Combined Analyses on Electronic Structure and Molecular Orbitals of d 10 Bimetal Oxide In 2 Ge 2 O 7 and Photocatalytic Performances for Overall Water Splitting and CO 2 Reduction.

Semiconducting photocatalytic overall water splitting and CO 2 reduction are possible solutions to the emerging worldwide challenges of oil shortage and continual temperature increase, and the key is to develop an efficient photocatalyst. Most photocatalysts contain the d 0 , d 10 or d 10 ns 2 metals, and a guiding principle is desired to help to distinguish outstanding semiconductors. Here, the d 10 bimetal oxide In 2 Ge 2 O 7 was selected as the target. First, density functional theory (DFT) calculations point out that the nonbonding O 2p orbitals dominate the valence band maximum (VBM), and In 5s-O 2s and Ge 4s-O 2s antibonding orbitals are the major components of conduction band minimum (CBM). Moreover, the molecular orbitals were analyzed to consolidate the DFT calculations and make it more understandable for chemists. Due to the very small specific surface area (0.51 m 2 /g) and wide band gap (4.14 eV), as-prepared In 2 Ge 2 O 7 did not exhibit any overall water splitting activity; nevertheless, when loading with 1 wt% cocatalyst (i.e., Pt, Pd), the surficial charge recombination can be greatly eliminated and the overall water splitting activity is significantly improved to 33.0(4) and 17.2(7) μmol/h for H 2 and O 2 generation, respectively. The apparent quantum yield (AQY) at 254 nm is 8.28%. This observation is proof that the inherent electronic structure of In 2 Ge 2 O 7 is beneficial for the charge migration in bulk. Moreover, this catalyst also exhibits an observable CO 2 reduction activity in pure water, which is a competition reaction with water splitting, anyway, the CH 4 selectivity can be enhanced by loading Pd. This is a successful attempt to unravel the structure-property relationship by combining the analyses on electronic structure and molecular orbitals and is enlightening to further discover good candidates to photocatalysts.