posted on 2020-03-19, 16:04authored byKan Zhang, Jiali Liu, Luyang Wang, Bingjun Jin, Xiaofei Yang, Shengli Zhang, Jong Hyeok Park
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.