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

Abstract

The (Ga_1−xZn_x)N_1−xO_x 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. H₂ and O₂ production occur simultaneously and stoichiometrically on the surface of (Ga_1−xZn_x)N_1−xO_x particles. In this work, we characterize the redox ability of (Ga_1−xZn_x)N_1−xO_x 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 (Ga_1−xZn_x)N_1−xO_x is achieved at x = 0.13. The thermal reactions of water splitting are modeled on both the GaN and an idealized (Ga_1−xZn_x)N_1−xO_x (100) 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 (100) and polar (0001) surfaces may play different roles in water splitting, i.e., the (100) surface is responsible for O₂ production, while hydroxyl groups could dissociate on the (0001) surface.