Amplified electron transfer at poly-ethylene-glycol (PEG) grafted electrodes

Christopher E. Hotchen, Ian J. Maybury, Geoffrey W. Nelson, John S. Foord, Philip Holdway, Frank Marken

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"Amplified" electron transfer is observed purely based on electron transfer kinetic effects at modified carbon surfaces. An anodic attachment methodology is employed to modify the surface of glassy carbon or boron doped diamond electrodes with poly-ethylene glycols (PEGs) for polymerisation degrees of n = 4.5 to 9.1 (PEG200 to PEG400). Voltammetry and impedance data for aqueous Fe(CN)<inf>6</inf><sup>3-/4-</sup> suggest systematic PEG structure-dependent effects on the standard rate constant for heterogeneous electron transfer as a function of PEG deposition conditions and average polymer chain length. Tunnel distance coefficients are polymerisation degree dependent and estimated for shorter PEG chains, β = 0.17 Å<sup>-1</sup> for aqueous Fe(CN)<inf>6</inf><sup>3-/4-</sup>, consistent with a diffuse water-PEG interface. In contrast, electron transfer to 1,1′-ferrocene-dimethanol (at 1 mM concentration) appears un-impeded by PEG grafts. Mediated or "amplified" electron transfer to Fe(CN)<inf>6</inf><sup>3-/4-</sup> based on the 1,1′-ferrocene-dimethanol redox shuttle is observed for both oxidation and reduction with estimated bimolecular rate constants for homogeneous electron transfer of k<inf>forward</inf> = 4 × 10<sup>5</sup> mol dm<sup>3</sup> s<sup>-1</sup> and k<inf>backward</inf> = 1 × 10<sup>5</sup> mol dm<sup>3</sup> s<sup>-1</sup>. Digital simulation analysis suggests an additional resistive component within the PEG graft double layer.

Original languageEnglish
Pages (from-to)11260-11268
Number of pages9
JournalPhysical Chemistry Chemical Physics
Issue number17
Early online date2 Apr 2015
Publication statusPublished - 7 May 2015


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