Facet effect on the photoelectrochemical performance of a WO3/BiVO4 heterojunction photoanode

Abstract Different WO 3 facets have different surface energies and electronic structures, and exhibit different water oxidation abilities and photocatalytic performance as a result. Because of the material’s limited photoresponse region, loading a narrow bandgap material on WO 3 is a generally known method for improving photo-harvesting. In this paper, we have synthesized WO 3 films with different crystal facet ratios. After loading BiVO 4 on these WO 3 films, we measured the photoelectrochemical (PEC) performance to investigate the effects of WO 3 facet choice on the heterojunction film electrode’s performance. We found that a high-intensity ratio of the (002) WO 3 facet in X-ray diffraction (XRD) leads to a more negative onset potential and higher photocurrents in a lower potential region. The ultraviolet photoelectron spectra show a lower work function for the 002-dominant WO 3 film compared to other WO 3 films, which may result in a higher quasi-fermi level for the heterojunction electrode. Based on the XRD results, the high-intensity ratio of the (002) WO 3 facet preferentially exposes the (020) BiVO 4 facet, which may be a reason for the better charge extraction observed at low applied potential and high faradic efficiency on PEC water splitting. Together, this results in a high hole injection efficiency for 002-dominant WO 3 /BiVO 4 films compared with WO 3 /BiVO 4 films favoring other WO 3 facet ratios.