Efficient electrocatalytic energy conversion requires devices to function reversibly, that is, to deliver a substantial current at a minimal overpotential. Redox-active films can effectively embed and stabilize molecular electrocatalysts, but mediated electron transfer through the film typically makes the catalytic response irreversible. Here we describe a redox-active film for bidirectional (oxidation or reduction) and reversible hydrogen conversion, which consists of [FeFe] hydrogenase embedded in a low-potential, 2,2′-viologen-modified hydrogel. When this catalytic film served as the anode material in a H2/O2 biofuel cell, an open circuit voltage of 1.16 V was obtained—a benchmark value near the thermodynamic limit. The same film also acted as a highly energy efficient cathode material for H2 evolution. We explained the catalytic properties using a kinetic model, which shows that reversibility can be achieved even though intermolecular electron transfer is slower than catalysis. This understanding of reversibility simplifies the design principles of highly efficient and stable bioelectrocatalytic films, advancing their implementation in energy conversion.
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A polymeric hydrogel electrocatalyst for direct water oxidation
Nature Communications Open Access 13 February 2023
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Source data are provided with this paper and are also available from Zenodo at https://doi.org/10.5281/zenodo.4421107. Source data for the crystal structure of V2 in Supplementary Fig. 5 have been deposited at the Cambridge Crystallographic Data Centre, under CCDC deposition number 2046659.
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C.L. and V.F. are supported by CNRS, Aix Marseille Université, Agence Nationale de la Recherche (ANR-15-CE05–0020), and the Excellence Initiative of Aix-Marseille University-A*MIDEX, a French ‘Investissements d’Avenir’ programme (ANR-11-IDEX-0001–02). N.P., S.H. and S.S. acknowledge financial support from the ERC starting grant 715900, the ANR-DFG project SHIELDS (PL 746/2–1) and RESOLV, funded by the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) under Germany’s Excellence Strategy (EXC-2033—Projektnummer 390677874). J.A.B. and O.R. are supported by the Max Planck Society and J.A.B. acknowledges funding from the DFG Priority Programme ‘Iron–Sulfur for Life: Cooperative Function of Iron–Sulfur Centers in Assembly, Biosynthesis, Catalysis and Disease’ (SPP 1927) Project BI 2198/1–1. We thank A. Ruff and L. Castaneda-Losada for useful discussions regarding the polymer synthesis, N. Breuer for the preparation of the hydrogenase, B. Mallick for performing the crystal structure measurements, M. Sander and O. Trost for optimizing the fuel cells, A. Czepull for optimizing the film stability, H. Li for help with the CV experiments and T. Stalder for solving the crystal structure. The French authors are part of the French BIC network.
The authors declare no competing interests.
Peer review information Nature Catalysis thanks Kenji Kano and the other, anonymous, reviewer(s) for their contribution to the peer review of this work.
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Supplementary Methods, Notes 1 and 2, and Figs. 1–55.
Supplementary Data 1
Crystal structure of compound V2.
Source Data Fig. 2
Experimental and statistical source data.
Source Data Fig. 3
Experimental, statistical and calculated source data.
Source Data Fig. 4
Experimental and statistical source data.
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Hardt, S., Stapf, S., Filmon, D.T. et al. Reversible H2 oxidation and evolution by hydrogenase embedded in a redox polymer film. Nat Catal 4, 251–258 (2021). https://doi.org/10.1038/s41929-021-00586-1
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