Near-Complete Suppression of Oxygen Evolution for Photoelectrochemical HO Oxidative HO Synthesis.

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