A Dispersion-Invariant Model of the Electrochemical Impedance

The evaluation of Electrochemical Impedance Spectroscopy (EIS) data and, in particular, the determination of such key parameters as the polarization resistance and the double layer capacitance are essentially complicated by two factors: (i) the ambiguities of the Electrical Equivalence Circuits (EEC), especially in the low frequency range and (ii) the frequency dispersion of the circuit parameters. These phenomena are typically interpreted by means of the Constant Phase Element. In an alternative model we assumed that the impedance of the electrochemical interface could be separated into a Voigt circuit carrying the 'ideal' behaviour of the polarization resistance and the electrochemical double layer and into a series of Maxwell circuits, connected parallel to the #ideal# elements, carrying all additional effects related to the specific EEC and the dispersion of the kinetic parameters. This model resulted in a linear separation of the #ideal# kinetic parameters from the additional effects. The obtained formulae were tested experimentally against soluble redox and corrosion systems showing features that could not be interpreted in terms of the conventional concept of the EEC. The results verified that the new functions were capable of a close approximation of the polarization resistance and the double layer capacitance from the higher frequency EIS data only and also provided the density functions of the dispersion parameters. (c) 2021 The Author(s). Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license ( http://creativecommons.org/licenses/by-nc-nd/4.0/ )