Synchronous etching and W-doping for 3D CdS/ZnO/TiO2 hierarchical heterostructure photoelectrodes to significantly enhance the photoelectrochemical performance

Abstract Herein, the three-dimensional ZnO nanorod/TiO2 nanosheet films are constructed and optimized by synchronous etching and W-doping, which is demonstrated as an effective strategy to improve the photoelectrochemical performance of CdS/ZnO/TiO2 photoelectrodes. Notably, the ZnO nanorods preferentially grow on the {1 0 1} facet of TiO2 nanosheets, which can extend light scattering path-ways for light absorption, and effectively improve the electron transport due to the lower conduction band edge of {1 0 1} facet than that of highly exposed {0 0 1} facet for TiO2 nanosheets. Moreover, through the effects of synchronous etching and W-doping, the ZnO nanorods become ZnO nanotubes and the rough etched layers with W-doping are formed on the surface of ZnO/TiO2 films, which can improve the light absorption due to the enhanced light scattering, accelerate the photogenerated charges separation and transport owing to the introduction of W-doped energy level, and increase the electron density because of the different valences between W6+ and Zn2+. Benefiting by these superior properties, the CdS quantum-dots are densely and uniformly loaded on the surface of ZnO/TiO2 films, which can effectively improve the visible light absorption, heterojunction areas and charge injection efficiency. Therefore, the optimal photocurrent density (5.6 mA cm−2) of etched and W-doped CdS/ZnO/TiO2 photoelectrodes is remarkably enhanced.