Electrode reaction of Sr1−xLaxCo0.8Fe0.2O3−δ with x = 0.1 and 0.6 on Ce0.9Gd0.1O1.95 at 600 ≤ T ≤ 800 °C

The electrode reaction of the perovskite phases Sr1−xLaxCo0.8Fe0.2O3−δ (x = 0.1 and 0.6) on Ce0.9Gd0.1O1.95 has been investigated by impedance spectroscopy in the temperature range 600 ≤ T ≤ 800 °C. Thick porous electrodes (t ∼ 20 μm) were sprayed on Ce0.9Gd0.1O1.95 and ac impedance spectra were recorded on symmetrical cells at the equilibrium. The analysis of the complex impedance diagrams clearly indicates the presence of two contributions. The low frequency one was assigned to the gas phase oxygen diffusion through the porous electrode and a finite length diffusion (Warburg) impedance was used to describe the high frequency (HF) data. The polarization resistance of the HF impedance contribution (Rw) is higher for x = 0.1 while the activation energy of Rw is higher for x = 0.6. The variations of Rw versus the La content, temperature and thickness indicate that the Warburg-type impedance contains information of both bulk oxygen diffusion and surface processes.