Review of mechanistic analysis by electrochemical impedance spectroscopy

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The use of electrochemical impedance spectroscopy (EIS) for mechanistic analysis is briefly reviewed with particular emphasis on the mathematical techniques that may be used to derive theoretical impedance functions and to extract kinetic data. The advantages of EIS for kinetic and mechanism analysis include the fact that it is a steady-state technique, that it employs small signal analysis, and that it is capable of probing relaxations over a very wide frequency range (from <1 mHz to ⪢1 MHz) using readily available instrumentation. EIS also has an enormous advantage over classical transient techniques in that the validity of the data is readily checked using the Kramers—Kronig transforms. The principal disadvantage of the method is that many workers are discouraged by the level of mathematics required to properly analyze impedance data. This has led many researchers to analyze their data in terms of simple equivalent electrical circuits, and hence to ignore the great power of EIS for deriving mechanistic and kinetic information for processes that occur at electrochemical interfaces.