The Subtleties of the Reversible Hydrogen Evolution Reaction Arising from the Nonunity Stoichiometry

The proton/hydrogen redox couple underpins the electrochemical sciences; however, the nonunity stoichiometry of the reaction leads to distinct voltammetric complications. This Article provides a joint analytical, numerical, and experimental investigation into the reversible hydrogen evolution reaction at a platinum microelectrode. Literature obscurities and nuances are highlighted and corrected, allowing the presentation of an holistic overview of the electrochemical reaction at the reversible limit. Under such conditions, it is demonstrated, first, how the reaction may be misinterpreted as being <i>irreversible</i> and, second, that the transfer coefficient for the reversible (Nernstian) hydrogen evolution reaction is equal to 2. Importantly, the use of the reversible hydrogen electrode (RHE) as a reference potential in voltammetric experiments is critically evaluated