Electrochemical Impedance Study and Characteristics of Polyaniline Film Electrodes

Abstract

Abstract The ac response of polyaniline (PA) film electrodes in 0.5 M H2SO4 was investigated at different applied potentials and film thicknesses. The results of impedance analysis on the basis of the Randles equivalent circuit indicated that the electron exchange between metal and redox sites of the polymer controlled the rate of the charge transfer process at the film electrode. The oxidation of the PA film brought about a decrease in charge transfer resistance at lower potentials than the first half-wave potential of PA. The redox capacitance of the polymer indicated the dependence on the potential and film thickness, which was expected from a finite diffusion model. A large capacitance of the order of 3—30 mF cm−2 in the partially oxidized state is explained in terms of the charge saturation effect associated with the finite thickness. Impedance plots at high frequencies (the kHz range) suggested the occurrence of a hydrogen adsorption reaction in the reduced state. The PA film probably swells with the electrolyte. A counter ion to maintain the electroneutrality of the polymer can go into and out of the film with negligible resistance.