Publication date: 10th October 2023
Coupling the most abundant renewable energy source (sunlight) with the production of fuels as a long-term energy storage medium presents unparalleled prospects towards addressing the increasing global energy demand while reducing the dependence on fossil fuels. Photoelectrochemical cells (PECs) can directly convert absorbed photons and carbon dioxide into value-added e-fuels (e.g. CO, CH3OH) striving to combine the advantages of nature-inspired photosynthesis and electrocatalysis.[1,2] However, key challenges exist in the development of efficient photosynthetic hybrid materials providing light absorption, charge separation and transfer as well as catalysis. A new class of multifunctional materials combine light harvesting metal-organic frameworks (MOFs), metal oxide electrodes, and molecular catalysts suited for photo-cathodic solar fuel production from CO2. The photoactive MOF serves as a photosensitizer and offers a confined coordination space for the organometallic catalysts, thereby creating photoelectrochemical nanoreactors. Our PEC setup envisions the deposition of selected pyrene- and porphyrin-based Zr-MOFs (NU-1000, PCN-222) in the form of homogeneous polycrystalline thin films onto the surface of transparent conductive metal oxide electrodes via solvothermal growth and modular assembly, respectively.[3,4] Our objective is to attain an elaborate control over the thin film properties (e.g. film thickness, adherence, conductivity, defects, grain boundaries, crystal orientation), which play a substantial role in achieving high photon conversion efficiencies and stability under working conditions.[5] The decoration of the MOF-cathode samples with benchmark Re-based molecular catalysts for CO2 reduction can be achieved by anchoring the catalyst inside the MOF pore system via solvent-assisted ligand incorporation (SALI) following established concepts and protocols.[6,7] This step will be done either prior to the nano-MOF particle immobilization at the electrode surface or by utilizing a pre-fabricated colloidal solution of fully assembled nanozymes for electrode fabrication. By optimizing the fabrication techniques and performance of MOF-based photocathodes, we aim to unlock the full potential of solar fuel production.
This project is supported by the German Research Foundation (DFG) and by the Excellence Cluster 2089 ‘e-conversion’ (Fundamentals of Energy Conversion Processes).