Presentation Date: Feb 14, 2026
AGSA Abstract
Nickel-based oxyhydroxides are among the most active non-precious catalysts for the oxygen evolution reaction (OER), yet the atomistic mechanisms governing oxidation and surface restructuring under bias remain incompletely understood. In particular, the roles of hydration structure, surface topology, and cooperative proton-coupled electron transfer (PCET) in determining catalytic behavior are still debated. In this work, we present a first-principles investigation of the electrochemical oxidation of Ni(OH)₂, with explicit treatment of interfacial water and edge-site structure, to elucidate how surface geometry and hydration collectively control redox progression and stability. Density functional theory calculations were performed using VASP with GGA+U and an implicit solvation model to simulate electrochemical conditions across a wide potential window. Both the basal plane and multiple crystallographic edge terminations were examined under explicit hydration. On the basal surface, a stable water tetramer network persists across all oxidation states, enabling a clean, stepwise eight-proton deprotonation sequence from Ni(OH)₂ to NiO₂. Distinct free-energy crossovers calculated at ~1.3–1.4 V and ~1.6–1.7 V vs RHE align closely with experimentally observed Ni(OH)₂/NiOOH and NiOOH/NiO₂ redox transitions. At edge sites, oxidation proceeds via cooperative multi-proton events rather than sequential single-proton steps. Across all studied edge geometries, two-proton intermediates are consistently bypassed, revealing a concerted deprotonation mechanism stabilized by structured hydration motifs such as H₃O₂⁻-like bridge pairs and hydrogen-bonded hexamers. Despite initial geometric differences, all edges converge thermodynamically near the NiOOH/NiO₂ transition, indicating dynamic interconversion under operating conditions. These findings demonstrate that OER activity in Ni-based catalysts arises from a fluctuating ensemble of hydrated, oxidized surface states rather than from isolated active sites. The results underscore hydration as a fundamental structural element and provide mechanistic insights for the rational design of next-generation OER electrocatalysts.
