Electron Transfer in the Reduction of Cobalt Porphyrin Incorporated into Nafion and Poly(4-vinylpyridine-co-styrene) Films

Abstract

<jats:p> Potential step chronoamperospectrometry (PSCAS) measurement was carried out to investigate the one-electron transfer in the reduction of tetraphenylporphyrin cobalt(III) ([ Co <jats:sup> III </jats:sup> TPP (−2)]<jats:sup>+</jats:sup>) incorporated into a Nafion or poly(4-vinylpyridine-co-styrene) (P(VP-St)) film coated on an ITO electrode. The electron transfer of the redox centers in the two systems occurred by a physical diffusion mechanism. The fraction of the electroactive complex (R<jats:sub> ct </jats:sub>) was independent of the CoTPP concentration in P(VP-St) but decreased with increasing CoTPP concentration in Nafion, especially at high concentrations. In both systems the apparent diffusion coefficient D<jats:sub>app</jats:sub> decreased with increasing CoTPP concentration. The D<jats:sub>app</jats:sub> value in Nafion (1.6 × 10<jats:sup>−8</jats:sup> cm <jats:sup>2</jats:sup> s <jats:sup>−1</jats:sup> at 0.02 M) was much higher than that in P(VP-St) (1.1 × 10<jats:sup>−10</jats:sup> cm <jats:sup>2</jats:sup> s <jats:sup>−1</jats:sup> at 0.02 M). The difference in the electron transfer process in the two systems was ascribed to the interaction of the redox center with the polymer framework, the morphology of the polymer matrix, the localization of the redox species in the hydrophilic/hydrophobic region, and the counterion migration under the potential step. </jats:p>