INSITU MEASUREMENT OF THE CONDUCTIVITY OF POLYPYRROLE AND POLY[1-METHYL-3-(PYRROL-1-YLMETHYL)PYRIDINIUM]+ AS A FUNCTION OF POTENTIAL BY MEDIATED VOLTAMMETRY - REDOX CONDUCTION OR ELECTRONIC CONDUCTION

The electronic conductivity of polypyrrole and poly[1-methyl-3-(pyrrol-1-ylmethyl)pyridinium]+ (poly-MPMP+) films has been investigated by rotating disk voltammetry. In this in situ measurement, a solution redox species such as cobaltocene, ferrocene, or Cr(2,2'-bipyridine)3+ serves as an electron source at the polymer/solution interface, while electrons are removed at the polymer/electrode interface. The oxidation state of the polymer is controlled by the potential applied to the electrode. The experimental data have been interpreted in terms of both electronic and redox conduction models. A comparison of the results from these two models reveals that the electronic conductivity and the electron diffusion coefficient are related by the Nernst-Einstein equation. It is concluded that electron transport occurs by a hopping mechanism and that the two models are equivalent descriptions of this process in the pyrrole-based polymers. The electronic conductivity of both polymers initially increases linearly with the degree of oxidation of the polymer backbone (concentration of oxidized sites). The conductivity of polypyrrole rises exponentially from 10-8 to 5 ×10-6 Ω-1 cm-1 over the potential range of -0.7 to -0.4 V, while the electron diffusion coefficient remains constant at ca. 10-7 cm2 s-1. At higher potentials the conductivity is too high to be accurately determined by rotating disk voltammetry. The conductivity of poly-MPMP+ increases from ca. 10-9 Ω-1 cm-1 at +0.35 V to ca. 10-4 Ω-1 cm-1 at +1.0 V. © 1990, American Chemical Society. All rights reserved.