Photocatalytic Activity of (Ga₁₋xZnx)(N₁₋xOx) for Visible-Light-Driven H₂ and O₂ Evolution in the Presence of Sacrificial Reagents

The photocatalytic activity of (Ga 1- x Zn x )(N 1- x O x ), 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 (λ > 420 nm) is investigated in detail. (Ga 1- x Zn x )(N 1- x O x ) evolves H 2 from an aqueous methanol solution when loaded with nanoparticulate Rh 2- y Cr y O 3 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 (Ga 1- x Zn x )(N 1- x O x ) is the H 2 evolution process.