Polypyrrole and poly N-methylpyrrole — An electrochemical study in an aqueous medium

Polypyrrole (PP) and poly N-methylpyrrole (PMP) synthesized in acetonitrile solution containing 0.2 M LiClO₄ have been studied in an aqueous medium at different pH values by potentiometry at zero current, double pulse imposed current methods and cyclic voltammetry. The last was also used to determine the stability range. We observed from potential-pH measurements that PP has fairly good resistance towards sulphuric acid up to 4 M and shows less resistance towards strong basic media above pH 12. Cyclic voltammetry studies show that PP is more easily degraded at potentials greater than 1 V than in the less noble potential range. In the pH range studied, PP exchanges one proton for each electron. PP can exist in at least six forms and the exchange of the protons can precede or follow the electron exchange: two of these forms of PP can exist in oxidized and reduced forms without any counter anion.PMP presents a better stability from the electrochemical point of view, especially in a basic medium. Between pH 1 and pH 9.5 it exchanges only one proton for two electrons and above pH 9.5 two protons for one electron.