Impedance analysis of oxygen reduction in SOFC composite electrodes

The electrochemistry of oxygen reduction on porous composite electrodes consisting of La(1-x)SrxMnO(3-delta) (LSM) and Y-stabilised zirconia (YSZ) has been analyzed for better understanding of the mechanism of oxygen reduction and improvement of the cathode's performance. Half cells consisting of YSZ electrolyte pellets and slurry coated cathodes were tested with a three electrodes configuration. The composite cathodes considered in this study have a fixed volume ratio LSM/YSZ equal to 1 and variable apparent surfaces, ranging from 0.022 to 0.23 cm2. The dependence of electrode resistance on size indicates that the process takes place in the bulk of the cathodes. Part of the impedance data is additionally analyzed by the technique of the Differential Impedance Analysis (DIA), which does not need a preliminary working hypothesis. The application of DIA gives additional information about the dominant phenomena, based on comparative study of the cathode behavior of LSM and of the composite materials.