Template-engineered epitaxial BiVO₄ photoanodes for efficient solar water splitting

Bismuth vanadate (BiVO₄) has attracted significant attention as a promising photoanode material for hydrogen production via photoelectrochemical (PEC) water splitting because of its narrow optical band gap and suitable band edge positions for water oxidation. However, the actual photoactivity of BiVO₄ is considerably limited by its poor electron transport and slow water oxidation kinetics. Although several studies have been carried out to improve its photo-efficiency via the enhancement of electron transport and water oxidation kinetics, only a few studies have reported the growth of epitaxial BiVO₄ to explore the fundamental properties of BiVO₄ for PEC water splitting because extremely flat epitaxial films exhibit poor photo-efficiency because of their low surface-active area. However, studies of epitaxial BiVO₄ still have the potential to provide new routes for improving its photo-efficiency. In this study, the growth of epitaxial BiVO₄ is investigated using a thin γ-WO₃ template layer deposited on a SrTiO₃(001) substrate covered by a SrRuO₃ (SRO) bottom electrode using pulsed laser deposition. Consequently, at 1.23 V vs. the RHE (reversible hydrogen electrode), the photocurrent density of epitaxial BiVO₄ on the γ-WO₃ template layer (2.20 mA cm⁻²) is approximately 10 times that of bare BiVO₄, related to the effective charge transfer by the γ-WO₃ intermediate layers and the subsequent increase in the surface-active area of epitaxial BiVO₄. These results strongly suggest that epitaxial BiVO₄ grown using a template layer can be a cornerstone for the in-depth understanding of the fundamental properties of BiVO₄ for PEC water splitting.