Sunlight-Driven Generation of Hypochlorous Acid on Plasmonic Au/AgCl Catalysts in Aerated Chloride Solution

HClO is typically manufactured from Cl₂ gas generated by the electrochemical oxidation of Cl^- using considerable electrical energy with a large concomitant emission of CO₂. Therefore, renewable energy-driven HClO generation is desirable. In this study, we developed a strategy for stable HClO generation by sunlight irradiation of a plasmonic Au/AgCl photocatalyst in an aerated Cl^- solution at ambient temperature. Plasmon-activated Au particles by visible light generate hot electrons, which are consumed by O₂ reduction, and hot holes, which oxidize the lattice Cl^- of AgCl adjacent to the Au particles. The formed Cl₂ is disproportionated to afford HClO, and the removed lattice Cl^- are compensated by the Cl^- in the solution, thus promoting a catalytic HClO generation cycle. A solar-to-HClO conversion efficiency of ∼0.03% was achieved by simulated sunlight irradiation, where the resultant solution contained >38 ppm (>0.73 mM) of HClO and exhibited bactericidal and bleaching activities. The strategy based on the Cl^- oxidation/compensation cycles will pave the way for sunlight-driven clean, sustainable HClO generation.