Structure and Electronic Properties of Small Silver-Gold Clusters on Titania Photocatalysts for H2O2 Production: An Investigation with Density Functional Theory

Ag4-n-Au-n (n = 1-3) clusters deposited on the surface of TiO2(101) are more efficient than titania as photocatalysts. The mechanisms of this enhancement are, however, unclear. In this study, density functional theory was applied with the Hubbard correction to investigate the atomic and electronic structure of Ag4-n-Au-n (n = 1-3)@TiO2(101). The band gap of TiO2 in the presence of Ag3Au, Ag2Au2, and AgAu3 decreased to 1.00, 1.24, and 1.40 eV, respectively. The band edges of all systems satisfy the requirement for H2O2 production. H2O2 adsorption energies and O-O bond lengths have shown that A(g)3Au@TiO2(101) and Ag(2)Au(2)pTiO(2)(101) systems are good candidates for H2O2 production without poisoning of the catalyst surface and H2O2 dissociation. The results show that Ag3Au and Ag2Au2 can produce midgap states at the top of the valence band from the direct Au-Ti bonds. The midgap state in Ag2Au2@TiO2(101) has a suitable position for H2O2 formation, thereby boosting the photoresponse of the system in visible and infrared light by improving the charge separation.