ROLE OF THE FORMATION POTENTIAL ON THE REDOX PROCESSES OF POLYPYRROLESTUDIED BY AN ELECTROCHEMICAL QUARTZ MICROBALANCE

Oxidation of pyrrole yields a charged polymer film with incorporated a nions. During the following reduction electroneutrality can be maintai ned by expulsion of these anions or by incorporation of cations. The c ontribution of both processes to the overall charge transport is found to depend strongly on the formation potential during polymerizatlon. The redox process of polypyrrole formed at 1.0 V vs. Ag/AgCl is accomp anied by a simultaneous mass transport of anions and cations, while a lower formation potential leads to a separation of the charge transpor t In an either anion or cation balanced region. These differences are related to a cathodically shifted first reduction which occurs if a lo w formation potential was used. The charge transfer at the electrode a nd at the polymer-solution interface is illustrated by a physical mode l. It consists of an (E)n - C - (E)m - mechanism for the redox behavio r of the polymer and a first-order reaction for counter-ion incorporta tion and co-ion expulsion respectively. Voltammograms and mass curves are presented for different situations.