Balancing Oxygen Reduction and Thermal Expansion in Low-Temperature Solid Oxide Fuel Cell Cathodes via Codoping in SrCoO ₃

The performance of low-temperature solid oxide fuel cells (LT-SOFCs) is limited by sluggish oxygen reduction kinetics and thermal expansion mismatch between cathode and electrolyte materials. ABO3-type perovskites, such as SrCoO3-δ, exhibit excellent oxygen reduction reaction (ORR) activity but suffer from high thermal expansion and limited compatibility with ceria electrolytes in LT-SOFCs. Here, we introduce a codoping strategy in which Ce4+ is incorporated at the A-site of Nb5+/Ta5+ codoped SrCoO3-δ to simultaneously regulate lattice expansion and oxygen defect chemistry. The optimized composition, Sr0.95Ce0.05Co0.8Nb0.1Ta0.1O3-δ (SCCNT05), shows lattice contraction, improved lattice oxygen stability, and a significant reduction in thermal expansion coefficient to 14.42 × 10–6 K–1 down from 17.57 × 10–6 K–1 in the absence of Ce doping. Electrochemical impedance spectroscopy reveals competitive ORR performance with an area-specific resistance of 0.429 Ω cm2 at 500 °C. Distribution of relaxation time and density functional theory analyses confirm that Ce strengthens A–O bonding and increases oxygen vacancy formation energy, leading to improved thermal stability without severely compromising ORR kinetics. This A–B codoping approach offers a promising pathway for designing thermally compatible LT-SOFC cathodes.