Metal-Organic Framework-Based Cathodes for Photoelectrochemical Fuel Production

Nadine Schmaus^a

^aDepartment of Chemistry, Technical University of Munich

Proceedings of Catalyst Design Strategies for Photo- and Electrochemical Fuel Synthesis (ECAT23)

Keele, United Kingdom, 2023 December 4th - 5th

Organizers: Charles Creissen, Qian Wang and Julien Warnan

Poster, Nadine Schmaus, 026
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.

References:

[1] Galan-Mascaros, J. R. Photoelectrochemical solar fuels from carbon dioxide, water and sunlight. Catal. Sci. Technol. 2020, 10, 1967–1974.

[2] Ifraemov, R.; Mukhopadhyay, S.; Rozenberg, I.; Hod, I. Metal–Organic-Framework-Based Photo-electrochemical Cells for Solar Fuel Generation. J. Phys. Chem. 2022, 126, 5079–5091.

[3] Kung, C.-W.; Wang, T. C.; Mondloch, J. E.; Fairen-Jimenez, D.; Gardner, D. M.; Bury, W.; Klingsporn, J. M.; Barnes, J. C.; van Duyne, R.; Stoddart, J. F.; Wasielewski, M. R.; Farha, O. K.; Hupp, Metal–Organic Framework Thin Films Composed of Free-Standing Acicular Nanorods Exhibiting Reversible Electrochromism. J. T. Chem. Mater. 2013, 25, 5012–5017.

[4] Zhou, Z.; Mukherjee, S.; Hou, S.; Li, W.; Elsner, M.; Fischer, R. A. Porphyrinic MOF Film for Multifaceted Electrochemical Sensing. Angew. Chem. Int. Ed. 2021, 60, 20551–20557.

[5] Khajavian, R.; Mirzaei, M.; Alizadeh, H. Current status and future prospects of metal–organic frameworks at the interface of dye-sensitized solar cells. Dalton Trans. 2020, 49, 13936–13947.

[6] Stanley, P. M.; Hemmer, K.; Hegelmann, M.; Schulz, A.; Park, M.; Elsner, M.; Cokoja, M.; Warnan, J. Topology- and wavelength-governed CO2 reduction photocatalysis in molecular catalyst-metal–organic framework assemblies. Chem. Sci. 2022, 13, 12164–12174.

[7] Stanley, P. M.; Su, A. Y.; Ramm, V.; Fink, P.; Kimna, C.; Lieleg, O.; Elsner, M.; Lercher, J. A.; Rieger, B.; Warnan, J.; Fischer, R. A. Photocatalytic CO2 -to-Syngas Evolution with Molecular Catalyst Metal-Organic Framework Nanozymes. Adv. Mater. 2023, 35, 2207380.

Acknowledgements:

This project is supported by the German Research Foundation (DFG) and by the Excellence Cluster 2089 ‘e-conversion’ (Fundamentals of Energy Conversion Processes).

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