Self-adaptive amorphous CoOCl electrocatalyst for sustainable chlorine evolution in acidic brine.

Electrochemical chlorine evolution reaction is of central importance in the chlor-alkali industry, but the chlorine evolution anode is largely limited by water oxidation side reaction and corrosion-induced performance decay in strong acids. Here we present an amorphous CoOCl catalyst that has been deposited in situ in an acidic saline electrolyte containing Co and Cl ions to adapt to the given electrochemical condition and exhibits ~100% chlorine evolution selectivity with an overpotential of ~0.1 V at 10 mA cm and high stability over 500 h. In situ spectroscopic studies and theoretical calculations reveal that the electrochemical introduction of Cl prevents the Co sites from charging to a higher oxidation state thus suppressing the O-O bond formation for oxygen evolution. Consequently, the chlorine evolution selectivity has been enhanced on the Cl-constrained Co-O sites via the Volmer-Heyrovsky pathway. This study provides fundamental insights into how the reactant Cl itself can work as a promoter toward enhancing chlorine evolution in acidic brine.