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

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_0.2Nd_0.2Ba_0.2Sr_0.2Ca_0.2CoO_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 cm² at 650°C, significantly lower than the 0.196 Ω cm² of PrBaCo₂O_{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 CO₂ tolerance and structural stability of PNBSCC. Combined X-ray absorption spectroscopy and density functional theory calculations reveal weakened Co 3d-O 2p 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.