Solar Oxidative Hydrogen Peroxide Production: Is the Oxygen Vacancy Always a Promoter in Solar Water Oxidation?

Photoelectrochemical (PEC) water oxidation to hydrogen peroxide (H₂O₂) is an alternative route to the conventional anthraquinone process, but it is still restricted by the prevailing competitive oxygen evolution reaction (OER). Here, we reveal that intrinsic oxygen vacancies (OVs) of BiVO₄ photoanodes are detrimental to PEC water oxidation to H₂O₂. The superabundant OVs of the BiVO₄ photoanode are passivated by a thermal treatment in a pressurized O₂ atmosphere by a Parr reactor. The passivated BiVO₄ photoanode with the least OV concentration achieves ca. two times H₂O₂ selectivity enhancement than the BiVO₄ photoanode with introduced OVs, resulting from the weakened band bending, the positively shifted quasi-Fermi level, and the suppressed decomposition of as-formed H₂O₂. In particular, the photoexcited electrochemical impedance spectra demonstrate a hole distribution rearrangement of the OVs-passivated BiVO₄, which eliminates the OER-related surface states and steers the water oxidation reaction pathway toward H₂O₂ formation. This work reveals the importance of interfacial energetics induced by regulating intrinsic OVs in selective PEC water oxidation.