How Do Alkali Cations Affect Alkaline HER Activity of Nickel and Platinum?

Abstract Alkali cations substantially affect the kinetics of electrocatalytic reactions such as CO2 reduction and the alkaline hydrogen evolution reaction (HER). In this work, we investigate the effect of the electrolyte through grand-canonical density functional theory (GC-DFT) in conjunction with Quantum Mechanics/Molecular Mechanics (QM/MM) simulations and validate these results with electrochemical experiments of alkaline HER on commercially relevant and benchmark electrocatalysts, Ni and Pt, respectively. Our results show that the cation trend of alkaline hydrogen evolution depends on the electrocatalyst and is reflected in the activation barrier for water dissociation, studied as a proxy for the Volmer step. Meanwhile, the stability of *H and *OH does not depend significantly on the electrolyte cation.