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

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.