Monovalent ion doping to enhance the performance of cobalt-free Sm0.5Sr0.5FeO3-δ cathode for YSZ fuel cells

Abstract

Solid oxide fuel cells (SOFCs) are energy conversion devices that can solve the energy crisis and environmental pollution, but the low electrochemical performance at intermediate temperatures is still an urgent problem to be addressed. In this work, we investigate the effect of K and F doping on the performance of conventional cobalt-free cathode SSF. XRD demonstrates that SSF, SSKF, SSFF, and SSKFF each display a cubic perovskite structure. Additionally, HT-XRD reveals that SSF, SSKF, and SSFF exhibit exceptional thermal stability, while SSKFF produces the impurity phase Sr3Fe2O7 during the test. XPS suggests that the improvement in SSF performance, resulting from F and K doping, can be largely attributed to the increase in adsorbed oxygen content, which enhances the ORR catalytic activity. The O2-TPD outcomes indicate that F and K doping stimulate the formation of oxygen vacancies at higher temperatures, thus promoting ORR catalytic activity. Experimentally, the electrochemical impedance spectra results indicate that both K and F doping led to a reduction in the value of polarization resistance, which decreased by over 20% at 800 °C. Regarding the output performance, both K and F doping resulted in a substantial increase in the output power from 670.05 to 825.88 and 796.76 mW·cm−2 respectively, at 800 °C. However, co-doping with F and K led to a notable reduction in polarization impedance and output power, possibly due to the formation of heterogeneous phases during testing. The results indicate that enhancing the electrochemical performance of SSF can be achieved through the doping of K cations and F anions, but co-doping leads to a decreased performance.