Characterization of LSM–YSZ composite electrode by ac impedance spectroscopy

The characteristics of La1−xSrxMnO3 perovskite (LSM)–yttria-stabilized zirconia (YSZ) composite electrodes were studied over a range of compositions by ac impedance spectroscopy. The transfer and surface diffusion of oxygen ions were found to be rate-determining steps. The polarization resistance of oxygen ion transfer was found to be independent of the partial pressure of oxygen and proportional to the length of the three-phase boundary. The capacitance of oxygen ion transfer was approximately 10−4 F/cm2. The polarization resistance of O− surface diffusion was determined to be proportional to PO21/4, with a minimum at 40–50 wt.% YSZ. The polarization resistance of oxygen ion transfer was observed to remain largely unaffected by variations in cathodic potential, whereas that of O− surface diffusion decreased with increasing cathodic potential. At low partial oxygen pressure, the arc due to gas phase diffusion was observed in the low frequency region, with proportion to PO2 and having low activation energy.