Application of Impedance Spectroscopy to Electrochemical Instabilities

Abstract

The application of electrochemical impedance spectroscopy (EIS) to the analysis of stability of electrochemical systems, as a variant of linear stability analysis, is described. Practical problems with impedance measurements close to the bifurcation points are discussed. The crucial diagnosis of a Hopf and a saddle-node bifurcations from impedance spectra of the systems exhibiting negative differential resistance (NDR), under both potentiostatic and galvanostatic conditions, is described. The systems characterized with the explicit N-NDR region under dc conditions and with the hidden negative resistance under such conditions (HN-NDR type oscillators) are discussed in more detail. For the HN-NDR systems, several models producing this type of characteristics, which involve adsorption of electroactive or electroinactive (inhibitory) species, are described, including the impedance characteristics of such processes. The modern classification of electrochemical oscillators, based on impedance spectra, is given. For selected model systems, in which instabilities are related to strong adsorption on electrodes, described in terms of the Frumkin isotherm, their impedance responses are discussed in more detail. For the sake of generalization, the advantages of zero–pole representation of impedance for stability analysis are shown. Application of dynamic electrochemical impedance spectroscopy (DEIS) to the analysis of non-steady states is outlined. Finally, the recent development of the interpretation of impedance spectra for the patterned electrode states is mentioned.