Near-Complete Suppression of Oxygen Evolution for Photoelectrochemical H₂O Oxidative H₂O₂ Synthesis

Abstract

Solar energy-assisted water oxidative hydrogen peroxide (H2O2) production on an anode combined with H2 production on a cathode increases the value of solar water splitting, but the challenge of the dominant oxidative product, O2, needs to be overcome. Here, we report a SnO2–x overlayer coated BiVO4 photoanode, which demonstrates the great ability to near-completely suppress O2 evolution for photoelectrochemical (PEC) H2O oxidative H2O2 evolution. Based on the surface hole accumulation measured by surface photovoltage, downward quasi-hole Fermi energy at the photoanode/electrolyte interface and thermodynamic Gibbs free energy between 2-electron and 4-electron competitive reactions, we are able to consider the photoinduced holes of BiVO4 that migrate to the SnO2–x overlayer kinetically favor H2O2 evolution with great selectivity by reduced band bending. The formation of H2O2 may be mediated by the formation of hydroxyl radicals (OH·), from 1-electron water oxidation reactions, as evidenced by spin-trapping electron paramagnetic resonance (EPR) studies conducted herein. In addition to the H2O oxidative H2O2 evolution from PEC water splitting, the SnO2–x /BiVO4 photoanode can also inhibit H2O2 decomposition into O2 under either electrocatalysis or photocatalysis conditions for continuous H2O2 accumulation. Overall, the SnO2–x /BiVO4 photoanode achieves a Faraday efficiency (FE) of over 86% for H2O2 generation in a wide potential region (0.6–2.1 V vs reversible hydrogen electrode (RHE)) and an H2O2 evolution rate averaging 0.825 μmol/min/cm2 at 1.23 V vs RHE under AM 1.5 illumination, corresponding to a solar to H2O2 efficiency of ∼5.6%; this performance surpasses almost all previous solar energy-assisted H2O2 evolution performances. Because of the simultaneous production of H2O2 and H2 by solar water splitting in the PEC cells, our results highlight a potentially greener and more cost-effective approach for “solar-to-fuel” conversion.

Suppressing Water Dissociation via Control of Intrinsic Oxygen Defects for Awakening Solar H2O‐to‐H2O2 Generation

“…[16][17][18] The surface state associated with the intrinsic O vac influences the PEC water splitting activity by kinetically competitive between charge recombination and OER at a Schottky contacted solid/liquid interface, and reasonable controls have been a general strategy to improve PEC efficiency of BiVO 4 . [19][20][21] In recent two years, the surface passivation approaches were found to significantly enhance the H 2 O 2 evolution activity of BiVO 4 , [22,23] making the intrinsic O vac being one of the key considerations for the possibilities of low H 2 O 2 evolution selectivity of the synthetic BiVO 4 . Although there are numerous studies to elucidate the roles of O vac on charge transfer kinetics (e.g., like trap and donor), the dynamics of dissociation of water molecules on the O vac existing BiVO 4 surface is rarely considered.…”

Rational Design of Metal Oxide‐Based Heterostructure for Efficient Photocatalytic and Photoelectrochemical Systems

“…Furthermore, the research on PEC systems is still mainly focused on water splitting, and its application scope needs to be further expanded. Recently, H 2 O 2 synthesis via PEC water splitting has achieved a high conversion efficiency, [ 121 ] and the feasibility of using PEC system to realize solar ammonia splitting has also begun to attract attention. [ 122 ] Based on the achievements, we present the remaining challenges and future perspectives in the development of metal oxide‐based heterostructures.…”

Electrochemical Degradation of Lignin by ROS

“…Furthermore, owing to their wide bandgaps, these electrodes also serve as photoelectrochemical catalysts for H 2 O 2 production. BiVO 4 exhibited a high Faraday efficiency for producing H 2 O 2 in a photo-electrocatalytic process, which benefits from the excellent matching between its bandgap and the redox potential of 2e-WOR [35]. Another important fact for improving the selective of 2e-WOR is the introduction of bicarbonate ions in the electrolyte, either in the electrocatalytic or photo-electrocatalytic process [36].…”