Electrode materials with robust stability and outstanding catalytic activity are crucial for practical implementation of solid oxide fuel cells (SOFCs). To avoid the inherent thermal expansion from Co-based analogous, we report a double perovskite, SmBaFe₂O_5+δ (SBF), where purposive doping of larger Ca²⁺ (1.34 Å) in the Sm³⁺ (1.24 Å) site, widens the Fe-O-Fe angle from 162 to 168°, shortens the Fe-O (2) bond from 1.9898 to 1.9675 Å. Consequently, both the oxygen kinetics, i.e., oxygen vacancy (V_O) concentration, and electron conductivity are significantly improved, which finally leads to a high peak power density (PPD) of 2.14 and 1.18 W·cm⁻² at 800 °C among Fe-based perovskites, for single cell using Sm_0.9Ca_0.1BaFe₂O_5+δ (SCBF) as cathode and symmetrical-SOFC (Sym-SOFC) using SCBF as both cathode and anode, respectively. This work provides a fresh angle for the design of Co-free, high-performance, and cost-effective electrode materials for SOFCs.

Although intermediate temperature solid oxide fuel cells (IT-SOFCs) show great potential to address energy conversion challenges, the sluggish oxygen reduction reaction (ORR) kinetics of cathode materials has severely hindered extended applications. Herein, we have demonstrated that Bi³⁺ doping on the A-site synergistically regulates the phase transition and electron spin state in La_0.3Bi_0.3Ca_0.4FeO_3−δ (LBCF3) for improved performance. An orthorhombic to cubic phase transition occurred with Bi³⁺ doping increases oxygen vacancy concentration and thus increases oxygen ion migration capacity. Simultaneously, the change of Fe from low to medium electron spin state strengths O₂ adsorption and improves catalytic performances. Consequently, a peak power density improvement up to 48% (from 1.21 to 1.79 W·cm⁻²) at 800 °C is realized in the anode-supported single cell using LBCF3 as cathode, which remains stable for over 270 h at 750 °C.