Cation Acidity‐Driven Superior Catalytic Activity Enhancement in Perovskite Cobaltate Cathodes for Reversible Solid Oxide Cells

ABSTRACT Developing high‐performance and durable cathodes is crucial for efficient reversible solid oxide cells (R‐SOCs). While A‐site cation effects on perovskite cathodes are well‐established, the mechanistic role of B‐site cation acidity in regulating oxygen reduction reaction (ORR) and CO ₂ reduction reaction (CO ₂ RR) remains inadequately understood. This study systematically investigates the influence of B‐site cation acidity in BaCo _0.8 M _0.2 O _{3‐ δ} (M = Fe, Nb, and Ta) on electrochemical performance. Our findings reveal a direct correlation between dopant acidity and enhanced performance. Specifically, Fe doping (BCFO) leads to significant structural evolution with suppressed Jahn‐Teller distortion, resulting in a lower Co ⁴⁺ /Co ³⁺ ratio and increased oxygen vacancy concentration that promotes oxygen ion diffusion. At 800°C, BCFO achieves the highest peak power density in fuel cell mode (1520 mW·cm ⁻² ) and superior CO ₂ electrolysis current density (2.60 A·cm ⁻² at 1.3 V). Notably, a clear trend of performance enhancement with increasing dopant acidity is observed (BCFO > BCNO > BCTO). The superior performance of BCFO is attributed to its optimal metal‐oxygen bond energy, balancing facile bond dissociation and formation. This work establishes B‐site cation acidity as a predictive descriptor for the rational design of highly active and stable perovskite cathodes for advanced solid oxide fuel cells and electrolysis cells.