Characterization of LSM-YSZ Composites Prepared by Impregnation Methods

Composites of La 0 . 8 Sr 0 . 2 MnO 3 (LSM) and yttria-stabilized zirconia (YSZ) were prepared by impregnating porous YSZ with salts of Sr, La, and Mn to 40 wt % LSM. The effect of calcination temperature on cathode performance at 973 K was then studied using both symmetric cells and solid oxide fuel cells (SOFCs). Following calcination at 1123 K, the LSM in the composite remained porous. In symmetric-cell tests, LSM(1123)-YSZ electrodes exhibited a low loss, 0.5 Ω cm 2 , which was unchanged by polarization; however, in fuel cell tests, the performance was poor at current densities above 0.2 A/cm 2 . Following calcination at 1323 or 1523 K, LSM formed a dense layer coating on the YSZ. In symmetric-cell tests, the composite exhibited an ASR greater than 4 Ω cm 2 , but this decreased, reversibly, upon cathodic polarization or upon heating in humidified H 2 at 973 K. In fuel cell tests, the performance of composites calcined at 1323 K was superior to ones at 1523 K, primarily because the ohmic resistance of the cell was 0.25 Ω cm 2 higher after 1523 K, probably due to solid-state reactions with the electrolyte. The optimal conditions for forming impregnated LSM-YSZ cathodes and the reasons for the observed hysteresis in cathode polarization are discussed based on these results.