Data Analysis and Physical Model of Electrochemical Impedance Spectroscopy for Corrosion Systems: Progresses and Challenges

Electrochemical impedance spectroscopy (EIS) is one of the most important methods for studying the electrochemical corrosion behavior and failure mechanisms of metallic materials and their coating systems. With the development of corrosion electrochemistry theory, numerical calculation, and corresponding fitting software, significant progress has been made in the analysis of EIS data. Through data fitting and analysis, key parameters such as the thickness of the passive film, the resistivity distribution of the passive film, and the resistivity distribution of the coating can be obtained. When the passive film breaks down, the expression of the Faraday impedance Z_F can be derived through the kinetic model, correspondingly, the parameters such as the rate constants of each electrode reaction and the thickness of the diffusion layer can be analyzed. Taking passive metals and their organic coating systems as exam ples, this paper reviews the applications of the electrochemical equivalent circuit model (ECM), the point defect model (PDM), the electrochemical kinetic model, the power-law model (PLM), and the Young model in analyzing the properties of oxide films, the performance of coatings, and the kinetic parameters of electrode processes. Moreover, the advantages and disadvantages of each method are discussed. Finally, the development trends of EIS data analysis and physical models are pointed out.