life (EoL) panels. With only a 25-30-year life span, Australia alone will generate around 1500 kilotonnes of solar panel waste by 2050. The substantial quantity of waste generated diminishes the environmental benefits. To tackle this issue, product stewardship schemes have been implemented in Australia, the EU and several states of the USA, establishing an economic imperative to ensure, at minimum the sustainable disposal of the waste.

Silicon solar modules are composed of glass aluminium polymers and metals/semiconductors (including relatively valuable Cu and Silver), as well as hazardous materials such as lead, tin, copper and arsenic.

This seminar will present the recent status of recycling procedures for solare cells,  and details of our international collaborations on the identification of strategies to recycle solar cell components into useful end use products, as well as recovery of valuable components.

The increasing electrification of modern society is heavily dependent on electronic and energy storage devices, with lithium-ion batteries (LIBs) playing a pivotal role. Since their introduction to the market, their features — such as high energy density, large capacity, long cycle life, and minimal maintenance requirements — made them indispensable to the energy industry. As a result, the demand for LIBs is expected to grow by over twenty percent yearly by 2030,[1] stimulating demand for critical metals like lithium, cobalt, nickel, and manganese. End-of-life (EoL) LIBs present a valuable opportunity as a source of these metals, often offering higher concentrations compared to traditional mineral ores,[2] whilst their adequate management minimises environmental pollution, resource losses, and supply chain risks.[3] Although battery repurposing will also play a relevant role, the recycling industry will continue growing in the coming years driven by recent EU legislation (Regulation (EU) 2023/1542), with batteries from 2031 onwards requiring a minimum recycled content of 6 % Li, 16 % Co and 6 % Ni and further increased by 2036.

This presentation showcases the recent work at CICECO exploring the transition of EoL LIBs down the waste hierarchy, exemplifying reuse strategies for the cathodic black mass before advancing to hydrometallurgical recycling with a focus on exploiting non-aqueous solvents for the design of alternative recovery processes.

The growing demand for lithium-ion (LIBs) and sodium-ion batteries (SIBs) to support the global energy transition has made end-of-life (EOL) management a critical challenge. Conventional recycling methods, including pyrometallurgy and hydrometallurgy, are energy-intensive and environmentally taxing and often fail to efficiently recover all critical materials. Direct recycling presents an innovative alternative, enabling the recovery and reuse of active materials with reduced energy input and environmental impact.

This presentation highlights cutting-edge research on the direct recycling of lower value and lower cost active materials in batteries. For example, hard carbon (HC) and Prussian white from Sodium-ion Scrap and EOL cells, graphite and lithium iron phosphate from scrap and end-of-life lithium-ion batteries, utilizing low-energy and low environmental impact approaches for delamination and relithiation or sodiation.

The discussion will also explore criticality assessments for materials such as lithium, sodium, and cobalt, evaluating their environmental and geopolitical risks in battery manufacturing. Direct recycling emerges as a scalable solution to mitigate these risks, decrease reliance on raw material extraction, and establish closed-loop systems for battery components. Life cycle assessments (LCA) demonstrate significant reductions in greenhouse gas emissions and energy consumption compared to conventional techniques.

Rechargeable alkaline zinc–air batteries (ZAB) hold great promise as a viable, sustainable, and safe alternative energy storage system to the lithium-ion battery. However, the practical realization of ZABs is limited by their intrinsically low energy trip efficiency, stemming from a large charge and discharge potential gap. This overpotential is attributed to the four-electron oxygen evolution (OER) and reduction (ORR) reactions and their sluggish kinetics.

In this talk, I will show our new concept based on two-electron generation and consumption of hydrogen peroxide at the air electrode. The O₂/peroxide chemistry, facilitated by a newly developed low-cost Ni-based bifunctional electrocatalyst, enables fast peroxide generation/consumption, and high energy efficiency, durability, and capacity. The proposed strategy profoundly relies on the availability of bifunctionally active ORR and POR electrocatalysts. Therefore, we developed an efficient, highly stable, inexpensive ORR and POR bifunctional catalyst based on NiN_xC_y single sites and Ni-based nanoparticles (Ni(OH)₂ at the surface under operational conditions in an alkaline environment) engulfed in crystalline carbon. The new electrocatalyst exhibits state-of-the-art activity, selectivity (96 ± 2%) in the 0.15–0.79 V vs. RHE range, and long-term stability (>100 h) for both hydrogen peroxide synthesis (ORR) and oxidation (POR) in alkaline medium. The integration of the bifunctional catalyst in the ZPB results in an ultra-low initial charge potential of 1.28 V at a current density of 2 mA cm^–2 (fixed capacity: 20 mAh cm^–2) and 1.48 V at a high current density of 50 mA cm^–2, corresponding to 97.3% and 74.8% energy efficiency, respectively. The new ZAB operates for at least 1000 h at a capacity of 50 mAh cm^–2, demonstrating high durability. In situ measurements combined with theoretical calculations reveal that the bifunctional catalyst stabilizes an adsorbed hydroperoxyl intermediate, which constitutes a crucial step for both peroxide generation and oxidation reactions, allowing the battery’s unique performance. The new design offers substantial progress toward practical ZAB and green, cheap, and efficient electrochemical production of hydrogen peroxide, providing a step toward replacing the existing industrial energy-intensive and toxic process.

Contemporary photovoltaic materials research has devoted a significant effort to elucidate what makes halide perovskites unique. In this talk, I will consider possible origins of self-healing—a prominent property commonly ascribed to halide perovskites and considered by some as a part of the reason for their exceptional performance as PV materials. I will describe our efforts to push the boundaries of the current understanding of the self-healing process's chemistry and elucidate potential sources for propelling this property by looking at non-halide perovskites that show (a particular type of) self-healing.

In this talk, I will first describe the results of a study of a solid-state transformation reaction of antimony trichalcogenides to form chalcohalides (and the reverse reaction). This will be the setting for a subsequent description of a vibrational spectroscopy study of the self-healing reaction following intense light irradiation. Using Raman spectroscopy, we identified common intermediate species in the self-healing reaction in antimony trichalcogenides and chalcohalides. Comparing five different materials with a similar space group symmetry enabled us to uncover the common structural feature that leads to self-healing in these materials. We rationalize the chemical reaction and point at bonding states at the bottom of the conduction band as central origins in propelling a 'hidden phase,' which ensues (a particular type of) a self-healing reaction. Finally, we recently examined if this rationale overlaps with a novel chemical bonding concept by examining homologue series of bismuth-antimony trichalcogenides. We found a reciprocal correlation between the three occurrences: of metavalent bonding and bonding states at the bottom of the conduction band, and photo-induced phase transition. The prevalence of self-healing semiconductors is restricted to a few selected cases, limiting understanding of the phenomenon. Expanding the variety and number of self-healing materials and uncovering the underlying solid-state reactions will facilitate the development of self-healing electronic building blocks for making animate electronic devices.

Li-ion battery (LIB) technology is a cornerstone of the transition to a carbon-neutral economy, powering advancements in renewable energy storage and electric mobility. While LIBs have been transformative, achieving full environmental and economic sustainability requires addressing challenges across the entire value chain, including the recycling of spent Li-ion batteries (SLIBs). Current industrial recycling processes primarily focus on recovering valuable cathode metals from the black mass. However, graphite, a critical raw material present in significant quantities in SLIBs, is largely discarded, despite its designation as a critical material by the EU. To fully capitalize on the circular economy potential of LIBs, innovative strategies for the recovery and upcycling of spent graphite are urgently needed.

Recycling graphite from black mass leach residue faces significant challenges due to impurities, structural defects, and contaminants that make traditional recycling methods economically unfeasible. This presentation outlines a novel approach utilizing hydrometallurgically-leached black mass residue as a raw material for producing bifunctional oxygen electrocatalysts. By exploiting the residual metal content and defects in the waste graphite we are able to turn a disposal challenge into an opportunity for creating high-value materials. Our research [1, 2] demonstrates the potential of SLIB recycling residue as a sustainable resource for high-performance M-N-C catalyst materials. These novel catalysts, tested in Zn-air batteries, show high power density and long cycling stability, highlighting their applicability in next-generation energy devices, offering a pathway toward mitigating climate change while advancing the circular economy for battery technologies.

The exponentially growing demand for energy storage has reached a point where it outpaces the energy density of the lithium-ion battery, which is currently the dominant commercial option (~200 Wh kg^-1). This has led to an intense search for viable alternatives. Metal-sulfur technology has emerged as a promising candidate for the next generation of rechargeable batteries, offering a high theoretical gravimetric energy density and the additional benefits of low cost and non-toxicity of sulfur [1][2].

Notwithstanding, sulfur presents a number of challenges that impede battery performance, with the shuttle effect and slow reaction kinetics being the most extensively studied. Among the various strategies proposed to address these issues, the chemical trapping of polysulfides (LiPSs) has demonstrated considerable promise [3]. Furthermore, recent studies indicate that applying a magnetic field to materials with ferromagnetic properties can enhance cycling performance [4].

This study presents a novel approach that demonstrates the efficacy of combining recycled ferrite with an external magnetic field generated by a permanent magnet in significantly improving reaction kinetics and polysulfide adsorption, thereby enhancing electrochemical stability. A comprehensive kinetic analysis indicates that the external magnetic field reduces polarization, increases the Li⁺ diffusion coefficient, and reduces the activation energy between electrochemical stages. The electrode demonstrates a capacity retention of up to 40% and a capacity loss per cycle of only half that observed at a high rate of 1C. At an ultra-high rate of 10C, it maintains a capacity of 507 mAh g⁻¹ after 150 cycles and delivers an areal capacity of up to 3 mAh cm⁻² with an ultra-high loading of 13 mg cm⁻². In addition to its impressive electrochemical performance, this method is more sustainable, utilizing recycled electronic waste processed through dry milling, thus eliminating the need for fossil-derived carbons.

Widespread adoption of alkali metal ion batteries poses a challenge for the recycling industry. Efficient recovery and reuse of valuable metals from end-of-life batteries and manufacturing scrap is paramount. A novel, cost-effective, fast, and scalable with high purity electrode delamination approach, 'ice-stripping,' is proposed. An electrode is wetted with water and frozen using a cold plate, then peeled. Volume expansion and the increased cohesive strength of the ice over the electrode adhesion results in 100% delamination from the current collector and recovery of electrode coatings with minimal water use, material waste, or damage, in stark contrast to conventional high-temperature methods. Its effectiveness is illustrated with Li-ion and Na-ion battery electrodes comprised of different binder systems, and the scalability is considered for scrap. Direct recycling cases study for Na-ion, Li-ion and manufacturing scrap are presented. This innovation holds promise in meeting the escalating demand for efficient and sustainable battery recycling.

As technology continues to evolve rapidly and the world increasingly turns to alternative energy sources, the need for more efficient thermal management systems has become critical. Unfortunately, traditional Heat Transfer Fluids (HTFs) still face limitations due to their less-than-ideal thermal characteristics. To address these challenges, over the past thirty years, the scientific community has shifted its focus towards Nanofluids (NFs)—a promising class of fluids that contain suspended nano-scale particles. NFs have gained significant attention for their potential to improve the thermal properties of standard HTFs. A large body of research has explored how different Nanoparticles (NPs) affect various base fluids, with much of the work focused on boosting thermal conductivity—a key factor in heat transfer. However, while improvements in thermal conductivity are valuable, they often come at the cost of other important properties like specific heat capacity and viscosity.

The overall performance of NFs is shaped by a complex mix of factors, including the type of base fluid and nanoparticles, the presence of surfactants, and the impact of temperature. Other elements, like the shape, size, and concentration of the nanoparticles, also play a role. Despite the extensive research in this field, there's still a lack of comprehensive datasets that cover both specific heat capacity and thermal conductivity at the same time. Moreover, only a few studies have managed to enhance both properties simultaneously without significantly increasing viscosity.

This review aims to clarify the mechanisms behind the simultaneous improvements in specific heat capacity and thermal conductivity in Nanofluids. Achieving this balance is crucial not only for improving heat transfer efficiency but also for enhancing thermal energy storage. By exploring the potential of nanoparticles with solid-solid phase transitions, we hope to offer new directions for future research. Advancing these technologies is essential for supporting global efforts toward decarbonization and reducing carbon footprints.

The rapid development of perovskite solar cells (PSCs) has significantly advanced the field of renewable energy, offering high efficiency and cost-effectiveness. However, the widespread adoption of PSCs has raised serious environmental concerns, mainlydue to toxic lead-based components, such as lead iodide (PbI₂), which can pose substantial risks if not properly managed at the end of the product’s life cycle. As the need for sustainable practices in the disposal and recycling of these materials becomes more urgent, there is an increasing focus on finding efficient, environmentally friendly solutions for the recovery and reuse of lead from PSCs [1].

In this study, we introduce a novel and sustainable approach for up-cycling lead iodide (PbI₂) from PSCs using environmentally friendly functional liquids. Unlike conventional recycling techniques, which often rely on harsh chemicals and processes that can harm the environment [2],[3],[4]; our method focuses on harnessing green solvent systems to facilitate the efficient recovery and purification of PbI₂, making it suitable for reuse in the production of new  PSCs or other applications, thereby closing the material loop and reducing waste.

By employing green solvent systems, the process mitigates the environmental impact typically associated with the extraction and purification of lead but also maximizes the material recovery rate. The effectiveness of the recovery process will be rigorously validated through comprehensive analyses, including structural, chemical, and morphological characterization of the purified PbI₂ to confirm the quality and yield of the recovered material, and demonstrating its potential to meet the stringent requirements for reuse in PSC manufacturing.

This methodology offers a practical and scalable solution to address the toxicity concerns associated with PSC waste [5],[6], and it represents a significant advancement in sustainable recycling practices, providing a pathway to reduce the environmental footprint of PSCs while promoting a circular economy. By improving the recyclability of essential materials like lead—while mitigating its toxicity concerns—this research contributes to developing environmentally responsible solar energy technologies, helping to pave the way for a more sustainable future in renewable energy [7].

Abstract This talk will analyze CO2 electrolysis from a device perspective to provide insight into what are the bottlenecks in the field and how to resolve them.  We will focus on our synchrotron based results using small angle and wide angle x-ray scattering as well as x-ray fluorescence to observe CO2 electrolysis devices in real time while concomitantly measuring anode and cathode product distributions.  During higher current density (>100 mA/cm2) CO2 electrolysis devices are prone to cathodic ‘flooding’ leading to greatly enhanced hydrogen production, which can occur via a chaotic oscillatory nature.  Via our various in-situ analysis tools, we can explain the basis for this flooding, which is primarily due to salt deposition.1 By analyzing various salts (Li+, Na+, K+, Cs+) of differing solubility we show this trend more clearly.2 As Cs cations fluoresce,3 this allows us to show how an applied potential drags these cation salts through an anion exchange membrane, leading to the salt build-up and concomitant deposition in these electrolyzers.

As CO electrolysis allows us to switch to more soluble hydroxide salts, we show this is a major key to ensuring long-term stability (>100 hours).4  However practical issues such as anodic dissolution of IrO2 can redeposit on the cathode producing  hydrogen as shown by our synchrotron results.  Switching to a nickel anode resolve this, however we show that the anodic pH must be controlled to prevent acetate/acetic acid from driving the pH down, and thus corroding the device.

Electrochemical CO2 reduction is one of the potential negative emission technologies for mitigating climate change effects.[1] By synchrotron wide-angle X-ray scattering (WAXS) it is possible to follow transient changes in overall crystallinity and specific crystal phases of the catalyst phase, as well as to monitor background intensity attributed to the electrolyte.[2] By employing a specialized electrolyzer cell, gas diffusion electrodes on top of a microfluidic channel can be investigated along their z axis, delivering a bigger picture of processes in a 2D or even 3D scale down to μm resolution.[3] Precision and interpretation of such measurements, however, depend strongly on the algorithm used to process the vast amount of diffraction patterns. In this contribution, the challenges and possibilities are discussed, including baseline removal and peak picking for complex mixtures in electrolyzer operation. Different methods of baseline removal deliver varying results, indicating the need to optimize data processing strategies. By application of the right analysis method, different Bi-based catalyst materials or perspirating species present at operating conditions.

A decarbonized society is essential to maintain and further improve the standard of living for humankind. While the residential sector and short-distance transport have available solutions for electrification, several processes in the chemical industry (such as plastic manufacturing and base chemicals) still require carbon-based fuels as a resource [1].

One of the carbon-neutral technologies to produce base chemicals is electrochemical carbon dioxide reduction (CO₂R), powered by renewable electricity. CO₂R targets multiple base chemicals ranging from C₁- products like carbon monoxide (CO) to C₂+-products like ethylene (C₂H₄) [2].

CO₂R is already established at a lab scale. Implementation of gas-fed membrane electrode assembly (MEA) ‘zero-gap’ cells, as the state-of-the-art reactor design, demonstrates promising potential for a scale-up onto the commercial level [3,4]. However, the potential upscale MEA CO₂R electrolyzers are inevitably exposed to elevated temperatures, as a substantial part of the input energy dissipates as heat during the CO₂R process. Despite the higher temperatures once scaled up, limited research is available on the phenomena and bottlenecks present in CO₂R at industrial-relevant temperatures exposing a major knowledge gap in the field [5, 6].

This study presents the effects of industrial-relevant temperatures in MEA-based CO₂ electrolysis cells. In the first step, heat balance investigations are shown, proving that industry-size electrolyzers will require heat management and cooling. This acts as a basis for the main motivation why higher than ambient temperatures inevitably need to be investigated. We briefly demonstrate that a corridor of 40°C to 70°C is the most likely operatable range for low-temperature CO₂ electrolysis if industry-scale is achieved.

To investigate higher-than-ambient temperatures the usually present experimental setup has to be extended to provide temperature control for lab-scale MEA cells, the input gas, and the liquid electrolyte input. Thus, we will briefly introduce our experimental setup using a heating oven for the MEA cell and external heating of the anolyte reservoir. Additionally, the setup utilizes several devices to enhance the control over the humidity of the incoming gas-feed CO₂ to increase the control over the water balance of the system. We explicitly share our experimental setup to lower the entree bar to motivate other groups to expand their ambient temperature testing to industry-relevant temperatures.

Extensive flooding and salt formation are two of the main bottlenecks in the current state of the art for CO₂ electrolysis often occurring at the same time or briefly after each other [7-9]. To investigate the effect of higher temperatures on flooding and salt formation experiments in an AEM-based MEA cell, using Ag as the cathode-side catalyst partnered with an oxygen-evolving IrO₂ catalyst at the anode, are executed in a current density range of 100 mA/cm² to 400 mA/cm² in a temperature corridor from 25°C to 70°C degrees using KOH and KHCO₃ as anolytes. Our data shows that elevated temperature benefits the CO₂R runtime in MEA cells by diminishing the issue of salt formation, enabling operation at current densities of >200 mA/cm² even under high electrolyte concentration at temperatures of 50 °C and above. We link this to better solubility at higher temperatures combined with a smaller cation crossover rate. However, flooding remains an issue, especially at current densities higher than 300 mA/cm². Nevertheless,  higher temperatures also mitigate cell flooding time. The exact mechanisms transporting water from the anode to the cathode are currently debated. We suggest osmotic water drag as the main transport mechanism for water transport to the cathode side, backed up by our experimental temperature data with additional control experiments for the osmotic-pressure-relevant variables like anolyte concentration and cation type.

Multi-physical transport processes on multiple scales occur in electrochemical devices and components for CO₂ electroreduction. These complex coupled transport processes determine the local environment in the catalyst layer and subsequently also the reaction rates at the catalytic sites. I will discuss how the coupling between atomistic- and molecular-scale models, microkinetic models, and continuum-models can help in improving the understanding of the elecotrchemical CO₂ reduction. I will focus on silver as catalysts and discuss how (i) the presence of reaction products can affect the performance, (ii) how the electrolyte nature can affect the selectivity and activity [1], (iii) how pulsed operation can help to improve performance, and (iv) how the mesostructure of the electrode can affect the local conditions [2,3]. All these modeling efforts will demonstrate how multi-scale and multi-physics models can be used to guide the design, operation and material choice for electrochemical CO₂ reduction. In fact, such models are essential for the understanding of electrochemical CO₂ reduction since experimental investigations cannot provide the detail and locally resolved information required.

The re-utilization of CO2 via its electrocatalytic reduction (CO2RR) into value-added chemicals and fuels is a promising avenue to minimize the impact of existing technologies on the climate change. This requires the development of low cost, efficient, selective and durable electrocatalysts. However, their rational design requires in depth understanding of the modifications that structurally and chemically well-defined pre-catalysts undergo during operation, especially when the reaction conditions themselves change dynamically.

Here, the transformations that Metal-N-C catalysts (M=Cu, Ni, Co, Fe, Sn, Zn) experience during static and pulsed CO2RR will be unveiled. This will be achieved by a synergistic combination of operando quick X-ray absorption spectroscopy (XAS), high energy resolution fluorescence detected X-ray absorption near edge structure (HERFD-XANES) and X-ray emission spectroscopy (XES), coupled with unsupervised and supervised machine learning methodologies and density functional theory.

In particular, I will illustrate the astonishing behavior displayed by Cu-N-C catalysts during CO2RR, featuring reversible transformations from single atom sites towards small clusters and Cu nanoparticles. The switchable nature of these species, that can be achieved by applying different potential pulses, holds the key for the on-demand control of the distribution of the CO2RR products and thus, a wide-spread adoption of this process. Moreover, I will elucidate the nature of the ligands formed under CO2RR at singly dispersed Ni sites or Co sites in Ni- or Co-N-C catalysts, which are currently drawing great attention for their excellent CO yields.

Overall, my lecture will feature the importance of operando characterization of electrocatalysts in order to elucidate structure/composition-reactivity correlations during CO2RR.

The current state-of-the-art copper electrode lifetime falls several orders of magnitude short from the 10.000 hours industrially relevant timespan.[1] Most copper catalyst cannot maintain their activity towards ethylene and other multicarbon products for more than 100 hours. Contributors to limited catalyst lifetime are copper restructuring[2] , salt formation[3] , flooding[4]  and impurity deposition[5]. The restructuring of copper remains one of the least understood mechanisms. Scale up of CO₂ electrolysers therefore requires a deeper understanding of the chemical processes leading up to copper instability as well as solutions on both an atomistic and system design level.
Several fundamental works have demonstrated that anodic/cathodic dissolution and redeposition of copper species is one of the main components of the restructuring process.[6] The degree of dissolution and redeposition of the positively charged copper-carbonyl complex was found to proportionate to the applied current density.[7] Based on these results, one would expect that low current CO₂ electrolysis within H-cells results in very high electrode stability. Yet, it is the high current CO₂ electrolysis in gas diffustion electrode (GDE) based cell configurations that demonstrate the most impressive numbers of operational hours.

In this work, restructuring on a poorly in-plane conducting PTFE based copper electrode is captured through ex situ SEM analysis. It is shown that, over time, copper migrates from the center of the electrode to the perimeter closest to the negatively charged current collector. Subsequently, a nonporous structure erupts, favouring the hydrogen evolution reaction (HER) over CO₂ reduction reactions (CO2RR) after 45 minutes to 1 hour of operation at 200 mA cm^-2. We then present confinement procedures that are commonly applied within (GDE) based systems to minimize the dissolution of copper species such as metaloxide nanoparticle coatings and ionomers. In addition, the redeposition location is brought closer to the dissolution location by distributing the potential more uniformly across the GDE. Using one or a combination of the outlined strategies allowed the catalyst lifetime to be lengthened to several hours.

Copper is unique among metals for its ability to reduce CO₂ to high-value products. Despite its often-considered noble nature, copper readily degrades during electrochemical CO₂ reduction (ECR). Through extensive experimental results, theoretical modeling, and literature data, the mechanisms behind copper degradation have been elucidated.¹ A high-surface-area Cu catalyst exhibited significant changes in morphology and product selectivity over several hours under constant cathodic potentials relevant to ECR (-0.8 to -1.1 V vs. reversible hydrogen electrode). The formation of copper complexes with CO₂ reduction intermediates was identified as the main driving force behind this instability.

Our findings additionally suggest that these dissolved Cu species preferentially redeposit on sites with lower intermediate coverage, such as adsorbed CO (*CO). A dynamic equilibrium between dissolution and selective redeposition of these copper complexes drives morphological restructuring, leading to catalyst deactivation. This results in a shift in selectivity away from ECR towards hydrogen production during prolonged operation. The interconnected changes in nanoparticle size, crystallographic facet orientation, *CO coverage, and the CObridge vs. COatop ratio were proposed as the key factors contributing to catalyst deactivation.

To confirm the universality of this effect across copper-based catalysts, experiments on electrodeposited copper nanoparticles and copper foil were conducted, yielding similar trends. Understanding these processes is essential for developing strategies to mitigate instability and improve catalyst stability, addressing one of the critical barriers to the industrialization of ECR.

Metal- and nitrogen-doped carbons (M-N-Cs) represent a promising class of low cost electrocatalysts derived from nature-abundant elements for various electrochemical processes including CO₂RR [1,2]. Traditionally, M-N-Cs containing active metals (M = Fe, Co, Ni) are synthesized by direct pyrolysis of inorganic and organic precursors, a process that often results in the undesired formation of inorganic side phases through carbothermal reduction, impeding the effective integration of active metals like Fe, Co and Ni. Furthermore, comparing the intrinsic activities of different M-N-Cs can be complicated due to variations in catalyst morphology and active site concentration that arise during the pyrolysis.

To address these challenges, we developed an active-site imprinting strategy in which active metals are introduced post-pyrolysis via ion-exchange [3-5]. In this work, we employed the Mg imprinting strategy to produce Co-N-Cs and Ni-N-Cs with comparable morphology and metal dopant concentration. Our approach allows for a more direct comparison of the intrinsic activities that arise from the metal dopant. The Ni-N-Cs derived this way are consistently higher in activity and selectivity than the corresponding Co-N-Cs, exhibiting a CO Faraday efficiency of up to 95% at potentials between -0.5 to -0.8 V_RHE. The Ni-N-C catalyst maintains high stability at -0.65 V_RHE, with 92.5% retention of current density and 97.6% retention of CO selectivity after 100 hours of continuous operation.

While Ni-N-Cs are known to be relatively good CO₂RR catalysts, the origin of its activity remains rather elusive. Contrary to the widely accepted MN₄ active sites in M-N-Cs, NiN₄ sites are theoretically inert to both CO₂RR and HER due to the instability of the *COOH and *H intermediates respectively, often leading to the proposal of alternative but unproven NiN_x sites with various coordination structures to justify their performance. In this study, however, the absence of inorganic side phases allowed us to characterize the tetrapyrrolic NiN₄ coordination structure via Extended X-ray Absorption Fine Structure (EXAFS), suggesting that NiN₄ sites should in fact be CO­₂RR-active. Therefore, we performed mechanistic studies on the tetrapyrrolic NiN₄ sites using density functional theory (DFT), drawing inspirations from recent studies which elucidated the critical role of cations in enhancing CO₂RR activity on noble metal catalysts like Cu, Ag, and Au [6-7]. The presentation will further illustrate the influence of cations on the activity and selectivity of M-N-Cs towards CO₂RR, as well as well as the advantage of the pyrrolic nitrogen coordination in promoting the adsorption of these cations. 

Overall, this work not only highlights the potential of Mg-imprinted strategies in developing high-performance, morphological comparable electrocatalysts for sustainable energy applications and intrinsic activity studies, but also provides mechanistic insights on the involvement of cations in the valorization of the seemingly inert NiN₄ site.

The green transition requires discovery and development of new catalyst materials for sustainable production of chemicals and fuels. However, it is difficult to predict a material, which might have a high catalytic activity for a given reaction, therefore the development of catalysts up until now has been driven mainly by trial and error. It would increase the pace of development, if we could predict a range of promising materials or if we at least could understand the limitations of catalysis. In this context high entropy alloys offer a chemical space of possible materials where the composition can be smoothly varied and where the properties also might vary in a seamless manner. This is good news for catalysis as such a smooth space is easier to explore to determine the interesting regions in composition space. Furthermore, the highly heterogeneous nature of a high entropy alloy surface reveals fundamental effects which are important for chemistry on surfaces in general, but are overlooked in the classic mean field view on catalysis.

To alleviate CO₂ emissions and their impact on climate change, converting carbon dioxide into valuable products such as multi-carbon organic chemicals is of great importance. CO₂ can be converted via different pathways such as electrochemical, photo-electrochemical and biological etc. Each approach offers distinct merits but also certain challenges in terms of process efficiency, product selectivity and implementation at scale etc. Therefore, developing coupled CO₂ conversion systems, for instance bioelectrochemical reactors, can potentially address some of those challenges.^[1] In this work, the focus is on developing cost-efficient, biocompatible, and high activity porous M-N-C catalysts with M = Ni and Co that are atomically dispersed as NiN₄ and CoN₄ active sites in porous carbon matrix. Ni- and Co-N-Cs are prepared by active-site imprinting approach using Mg as an imprinter.^[2][3] Pyrolysis of Mg-N-C is carried out in a salt-melt at high temperatures (≥ 800 ^oC) and followed by an exchange with Ni or Co at low temperatures. N₂-sorption of the materials reveal a micro-mesoporous structure with high surface areas (> 1000 m² g^-1) and a mass-transport enabling pore system. Extended X-ray absorption fine structure (EXAFS) reveal the existence of atomically dispersed single atom active sites with defined active site structure. A variety of Ni-N-Cs and Co-N-Cs were tested for CO₂R activity in a rotating disc electrode (RDE) setup, showing high activity and selectivity towards CO₂R versus the competing HER. Subsequently, these catalysts were implemented in a home-made bio-electrocatalytical system (BES) consisting of a bioreactor coupled to a CO₂ electrolysis cell. Here, CO₂ is first electrochemically converted to CO in the electrolysis cell which is then directly fed to bacteria (Clostridium ragsdalei) in bioreactor who further metabolize it to valuable carbon compounds such as acetate. In the BES, partial pressures of CO reached a maximum of 5.7 mbar and that of hydrogen was 2.7 mbar after 30 h. A specific exponential bacterial growth rate of 0.16 h^-1 was observed with acetate formation rate of 1.8 mg L^-1 h^-1 and an acetate concentration of 0.103 g L^-1 corresponding to acetate formation rate of 0.73 mmol d^-1. As will be discussed in greater details in this talk, we have successfully demonstrated the validity of a coupled bio-electrocatalytical system concept operating with Co- and Ni-N-C catalysts for CO₂ conversion.

The electrochemical conversion of CO₂ has in recent years emerged as a promising technology towards allowing the conversion of CO₂ emissions to valuable chemicals and synthons. In recent years, molecular electrocatalysts have risen to the foreground as a tunable, more mass active and selective alternative to transition metal electrocatalysts. Despite the impressive results reached in recent years for a multitude of systems, transferring molecular systems to the large-scale is not yet a smooth endeavor.
Herein, we present our recent efforts towards a holistic transfer of molecular based assemblies, based on the Ag-BIAN (BIAN: N,N′-bis(arylimino)acenaphthene) structure in industrially relevant CO₂ electrolyzers operating at elevated current densities ≥ 300 mA cm^-2 at 60°C. Notably, we show how the performance and long-term stability of gas diffusion electrodes coated with Ag-BIANs is not only affected by the nature of the ligand system but also the operation conditions. Together with the performance of ex-situ and operando characterization, we show how ink compositions can play a crucial role in unlocking the activity and stability of previously though inactive complexes under electrolytic conditions at 600 mA cm^-2.

Furthermore, the currently running and future scale-up projects of Fraunhofer UMSICHT will be presented opening the discussion on the possible up-scaling of molecular systems.

The electrochemical reduction of CO₂ offers a promising route for converting renewable energy into carbon-based fuels through CO₂ hydrogenation, creating a net-zero carbon emissions energy cycle. Formate is one of the important value-added CO₂ reduction products. It is highly demanded in textile and food preserving industries. So, we targeted formate as selective product in CO₂ reduction in aqueous electrolyte.[1] Among the catalysts explored, Bismuth (Bi) stands out for being earth-abundant, environmentally friendly, cost-effective, and highly stable, with excellent selectivity for formate production. We developed a controlled synthesis process to produce uniform height 2D Bi flakes with (012) facets, using the chemical reduction of a sacrificial 2D BiOCl template under ambient conditions.[2] These Bi flakes demonstrate an impressive formate partial current density of 18.7 mA/cm² at -1.14 V_RHE during chronoamperometry, along with a peak formate Faradaic Efficiency (FE) of around 90% at -0.84 V_RHE. However, due to weak solubility of CO₂ in water, at higher potential, CO₂ saturation at the electrode surface drops which cause severe formate selectivity drop, giving rise to competitive Hydrogen Evolution Reaction (HER). To address this, we strategically modified the 2D Bi flakes with an ultrathin coating of Polyaniline (PANI), a redox-active conducting polymer. The basic amine groups in the polymer chain of PANI attract weakly acidic CO₂ molecules to the electrode surface. We found, PANI is not at all active for CO2RR but when it is coated on 2D Bi flakes, it significantly improved performance, increasing the formate partial current density to 35.5 mA/cm² at -1.14 V_RHE. Moreover, this modification also reduced the formate selectivity drop at higher potentials in comparison to bare 2D bismuth flakes, demonstrating the synergy between PANI and 2D Bi flakes in enhancing CO₂ reduction. We also have postulated a different mechanistic path that shows the role of PANI which is working behind this enhanced activity.

It is widely recognized that CO₂ is one of the driving forces behind the climate change. However, CO₂ is also a valuable resource for the formation of industrially relevant chemicals, and thus carbon capture and utilization, especially its electrical conversion, is becoming increasingly important. A major challenge for electrochemical fixation of CO₂ is the low energy efficiency of electrocatalysts due to high overpotentials. A cost-effective and sustainable material in the field of CCU is nitrogen-rich polymers such as polyethyleneimine (PEI) [1] or polyimidazolium (PI). These polymers are particularly well suited for CO₂ adsorption at low partial pressures, which would allow for the direct utilization of industrial flue gas. However, they lack the necessary electrical conductivity. Therefore, the design of hybrid materials combining porous carbons with high electrical conductivity and the CO₂-absorbing polymer is key. In this work, these nitrogen-rich polymers were incorporated into carbon substrates via a sonication-assisted impregnation process to improve transport properties and conductivity, both of which are important for subsequent electrochemical CO₂ conversion.

The pristine mesoporous carbon substrate was synthesized via zinc oxide-templated carbonization of sucrose at 950 °C and exhibits a specific BET surface area of 1750 m²/g, a high pore volume of 3 cm³/g as well as a hierarchical pore system [2]. These polymer-carbon composites have been characterized by physisorption measurements (N₂/CO₂), thermal response measurements (Infrasorp) and DRIFTS. All these measurements indicate a strong interaction of these polymer-carbon composites with CO₂ even at low pressures. By using a highly porous carbon support matrix, the initial CO₂ uptake is increased at least 10-fold compared to the bulk polymer. In addition, the irreversibility of CO₂ adsorption is proposed to follow a chemisorption mechanism and thus activate the CO₂ molecule.

First electrochemical measurements were performed on a rotating ring-disk electrode (RRDE). The results exemplify how the material can be used as an electrocatalyst for the reduction of CO₂. These hybrids were found to exhibit significant selectivity between the hydrogen evolution reaction (HER) and the CO₂ reduction reaction (CO2RR), as no hydrogen was detected in CO₂-saturated KHCO₃ solutions. It is anticipated that, due to their enhanced affinity for CO₂, a selective conversion process can be achieved without the need for metallic catalyst centers. Current work aims at transitioning from these fundamental RRDE investigations to more application-oriented measurements in a GDE/zero gap setup [3]. The goal is to enhance the faradaic efficiency further towards CO formation under flue gas conditions by using diluted CO₂ as a feed gas.

The rising levels of CO₂ in the atmosphere require the development of novel approaches to carbon management. Moreover, the installed capacity of photovoltaic (PV) systems is expanding at a considerable rate, resulting in a significant discrepancy between the generation of electricity from PV sources and the actual demand for electricity. The long-term storage of energy in molecules such as fuels or other industrially useful chemicals is of particular significance in counterbalancing the seasonal variations in photovoltaic power generation. The direct-coupled photovoltaic-electrochemical (PV-EC) system addresses these issues by converting excess PV energy into chemicals prior to feeding it to the grid. This enhances the utilization of photovoltaic power and improves grid stability. In this study, we have designed and tested a direct-coupled photovoltaic (PV) electrocatalytic (EC) device for the conversion of carbon dioxide (CO₂) into carbon monoxide (CO) and hydrogen (H₂) (see Figure 1). The device employs emulated PV that reproduces the IV characteristics of real PV modules in the field at the most relevant irradiance and temperature combinations (Figure 1(a)). The characteristic operating points of the PV-EC were obtained using the NREL public database for silicon heterojunction (SHJ) modules installed in specific regions of the USA. The newly developed PV emulator routine enables the precise and accurate reproduction of any IV characteristic of a PV module, at a level comparable to that of a Class A+ solar simulator. In our study, a SHJ module with an emulated area of 44.5cm² drives a flow-type stack EC cell (area 9.5cm²) with a silver/gas diffusion layer (GDL) cathode and an iridium oxide anode (see Figure 1(b)). The operation of the PV-EC system was evaluated under dynamic conditions, represented by three sunny days in a cycling procedure. This procedure involved eleven steps of irradiance-temperature pairs, ranging from 0.2 Sun to 1.1 Sun and 20°C to 54°C, followed by idle 'night' periods. The operating voltages achieved were in the range of 2.4 to 3.2V, while the operating currents were between 70 and 335mA corresponding to current densities of 7.4 to 35.2mA/cm2. The solar-to-chemical efficiency was observed to range between 8.7 and 10.8% at a high degree of coupling (0.85 to 1) in the absence of power electronics. Finally, a consistent and stable dynamic operation towards CO as the primary product with 75% faradaic efficiency and H₂ (25%) as a by-product over one to three-day cycles was demonstrated. This coupling, in conjunction with the high selectivity towards CO, renders the approach an attractive one for the decentralized storage of excess PV energy, offering a material-saving route.
 

(Photo)electrochemical conversion of solar energy represents a sustainable approach for generating chemical fuels, such as hydrogen (H₂) and hydrocarbons. Recent advances have highlighted the potential of PEC systems to drive convert carbon dioxide (CO₂) into various hydrocarbons. Despite these advancements, several critical challenges persist, particularly regarding the selectivity of the systems and the suboptimal efficiency and limited long-term stability of current PEC systems. Overcoming these limitations is crucial for realizing the full potential of PEC technology in renewable fuel production and for its broader adoption within the energy sector.

Here we will share the most recent results in our group on two main aspects regarding (photo)electrochemical CO2 reduction. On the one hand, we will focus on the importance of the microenvironment in determining and tuning selectivity by changing the local environment on metal electrodes or the chemical environment of metal centers otherwise selective for H₂ production. On the other hand, we will show examples of stabilized and stable system for CO₂ (photo)electroreduction.

The electrochemical carbon dioxide (CO₂) conversion to fuels and chemicals, powered by renewable electricity, presents a compelling avenue for reducing CO₂ emissions while facilitating large-scale and long-term renewable energy storage. Over the past decade, there have been promising steps in the production of fuels and chemicals (e.g., methane, ethylene, and ethanol) through electrochemical CO₂ conversion. Specifically, advancements in catalyst and system designs have enabled high selectivity for methane and ethylene (>70%) at high current densities (100 – 1000 mA/cm²).

While high selectivity at high current densities has been achieved, the stability of electrochemical hydrocarbon production remains insufficient for practical applications. Copper (Cu)-based materials are the most efficient catalysts for hydrocarbon production, but they experience morphological, structural, and chemical transformations under CO₂ reduction conditions, leading to changes in product selectivity.

In this study, we introduce the concept of reversible catalysts for CO₂ conversion to methane. This approach leverages the dynamic behavior of copper catalysts during CO₂ reduction. Using this method, we achieved CO₂-to-methane conversion at a current density of 200 mA/cm², with a methane Faradaic efficiency exceeding 50% sustained over 1,000 hours of operation.

The electrochemical CO₂ reduction reaction (CO₂RR) has garnered significant attention over the past decade due to its distinct advantages, including operation under ambient conditions, compatibility with renewable electricity, and the ability to produce a diverse array of value-added products. Most CO₂RR research to date has utilized pure CO₂ as the feedstock. However, real-world CO₂ waste streams, such as those in flue gas or biogas, typically contain no more than 40% CO₂. This discrepancy poses challenges for the economic feasibility and sustainability of CO₂RR, as CO₂ purification steps prior to electrolysis—such as CO₂/N₂ separation—can cost $70–100 per ton of CO₂ and significantly increase the carbon footprint [1].

In recent years, integrating CO₂ capture with electroreduction into a single unit has emerged as a promising strategy to address these limitations. Many studies have focused on using CO₂ capture solutions as electrolytes, achieving encouraging results in improving the overall cost-efficiency of CO₂RR. Beyond solution- or electrolyte-based capture methods (e.g., amine solutions and ionic liquids), integrating alternative approaches such as solid adsorption and membrane-based processes into CO₂RR systems offers considerable potential. For instance, combining these methods with gas-diffusion electrode designs could enhance the efficiency and practicality of CO₂ capture-electroreduction systems [2,3].

Herein, we showcase the scenarios to integrate adsorption and membrane separation within gas-diffusion electrodes (GDEs) and present our recent research data of CO₂ conversion by an ionic liquid-mediated CO₂-selective GDE. GDEs have been tested with gaseous feed with CO₂ concentration as low as 15% containing O₂, resembling flue gas, and showed high-rate syngas production with a polymer-ionic liquid selective layer.

Bipolar membranes under reverse-bias (r-BPM) offer a possibility of using PGM-free anodes in CO₂ electrolysers. Under ideal circumstances, the OH- generated from the BPM can fully replenish the OH- consumed by the OER, maintaining a stable anolyte pH over time. However, the OH- regeneration rate, and hence the stability of such systems, is dependent on the Water Dissociation Efficiency (WDE). In non-ideal BPM, the transport of co-ions through the membrane lowers the WDE below 100%. In this case, a pH decrease in the anolyte over time is expected, compromising the long-term stability of PGM-free anodes in CO₂ electrolyser.

In our study we aim to explore the feasibility of replacing PGM anodes under industrially relevant conditions. To simulate the long-term stability of a PGM-free CO₂ electrolyser, we have developed a methodology that combines both an experimental and modelling approach. Using a MEA cell architecture, we have determined the WDE of commercial BPMs under various process conditions, including current density, anolyte concentration, or cation identity. The experimental results have been used as the model input to extrapolate the long-term performance of a r-BPM CO₂ electrolyser. Our results suggest that current commercial BPM WDEs are not high enough to allow for the replacement of PGM anodes in CO₂ electrolysers. In addition, we highlight the importance of assuming realistic industrially relevant anolyte volumes when assessing the stability of PGM-free anodes.

Meeting the growing demand for lithium-ion batteries in electric vehicles and portable devices requires efficient lithium extraction methods. Electrochemical approaches, particularly those that leverage energy-efficient direct lithium extraction, are emerging as promising solutions. This talk explores both continuous and intermittent concepts for lithium-ion recovery, emphasizing advancements in material selection, membrane integration, and electrode stability.

Intermittent lithium-ion extraction is explored using lithium iron phosphate (LFP), a widely available battery material with a high theoretical capacity and favorable lithium insertion potential. Despite these benefits, LFP faces performance stability challenges. Our work investigates the role of additional cations and dissolved oxygen on LFP stability, finding that calcium cations and dissolved oxygen contribute to capacity fading. In contrast, sodium and magnesium cations have minimal impact. Performance is enhanced through continuous nitrogen flushing of the electrolyte and carbon coating of the LFP electrode, resulting in a lithium extraction capacity of 21 mg per gram of electrode material. This approach achieves an energy consumption of 3.03 ± 0.5 Wh per mole of lithium, with a capacity retention of 82% over 10 cycles. This system is of particular use for the processing of hydrometallurgical media within the context of lithium-ion battery recycling.

To continuously extract lithium from seawater, mine water, or other aqueous media, one can use continuous operation of electrochemical systems that integrate lithium-ion-selective ceramic membranes (LISICON). We show the facile operation of a simple redox-flow electrolyte, enabling continuous lithium recovery at a high purity of 93.5% and a Li/Mg selectivity factor of approximately 500,000:1. This concept is not limited to redox-flow battery technology; instead, our work shows that a fuel cell (fueled with oxygen and hydrogen) can also co-produce electricity and separate lithium-ion during continuous operation.

A robust supply chain of main Li-ion battery (LIBs) components has become critical since the rapid growth in energy demand storage, the so-called Green transition promoting the market of electric vehicles, and the ubiquitous presence of batteries in portable applications has spread out LIBs manufacturing and components needs. The dependence of these materials on third countries, with China as the main battery grade supplier, has prompted the European Committee to develop a new EU regulatory framework for batteries, which encourages battery recycling as an alternative supply chain, targeting, for example the recovery by 2027 of at least 50% of the lithium contained in spent batteries and its reutilization for the manufacturing of new cathode materials by 2035 at 10%, value increased to 12% and 20%for Ni and Co respectively. [1] Current LIBS recycling is carried out at an industrial scale using pyrometallurgical and hydrometallurgical processes. However, these technologies have several inherent limitations; in most cases, these methods face difficulties in recovering lithium and focus on extracting nickel and cobalt; in addition, they suffer from an intensive consumption of energy or chemical reagents, lengthy operational procedures with low recovery rates, and the generation of hazardous wastewater or polluting gas emissions, thus involving severe environmental impacts [2, 3].

In this communication, we develop an electrochemical method - ion pumping technology- to selectively extract lithium from battery spent; based on the use of lithium-selective-electrodes, such as olivine LiFePO₄ (Figure 1), as well as, we have proven the viability of the same technology to recover Ni and Co from NMC spent, in this case based on the use of Prussian Blue Analogues, K_xNi[Fe(CN)₆]y - z H₂O. The materials selectivity and the influence of critical extraction parameters (current density, time…) were analyzed by constant current measurements and Inductively coupled plasma mass spectrometry. The results demonstrate this technology's potential for electrochemical recovery of lithium and multivalent cations in short operational times.

Pyrometallurgy is one of the most relevant processes to recycle Lithium-ion Batteries (LIB). It involves the melting of the waste batteries in a shaft furnace at around 1500ºC. Two main products are obtained: an alloy, rich in Ni, Co, Cu, Fe; and a slag, which mainly contains Li and Al [1]. Typically, this slag was not valorised, and its main application was as a filling material in the construction sector. In 2021, one of the main European companies in the field of battery recycling published a patent where they claim a hydrometallurgical process to recover lithium from this slag, by leaching with H₂SO₄ and then precipitating Al to leave Li in solution [2]. The present study arose as an attempt to investigate the possibility of lithium extraction from leaching solutions containing aluminium.

Our approach focuses on exploring electrochemical capture technologies, such as faradaic deionization, to minimize the chemical usage and provide a more cost-effective, energy-efficient and environmentally sustainable solution. For that purpose, various lithium metal oxides (LMO, LFP, LMFP, NMC) were tested as active materials for electrochemical lithium recovery. Lithium manganese oxide (LMO) emerges as a promising candidate leading to the synthesis of Truncated-Octahedral LMO (Tr-Oh-LMO) [3], theoretically more stable than commercial LMO, to enhance the robustness of the process. Electrodes were prepared in two configurations, carbon paper (CP) and buckypaper (BP), and tested across different electrolyte compositions and pH values.To assess the performance, a novel Electrode Endurance Diagram was proposed to visualize the influence of pH on electrode stability during cycling. This tool enables a quick and comparative evaluation of the performance of different materials across a range of pH levels. Additionally, various characterization techniques, such as XRD and SEM-EDS, are employed to investigate electrode degradation mechanisms as a function of pH and aluminum presence.

Overall, this work provides valuable insights into the influence of pH and aluminum on the stability of lithium oxide electrodes, emphasizing the need to optimize process conditions and explore alternative active materials to enhance the feasibility of electrochemical lithium extraction from aluminum-rich solutions.

Li-ion battery recycling is currently a topic of significant scientific interest, with numerous studies and research projects exploring new techniques and optimizing existing ones. This is further encouraged to cope with the need for an independent supply of the main battery materials (e.g. Li, Co, Ni), most of them classified as Critical Raw Materials (CRM) by international organisations such as the EU [1]. Battery recycling therefore aims at facing the rapid growth in energy demand and the so-called Green transition promoting the market of electric vehicles. Not to mention that battery recycling tackles environmental problems related to their disposal. Current recycling methods employed are primarily based on hydrometallurgical and pyrometallurgical processes. However, these technologies have several inherent limitations, including an intensive consumption of energy or chemical reagents, lengthy operational procedures with low recovery rates, and the generation of hazardous wastewater or polluting gas emissions, thus involving severe environmental impacts [2]. Consequently, the development of novel alternative and sustainable recycling techniques is imperative, with electrochemical recycling representing a promising avenue for advancement [3].
In this work, an electrochemical technique has been the subject of study using materials like Prussian Blue Analogues (KxNi[Fe(CN)6]y - z H2O), capable of reversible intercalation of divalent cations (Co and Ni). Following the acquisition of encouraging results from 965 ppm  of recovered CRM under static conditions in a microcell, the method was fully automated simulating a scenario closer to the final application utilising a semicontinuous  flow-through reactor and resulting in the recovery of 1600 ppm CRM and 121 Wh/g of energy consumption. This is accomplished through the integration of electrochemical techniques to study the electrochemical properties of the PBA and to develop the operational modes of the setup. Furthermore, an examination of the material's structural, morphological, compositional, and characteristics is conducted.
Accordingly, this study represents a novel automated electrochemical method for the recovery of nickel and cobalt from battery recycling wastewater
 

In recent years, there has been a notable increase in lithium production, mainly due to the development and widespread adoption of Li-ion batteries (LiBs) in electronic devices; additionally, further increments are expected since vehicle electrification is based on LiBs because of its high energy density, safety and relatively low cost [1]. Lithium could be produced from hard-rock ores and continental brines. The dependence of this metal on third countries has prompted the European Committee to develop a new EU regulatory framework for batteries, which requires ensuring the recovery by 2027of at least 50% of the lithium contained in spent batteries and its reutilization for the manufacturing of new cathode material by 2030 [2]. Current LIBs recycling is carried out at an industrial scale using pyrometallurgical and hydrometallurgical processes. However, in most cases, these methods face difficulties in recovering lithium and focus on extracting nickel and cobalt [3].

In this communication, we develop an electrochemical method - ion pumping technology- to selectively extract lithium from battery spent, based on the use of lithium-selective-electrodes, such as olivine LiFePO₄ (Figure 1A), which can intercalate lithium while neglecting the insertion of other co-cations present in the solution, e.g., case of Ni, Co, and Mn for NMC based spent. The value of material selectivity towards lithium and the influence of critical extraction parameters (current density, time…) were analyzed by constant current measurements (Figure 1B) and inductively coupled plasma mass spectrometry. The results demonstrate this technology's potential for electrochemical recovery of lithium, reaching purities higher than 98% in short times - 120 minutes.

Materials science has proven to be valuable in tuning the selectivity in the electrochemical separation of ions. In this contribution, we specifically focus on the exploration of polymers to address the selectivity of membranes and electrodes that are employed in electrochemical deionization (EDC) and electrodialysis (ED).

Several approaches with different types of polymers will be discussed. First, the build-up of a multilayer of charged polymers (poly(allylamine hydrochloride), PAH and poly(styrene sulfonate), PSS) onto commercial available cation-exchange membranes proved to be a facile and versatile approach in switching from Mg²⁺-selectivity to Na⁺-selectivity when applied in ECD [1]. Next, in the presence of a series of mineral acids (HCl, HNO₃, H₂SO₄, and H₃PO₄) a conductive polymer (polyaniline, PAni) was electrodeposited onto carbon electrodes. When employed under ECD conditions, the PAni/H₂SO₄ system exhibits promising behavior for tuning ion selectivity [2]. Among the tested ECD electrodes, this system achieved a notable 20% reduction in chloride adsorption while maintaining consistent sulfate adsorption. Lastly, hydrophobic polymers (poly(vinylidene fluoride), PVDF, poly(vinyl chloride), PVC, polyacrylonitrile, PAN) were blended with an ionomer to obtain anion-exchange membranes.[3,4] In electrodialysis, the nitrate over chloride selectivity trend was found to be PVC > PVDF > PAN.

While evaluation of the complete set of charged, conductive, and hydrophobic polymers shows that a ‘one‐size‐fits‐all’ approach is not readily accessible when pursuing ion selectivity, the extraction of several general principles contribute to guiding the development of advanced materials set to further tune electrochemical separation.

Lithium has emerged as a critical raw material because of its indispensable role in the energy transition, especially in manufacturing lithium-ion batteries for electric vehicles and portable devices. However, 95% of such batteries are discarded without recycling once they reach the end of their life. When recycled, the batteries are shredded to form a black mass, which is leached by sulfuric acid. The resulting leachate contains transition cations such as nickel, cobalt, and manganese, besides Li. Thus, it is necessary to separate these elements, which is typically achieved through successive precipitation by increasing the pH of the leachate. However, this process results in a 40-60% loss of lithium which is the last element to be recovered.

Flow Electrode Capacitive Deionization (FCDI) is a very recent electromembrane desalination technology which employs flow electrodes (carbon slurries) to remove ions from saline water. We hypothesised that replacing standard cation exchange membranes with lithium-selective ones could allow for lithium recovery from brines and spent Li-ion batteries. In this talk, the journey behind the creation of Lithium Membrane Flow Capacitive Deionization (Li-MFCDI) [1] will be disclosed.

Several key challenges were addressed to optimise the FCDI/Li-MFCDI performance regarding energy efficiency and the possibility of scale-up. Polymeric lithium-selective membranes were developed [2] to overcome the limitations of ceramic membranes, which are brittle and expensive, limiting their scalability. Another challenge in FCDI and Li-MFCDI is to maintain the uninterrupted flow of carbon slurry electrodes while preventing channel blockage. In this context, the design of flow electrode channels was investigated experimentally and by computational fluid dynamics (CFD), considering the shear-thinning behaviour of flow electrodes [3]. Furthermore, innovations, including the utilisation of 3D-printed flow electrode gaskets as a substitute for the state-of-the-art computer numerical control (CNC) milled graphite current collectors, were explored to improve system scalability and efficiency. The research also assessed various operational modes under the same operating conditions to identify the most efficient operational mode for continuous and scalable desalination or lithium recovery. Finally, several different activated carbons were tested in the FCDI system to hunt out the best material for flow electrodes to enhance performance, scalability, and overall system efficiency.

Faradaic electrochemical deionization (FDI) is emerging as a transformative technology for water treatment, addressing critical challenges in conventional capacitive deionization (CDI) such as low desalination capacity, carbon anode oxidation, and co-ion expulsion effects [1]. Utilizing faradaic electrode materials—engineered by incorporating the electrochemical principles of battery electrodes—FDI employs redox and intercalation mechanisms to selectively remove ions. This innovative approach not only achieves higher desalination capacity but also offers superior energy efficiency, particularly at lower salinity levels.

In this work, we compare two advanced battery-type electrode materials for FDI: inorganic sodium-manganese oxides (NMOs) and organic polymers. NMOs, known for their open crystal structures, allow efficient ion insertion and extraction, making them ideal for Na-ion storage in aqueous systems [2]. Meanwhile, redox-active polymers like poly[N,N′-(ethane-1,2-diyl)-1,4,5,8-naphthalenetetracarboximide] (PNDIE) offer advantages in terms of low weight, stability, safety, and sustainability [3].

Our study explores two innovative FDI approaches to enhance salt removal capacity (SRC) and cycling stability:

i) All-polymer symmetric FDI cells: Utilizing buckypaper electrodes made from PNDIE, these cells achieved a superior salt removal capacity of 155.4 mg g⁻¹. The all-polymer design enhances production, reduces energy costs and promotes sustainability.

ii) Optimization of Sodium-Manganese Oxides: This study highlights the critical role of morphology and crystal structure in the desalination performance of NMOs. The mixed-phase NMO (mp-NMO) demonstrates outstanding stability, effectively mitigating the Jahn-Teller effect—a common issue in manganese oxides that can lead to stability challenges depending on the crystalline phase.

Both approaches employ rocking-chair flow cell configurations for continuous desalination, showcasing the potential of these novel electrode materials and designs. The findings underscore their promise for efficient, sustainable brackish water desalination, offering significant contributions to global water scarcity solutions.

In proton exchange membrane water electrolyzers (PEMWE), the oxygen evolution reaction (OER) is considered the limiting process in water splitting. To date, iridium has been recognized as having the best OER performance in acidic conditions when regarding both, activity and stability. This instigated study of various Ir-based materials using different techniques, but some questions about the mechanisms are still debated [1]. Interesting insights into the redox Ir(III)/Ir(IV) reaction and the OER process can also be gained via Raman spectroscopy [2,3], and we apply this technique in our work using an ex situ [4] and in situ approach.

Since Ir is a scarce metal, its amount in electrocatalysis is reduced by the preparation of dispersed Ir NPs on different supports. When Raman spectroscopy of iridium has been reported in the literature, it has been recorded on metal foil [2], electrochemically deposited IrO_x film on GCE [3] or drop-casted samples on GCE [4], i.e. more bulk samples. The question arises whether it is possible to perform Raman measurements directly on supported Ir NPs. We made these measurements ex situ and showed that the formation of iridium oxide can be detected for degraded states. However, the relatively low loading of Ir NPs causes the low intensity of the iridium oxide bands (E_g, B_2g and A_1g vibrations). The two supports that are used in this investigation were carbon and TiO₂ (i.e. P25).

Consequently, we continued to investigate the performance of two commercial Ir-based compounds, Ir nanoparticles (Ir NPs) and rutile IrO₂, and the measurements were made on unsupported samples. Both compounds were drop-casted from suspensions on glassy carbon electrode (GCE) and activated in a 0.1 M HClO₄ electrolyte. The Raman spectrum of GCE/IrO₂ consists of three active modes at 557 cm^-1 (E_g), 728 cm^-1 (B_2g) and 746 cm^-1 (A_1g), while the fourth low-intensity B_1g mode at 145 cm^-1 [2-4] could not be identified. In the GCE/Ir NPs sample, the E_g mode appears at 552 cm^-1, while the B_2g and A_1g modes appear as an overlapping band at 724 cm^-1. Such spectrum indicates that the Ir NPs oxidize in air and the amorphous Ir-oxide forms on the surface. During the in situ Raman measurements of the GCE/Ir NPs a composed, broad band feature evolves. The previous works were carried out in different electrolytes, potential ranges and conditions [2,3] which makes it difficult to compare the results. We consequently decided to make a systematic study in three different potential ranges: 0.05 to 1.45 V_RHE , 0.05 to 1.6 V_RHE, and 1.1 to 1.6 V_RHE and in the 0.1 M HClO₄ electrolyte, which has not been used for in situ Raman spectroelectrochemical measurements before. The evolved broad bands are explored after initial, soaked and activated states. In addition, the possible perchlorate adsorption [4] at the electrode is considered.

Hydrogen is  a clean energy source and an important candidate to replace fossil fuels in the near future (energy transition). However, traditional hydrogen production is achieved through processes that are expensive and non-sustainable require high amounts of energy, such as carbon gasification or steam methane reforming. Waste waters are considered a cheap and abundant energy source, as they contain high amounts of organic compounds. Therefore, the hydrogen production from waste water can be a useful solution in order to reduce the energy costs associated with traditional processes. 

REGENERA project (CDTI- Misiones 2019) investigates the delocalized storage of energy from renewable energies in the form of green fuels, hydrogen and methane. This communication presents the BES-BioH₂ laboratory concept, a “Power-to-Gas” technology that aims to generate hydrogen (H₂) by using a microbial electrochemical cell. The objective is to achieve an integrated system at laboratory scale which allows the simultaneous waste water treatment, hydrogen production and biogas upgrading (achieving a purity >95% of CH₄). 

Bioelectrochemical systems (BES) combine electrochemistry with the metabolism of electroactive microorganisms for energy production. In Microbial Electrolysis Cells (MECs), electroactive bacteria grow building a biofilm on the surface of a conductive anode, which acts as electron acceptor. The electroactive microorganisms oxidize organic matter to CO₂ under anaerobic conditions and the electrons obtained in the process are transferred from the anode to the cathode through an electrical circuit [1]. The cathodic reaction is the H₂ formation through H₂O reduction under alkaline conditions. The reduction of water to hydrogen is a non-spontaneous process, so the application of an external potential is required.

This study presents the experimental results using different real waste waters (urban and industrial) and discusses on the potential of various organic substrates for hydrogen production. Thus, the energy cost for hydrogen production (kWh/kg H₂), the chemical organic demand removal rate (g/m³ day) and the hydrogen production rate (m³ hydrogen/m³ reactor) are presented in order to compare the present system with conventional system for urban waste water treatment. Finally, the study suggests main limitations and opportunities for the implementation at real scale, as the final objective of REGENERA project is the development of a prototype of 500 L capacity by the end of year 2024, with capacity to produce 1-10 Nm³H₂/day.

Conductive carbon materials gather a matchless combination of exceptional properties, highlighting their availability, relatively low-cost, lightness, sufficient stability and enormous versatility to be prepared in different sizes, shapes, conformations, porous textures and surface compositions, making them excellent candidates to be used as electrodes in various electrochemical technologies. Among them, there stand out the technologies applied in the field of water treatment, like those based on pollutants electrosorption, electrooxidation and biodegradation (in the so-called microbial electrochemical technologies (METs)). In addition, these technologies show great interest in addressing the challenges of water-energy nexus. In this context, the design of carbon properties is of paramount importance for the feasibility and optimization of these technologies. On the other hand, the availability, cost and environmental impact of these materials are key factors for their development and full-scale application.

This contribution revises the carbon properties that determine their performance in electrochemical water treatment applications. Particularly, the influence of microstructure, porosity and surface chemistry on the electrochemical properties of carbons (conductivity, stability, electrochemical double layer, electron transfer, etc.) is analyzed. Furthermore, advances in strategies and tools to control and optimize these properties are discussed. Finally, recent findings on carbon properties stimulating microbial extracellular electron transfer for METs are summarized. In this respect, recent studies demonstrate that certain oxygen surface groups can promote anchorage and/or electron transfer with electroactive bacteria; whereas nanoscale (bacteria-inaccessible) porosity remarkably enhances the microbially derived electrical current. Among different carbon materials, electroactive biochar is proposed as a good candidate for large-scale environmental applications of METs.

　In recent years, the utilization of renewable energy, particularly solar power, has been accelerating globally from the perspectives of both the global energy problem and the decarbonization of society. To expand the use of renewable energy, it is necessary to store energy, and hydrogen is particularly suitable for large-scale, medium- to long-term storage. In a world aiming for carbon neutrality, hydrogen is a clean energy that can be produced by electrochemically splitting water, and water electrolysis cells that enable this are being researched and developed for practical use, with simulator development being part of this effort.

　However, current simulator development involves detailed simulation environments at the particle level that represent reaction mechanisms and electrochemical phenomena. Using these as a system places a heavy burden on the calculations, making them difficult to use. When considering device requirements, there are currently no simulators available that can represent current-voltage characteristics in a simple but reasonably detailed manner.

 Therefore, we constructed a physical model of a PEM water electrolysis cell using MATLAB/Simulink, which takes into account the frequency characteristics and capacitance characteristics, and can also represent the current-voltage characteristics.

　In this study, with the cooperation of RIKEN, we measured actual data from water electrolysis cells used in distributed hydrogen systems. To express both static and dynamic characteristics, we conducted I-V measurements and FRA measurements, respectively, and performed parameter fitting using the measurement results.

　As a result, the current-voltage characteristics within the compatible range could be expressed with an accuracy of over 95%, and the electrical transient characteristics of the water electrolysis cell, such as inrush current, could be expressed qualitatively.

　Furthermore, by accurately expressing the behavior of water electrolysis cells while ensuring sufficient simulation speed as a simulation environment for the system, it became possible to verify the necessary device requirements. We expect this to be utilized in system studies using water electrolysis cells and in device prototyping using electrochemical expressions.

The activation of O₂ through electrochemical reduction (ORR, oxygen reduction reaction) has shown promising results as alternative energy conversion technologies that can produce added-value chemicals from simple and abundant feedstocks. However, despite extensive efforts to develop catalytic materials with high reactivity and high selectivity, one can currently observe the lack of demonstrative performance for viable industrial applications. The deliberate surface modification of catalyst has been recently recognized as a powerful approach to design efficient and durable electrocatalysts [1]. It then becomes essential to obtain a good control over the spatial distribution of the chemical functions over the nanoobject surfaces. Recently, excellent catalytic properties towards ORR have been obtained in alkaline media of gold [2], silver [3], and platinum [4] nanoparticles when modified through the reductive grafting of rigid macrocycle calix[4]arene-tetradiazonium salts [5]. However, many fundamental questions, with important operational implications, remain open about these calixarene-modified surfaces. In particular, the conformation of the calixarene on the surface, and the structural, thermodynamic and electronic description of the interface. In addition, the C-Au bond has been poorly investigated in comparison to the S-Au bond.

Here, using spectroscopic studies coupled with computational modeling performed with density functional based tight-binding (DFTB) approaches, we investigate the interaction between calix[4]arene macrocycles and gold and platinum nanoparticles. After exploring the nature of the bond between the macrocycle and the gold surface thanks to a good agreement between measured and calculated Raman spectra, we describe the effect of calix[4]arenes on nanoparticles electrocatalytic properties [6].

The alkaline oxygen evolution reaction (OER) is crucial for green hydrogen production via water electrolysis. However, its industrial implementation at high current densities remains limited due to the scalability, overpotential, and stability challenges of current commercial electrocatalysts. Layered hydroxides (LH), particularly those based on abundant transition metals, are emerging as promising alternatives owing to their remarkable electrochemical properties.

In this talk, we will present the latest advances from the 2D-Chem research group (www.icmol.es/2dchem) in the synthesis and characterization of novel two-dimensional (2D) LH materials. Specifically, we have developed an industrially scalable, room-temperature, atmospheric-pressure homogeneous alkalinization synthetic pathway to produce optimized NiFe layered double hydroxide (NiFe-LDH). By leveraging the nucleophilic attack of chloride on an epoxide ring, we have achieved a low-dimensional, highly defective NiFe-LDH exhibiting pronounced cation clustering and excellent electrochemical performance. Spectroscopic studies, including in-operando XANES, EXAFS, SAXS or Raman combined with ab-initio calculations reveal the critical role of Fe clustering in lowering the energy pathway for improved catalytic activity.

Furthermore, we have extended this synthetic route to other compositions that will demonstrate the versatility of these materials beyond green hydrogen production. Indeed, in-situ XAS and PXRD studies provide further insights into the behavior of these layered materials during operation, allowing their use as precursors for metallic nanocomposites with applications in energy storage. Finally, optimized LDH and hybrid LDH-nanocarbon electrocatalysts with tailor made compositions can also play a pivotal role in alkaline electrochemical water treatment for the remediation of contaminated water systems, offering a sustainable approach for pollutant degradation and removal.

Over the past century, humans have altered the global nitrogen cycle so drastically that managing nitrogen has emerged as a grand engineering challenge and urgent need. The emissions-intensive Haber-Bosch process for industrial fertilizer production, which converts nitrogen gas into ammonia, outpaces wastewater nitrogen removal due to fertilizer runoff and 80% of wastewater being discharged without treatment. Refining nitrate and ammonia into valuable products through reactive separations, which integrate catalysis and separations, is a useful approach for addressing both water pollution and chemical manufacturing. For example, selective membranes and adsorbents can be leveraged to control catalytic performance by tuning microenvironments near catalyst active sites. This seminar will focus on recent work designing metal electrocatalysts for selective reduction of nitrate to ammonia, along with separation of high-purity ammonia from real wastewaters. Specifically, we focus on understanding the reaction microevenionment of titanium and cobalt in multiple catalyst architectures while leveraging a systematic study of electrolyte composition on catalyst activity, selectivity, and stability. We complement these efforts with reactive separation devices that leverage electrochemical potential to drive nitrate and ammonia transport, which advances the vision of wastewater refining: producing a tunable portfolio of products from real wastewaters. 

Among the electrochemical advanced oxidation processes (EAOPs) for wastewater treatment, which exhibit high effectiveness combined with green deployment, some of them primarily rely on the efficiency of anode materials in generating potent oxidants like hydroxyl radicals (•OH). Hence, the development of novel, cost-effective nickel-manganese-based anodes has been investigated in this work, aiming to revolutionize the electro-oxidation of organic pollutants. Key to this endeavor is the use of 3D porous conductive substrates, akin to those employed in redox-flow batteries and water electrolyzers. These substrates are crucial for maximizing the electrode-electrolyte interactions and facilitating efficient flow-through designs, thereby significantly boosting the EAOPs performance. The synthesis, characterization, and optimization of these Ni-Mn-based electrodes, including their physicochemical structure and electrochemical properties, have been studied. It has been found that by employing Ni-Mn-based materials as the active material and utilizing the high surface area of 3D substrates such as nickel foam and graphite felt, our electrodes achieved a remarkable 100% removal of phenol, coupled with an 80% reduction in chemical oxygen demand (COD), thus marking a significant advancement over traditional anodes. Comparative analyses with boron-doped diamond (BDD) and dimensionally stable anode (DSA) highlight the superior activity and efficiency of our anodes. Further, a detailed mechanistic study was undertaken to elucidate the electrochemical pathways and interactions. This investigation reveals an enhanced generation of hydroxyl radicals and other oxidizing species on the anode surface, justifying the observed degradation efficiency. The implications of these findings are substantial in the field of wastewater treatment. Developing our Ni-Mn oxides not only sets a new benchmark in pollutant degradation efficiency but also offers valuable insights into the electrochemical mechanisms underpinning EAOPs.

The water crisis is a major concern at global scale, which underscores the need for alternative freshwater resources. In this context, urban wastewater is one of the main targets to feed regenerated water for many applications, but it faces challenges from persistent pharmaceuticals resistant to conventional treatments. Advanced methods like electrochemical advanced oxidation processes (EAOPs), particularly the electro-Fenton (EF) process, offer a highly promising performance [1]. However, limitations such as narrow pH range and low H₂O₂ yields must be addressed by developing new electrocatalysts and heterogeneous catalysts.

This work addresses these issues through two innovations: (1) Electrocatalysts for highly selective two-electron oxygen reduction reaction (2e^– ORR) to generate H₂O₂ in situ, and (2) advanced heterogeneous catalysts with enhanced H₂O₂ activation efficiency.

In EF, 3.0 to 15.0 mM H₂O₂ is sufficient to purify wastewater [2], making the electrochemical 2e^– ORR with a gas-diffusion electrode (GDE) an attractive alternative to the industrialized anthraquinone process to synthesize H₂O₂. Tin (Sn) exhibits strong O₂ adsorption under alkaline conditions [3]; accordingly, Sn-doped carbon materials are demonstrated to have outstanding H₂O₂ selectivity (98%) and high H₂O₂ production efficiency at near-neutral pH, with an electron transfer number of 2.04. Nitrogen-doped carbons, optimized for pyrrolic nitrogen content, delivered superior H₂O₂ yields (reaching 18 mg h^–1 cm^–2) compared to commercial GDEs.

For H₂O₂ activation, Cu/NC and FeCu/NC catalysts derived from MOFs exhibited great performance. Cu/NC enabled the effective pollutant mineralization at pH 6–8, being superior to the EF process with soluble Fe²⁺ at pH 3. The core-shell structure of FeCu/NC minimized metal leaching and extended catalyst lifespan. This brought about an accelerated Fe(II) regeneration, achieving 100% removal of lisinopril within 75 min.

This research shows significant progress in the development of sustainable EF systems, integrating the efficient electrogeneration and activation of H₂O₂, which allows addressing the problem of pharmaceutical pollutants in wastewater.

Water issues represents one of the biggest challenges of the 21st century. The United Nations has addressed Sustainable Development Goal (SDG) to answers the water crisis. The increase of water demand in the different sectors (agriculture, industry and household), and the water stress that is globally rising in the meantime, are responsible for this critical issue. To face it, the water reuse approach is more and more considered. However, before reusing wastewater there is the need to completely remove emerging pollutants (e.g., pharmaceuticals, pesticides, personal care products) since they are not eliminated by the bioprocesses typically applied in plants. Still, wastewater contains valuable chemicals (e.g., phosphate, magnesium) that could be recovered in the meantime. Electrochemical systems can tune the removal and recovery steps by playing on the applied potential/current, in contrast with chemical processes. They also offer the advantages of operating several unit operations (separation and conversion technologies) without the need for chemicals addition and within the same reactor design. Moreover, vector of energy could be electrogenerated (e.g., hydrogen (H2)). This presentation will focus on case studies implementing electro-precipitation, electro-sorption and electro-reduction/-oxidation for resource recovery in wastewater under microfluidic conditions.

Feeding long-term sustainability to our planet is becoming a major must, given the urgent need to preserve our natural resources, reduce pollution and protect the natural ecosystems. Sustainable development holds on three pillars, namely environmental sustainability and protection, economic viability, and social equity. Among them, the former receives great attention and it is build up on reducing carbon emissions and footprint, packaging waste, water usage, and other negative environmental impacts. New paradigm towards green chemistry, sustainability, and circular economy in the chemical sciences must be developed, in order to better employ, reuse, and recycle the materials employed in every aspect of modern life. Following this approach, electrochemical reactions have found technological applications in various fields, including electrochemical synthesis, energy storage, and environmental remediation [1]. Sustainability and electrochemistry are therefore closely related. In this talk, the utilization of electrochemical tools together with bio-based or sustainable materials is presented.

First, the exploration of new synthetic routes to reduce the toxicity of residual monomer and other chemicals employed (initiators, surfactants) during the fabrication of polymer hydrogels, one of the most promising groups of biomaterials, is required. With a similar approach to the previously developed "green" and clean production of polymer nanogels, largely used in biomedicine, based on the recourse to high energy irradiation, electrochemical advanced oxidation technologies were used to crosslink hydrogels of poly(vinylpyrrolidone)(PVP) by means of electrogenerated hydroxyl radicals. This facile electrosynthesis route showed that the kind of radicals strongly drives the transformation of the architecture of linear, inert polymer chains into a functionalized nanogel (with -COOH and succinimide groups), more suitable for further conjugation [2-4].

Second, the conversion of bio-based polymers such as chitosan and agarose, into eco-friendly carbonaceous electrodes is described, as a suitable choice for promoting sustainability due to their low cost and high activity/selectivity [5-6]. The use of mesoporous carbon supports both reduce the amount of noble metals employed as electrocatalysts and enhance the accessibility of reactants to the active sites. On the one hand, excellent electrocatalytic performance of N-doped chitosan-derived carbons and large surface area agarose-derived carbons are responsible of the high efficiencies achieved (above 95%), allowing the fast destruction of pharmaceutical residues in electro-Fenton treatment. On the other hand, chitosan-derived mesoporous carbons served as optimal supports for PtCu electrocatalysts, evidencing an increased activity of both the four-electron ORR and the methanol oxidation reaction as compared to commercial supported Pt and PtCu catalysts, which is attributed to the good balance achieved between micro/mesoporosity.

Finally, one of the most appealing and recent trends in the application of biopolymers in electrochemical water treatment is reported. The co-generation of freshwater and sustainable energy in a closed loop where the solar energy is used not only for water purification treatment with porous materials like hydrogels, but also for thermoelectric power generation, by means of material transpiration and diffusion processes. The photothermal electricity production is promoted by hydrogels based on biopolymers such as alginate (ALG) and thermosensistive materials like poly(N-isopropylacrylamide) (PNIPAAm). ALG-PNIPAAm bio-hydrogel, modified with conducting polymer (CP), as thermal absorber component, was used to obtain freshwater from seawater desalination under sunlight. Higher evaporation rates (> 4 kg/h*m²) have been observed in the presence of lineal CP, if compared with nanoparticles of CP [7-8]. Impedance measurements elucidate the ion diffusion dynamics within the hydrogel, directly correlating this behavior to enhanced power generation; these results revealed that the presence of hydrophilic groups (─OH, ─SO₃H), present in the CP backbone, promotes the capillary flow of the electrolyte during the sunlight irradiation. The doped CP molecules facilitate a fast ion transport thanks to a good balance between the material hydrophilicity and the interconnected pores.

Electrocatalysis is increasingly important in water treatment for its efficiency and eco-friendliness, and materials play important role in performance. In this work, we synthesized an efficient single-atom Co-N/C catalyst for electrocatalytic dehalogenation, which provided more active sites and a faster charge transfer rate. Co-N/C effectively removed florfenicol (FLO) over a broad pH range, with rate constants that were 3.5 and 2.1 times higher than those of N/C and commercial Pd/C, respectively. The defluorination and dechlorination efficiencies were 67.6 and 95.6%, respectively, with extremely low Co leaching (6 μg L^-1) and low energy consumption (22.7 kWh kg^-1). H* and direct electron transfer were the primary causes of dehalogenation. The Co-N/C was minimally affected by pH, co-existing ions, and water quality, maintaining a high removal rate (>90%) after ten cycles [1]. To enhance H* production, the phosphorus-doped cobalt nitrogen carbon catalyst (Co-NP/C) was prepared for electrocatalytic dechlorination, which had high catalytic activity in a wide pH range (3-11). The introduction of phosphorus was found enhanced the electron density of cobalt and regulated the electron transfer.

We further developed the heterogeneous electro-Fenton process based on dual-functional cathodes. The catalyst composed of nitrogen-doped carbon nanotubes encapsulating zero-valent iron (Fe@N-C) was synthesized, which demonstrated superior degradation of sulfamethazine (SMT) under mildly alkaline conditions. The primary reactive species generated by Fe@N-C were H* and singlet oxygen (¹O₂), with hydroxyl radicals (∙OH) playing a supportive role [2]. Additionally, the catalyst with boron and nitrogen co-doped carbon nanotubes encapsulating zero-valent iron (Fe@BN-C) was fabricated, which significantly increased the selectivity for H₂O₂ to 94%, and H₂O₂ was directionally converted to ¹O₂ via surface ∙OH. Theoretical calculations confirmed the confinement effect of Fe⁰ overcame the rate-limiting step for H₂O₂ formation, achieving high efficiency and selectivity for ¹O₂ transformation[3].

Traditional free radicals-dominated electrochemical advanced oxidation processes (EAOPs) and sulfate radical-based advanced oxidation processes (SR-AOPs) are limited by pH dependence and weak reusability, respectively. To address these shortcomings, electro-enhanced activation of peroxymonosulfate (PMS) was proposed. Firstly, a novel perovskite-Ti₄O₇ composite anode activating PMS (E-PTi-PMS) system achieved an ultra-efficient removal rate (k = 0.467 min^-1) of carbamazepine (CBZ). The electric field expedited the decomposition and utilization of PMS, promoting the generation of radicals and expanding the formation pathway of ¹O₂. This system presented superiorities over wide pH (3-10) and less dosage of PMS (1 mM), expanding the pH adaptability and reducing the cost of EAOPs [4].

Introducing chiral organic spacers in low-dimensional metal-halide perovskites triggers chiroptical activity, making these materials of great interest for spintronic applications. To enable such applications, it is necessary to develop a deep understanding of the structure formation of chiral two-dimensional (2D) perovskites and its impact on their optical properties. While much attention has been dedicated to developing processing routes to control the properties of achiral 2D perovskites, the use of chiral cations introduces higher steric hindrance, thus significantly impacting structure formation. I will discuss how changing the processing conditions impacts the phase purity, microstructure, and chiroptical properties of chiral 2D perovskites. For example, in solution-processed chiral 2D perovskites, the choice of solvent or the use of additives enables control over the structure and microstructure of the deposited thin films. Alternatively, I will show that chiral 2D perovskites can be processed by thermal evaporation, opening new pathways to large-scale deposition and microstructuring. 

The chemical and structural flexibility of layered (2D) hybrid organic–inorganic metal-halide perovskites (HOIPs) has been proposed as an ideal platform for the synthesis of novel circularly polarized light emitters through the incorporation of chiral organic molecules, showing potential application in optoelectronics and spintronics.[1,2] Furthermore, the weak forces between the organic layers in the case of Ruddlesden-Popper 2D HOIPs, allow mechanical exfoliation of bulk crystals to obtain flakes[3] making possible their integration in nanodevices. Most studies to date have focused on bulk compounds, specifically on the unstable and toxic Pb-based HOIPs,[1,2] although Mn-based HOIPs apart from lower toxicity can show not only chiroptical but also magnetic properties[4]. In this work, we report the chiroptical properties of R- and S-β-methylphenethylammonium Mn chloride HOIPs, which exhibit antiferromagnetic order,[5] in both bulk and mechanically exfoliated flakes. In these compounds, we observe the red photoluminescence (PL) emission originating from the octahedrally coordinated Mn²⁺, with a PL redshift as they transition from bulk to flake form. Circular dichroism (CD) and circularly polarized luminescence (CPL) mirrored signals confirm the chirality transfer from the organic cations to the inorganic lattice in bulk materials, presenting g_lum values (0.01) among the highest reported for chiral hybrid Mn halides. This chirality is preserved in the exfoliated flakes, reaching degrees of circularly polarized PL (P) of up to 17% at 80K, which systematically decrease with increasing temperature as previously observed in 2D Pb-based HOIPs[6]. Additionally, angle-resolved PL measurements show that the PL emission and P are isotropic. Therefore, our results demonstrate that these 2D Mn-based HOIPs are highly valuable, as they can compete with their Pb analogs and offer additional functionalities for spin-optoelectronic applications, thanks to the magnetic behavior associated with Mn²⁺.[7]

Hybrid organic–inorganic perovskites have emerged as exceptional materials for optoelectronic and energy conversion devices[1]. Recently, chiral hybrid perovskites, which incorporate chiral organic ligands into the inorganic framework, have attracted increasing attention as promising chiroptoelectronic systems with potential applications in optoelectronics, spintronics, and beyond [2]. The chirality and associated chiroptical responses in these materials are attributed to a chiral bias originating from the chiral organic ligands, which propagates through the inorganic framework, influencing the geometry of the entire hybrid perovskite structure [3].

Modern multiscale modeling and simulation techniques have now reached unprecedented levels of accuracy, enabling the efficient design of chiral materials and the precise optimization of their chiroptical properties. In this discussion, I will present simulation workflows developed over the years to predict the circular dichroism (CD) and circularly polarized luminescence (CPL) of soft [5]and hybrid materials [6].

Enhanced sampling simulations, particularly through parallel bias metadynamics, in conjunction with ab-initio molecular dynamics (AIMD) based on density functional theory (DFT) methods and their time-dependent extensions, were employed to investigate the structure, dynamics, and chiroptical spectra, with a focus on CD and CPL.

This simulation strategy enables the prediction of how non-covalent interactions in excited states drive the generation of CPL spectra and the associated dissymmetry factors.

References

[1] Grancini, Nazeeruddin. Nat. Rev. Mater. 4, 4-22.

[2] Pietropaolo, Mattoni, Pica, Fortino, Schifino, Grancini. Chem 8: 2022, 1231.

[3] Long, Sabatini, Saidaminov, Lakhwani, Rasmita, Liu, Sargent, Gao. Nat. Rev. Mater. 2020 5 423.

[4] Albano, Pescitelli, Di Bari. Chem. Rev. 120: 2020, 10145.

[5] Wu, Pietropaolo, Fortino, Shimoda, Maeda, Nishimura, Bando, Naga, Nakano. Angew. Chem. Int. Ed. 61: 2022, e202210556.

[6] Fortino, Mattoni, Pietropaolo. J. Mater. Chem. C 11: 2023, 9135.

Over the last ten years, the role of hybrid metal halide perovskites has received significant attention as suitable materials for various electronic applications. Indeed, their outstanding optoelectronic properties such as high-power conversion efficiency, tunable bandgap, and high absorption coefficient, make them suited for several applications in different devices as photovoltaic cells, photodetectors, light emitting diodes, and sensors^[2]. Starting from the hybrid organic-inorganic perovskites (HOIPs), the introduction of a chiral molecule as organic cation leads to the breaking of the spatial inversion symmetry, allowing new possible designs based on the combination of polarity and chirality^[1,3].  In the scientific scene, this opened plenty of novel applications provided by outstanding chiroptical properties, such as circular dichroism, circular polarized emission, chiral induced spin selectivity and so on. To extend the actual knowledge of these chiral systems, it is important to investigate those parameters which have a major impact on the chirality transfer mechanism, with the final aim to unveil it. From a material chemistry point of view this involve an important work on materials’ structure, involving several modulations/substitutions on the latter. More specifically, in this contribution we will present the results of the role of the organic cation, showing the modulation of the optoelectronic properties engineering unconventionally chiral cation. Firstly, we decide to move away from the commercial chiral cation and to synthesize homologous series that can help unveil the role of the chemical nature of the cation on the chiroptical properties. We obtained a new phase (R-/S-AMOL)PbI₃ and the correspondence with the Sn^[4]. The work provides a comparison not only in terms of structural features and chiroptical properties but also in terms of computational modelling, which helps us to deeply understating the role of organic cation and the difference in terms of efficiency moving from a Pb-based perovskites to a Pb-free one. Final aim of this work is to unveil the impact of chemical degrees of freedom on the chirality transfer between the organic cation and the inorganic framework to provide tuning strategies for materials engineering.

Metal Halide Perovskites (MHPs) and their derivatives are the subject of intense research due to their remarkable optoelectronic properties and tunable bandgap [1]. Major applications include photovoltaic cells for three-dimensional perovskites, as well as photodetectors, photodiodes, and lasers for other perovskite-based materials. A significant modification that can be made to organic-inorganic metal halides is the introduction of chiral organic cations, leading to the emergence of chiroptical properties and the Rashba-Edelstein effect [2]. The latter is particularly interesting for spin-related phenomena such as chirality-induced spin selectivity (CISS).To date, most chiral metal halides contain lead, a toxic element subject to strict regulations. Therefore, the exploration of lead-free materials is crucial. In this study, we report the synthesis of bismuth (III)- and antimony (III)-containing chiral iodides, including R/S-1-(4-Chloro)-Phenylethylammonium (abbreviated as Cl-PEA) as the organic chiral cation. Single crystals with the stoichiometry Cl-PEA₄M₂I₁₀ (where M represents Bi or Sb) have been prepared for both enantiomers and the racemic compound, and their structures have been resolved via single-crystal XRD. Additionally, mixed Sb/Bi systems have been synthesized to investigate potential bandgap bowing, which has already been observed in analogous vacancy-ordered achiral perovskites [3], and already analysed via powder diffraction.The optical properties of the prepared samples have been analyzed using UV-Vis and CD spectroscopy. Finally, starting from the experimental data, computational modeling has been employed to optimize the crystal structures, determine the electronic band structure, and evaluate the presence and extent of Rashba splitting. The modeling has also been used to calculate the projected density of states (PDOS) and the total density of states (DOS) of our compounds. These calculations provide insights into the orbital contributions to the observed bandgap bowing and identify the contributing species.

During the  recent years, chiral hybrid organic-inorganic perovskites where the organic cations are the “source” of chirality, have received great attention from the physics and chemistry research community. Their functional properties enable the control of light, charge, and electron spins in the same materials. Here, we will discuss the intriguing “chirality transfer mechanism” in some newly synthesized ferromagnetic chiral hybrid inorganic perovskite along with their interplay with magnetism. Although the organic cations are chiral and polar molecules, their arrangement in the crystal structure results in a chiral non-polar space-group P212121. Moreover, we discuss a new chirality order parameter such as the electronic chirality measure (ECM) aiming at quantify the molecular cation chirality taking into account ionic and electronic degrees of freedom simultaneously. Also, the relation of ECM to physical properties of chiral hybrid perovskites will be discussed, so shedding light on the fundamental principles governing their behavior and paving the way for the development of innovative optoelectronic and spintronic devices. 

Coupling chiral organic cations with the inorganic skeleton of perovskites is paving the way for new materials combining the second-order non-linear optical responses granted by the chiral molecules [1] and the modulable absorption and luminescence features settled by the perovskite or perovskite-derivative structures [2,3]. The heightened flexibility of design permitted by the vastity of available chemical constituents allows creating materials where the structural and functional parameters can be engineered, resulting in elevated circular dichroism, tunable photoluminescence, elevated spin selectivity, and more. Within this growing field, a deep understanding of how chemical composition and structural parameters impact on photophysical properties and chirality transfer mechanism is crucial, and parameters such as framework dimensionality, octahedral distortion and hydrogen bond network must be taken into account.

In this perspective, the current presentation will focus on novel hybrid organic inorganic perovskites (HOIPs) and their derivatives, attained through a rational tuning of the components to evaluate its impact on crystal structure and chiroptical properties. The effect of materials dimensionality on the chiral response will be discussed, including examples of 3D HOIPs derivatives which are not common due to the steric constrains of chiral cations. The metal centres impact on octahedra distortion, bandgap and chiroptical features will be examined, reporting results from our group with cations such as Sn^II and Ge^II in addition to the well-known Pb^II. The chiral cations modulation will also be presented, exploring molecules with mixed functionalities, i.e. simultaneously containing amino and hydroxyl groups, synthesized ad hoc to move away from the few commercially available ones. Finally, high-pressure studies unveiling the structural and optical response of chiral HOIPs upon external stimuli will be outlined.

It is generally accepted that spin-dependent electron transmission may appear in chiral systems, even without magnetic components, as long as significant spin–orbit coupling (SOC) is present in some of its elements [1]. However, this chirality-induced spin selectivity (CISS) can only manifest in experiments when system is taken out of equilibrium. Aided by group theoretical considerations and nonequilibrium DFT-based quantum transport calculations, here we show that, when spatial symmetries that forbid a finite spin polarization in equilibrium are broken, a net spin accumulation appears at finite bias in an arbitrary chiral two-terminal nanojunction. Furthermore, when a suitably magnetized detector is introduced into the system, the net spin accumulation, in turn, translates into a finite magneto-conductance [2]. These calculations have been possible thanks to new SOC implementation in our code ANT.Gaussian (https://github.com/juanjosepalacios/ANT.Gaussian). We also extend this analysis to chiral crystals where a similar phenomenology should be present in bulk. We do so thanks to a new code based on the computation of k-dependent transmission and polarization on top of a Hamiltonian obtained with CRYSTAL23.

Low-dimensional (LD) organic metal halide hybrids (OMHHs), comprising diverse organic cations and metal halide anions, represent an emerging class of perovskite-related hybrid materials with exceptional structural and property tunability. By carefully selecting organic and metal halide components, their crystallographic structures can be precisely tailored at the molecular level, with metal halide units forming two-dimensional (2D), one-dimensional (1D), or zero-dimensional (0D) structures. The site isolation and confinement of metal halides by organic cations endow LD OMHHs with unique properties distinct from conventional three-dimensional (3D) metal halide perovskites. For example, 2D and 1D OMHHs have demonstrated broadband white emissions, while 0D OMHHs have achieved near-unity photoluminescence quantum efficiency (PLQE) with tunable emissions spanning blue, green, yellow, orange, and red wavelengths. The true significance of LD OMHHs lies not only in these specific accomplishments but also in their role as a new paradigm in materials design. In this talk, I will present our recent progress in the development and study of LD OMHHs, from synthetic control to device integration. Applications of LD OMHHs in various areas, including optically pumped white LEDs, electroluminescent devices, X-ray scintillators, and direct X-ray detectors will be discussed.

Layered metal-halide perovskites, or two-dimensional perovskites, can be synthesized in solution, and their optical and electronic properties can be tuned by changing their composition. In this talk, I will present a molecular templating method that restricted crystal growth along all crystallographic directions except for [110] and promoted one-dimensional growth out of the inherently layered 2D structures. This templating effect is achieved via introducing directional intermolecular interlayer hydrogen bonding interactions. This approach is widely applicable to synthesize a range of high-quality layered perovskite nanowires with large aspect ratios and tunable organic-inorganic chemical compositions (including Sn and Pb based perovskites, different quantum well thickness, and different halides). These nanowires form exceptionally well-defined and flexible cavities that exhibited a wide range of unusual optical properties beyond those of conventional perovskite nanowires. We observed anisotropic emission polarization, low-loss waveguiding (below 3 decibels per millimeter), and efficient low-threshold light amplification (below 20 microjoules per square centimeter). The 1D-2D mixed dimensional nanostructures provide unprecedented opportunities for next-generation optoelectronics and photonics.

The continuous development in smart devices and microsystems for the control of industrial processes, biomedical sensors and instruments, visible and NIR light communications, as many other applications, is triggering new demands for photonic chips. Metal halide perovskites (MHPs) can be a good solution, because of their good optoelectronic properties and tolerance against crystalline defects, other than low-cost processing and low CO2 footprint. In the present talk the optical properties of several 2D MHPs of formula ABX3 (A = organic cation, B = Pb, Sn, X = I) have been investigated and will be presented in this talk.

First of all, basic optical properties of Pb-perovskites, as PEA2PbI4 (and higher order Ruddlesden-Popper phases), will be presented, both in the case of polycrystalline thin films and nanoflakes with lateral size greater than 10 µm. Moreover, these nanoflakes can be the base of micrometric photodevices by using Pt-prepatterned Si/SiO2 substrates with channel lengths in the range 2-10 µm. Measured photocurrent is highly dependent on the thickness flake due to the great absorption coefficient and negligible carrier transport in the vertical direction. Interestingly, in the case of few layer nanoflakes, photocurrents from 10 pA to 100 nA can be measured in the range 10 pW to more than 500 nW.

Sn-perovskites are also very interesting 2D semiconductors, because they are non-toxic alternatives of Pb-perovskites for applications as photodevices. However, the use of Sn-perovskites still suffers from very low stability and most of the synthesis, fabrication and/or characterization work must be done under inert atmosphere or vacuum, even if antioxidative synthetic routes can be followed for reducing the negative effect of ambient conditions. 2D tin-perovskites, TEA2SnI4, are gaining more stability and resistance to ambient condition, whose deposition is possible by scalable solution processing techniques as Inkjet-printing. Room- and low-temperature excitonic PL and charge carrier recombination dynamics in (TEA)2SnI4 thin films were studied and demonstrated two excitonic optical transitions. The analysis of micro-PL measurements suggests that the low-energy emission line is associated to the volume of perovskite grains (platelets), while the high-energy excitonic transition seems to be originated at the platelet edges (as identified in the biggest ones). Photoconductive detectors based on TEA2SnI4 inkjet-printed films were also studied after encapsulation. High electrical (dark currents as low as » 10 - 20 nA at 10 V of bias voltage) and electro-optical parameters (responsivities in the range 1-20 A/W) were obtained for these photodevices under ambient conditions over several weeks.

Hybrid halide perovskites (HHPs), whose every branch generates intrusiveness, have been utilized in solar cells from a wider perspective. However, the inclusiveness of employing HHP as a photocatalyst is still in its initial stage. We have explored the so far undesirable material, MA₂SnBr₆ synthesized from MASnBr₃ and discovered a new vacancy-ordered MA₂SnBr₆ perovskite as a potential photocatalyst for efficient solar-driven C(sp³)─H activation of cyclohexane and toluene under ambient conditions. The as-synthesized MASnBr₃ and its oxidized form having different ratios of Sn²⁺ and Sn⁴⁺ were subjected to cyclohexane oxidation and it was observed that the completely oxidized form i.e. MA₂SnBr₆ gave the highest yield of cyclohexanol and cyclohexanone.[1] Further, we have addressed four major key challenges in the domain of halide perovskites i.e. toxicity, stability, reusability, and efficiency of halide perovskites. To tackle these issues, we synthesized a vacancy-ordered HHP, specifically methyl ammonium tin bromide quantum dots (MA₂SnBr₆ QDs) directly from its raw precursors this time, which had not been explicitly synthesized so far. MA₂SnBr₆ was synthesized through a greener approach, a simple yet effective solvent-free mechanochemical synthesis at room temperature without the use of additional capping agents. Interestingly, the synthesized MA₂SnBr₆ QDs exhibit stability in air and moisture, addressing a common issue with HHPs. To our surprise, we also discovered that these MA₂SnBr₆ QDs are stable in the polar solvents such as isopropanol, ethanol, and acetonitrile, overcoming a major challenge typically encountered with halide perovskites. The air and moisture-stable MA₂SnBr₆ QDs were applied for photocatalytic CO₂ conversion. The icing on the cake is the simultaneous conversion of biomass-derived alcohol to valuable chemicals which was not attempted previously with CO₂ reduction. The yield of the CO and CH₄ is highest than the so far reported perovskite used for photocatalytic CO₂ reduction.[2] Moreover, comparing with the complex photocatalytic system previously reported, our single catalytic (MA₂SnBr₆) system presented impressive results for simultaneous biomass derived alcohol oxidation with CO₂ reduction.

Developing high-mobility p-type semiconductors that can be grown using silicon-compatible processes at low temperatures, has remained challenging in the electronics community to integrate complementary electronics with the well-developed n-type counterparts.

This presentation will discuss our recent progress in developing high-performance p-type semiconductors as channel materials for thin film transistors. For the first part of my talk, I will present high-performance tin (Sn²⁺) halide perovskite transistors using high-crystallinity and uniform cesium-tin-triiodide-based semiconducting layers [1.2]. The optimized devices exhibit high field-effect hole mobilities of over 50 cm² V⁻¹ s⁻¹, large current modulation greater than 10⁸, and high operational stability and reproducibility [3]. In addition, we explore triple A-cations of caesium-formamidinium-phenethylammonium to create high-quality cascaded Sn perovskite channel films. As such, the optimized TFTs show record hole mobilities of over 70 cm² V⁻¹ s⁻¹ and on/off current ratios of over 10⁸, comparable to the commercial low-temperature polysilicon technique level.

Next, I present an amorphous p-type oxide semiconductor composed of selenium-alloyed tellurium in a tellurium sub-oxide matrix, demonstrating its utility in high-performance, stable p-channel TFTs, and complementary circuits [4]. Theoretical analysis unveils a delocalized valence band from tellurium 5p bands with shallow acceptor states, enabling excess hole doping and transport. Selenium alloying suppresses hole concentrations and facilitates the p orbital connectivity, realizing high-performance p-channel TFTs with an average field-effect hole mobility of ~15 cm² V^-1 s^-1 and on/off current ratios of 10⁶~10⁷, along with wafer-scale uniformity and long-term stabilities under bias stress and ambient aging.

References

[1] A. Liu, Y.-Y. Noh et al, Nature Electronics 5, 78-83 (2022)

[2] H. Zhu, Y.-Y. Noh et al, Nature Electronics 6, 650-657 (2023)

[3] A. Liu, Y.-Y. Noh et al, Nature Electronics 6, 559-571 (2023)

[4] A. Liu, Y.-Y. Noh et al, Nature, 629, 798–802 (2024)

Lead-free halide double perovskites (HDPs, A₂BB^’X₆) with attractive optical and electronic features are regarded as one of the most promising alternatives to overcome the toxicity and stability issues of lead halide perovskites. They provide a wide range of possible combinations and rich substitutional chemistry with interesting properties for various optoelectronic devices.^[1] However, the performance of state-of-the-art lead-free HDPs is not yet comparable to that of lead halide perovskites, especially in the photovoltaic field.^[2] One of the main reasons for this is that HDPs usually have large and/or indirect bandgaps, which limit their optical and optoelectronic properties in the visible and infrared regions. In this presentation, I will talk about our work on double perovskites, including the fabrication of the first planar double perovskite solar cell devices, and the modification of the bandgap and optical properties of HDPs using metal doping/alloying and crystallization control,^[3],[4] as well as provide detailed understanding of the alloying at the atomic level.

Cs₂TiBr₆, a promising lead-free and earth-abundant double perovskite, exhibits excellent photovoltaic and optoelectronic potential due to its 1.8 eV bandgap and theoretical stability under various conditions. Despite its advantages, challenges in conventional synthesis—such as high temperature, pressure, and solubility issues—have limited its practical application. Additionally, its susceptibility to air-induced degradation raises further concerns about its stability.

This work introduces a novel, microwave-assisted synthesis method that significantly reduces time, temperature, pressure, and cost while maintaining structural stability under diverse atmospheric conditions, including air, oxygen, white light, and temperatures exceeding 130°C. A gradual cation exchange process was implemented to enhance stability by substituting Ti⁴⁺ with Sn⁴⁺ in the efficient microwave-assisted synthesis method, developing a double perovskite Cs₂Sn_xTi_1-xBr₆ type. A systematic study of Sn-doping revealed improved air stability for over a week, uniform polygonal crystal morphology, and a slight bandgap broadening.

This efficient and sustainable synthesis approach offers a pathway to more durable and environmentally friendly perovskites, unlocking new opportunities for advanced optical and electronic devices.

Quasi-2D metal halide perovskites (MHPs) employed in photovoltaics involve the use of monoammonium or diammonium spacer cations to form the Ruddlesden-Popper or the Dion-Jacobson phases, respectively.¹ Moreover, the chemical nature of the bulky cations plays a significant role in the optoelectronic properties of the quasi-2D MHPs, controlling the orientation of the inorganic octahedral layers, the interlayer distance and thickness of the inorganic layers, phase distribution and the dielectric constant and dipole moment of the organic barriers which all determines the charge transport in the quasi-2D MHPs.² Moreover, additive engineering and processing strategies can also modulate the charge carrier transport.

We have used a p-conjugated bulky cation, 4,4′-diaminostilbene dihydrochloride (Sb), to synthesize a Dion-Jacobson 2D MHPs that is employed to fabricate photovoltaic devices. The relative ratio of the employed precursors is selected to define the n = 5 phase, (Sb)FA_2.8MA_1.2Pb₅I₁₅. However, a distribution of low dimensional phases is found (n = 1, 2 and 3) although other phases with longer n values are also present. The quasi-2D DJ MHP in the film is highly oriented and the deactivation of the photoexcited charge carriers (mostly excitons) is through a radiative recombination pathway assisted by the quantum confinement in the low dimensional phases. This fast deactivation of the excited state prevents a rapid extraction of the charges from the material and therefore, the short circuit current (J_sc) in the solar devices prepared with this perovskite is low, J_sc = 9.03 mA·cm^-2.

On the contrary, the addition of the MASCN additive to the initial precursor solution modifies the distribution of the phases in the film. Thus, the low dimensional phases are scarce now but phases with higher dimensionality are more present in these films. This is clearly demonstrated by the absence of steady-state and transient absorption features of the low dimensional phases. Moreover, the PL decays display a much longer time constant, which is a hint for a less intense quantum confinement in these samples. The reduction of the defect concentration calculated with the space-charge limited current measurements suggests that the excess of the stilbene derivative is localized in between the perovskite grain passivating the superficial defects and, therefore, reducing the non-radiative recombination pathway.

Three-dimensional tin halide perovskites are promising materials for photovoltaic applications due to their ability to achieve narrower bandgaps compared to their lead-based counterparts. However, a major challenge in advancing their performance is their intrinsic self-p-doping, which occurs even in the absence of external oxidizing conditions. This native p-type behavior is driven by the unique defect chemistry of the material, leading to reduced minority carrier lifetimes and ultimately limiting charge transfer, extraction, and power conversion efficiency. In this talk, we gain deeper insights into the defect chemistry of tin halide perovskites by combining experimental and computational approaches. Spectroscopic techniques, such as photoluminescence quantum yield and carrier lifetime measurements, are used to evaluate key optoelectronic figures of merit, while density functional theory calculations provided insights into defect formation energies. We first highlight pristine stoichiometric films and explored the role of SnF₂, a commonly used additive in this class of materials, to understand its impact on defect passivation and optoelectronic properties. Then, we extend our studies to compositional engineering, systematically modifying: A-site cations, B-site cations through Sn-Pb mixing with varying ratios, and X-site halides by introducing iodide-bromide mixed systems. Our findings highlight strategies to modulate defect chemistry and charge carrier dynamics, offering pathways to optimize 3D Sn perovskites for efficient photovoltaic applications.

Tin halide perovskites are highly interesting alternatives to lead-based materials for a range of optoelectronic applications. However, their defect content and characteristics, heavily determined by the crystallization process of these materials, has slowed down their development. In this talk, we will cover the main differences in solution properties between lead and tin defining the current limitations of the latter. We will also discuss the actual potential of traditional and novel strategies to deal with this challenge, particularly regarding the solvent nature. Finally, a wide range of solution and thin-film characterization will give us a comprehensive understanding of the key parameters and how to use them to effectively control tin-based perovskite crystallization. This talk aims to provide both an overview and a set of directions to overcome current limitations in tin halide perovskite applications through completely new processing systems. Furthermore, beyond tin-containing perovskites, the fundamental character of this work maked it of high interest also for other similar novel materials under development.

The development of new transparent conducting polymers has gained significant interest due to their potential in various optoelectronic applications. We report new generation of highly transparent bisEDOT-based conducting polymers as an alternative to PEDOT/PSS. The synthetic approach is based on the in situ polymerization of bis-EDOT, a dimer of 3,4-ethylenedioxythiophene, inside polymethylmetacrylate (PMMA) via an oxidative polymerization reaction by Cu(ClO₄)₂. This approach yields a homogeneous transparent conducting polymer with enhanced electrical conductivity, mechanical stability, and excellent film-forming properties, offering significant advantages for high-performance applications in electronic and optoelectronic devices. The bis-EDOT-based conducting polymer can be processed in the form of inks for the formation of layers with thickness control, the possibility of tuning electrical conductivity, high transparency in the visible and near-infrared spectrum, and the possibility of adapting its formulation with various solvents, and additives to be fully compatible with perovskite in manufactured devices. The resulting conducting polymer films exhibit superior charge transport properties and long-term stability, making them ideal candidates for hole transport materials (HTMs) in perovskite-based photovoltaics. Moreover, the simplicity, scalability, and cost-effectiveness of this method make it highly suitable for large-scale production, with applications extending to flexible electronics, organic light-emitting diodes (OLEDs), sensors, and transparent conductive coatings. Overall, this in situ polymerization strategy provides a promising route for fabricating high-performance materials for advanced electronic and energy conversion technologies.

The efficiencies of tin-lead alloyed perovskite solar cell and lead-free tin perovskite solar cells are now 24-25% and 15-16%, respectively, which are still lower than that of lead perovskite solar cells.  Besides the efficiency enhancement of these tin-based solar cells, stability improvement is another important research theme. In this presentation we focuse on the stability improvement of these tin-based perovskite solar cells. We learnt from the stability study of lead perovskite solar cells that ion-migration has to be suppressed for the improvement of stability. To do this for the tin-lead alloyed perovskite solar cells, Ge ions which finally cover the grain boundary as GeOx, were added to the perovskite layer. In addition, ALD SnOx layer was inserted between the electron-transporting layer (Fullerenes).  The stability of the tin-lead alloyed perovskite solar cells was improved drastically.  The conventional composition consisting of FTO/PEDOT-PSS/SnPb-PVK/PCBM/C60/BCP/Ag degraded to 40% of the initial efficiency after the solar cell was put in the 85 ℃ under N2 atmosphere for 200 h. The efficiency decrease of the improved solar cell was suppressed to around 5% of the initial efficiency after the sample was kept for 1000h in the same condition. It is well-known that PEDOT-PSS frequently employed as the hole-transporting layers damages the tin-based perovskite layer by the proton migration. The proton migration is somehow retarded by the GeOx. The ALD SnOx layer suppressed the iodine migration to the electron-transporting layer and the Ag electrode. In the same way, the thermal stability of the lead-free tin perovskite solar cell was improved.  The efficiency of the conventional solar cells consisting of FTO/PEDOT-PSS/Sn-perovskite/C60/BCP/Ag decreased to 20% of the initial efficiency after the sample was put in the 85 ℃ under N2 atmosphere for 100 h. The decrease of the improved sample was suppressed to 20% after the sample was kept for 400 h in the same condition.  It was proved that the thermal stability of the tin-based perovskite solar cells is improved by suppressing the ion migration, which is similar to that of lead perovskite solar cells.

In recent years, the integration of emerging perovskite solar cells with traditional c-silicon solar cells to construct tandem devices has become to a promising photovoltaic technology. However, the integration of commercial silicon cells with perovskite solar cells, particularly on textured silicon substrates featured with large pyramids (2~5μm), presents a significant challenge in achieving effective charge transfer, which is critical for highly efficient tandem solar cells. This report focuses on our recent works on developing molecular-level nanotechnology that involves the design of charge transport layers, alongside optimizing the crystallization of conformal perovskite layers on the textured silicon sub-cells, leading to highly efficient perovskite/silicon tandem solar cells with certified power conversion efficiencies over 33%. Moreover, the efficiency degradation under 2000 hours of maximum power point (MPP) continuous illumination is less than 5%. This series of work aims to further enhance the performance of perovskite/silicon tandem photovoltaic technology and push its industrial application.

Scintillating materials aim to detect ionizing radiations and are currently widely used in many detection systems addressing different fields, such as medical imaging, homeland security, high energy physics (HEP) calorimetry, industrial control, and oil drilling exploration. Quality criteria for these materials span over several parameters, three of which are of primary importance: the scintillation yield, the density, and the timing response. In the case of the interaction with a high-energy photon such as X-ray or gamma ray, the time response shows a very complex structure in the multi time-scale regime, making it critical for several applications. Solution-processable perovskite scintillators have been shown to be the solution for the replacements for the current expensive lanthanide scintillators as they share the same or even better properties for state-of-the-art imaging and detection applications. As examples, time-of-flight (TOF) functionalities require time resolution below 100 ps, coincidence techniques often need sub-tens of ns time response [1], counting regime detection prefer sub-μs time response, and afterglow over ms is detrimental for X-ray imaging [2]. Among all perovskite materials, two-dimensional lead halide perovskites have shown remarkable environmental and thermal stability, a large Stokes’ shift, usually coupled with very broad emission compared to their three-dimensional and quantum dot counterparts [3]. Here, we will show the progress for the research towards those applications since the beginning of our activities with perovskite scintillators. Moreover, we will discuss our approaches to tackle problems in some perovskite materials through energy sharing concept and nanophotonic structures. The latter will bring faster and brighter scintillators through Purcell enhancements while we will demonstrate how we can reach this goal through photonic crystals and plasmonic structures [4.5]. Such visions will pave the way towards new research directions and applications on the high-energy physics and nanophotonics interactions.

The quest for low cost, non-toxic and Earth abundant materials solutions for thin film PV, has sparked significant interest in new inorganic semiconductors with complex compositions. One of the challenges with material discovery and new material compositions, is their fabrication in thin film form. Challenges such as volatility or solvent incompatibility, hinders progress in either high quality material demonstration or functionality via device integration.

To overcome these barriers, we employ mechanochemical synthesis to identify promising halide and chalco-halide powders as candidate materials. These powders serve as targets for thin-film deposition via pulsed laser deposition (PLD), a technique that uniquely enables near-stoichiometric transfer of complex compositions, regardless of elemental volatility. This capability facilitates the fabrication of high-quality thin films for proof-of-concept solar cells, with critical PLD parameters optimized to tailor the properties of complex halide, chalco-halide, and chalcogenide semiconductors.

The versatility of PLD is further leveraged for material discovery through compositional gradient screening on substrates, enabling rapid evaluation via photoluminescence and compositional mapping. The resulting materials, selected based on their band gaps, are explored as photo-absorbers or contact layers, advancing their integration into thin-film solar cell devices. This presentation will highlight strategies for experimental material discovery, thin-film synthesis, and device integration, contributing to the development of the next generation of optoelectronic materials and devices.

References:

https://pubs.acs.org/doi/10.1021/acsenergylett.4c01466

https://doi.org/10.1002/adfm.202316144

https://doi.org/10.1021/acs.chemmater.1c02054

https://doi.org/10.1021/acs.chemmater.3c01349

https://doi.org/10.1016/j.matt.2023.10.003

Bismuth-based semiconductors, including the double perovskite Cs₂AgBiBr₆ but also perovskite-inspired materials such as bismuth oxyhalides, show great promise for sustainable light-energy conversion due to their low toxicity, abundance, and tunable electronic properties. This presentation will explore strategies to enhance the efficiency, stability, and scalability of these materials in photoelectrocatalytic and photovoltaic applications. Methods like automated film production, surface modifications, and heterojunction formation have been employed to improve the performance of BiOI and BiOBr in water splitting and hydrogen evolution reactions. A continuous automated film production method for BiOI photoelectrodes was introduced, significantly improving the reproducibility and efficiency of large-scale production. Surface modifications and heterojunction formation have been explored to optimize PEC performance, with enhanced water oxidation and hydrogen evolution reactions observed. Additionally, the lead-free double perovskite Cs₂AgBiBr₆ was optimized for use in solar cells with improved efficiency through interface engineering and low-cost carbon-based electrodes. These advancements position bismuth-based semiconductors as viable, eco-friendly alternatives for energy conversion technologies.

Chalcogenide perovskites have much to recommend them for photovoltaics (PV). They absorb light strongly, with direct band gap tunable (at least) over the range 1.4 – 1.9 eV. They have limited polymorphism and are stable in air, water, and at high temperature. They are made of Earth-abundant, and (mostly) non-toxic elements, and have isotropic properties. However, there are substantial challenges facing the development of chalcogenide perovskite PV. Synthesis requires aggressive conditions - oxygen-free sulfurization or selenization at high temperature – that severely constrain thin-film growth. The few published reports of transport properties describe n-type material with high electron concentration, undesirable for thin-film PV. Photoluminescence (PL) has been reported, but the quantum yield is often low, and sample-to-sample variability is high. The defects that limit performance are not yet understood, and even less is known about interface and heterojunction design. Clearly, it will be a long road to chalcogenide perovskite PV technology.

I will motivate why, despite these challenges, research on chalcogenide perovskites for PV is worthwhile and exciting. I will then describe our own efforts, which center on the processing and properties of thin films. We have achieved a number of synthesis milestones, including growing thin films of BaZrS₃ and BaZr(S,Se)₃ alloys with tunable band gap, in epitaxial and polycrystalline forms. Selenium alloying can produce films with band gap suitable for single- and dual-junction PV, but the vast majority of synthesis procedures reported to-date focus on pure sulfides. I will discuss our finding of rapid alloying by post-growth selenization of sulfide thin films. This recalls the sulfurization-after-selenization process in CIGS manufacturing, and may make alloy studies more widely accessible. I will also present findings on how variations in cation composition affect crystallization kinetics. These results bolster evidence for BaS₃-liquid-assisted crystal growth, and may be useful for lowering the temperature of thin film synthesis.

I will then discuss our ongoing studies of photoluminescence (PL) and electronic transport. We have previously reported long excited-state PL lifetimes for BaZrS₃ and Ba₃Zr₂S₇, and others have reported band-edge PL even from powder samples. However, PL emission is highly variable, sample-to-sample, and many samples have no measurable band-edge emission. To understand this variability, we carry out a quantitative comparison of temperature-dependent PL of BaZrS₃ and a prototypical halide perovskite, CsPbBr₃. The halide has PL yield between 100 and 10,000 times larger than the chalcogenide. By comparing the vibrational properties of the chalcogenide and the halide, we suggest why defect-assisted recombination may be faster in the chalcogenide. On the other hand, the variability between chalcogenide samples suggests a substantial upside, if the recombination-active defect(s) can be identified and diminished. Our temperature-dependent Hall transport studies find that mobility at room temperature is limited by electron-phonon scattering, even in highly-doped samples; this may be related to our previous finding that chalcogenide perovskites have exceptional dielectric polarizability. At cryogenic temperature, the role of ionized defect scattering varies sample-to-sample. We also find that photoconductive responsivity varies tremendously from sample-to-sample, apparently due to variations in processing that affect the concentration of extended defects. All films are n-type as grown, but with tremendous variability in electron concentration. Studies of post-growth annealing support the hypothesis that the predominant intrinsic shallow donors are sulfur vacancies; we use this understanding to vary electron concentration by over a million-fold.

I will end by highlighting exciting next-steps including alternative methods of thin film deposition to make thicker films at lower temperature, studies of device semi-fabricates including detailed investigation of Mo/BaZrS₃ interfaces, and controlling carrier concentration.

Chalcogenide perovskites are a new emerging group of Pb-free perovskites featuring high environmental stability, direct band gap with extraordinary absorption coefficient, and good carrier transport properties, that can be suitably tailored for photovoltaic applications. Their constituent elements can vary, with the A and B cations having oxidation +2 and +4, respectively, while the anion is a chalcogen, such as S, Se, and Te, with an oxidation state -2. Currently, the most researched chalcogenide perovskite is BaZrS₃, due to its natural abundance of elements and its bandgap, which is favorable for tandem solar cells.

A prerequisite to adapt BaZrS₃ in device architectures is to understand how the complex surface chemistry affects optoelectronic properties of BaZrS₃ thin films. Our research focuses on the study of the BaZrS₃ surface/interfaces, developing methodologies for investigating the interfaces and the band alignment for devices. In our work, the measurements of the surfaces for varied films are achieved by photoelectron spectroscopy (XPS) performed both at in-house laboratories and at synchrotrons, exploiting the variable X-ray energy and the high flux.

In this presentation, I will report the advances of the BaZrS₃ as studied in our research on BaZrS₃ thin films. First, the bulk quality of our samples will be highlighted correlating the bulk properties to the functionality in terms of XRD, XAS and PL [1] . The surface chemistry and electronic structure, specifically orbitally-resolved valence band characteristics in relation to charge-carrier type, will be described as revealed by XPS measurements, differentiating the perovskite peaks from the secondary phases and performing a depth profile analysis of the top few nanometers from the film surface [2]. Our recent highlight includes in situ high-temperature post-annealing in ultra-high vacuum, allowing us to access the perovskite peaks by soft X-ray XPS from the purest film surface achieved so far. Our work is fundamental for unraveling the interfacial properties and the band alignment that directly impact charge transport. The findings will help identifying optimal design parameters for utilization of chalcogenide perovskites in optoelectronic devices, such as photodiodes and solar cells.

Ternary nitrides represent an emerging class of materials with immense potential in solar energy conversion, thermoelectrics, power electronics, coatings, and superconductivity, combining distinctive bonding properties, defect tolerance, and tunable functionalities. [1], [2] However, challenges in synthesis and metastability have limited their exploration compared to oxides. Recent synthetic and computational advances are now opening pathways for their development as next-generation solar materials.

This talk showcases two visible-light-absorbing nitrides that have recently emerged and offer especially interesting optoelectronic properties for solar energy conversion, copper tantalum nitride (CuTaN₂) [3] and zirconium tantalum nitride (ZrTaN₃) [4], with an emphasis on complex physical interactions that define their electronic structures. CuTaN₂ exhibits highly anharmonic structural dynamics, as displayed by phonon calculations and finite-temperature Raman experiments. Ab initio molecular dynamics is used to reveal the microscopic mechanisms of atomic motion, which are linked to macroscopic properties including its negative thermal expansion and temperature-dependent increase in the bandgap, thus emphasizing the critical role of structural dynamics in defining optoelectronic properties. In a second example, ZrTaN₃ thin films synthesized via reactive magnetron co-sputtering are shown to exhibit strong visible light absorption and significant photoelectrochemical activity. Complementary density functional theory calculations reveal that cation disorder, particularly Wyckoff-site occupancy, significantly modulates the bandgap and orbital hybridization in this ternary compound, underscoring the impact of cation arrangement on optoelectronic properties.

These findings highlight the versatility of ternary nitrides as advanced photoactive materials and offer insights into tailoring their properties through atomic-scale engineering.

Thin film photovoltaic technology has advantages to silicon in terms of flexibility, lower energy manufacturing needs or use in tandem cells. However, the high efficiency thin film technologies available (e.g., CIGS, CdTe or halide perovksites) have all issues in terms of cost, element abundance or long-term stability. Finding new solar absorber is a cumbersome process involving complex synthesis and characterization. First principles computations on the other hand offers an attractive way to speed up this process. Here, we will report on a large scale high-throughput computational search for new solar absorbers among known inorganic materials. Importantly, the need for high carrier lifetime is taken into account by including in the screening intrinsic defects and their role as potential Shockley-Read-Hall recombination centers. Screening 30,000 known inorganic compounds, we identify a handful very promising solar absorbers. I will discuss the chemistries that we identified and highlight a few interesting new materials. I will especially focus on BaCd₂P₂, a new phosphide where our experimental follow-up work confirms the promising properties including adequate band gap but also long carrier lifetime and very high stability. Beyond BaCd₂P₂, our work highlights the discovery of an entire family of AM₂P₂ phosphides with exciting recent results on CaZn₂P₂ thin films. I will finish my talk highlighting the opportunities and challenges ahead in computationally-driven discovery of new solar absorbers.

In this talk, I will start with the brief introduction of first principles electronic structure calculations in perovskite materials, and how it could be connected to the Computational Screening for achieving highly efficient and stable solar cell materials [1, 2]. Next, I will delve into the fundamentals and possible implications of Rashba phenomena in both hybrid and inorganic perovskite materials [3-5]. The fundamental interplay between structural distortions and the Rashba splitting in the considered one-dimensional system under the influence of compression along with the evolution of spin texture could hold great potential for the pursuit of sustainable energy. The rest of the talk would be devoted to theoretical understanding of piezochromism, where hydrostatic pressure could be employed as an effective tool, giving rise to novel crystal structures and optical properties, while it has proven to be an alternative to chemical pressure [4,5]. I will end my talk touching upon our recent successful endeavour of pre-intercalation mechanism in Li-ion battery based on transition pathway prediction [6].

Toxicity and instability of lead-based metal halide perovskites (MHP) have fueled explorations of new lead-free all-inorganic materials, especially in the CuI-AgI-BiI₃ phase space. In particular, Cu₂AgBiI₆ shows promising optoelectronic properties such as a high absorption coefficient of ~ 10⁵ cm^-1, a direct band gap of ~ 2 eV, a low exciton binding energy comparable to the thermal energy at room temperature, a modest mobility of 1.7 cm²V^-1s^-1 and a nanosecond charge-carrier lifetime.[1] However, the champion power conversion efficiency (PCE) of the Cu₂AgBiI₆ solar cells was only 2.39 %,[2] significantly lagging behind the PCE of the MHP counterparts. It has been shown that Cu₂AgBiI₆ exhibits ultrafast charge-carrier localization, which imposes the fundamental limits on its PCE.[3] However, such low PCEs cannot be solely attributed to the ultrafast charge-carrier localization, given that Cs₂AgBiBr₆, which also shows ultrafast charge-carrier localization and has an indirect bandgap, has achieved the champion PCE of 6.37 %.[4]

Herein, we aim to understand additional factors limiting the PCE of Cu₂AgBiI₆ beyond intrinsic ultrafast localization by investigating optoelectronic properties of charge transport layer (CTL)/Cu₂AgBiI₆ half stacks using CuI and PTAA as hole transport layers and SnO₂ and PCBM as electron transport layers. By analysing absorption spectra, X-ray diffraction (XRD) patterns and optical-pump terahertz-probe (OPTP) transients, we observe that the formation of quaternary phase Cu₂AgBiI₆ is influenced by the deposition of charge transport layers, especially by CuI and SnO₂, which modify its optoelectronic properties. Materials within the CuI-AgI-BiI3 phase space share similar band gaps and lattice parameters, making it challenging to confidently distinguish Cu₂AgBiI₆ from other impurity phases by using absorption spectra and XRD patterns alone. By extracting THz mobilities from OPTP, we confidently factor out Cu₂AgBiI₆ phase and identify impurity phases induced by the transport layer deposition. We find that deposition of CuI on Cu₂AgBiI₆ induces the formation of copper-rich quaternary Cu_xAgBiI_4+x phases near the interface and deposition of Cu₂AgBiI₆ on SnO₂ hinders the formation of the quaternary phase and instead forms ternary and binary phases, leading to the decrease in the mobility. Overall, we highlight that the deposition of CTLs can significantly affect the formation and optical properties of Cu₂AgBiI₆. Characterization of CTL/Cu₂AgBiI₆ half stacks is therefore critical to improve the device performance. Moreover, further developments are needed to suppress the formation of unwanted impurity phases upon deposition of transport layers.

In the search for lead-free alternatives for halide perovskites, a number of different research routes are being pursued. Here we will discuss three different pathways presently under investigation. For example, silver pnictohalides have emerged as perovskite-inspired materials for photovoltaics due to their high stability, low toxicity, and promising early efficiencies, particularly for indoor applications. While most research has focused on silver bismuth iodides (Ag–Bi–I rudorffites), antimony analogs remain underexplored due to difficulties in synthesizing Sb-based thin films. Here, a novel synthesis route using thiourea as a Lewis-base additive enabled the preparation of Ag–Sb–I films, which were further optimized by Cu alloying to improve thin-film morphology and increase power conversion efficiency to 0.7% [1]. Theoretical and optical studies confirmed Cu incorporation into a Cu₁₋ₓAgₓSbI₄ phase without altering bandgap properties. Our studies also identified Ag point defects as traps reducing open-circuit voltage, with minor Bi additions enhancing efficiency and stability.

Heteroatom alloying presents an additional strategy for tuning the optoelectronic properties of lead-free perovskite derivatives. Tin-alloyed layered MA₃Sb₂I₉ thin films were synthesized using a solution-based approach with precursor engineering, blending acetate and halide salts [2]. Increasing tin halide concentrations expanded visible-spectrum absorption and improved stability. Tin incorporation into the MA₃Sb₂I₉ lattice introduced new electronic states in the bandgap, confirmed by theoretical calculations. These features enhanced absorption through intervalence and interband transitions while stabilizing charge transport. This system’s robustness toward mixed oxidation states improved ambient stability, demonstrating its potential for various optoelectronic applications.

Finally, the integration of organic semiconducting materials with inorganic halide perovskites offers promising opportunities for tuning optoelectronic properties. Using stable, nontoxic double perovskites as hosts for electroactive organic cations enables the creation of two-dimensional (2D) hybrid materials that are both functional and lead-free for optoelectronic applications. By incorporating naphthalene and pyrene moieties into Ag–Bi–I and Cu–Bi–I double perovskite lattices, we address intrinsic electronic limitations of double perovskites, and modulate the anisotropic electronic properties of 2D perovskites [3]. Among eight newly developed 2D double perovskites, (POE)₄AgBiI₈ containing pyrene moieties was identified as having a favorable electronic band structure, exhibiting a type IIb multiple quantum well system conducive to out-of-plane conductivity and achieving a photocurrent response ratio of nearly three orders of magnitude under AM1.5G illumination. This material was used to create the first pure n = 1 Ruddlesden–Popper 2D double perovskite solar cell. Concluding, these and additional examples discussed in the presentation illustrate the enormous design space available for the generation and tuning of novel lead-free perovskite-derived absorber materials.

[1] Hooijer, R.; Weis, A.; Kaiser, W.; Biewald, A. ; Dörflinger, P. ; Maheu, C.; Arsatiants, O.; Helminger, D.; Dyakonov, V.; Hartschuh, A.; Mosconi, E.; De Angelis, F.; Bein, T. Cu/Ag–Sb–I Rudorffite Thin Films for Photovoltaic Applications. Chem. Mater. 2023, 35, 23, 9988–10000.

[2] Weis, A.; Ganswindt, P.; Kaiser, W.; Illner, H.; Maheu, C.; Glück, N.; Dörflinger, P.; Armer, M.; Dyakonov, V.; Hofmann, J.P.; Mosconi, E.; De Angelis, F.; Bein, T. Heterovalent Tin Alloying in Layered MA₃Sb₂I₉ Thin Films: Assessing the Origin of Enhanced Absorption and Self-Stabilizing Charge States. J. Phys. Chem. C 2022, 126, 49, 21040–21049.

[3] Hooijer, R.; Wang, S.; Biewald, A.; Eckel, C.; Righetto, M.; Chen, M.; Xu, Z.; Blätte, D.; Han, D.; Ebert, H.; Herz, L.M.; Weitz, R.T.; Hartschuh, A.; Bein, T. Overcoming Intrinsic Quantum Confinement and Ultrafast Self-Trapping in Ag–Bi–I- and Cu–Bi–I-Based 2D Double Perovskites through Electroactive Cations. J. Am. Chem. Soc. 2024, 146, 39, 26694–26706.

Solar cells based on nanocrystals have seen increasing interest in recent years due to the continuous rise in their power conversion efficiency. The most efficient cells are often based on nanocrystals that contain lead, such as lead sulfide (PbS) or metal halide perovskites (e.g., FAPbI3 or CsPbI3). While these nanocrystals lead to high efficiencies, they raise concerns regarding their large-scale applicability due to the environmental hazards they pose. In this talk, I will discuss the synthesis and application in solar cells of lead-free nanocrystals, such as those based on bismuth and antimony. I will present a method to synthesize an array of compositions by cation exchange, a simple, low-temperature process. Finally, I will introduce a facile templated growth of small antimony sulfide (Sb2S3) nanorods that are of great interest for application in photovoltaics.

Chalcohalide semiconductors are attracting a fast-growing interest for energy conversion purposes.¹ These materials may indeed combine promising optoelectronic properties with a high chemical stability, thus representing a potentially valid alternative to metal chalcogenides and halides. Nevertheless, synthetic protocols to prepare mixed anion semiconductor nanomaterials are lacking.

It is here presented a colloidal method to synthetize phase pure nanocrystals (NCs) of heavy pnictogen chalcohalides. Such a method relies on the hot-co-injection of both the chalcogen (E = S, Se) and the halogen (X = Cl, Br, I) precursors to a solution of heavy pnictogen metal (M = Sb, Bi) complexes.

With this method, we prepared colloidal NCs of the orthorhombic MEX phase.² The colloidal MEX NCs display composition-dependent band gap spanning the visible spectral range with high absorption coefficients and are chemically stable at ambient conditions. The solution processing of these NCs yield robust solid films generating stable photoelectrochemical current densities.

With this method, we prepared colloidal NCs of the hexagonal Bi₁₃S₁₈X₂ phase.³ These colloidal NCs show a mixed valence character related to the presence of subvalent Bi atoms, which results in an anomalously narrow band gap extending the NC optical absorption to the near infrared spectral range.

With such a method, we also prepared quaternary chalcohalide semiconductor NCs.⁴ As distinct from ternary chalcohalide semiconductor NCs that commonly show an indirect band gap, the quaternary AgBiSCl₂ NCs feature a direct band gap, further supporting the potential relevance of the chalcohalide semiconductor NCs to light harvesting purposes.

With this method, we also unsuccessfully attempted the synthesis of prospective chalcohalide perovskite NCs, namely CsBiSCl₂ phase.⁵ We could prepare NCs of anion segregated secondary phases only, suggesting that heavy pnictogen chalcohalides are hardly prone to adopting a perovskite structure.

Inorganic semiconductor photoabsorbers such as colloidal nanocrystals are frequently employed for a wide variety of energy-related applications by themselves or as part of a hybrid nanostructure,^[1] including photocatalysis and photovoltaic devices. However, using them as the photoactive layer in photoelectrochemical (PEC) is less common due to the difficulty in binder-free attachment to transparent conductive oxide (TCO) substrates. On the other hand, polymeric carbon nitrides(CNs) are a family of cheap and highly stable semiconductor materials that can be in situ grown on TCOs. Unfortunately, their successful utilization for PEC has yet to reach the performance of state-of-the-art metal-oxide-based systems, among others, due to insufficient light harvesting and inferior conductivity.^[2,3]

In this talk, I present a simple method based on electrophoretic deposition of ZnSe nanocrystals into a porous modified CN layer as the scaffold to form an efficient hybrid photoactive layer over TCO.4 The merits of this simple yet scalable solution processing method will be discussed, including the crucial step of stripping long-chain alkyl surfactant from the nanocrystals. The resulting hybrid structure achieves an impressive Faradaic efficiency towards the oxygen evolution reaction at ca. 87% and doubles the measured photocurrent and IPCE values relative to samples without ZnSe. Our results show the benefit of such a combination in terms of charge separation, stability, and successful water-splitting without using additional co-catalysts—evolving oxygen while minimizing parasitic self-oxidation.^[4] This method paves the way for the incorporation of other nanocrystals into porous organic hosts.

Electrochemical impedance spectroscopy measurements of perovskite solar cells (PSCs) show characteristic features at low frequencies, such as a large illumination-dependent capacitance [1,2]. While this effect is well known, the debate on its origin persists [3,4]. An illumination-dependent increase in the conductivity of ionic charge carriers was suggested early on [2]. However, experiments to elucidate the presence of such a photo-conductive effect require special devices or measurement techniques and neglect possible influences of the enhanced electronic charge concentrations. Thus, only a few studies investigated this effect in detail.

Using drift-diffusion simulations and two novel techniques to analyze the simulation results, we show how the illumination-dependent part of the capacitance originates from electronic currents that are amplified due to the screening of the alternating electric field by the ions [5]. This is inherently caused by the mixed electronic-ionic interaction. Counter-intuitively, an illumination-dependent ion conductivity even reduces the magnitude of the capacitance increase.

As the presence and magnitude of a low-frequency capacitance increase by itself are unsuited to assess the presence of illumination-dependent ion conductivity, we propose a novel characterization technique based solely on capacitance measurements at short-circuit on fully integrated devices. The frequency shift of the onset in capacitance is extracted at varying illumination intensity. This quantity shows a distinct qualitative difference depending on whether the ion conductivity depends on illumination or is constant. As these measurements can be performed on unaltered, fully integrated devices and with standard equipment, the method is well suited for widespread investigation of a photo-conductive effect in different materials and devices or in response to degradation.

The method is applied to a range of perovskite solar cells with different active layer materials. Remarkably, all measured samples show a clear signature of photoenhanced ion conductivity, posing fundamental questions on the underlying nature of the photosensitive mechanism.

The study of perovskite solar cells degradation is a complex issue due to the multitude of phenomena that can contribute to it. Normally the degradation can produce two main impacts, decrease of charge collection (lowering photocurrent) or increase of recombination (lowering photovoltage). We need to find dynamical signatures of the phenomena causing these effects to discover the physical reasons for the devaluated performance. Recently, we have obtained new insights using a model that combines several electronic and ionic processes, that can produce capacitive and inductive response in different circumstances. These models are very successful to describe huge memory effects and hysteresis in perovskite memristors, by the combination of different techniques: current-voltage scan, time transients, and impedance spectroscopy. Here we show the changes of impedance spectroscopy and time transients as a diagnosis of evolution of degradation in the perovskite solar cells. This analysis expands the tools available for understanding the transformation of perovskite solar cells under working conditions.

Semitransparent perovskite solar cells are emerging as a promising technology for applications such as energy-generating windows and integrated photovoltaics, where a balance between efficiency, transparency, and aesthetics is essential. [1-5] Designing such devices demands a deep understanding of light absorption, reflection, and transmission within the cell structure. In this work, we outline a simulation-based methodology for optimizing these devices, beginning with the calculation of optical constants for each layer in the cell, which is key not only for understanding the limitations associated to different devices, but also for accurately predicting the best design for each application. [6-7] We show the importance of validating the accuracy of the optical model by comparing simulated results with experimental data of full devices, performing global fits of different devices which ensures the model reliability. Finally, we explore various optimization strategies aimed at achieving specific performance targets, such as maximizing power conversion efficiency while maintaining desired levels of transparency and color rendering properties. By integrating accurate material characterization, rigorous simulation validation, and strategic optimization, this approach accelerates the development of high-performance, semitransparent perovskite solar cells tailored for diverse applications. This framework offers a practical pathway for bridging the gap between fundamental research and scalable device design.

In this talk we set out to explain the physics that gives rise to two surprising phenomena that are frequently observed in perovskite solar cells, namely inverted hysteresis (IH) and the appearance of a third (intermediate frequency) feature in PSC impedance plots. Both these phenomena are caused by the leakage of charge carriers from one of the transport layers into the perovskite in sufficient numbers that they are able to partially screen electric fields in the interior of the perovskite layer.  In order to better understand these phenomena, we analyze the standard drift-diffusion model of a planar three-layer PSC, using asymptotic techniques, to derive a reduced order model capable of describing the screening effects in the perovskite layers arising both from the presence of ions (which redistribute slowly) and from that of charge carriers (which adjust almost instantaneously). This approximate reduced order model shows excellent agreement with numerical simulations to the full drift-diffusion model and provides fundamental insights into the causes of inverted hysteresis reconciling the alternative explanations of this phenomenon found in the literature. Furthermore it can be used to explain the appearance of the third (intermediate frequency) feature in PSC impedance plots. Understanding why these atypical phenoneman occur is important for the device physicist because their appearance can be used to diagnose certain properties of the cell. 

In the last 10+ years of development, perovskite solar cells have achieved excellent efficiencies and a more gradual improvement in stability. Perovskite materials for photovoltaics are mixed electronic-ionic conductors [1]. It is therefore essential to consider the density and mobility of ionic defects in continuum-level models of perovskite-based devices, including tandem cells. Ionic defects impact both the steady-state and dynamic behaviour of perovskite cells [2] by modulating the electric field and charge carrier recombination rates.

An initial density of ionic defects is formed during cell fabrication; however studies suggest that additional defects can form during operation, under bias and illumination. Accumulation of mobile ion defects at the perovskite/transport layer interfaces results in undesirable degradation and performance loss over a timescale of hundreds of hours [3].

Improved modelling and simulation is required to understand the process of defect generation and quantify its impact on device characteristics over relevant timescales. We extend the charge-transport model that underpins our open-source IonMonger tool [4] and perform simulations to investigate the impact of defect generation and migration on perovskite solar cell performance.

Zinc Phosphide (Zn₃P₂) is a promising earth abundant absorber for photovoltaics, offering direct bandgap of (1.5 eV), high optical absorption coefficient in the visible range (10⁴ - 10⁵ cm^-1) and long carrier diffusion length, making it ideal for thin-film solar cells.

Monocrystalline Zn₃P₂, grown via Selective Area Epitaxy (SAE) naturally forms textured films with periodic pyramid-shaped nanostructures [1], [2], [3]. The growth mechanism necessitates a SiO₂ patterned substrate, where Zn₃P₂ can grow on selectively exposed area of the substrate.

These naturally occurring nanostructures can be controlled in height and periodicity, depending on the opening dimension, and offer potential light management benefits to minimize in-coupling and out-coupling losses. The patterned substrate is a consequence of the growth mechanism; however, it provides the advantages of shaping and reducing the p-n junction contact area with valuable prospects for enhanced carrier management.

In this study, we present comprehensive device modelling of textured Zn₃P₂-based solar cells using coupled 3D optical and electrical simulations, employing FDTD and a Schrödinger-Poisson drift-diffusion solver to optimize the solar cell design.

Optical simulations are used to study the optical phenomena occurring within this complex structure including Mie modes, Rayleigh anomalies, and Fabry-Perot resonances. These effects are analyzed as a function of the pyramid height, periodicity, and thickness of the thin film beneath the pyramid. By tuning these modes and their interactions through geometric adjustments, the photocurrent is optimized to approach up to 89% of the Lambertian limit.

Electrical simulations are employed to study the effect of the reduced p-n junction contact area between Zn₃P₂ and the substrate.  The junction area fraction was varied from 100% (continuous interface) down to 1.4%.  Analysis of the simulated JV curves under both illumination and dark conditions highlighted the benefits of reducing the junction area fraction, for enhancing the open-circuit voltage (V_oc) up to 0.12V.

This optical-electrical model exploits the potential for Zn₃P₂-based solar cells grown by SAE combining advanced light management and optimized junction design to enhance performance.

We present a tour through the many and varied impedance spectra observed in perovskite solar cells, including loops, mid-frequency features, and the so-called ‘giant’ and ‘negative’ capacitances. Beginning with single-arc spectra, progressing through double- and triple-arcs, and finishing with discussion of the effects of degradation, we classify observed spectra into generic types, named for animals resembling their Nyquist plot. Remarkably, all of these spectral ‘animals’ can be faithfully replicated using the well-established ionic-electronic drift-diffusion model with a single mobile ion species, eliminating the need for speculative physics.  Perovskite solar cell spectra often defy traditional interpretations, prompting increasingly intricate equivalent circuit models comprising elements without a sensible physical meaning. However, our animal-inspired framework offers a simpler, more intuitive approach to spectral analysis. This ‘spotter’s guide’ allows researchers to identify spectral features and their underlying physical origins based only shape recognition from a safe distance, unlocking insights without the need to venture into the wilds of computational modelling.

Ion migration lies at the heart of perovskite solar cell (PSC) performance and stability. Different experimental techniques have been used to better understand the puzzling performance of ion migration in PSCs. In this talk, I will present our last results on the characterization of ion migration by two characterization measurements, X-Ray Photoemission Spectroscopy (XPS) [1] and impedance spectroscopy (IS) measurements [2] interpreted by drift-diffusion (DD) simulations.

For the characterization of the electronic and chemical properties of halide perovskites surface and interfaces to adjacent layers, XPS is a versatile technique. We use a lateral microstructure in which two different charge transport layers in co-planar contact configuration are separated by a perovskite channel constituting a lateral solar cell [1]. We apply reverse and forward bias with typical PSC operational conditions to the lateral microstructure to analyze the performance of the PSCs focusing on the evolution of band bending. 

 On the other hand, Impedance Spectroscopy is a consolidated tool to analyze the opto-electronic response of PSCs. Lately, it has been proved the proof of concept of the coupling of DD simulations with IS for a better understanding of device degradation [2]. I will present our last results on numerical DD simulations, and in particular, the study case of NiOx-based PSCs with various interface passivation treatments [2]. Our simulations approach several experimental measurements of IS under short-circuit conditions at different illumination intensities, along with bias-stress accelerated operational stability tests under constant illumination. Drift-diffusion simulations suggest that interface modification with the hole transport material may modify ion mobility within the perovskite layer. Our findings provide a systematic approach for characterizing instability mechanisms in PSCs using IS under short-circuit conditions.

Dye-sensitized solar cells (DSSCs) are promising for glazing applications due to their potential for semi-transparency. However, their photovoltaic performance and light transmittance are largely determined by the dye and electrolyte used, both of which are fixed during the manufacturing process. Electrolytes are critical to energy technologies, yet their optimization is challenging due to the complexity of their formulations and the multitude of interacting chemical components. Typically, optimization requires numerous experiments, as the effects of these components are often correlated and difficult to analyze independently.

In this study, we employed a design of experiments (DoE) methodology combined with machine learning (ML) to design electrolytes that effectively balance two typically conflicting properties: visible transparency and power conversion efficiency (PCE). The model required only a limited number of experiments for training and exhibited excellent predictive agreement with experimental results.

First, we optimized iodine-based electrolytes to fabricate solar cells with a visible transparency range of 34% and a maximum PCE of 2.94%. We then extended this approach to electrolytes based on alternative redox systems. Using our data-driven modeling approach, we optimized a TEMPO-based electrolyte, achieving photochromic semi-transparent cells with a 42% transmittance variation and a PCE of 2.16%. For opaque cells, this novel electrolyte delivered a PCE of 3.46% with a photochromic dye and an impressive 7.64% PCE when paired with a non-photochromic dye.

An efficient way to substantially increase the surface area coverage of photovoltaic (PV) modules, while maintaining the existent electricity infrastructure, is to integrate such modules into the roofs and facades of buildings. Aside from the practical technical requirements, such as high power conversion efficiency (PCE), low cost, and long lifetime, photovoltaic modules for building applications also necessitate an aesthetically attractive design, which can be achieved by finetuning their color according to the specific architectural needs of the building [1,2].

For some PV technologies, intrinsic coloration with a limited selection of colors can be attained by selecting absorbing materials with specific spectral absorption behavior [3,4]. To achieve a broader range of colors typically requires the addition of colored encapsulants, printed glass covers or interlayers in front of the PV module. Most commonly, pigments or chemical colorants are employed to accomplish such coloration, but they tend to absorb a significant portion of the solar spectrum, drastically reducing the PCE of the resulting PV module. A promising alternative to overcome such issues is to take advantage of the interference effects between non-absorbing dielectric materials with contrasting refractive indexes to design PV modules with vivid structural colors and low optical losses [5,6].

Periodic distributed Bragg reflectors (DBRs) have been considered in some previous works to realize structural coloration in PV modules [7,8], but they typically fail to reproduce some colors, especially reds, owing to the appearance of higher-order interference peaks in the reflectance spectra. To reach a broader color gamut thus requires breaking up the periodicity inherent to DBRs in a controlled way, such that the optical response of the PV module is tuned to achieve the desired coloration. In the present work, a numerical approach combining the electromagnetic description of light propagation together with the use of optimization algorithms is considered to optimize the configuration of a dielectric multilayer structure deposited directly on top of a polymer foil interlayer that is placed in between the substrate and the PV cell, targeting different structural colors for the PV module. As it will be demonstrated, the non-trivial aperiodic structures obtained from this method cover a broader color gamut than the simpler DBRs, and are key to achieve different red hues, including the ones of commonly used raw construction materials, such as clay or brick. As a proof-of-concept, a mini-module with a selected color is assembled by depositing an aperiodic multilayer structure with a numerically optimized configuration on top of a polymeric foil, using a roll-to-roll physical vapor deposition method. This allows not only to validate the numerical predictions regarding the structural color achieved, but also to demonstrate the low photovoltaic loss associated with this sort of multilayers and the scalability of the processes used to fabricate such colored modules.

Extracting relevant material properties from experimental measurement is challenging, especially in the field of organic semiconductors. The models used to fit and reproduce experimental results are complex with multiple correlated parameters, which render the use of such model to extract relevant material properties very complicated. To overcome such limitations, we consider in this work the use of Bayesian inference for parameter estimation. Bayesian inference is a powerful tool to extract parameters distribution considering the experimental observations and the models considered [1].

 In this study, we apply Bayesian inference techniques to analyze temperature-dependent photoluminescence spectra obtained from organic solar cells. We model the photoluminescence spectra of organic semiconductor films using a semi-classical marcus-levich-jortner expression [2, 3]. We model the spectra under different temperature and reproduce the change in spectral shape and relative intensity. Using the model and a Bayesian inference approach, we extract distributions for the different relevant properties of interest such as: Energy of the first excited state, the static disorder in energy, the reorganization energies (low and high frequency) as well as the dominant frequency mode. Our approach provides robust parameter estimation and quantifies uncertainties, enabling more accurate characterization of organic semiconductor materials. The results demonstrate the effectiveness of Bayesian inference in unraveling complex material properties and guiding future research in renewable energy applications.

Organic light-emitting diodes have been successfully commercialized by the display industry, yet there are still basic challenges in modeling their operation and degradation. In this talk, I will highly recent work establishing the thermodynamic limit of OLEDs, which shows that strong exciton binding in these devices requires a higher voltage to achieve the same luminance as a comparable inorganic LED, and that the best OLEDs reported to date have likely reached this limit. I will discuss how the well-known Shockley-Read-Hall (SRH) expression for trap-mediated recombination in OLEDs is modified to account for the finite lifetime of dopant excitons and its implication for minimizing OLED drive voltage. Finally, I will discuss recent work focused on understanding blue OLED degradation where exciton-polaron-based degradation kinetics are implemented into a drift-diffusion-based device model.  The results suggest that OLED luminance loss and voltage rise largely originate from different sets of degradation-induced defect states formed in the emissive and transport layers, respectively, which opens up new opportunities to optimize the performance and lifetime of these devices.

On of the most fascinating properties of tetrahedrally coordinated solids is their negative thermal expansion. For Si, Ge and a number of binary compounds (cubic materials crystallizing in the diamond-type and sphalerite- or wurtzite-type crystal structure) it was shown that their thermal expansion coefficient becomes negative at temperatures between 50 to 100 K [1-3]. In ternary A^IB^IIIX₂^VI chalcogenides, crystallizing in the tetragonal chalcopyrite-type structure, the linear thermal expansion behaviour is described by the both independent linear thermal expansion coefficients α_a and α_c, which are anisotropic. It was shown that CuBX₂ chalcopyrites (B=In,Ga) exhibit negative linear thermal expansion at temperatures below 30 K, for both a and c. The lattice parameter in these compounds first decrease with decreasing temperature going through a minimum and increase at low temperatures [4-8]. In the exceptional case of  AgBX₂ semiconductors the lattice parameter c increases with decreasing temperature in the whole temperature range [9].

Because of negative linear thermal expansion coefficients α_a and α_c, negative Grueneisen parameters may be expected in the low-temperature region and as a consequence the existence of low-energy lattice vibrational modes [10]. Moreover high-pressure induced structural phase transitions are caused by low-energy lattice vibrational modes with negative Grueneisen parameters. It is known from literature that the binary compounds ZnS and ZnSe as well as ternary CuInSe₂ show a pressure induced structural phase transition to the rocksalt-type structure [11-12].

Not much is known about the low temperature behaviour of quaternary chalcogenide compound semiconductors, like A₂^IB^IIC^IVX₄^VI. According to the tetrahedrally coordinated crystal structure, a negative thermal expansion can be expected. This assumption is strenghtened by the observation of a pressure induced structural phase transition in Cu₂ZnSnS₄ [13]. This compound shows a transition from the tetragonal kesterite-type structure to ta distorted rocksalt-type structure at ~ 15 GPa [13].

The compound semiconductors discussed above are used as absorber layers in thin film solar cells. Photovoltaic (PV) devices with chalcopyrite-type Cu(In,Ga)Se₂ absorbers show very high efficiencies [14]. The quaternary semiconductors Cu₂ZnSn(S,Se)₄, crystallizing in the tetragonal kesterite-type structure, are the absorbers in the only critical raw material free PV technology. Record efficiencies have been reached with an (Ag,Cu)₂ZnSnSe₄ absorber layer [15].

Thin film solar cells are the most ubiquitous and reliable energy generation systems for aerospace applications, because of their appealing properties such as lightweightness, flexibility, cost-effective manufacturing, and exceptional radiation resistance [16]. For  longer  missions,  PV devices  in  conjunction  with  rechargeable  batteries  are  the  only  available  option  to  provide  uninterrupted, sustainable and stable  electrical  power. Especially satellites  on  inner  planets  missions  employ  solar  cells, because at  these  distances  the  power  density  of  sunlight  is  sufficient  for  the  production  of  electricity [16]. For these applications the harsh conditions in space, like radiation and low temperatures, have to be taken into account. The temperature in outer space far away from earth is just 3 K [17], and extreme temperature swings occur. Thus the low temperature behaviour of absorber materials in solar cells potentially used in space applications, are of extreme importance. 

The presentation will give an overview of our detailed in situ neutron diffraction based structural investigation comparing the thermal expansion behaviour of Cu₂ZnSnSe₄, Ag₂ZnSnSe₄ and (Ag,Cu)₂ZnSnSe₄ mixed crystals from room temperature to 3 K. These materials crystallize in the tetragonal kesterite-type structure in the whole temperature range studied. The linear thermal expansion coefficients α_a and α_c are highly anisotropic. The end member Cu₂ZnSnSe₄ shows negative thermal expansion coefficients below 50K. In case of Ag₂ZnSnSe₄ the lattice parameter c increases with decreasing temperature thus showing a negative thermal expansion coefficient over the whole temperature range studied, indicating the special behaviour of Ag-containing tetrahedrally coordinated semiconductors.

The synthesis of multinary semiconductors for solar energy conversion applications such as kesterite (Cu₂ZnSn(S,Se)₄, CZTSSe) is extremely challenging due to the complexity of this type of compounds. In particular, quaternary kesterite-type compounds are not the exception, and all these detrimental issues explain why during almost 10 years the world record efficiency was unchanged. But the very recent development of molecular inks route with special precursors, allows the accurate control of single kesterite phase with high crystalline quality, contributing to increase the conversion e"ciency record of kesterite based solar cells up to 15% in a short time.

This presentation will be focused first in demonstrating how the molecular inks synthesis route was of key relevance for the control of high-quality single phase kesterite, through the modification of the synthesis mechanisms. The relevance of the composition of the ink, the precursor salts, and the interaction between the solvent and the cations in the solution is key for a reliable and reproducible high efficiency kesterite production baseline. Then, diluted alloying/doping strategies will be presented including Cu, Zn and Sn partial substitution with elements such as Ag, Li, Cd or Ge, that allowed e"ciencies close to 15%. The positive impact of these cation substitutions will be discussed in regards of their impact on the kesterite quality, as well as on the annihilation of detrimental punctual defects, allowing for new efficiency records at 15% level. In addition, the main characteristics and challenges of key kesterite interfaces (front, back and grain boundaries) will be discussed. Finally, very recent, and innovative interface passivation strategies will be discussed, showing the pathway to increase the record efficiency beyond 20%.

With the motivation of absorber layers which contain Earth-abundant, cheap and low-toxicity elements, the material Cu₂ZnSn(S,Se)₄ (CZTSe) has been a popular choice in the inorganic thin-film photovoltaics (PV) research community. After an extended period with no improvements to efficiency, recent records of ~13.8% [1] suggest a possible resurgence in research. Here we explore quantifying the environmental impacts of fabricating a CZTSe solar cell at the laboratory-scale using a mix of vacuum techniques (sputtering, electron beam evaporation, tube furnace annealing) and non-vacuum techniques (CZTS nanocrystal synthesis, slot-die coating, chemical bath deposition) with a structure of glass/Mo/CZTSe/CdS/i-ZnO/ITO/Ag,Ni. The intention is to determine which processes or layers are the most significant on the overall environmental impact of the fabrication and hence which may inhibit future scale-up. A life cycle assessment (LCA) is conducted which includes the materials used, electricity consumed as well as the waste produced. Previously we have used LCA to show how to reduce environmental impacts during the synthesis of CZTS nanocrystals [2]. We now extend the LCA analysis to the whole device. The selenization step (where selenium substitutes for sulfur), whilst essential for improved device performance, contributes significantly to the overall environmental impacts of cell fabrication. This results in the impacts from the solution-processed absorber layer to be similar to the vacuum-deposited transparent conducting oxide (TCO) layer due to the necessity of a high temperature, low pressure anneal. This work is hence a timely contribution to discussions surrounding the environmental impacts of vacuum versus non-vacuum deposition. In future work, a functional unit of 1 kWh is chosen such that device performance is included. This will allow for comparison to other research-scale solar cells with absorber layers such as Sb₂(S,Se)₃ and BaZrS₃.

A new power conversion efficiency record of 15.1% was reported just recently for a CZTSSe-based thin film device in which the polycrystalline CZTSSe absorber layer shows an off-stoichiometric composition. Deviations from stoichiometry cause intrinsic point defects which determine the electronic properties of a semiconductor significantly. A special kind of structural disorder, the Cu/Zn disorder, is always present in these compounds and is discussed as a possible reason for band tailing as well.

To minimize or avoid Cu/Zn disorder cation mutation strategies can be applied. In this way the crystal structure of the material can change from kesterite- to stannite-type to completely avoid this disorder. Substituting Zn²⁺ with Cd²⁺ in CZTS is one of the options. In the resulting solid solution series, both end members adopt different crystal structures: Cu₂ZnSnS₄ crystallizes in the kesterite-type structure whereas Cu₂CdSnS₄ adopts the stannite-type crystal structure.

We studied crystal structure, cation distribution and intrinsic point defect scenario in Cu₂(Zn_1-xCd_x)SnS₄ monograins  by neutron diffraction. This method enables us to differentiate the isoelectronic cations Cu⁺ and Zn²⁺ in the crystal structure analysis. At the same time the presence of Cd²⁺ in the samples introduces a huge challenge for neutron diffraction, as Cd is absorbing neutrons, in this way increasing the measuring times significantly.

These investigations enabled us to deduce that in the range between x=0 and 0.38 the mixed crystals adopt kesterite type structure with increasing Cu/II disorder with increasing Cd content. Starting with x=0.57 and until x=1.0 the material adopt stannite type structure, with a complete absence of Cu/II disorder. The change in the cation distribution being so abrupt suggests us that in this solid solution the complex cation re-distribution process within the crystal structure is happening in a very narrow compositional range 0.38 < x < 0.57.

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The evolution of Sb₂Se₃ heterojunction devices away from CdS electron transport layers (ETL) to wide band gap metal oxide alternatives is a critical target in the development of this emerging photovoltaic material. Metal oxide ETL/Sb₂Se₃ device performance has historically been limited by relatively low fill-factors (FF), despite offering clear advantages with regards to photocurrent collection. In this work, TiO₂ ETLs were fabricated via direct current (DC) reactive sputtering and tested in complete Sb₂Se₃ devices. A strong correlation between TiO₂ ETL processing conditions and the Sb₂Se₃ solar cell device response under forward bias conditions was observed and optimised. Ultimately, a SnO₂:F/TiO₂/Sb₂Se₃/P3HT/Au device with the reactively sputtered TiO₂ ETL delivers an 8.12% power conversion efficiency (η), the highest cadmium-free Sb₂Se₃ device reported to-date. This is achieved by a substantial reduction in series resistance (Rs), driven by improved crystallinity of the reactively sputtered anatase-TiO₂ ETL, whilst maintaining almost maximum current collection for this device architecture. This paper will also discuss the role of organic hole transport materials ‐ namely P3HT, PCDTBT, and spiro‐OMeTAD to modify device performance. By comparing these against one another, and to a reference device, their role in the device stack are clarified. These organic HTM layers are found to serve a dual purpose, increasing both the average and peak efficiency by simultaneously blocking pinholes and improving the band alignment at the back contact.

Antimony selenide (Sb₂Se₃) has emerged as a promising photoelectric material owing to its excellent material properties. The power conversion efficiency of Sb₂Se₃ thin-film solar cells has reached an impressive 10.57% within a decade. Despite rapid development, the efficiency of Sb₂Se₃ thin-film solar cells remains significantly below the theoretical prediction of 30%. Therefore, considerable efforts are still required to enhance the material quality of Sb₂Se₃, a critical factor in boosting solar cell efficiency. Post-deposition annealing treatments have been carried out as an effective method to improve the qualities of Sb₂Se₃ thin films, such as crystallinity and optical properties. However, these treatments typically require tens of minutes or more of thermal annealing at high temperatures (>300 °C), which severely limits both the throughput and substrate choice. For the first time, a low thermal budget annealing technique was used for post-deposition annealing of Sb₂Se₃, which was carried out to enhance the film properties of Sb₂Se₃ thin film solar cells. Photonic curing uses pulsed light annealing with a broadband light source and Sb₂Se₃ samples annealed with single pulse light in pulse lengths of 1 to 15 ms. This process heats the Sb₂Se₃ film above 400 °C within milliseconds without damaging the underlying layers of the material stack. Short pulses (less than 5 ms) having higher radiant power damage the Sb₂Se₃ thin films compared to longer pulses. In contrast, during longer pulses, the temperature rises quickly and decreases gradually, even while the light remains on. This is due to the power in the capacitor bank draining, which reduces the lamp’s output and limits the peak temperature at the sample surface. As a result, longer pulses cause less damage and lead to more crystalline films. Therefore, increasing pulse duration or reducing radiant exposure can minimise damage to the Sb₂Se₃ film. Photonic curing has increased the crystal orientations in the hkl, l ≠ 0 ([211] and ([221]) direction of Sb₂Se₃, reduced the surface roughness and decreased the leakage current of the solar cells. The reduced open circuit voltage effectively lowers recombination rates of charge carriers and improves carrier transport. These enhance the power conversion efficiency of Sb₂Se₃ by 46%. Hence, photonic curing shows the capability of curing Sb₂Se₃ thin films and creating high-quality Sb₂Se₃ thin films with high crystallinity without sacrificing surface coverage. This eliminates the rate-limiting annealing step and opens up new opportunities for Sb₂Se₃ photovoltaics.

Low-dimensional antimony-chalcogenide materials have received an outstanding interest for photovoltaic (PV) devices in the last years. They show high stability, low environmental impact, low cost, low carbon footprint and high technological flexibility. Currently, efficiencies above 10% have already been achieved for Sb2(S,Se)3-based solar cells [1]. On the other hand, Sb-Ge chalcogenide material is well studied as phase change material for different applications, especially when using Te as chalcogen [2]. However, up to our knowledge, the combinations of Sb-Ge chalcogenide semiconductors have not been integrated in solar cell devices. In this work, Sb-(Ge)-Se thin films are grown by selenization of co-evaporated Sb-(Ge) films on Mo/SLG and SLG substrates. The properties of Sb-Ge-Se layers are compared with those of Sb2Se3 thin films. The effect of the selenization process on the structural, morphological, compositional and optical properties of the Sb-(Ge)-Se compounds is investigated. Different growth parameters, such as the maximum selenization temperature and Se added during the thermal treatment, have been investigated in these devices. Independently from the used growth parameters, all Sb2Se3 absorbers show an orthorhombic structure with [hk1] preferred orientation, and a compact structure free of pinholes, while the Sb-Ge-Se active layers show the co-existence of Sb2Se3 and GeSe2 phases. The co-existence of these two phases is corroborated by Fourier-transform infrared spectroscopy (FTIR). Sb-Ge-Se thin films´ band gap energy Eg varies from 1.4 to 1.8 eV depending on the Ge content, as determined by ellipsometry spectroscopy. First efficient Sb-Ge-Se thin-film solar cells have been fabricated using these new absorbers and device efficiencies of 5.4 % and 1.3 % are achieved for Sb2Se3 and Sb26Ge6Se68-based films respectively. C-V and DLCP measurements performed in both type of solar cells, indicate a high defects concentration when introducing Ge in the absorber layer, in agreement with the device performance. This is an indication that the (GeSe2)x(Sb2Se3)1-x system is more defective than the Sb2Se3 material. TEM investigation of Sb-Ge-Se and Sb2Se3 solar cells reveal a different CdS/Sb-(Ge)-Se heterojunction that can explain the limitation of the PV devices when Ge is incorporated in the structure.
More investigations are carried out to understand performance limitation in the solar cells based on these new thin-film absorbers. Finally, we will discuss the possible
improvements of the current devices and the potential of these promising and sustainable chalcogenide material for outdoor/indoor/thin film PV applications

New materials of interest for photovoltaics or other applications are invariably multi-cation compounds or alloys. Therefore, to properly explore their properties, synthesis experiments must be carried out over a broad parameter defined by several compositional variables, core thermodynamic variables of temperature and pressure, and kinetic variables such as reaction time and heating rate. Each of these can affect the outcomes of synthesis: the phases formed and their microstructural and defect characteristics that are so important for functional properties. A special challenge in the context of inorganic materials such as multinary chalcogenides is that they can be grown over a very wide range of temperatures and pressures as well as off-stoichiometric compositions. Thus, the parameter space to be explored is particularly extensive.  

In this contribution, we will present our concept for automated exploration of new inorganic chalcogenides in a self-driving lab. This combines a powerful and rapid PVD-based synthetic method with automation and machine learning, to rapidly map the phase space and functional properties of new materials, without needing prior information. The developments to-date will be presented, starting with our approach for automated generation of co-sputtering processes. This involves two machine-learning stages coupled to a geometrical model of the sputter flux, fitted in real time using input from a trio of QCM sensors. Outputs of the trained models can be used to produce co-sputtering recipes that yield a specified composition, while allowing other parameters (e.g. pressure) to vary. In addition, compositional maps for each sample are obtained directly without time-consuming mapping in an external system.  We will preview coming developments in automation of the subsequent process stage – rapid thermal sulfurization – and some initial work in image-based high-throughput characterisation combined with simulations, to derive optical properties of the target materials.  Perspectives for the application of self-driving labs in development of new device materials will be discussed. 

Chalcogenide perovskites, in particular BaZrS3, have gained a lot of popularity in the last few years due to its great potential as an alternative lead-free photovoltaic absorber material. This is due to promising optoelectronic properties such as defect tolerance, strong dielectric screening, and light absorption [1]. However some of the fundamental material physics, in particular polymorphic phase transitions, have not been explored in detail. Experimental studies have given conflicting results with Raman spectroscopy showing no signs of a phase transition[2], whilst XRD studies show an orthorhombic-to-tetragonal phase transition at 800K [3].
In this talk, we will introduce our machine learning potential model trained on perovskite structures with the neuroevolution potential method [4]. Through molecular dynamics calculations, we heat the experimentally reported orthorhombic Pnma phase and observe a first-order phase transition to a tetragonal I4/mcm phase at 610K. Upon further heating, we observe a second-order phase transition from the tetragonal phase to the cubic Pm-3m phase at 880K. We explain the order of these phase transitions through group-subgroup relationships and Landau theory.
Further analysis shows that the phase transitions are mediated through the M and R phonon modes associated with octahedral tilting, as is typically found in perovskite structures [5]. We analyze all possible Glazer tiltings to show that for the BaZrS3 perovskite only the Pnma --> I4/mcm --> Pm-3m phase transition route is accessible through heating. We also show temperature-dependent static structure factors and compare them to published experimental work[3]. To end, we highlight the dependence of stability of different polymorphs of the perovskite across various pressures and temperatures through a phase diagram. 

Barium sulphide (BaS) serves as a crucial precursor for advanced barium-based materials, including the emerging perovskite absorber BaZrS₃.^[1] However, conventional BaS production methods are highly energy-intensive, requiring temperatures exceeding 1000 °C ^[2,3] and emitting large quantities of CO₂ and SO₂,^[3,4] raising environmental concerns.

This work presents a novel solid-state synthesis route for BaS that drastically reduces the environmental and energy demands. By employing a finely milled mixture of barium hydroxide [Ba(OH)₂] and elemental sulphur, we achieve an efficient conversion (85%) to BaS at a remarkably low annealing temperature of 500°C.

The process is enabled by a unique low-pressure annealing environment, which facilitates the rapid vaporization of H₂O byproducts while maintaining a controlled sulphur partial pressure. This balance prevents unwanted side reactions and enhances the conversion efficiency. Furthermore, this method is highly scalable and compatible with industrial processes, offering a sustainable and economically viable pathway for BaS production.

Ternary chalcogenide nanocrystals have emerged as a promising material in the field of renewable energy, particularly as absorber materials for solar cells. In recent years, there has been a notable focus on the development of environmentally friendly materials, such as AgBiS₂ and AgSbS₂, as an alternative to traditional quantum dots containing heavy metals, including lead and cadmium. The components of these materials are plentiful and less toxic, reflecting the growing emphasis on sustainability and green energy solutions. These materials display high absorption coefficients, tunable band gaps, efficient charge separation, and impressive stability, rendering them ideal for emerging applications in solar cells, photodetectors, photocatalysis, and thermoelectrics. [1-3]
Nevertheless, the synthesis of quantum dots has traditionally been performed using the hot injection method, which involves prolonged high-temperature and vacuum processes. This approach presents significant challenges in terms of scalability, cost, and reproducibility, which must be overcome for these materials to be suitable for commercial applications. In this study, we present a straightforward and low-temperature synthesis of AgBiS₂ and AgSbS₂ quantum dots via cation exchange. This study presents a novel approach to the synthesis of Ag₂S nanoparticles (NPs) that employs unconventional sulfur precursors and a sequential exchange of silver ions for bismuth and antimony ions. This method allows the preparation of high-quality ternary quantum dots with precise control of size and atomic ratio. Furthermore, the incorporation of the ternary nanocrystals into photovoltaic devices provides evidence of the viability of the novel synthetic approach for the fabrication of high-performance solar cells.

Bismuth sulfide (Bi₂S₃) is a nontoxic and inexpensive semiconductor that has potential for use in low-cost thin film photovoltaics owing to its near optimal 1.2eV bandgap and high absorption coefficients greater than 1x10⁴cm^-1 within the IR to UV range [1][2]. Although Bi₂S₃ has potential in photovoltaics, devices have performed poorly with typical efficiencies not surpassing 2% [3][4][5]. One of the challenges of creating high performance cells is from the bulk defects that can exist due to stoichiometric imbalances acting as effective recombination centres [6]. These defects such as the sulfur vacancy and interstitials act mostly as donors making p-type doping difficult [6][7]. The reported properties of Bi₂S₃ are also inconsistent and depend on how the film was prepared. Its lack of crystallinity for example can blue shift the band gap to as high as 1.8eV due to quantum confinement effects [9][4]. Carrier mobilities have varied greatly from 5 cm²V^-1s^-1 prepared by chemical bath to much higher values of 257 cm²V^-1s^-1 and 588 cm²V^-1s^-1 for rapid thermal evaporation and spray pyrolysis [9][4][10]. The latter tow is greater than the typical carrier mobilities reported of 21 cm²V^-1s^-1 to 50cm²V^-1s^-1 for monocrystalline Bi₂S₃ grown via the Bridgman technique, suggesting the importance of purity [12][11]. The choice of substrate can influence the charge transfer efficiency in photovoltaic devices due how the bands bend at the interface. Bi₂S₃ deposited onto fluorine doped tin oxide (FTO) for example exhibited better photocurrent than those on tin doped indium oxide (ITO), Molybdenum or Gold [8]. This research has embarked on a systematic study of Bi₂S₃ thin films for photovoltaic devices. These thin films were synthesised via sulfurization of sputtered bismuth films on FTO substrates within a tube furnace. By varying the holding temperatures, ramp rates and holding times different optical and structural properties can be obtained.  The effect of different film properties such as crystallite size, stichometry and thickness will be tested in a ITO/ZnO/CdS/Bi₂S₃/FTO cell architecture. By gaining control over the film properties, they can be tuned to improve the performance as an absorbing layer in photovoltaic devices.

Halide perovskite semiconductors made a great impact on the field of solar cells with efficienies soaring beyond 26% [1]. On the other hand, halide perovskites are attractive materials for light emitting devices, i.e. LEDs and lasers. Perovskite lasers can be prepared from solution at low temperatures on a wide range of substrates, which provides exciting opportunities in the field of integrated optoelectronics.[2]

Amplified spontaneous emission (ASE) and optically driven lasing were achieved in so-called hybrid organic-inorganic lead halide perovskites, where the A-site cation is based on an organic compound, such as methylammonium or formamidinium. [3,4] Intriguingly, these crystalline compounds are soft and photonic nanostructures can be directly patterned into them by thermal imprint at moderate temperatures.[5]

All-inorganic halide perovskites, such as those where the A-site cation is Cs⁺, are frequently claimed to provide improved thermodynamic stability.[6] Among them, CsPbBr₃ has been shown to be an excellent gain medium for perovskite lasers in the green spectral region. [7] More recently, we could show that b-CsPbI₃ stabilized with 2.5wt% of PEO demonstrates a low lasing threshold of 45 μJ cm^-2 at room temperature with tunable emission from 714.1 nm to 723.4 nm [8]_.

For the Cl-based representative, i.e. CsPbCl₃, deposition of thin films from solution is essentially impossible due to the poor concomitant solubility of the precursor salts PbCl₂ and CsCl.[9]

Here, we will show two concepts to achieve CsPbCl₃ thin films as gain medium. As a first strategy, we use superlattice structures of PbCl₂ and CsCl with a thickness of the sublayers on the order of 3-5 nm by thermal evaporation. We evidence the formation of CsPbCl₃ at the interface of PbCl₂ and CsCl. Already a 1 nm thick CsCl layer deposited on top of PbCl₂ gives rise to a notable photoluminescence at 409 nm with a narrow line width of 8 nm (FWHM), which agrees with reports of CsPbCl₃ single crystals. The superlattices show amplified spontaneous emission (ASE) in the deep blue spectral region at 427 nm above a threshold energy density of 190 µJ/cm² at room temperature (RT).

In a second approach, we subject thin-films of CsPbBr₃ to halide exchange. Upon pulsed exposure to TiCl₄ gas in an atomic layer deposition system, the CsPbBr₃ film is step-wise converted to CsPbCl₃. Depending on the number of TiCl₄ pulses, the emission of the resulting material can be tuned between 523 nm (CsPbBr₃) to 413 nm (CsPbCl₃). Thermal imprint is shown to significantly improve the material quality affording a narrow luminescence linewidth of 8 nm (FWHM). The resulting CsPbCl₃ show ASE at 427.6 nm with a low threshold of 70 µJ/cm². Our work states the first report of CsPbCl₃ thin films showing ASE at room temperature.

Fully inorganic perovskite nanocrystals (NCs) have proved to be efficient materials for optoelectronic applications. In this context, the surface chemistry and, in particular, the surfactant molecules use to passivate NCs surface are demonstrated to have a relevant role in the photoluminescence and stability properties of colloidal nanocrystals. In addition, perovskites have been demonstrated to be valid candidates as active materials for sensing applications; however, the role of the NCs ligand on the sensing properties is today almost unexplored. 
Here we present a systematic investigation of the PL and ASE properties of CsPbBr₃ NCs thin films, their photostability and their sensitivity to ambient air on the NCs capping ligand. In particular, our analysis include the study of three generations of capping ligand, for a total of four samples: oleic acid and oleylamine (OAcOAm) as the first generation, didodecyldimethylammonium bromide (DDAB) as the second, 3-(N,N-dimethyloctadecylammonio)propanesulfonate (ASC18) and lecithin as the third generation. A strong correlation between the ligand used to passivate the nanocrystals and their optical properties is evidenced. Our results demonstrate that the best ASE properties are provided by the lecithin-capped NCs thin film, that shows the lowest ASE threshold and good ASE stability under laser excitation. A strong air sensitivity is also demonstrated with a 60% Relative Quenching (RQ), noticeable as a higher ASE intensity in air with respect to the vacuum conditions, highlighting the possibility to exploit lecithin-capped CsPbBr₃ NCs films for highly efficient sensing application.
 

Lead halide perovskite (ABX₃) nanocrystals are luminescent nanomaterials of significant interest for applications in displays, solar concentrators, and photodetectors due to their bandgap tunability across the visible spectrum, narrow emission profiles, and high radiative carrier recombination rates.[1] However, their emission properties are not uniform across the visible range. Blue emission remains challenging to achieve, while red emission often suffers from lower efficiency and stability compared to green, posing difficulties for pure perovskite-based white light generation. Porous scaffolds have been employed to fabricate various ligand-free perovskite nanostructures.[2-5] However, scaffold preparation methods have involved only the use of optically passive elements. In this work, we have developed GdVO₄:Eu³⁺ and GdVO₄:Dy³⁺ nanoparticles films with a regular pore size that can be infiltrated with perovskite precursors from the liquid phase. In this context, we prepare CsPbBr₃ and Cs₄PbBr₆ nanocrystals, which emit green and blue light respectively. Upon ultraviolet excitation, Eu³⁺-doped nanophosphors emit red light, while Dy³⁺-doped nanophosphors emit light in the blue and yellow regions of the visible spectrum.[6] The combination of perovskite nanomaterials and multifunctional phosphor-based scaffolds enables the fabrication of transparent photoluminescent coatings with tunable spectral emission, controlled by the excitation wavelength. This synergy allows for the generation of white light with customizable hues ranging from warm (2300 K) to neutral (5500 K).

Low-dimensional metal halide perovskites are attracting great interest for photovoltaics and photonics. In particular, 2D tin perovskites have been shown to have good optical gain properties which make them promising for applications as coherent light sources. [1] On the other hand, the ability of lead-based 2D perovskites to sustain lasing remain highly controversial. [2]  Here we show that both Sn and Pb-based 2D perovskites thin films can achieve amplified stimulated emission, and compare their properties as function of the optical pumping conditions as well as of the materials’ structural characteristics. By employing ¹H, ¹³C, ¹⁵N, ¹¹⁹Sn and ²⁰⁷Pb solid state NMR spectroscopy, we were able to discern the local structural environments of the 2D perovskite of interest through their characteristic spectral fingerprints. Spin relaxation dynamics measurements reveal that the local supramolecular spatial arrangements, the molecular motions and structural rigidity are key factors shaping the energetic landscape of the material and its luminescence properties. Our work provides a deeper understanding of the structure-properties relationship of these soft semiconductors to assist the rational engineering of materials with improved optical properties for lasing applications.

In recent years, 2D metal halide perovskites (MHPs) have become a prominent organic-inorganic solution-processable semiconductor due to their superior structural stability and distinct optoelectronic characteristics over 3D MHPs [1-4]. The two primary phases of 2D MHPs based on the type and arrangement of organic spacers are Ruddlesden-Popper (RP) and Dion-Jacobson (DJ) perovskites [2,3]. To study the effect of integrated organic spacers in RP and DJ perovskites on optoelectronics and how they affect their fundamental properties. In this work, we synthesized similar RP-EA and DJ-EDA perovskites (n=1-4) by incorporating the smallest and analogous organic spacers, ethylenediammonium (EDA) and ethylammonium (EA), in MAPbI3. In addition, we examined the structural, morphological, dielectric, and optoelectronic properties of these perovskites [4]. Furthermore, the optical properties of RP-EA and DJ-EDA are correlated with their estimated effective high-frequency dielectric constants (εeff), which indicates that the sharp exciton absorbance behaviour observed in the DJ-EDA perovskite thin films can be attributed to a higher εeff mismatch from bulk counterparts (MAPbI3). The DJ-EDA perovskite-based photodetectors showed improved stability and a higher photoresponsivity of ∼1.00 mA/W (n=4) because of their van der Waals gap-free structure. The DJ-EDA perovskites also retained 97.67% (n=2) of the initial photocurrent after 50 cycles under 1 Sun illumination in the ambient atmosphere conditions. Conversely, the RP-EA perovskite photodetectors had shown faster response times, possibly due to improved in-plane crystal structure and better band alignment. Therefore, the structural and photophysical properties of the smallest carbon chain organic spacers-based RP and DJ perovskites are fundamentally understood in this work and can be further used for the development of different optoelectronic applications.

Exciton-polaritons are half-light, half-matter excitations arising from the strong coupling regime between cavity photons and excitons of semiconductors [1]. Behaving as superlative non-linear photons due to their hybrid nature, exciton-polaritons have been providing a fruitful ground for studying quantum fluid of light and realizing prospective all-optical devices. In this presentation, we present experimental studies on exciton-polaritons in resonant metasurfaces, which are composed of sub-wavelength lattices of perovskite pillars (see Figure). Room temperature polaritons are demonstrated with a remarkable Rabi splitting in the 200 meV range. We show that polaritonic dispersion can be tailored on-demand. This includes creating linear, slow-light,  multi-valley shaped dispersions [2] as well as polarization vortex emission [3]. Finally, we observe experimentally the ballistic propagation of polaritons over hundreds of micrometers at room temperature, even with large excitonic components, some up to 80%. This long-range propagation is enabled by the high homogeneity of the metasurface, and by the large Rabi splitting which completely decouples polaritons from the phonon bath at the excitonic energy [4]. Our results suggest a new approach to study exciton-polaritons and pave the way for the development of large-scale and low-cost integrated polaritonic devices operating at room temperature.

Materials that combine optoelectronic function with control over the spin degree of freedom are central for emerging quantum technologies, opto-spintronics, and provide exciting avenues for generating polarized light-emission. Hybrid metal-halide perovskites exhibit spin-split Rashba bands and strong spin-orbit coupling, which offer directions for extended spin life-times of excited states and efficient optical spin manipulation. To achieve optimal performance in applications, an understanding how material chirality links to spin state properties and dynamics needs to be established.

In the first part of this talk, we will present our efforts on gaining control over spin state properties and dynamics in solution-processable chiral hybrid perovskites through compositional and structural tuning. For this, we tailor the chiral crystal symmetry in novel chiral lead-free bismuth-based materials, highly-emissive low-dimensional chiral lead-halide systems, as well as chiral-achiral heterostructures.

In the second part, we will discuss time- and space-resolved investigations of excited state and spin dynamics in our novel chiral perovskites. We will present results on spin dynamics from ultrafast Faraday Rotation, polarized recombination dynamics, as well as spatio-temporal imaging of excitations using ultrafast transient microscopies.

By combining the optoelectronic properties of halide perovskites (HPs) with chirality from inserted organic cations, chiral HPs brought new perspectives for chiroptical properties, such as non-linear optics or circularly polarized luminescence (CPL), or spintronic devices such as spin valves or spin-LEDs. Indeed, the emergent field of chiro-spintronics proposes to use chiral molecules as a substitute for ferromagnetic materials thanks to the spin-specific interaction between electrons and chiral molecules, a phenomenon called CISS, “chirality-induced spin selectivity”. Following this strategy, we prepared a series of chiral HPs and revealed both experimentally (mc-AFM) and theoretically (band structure and spin texture calculations) the influence of crystal symmetry elements on the spin polarization ability of this family of molecular materials (Figure a).[1] We also demonstrated the possibility to use such materials as spin valves. More recently, we reported a full series of lead-free chiral double perovskites showing strong structural distortions in the inorganic network.[2] In combination with their lead-based counterparts, such series will ultimately allow us to investigate the fundamental role of the metal ions on the CISS effect. On the other hand, revealing the ability of chiral HPs for chiroptical applications require a proper characterization of the thin film chiroptical responses, in particular circular dichroism (CD), considering the macroscopic interferences (linear dichroism LD, linear birefringence LB) inherent to solid-state samples, leading to the so-called antisymmetric LDLB effect (aLDLB) and symmetric LDLB effect (sLDLB). Since these macroscopic effects can be very strong in highly crystalline metal-halide thin films, an experimental guide to accurately discriminate between both CD, aLDLB and sLDLB was recently reported with the example of 1D chiral lead-halide networks.[3] However, in compounds with large optical anisotropy, such effects can be minimized by controlling the orientation of the polar axis with respect to the light beam propagation (Figure b). This strategy allowed us to characterize artefact-free CPL on both single crystals and thin films of 1D chiral lead-bromides with white-light emission (manuscript under revision).

The solution processed semiconductors known as perovskites, or semiconductor perovskites (SP), has been widely studied as an idoneal platform to implement cost-effective integrated lasers.  From this perspective, there is an important concern on developing a SP technology to implement photonic integrated circuits. In this context, we have recently demonstrated that a nickel acetate, Ni(AcO)₂, sol-gel is an exceptional and non-expensive matrix for SP nanocrystals. The distinctive advantage of this alternative technology relies on the in-situ crystallization of the perovskite nanocrystals during the spin-coating deposition, resulting on thin films with PL quantum yields exceeding 80 % and outstanding ambient and mechanical stability. This work successfully demonstrates the potential of Ni(AcO)₂ containing MAPbBr₃ (MA:methylamonium) SPs nanocrystals for active photonics. These nanocomposites are easily spin-coated on a SiO₂/Si to conform planar waveguides. Moreover, the concentration of nanocrystal in the matrix allows the tunability of the optical properties, resulting in thin films with a tailor-made refractive index and absorption. Under optimal concentrations, the nanocrystals are homogeneously dispersed in the film and the waveguide efficiently propagates the light with relatively low losses. Here, the excitation beam injected in the structure gives rise to the generation of photoluminescence (PL) of the nanocrystals, and under certain excitation and propagation conditions, the generation of amplified spontaneous emission (ASE) and the formation of narrow random lasing (RL) under relatively small threshold (µJ/cm²). These results mark a significant step towards realizing the potential of perovskite nanocomposites in the field of optical waveguides.

Lead halide perovskite quantum dots have recently emerged as promising nano-emitters due to their excellent optical properties, including high brightness, tunable optical bandgap, reduced blinking, and easy and low-cost fabrication [1]. These properties make them potential candidates for realising a new generation of optoelectronic devices such as light-emitting diodes (LEDs), lasers, or photodetectors. At the individual quantum dot level, single photon emission at room temperature [2,3], long coherence times and photon indistinguishability with 50% visibility at cryogenic temperatures [4,5] have also been reported. These properties suggest that perovskite quantum dots could play a key role in the realisation of efficient single-photon sources based on solution-processed nanoemitters for applications in quantum optics and quantum communication. In this context, one of the main challenges is to couple individual perovskite quantum dots to optimised photonic structures in order to control and enhance the spontaneous emission properties of the nano-emitters using cavity quantum electrodynamics (cQED) effects.

In this talk I will present our recent results on cQED experiments on single perovskite quantum dots coupled to an optical microcavity. We have designed and implemented a reconfigurable open fibre-based Fabry-Pérot microcavity, specifically suited for CsPbBr₃ perovskite quantum dots. It is based on a highly versatile setup that has previously been successfully optimised for single carbon nanotubes [6]. Unlike conventional monolithic microcavities, which are designed to ensure spatial and spectral matching to a specific nano-emitter and cannot be subsequently modified, this fibre microcavity is perfectly suited to solution-processed nano-emitters. It consists of a planar mirror on which the quantum dots are deposited and a movable concave fibre mirror. This geometry allows us both to ensure spatial and spectral matching for different perovskite quantum dots and to study the same nano-emitter in free space and in cavity configurations. I will show that previously characterised single CsPbBr₃ quantum dots [7,8] have been successfully coupled to this microcavity. By comparing their photoluminescence lifetime in free space with that in the cavity configuration, a twofold acceleration of the emission lifetime due to the Purcell effect was consistently observed, corresponding to Purcell factors of up to 4.5. Furthermore, the reversible coupling of individual CsPbBr₃ quantum dots to the cavity provides a highly interesting tool to precisely analyse the modification of the spectral features induced by the cavity coupling and to extract fundamental properties such as the vacuum Rabi coupling, which is of the order of 30 µeV in our system. These results pave the way for the realisation of a narrow-band efficient single-photon source at the cavity resonance frequency in the weak coupling regime using perovskite quantum dots.

Halide perovskites show excellent optoelectronic properties including bandgap tunability, high radiative recombination rates and narrow emission lines that make them promising candidates for the next generation solar cells, LEDs and detectors.^[1],[2],[3] Their optical properties and ease of processing make them very interesting to control light matter interactions to deliver devices with unique properties and enhanced performance. However, their thin film character is yet to be exploited to enable full control over the emission properties, something that would open avenues to surpass the luminous efficacies of conventional LEDs and facilitate their widespread adoption.

In this talk, we present a novel green perovskite LED architecture where enhanced emission and directionality on demand are achieved by means of a hybrid photonic-plasmonic structure.^[4] We show how a code based on the transfer matrix model boosted by a genetic algorithm identifies the best combination of materials and thin film thicknesses to maximise outcoupled light with very narrow and controllable angular dispersion; all in a realistic fashion compatible with the fabrication of efficient LEDs. The experimental realization of the optimum designs allows us to demonstrate devices with amplified green emission selectively enhanced at different angles. Our low temperature process can tune the perovskite thickness on a nanometric scale to enhanced electroluminescence on demand from forward direction (0°) to up to 40°. This approach expands the role of the perovskite film from a mere emitter to an active photonic layer participating in the strong interference phenomena arising from the designed photonic-plasmonic nanostructures. Our methodology is versatile and easily integrable into cost-effective perovskite LEDs with emission lines covering the entire visible spectrum. Finally, we adapt this resonant cavity concept to demonstrate a highly spectral selective and robust perovskite photodetector, showing 2.4-fold EQE enhancement at the narrowband peak with respect to a broadband photodetector counterpart of the same perovskite thickness.^[5]

Metal halide perovskites (MHPs), particularly CsPbBr₃, have emerged as a transformative material for optoelectronic applications, offering unparalleled properties such as high carrier mobility, exceptional optoelectronic performance, large photoluminescence quantum yield, and superior stability under humidity and thermal stress. Its solution processability allows for easy fabrication using inkjet printing, an environmentally sustainable alternative to conventional manufacturing techniques [1].

In inkjet printing of perovskites, the characteristics of the functional ink and printing conditions are crucial in determining the final device performance, with annealing temperature playing a critical role in influencing the crystal structure and, consequently, the optoelectronic properties of the printed films. This study comprehensively investigates the impact of annealing temperature in vacuum oven from 45-200 °C on the properties of inkjet-printed CsPbBr₃ nanocrystal films printed on glass substrate [2]. The CsPbBr₃ nanocrystal inks were prepared in the ratio of 3:1 in dodecane and hexane solvent with each nanocrystal measuring 7-13 nm and the printing was performed using Dimatix inkjet printer.

 The results reveal a significant dependence of photoluminescence (PL) intensity on the annealing temperature, with the optimal PL emission observed for devices annealed at 180°C. The change in the PL properties are related to the impact of annealing temperature on grain size, crystallinity, and film uniformity, which directly affect optoelectronic properties and stability corroborated by various characterizing techniques such as X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), Fourier-transform infrared (FTIR) spectroscopy, and ultraviolet-visible (UV-Vis) absorption spectroscopy providing conclusive evidence of the temperature-induced changes in crystal structure, phase purity, and optoelectronic performance. These findings underline the critical role of precise thermal processing in achieving high-performance inkjet-printed perovskite films, positioning CsPbBr₃ as a viable material to be printed on ITO coated glass substrate for LED applications [3].

Halide perovskite materials hold significant potential for solar energy and optoelectronic applications. However, enhancing their efficiency and stability necessitates addressing challenges related to lateral inhomogeneity. Photoluminescence imaging techniques are widely employed to measure their optoelectronic and transport properties¹. While achieving high precision typically requires longer acquisition times, extended light exposure can significantly alter the perovskite layers due to their high reactivity, compromising data quality.

To address this issue, we propose a method to extract high-quality lifetime images from rapidly acquired, noisy time-resolved photoluminescence images². Our approach leverages constrained reconstruction techniques, incorporating the Huber loss function and a specific form of Total Variation Regularization. This method effectively mitigates limitations imposed by local signal-to-noise ratios (SNR), allowing access to greater detail and features in the results. Through simulations and experimental validation, we demonstrate that our approach outperforms traditional pointwise techniques. Additionally, this analysis can be extended to determine the surface recombination rate, providing valuable insights for the advancement and optimization of halide perovskite materials. Furthermore, we identify optimal acceleration and optimization parameters tailored to decay time imaging of perovskite materials, offering novel perspectives for accelerated experiments essential to characterizing degradation processes.

Importantly, our methodology has broader applications. It can be extended to other beam-sensitive materials, various imaging characterization techniques, and more complex physical models for time-resolved decays.

Metal halide perovskites (MHPs) are direct bandgap semiconductors with excellent potential and perspectives to become an alternative to traditional semiconductors in the implementation of future devices for optoelectronics and photonics. Furthermore, MHPs have shown remarkable performance for potential optoelectronic applications beyond photovoltaics. The continuous development in smart devices and microsystems for the control of industrial processes, biomedical sensors and instruments, visible and NIR light communications (in the internet of things, for example), object imaging, and cameras for artificial intelligence and robotics is triggering new demands for photodetection concepts and their integration in photonic chips. However, for the explosion of such future photodetector technologies, some other requirements are important: low cost and low CO₂ footprint in fabrication, low operation voltage, small volume, high speed, flexibility, biocompatibility, solar-blind and many other features (for different applications). Therefore, a real and very interesting technology for a future generation of photodetectors can arise on the basis of MHPs, given their excellent optoelectronic properties and the fact that they can be synthesized at low temperatures via fast and simple processes, and films can be easily formed by low-cost solution processing techniques (spin-coating, spray-coating, dip-coating, doctor blading, inkjet printing). Among the MHPs, lead-free perovskite compounds are the most promising non-toxic alternative for developing photodetectors.

This study investigates the development of (PEA_0.5,BA_0.5)₂FA₉Sn₁₀I₃₁-based photodetectors fabricated using inkjet printing on both glass and flexible substrates, emphasizing their potential for advanced optoelectronic applications. The focus is on optimizing the crystallization process of (PEA_0.5,BA_0.5)₂FA₉Sn₁₀I₃₁ layers, ensuring high-quality films with minimal defects, and enhancing charge carrier mobility. The fabrication process employs solution-based techniques compatible with large-scale production, making the devices suitable for integration into wearable electronics and curved displays. Various strategies, such as interface engineering, compositional tuning, and passivation layers, were explored to improve stability and light sensitivity. The research demonstrates that inkjet-printed (PEA_0.5,BA_0.5)₂FA₉Sn₁₀I₃₁ layers (200 nm thickness) exhibit uniform crystal structures, enabling high responsivity and stable performance under different environmental conditions. The fabricated devices exhibited high responsivity across a wide range of light intensities and wavelengths, including visible and near-infrared regions. Persistent photoconductivity due to carrier trapping mechanisms was observed, highlighting the need for further engineering to enhance performance stability. Photoconductive properties were evaluated using continuous and modulated light sources. Devices on glass substrates showed higher efficiency and responsivity compared to flexible PET substrates, likely due to substrate interactions and defect levels. Responsivities ranged up to 50 A/W under low light intensity, with stability improvements observed even after 30 days of operation. Notably, the devices showed improved performance over time, indicating slow film curing and effective encapsulation. The results highlight the potential of inkjet-printed (PEA_0.5,BA_0.5)₂FA₉Sn₁₀I₃₁ photodetectors for next-generation photonic applications, where flexibility and low-cost fabrication are crucial. Despite the promising performance, challenges such as sensitivity to moisture and oxidation in tin-based perovskites remain, impacting long-term device stability. This research provides valuable insights into the practical deployment of lead-free perovskites in photodetection technologies.