Changes in Surface Oxygen Vacancy Formation Energy at Metal/Oxide Perimeter Sites: A Systematic Study on Metal Nanoparticles Deposited on an In2O3(111) Support

Metal/oxide support perimeter sites can provide unique properties because the local environment on the support surface is changed by the nearby metal. This study modeled perimeter sites when metal nanorods were adsorbed in lieu of nanoparticles on the (111) surface of an In2O3 support. The metal element M was one of Ag, Au, Cu, Ir, Pd, Pt, and Re. Changes in the surface oxygen vacancy formation energy (EOvac) with nanorod adsorption were evaluated using systematic first-principles calculations under the same approximations and conditions and were found to be driven by two major factors. First, if the Fermi energy of the metal is deeper than the defect energy level of surface O vacancies, the metal may act as an electron scavenger to accept excess electrons upon O removal from sites close to the metal. The minimum EOvac for each M correlated very well with the Bader charge transfer to the nanorod upon O removal. The effect of geometrical relaxation of the nanorod after O removal was not found because there was barely any spontaneous rearrangement of nanorod atoms after O removal. As a consequence, the minimum EOvac in a surface tends to decrease with the increasing work function of M. Second, among different O sites on the same surface, EOvac is lower in O sites when there are interface states with the adsorbed metal at energy levels higher than the valence band of the support. These insights would help in planning strategies to obtain active O sites.