Effect of electrolyte addition on activity of (Ga1−xZnx)(N1−xOx) photocatalyst for overall water splitting under visible light

Effects of electrolyte addition on photocatalytic activity of (Ga1−xZnx)(N1−xOx) modified with either Rh2−yCryO3 or RuO2 nanoparticles as cocatalysts for overall water splitting under visible light (λ > 400 nm) are investigated. The cocatalyst Rh2−yCryO3 is confirmed to selectively promote the photoreduction of H+, while RuO2 functions as both H2 evolution sites and as efficient O2 evolution sites. The activity of Rh2−yCryO3-loaded (Ga1−xZnx)(N1−xOx) is found to be suppressed in the presence of Cl−, which undergoes oxidation by photogenerated holes in the valence band of (Ga1−xZnx)(N1−xOx). Alkaline- and alkaline earth-metal cations in the reactant solution compensate the negative effect of Cl− to a certain extent depending on the metal cation employed. Among the electrolytes examined, the addition of an appropriate amount of NaCl or A2SO4 (A = Li, Na, or K) to the reactant solution without pH control is found to increase activity by up to 75% compared to the case without additives. Direct splitting of seawater to produce H2 and O2 is also demonstrated using Rh2−yCryO3-loaded (Ga1−xZnx)(N1−xOx) catalyst under visible light.