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Understanding two voltammetric features of water reduction and water oxidation in mild pH solutions

Nature Catalysis volume 8, pages 495–506 (2025)Cite this article

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Abstract

Electrification of many processes requires the use of aqueous solutions under mild pH conditions where the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER) can become competing reactions. The HER and OER under mild pH conditions show peculiar voltammetric behaviours, specifically two reductive or oxidative features, that are not observed in strongly acidic and basic solutions. These behaviours cannot be fully explained by thermodynamic considerations only and are particularly complex owing to the involvement of multiple water species (H3O+, H2O and OH–) and the conversion between these species via water autodissociation and acid–base neutralization reactions. This Analysis provides a systematic and conceptual explanation of the effect of pH, potential, stirring and buffer on the thermodynamics and kinetics of the HER and OER, providing fundamental and yet essential insights into comprehending HER and OER behaviours under mild pH conditions, and their implications for other aqueous reactions more broadly.

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Fig. 1: Expected and observed LSVs for the HER.
Fig. 2: Results from unbuffered pH 1–3 solutions with convection.
Fig. 3: LSVs in unbuffered pH 0–14 solutions with convection.
Fig. 4: LSVs of poor HER catalysts in an unbuffered, unstirred pH 2 solution.
Fig. 5: LSVs in buffered solutions with convection.
Fig. 6: LSVs collected for the OER.
Fig. 7: LSVs for ammonia oxidation.

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Data availability

The source data files for the plots contained in the current study are attached. Source data are provided with this paper.

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Acknowledgements

This work was support by the Division of Chemical Sciences, Geosciences, and Biosciences, Office of Basic Energy Sciences of the US Department of Energy through grant DE-SC0024211.

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  1. These authors contributed equally: Xin Yuan, Michael T. Bender.

Authors and Affiliations

  1. Department of Chemistry, University of Wisconsin–Madison, Madison, WI, USA

    Xin Yuan, Michael T. Bender, Myohwa Ko & Kyoung-Shin Choi

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  1. Xin Yuan
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Contributions

K.-S.C. and M.T.B. conceived the project. Under the supervision of K.-S.C., X.Y. and M.T.B. performed all experiments with the contribution of M.K. for HER LSVs with various metals. All authors discussed the results and contributed to writing the manuscript.

Corresponding author

Correspondence to Kyoung-Shin Choi.

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Supplementary information

Supplementary Information

Supplementary Note 1, Supplementary Tables 1 and 2, and Supplementary References 1–8.

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Source Data Fig. 6

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Yuan, X., Bender, M.T., Ko, M. et al. Understanding two voltammetric features of water reduction and water oxidation in mild pH solutions. Nat Catal 8, 495–506 (2025). https://doi.org/10.1038/s41929-025-01339-0

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