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  • Perspective
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Absolute band-edge energies are over-emphasized in the design of photoelectrochemical materials

Abstract

The absolute band-edge potentials of semiconductors and their positions relative to solution redox potentials are often invoked as design principles for photoelectrochemical devices and particulate photocatalysts. Here we show that these criteria are not necessary and limit the exploration of materials that may advance the fields of photoelectrochemistry, photochemistry and photocatalysis. We discuss how band-edge energies are not singular parameters and instead shift with pH, electrolyte type and surface chemistry. The free energies of electrons and holes, rather than those of solution redox couples, dictate overall reaction spontaneity and thus reactivity. Favourable charge-transfer kinetics can occur even when the relevant electrolyte redox potential(s) appear outside the bandgap, enabled by the inversion or accumulation of electronic charge at the semiconductor surface. This discussion informs design principles for photocatalytic systems engineering for both one-electron and multi-electron redox reactions (for example, H2 evolution, H2O oxidation and CO2 reduction).

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Fig. 1: Interface energies and reactions.
Fig. 2: Accumulation, depletion and inversion at photochemical junctions.
Fig. 3: Band diagrams and photochemical charge accumulation in nanoscopic and molecular systems.

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Acknowledgements

A.C.N. and S.W.B. were supported in this work through the Liquid Sunlight Alliance (grant no. DE-SC0021266) and G.J.M. through the Center for Hybrid Approaches in Solar Energy to Liquid Fuels (grant no. DE-SC0021173), both Energy Innovation Hubs funded by the US Department of Energy, Office of Science, Office of Basic Energy Sciences. S.A. acknowledges support as part of Ensembles of Photosynthetic Nanoreactors (EPN), an Energy Frontier Research Center funded by the US Department of Energy, Office of Science (grant no. DE-SC0023431). A.J.K. acknowledges funding by the Department of Energy, Basic Energy Sciences (grant no. DE-SC0014279). S.M. acknowledges support from the Department of Energy (grant no. DE-SC0006628).

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A.J.K. and S.W.B. initiated the Perspective. A.J.K. wrote the first draft and generated its figures. A.C.N., G.J.M., S.M. and S.A. edited and contributed substantially to articulating the concepts. A.J.K. and S.W.B. wrote the final paper with input from all authors.

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Correspondence to Shannon W. Boettcher.

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Kaufman, A.J., Nielander, A.C., Meyer, G.J. et al. Absolute band-edge energies are over-emphasized in the design of photoelectrochemical materials. Nat Catal 7, 615–623 (2024). https://doi.org/10.1038/s41929-024-01161-0

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