Fabrication of an Efficient BiVO4–TiO2 Heterojunction Photoanode for Photoelectrochemical Water Oxidation

In this work, a simple planar BiVO4/TiO2 heterojunction photoanode was prepared on a fluorine-doped tin oxide (FTO) substrate for photoelectrochemical (PEC) water oxidation. The measurements of surface photovoltage, photocurrent transient behavior, and hole-scavenger-assisted PEC performance indicate that charge separation efficiency is improved compared to that of the BiVO4/FTO photoanode. This improvement is caused by the formation of the staggered BiVO4/TiO2 heterojunction. However, the photocurrent densities of the BiVO4/TiO2/FTO photoanode are higher than those of the BiVO4/FTO one only at potentials >1.2 V vs reversible hydrogen electrode, although the two BiVO4 layers with comparable light harvesting efficiencies were prepared by the same method. The hole-scavenger-assisted PEC measurements reveal that the hole injection efficiency of the BiVO4/TiO2/FTO photoanode is inferior to that of the bare BiVO4/FTO anode for oxygen evolution. It shows that the surface property of the BiVO4 layers is altered as they are deposited on different substrates. On the basis of these characterizations, the cocatalyst cobalt phosphate (Co-Pi) was further deposited on the surface of BiVO4/TiO2/FTO photoanode to improve the hole injection efficiency. Subsequently, the photocurrent density and stability of the Co-Pi/BiVO4/TiO2/FTO photoanode were significantly improved compared to those of the bare BiVO4/FTO photoanode.