Lasia A. Electrochemical Impedance Spectroscopy and its Applications

In: 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.