Growth of BiVO4 nanoparticles on a WO3 porous scaffold: improved water-splitting by high band-edge light harvesting

Abstract

The BiVO₄/WO₃ heterojunction is the ideal photoanode for highly efficient solar water splitting. Despite much effort, the low light absorption efficiency near the BiVO₄ band gap wavelength is still a major cause of loss of water-splitting efficiency. To address this issue, we introduce a BiVO₄/WO₃ photoanode in which BiVO₄ single crystal nanoparticles (NPs) are decorated. In particular, we present a limited growth method in confined geometry to synthesize BiVO₄ NPs. These BiVO₄ NPs enhance Rayleigh-type light scattering, especially at the absorption edge wavelengths, resulting in increased light absorption efficiency (η_abs) at the corresponding wavelengths; the BiVO₄ NPs dramatically improved the η_abs up to 60% at 500 nm, which is more than twice as high as the η_abs values obtained for previously reported BiVO₄ photoanodes. In addition, BiVO₄ NPs exhibit high charge separation efficiency, especially at low bias potentials. This result indicates effective charge transport in the NP morphology. As a result, the BiVO₄ NP-coated WO₃ photoanode achieves a remarkably high water splitting photocurrent of 5.8 ± 0.18 mA cm⁻². This is the highest water-splitting photocurrent among those previously reported for BiVO₄-based photoanodes.