Electrochemical Impedance Spectroscopy and its Applications

What is it about?

Modern Aspects of Electrochemistry, B. E. Conway, J. Bockris, and R.E. White, Edts., Kluwer Academic/Plenum Publishers, New York, 1999, Vol. 32, p. 143-248. Electrochemical Impedance Spectroscopy (EIS) or ac impedance methods have seen tremendous increase in popularity in recent years. Initially applied to the determination of the double-layer capacitance1-4 and in ac polarography,5-7 they are now applied to the characterization of electrode processes and complex interfaces. EIS studies the system response to the application of a periodic small amplitude ac signal. These measurements are carried out at different ac frequencies and, thus, the name impedance spectroscopy was later adopted. Analysis of the system response contains information about the interface, its structure and reactions taking place there. EIS is now described in the general books on electrochemistry,8-17 specific books18,19 on EIS, and there are also numerous articles and reviews.6,20-31 It became very popular in the research and applied chemistry. The Chemical Abstract database shows ~1,500 citations per year of the term "impedance" since 1993 and ~1,200 in earlier years and ~500 citations per year of "electrochemical impedance". Although the term "impedance" may include also nonelectrochemical measurements and "electrochemical impedance" may not include all the electrochemical studies, the popularity of this technique cannot be denied. However, EIS is a very sensitive technique and it must be used with great care. Besides, it is not always well understood. This may be connected with the fact that existing reviews on EIS are very often difficult to understand by non-specialists and, frequently, they do not show the complete mathematical developments of equations connecting the impedance with the physico-chemical parameters. It should be stressed that EIS cannot give all the answers. It is a complementary technique and other methods must also be used to elucidate the interfacial processes. The purpose of this review is to fill this gap by presenting a modern and relatively complete review of the subject of electrochemical impedance spectroscopy, containing mathematical development of the fundamental equations.

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