NUMERICAL-STUDIES OF THE IMPEDANCE OF BLOCKING ELECTRODES WITH FRACTAL SURFACES

We study how fractal roughness on inert electrode surface affects the ac impedance of electrochemical cells. Using Koch curves to represent the electrode surface in two dimensions, we analyze the diffusion and migration of ions in an ac field from first principles. We find that, although fractal roughness leads to a constant-phase-angle (CPA) impedance, it is both outside the experimental frequency range and masked by the bulk relaxation of the electrolyte. This result rules out previous attempts to explain the CPA impedance in terms of transport processes. We suggest that ion adsorption and/or desorption on the surface is the most likely explanation.