Enhancing interfacial charge transfer in a WO3/BiVO4 photoanode heterojunction through gallium and tungsten co-doping and a sulfur modified Bi2O3 interfacial layer

Abstract

Photoanodes containing a WO₃/BiVO₄ heterojunction have demonstrated promising photoelectrochemical water splitting performance, but the ability to effectively passivate the WO₃/BiVO₄ interface has limited charge transport and collection. Here, the WO₃/BiVO₄ interface is passivated with a sulfur-modified Bi₂O₃ interfacial layer with a staggered band edge alignment to facilitate charge transfer and lifetime. Additionally, BiVO₄ was 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):BiVO₄ photoanode exhibited a photocurrent density of 4.0 ± 0.2 mA cm⁻² compared to WO₃/(Ga,W):BiVO₄ with 2.8 ± 0.12 mA cm⁻² at 1.23 V_RHE in K₂HPO₄ under simulated AM 1.5G illumination. Time-resolved photoluminescence spectroscopic analysis of the WO₃/S:Bi₂O₃/(Ga,W):BiVO₄ electrode validated the enhanced interfacial charge transfer kinetics. In operando femto- 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⁻² and corresponding H₂ generation rate of 67.3 μmol h⁻¹ cm⁻² for the WO₃/S:Bi₂O₃/(Ga,W):BiVO₄/Co-Pi photoanode.