The effective oxygen conductivities in the zirconia networks of porous LSM-YSZ and LSM-SYSZ composites [i.e. La0.85Sr0.15MnO3 (Y2O3)0.08(ZrO2)0.92 and La0.85Sr0.15MnO3-c2O3)0.1(Y2O3)0.01(ZrO2)0.89, respectively] were evaluated by an AC impedance technique using specimens in which LSM was removed by hydrochloric acid leaching. The oxygen conductivities of porous YSZ and SYSZ alone followed a Koh-Fortini relationship. LSM-containing zirconia network conductivities were additionally decreased by the presence of the LSM, presumably by increased grain boundary resistances. Constriction resistances were estimated to have a minor effect.

The fabrication and electrochemical performance of co-fired, LSM-SYSZ [i.e., La0.65Sr0.30MnO3 (LSM) - (Sc2O3)0.1(Y2O3)0.01(ZrO2)0.89] supported thin-film cells were examined using humidified hydrogen as a fuel. Co-firing of bi-layers and tri-layers was successful at 1250oC by optimizing the amount of carbon pore formers. A power density of a factor of 2.5 higher than that recently reported for the same type of cell at 800oC [3] was obtained for a cell with cobalt infiltration into the supporting cathode: the peak power densities were 455, 389, 285, 202, 141 mW/cm2 at 800, 750, 700, 650, 600oC, respectively, and in most cases power densities at 0.7V exceeded more than 90 percent of the peak output. Increasing the cathode porosity from 43 to 53 percent improved peak power densities by as much as 1.3, shifting the diffusion limitation to high current densities. Cobalt infiltration into the support improved those by as much as a factor of 2 due to a significant reduction in non-ohmic resistance. These results demonstrate that cobalt catalyst-infiltrated LSM can be effective and low-cost supporting electrodes for reduced temperature, thin film SOFCs.