Enhanced ionic conductivity of polypyrrole due to incorporation of excess electrolyte during potential cycling

Abstract

The anomalous initial reduction peak in cyclic voltammograms of polypyrole in acetonitrile has been shown, by impedance spectroscopy and X-ray emission analysis, to be due to the uptake of cations. Reoxidation is accompanied by anion uptake. As a result of these two processes, polypyrrole that has been electrochemically cycled in acetonitrile contains a large non-equilibrium concentration (several mol dm^–3) of electrolyte and exhibits a greatly enhanced ionic conductivity. Contrary to a previous report, the ionic conductivity of (cycled) polypyrrole was found to be independent of the electrolyte solution concentration. At equilibrium, polypyrrole appears to be permselective in dilute acetonitrile and aqueous electrolyte solutions. Its ionic conductivity is much higher in water and is much less influenced by potential cycling. Electrolyte uptake during potential cycling in acetonitrile therefore appears to be due to poor solvation of the polymer and the consequent low mobility of its counterions.