Dynamics, Stability, and Adsorption States of Water on Oxidized RuO₂(110)

Identifying and understanding how excess oxygen atoms affect the adsorption of water on metal oxides is crucial for their use in water splitting. Here, by means of high-resolution scanning tunneling microscopy and density-functional calculations, we show that excess oxygen atoms on the stoichiometric RuO₂(110) significantly change the clustering, conformation, and deprotonation equilibrium of adsorbed water. We considered two reactive scenarios during which the stoichiometric surface was exposed (i) first to oxygen, followed by water, and (ii) first to water, followed by oxygen. In both cases, the [OH-OH] complex on Ru rows is the dominant species, showing a significant difference from water-only adsorption on the stoichiometric surface in which the [OH-H₂O] species is found to be prevalent. Surface reactivity at almost full O coverage is also addressed; there we show that site selectivity of the surface for H adsorption and dissociation of H₂O is hindered, notwithstanding the increase of the dynamic motion of both species. We found that the work function of RuO₂ can serve as a descriptor for the reactivity of this surface to water and its constituents.