Time domain diffusion parameters identification of electrochemical impedance models using fractional order system

Abstract In this paper, identification of the diffusion impedance parameters of an electrochemical cell in time domain is presented. As Electrochemical Impedance Spectroscopy (EIS) requires long time to obtain experimental data for low frequencies, a method using chronopotentiometric experiments is studied in order to reach more quickly diffusion parameters. The electrochemical cell is modeled using an equivalent electrical circuit describing separately the charge transfer and the diffusion phenomena. The electrochemical model provides then a transfer function whose parameters can be identified only in the frequency domain. Thus, thanks to a fractional operator approximation, a half order integrator is able to perform simulations in the time domain. Therefore, a fractional model is proposed in order to identify the slow dynamics due to diffusion thanks to the Levenberg-Marquardt algorithm. Experimental results obtained from an electrochemical test-bench including Ferri-Ferro solution demonstrate the interest of fractional modeling. Diffusion parameters are identified in the time domain and cross-validation in the frequency domain using EIS measurements demonstrates the relevance of the proposed method.