Trace Chlorine‐Induced Lattice Oxygen Activation for Enhanced High‐Temperature CO 2 Electrolysis

Abstract Tuning lattice oxygen activity in perovskite oxides (ABO 3 ) offers a promising approach to overcome the intrinsic trade‐off between catalytic activity and stability in redox reactions. However, precise modulation and mechanistic understanding of lattice oxygen activation remain elusive under high‐temperature CO 2 electrolysis conditions. Herein, a novel anion activation strategy is proposed by incorporating trace chloride ions (Cl − ) into the O‐sites of Sr 2 Fe 1.5 Mo 0.5 O 6−δ perovskite forming an oxychloride cathode. This Cl − substitution activates lattice oxygen reactivity by weakening Mo−O/Fe−O covalency, thereby facilitating the formation and redistribution of oxygen vacancies, accelerating bulk oxygen ion transport, enhancing CO 2 adsorption and carbonate intermediate formation, and ultimately promoting CO 2 reduction kinetics. As a result, the oxychloride cathode achieves a 60.2–80.8% enhancement in CO 2 ‐to‐CO electrolysis, reaching 2.02 A cm −2 at 800 °C and 1.5 V with ≈100% Faradaic efficiency, while maintaining exceptional stability of 500 h. This work establishes a new paradigm of O‐site anion engineering to unlock lattice oxygen activity for electrocatalytic reactions.