Deprotonated Water Dimers: The Building Blocks of Segmented Water Chains on Rutile RuO₂(110)

Despite the importance of RuO₂ in photocatalytic water splitting and catalysis in general, the interactions of water with even its most stable (110) surface are not well understood. In this study we employ a combination of high-resolution scanning tunneling microscopy imaging with density functional theory based ab initio molecular dynamics, and we follow the formation and binding of linear water clusters on coordinatively unsaturated ruthenium rows. We find that clusters of all sizes (dimers, trimers, tetramers, extended chains) are stabilized by donating one proton per every two water molecules to the surface bridge bonded oxygen sites, in contrast with water monomers that do not show a significant propensity for dissociation. The clusters with odd number of water molecules are less stable than the clusters with even number and are generally not observed under thermal equilibrium. For all clusters with even numbers, the dissociated dimers represent the fundamental building blocks with strong intradimer hydrogen bonds and only very weak interdimer interactions resulting in segmented water chains.