Study on the Role of the Morphology of SOFC Cathodes

The role of the morphology of strontium doped lanthanum manganite (LSM) and LSM/yttria stabilized zirconia (YSZ) composite electrodes was studied by using DC polarization measurement and impedance spectroscopy. Different electrodes were tested: single pure LSM with small porosity layer, porous LSM layer over pure LSM layer and LSM-YSZ composite (50wt% YSZ) with a porous LSM layer. Electrochemical properties of these structures were investigated as a function of temperature. Impedance diagrams show that the electrode reaction of pure LSM electrodes could be related to a high frequency contribution attributed to a charge transfer between LSM and YSZ and a low frequency one semicircle related to an oxygen adsorption step. The impedance response of the electrode based on a LSM-YSZ composite could be related to only the high frequency contribution. No electrochemical activation was evidenced in this case. Maximum current density was around -0.1 A.cm-2 for a cathodic overpotential equal to -0.1 V.