Coupling of ion and electron transport during impedance measurements on a conducting polymer with similar ionic and electronic conductivities

Abstract

The ionic and electronic conductivities of poly-[1-methyl-3-(pyrrol-1-ylmethyl)pyridinium perchlorate] have been measured as a function of potential in various solvents by impedance spectroscopy. The ionic conductivity of this polymer shows a strong solvent dependence, ranging from 0.31 mS cm^–1 in water to 8.0 µS cm^–1 in propylene carbonate. By changing the solvent and the potential, the ionic to electronic conductivity ratio for the polymer has been varied from 1 to 1, allowing a thorough exploration of the validity of a dual resistance transmission line model of the polymer. Overall, the experimental results support the model, and reasonably accurate electronic and ionic conductivities are obtained when data are analysed according to the model. However, an anomalous dependence of ionic conductivity on oxidation state has been observed. There appears to be a direct relationship between the electronic and ionic conductivities of the polymer when they are of similar magnitude, indicating a coupling of ion and electron transport.