Enhanced photoelectrochemical performance of cobalt phosphate modified GaN-ZnO Nanowires/GaN microrods heterostructure photoanode by vacancy defect modulation

Gallium-zinc oxynitride solid solution has been considered as a promising candidate material for photoelectrochemical (PEC) water splitting. However, its PEC performance is severely limited by the poor charge separation efficiency and the adverse intrinsic vacancy defects. Herein, to solve these problems, we developed a novel strategy for constructing dendritic (GaN)1-x(ZnO)x/GaN arrays with type-Ⅱ heterojunction on a conductive GaN crystalline substrate by an Au-assisted chemical vapor deposition method. Then, an additional annealing treatment in Ar is carried out to further decrease the density of surface oxygen vacancy and to increase the density of ON-VGa vacancy complexes for enhancing photoelectrochemical performance. Under the synergistic effect of type-Ⅱ heterojunction and vacancy modulation, the optimized (GaN)1-x(ZnO)x/GaN photoanode exhibits a photocurrent density of 0.25 mA cm−2 at 1.23 V vs. RHE and the surface modification with CoPi co-catalyst can further increase the photocurrent density to 0.45 mA cm−2 at 1.23 V vs. RHE. It is demonstrated that the ON-VGa vacancy complexes are beneficial to increase the PEC performance of gallium zinc oxynitrides.