Thin Zinc Oxide Layer Passivating Bismuth Vanadate for Selective Photoelectrochemical Water Oxidation to Hydrogen Peroxide

Selective photoelectrochemical (PEC) water oxidation to hydrogen peroxide is an underexplored option as opposed to the mainstream oxygen reduction reaction. Albeit interesting, selective H₂O₂ production via oxidative pathway is plagued by the noncontrollable two-electron transfer reaction and the overoxidation of the thus-formed H₂O₂ to O₂. Here, ZnO passivator-coated BiVO₄ photoanode is reported for selective PEC H₂O₂ production. Both the H₂O₂ selectivity and production rate increase in the range of 1.0–2.0 V versus RHE under simulated sunlight irradiation. The photoelectrochemical impedance spectra and open-circuit potentials suggest a flattened band bending and positively shifted quasi-Fermi level of BiVO₄ upon ZnO coating, facilitating H₂O₂ generation and suppressing the competitive reaction of O₂ evolution. The ZnO overlayer also inhibits H₂O₂ decomposition, accelerates charge extraction from BiVO₄, and serves as a hole reservoir under photoexcitation. This work offers insights into surface states and the role of the coating layer in manipulating two/four-electron transfer for selective H₂O₂ synthesis from PEC water oxidation.