Nd0.5Sr0.5Fe0.8Cu0.2O3−δ–xSm0.2Ce0.8O1.9 cobalt-free composite cathodes for intermediate temperature solid oxide fuel cells

•Composite cathode can significantly improve the performance of cathode in SOFC.•Addition of the second phase has an optimum value for composite cathode.•Overloading second phase has a negative influence on composite cathode.•The cell shows the best performance at 40 wt% SDC as second phase.

Cobalt-free composites Nd0.5Sr0.5Fe0.8Cu0.2O3−δ (NSFCu)–xSm0.2Ce0.8O1.9 (SDC) (x = 0–60 wt%) are investigated as IT-SOFC cathodes. The characteristic properties of cobalt-free composite cathodes comparing to cobalt-based composites are revealed. The DC conductivity and thermal expansion coefficient of the composite cathodes decrease with the content of SDC x, while the polarization resistance Rp shows the least value with addition of 40 wt% of SDC. The power density of the single cell with NSFCu-40% SDC composite cathode improved significantly compared with that of undoped NSFCu cathode, with peak values of 488, 623, 849 and 1052 mW cm−2 at 600, 650, 700, and 750 °C, respectively. Moreover, the performance of the composite cathode is stable within testing period of 370 h at 700 °C, indicating that the NSFCu-40% SDC is an excellent cobalt-free composite cathode applied in IT-SOFC.