Effect of Hydrogen and Oxygen Evolution Cocatalysts on Photocatalytic Activity of GaN:ZnO

The coloading effect of H-2 and O-2 evolution cocatalysts on the overall water splitting reaction was investigated using a solid solution of GaN and ZnO (hereafter termed GaN: ZnO) as a photocatalyst. GaN: ZnO was modified with nanoparticulate Mn3O4, RuO2, and IrO2 as O-2 evolution cocatalysts and with core/shell-type Rh/Cr2O3 composites as H-2 evolution cocatalysts. The photocatalytic activity of the coloaded samples for overall water splitting was higher than that of the samples modified with either of the O-2 or H-2 evolution cocatalysts alone. The activity enhancement induced by coloading was comparable for the three O-2 evolution cocatalysts investigated at the optimized loading amounts. Loading of a more efficient Rh/Cr2O3 cocatalyst prepared by adsorption of Rh nanoparticles further improved the photocatalytic activity. It was concluded that a simultaneous improvement in both oxidation and reduction reactions was effective at enhancing the photocatalytic activity of GaN:ZnO, whereas the reduction reactions limited the overall reaction rate of the coloaded system more significantly.