Rational B‐Site Engineering of a Co/Sr‐free Ba 0.95 La 0.05 FeO 3‐δ Cathode With Superior CO 2 Resistance and High Activity for Microtubular Ceramic Fuel Cells

ABSTRACT Co/Sr‐based perovskite oxides are extensively utilized as cathodes for both solid oxide fuel cells (SOFCs) and protonic ceramic fuel cells (PCFCs), mainly because of their excellent oxygen reduction reaction (ORR) activity and superior electrical conductivity. However, the high cost and intrinsically unstable nature of Co, coupled with Sr segregation tendency, severely degrade the long‐term durability of these cathode materials. In this study, a Co/Sr‐free perovskite oxide, Ba 0.95 La 0.05 Fe 0.95 Zr 0.05 O 3‐δ (BLFZ), was designed and synthesized via rational doping of 5% high‐valent Zr 4+ cation at the B‐site of Ba 0.95 La 0.05 FeO 3‐δ (BLF) as a bifunctional mixed‐conducting cathode material. Systematic measurements coupled with density functional theory (DFT) calculations revealed that Zr incorporation effectively enhances the hydration capacity, CO 2 tolerance, oxygen‐vacancy concentration, and ORR activity. As a result, excellent electrochemical performance was obtained with BLFZ‐based composite cathodes on microtubular PCFCs and SOFCs, achieving peak power densities of 968 mW cm −2 at 700°C and 877 mW cm −2 at 800°C, respectively. The cells also showed favorable long‐term stability for over 200 h. Collectively, these results highlight BLFZ as a robust and versatile cathode candidate for dual application in PCFCs and SOFCs.