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

Selective photoelectrochemical (PEC) water oxidation to hydrogen peroxide is an underexplored option as opposed to the mainstream oxygen reduction reaction. Albeit interesting, selective H₂ O₂ production via oxidative pathway is plagued by the noncontrollable two-electron transfer reaction and the overoxidation of the thus-formed H₂ O₂ to O₂ . Here, ZnO passivator-coated BiVO₄ photoanode is reported for selective PEC H₂ O₂ production. Both the H₂ O₂ 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 H₂ O₂ generation and suppressing the competitive reaction of O₂ evolution. The ZnO overlayer also inhibits H₂ O₂ 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 H₂ O₂ synthesis from PEC water oxidation.