Photoelectrochemical H2O2 Production over Defect-Modulated WO3 via WV-Involved Proton−Electron Transfer Relay

Abstract Tungsten oxide (WO3) is a promising photoanode material for photoelectrochemical (PEC) hydrogen peroxide (H2O2) evolution, but its performance is limited by inefficient bulk/surface charge transfer and defect-induced recombination. Here, a simple electrodeposition strategy with moderate placement has been developed to optimize bulk/surface defects in WO3 photoanodes. The WO3-1 sample (1-day placement) achieves superior PEC performance, exhibiting a 2.4 times higher photocurrent density than the original photoanode. It affords a 0.276 μmol min−1 cm−2 at 1.8 VRHE H2O2 production rate and high charge separation/injection efficiencies (ηsep = 87%, ηinj = 93%). Characterizations reveal that moderate placement passivates harmful surface oxygen vacancies (OV) while preserving beneficial bulk defects, suppressing carrier recombination, and facilitating surface reaction. Furthermore, a carbonate-mediated 2e− water oxidation reaction (WOR) mechanism involving pentavalent tungsten (WV) as an electron−proton transfer relay has been proposed. This work provides an effective defect-engineering approach to advance PEC H2O2 synthesis.