First principles studies on the redox ability of (Ga1-xZnx)N1-xOx solid solutions and thermal reactions for H2 and O2 production on their surfaces

The (Ga1-xZnx)N1-xOx solid solution has been emerging as an effective photocatalyst for water splitting utilizing the visible solar spectrum, regarded as a host GaN bulk doped with ZnO impurities. H-2 and O-2 production occur simultaneously and stoichiometrically on the surface of (Ga1-xZnx)N1-xOx particles. In this work, we characterize the redox ability of (Ga1-xZnx)N1-xOx and find that a solid solution with a ZnO concentration of 0.125 < x < 0.250 is optimal for water splitting. This is consistent with the experimental finding that the maximum photocatalytic activity of (Ga1-xZnx)N1-xOx is achieved at x = 0.13. The thermal reactions of water splitting are modeled on both the GaN and an idealized (Ga1-xZnx)N1-xOx (10 (1) over bar0) surface. The computed activation barriers allow us to gain some clues on the efficiency of water splitting on a specific photocatalyst surface. Our results suggest that the non-polar (10 (1) over bar0) and polar (0001) surfaces may play different roles in water splitting, i.e., the (10 (1) over bar0) surface is responsible for O-2 production, while hydroxyl groups could dissociate on the (0001) surface.