Comparison between the experimental and theoretical electrochemical impedance for microcrystalline and nanocrystalline copper immersed in near neutral chloride solution

The electrochemical impedance of an electrode is one of the important characteristics of materials surface. This work aims to study the corrosion resistance of microcrystalline and nanocrystalline copper using electrochemical impedance spectroscopy (EIS); plus, a mathematical model was developed to investigate the diffusion process in the chloride solution. The obtained impedances by the mathematical model were in agreement with the experimental data trend. Furthermore, the electrochemical impedance ratio between theoretical and experimental impedance for microcrystalline and nanocrystalline copper was 0.8 and 0.76, respectively. Assuming only diffusion term in the theoretical model, appropriate solution of electrochemical behaviour in the corrosive solution was obtained. In addition, electrochemical impedance obtained for the nanocrystalline copper was higher than its microcrystalline counterpart. It was related to the higher adsorption of grain boundaries in the nanocrystalline state. Adsorption of ions could hinder the charge transfer mechanism and therefore the corrosion rate becomes lower than the microcrystalline state.