Synergistic surface and bulk engineering enables highly active Sr₂Fe_1.5Mo_0.5O_6-δ cathodes for efficient oxygen reduction in solid oxide fuel cells

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.