Effect of the Ionic Conductivity of the Electrolyte in Composite SOFC Cathodes

Solid oxide fuel cell (SOFC) cathodes were prepared by infiltration of 35 wt % La_0.8Sr_0.2FeO₃ (LSF) into porous scaffolds of three, zirconia-based electrolytes in order to determine the effect of the ionic conductivity of the electrolyte material on cathode impedances. The electrolyte scaffolds were 10 mol % Sc₂O₃-stabilized zirconia (ScSZ), 8 mol % Y₂O₃-stabilized zirconia (YSZ), and 3 mol % Y₂O₃- 20 mol % Al₂O₃-doped zirconia (YAZ), prepared by tape casting with graphite pore formers. Each electrolyte scaffold was 65% porous, with identical pore structures as determined by scanning electron microscopy (SEM). Both symmetric cells and fuel cells were prepared and tested between 873 and 1073 K, using LSF composites that had been calcined to 1123 or 1373 K. Literature values for the electrolyte conductivities were confirmed using the ohmic losses from the impedance spectra. The electrode impedances decreased with increasing electrolyte conductivity, with the dependence being between to the power of 0.5 and 1.0, depending on the operating temperature and LSF calcination temperature.