ZnO-ZnGa2O4 core-shell nanowire array for stable photoelectrochemical water splitting

A dense array of vertically aligned ZnO-ZnGa2O4 core-shell nanowires was synthesized on a large scale on an a-plane sapphire substrate by a simple two-step chemical vapor deposition method. The ZnO cores and ZnGa2O4 shells of the nanowires are of single crystal quality and have aligned crystallographic orientations as evidenced from XRD and TEM analyses. Mott-Schottky analysis and voltage onset from the photocurrent-voltage curve confirm an n-type semiconductor property, a flatband potential of -0.4 V (versus NHE) and a carrier density of 7 x 10(18) cm(-3) for the ZnO-ZnGa2O4 core-shell nanowires. A stable and large photocurrent of 1.2 mA cm(-2) was obtained with the ZnO-ZnGa2O4 core-shell nanowire array when used as a photoanode at an applied bias of +0.7 V (versus Ag/AgCl) under a 300 W xenon lamp illumination. Moreover, a low dark current of <10(-4) mA cm(-2) was obtained at an applied bias of +0.7 V (versus Ag/AgCl) without light illumination for the ZnOZnGa2O4 nanowire array. These results suggest that the dense array of ZnO-ZnGa2O4 core-shell nanowires provides enhanced electronic properties and stable anti-photocorrosion ability and, therefore, is promising as a photoanode in photoelectrochemical water splitting.