Solar-light-driven non-bias photoelectrolysis for bleach production from sea water and atmospheric oxygen

Non-bias production of bleach aqueous solution was successfully demonstrated using solar-driven photoelectrochemical cell consisting of the metal-oxide-semiconductor photoanode and Pt-based cathode. Both hypochlorous acid (HClO) and hypobromous acid (HBrO) were generated via two-electron oxidation of chloride (Cl−) and bromide (Br−) at the photoanode. The Faradaic efficiency for HBrO production gradually improved with increasing Br− concentration in the electrolyte solution. Although a certain amount of HBrO was produced from 1 mM NaBr aqueous solution, the co-existence of Cl− drastically enhanced the amount of HBrO produced from the dilute Br− solution. The use of a gas diffusion electrode (GDE) composed of a Pt/carbon catalyst layer for efficient 4-electron O2 reduction enabled us to achieve the anodic photocurrent derived from the oxidation of Cl− and Br− under AM-1.5 simulated solar light irradiation. Moreover, we successfully accomplished convenient and simple production of aqueous bleaches from artificial sea water via irradiating the photoanode with simulated solar light without applying external bias.