Nonlinear Electrochemical Impedance Spectroscopy as a Novel Approach to Identify an Electrochemical Reaction Mechanism at Electrode-Electrolyte Interface

The ability of the nonlinear electrochemical impedance spectroscopy (NLEIS) technique to differentiate the reaction mechanisms was investigated. Cu electrodeposition from acidic CuSO4 solution is considered as a case study. NLEIS response, i.e., the signal at fundamental and higher harmonics, was recorded using a custom-built experimental setup. A numerical framework is proposed to calculate the polarisation and NLEIS response of a reaction mechanism while incorporating both kinetics and mass transfer effects. Three candidate reaction mechanisms with adsorbed intermediates were evaluated to model the Cu electrodeposition process. A comparison of the model predicted, and experimental results show that higher harmonic response along with fundamental data can be used for better model discrimination and identify the exact reaction mechanism at the interface of an electrochemical system.