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

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 a great abil-ity 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 pho-toanode/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 favour H2O2 evolution with great selectivity by reduced band bending. Simultaneously, the 1-electron water oxidation reaction is triggered to generate hydroxyl radical (OH) over SnO2-x/BiVO4 photoanode, which, however, is never de-tectable for the BiVO4 photoanode in PEC water splitting. 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 electrocataly-sis 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/cm-2 at 1.23 V vs. RHE; this performance sur-passes almost all previous solar energy-assisted H2O2 evolution performances. Because of the simultaneous produc-tion of H2O2 and H2 by solar water splitting in the PEC cells, our results demonstrate a green, cost-effective approach for "solar-to-fuel" conversion.