Enhanced Charge Separation and Transfer by BiVO4 Heterojunction and N-Doped for TiO2 Nanotubes during Photoelectrochemical Water Splitting

Photoelectrochemical water splitting for hydrogen and oxygen evolution by a TiO2 photoanode is a promising strategy for clean energy generation. The BiVO4 decorated N-Doped TiO2 nanotubes (BiVO4/TiO2–N) were synthesized by the anodization and hydrothermal procedure. The physical and chemical characterization indicates that the BiVO4 nanoparticles are successfully decorated on the surface of the TiO2–N nanotubes (∼600 nm) to form the heterojunction structure. After the nitrogen doping and BiVO4 modification of TiO2, the UV–visible light absorption ability is broadened, the band gap energy shifts from 3.2 to around 2.82 eV, and the injection and separation efficiency of charge carriers is increased. Nitrogen doping and BiVO4 modification have little effect on TiO2 crystallization. The optimal photocurrent density of BiVO4/TiO2–N reached 1.02 mA/cm2 at 1.23 VRHE, which is about 1.76-fold more than that of the TiO2 photoanodes. The mechanism studies for BiVO4/TiO2–N indicate that the key factors for boosting PEC performance are the light absorption and the charge separation enhancement by the N-doping and the n–n heterojunction by BiVO4 with the TiO2 photoanode. The mechanism for the BiVO4/TiO2–N photoanode during the PEC water splitting process is proposed for further understanding and designation.