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/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 VRHE 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.