Facile Synthesis of a Porous ZnO Nanorod Array with Enhanced Photocatalysis for Photoelectrochemical Water Splitting Application

Highly efficient and effective porous ZnO nanorod arrays were fabricated by annealing ZnO nanorod arrays grown on a substrate using a simple hydrothermal method. The annealing had a positive effect on the nanorod morphology, structure and optical properties. The porosity was closely related to the annealing temperature. After heating at 450 °C, pores appeared on the nanorods. It was demonstrated that the porosity could be exploited to improve the visible light absorption of ZnO and reduce the bandgap from 3.11 eV to 2.99 eV. A combination of improved charge separation and transport of the heat-treated ZnO thus led to an increase in the photoelectrochemical properties. At an irradiation intensity of 100 mW/cm⁻², the photocurrent density of the porous nanorod array was approximately 1.3 mA cm⁻² at 1.2 V versus Ag/AgCl, which was five times higher than that of the ZnO nanorods. These results revealed the synthesis of promising porous ZnO nanorods for photoelectrochemical applications.