(645f) Water Dissociation, Diffusion, and Clustering on RuO2(110)

This work describes the binding, diffusion, and acid/base equilibrium of water molecules bound on RuO₂(110). RuO₂ acts as a co-catalyst in photocatalytic water splitting. Its unique redox properties also make it efficient for catalyzing CO oxidation, dehydrogenation of HCl, NH₃, and methanol. Additionally, RuO₂ is industrially used in electrocatalysis as a component of stable anodes to produce Cl₂ and NaOH. Density functional theory calculations and ab initio molecular dynamics simulations were performed, in collaboration with variable temperature scanning tunneling microscopy experiments, to find the detailed mechanistic behavior of water on RuO₂(110). Water monomers adsorb on Ru-sites, diffuse at low temperatures, and combine to form water dimers. We find that dimers deprotonate readily to form Ru-bound H₃O₂ and bridging OH species. Transition states and energy barriers for deprotonation and diffusion events of water monomers and dimers were identified. Calculated diffusion rates agree with experimentally measured ones. Further, H₃O₂ species serve as building blocks to form larger water clusters, and a full water monolayer is comprised of contiguous H₃O₂ species. The observed behavior is compared and contrasted with that observed for water on isostructural rutile TiO₂(110).