Evaluating the promotional effects of WO3 underlayers in BiVO4 water splitting photoanodes

Monoclinic-phase BiVO4 is one of the most promising photoanode materials for solar water splitting. Besides commonly applied strategies of morphology control, dopant/defect engineering, and electrocatalyst deposition, the introduction of WO3 underlayers has afforded desirable performance improvements in BiVO4 photoanodes. However, the fundamental issue regarding how the material properties of WO3 underlayers affect the photoelectrochemical behaviors of BiVO4 photoanodes is not clearly understood so far. Herein, crystallinity- and thickness-varied WO3 underlayers are established to analyze their contributions to the performance of BiVO4 photoanodes. The results show that surface defects, electron transferring capabilities of WO3 underlayers, and the coverage ratios of conducting substrates by them are key parameters to consider for the construction of efficient BiVO4 photoanodes. This study presents a deeper understanding on the functions and promotional effects of WO3 underlayers for BiVO4 photoanodes, and will also provide valuable guidelines for the design and optimization of other photoelectrodes toward efficient solar energy conversion.