Electrode Kinetics of Viologen Polymers Attached on Graphite Surfaces

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Abstract
A “heterogeneous” electron-transfer process of three kinds of viologen polymers, i.e., N,N′-dimethyl-4,4′-bipyridinium (methylviologen, MV)–NafionR, poly(xylylviologen) (PXV)-poly(p-styrenesulfonate) (PSS) and poly(methylviologen) (PMV), in which MV and PXV were electrostatically trapped in Nafion and PSS, respectively, on a basal-plane pyrolytic graphite (BPG) electrode and PMV was directly attached to the BPG electrode surface, was examined by normal pulse voltammetry. The relevant kinetic parameters (i.e., the standard rate constant, koel and the cathodic transfer coefficient, α) of the electrode reaction and the apparent diffusion coefficients, Dapp, for the “homogeneous” charge transport within these polymer films were determined at the various surface concentrations (ΓMV2+ in units of mol cm−2) of viologen dication site. With the PMV and PXV–PSS systems, both koel and Dapp were independent of ΓMV2+, while with the MV–Nafion system both koel and Dapp decreased with an increase in ΓMV2+ under the constant concentration of Nafion. The values of α were independent of ΓMV2+ and constant (i.e., 0.56, 0.58, and 0.20 for the PMV, MV–Nafion and PXV–PSS systems, respectively).

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