Self‐Assembled Ag/NiO‐Perovskite Multiphase Composite Catalyst for Enhanced Oxygen Evolution Catalysis

Developing oxygen evolution reaction (OER) catalysts that balance high activity and long‐term durability remains a key challenge for alkaline water electrolysis. Herein, we report a perovskite‐dominant Ag/NiO multiphase composite catalyst derived from nominal Sr 0.8 Ag 0.2 Co 0.6 Fe 0.2 N i0.2 O 3‐δ (SACFN2), featuring in situ segregation of Ag and NiO nanophases on a defect‐rich perovskite matrix through self‐driven lattice reconstruction. A‐site Ag + exsolution creates oxygen vacancies and lattice distortion, facilitating B‐site Ni migration and surface NiO segregation. Under OER conditions, NiO nanophases reconstruct toward NiOOH/(Ni,Co,Fe)O(OH)‐like active species, while Ag‐containing domains promote charge redistribution and stabilize the Ag/NiO–perovskite interface. SACFN2 achieves an overpotential of 231 mV at 10 mA cm −2 , a Tafel slope of 51.28 mV dec −1 , and sustained operation over 1000 h at 100 mA cm −2 . Furthermore, anion exchange membrane water electrolyzer (AEMWE) testing with SACFN2 as the anode and Pt/C as the cathode demonstrates stable long‐term operation at 500 mA cm −2 for 1000 h, with only a 54 mV voltage increase. Structural analyses confirm a stable Ag/NiO–perovskite composite interface and oxygen‐deficient lattice framework, demonstrating the value of perovskite‐based multiphase interface and defect engineering for alkaline OER catalysis.