Cation effects on electrocatalytic reduction processes at the example of the hydrogen evolution reaction

Cation effects provide invaluable insights into electrochemistry. In this review, I discuss them with a main focus on the hydrogen evolution reaction and a summary of recent in situ spectroscopic and electrochemical measurements as well as advanced computational simulation results conducted at varying cation identities, concentrations, and pH. According to these works, the interfacial cation concentration is the main descriptor to explain cation and pH effects. The detailed mechanism (such as e.g. water polarization, water structure changes, field-stabilization of intermediates) depends strongly on potential, pH, oxophilicity of the electrode, or the nature of the rate-limiting step and proton donor. With growing convergence in this field, cation effects remain a highly challenging and promising topic for research.