Ion Movements during Redox Switching of Polypyrrole — Experiment and Simulation

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 polymerization. The redox process of polypyrrole formed at +1.0 V vs. Ag/AgCl is accompanied by a change in mass, which can be interpreted by a simultaneous transport of anions and cations. A lower formation potential leads to a separation of the charge transport in an either anion or cation dominated 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 incorporation and expulsion of ions. Computed voltammograms and mass curves are presented for different situations and compared to experimental conditions.