ELECTROCHEMICAL PROPERTIES OF POLYPYRROLE FILMS POLYMERIZED IN THE PRESENCE OF METHYLENE-BLUE

The electrochemical properties of polypyrrole (PPy) electropolymerized in 0.1 M KCl solution containing Methylene Blue (MB) are investigated. It is found that a large amount of Methylene Blue is incorporated in the film during the electropolymerization process, which indicates that the Methylene Blue cation plays a role in the film formation process. In strong acidic medium, two redox processes are observed in cyclic voltammograms of the film, corresponding to the redox couples of PPy and MB, respectively. The redox potential of the incorporated MB depends on the pH of the electrolyte solutions and a highly stable and reversible cyclic voltammogram is obtained at pH values lower than 2.0. In neutral or alkaline medium, the redox waves of MB are overlapped by the waves of PPy and the electrochemical behaviour of the film is similar to that of normal PPy films doped with chloride. However, a more pronounced relaxation behaviour of the film is obtained and a logarithmic law for the shifts of the anodic peak parameters as a function of waiting time in the insulating state is observed. Electrochemical impedance spectra clearly show two charge transfer processes in the film. The electroactivity of the polymer films is also investigated with respect to the ionic nature of the electrolytes. The results indicate that the redox process of MB is mediated by PPy and can only occur when PPy is in its oxidized state.