High‐Entropy‐Tailored d‐p Orbital Hybridization for Enhanced Oxygen Reduction Reaction in Perovskite Air Electrodes of Solid Oxide Fuel Cells

ABSTRACT Developing high‐performance and durable air electrodes is crucial for the commercialization of medium‐temperature solid oxide fuel cells (MT‐SOFCs). Herein, we report a high‐entropy Pr 0.2 Nd 0.2 Ba 0.2 Sr 0.2 Ca 0.2 CoO 3−δ (PNBSCC) air electrode that demonstrates superior oxygen reduction reaction (ORR) catalytic activity and stability. The symmetrical cell with PNBSCC exhibits a polarization impedance (R p ) of 0.048 Ω cm 2 at 650°C, significantly lower than the 0.196 Ω cm 2 of PrBaCo 2 O 5 ± δ (PBC) counterpart. A single cell with the PNBSCC air electrode achieves an outstanding peak power density of 2.03 W cm −2 at 800°C, representing a 153% improvement over that with PBC. Furthermore, the single cell maintains a voltage decay rate of only 0.047 mV h −1 after 450 h of stable operation at 700°C. In situ high‐temperature XRD and electrochemical impedance spectroscopy (EIS) reveal excellent CO 2 tolerance and structural stability of PNBSCC. Combined X‐ray absorption spectroscopy and density functional theory calculations reveal weakened Co 3 d ‐O 2 p hybridization and reduced Co─O covalency in PNBSCC, which favors lattice‐oxygen activation and oxygen‐vacancy formation. The increased oxygen‐vacancy population facilitates oxygen‐ion transport, thereby accelerating ORR kinetics and improving cell performance.