Electro- and Photo-induced Interfacial Charge Transfers in Nanocrystalline Mesoporous TiO2 and TiO2/Iron Porphyrin Sensitized Films Under CO2 Reduction Catalysis

Beatriu Domingo Tafalla^a^,^b, Tamal Chatterjee^a, Federico Franco^a, Emilio Palomares Gil^a^,^c

^aInstitute of Chemical Research of Catalonia (ICIQ), The Barcelona Institute of Science and Technology, Avinguda Països Catalans 16, 43007 Tarragona, Spain

^bDepartament d’Enginyeria Electrònica, Elèctrica i Automàtica, Universitat Rovira i Virgili, Avinguda dels Països Catalans, 26, Tarragona, Spain

^cICREA, Passeig LLuis Companys 23, E-08010, Spain

Materials for Sustainable Development Conference (MATSUS)
Proceedings of MATSUS23 & Sustainable Technology Forum València (STECH23) (MATSUS23)

#e-FuelSyn - Electrocatalysis for the Production of Fuels and Chemicals

VALÈNCIA, Spain, 2023 March 6th - 10th

Organizers: Carla Casadevall Serrano and Julio Lloret Fillol

Oral, Beatriu Domingo Tafalla, presentation 109
DOI: https://doi.org/10.29363/nanoge.matsus.2023.109
Publication date: 22nd December 2022

Artificial photosynthesis requires a hybrid assembly that integrates light absorption, electron transfer, and catalysis. Covalent anchoring of a molecular catalysts to a light harvesting semiconductor results in a photocathode that is able to perform selective photoelectrocatalytic CO₂ reduction (PEC-CO₂RR). In hybrid materials, the molecular catalyst provides with selective catalytic activity whereas the photoactive semiconductor material is used as support and for light harvesting [1]. In these systems, charge accumulation and kinetics of photoinduced electron transfer from the photocathode to the molecular catalyst and to the CO₂ are crucial for an efficient CO₂ conversion [2, 3]. In this work, a mesoporous anatase TiO₂ layer is used as a solid photosensitizer support to anchor iron porphyrin-based molecular catalysts for CO₂ to CO obtention. Micro to mili second Transient absorption spectroscopy (TAS) is employed to investigate the accumulation and lifetime of photogenerated electrons in TiO₂ by controlling the applied bias and in the presence of CO₂. By probing the transient signal of TiO₂ conduction band electrons, we observe a decrease in the accumulation of charges in non-functionalized TiO₂ under applied bias when CO₂ is present (at -0.5 V vs. Ag/AgCl, by 35%), which proves the transference of electrons from the photocathode to the CO₂. Furthermore, we observe a shorter lifetime of photogenerated electrons when the TiO₂ is functionalized with iron porphyrins (10-fold decrease) derived from a fast electron transfer from the photocathode to the molecular catalyst. Ultimately, we correlate the results to the potentiostatic electrocatalysis performance of TiO₂ and TiO₂-Iron porphyrin hybrid materials under CO₂; with bare TiO₂, CO and CH₄ along with H₂ are produced, whereas TiO₂-Iron porphyrin shows 100% selective CO formation. However, we identify moderate CO₂RR performances caused by interfacial charge recombination between the oxidized iron porphyrin and conduction band electrons of TiO₂ which decrease the charge transfer process to the CO₂ molecule.

References:

[1] Liu, C., Colón, B. C., Ziesack, M., Silver, P. A., & Nocera, D. G. Water splitting–biosynthetic system with CO2 reduction efficiencies exceeding photosynthesis. Science, 2016, 352(6290), 1210-1213.

[2] Garcia Osorio, Dora Alicia, Gaia Neri, and Alexander J. Cowan. Hybrid photocathodes for carbon dioxide reduction: interfaces for charge separation and selective catalysis. ChemPhotoChem, 2021, 5(7), 595-610.

[3] Bozal-Ginesta, C., Mesa, C. A., Eisenschmidt, A., Francas, L., Shankar, R. B., Antón-García, D., ... & Durrant, J. R.. Charge accumulation kinetics in multi-redox molecular catalysts immobilised on TiO2. Chemical science, 2021, 12(3), 946-959.

Acknowledgements:

This work was supported by the MCIN/AEI/10.13039/501100011033 and ESF for a predoctoral grant PRE2020-092525 (MCIN: Ministerio de Ciencia e Innovación, AEI: Agencia Estatal de Investigación, DOI: 10.13039/501100011033, ESF: European Social Fund).

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