Permselectivity and thickness-dependent ion transport properties of overoxidized polyaniline: a mechanistic investigation

We report here the permselectivity of overoxidized polyaniline obtained using anodic polarization of polyaniline on glassy carbon electrodes. The contrasting redox behavior of overoxidized polyaniline coated electrodes towards [Fe(CN)(6)](3-) and [Ru(NH3)(6)](3+) has been analyzed using cyclic voltammetry, hydrodynamic voltammetry and electrochemical impedance spectroscopy. This permselectivity vis a vis anion exclusivity arises from the incorporation of counter anions rather than by the formation of new functional groups in the polymer upon overoxidation - as inferred from FT Raman and UV-Visible spectral data. The surface charges of the polymeric films are also deduced from the zeta potential analysis. The thickness-dependent anion exclusion behavior of overoxidized polyaniline is quantitatively interpreted using diffusion coefficient measurements with rotating disc electrodes. The mechanism pertaining to the non-trivial role of film thickness in influencing anion exclusion is confirmed by additional impedance spectroscopy carried out during the overoxidation of polyaniline.