Thermodynamic and Electrical Properties of Layered Perovskite NdBaCo2-xFexO5+delta-YSZ (x=0, 1) Composites for Intermediate Temperature SOFC Cathodes

Abstract

The thermodynamic and electrical characteristics of the NdBaCo2O5+delta (NBCO) have been studied as a competitive candidate of cathode material for intermediate-temperature solid oxide fuel cells (IT-SOFCs). NBCO has got extensive attention because it shows rapid oxygen diffusion, fast surface exchange kinetics, and high electrical conductivity, but a lack of long term stability is a concern. We investigated Fe doped NBCO based on the fact that stability of the NBCO-YSZ composite was increased by Fe doping. As expected, our results confirm that NdBaCoFeO5+delta(NBCF) is more stable than the NBCO because the partial molar enthalpies of oxidation for the NBCF are higher than those for the NBCO. The higher partial molar entropies of oxidation for the NBCF is attributed to the fact that excess oxygen can be added into the interstitial lattice more freely in the NBCF than in the NBCO. However, the electrical conductivity of the NBCF (similar to 1 S cm(-1)) is about one order of magnitude lower than that of the NBCO (similar to 10 S cm(-1)), but it is still manageable if proper current collectors are used. The maximum power density obtained for a single cell with NBCF-YSZ and NBCO-YSZ composites is 1.034 and 0.866 W cm(-2) at 1023 K, respectively.