The electrochemical impedance behaviour of heterogeneous or/and rough electrodes has usually been associated with some geometrical parameters of the surface structure or to a statistical description of the surface properties. An experimental method for sample preparation of graphite + polyethylene composite electrodes based on plasma etching is proposed. After plasma etching, the statistical properties of the electrode, such as the graphite particle size distribution and fractional coverage are measured from scanning electron microscopy pictures using image processing software. The statistical information obtained for the surface is combined with impedance equations of independent microelectrodes to evaluate the electrochemical behaviour of the composite electrode. An impedance expression considering a log-normal particle size distribution has been obtained and its asymptotic behaviour has been demonstrated. Impedance measurements show Warburg-like behaviour in contrast with the model developed. The interaction between diffusion fields of neighbouring particles is discussed.