Photocatalytic Activity for Water Decomposition of RuO₂-Dispersed Zn₂GeO₄ with d¹⁰ Configuration

RuO 2 -dispersed Zn 2 GeO 4 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 Zn 2 GeO 4 was revealed based on the DFT calculation. The photocatalytic activity depended on calcination temperatures of Zn 2 GeO 4 and the amount of RuO 2 loaded, and the combination of highly crystallized Zn 2 GeO 4 with dispersed small RuO 2 particles provided large photocatalytic activity. The GeO 4 tertrahedron of Zn 2 GeO 4 is so heavily distorted to generate a dipole moment inside, and the good photocatalytic performance of RuO 2 -dispersed Zn 2 GeO 4 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 photocatalytic activity with geometric and electronic structures of Zn 2 GeO 4 is discussed.