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We have investigated electronic structures and charge transfers of Ag and Au supported on the TiO 2 (110) surface, using first-principles calculation. In order to investigate the effect of stoichiometry on the electronic structures, we examined Au and Ag adsorption on three kinds of TiO 2 (110) surface with different stoichiometry; the perfect stoichiometric surface, Ti-rich surface, and O-rich surface. We considered the on-top site above the bridging-oxygen atom (site A) and above the five-fold titanium atom (site B) for the perfect stoichiometric surface, the bridgingoxygen vacant site (site C) for the Ti-rich surface, and the six-fold titanium vacant site (site D) for the O-rich surface as the adsorption site. The adhesive energies between the metal layer and the TiO 2 (110) surface for the non-stoichiometric surfaces are much larger than that for the stoichiometric surface. And the Ag atom strongly interacts with the surface oxygen atoms at surface, while the Au atom strongly interacts with the surface titanium atoms at surface. The interaction between the metal and the TiO 2 (110) surface depends on the surface stoichiometry and the kind of metal species.

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The usage of Au nano-particles as a catalytic electrode may be effective for the CO-poisoning problem in the anode of a proton-exchange membrane fuel cell (PEMFC), because Au nano-particles supported on metal oxides have novel catalytic activity of low-temperature CO oxidation or water gas-shift reaction. As the first step to examine this possibility, we have performed first-principles calculations of a Au 10 cluster on graphene as well as a Pt 10 cluster on graphene, based on the density functional theory (DFT). There are no strong interactions between the cluster and graphene such as substantial charge transfer or orbital hybridization, although the interaction for Pt is stronger than that for Au. We have further examined the H-atom adsorption on the clusters on graphene, and found that the adsorption energy is much larger for the Pt cluster than for the Au cluster. However, we have observed that the energy gain in the dissociation and adsorption from a H 2 molecule is indeed obtained for the Au small cluster in spite of no energy gain for the Au(111) surface.