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 H 2 O 2 production via oxidative pathway is plagued by the noncontrollable two-electron transfer reaction and the overoxidation of the thus-formed H 2 O 2 to O 2 . Here, ZnO passivator-coated BiVO 4 photoanode is reported for selective PEC H 2 O 2 production. Both the H 2 O 2 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 BiVO 4 upon ZnO coating, facilitating H 2 O 2 generation and suppressing the competitive reaction of O 2 evolution. The ZnO overlayer also inhibits H 2 O 2 decomposition, accelerates charge extraction from BiVO 4 , 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 H 2 O 2 synthesis from PEC water oxidation.