Oxygen vacancies at oxide surfaces: ab initio density functional theory studies on vanadium pentoxide

The local electronic structure at the V2O5(010) surface is studied by ab in itio density functional theory (DFT) methods using gradient-corrected funct ionals (RPBE) where embedded clusters as large as V20O62H24, representing o ne or two crystal layers of the substrate, are used as models. Results of l ocal binding and charging of differently coordinated surface-oxygen sites a s well as densities of states allow a characterization of the detailed elec tronic structure of the surface. Electronic and geometric details of surfac e-oxygen vacancies as well as hydrogen adsorption are studied by appropriat e clusters. A comparison of the data, concerning vacancy energies, charging , geometric relaxation, and diffusion, shows sizeable variations between di fferent oxygen sites and can give further insight into possible mechanisms of surface relaxation and reconstruction. Hydrogen is found to stabilize at all surface-oxygen sites forming surface-OH and H2O species. As a result, the binding of surface oxygen with its vanadium neighbors is weakened. Ther efore, the presence of hydrogen at the oxide surface facilitates oxygen rem oval and can contribute to the enhanced yield of oxygenated products near v anadia-based surfaces.