Non - Linear Electrochemical Impedance Spectroscopic Analysis of Instabilities in Electrochemical Systems

摘要

This work presents nonlinear electrochemical impedance spectra (NLEIS) analysis of an unstable system - in the kinetics and diffusion - controlled regime. The classical Fe~(2+)/Fe~(3+) redox couple is chosen for experimental and numerical analyses. A setup was established to acquire NLEIS data with the help of an in-house developed software. The applied perturbation frequency was varied from ～100 kHz to 125 mHz with different amplitude of perturbation. System instabilities were introduced by continuously changing the dc potential or by changing the active species concentration, during the NLEIS measurements. The governing equations were solved without linearization, using numerical methods. The impedance data were subjected to Kramers Kronig transform (KKT) and the results show that KKT successfully flags the violation of stability condition. The NLEIS results show that, in the high frequency domain, the effect of instabilities manifested more clearly at higher harmonic currents than at the fundamental.