Trace Chlorine-Induced Lattice Oxygen Activation for Enhanced High-Temperature CO₂ Electrolysis

Tuning lattice oxygen activity in perovskite oxides (ABO₃) 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 CO₂ electrolysis conditions. Herein, a novel anion activation strategy is proposed by incorporating trace chloride ions (Cl^-) into the O-sites of Sr₂Fe_1.5Mo_0.5O_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 CO₂ adsorption and carbonate intermediate formation, and ultimately promoting CO₂ reduction kinetics. As a result, the oxychloride cathode achieves a 60.2-80.8% enhancement in CO₂-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.