ION-TRANSPORT IN POLYPYRROLE AND A POLYPYRROLE POLYANION COMPOSITE

The ionic conductivities of polypyrrole poly(styrenesulfonate) (PPY/PSS) and polypyrrole perchlorate (PPY/ClO4-) films on electrodes have been measured in 0.2 M NaClO4(aq) as a function of oxidation level by impedance, spectroscopy. As the oxidation level is increased, the ionic conductivity of PPY/ClO4- increases, while that of PPY/PSS decreases. It is concluded that anion transport is primarily responsible for the ionic conductivity of PPY/ClO4-, while cation transport dominates in PPY/PSS. This difference in the mode of ion transport is reflected in cyclic voltammetry by differences in the scan rate dependence of peak potentials. In both cases, the voltammetric peak corresponding to insertion of the mobile ion into the films is most sensitive to increasing scan rate. The ionic conductivity of PPY/PSS is significantly higher than that of PPY/ClO4- at all potentials, indicating that Na+ in PPY/PSS is more mobile than ClO4- in PPY/ClO4-. The low mobility of ClO4- is attributed to ion pairing with oxidized polypyrrole sites. Evidence for this interpretation is provided by the impedance behavior of PPY/PSS in solutions containing methylviologen. The methylviologen dications become immobilized by the sulfonate groups in the film and inhibit cation transport during potential cycling. Oxidation of the polymer therefore involves ClO4- uptake and the potential dependence and magnitude of its ionic conductivity become characteristic of PPY/ClO4-.