Conditioning effects on La1−xSrxMnO3-yttria stabilized zirconia electrodes for thin-film solid oxide fuel cells

Composite cathodes of 50/50 vol.% La1−xSrxMnO3-yttria stabilized zirconia (LSM-YSZ) were deposited onto dense YSZ electrolytes by colloidal deposition technique. The cathode characteristics were then examined by scanning electron microscopy (SEM) and studied by ac impedance spectroscopy (IS). Conditioning effects of the LSM-YSZ cathodes were seen, and remedies for these effects were proposed for improving the performance of a solid oxide fuel cell (SOFC). LSM surface contamination and modification, cathode bonding to the YSZ electrolyte, changing Pt electrode and bonding paste, and curvature of sintered YSZ electrolytes led to some changes in microstructure and variability in cell performances. Much of the variability could be eliminated by using only one batch of Pt paste, using flat and sanded YSZ plates as well as consistent processing procedures. Reproducible impedance spectra were obtained by using the improved cell configurations. Typical IS spectra measured for an (air) LSM-YSZ/YSZ/LSM-YSZ (air) cell at 900 °C showed two depressed arcs. The impedance characteristics of the LSM-YSZ cathodes were also affected by experimental conditions such as surface modification of the LSM by Ni or Sr, cathode compositions and applied current.