Ion transport in pyrrole-based polymer films

Abstract

Ionic resistivities and counterion diffusion coefficients for polypyrrole, poly-[1-methyl-3-(pyrrol-1-ylmethyl)pyridinium](poly-MPMP⁺) and pyrrole_x-[Ru(2,2′-bipyridine)₂(3-(pyrrol-1-ylmethyl) pyridine)Cl]⁺ copolymer films have been obtained by chronoamperometry using the single-pore model. For poly-MPMP⁺ both the electronic resistivity and the ionic resistivity can be simultaneously determined. Finite-difference simulations have been used to confirm the validity of the equations used and to extend the applicability of the model.

Counterion diffusion coefficients in polypyrrole and poly-MPMP⁺ have also been determined by rotating-disc voltammetry and d.c. conductivity measurements. Where possible the results have been confirmed by the use of two independent methods. Diffusion coefficients for I^–, Cl^–, ClO₄^– and Fe(CN)₆^4– in the above polymers in water and/or acetonitrile are compared and discussed. It is concluded that: (a) polypyrrole and poly-MPMP⁺ are solvated and swollen to a much greater extent in water than in acetonitrile, (b) permanent cationic sites increase the permeability of polypyrrole in water but not in acetonitrile and (c) the permeability of polypyrrole in acetonitrile can be increased by the incorporation of bulky metal complexes.