Sr-deficient medium-entropy Sr1-xCo0.5Fe0.2Ti0.1Ta0.1Nb0.1O3-δ cathodes with high Cr tolerance for solid oxide fuel cells

In this work, Sr-deficiency is proposed as an effective strategy to improve the oxygen reduction reaction (ORR) activity and Cr tolerance of medium-entropy Sr1-xCo0.5Fe0.2Ti0.1Ta0.1Nb0.1O3-δ (S1-xCFTTN, x=0–0.15) cathodes for intermediate temperature solid oxide fuel cells (IT-SOFCs). With proper Sr-deficiency, S0.95CFTTN possesses the highest electrical conductivity and fastest oxygen exchange kinetics within tested samples. The optimized cathode yields outstanding ORR activity with a polarization resistance of 0.024 Ω cm2 at 700 °C, much lower than 0.037 Ω cm2 for SCFTTN cathode. Based on these, an anode-supported cell with S0.95CFTTN cathode exhibits a peak power density of 1153.5 mW cm−2 at 800 °C, much higher than that with SCFTTN cathode. Moreover, the S0.95CFTTN cathode displays dramatically enhanced Cr tolerance ability, which is due to the Sr-deficient diminishes surface Sr segregation and subsequent the formation of SrCrO4. Our results indicate appropriate Sr-deficiency is an effective approach to enhance the ORR activity and stability of SOFC cathodes.