Highly Selective Active Chlorine Generation Electrocatalyzed by Co ₃ O ₄ Nanoparticles: Mechanistic Investigation through in Situ Electrokinetic and Spectroscopic Analyses

The reaction mechanism of electrochemical chloride oxidation at neutral pH is different from that at acidic pH, in which a commercial chlor-alkali process has been developed. Different proton concentrations and accelerated hydrolysis of the generated chlorine into hypochlorous acid at high pH can change the electrokinetics and stability of reaction intermediates. We have investigated a unique reaction mechanism of Co ₃ O ₄ nanoparticles for chloride oxidation at neutral pH. In contrast with water oxidation, the valency of cobalt was not changed during chloride oxidation. Interestingly, a new intermediate of Co-Cl was captured spectroscopically, distinct from the reaction intermediate at acidic pH. In addition, Co ₃ O ₄ nanoparticles exhibited high selectivity for active chlorine generation at neutral pH, comparable to commercially available RuO ₂ -based catalysts. We believe that this study provides insight into designing efficient electrocatalysts for active chlorine generation at neutral pH, which can be practically applied to electrochemical water treatment coupled to hydrogen production.