Contribution of proton concentration to the kinetics of the hydrogen evolution reaction by a rotating disk electrode configuration

The reaction order is a fundamental problem in kinetics, yet it remains unclear in the hydrogen evolution reaction (HER) of acidic systems. In this study, we systematically investigated the reaction order of the HER on Pt(111) in acidic solutions using a rotating disk electrode configuration. Our experimental findings reveal that the reaction order of the HER decreases with increasing proton concentration up to a critical saturation concentration, where the HER exhibits a zero-order reaction. We attribute this phenomenon to the saturation of the active sites by the reactants, which is limited by the number of active sites. Our results provide support for the Volmer-Tafel mechanism in the HER and suggest that this phenomenon may be prevalent in electrocatalytic reactions where the number of active sites is limited and dependent on the reaction mechanism. This study contributes to a deeper understanding of the kinetics and pH effects in electrocatalytic reactions.