Polypyrrole-Montmorillonite Nanocomposite: A Composite Fast Ion Conductor

Abstract

Cu(II)-exchanged montmorillonite [Cu(II)-MMT] takes up pyrrolium ions by ion exchange. Two pyrrolium ions are inserted for each Cu(II) ion expelled from its interlayers. These pyrrolium ions undergo spontaneous polymerization because of the remaining Cu(II) ions present within the intergalleries to form Cu(I)-polypyrrole-MMT nanocomposite. The polypyrrole (PPY) dispels any water already present within the intergalleries and the material becomes hydrophobic and reluctant to take up water. The inherent d-spacing due to anhydrous PPY present within the intergalleries is 16.0 A, which is a 6.4 A enhancement from the situation, which contains a bare inorganic ion. The material possesses unusually high mixed electrical conductivity. The conjugation length (and hence the electronic conductivity) decreases as the temperature is increased as confirmed by the Fourier transform infrared spectroscopy. However, the ionic component of the conductivity increases with temperature. The temperature dependence of conductivity shows Arrhenius behavior but two different activation regions are clearly visible. The activation energy for Cu(I) migration within the nanocomposite is much lower than 100 C (Ea1/4 0.09 eV). At the higher temperature region, the activation energy is 0.23 eV and this value is also comparatively low suggesting the favorable motion of Cu(I) ions within the PPY-MMT nanocomposite thus making it a fast Cu(I) ion conductor. The ionic conductivities are in the range 0.66-1.15 mS cm 1 in the temperature range from 25 to 120 C.