Effect of Phase Junction Structure on the Photocatalytic Performance in Overall Water Splitting: Ga2O3 Photocatalyst as an Example

The fabrication of surface phase junctions has proven to be an efficient strategy for the enhancement of photocatalytic activity; however, some questions about these systems are not yet well understood. In this study, the photocatalytic overall water splitting reaction was achieved on photocatalysts with pure and mixed phase compositions of cubic gamma-Ga2O3 and monoclinic beta-Ga2O3. All the Ga2O3 photocatalysts can split water stoichiometrically into H-2 and O-2; however, the phase-mixed gamma/beta-Ga2O3 photocatalyst with a small amount of beta phase shows the lowest activity. This is opposite from that of the reported alpha/beta-Ga2O3 system in which the phase-mixed alpha/beta-Ga2O3 photocatalyst with a small amount of beta phase shows much higher photocatalytic activity than the individual phases. Much more disordered structure is found between the gamma and beta phases in the gamma/beta-Ga2O3 photocatalyst with low content of beta phase due to the defective spinel structure of gamma phase. Spectroscopic characterization and theoretical calculations indicate that the disordered structure serves as defect and charge recombination centers resulting in the decrease of photocatalytic activity. Based on the analysis of alpha/beta-Ga2O3 and gamma/beta-Ga2O3 systems, it is proposed that a prerequisite for the formation of phase junction boosting photocatalytic reactions is that the interfacial structure between two phases should not be disordered or defective.