Influence of Ag Clusters on the Electronic Structures of β-Ga₂O₃ Photocatalyst Surfaces

In order to understand the photocatalytic carbon dioxide reduction over Ag-loaded β-Ga₂O₃ photocatalysts, first principles calculations based on density functional theory were performed on the surface model of a Ag cluster-adsorbed β-Ga₂O₃ system. The stable adsorption structures of Ag (n = 1 to 4) clusters on the β-Ga₂O₃ (100) surface were determined. In the electronic structure analysis, the valence states of all Ag clusters mixed with the top of the O 2p valence band of Ga₂O₃, leading the Fermi level of Ag /β-Ga₂O₃ to shift to the bottom of the conduction band. It was also revealed that the unoccupied states of Ag clusters overlapped with the Ga unoccupied states, and occupied electronic states of Ag clusters were formed in the band gap. These calculation results corresponded to the experimental ones obtained in our previous study, i.e., small Ag clusters had strong interaction with the Ga₂O₃ surface, enhancing the electron transfer between the Ag clusters and the Ga₂O₃ surface. That is, excited electrons toward Ag clusters or the perimeter of Ag-Ga₂O₃ should be the important key to promote photocatalytic CO₂ reduction.