Enhanced charge separation in copper incorporated BiVO4 with gradient doping concentration profile for photoelectrochemical water splitting

•BiVO4:Cu with gradient doping profile was synthesized by depositing an underlayer and followed with annealing.•BiVO4:Cu with gradient doping profile showed enhanced PEC water splitting compared to undoped BiVO4.•Significant different behaviors between gradient doping and homogeneously doping in BiVO4:Cu were demonstrated.

BiVO4 is one of promising materials that are stable, abundant, non-toxic and inexpensive for hydrogen production by water splitting. High recombination rate inside BiVO4 was reported as a limiting factor for photoelectrochemical (PEC) performance of BiVO4 photoanode. In this work, Cu incorporated BiVO4 with gradient doping concentration profile was synthesized by depositing a CuO layer between BiVO4 and FTO followed with annealing. Cu-doped BiVO4 films with homogeneous concentration profile were prepared as a counter part to show the different behaviors between the gradient doping and homogeneously doping on charge transport and separation. It is found that the PEC performance of BiVO4 electrode is significantly improved by gradient doping concentration profile in BiVO4 layer, especially at the high applied bias range. While homogeneously doped BiVO4 showed a decreased PEC performance as Cu element acts as a recombination center. Mott–Schottky test showed that the flat band level of CuO-BiVO4 shifts negative slightly, which is beneficial for hydrogen production. While a positive shift is observed for homogeneously Cu-doped BiVO4 which could be a result from the recombination centre nature of Cu in BiVO4. This work provide an efficient and inexpensive means to reduce charge recombination in BiVO4 and improve its of solar water splitting efficiency.