Photoelectrochemical Synthesis of Hydrogen Peroxide from Saline Water via the Two-Electron Water Oxidation Reaction

Hydrogen peroxide (H₂O₂) production on the anode is more valuable than oxygen and chlorine evolution for photoelectrochemical saline water splitting. In this work, by the introduction of bicarbonate (HCO₃^-), H₂O₂ is produced from saline water (2 M KHCO₃ + 0.5 M NaCl aqueous solution) via the two-electron water oxidation reaction by a photoanode of bismuth vanadate (BiVO₄). Furthermore, the Faradaic efficiency (FE) and accumulation for H₂O₂ are improved by coating antimony tetroxide (Sb₂O₄) on BiVO₄. A H₂O₂ FE of 26% at 1.54 V vs RHE is obtained by Sb₂O₄/BiVO₄ and 49 ppm of H₂O₂ is accumulated after a 135 min chronoamperometry. Similar to that in KHCO₃ pure water solution, infrared spectroscopy and electrochemical analysis confirm that HCO₃^- plays a surface-mediating role in the formation of H₂O₂ in KHCO₃ saline water solution. The presence of HCO₃^- in the electrolyte is able to not only increase the photocurrent density but also effectively inhibit the chlorine evolution reaction.