Combined Equivalent Circuits and Distribution of Relaxation Times Analysis and Interfacial Effects of (La0.60Sr0.40)0.95Co0.20Fe0.80O3-Xcathodes

In this work, symmetrical cells with a commercial (La0.60Sr0.40)0.95Co0.20Fe0.80O3-x, (LSCF) cathode and electrolyte have been fabricated and studied using a combination of complex non-linear least square fitting (CNLS), distribution of relaxation times (DRT), and high resolution SEM/EDS techniques. The cathode has been fired at different temperatures from 1050 °C to 1125 °C at 25 °C intervals. Electrochemical impedance spectroscopy (EIS) data indicate that at 1050 °C interfacial ionic resistances are dominant while chemical diffusion plays a larger role between 1075 °C and 1100 °C. At 1125 °C the cathode has over densified affecting both interfacial and diffusion resistances. Both CNLS and DRT have been used to identify the electrochemical processes; however, the resistance values obtained for the two methods are different in some cases. This problem is exacerbated when inductance is present in the data especially for resistance and constant phase elements equivalent circuits. In this case, CNLS analysis can give back the same values used for the simulation, while the DRT approach cannot produce the same values with negligible differences. SEM/EDS chemical maps show that no chemical interactions have occurred at the highest sintering step, reaffirming that gadolinium doped ceria (GDC) is a good barrier layer when fully dense.