Near-Complete Suppression of Oxygen Evolution for Photoelectrochemical H 2 O Oxidative H 2 O 2 Synthesis

Solar energy-assisted water oxidative hydrogen peroxide (H 2 O 2 ) production on an anode combined with H 2 production on a cathode increases the value of solar water splitting, but the challenge of the dominant oxidative product, O 2, needs to be overcome. Here, we report a SnO 2– x overlayer coated BiVO 4 photoanode, which demonstrates the great ability to near-completely suppress O 2 evolution for photoelectrochemical (PEC) H 2 O oxidative H 2 O 2 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 BiVO 4 that migrate to the SnO 2– x overlayer kinetically favor H 2 O 2 evolution with great selectivity by reduced band bending. The formation of H 2 O 2 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 H 2 O oxidative H 2 O 2 evolution from PEC water splitting, the SnO 2– x /BiVO 4 photoanode can also inhibit H 2 O 2 decomposition into O 2 under either electrocatalysis or photocatalysis conditions for continuous H 2 O 2 accumulation. Overall, the SnO 2– x /BiVO 4 photoanode achieves a Faraday efficiency (FE) of over 86% for H 2 O 2 generation in a wide potential region (0.6–2.1 V vs reversible hydrogen electrode (RHE)) and an H 2 O 2 evolution rate averaging 0.825 μmol/min/cm 2 at 1.23 V vs RHE under AM 1.5 illumination, corresponding to a solar to H 2 O 2 efficiency of ∼5.6%; this performance surpasses almost all previous solar energy-assisted H 2 O 2 evolution performances. Because of the simultaneous production of H 2 O 2 and H 2 by solar water splitting in the PEC cells, our results highlight a potentially greener and more cost-effective approach for “solar-to-fuel” conversion.