Charge transport in polypyrrole-based conducting polymers

Ren, Xiaoming (1993) Charge transport in polypyrrole-based conducting polymers. Doctoral (PhD) thesis, Memorial University of Newfoundland.

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Abstract

Impedance spectroscopy has been used to study polypyrrole/perchlorate (PPY/CIO₄), PPY/poly(styrene sulphonate) (PPY/PSS), poly-(3-methyl-pyrrole-4-carboxylic acid) (poly-MPCA), poly-[1-methyl-3-(pyrrol-1-ylmethyl)pyridinium] (poly-MPMP), bilayers of PPY/CIO₄ and PPY/PSS, and polypyrrole formed in mixed perchlorate and poly(styrene sulphonate) (PPY/CIO₄ +PSS) polymer films coated Pt electrodes in electrolyte solutions. All impedance responses can be modelled with a porous electrode theory to extract reliable electronic and ionic conductivities, which agree with the results of other independent measurements. -- The impedances of PPY/CIO₄ and PPY/PSS reveal dominant anion and cation transport, respectively, in these polymers. A strong interaction between the anions and the positive charges on the oxidized polypyrrole chains hinders anion movement in PPY/CIO₄. Absence of such an interaction for the mobile cations in PPY/PSS gives this polymer a ca. 20 times higher ionic conductivity than PPY/CIO₄. -- Deviation from the ideal model impedance response occurs for poly-MPCA because of its non-uniform structure. Mixed ion conduction can cause another type of deviation as shown by the impedance of PPY/CIO₄ +PSS polymers and the simulated data. High frequency data for reduced films of PPY/PSS and poly-MPCA form a semicircle in the complex impedance plane. This semicircle is attributed to electron transfer at the Pt/polymer interface for PPY/PSS but ion transfer at the polymer/solution interface for poly-MPCA. -- The impedances of the PPY/CIO₄ and PPY/PSS bilayer films show that the location of the initial reaction induced by a potential perturbation for a highly conducting PPY film coated electrode is at the polymer/solution interface. The impedances of poly-MPMP and PPY/PSS show that the location of the initial reaction depends on the relative magnitudes of the film's electronic and ionic conductivities, as theoretically predicted. -- Ionic conductivity measurements were used to probe polymer structure. Films of PPY/CIO₄, PPY/PSS and poly-MPCA all have a two phase structure, a polymer phase and a pore solution phase. Ionic conduction in the polymer phase occurs mainly through the movement of mobile counterions via an ion-exchanging process, while in the pore solution phase migration of both electrolyte cations and anions contributes to conduction.

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