Anatomy of a Visible Light Activated Photocatalyst for Water Splitting

The supported mixed oxide (Rh 2– y Cr y O 3 )/(Ga 1– x Zn x )(N 1– x O x ) photocatalyst, highly active for splitting of H 2 O, 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 (Ga 1– x Zn x )(N 1– x O x ) support are not perturbed by the deposition of the (Rh 2– y Cr y O 3 ) NPs. Photoluminescence (PL) spectroscopy, however, showed that the oxynitride (Ga 1– x Zn x )(N 1– x O x ) support is the source of excited electrons/holes and the (Rh 2– y Cr y O 3 ) 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 (Rh 2– y Cr y O 3 ) NPs consist of Rh 3+ and Cr 3+ mixed oxide species. In situ AP-XPS help to reveal that the Rh 3+ and surface N atoms are involved in water splitting. Dispersed RhO x species on the (Ga 1– x Zn x )(N 1– x O x ) support and on CrO x NPs were found to be the photocatalytic active sites for H 2 generation and N and Zn sites from the (Ga 1– x Zn x )(N 1– x O x ) 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.