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

Oxidation of pyrrole yields a charged polymer film with incorporated anions. During the following reduction electroneutrality can be maintained by expulsion of these anions or by incorporation of cations. The contribution 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 accompanied by a simultaneous mass transport of anions and cations, while a lower formation potential leads to a separation of the charge transport In an either anion or cation balanced region. These differences are related to a cathodically shifted first reduction which occurs if a low formation potential was used. The charge transfer at the electrode and at the polymer-solution interface is illustrated by a physical model. It consists of an (E)n - C - (E)m - mechanism for the redox behavior of the polymer and a first-order reaction for counter-ion incorportation and co-ion expulsion respectively. Voltammograms and mass curves are presented for different situations.