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.
Bibliographical noteFunding Information:
This work was supported by NSFC (51802157, 21902104), the Natural Science Foundation of Jiangsu Province of China (BK20180493), NRF Korea (NRF-2019R1A2C3010479, 2019M1A2A2065612, 2019M3E6A1064525, 2019R1A4A1029237), and the Fundamental Research Funds for the Central Universities (No. 30918012202). L.Y.W. acknowledges the support by the Natural Science Foundation of Top Talent of SZTU (Grant No. 2019106101003).
© 2020 American Chemical Society
All Science Journal Classification (ASJC) codes
- Colloid and Surface Chemistry