Theoretical Model of Oxidative Adsorption of Water on a Highly Reduced Reconstructed Oxide Surface

Highly reduced surface reconstructions of BaTiO₃ (001) have been found to be composed of a TiO₂ surface covered with Ti adatoms occupying surface interstitial sites. We predict the reactivity of these highly oxophilic and reduced surface Ti species through density functional theory, where we calculate the adsorption of H₂O on the (√5 × √5)R26.6° TiO₂–Ti_3/5 reconstruction. H₂O serves as the primary O source and oxidizing agent. We demonstrate that H₂O oxidizes some of the Ti adatoms, shifting their occupied 3d states to the surface conduction band edge. We find that, due to the high concentration of reduced Ti species on the surface, a dissociative adsorption of water on the reconstructed surface can also lead to the formation of surface hydrides, which serve as a precursor for H₂ evolution. This suggests that the reconstructed surface may be an attractive single-phase hydrogen evolution catalyst.