Photocatalytic activity for water decomposition of RuO2-dispersed Zn2GeO4 with d10 configuration

RaO2-dispersed Zn2GeO4 was found to become a stable photocatalyst for the overall splitting of water to produce H-2 and O-2. The photocatalytic properties were examined under various experimental conditions, and the band structure of Zn2GeO4 was revealed based on the DFT calculation. The photocatalytic activity depended on calcination temperatures of Zn2GeO4 and the amount of RuO2 loaded, and the combination of highly crystallized Zn2GeO4 with dispersed small RuO2 particles provided large photocatalytic activity. The GeO4 tertrahedron of Zn2GeO4 is so heavily distorted to generate a dipole moment inside, and the good photocatalytic performance of RuO2-dispersed Zn2GeO4 is in line with the view that the electron-hole separation upon photoexcitation is promoted by a local electric field due to dipole moment. The DFT calculation showed that the top of the valence band (HOMO) was composed of the O 2p orbital, whereas the bottom of conduction band (LUMO) was formed by the Ge 4p orbital with a small contribution of the Zn 4s4p orbitals. The conduction band had large dispersion, indicative of large mobility of photoexcited electrons. The correlation of photoc.atalytic activity with geometric and electronic structures of Zn2GeO4 is discussed.