Anatomy of a Visible Light Activated Photocatalyst for Water Splitting

The supported mixed oxide (Rh2-yCryO3)/(Ga1-xZnx)(N1-xOx) photocatalyst, highly active for splitting of H2O, was extensively characterized for its bulk and surface properties with the objective of developing fundamental structure-photoactivity relationships. Raman and UV-vis spectroscopy revealed that the molecular and electronic structures, respectively, of the oxynitride (Ga1-xZnx)(N1-xOx) support are not perturbed by the deposition of the (Rh2-yCryO3) NPs. Photoluminescence (PL) spectroscopy, however, showed that the oxynitride (Ga1-xZnx)(N1-xOx) support is the source of excited electrons/holes and the (Rh2-yCryO3) NPs greatly reduce the undesirable recombination of photoexcited electron/holes by acting as efficient electron traps as well as increase the lifetimes of the excitons. High Resolution-XPS and High Sensitivity-LEIS surface analyses reveal that the surfaces of the (Rh2-yCryO3) NPs consist of Rh3+ and Cr3+ mixed oxide species. In situ AP-XPS help to reveal that the Rh3+ and surface N atoms are involved in water splitting. Dispersed RhOx species on the (Ga1-xZnx)(N1-xOx) support and on CrOx NPs were found to be the photocatalytic active sites for H-2 generation and N and Zn sites from the (Ga1-xZnx)(N1-xOx) support are the photocatalytic active site for O-2 generation. The current investigation establishes the fundamental structure photoactivity relationships of these visible light activated photocatalysts.