Optimization of photogenerated charge transport using type-II heterojunction structure of CoP/BiVO4:WO3 for high efficient solar-driver water splitting

Abstract

Bismuth vanadate oxide (BiVO4) is one of the most efficient light-absorber metal oxides for the photoelectrochemical (PEC) water splitting; however, the fast charge recombination and poor kinetics for water oxidation have hindered full utilization of their theoretical performance. The optimization of the band alignment to facilitate charge transport and injection is of paramount importance to achieve the ideal water splitting performance of the photoelectrode. In this study, a type-II heterojunction CoP/BiVO4:WO3 structure has been fabricated for highly efficient PEC water splitting. The WO3 layer in the junction readily collects the photoelectrons harvested from the BiVO4 layer owing to its highly conducting nature, enabling efficient bulk charge transport from the BiVO4:WO3 junction to the fluorine-doped tin oxide (FTO) substrate. In addition, the cobalt phosphide (CoP) nanoparticles (NPs) play the role of the hole conducting layer from the light-absorber layer to the water as well as a catalyst to enhance surface charge injection efficiency at the photoelectrode surface. As a result, the CoP/BiVO4:WO3 photoanode reveals a remarkable photocurrent density of 2.81 mA cm−2 at 1.23 V (vs. RHE) with a negative shift of the onset potential (610 mV) compare to that of bare BiVO4. Moreover, the CoP/BiVO4:WO3 electrode shows a highly stable photocurrent density for at least 5 h.