Fractal dimension of the active zone for a p-doped poly(3,4-ethylenedioxythiophene) modified electrode towards a ferrocene probe

The electrochemical properties of p-doped poly(3,4-ethylenedioxythiophene) (PEDOT) modified electrodes obtained by anodic electrooxidation of 3,4-ethylenedioxythiophene on a platinum electrode have been studied. The heterogeneous electron transfer concerning the oxidation of the ferrocene occurs at the p-doped PEDOT film ∣ solution interface. Because of the interface heterogeneity, an anomalous diffusion is observed and the kinetics of the electron transfer during the oxidation of the ferrocene have been examined in terms of the fractal concept. A reaction dimension or an active zone that is defined as the operative fractal dimension is determined by means of rotating disk electrode measurements. A functional equation corresponding to the limiting current density at different rotating rates is given. A fractal dimension of random walk dw of 1.80 is obtained. A representative plot that allows us to normalize the measured current density with respect to the anomalous diffusion is proposed. In acetonitrile, the oxidized heavy p-doped PEDOT film may be viewed as an amorphous organic metal which induces an anomalous diffusion process in its vicinity for diffusion—convection limited reactions.