Type-II BiVO4/Ni3(hexahydroxytriphenylene)2 heterojunction photoanodes for effective photoelectrochemical reaction

Abstract

Semiconducting M₃(hexahydroxytriphenylene)₂ (M = Ni, Co, Cu; hexahydroxytriphenylene (HHTP)) was uniformly coated onto BiVO₄ thin films via a facile solvothermal process, and the photoelectrochemical performance of the BiVO₄/M₃(HHTP)₂ photoanodes was investigated. All three BiVO₄/M₃(HHTP)₂ photoanodes exhibited higher photocurrent densities than pristine BiVO₄. This can be attributed to the formation of type-II heterojunctions, as confirmed by ultraviolet photoelectron spectroscopy (UPS) and ultraviolet-visible spectroscopy. BiVO₄/Ni₃(HHTP)₂ exhibited the highest photocurrent density of 4.66 mA cm⁻² at 1.23 V vs. a reversible hydrogen electrode (RHE), an approximately 3.2-fold increase from that of pristine BiVO₄. The results suggest that the type of metal ion in M₃(HHTP)₂ affects the electrical conductivity, which significantly influences the charge transport kinetics in the photoelectrochemical reactions of BiVO₄. The mechanism underlying the enhanced photoelectrochemical reaction was also investigated.