The performance of composite electrodes as a function of the electrode composition is investigated experimentally through electrochemical impedance spectroscopy (EIS). In particular, two different composite cathodes are analysed, i.e. Pt/YSZ and LSM/YSZ. Typical impedance spectra have been obtained and used to evaluate the overall electrode polarisation resistance Rp. The qualitative features are similar for both cathodes; in particular, in both cases the electrode performance (expressed in terms of Rp?1) shows a dome-shaped curve as a function of the electrode composition. Nevertheless, the quantitative aspects are very different; in particular, the maximum value of Rp?1 is much higher for the LSM/YSZ electrode than for the Pt/YSZ one (22 vs. 1.5 S cm?2). Also, the composition which gives the maximum performance and the experimental values of the percolation thresholds are different. The reasons for the discrepancies are analysed and discussed.
