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

Abstract

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.

Prospects and Promises in Two-Electron Water Oxidation for Hydrogen Peroxide Generation

“…Copyright 2022 Nature Publishing Group. (j) Reprinted with permission from ref . Copyright 2023 Wiley-VCH.…”

“…Qu et al. designed a feasible photocatalyst with satisfied selectivity of H 2 O 2 production . They fabricated BiVO 4 upon ZnO overlayer coating of the photoanode, facilitating H 2 O 2 generation and suppressing the competitive reaction of O 2 evolution.…”

“…The PEC performance was recorded under AM 1.5G illumination (solid curves) and in the dark (dashed curves) in 2 M KHCO 3 . Reproduced with permission from ref . Copyright 2023, Wiley-VCH.…”

Promoting Water Oxidative Hydrogen Peroxide Production by Dynamic Anion Exchange on BiVO4 Photoanodes

“…Since Sayama et al found that the HCO 3 – electrolyte could promote the water oxidative H 2 O 2 formation in the photoelectrochemical (PEC) cell in 2016, PEC water oxidative H 2 O 2 production has been attracting great attention to pair with H 2 evolution and other interest reduction reactions due to the outstanding features of faster reaction kinetics, higher value-added, and easier separation of gas/liquid products compared to conventional oxygen evolution reaction (OER). − The role of HCO 3 – was determined as an “Electron Donor”, which is first oxidized to HCO 4 – and then hydrolyzes H 2 O to return the HCO 3 – and produce H 2 O 2 . , Although some strategies, such as heterojunction construction, , surface passivation, , wettability regulation, , etc., have been developed to enhance the performance of H 2 O 2 production in the HCO 3 – -containing electrolyte, the selectivity of H 2 O 2 product leaves room to be improved due to the higher redox potential of HCO 3 – /HCO 4 – (1.8 ± 0.1 V vs normal hydrogen electrode (NHE)) than that of OER. , An understandable strategy for enhancing the HCO 3 – oxidation kinetics is to increase the HCO 3 – concentration in the electrolyte . However, for most bicarbonates, the solubility is limited to about 1.0 M.…”

“…2−5 The role of HCO 3 − was determined as an "Electron Donor", which is first oxidized to HCO 4 − and then hydrolyzes H 2 O to return the HCO 3 − and produce H 2 O 2 . 6,7 Although some strategies, such as heterojunction construction, 8,9 surface passivation, 10,11 wettability regulation, 12,13 etc., have been developed to enhance the performance of H 2 O 2 production in the HCO 3 − -containing electrolyte, the selectivity of H 2 O 2 product leaves room to be improved due to the higher redox potential of HCO 3 − /HCO 4 − (1.8 ± 0.1 V vs normal hydrogen electrode (NHE)) than that of OER. 14,15 An understandable strategy for enhancing the HCO 3 − oxidation kinetics is to increase the HCO 3 − concentration in the electrolyte.…”