ON THE APPLICABILITY OF A CONSTANT PHASE ELEMENT (CPE) TO THE ESTIMATION OF ROUGHNESS OF SOLID METAL-ELECTRODES

The dispersive behaviour observed at rough electrodes can be described by a constant phase element (CPE) of the form Z(ω) = K(jω)-α, where α has a value between 0·5 (porous electrodes) and unity (ideally flat electrodes). It is shown experimentally, that α unequivocally reflects the roughness of solid electrodes and is independent of the electrode material. Using the concept of fractal geometry the parameter α, often denoted only as a fit parameter, is characterized as a purely geometric size. If the rough surface has self-similar scaling characteristics, the CPE is directly related to the so-called fractal dimension D and therefore α can be understood as a measure of microscopic irregularities. © 1990.