Fitting EIS Data to Equivalent Circuits

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Although the equivalent circuit approach is looked down upon by some, analyzing EIS data by fitting it to equivalent circuit models can be a valid and rewarding approach, particularly in the early stages of an investigation.

When you first begin an electrochemical investigation, very often you may know little or nothing about the process or mechanism you are studying. Electrochemical Impedance Spectroscopy (EIS) can be a very useful tool to help you formulate a hypothesis, particularly when EIS data is fit to equivalent circuit models. Often, an equivalent circuit model which fits the data will suggest some chemical model, process, or mechanism which can be proposed and tested. EIS data and the equivalent circuit model provide a useful tool to help you think about your electrochemical problem.

However, the relative ease with which impedance data can be acquired and analyzed today makes it all together too easy to just take some data, fit it to a simple equivalent circuit model, and then keep adding components to the circuit until you have a perfect fit.

What guidelines are there for how many circuit components you should use? When should you keep the model you have rather than add one more circuit element? What sort of circuit models should you consider?

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