Abstract
The platinum-catalysed hydrogen evolution reaction (HER) generally shows poorer kinetics in alkaline electrolyte and represents a key challenge for alkaline water electrolysis. In the presence of alkali metal cations and hydroxyl anions, the electrode–electrolyte (platinum–water) interface in an alkaline electrolyte is far more complex than that in an acidic electrolyte. Here we combine electrochemical impedance spectroscopy and an electrical transport spectroscopy approach to probe and understand the fundamental role of different cations (Li+, Na+ and K+) in HER kinetics. Our integrated studies suggest that the alkali metal cations play an indirect role in modifying the HER kinetics, with the smaller cations being less destabilizing to the hydroxyl adsorbate (OHad) species in the HER potential window, which favours a higher coverage of OHad on the platinum surface. The surface OHad species are highly polar and act as both electronically favoured proton acceptors and geometrically favoured proton donors to promote water dissociation in alkaline media, thus boosting the Volmer-step kinetics and the HER activity.

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Data availability
The data that support the plots within this paper and other findings of this study are available from the corresponding author upon reasonable request. The DFT-optimized geometries and AIMD trajectories are available in the Zenodo data repository at https://doi.org/10.5281/zenodo.7026971.
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Acknowledgements
X.D. acknowledges support from the National Science Foundation award 1800580. Y.H. acknowledges the gracious support by NewHydrogen, Inc. Theoretical research was supported by the DOE-BES DE-SC0019152 grant to A.N.A. An award of computer time was provided by NERSC and the Innovative and Novel Computational Impact on Theory and Experiment (INCITE) program. This research used resources of the Argonne Leadership Computing Facility, which is a DOE Office of Science User Facility supported under Contract DE-AC02-06CH11357.
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X.D. conceived the research. The experiments were carried out by A.H.S. with assistance from Z.H., S.W., G.Z. and C.W. under the supervision of Y.H. and X.D. The calculations were carried out by Z.Z. under the supervision of A.N.A. The manuscript was written by A.H.S., Z.Z., A.N.A., Y.H. and X.D.
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Shah, A.H., Zhang, Z., Huang, Z. et al. The role of alkali metal cations and platinum-surface hydroxyl in the alkaline hydrogen evolution reaction. Nat Catal 5, 923–933 (2022). https://doi.org/10.1038/s41929-022-00851-x
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DOI: https://doi.org/10.1038/s41929-022-00851-x
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