Ion solvation kinetics in bipolar membranes and at electrolyte–metal interfaces

Abstract Ion (de)solvation at solid–electrolyte interfaces is pivotal for energy and chemical conversion technology, such as (electro)catalysis, batteries and bipolar membranes. For example, during the electrocatalytic hydrogen evolution reaction in alkaline media, water needs to be dissociated and hydroxide ions solvated—a process that is not well understood. Here we study water dissociation and ion solvation kinetics in isolation at polymeric bipolar membrane and electrolyte–metal interfaces. We discover bias-dependent relationships between the activation entropy and enthalpy, which we link to a bias-dependent dispersion of interfacial capacitance. Furthermore, our results indicate that OH − solvation is kinetically slower than H + solvation and that the solvation kinetics display characteristics that are independent of the catalyst structure. We attribute this to a universal amount of excess charge needed to induce electric fields that alter the interfacial entropy of water. Of fundamental interest, these results are critical to enable knowledge-driven bipolar membrane and electrocatalyst design.