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Description

EIS data are generally analyzed in terms of an equivalent-circuit model. The analyst tries to find a model whose impedance matches the measured data.

 

The type of electrical components in the model and their interconnections controls the shape of the model's impedance spectrum. The model's parameters (i.e., the resistance value of a resistor) controls the size of each feature in the spectrum. Both these factors affect the degree to which the model's impedance spectrum matches a measured EIS spectrum. Some knowledge of the impedance of the standard circuit components is therefore quite useful. The following table lists the common circuit elements, the relevant equation relating current to voltage, and their impedance.

 

 

In a physical model, each of the model's components is postulated to come from a physical process in the electrochemical cell. All of the models discussed earlier in this section are physical models. The choice of which physical model applies to a given cell is made from knowledge of the cell's physical characteristics. Experienced EIS analysts use the shape of a cell's EIS spectrum to help choose among possible physical models for that cell.

 

Models can also be partially or completely empirical. The circuit components in this type of model are not assigned to physical processes in the cell. The model is chosen to give the best possible match between the model's impedance and the measured impedance. An empirical model can be constructed by successively subtracting component impedances from a spectrum. If the subtraction of an impedance simplifies the spectrum, the component is added to the model, and the next component impedance is subtracted from the simplified spectrum. This process ends when the spectrum is completely gone (Z = 0).

 

As we shall see, physical models are generally preferable to empirical models.

 

Literature

The following sources were used in preparing the information in these help topics. We encourage you to consult them for additional information:

 

1.E. Barsoukov and J.R. Macdonald, Impedance Spectroscopy: Theory, Experiment, and Applications, 2nd Ed., Wiley Interscience Publications, 2005.

2.A.J. Bard and L.R. Faulkner, Electrochemical Methods: Fundamentals and Applications, 2nd Ed., Wiley Interscience Publications, 2000.

3.J.R. Scully, D.C. Silverman, and M.W. Kendig, editors, Electrochemical Impedance: Analysis and Interpretation, ASTM, 1993.

4.P.W. Atkins, Physical Chemistry, Oxford University Press ,1990.

5.A.V. Oppenheim and A.S. Willsky, Signals and Systems, Prentice-Hall, 1983.

6.J.A.L. Dobbelaar, The Use of Impedance Measurements in Corrosion Research: The Corrosion Behavior of Chromium and Iron Chromium Alloys, PhD thesis TU-Delft, 1990.

7.F. Geenen, Characterization of Organic Coatings with Impedance Measurements: A Study of Coating Structure, Adhesion and Underfilm Corrosion, PhD thesis, TU-Delft, 1990.

8.C. Gabrielle, Identification of Electrochemical Processes by Frequency Response Analysis, Solartron Instrumentation Group, 1980.

9.M. Sluyters-Rehbach, J.H. Sluyters, in Comprehensive Treatise of Electrochemistry, Volume 9, Plenum Press, 1984.

10.F. Mansfeld, Electrochemical Impedance Spectroscopy (EIS) as a New Tool for Investigation Methods of Corrosion Protection, Electrochimica Acta 35(10), pp. 1533–1544, 1990.

11.G.W. Walter, A Review of Impedance Plot Methods Used for Corrosion Performance Analysis of Painted Metals, Corrosion Science 26(9), pp. 681–703, 1986.

12.M. Kendig and J. Scully, Basic Aspects of Electrochemical Impedance Application for the Life Prediction of Organic Coatings on Metals, Corrosion(1) 1990 , p. 22.