Improved oxygen kinetics on both cathode and anode of SmBaFe₂O_5+δ-based solid oxide fuel cells through Ca²⁺ doping

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 purposely 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.