Distortions in electrochemical impedance spectroscopy measurements using 3-electrode methods in SOFC. II. Effect of electrode activity and relaxation times

The 3-electrode configuration is commonly applied to quantify the overpotential of anodes or cathodes in solid-oxide fuel cells (SOFC). In this type of set-up, a reference electrode (RE) is used to isolate the potential loss of one electrode from that of the entire cell; however, erroneous results can be obtained whenever the RE does not precisely separate the potential drop between the two active electrodes. In this study, we present the results of a theoretical and experimental analysis focused on verifying the effectiveness of the 3-electrode configuration in electrochemical impedance spectroscopy measurements for the kinetic characterisation of SOFC electrode reactions. The focus of this paper is on the distortion of impedance measurements caused by differences in the area-specific polarisation resistance and impedance time constants of the working and counter electrodes. The results obtained numerically and experimentally, both for planar and tubular SOFC cell geometries, prove the reliability of the theoretical model used. From the systematic simulation presented here and in our previous work, it was possible to formulate general guidelines for the design of 3-electrode experimental SCIFC. The theoretical model used here can also be used to verify the consistency of EIS measurements obtained with thin planar cells.