Analytical Sciences

Abstract − Analytical Sciences, 18(6), 641 (2002).

Deviations of Capacitive and Inductive Loops in the Electrochemical Impedance of a Dissolving Iron Electrode
Masayuki ITAGAKI,* Akihiro TAYA,* Kunihiro WATANABE,* and Kazuhiko NODA**
*Department of Pure and Applied Chemistry, Faculty of Science and Technology, Tokyo University of Science, Noda, Chiba 278-8510, Japan
**Corrosion Research Group, National Institute for Materials Science, Sengen, Tsukuba, Ibaraki 305-0047, Japan
The electrochemical impedance of an iron electrode often shows the capacitive and inductive loops on the complex plane. The capacitive loop originates from the time constant of the charge transfer resistance and the electric double layer capacitance. The inductive loop is explained by Faradaic processes involving the reaction intermediate. In some cases, these loops deviate from a true semicircle. In this paper, the origins and curve-fitting methods for the deviated loops of electrochemical impedance are discussed. The constant phase element (CPE) was used to present the deviation of the capacitive loop instead of electric double layer capacitance. The reaction rate constants, which are a function of the frequency, are proposed for the Faradaic impedance to present the deviated inductive loop.