Composite Cathode Study for Low Temperature SOFC

Abstract

Since the kinetics of cathode is slow In low temperature solid oxide fuel cells, full attention has to be given to boost cathode performance through optimization of cathode composition and microstructure. In this contribution, the effect of composition of (1-x) Sm0.5Sr0.5CoO3 (SSC) + x Sm0.2Ce0.8O1.9 (SDC) cathodes (x=0, 10, 25, 40 wt%) sintered at 1000{degree sign}C for 2hrs has been investigated using symmetric cells with Sm0.2Ce0.8O1.9 (SDC) electrolytes. The results showed that an increase in SDC content in the composite cathodes led to an increase in cathode polarization resistance (Rc). The Rc values on average were 0.042 W cm2 for the cathode without SDC addition, 0.063 W cm2 for the cathode with 10 wt% SDC, 0.079 W cm2 for the cathode with 25 wt% SDC, and 0.207 W cm2 for the cathode with 40 wt% SDC at 650{degree sign}C. The calculated activation energy values of the composite cathodes were in the range of 120{plus minus}20 kJ mol-1. We also investigated an in-situ (650{degree sign}C) sintered SSC cathode, and found that it showed the lowest electrochemical polarization resistance, approximately 0.028 W cm2 at 650{degree sign}C. The cathode stability of the symmetric cells has also been tested at 650{degree sign}C in air. No obvious voltage degradation under constant current density (0.5 A cm-2) has been observed in the cells with 1000oC-sintered SSC with 25 wt% SDC. However, the cell with in-situ sintered SSC cathode showed a steady decay rate of -4mV/hr. EIS analysis of the cell before and after the stability test revealed that the