Solar Oxidative Hydrogen Peroxide Production: Is the Oxygen Vacancy Always a Promoter in Solar Water Oxidation?
Songying Qu, Hao Wu, Yun Hau Ng
Abstract
Photoelectrochemical (PEC) water oxidation to hydrogen peroxide (H 2 O 2 ) 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 BiVO 4 photoanodes are detrimental to PEC water oxidation to H 2 O 2 . The superabundant OVs of the BiVO 4 photoanode are passivated by a thermal treatment in a pressurized O 2 atmosphere by a Parr reactor. The passivated BiVO 4 photoanode with the least OV concentration achieves ca. two times H 2 O 2 selectivity enhancement than the BiVO 4 photoanode with introduced OVs, resulting from the weakened band bending, the positively shifted quasi-Fermi level, and the suppressed decomposition of as-formed H 2 O 2 . In particular, the photoexcited electrochemical impedance spectra demonstrate a hole distribution rearrangement of the OVs-passivated BiVO 4, which eliminates the OER-related surface states and steers the water oxidation reaction pathway toward H 2 O 2 formation. This work reveals the importance of interfacial energetics induced by regulating intrinsic OVs in selective PEC water oxidation.