Dual active sites over TiO2 homojunction through tungsten doping and oxygen vacancies for enhanced photoelectrochemical properties

The introduction of dual active sites is a feasible strategy to enhance the photoelectrochemical (PEC) water splitting, but rational design based on structural construction and chemical composition is still a challenge. Herein, a homojunction composed of tungsten (W) doped titanium dioxide (TiO2) nanorods and oxygen vacancies modified TiO2 nanosheets is prepared via solid-state diffusion-hydrothermal method to improve the PEC activities. The TiO2 homojunction with dual active sites shows a 136 times enhancement in photocurrent density over the pristine TiO2 nanorods. PEC investigation reveals that the element W doped into the lattice of TiO2 causes the downshift of conduction band, and the formed defects state acting as the trapping sites could reduce photoinduced electron-hole pairs recombination rates. Moreover, the addition of polyvinylpyrrolidone leads to the generation of oxygen vacancies within TiO2 nanosheets, which facilitates the carrier transfer, and meanwhile suppresses the charge recombination. In addition, the type-II homojunction within the hierarchical nanostructure could not only advance the separation of photogenerated electron-hole pairs, but also provide more exposed active sites due to the enhanced specific surface area. The synergistic effect of doping, oxygen vacancies and homojunctions endows the considerably improved PEC performance.