The influence of main geometric parameters of the micro-capillary electrochemical cell such as the capillary diameter and the position of the counter electrode inside the capillary was analysed. For this purpose, Local Electrochemical Impedance Spectroscopy (LEIS) was performed to investigate the corrosion of copper electrode in a dilute sodium chloride aqueous solution using the electrochemical microcell technique. A linear diffusion through a finite diffusion layer was evidenced by LEIS spectra. These experimental data were confronted with digital simulations. It was shown that the diffusion process is taking place through the copper chloride layer on the surface. The capillary diameter and the distance between the counter and the working electrodes are affecting both the thickness and the porosity of the diffusion layer.