Study on the Synergistic Regulation of Oxygen Reduction Reaction Kinetics and Structural Stability of the Sm0.5Sr0.5FeO3−δ Cathode via Ni Doping

Abstract Efficient and stable cathodes are crucial for intermediate-temperature solid oxide fuel cells (IT−SOFCs). Here, a rational B-site Ni-doping strategy is proposed to simultaneously regulate ORR kinetics and structural stability in Sm0.5Sr0.5FeO3−δ-based cathodes. Introducing Ni2+ into Sm0.5Sr0.5Fe1−xNixO3−δ (SSFNx) strengthens the σ-bond hybridization between O 2p and Fe 3d orbitals, enhancing Fe−O covalency and promoting oxygen-ion migration, while moderately increasing oxygen vacancy concentration to favor oxygen adsorption/dissociation. The optimized SSFN0.1 exhibits high conductivity (237.54 S·cm−1), ∼3× that of the undoped sample (76.81 S·cm−1), and shows good thermo-mechanical compatibility with SDC (14.37−14.81 × 10−6 K−1 vs 12.6 × 10−6 K−1). A SSFN0.1 single cell delivers 645.69 mW·cm−2 at 800 °C and remains stable for >120 h at 750 °C. DFT confirms reduced oxygen vacancy formation energy (4.85→3.99 eV), migration barrier (0.52→0.27 eV), and band gap (0.78→0.55 eV), validating this innovative pathway for durable, high-performance IT−SOFC cathodes.