The sluggish oxygen reduction reaction kinetics of cathodes remains a major obstacle to the development of intermediate temperature solid oxide fuel cells. Herein, a synergistic surface and bulk engineering strategy is proposed to enhance the oxygen reduction activity of Sr₂Fe_1.5Mo_0.5O_6−δ (SFM) based cathodes. Bulk lattice regulation is achieved by introducing Zr⁴⁺ into the B site, which induces lattice expansion, modulates oxygen defect chemistry, and promotes oxygen ion transport. Meanwhile, surface engineering with BaCoO_3-δ (BCO) nanoparticles enriches reactive oxygen species and constructs active heterointerfaces for oxygen adsorption and dissociation. Benefiting from the coupled enhancement of bulk oxygen transport and surface oxygen activation, the optimized Sr₂Fe_1.5Mo_0.4Zr_0.1O_6−δ-20BaCoO_3-δ (SFMZ-20BCO) composite cathode exhibits accelerated oxygen exchange kinetics and significantly reduced polarization resistance. A low polarization resistance (Rp) of 0.0237 Ω·cm² is achieved at 800 °C, and an anode supported single cell delivers a high peak power density of 2.34 W·cm^-2. Moreover, the cell maintains stable operation for over 400 h at 700 °C under a constant voltage of 0.7 V. This work highlights the broad potential of coupling surface catalytic activation with bulk defect regulation as a general strategy for developing high performance cathodes for solid oxide fuel cells.

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.