OXIDATION-REDUCTION OF POLYPYRROLE FILMS - KINETICS, STRUCTURAL MODEL AND APPLICATIONS

Empirical kinetic parameters have been obtained in polypyrrole oxidation from potential steps experiments. The activation energy for the overall process has a value of 17 kJ mol-1 when the polypyrrole is oxidized at 300 mV versus SCE, 22 kJ mol-1 at 0 mV versus SCE and 44 kJ mol-1 at -300 mV. The reaction order for the active sites in the polypyrrole chains is 1, according to a solid-state reaction. The reaction order for the electrolyte concentration is independent of the applied potential and has a value near 0.6. On the other hand, the influence of the molecular entanglement opening of the polymeric film during the transition has been shown as a maximum in the chronoamperometric responses or as an induction time in the charge-time evolutions. This opening structure phenomenon was more important when the film was polarized at more negative potentials. At high cathodic limits the oxidation does not occur uniformly on the surface, but on singular points expanding on the surface.