Some features of the overoxidation of polypyrrole synthesized on austenitic stainless steel electrodes in aqueous nitrate solutions

The overoxidation of polypyrrole (Ppy) films in aqueous nitrate solutions is studied via cyclic voltammetry and in situ spectroelectrochemical measurements. During the potentiodynamic growth of Ppy on austenitic stainless steel electrodes, the onset of overoxidation is observed at 1.3 V saturated calomel electrode (SCE). Voltammograms of the films obtained near and far from the threshold of overoxidation show remarkable differences. For the former, a nucleation loop in the first scan and, a current decrease during successive cycles, are observed. The voltammetric response of Ppy synthesized at less positive potentials shows a rise in the current with the number of scans without trace crossing. Several voltammetric experiments confirm the irreversibility of polymer overoxidation. Absorption spectra at different potentials and, transmittance (%T) change at different wavelengths as a function of potential, are presented for non-overoxidized and overoxidized Ppy. Some differences in %T versus potential are found. (C) 2004 Elsevier B.V. All rights reserved.