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 O-2 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.