ION MOVEMENTS DURING REDOX SWITCHING OF POLYPYRROLE - EXPERIMENT AND SIMULATION

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 polymerization. The redox process of polypyrrole formed at + 1.0 V vs. Ag/AgCl is acco mpanied by a change in mass, which can be interpreted by a simultaneou s transport of anions and cations. A lower formation potential leads t o a separation of the charge transport in an either anion or cation do minated region. These differences are related to a cathodically shifte d first reduction which occurs if a low formation potential was used. The charge transfer at the electrode and at the polymersolution interf ace 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 reac tion for incorporation and expulsion of ions. Computed voltammograms a nd mass curves are presented for different situations and compared to experimental conditions.