Hexavalent Iridium Sites Drive Highly Efficient and Selective Chlorine Evolution via a Two‐Step Chemical‐Electrochemical Cycle Reaction Mechanism

Chlorine evolution reaction (CER) is pivotal to the chlor-alkali industry, while its operation still relies on the dimensionally stable anode (DSA) developed decades ago, which is hindered by high costs, moderate selectivity, and limited energy efficiency. Here, we present a spinel-type hexavalent iridium single-site electrocatalyst (spinel-iso-Ir^VI) via strategic modulation of delocalized electron distribution that demonstrates exceptional CER performance. This catalyst operates with an ultralow overpotential of 27 mV at 10 mA cm^-2 (57 mV for commercial DSA), a nearly 100% CER selectivity across a wide potential range, and a record energy efficiency of 83.5% at an industrial-level current density of ∼300 mA cm^-2. At the overpotential of 100 mV, spinel-iso-Ir^VI delivers a mass activity of 9671 mA mg_Ru+Ir ^-1 and a turnover frequency of 0.278 s^-1, surpassing those of the benchmark DSA by over 386-fold and 20-fold, respectively. The high-performance of spinel-iso-Ir^VI results in a low production cost of US$0.04 per kilogram of chlorine. Mechanism studies reveal a two-step chemical-electrochemical cycle reaction mechanism, in which the chemical reaction step involves a spontaneous redox reaction triggered by hexavalent Ir^VI sites. This process enables the spontaneous adsorption, bonding, and oxidation of Cl^- to generate Cl₂, thereby significantly boosting the reaction kinetics.