Characterization of Sr-Doped LaCoO[sub 3]-YSZ Composites Prepared by Impregnation Methods

Porous yttria-stabilized zirconia (YSZ) was impregnated with aqueous solutions of the nitrate salts of Sr, La, and Co to obtain composites of La 0.6 Sr 0.4 CoO 3-δ (LSCo) and YSZ. X-ray diffraction showed that the perovskite phase formed after heating to 973 K and conductivities as high as 7 S/cm were achieved at 973 K with only 30 wt % LSCo. Coefficient of thermal expansion (CTE) measurements of the composites with as much as 50 wt % LSCo indicated that the CTEs were much lower than the weighted average of the YSZ and LSCo. Electrochemical measurements using symmetric cells in air indicated that the area-specific resistance (ASR) of the composites could be as low as 0.03 Ω cm 2 at 973 K and 0.01 Ω cm 2 at 1073 K. These low ASR were verified in a cell with an LSCo-YSZ cathode and a Co-ceria-YSZ anode, which exhibited a total electrode polarization loss of 0.25 Ω cm 2 at 973 K and 0.1 Ω cm 2 at 1073 K for operation in humidified H 2 . However, changes in electrochemical performance with time showed that some electrode degradation occurred over a period of 250 h, even at 973 K.