Electrochemical Impedance Spectroscopy is a powerful technique for the assessment of the behaviour of a metal/environment system and the reaction mechanisms involved.
There are two distinct ways to approach the analysis of EIS results: in the first one, a purely analytical treatment of impedance is done, normally involving highly complex mathematical models which are based on the kinetics of the heterogeneous reactions involved, whereas the second way, which is also the most common approach for EIS data analysis, makes use of the ’equivalent circuit’ concept.
In principle, any electrode/electrolyte interface may be represented by an electrical model and that allows to characterize an electrochemical system through a physically reasonable electrical circuit (the equivalent circuit) that shows the same response. This equivalent circuit should allow to separate the contributions of the different processes and to quantify the parameters relative to each one of them.
As the use of EIS is spreading and the fitting software becomes more user-friendly, inexperienced users tend to accept any circuit that fits the data, no matter the meaning of its elements. Thus, the equivalent circuits presented in the literature often lack a physical meaning.
This lecture will focus the above topics, showing some of the basic rules that must be followed when choosing an equivalent circuit, and will be illustrated by some examples.
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