Effect of charge transport in electrode-confined N,N′-dialkyl-4,4′-bipyridinium polymers on the current-potential response for mediated, outer-sphere electron-transfer reactions

Nathan S. Lewis, Mark S. Wrighton

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Mediated outer-sphere redox processes have been examined at rotating disk Pt/[(PQ2+/+)n]surf electrodes. The [(PQ2+/+)n]surf is a redox polymer anchored to the surface and is formed from N,N′-bis[(trimethoxysilyl)propyl]-4,4′-bipyridinium, I. The polymer coverages for the electrodes selected for study are sufficiently great that Fe(phen)3 3+/2+, E°′ = +1.03 V vs. SCE, shows no electrochemical response near its E°′. The mediated reduction of Fe(phen)3 3+ and a number of other outer-sphere oxidants is mass-transport limited when the Pt/[(PQ2+/+)n]surf electrode is held ∼100 mV more negative than E°′[(PQ2+/+)n]surf = -0.45 V vs. SCE in CH3CN/0.1 M [n-Bu1N]ClO4. However, contrary to theoretical expectations based only on the rate constant for reaction of Fe(phen)3 3+ with a surface PQ+, the onset of current for the mediated reduction is at the onset for [(PQ2+)n]surf → [(PQ+)n]surf reduction; in fact, the mediated reduction current in the onset region is directly proportional to the concentration of PQ+ in the surface-confined polymer. Data for Pt/[(PQ2+·xFe(CN)6 3-/4-) n]surf electrodes show directly that charge transport in the polymer can be a limitation to the maximum steady-state mediation current in aqueous electrolyte solution at the coverages of [(PQ2+/+)n]surf that have been employed. The charge-transport properties of the polymer are concluded to control the current-potential profile, as has been reported previously for other surface-modified electrodes, for the large polymer coverages employed in these studies.

Original languageEnglish
Pages (from-to)2009-2017
Number of pages9
JournalJournal of Physical Chemistry
Issue number10
Publication statusPublished - 1984


ASJC Scopus subject areas

  • Physical and Theoretical Chemistry

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