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

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.