Distinct solvation patterns of OH− versus H3O+ charge defects at electrified gold/water interfaces govern their properties

Understanding the solvation structures of OH^- and H₃O⁺ at metal interfaces is crucial for developing efficient electrochemical devices. In this paper, we present a detailed investigation of the solvation structures of OH^- and H₃O⁺ near gold electrodes under alkaline and acidic aqueous conditions, using ab initio molecular dynamics simulations at controlled surface charge density conditions. Our findings reveal that the adsorption tendencies of OH^- and H₃O⁺ are strongly influenced by the oscillating net atomic charge of water normal to the electrified interface in concert with the distinct solvation patterns of these charge defects. While OH^- preferentially adsorbs onto the gold surface within the first water layer, the positive net atomic charge restricts the closest approach of H₃O⁺ to beyond the first water layer. We unveil resting and active states that support charge transfer processes at the gold/water interface, which critically involve Au atoms in a unique Grotthuss-like mechanism.