Photocatalytic activity of (Ga1-xZnx)(N1-xOx) for visible-light-driven H2 and O2 evolution in the presence of sacrificial reagents

photocatalytic activity of (Ga1-xZnx)(N1-xOx), a solid solution of GaN and ZnO, for H-2 and O-2 evolution in the presence of methanol and silver nitrate as sacrificial reagents under visible light (lambda > 420 nm) is investigated in detail. (Ga1-xZnx)(N1-xOx) evolves H-2 from an aqueous methanol solution when loaded with nanoparticulate Rh2-yCryO3 as a cocatalyst, and evolves O-2 from an aqueous silver nitrate solution without a cocatalyst. Structural analyses indicate that the H-2 evolution activity is strongly dependent on the crystallinity and composition of the catalyst, while the rate of O-2 evolution is proportionally related to the specific surface area. The activity for H-2 evolution from methanol solution is of the same order as for overall water splitting, but is an order of magnitude lower than that for O-2 evolution from silver nitrate solution. The results of photocatalytic reactions and photoelectrochemical measurements suggest that the rate-determining step for overall water splitting using (Ga1-xZnx)(N1-xOx) is the H-2 evolution process.