Chloride‐Driven Reconstruction of Perovskite Oxides for Durable High‐Activity Oxygen Reduction Catalysis in Fuel Cells

Abstract Solid oxide fuel cells are promising technologies for renewable energy conversion, yet their practical deployment requires oxygen electrodes that simultaneously support rapid oxygen‐ion transport and sustained high‐activity oxygen reduction reaction (ORR) catalysis. However, constructing such a microchemical environment remains a persistent challenge for perovskite oxides. Here, it is demonstrated that Cl − incorporation into PrBaCo 2 O 5+δ partially replaces lattice oxygen, inducing localized metal–oxygen electronic states, enhanced lattice distortion, and Pr 3+ intermixing into BaO layers, collectively generating 3D fast pathways for oxygen‐ion diffusion. More significantly, it is revealed for the first time that Cl − preferentially segregates at the surface, forming an amorphous layer that creates an adaptive ORR interface and effectively overcomes the long‐standing issue of surface passivation. As a result, Cl − ‐engineered PrBaCo 2 O 5+δ achieves a 3–5‐fold increase in ORR activity relative to the parent oxide and exhibits outstanding durability at 750 °C, transforming ≈15.1% degradation over 100 h into a ≈2.7% performance gain. This work establishes a halogen‐mediated mechanism for tailoring perovskite microchemistry, challenges the prevailing view that halogens merely stabilize oxide lattices, demonstrates one of the most pronounced catalytic enhancements reported to date, and offers a broadly applicable strategy for designing advanced oxygen electrodes.