Enhancing Interfacial Charge Transfer in a WO3/BiVO4 Photoanode Heterojunction through Gallium and Tungsten Co-Doping and a Sulfur Modified Bi2O3 Interfacial Layer

Photoanodes containing a WO₃/BiVO₄heterojunction have demonstrated promising photoelectrochemical water splitting performance, but the ability to effectively passivate the WO₃/BiVO₄interface has limited charge transport and collection. Here, the WO₃/BiVO₄interface is passivated with a sulfur-modified Bi₂O₃interfacial layer with a staggered band edge alignment to facilitate charge transfer and lifetime. Additionally, BiVO₄was co-doped with Ga³⁺at Bi³⁺sites and W⁶⁺at V⁵⁺sites (i.e., (Ga,W):BiVO₄) to improve the light absorption and photogenerated charge carrier concentration. The optimized WO₃/S:Bi₂O₃/(Ga,W):BiVO₄photoanode exhibited a photocurrent density of 4.0 ± 0.2 mA cm⁻²compared to WO₃/(Ga,W):BiVO₄with 2.8 ± 0.12 mA cm⁻²at 1.23 V_RHEin K₂HPO₄under simulated AM 1.5G illumination. Time-resolved photoluminescence spectroscopic analysis of the WO₃/S:Bi₂O₃/(Ga,W):BiVO₄electrode validated the enhanced interfacial charge transfer kinetics. Inoperandofemto- and nano-second transient absorption spectroscopy confirmed the presence of long-lived photogenerated charge carriers and revealed lower recombination initially due to rapid charge separation of WO₃/S:Bi₂O₃/(Ga,W):BiVO₄. The distribution and role of sulfur was further investigated using EDAX, XPS and TOF-SIMS depth profiling. Finally, a Co-Pi co-catalyst layer was added to achieve a photocurrent of 5.1 ± 0.25 mA cm⁻²and corresponding H₂generation rate of 67.3 μmol h⁻¹cm⁻²for the WO₃/S:Bi₂O₃/(Ga,W):BiVO₄/Co-Pi photoanode.