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 TiO 2 photoanode is a promising strategy for clean energy generation. The BiVO 4 decorated N-Doped TiO 2 nanotubes (BiVO 4 /TiO 2 –N) were synthesized by the anodization and hydrothermal procedure. The physical and chemical characterization indicates that the BiVO 4 nanoparticles are successfully decorated on the surface of the TiO 2 –N nanotubes (∼600 nm) to form the heterojunction structure. After the nitrogen doping and BiVO 4 modification of TiO 2, 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 BiVO 4 modification have little effect on TiO 2 crystallization. The optimal photocurrent density of BiVO 4 /TiO 2 –N reached 1.02 mA/cm 2 at 1.23 V RHE, which is about 1.76-fold more than that of the TiO 2 photoanodes. The mechanism studies for BiVO 4 /TiO 2 –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 BiVO 4 with the TiO 2 photoanode. The mechanism for the BiVO 4 /TiO 2 –N photoanode during the PEC water splitting process is proposed for further understanding and designation.