Atomic-Scale Analysis of the RuO2/Water Interface under Electrochemical Conditions

The structure of the interface between ruthenium oxide and water was examined using density functional theory calculations for a range of pH and electrode potential values, and the results were summarized in a surface Pourbaix diagram. The results indicate that pH affects the interfacial structure as a consequence of the formation of a stable hydrogen network and the impact of the electric field on the interfacial Gibbs energy. Focusing on the potential region of the oxygen evolution reaction (1.23 V vs a reversible hydrogen electrode (RHE) + overpotential), variations in pH were found to change both the formal Ru valency and the structure of the primary water layer by altering the work function of the interfacial structure. We hypothesize that the effects of pH on the hydrogen bond network and formal valency observed in this work also apply to other transition-metal oxides.