Tuning the Phase Transition of SrFeO_3−δ by Mn toward Enhanced Catalytic Activity and CO₂ Resistance for the Oxygen Reduction Reaction

Developing high-performance cathodes with sufficient stability against CO2 rooting in ambient atmosphere is crucial to realizing the practical application of solid-oxide fuel cells. Herein, the Mn dopant is investigated to regulate the phase structure and cathode performance of SrFeO3−δ perovskites through partially replacing the B-site Fe. Compared with parent SrFeO3−δ, Mn-doped materials, SrFe1–xMnxO3−δ (x = 0.05 and 0.1), show stabilized cubic perovskites at room temperature. Meanwhile, doping Mn accelerates the oxygen reduction reaction process, showing a reduced polarization resistance of 0.155 Ω·cm2 at 700 °C for SrFe0.95Mn0.05O3−δ, which is less than 30% of SrFeO3−δ. In addition, the Mn dopant improves the chemical oxygen surface exchange and bulk diffusion coefficients. Furthermore, Mn enhances the tolerance toward CO2 corrosion in various CO2 atmospheres. Density functional theory calculations also reveal that Mn can strengthen the structural stability and increase the activity for the oxygen reduction reaction.