Charge-Transport Rates in Nafion Coatings on Electrodes. Surprisingly Disparate Diffusion Coefficients for a Single Molecule Containing Two Electroactive Centers

摘要

The diffusion coefficient of the heterobinuclear complex (NH3)5RuC5H4NCH2NHC(= = O)-CpFeCp (triple bond) RuLFe (Cp = cyclopentadienide or substituted cyclopentadienide) within Nafion coatings was measured chronocoulometrically in all three of its possible redox states (Ru(II)LFe(II), Ru(III)LFe(III). The three oxidation states exhibited large differences in their diffusional rates. Possible origins of the differences and their concentration dependences are considered including intermolecular electron self-exchange, single-file diffusion, and electrostatic cross-linking. Both enhancement and depression of charge-transport rates produced by intermolecular electron-transfer cross-reactions between the fully oxidized and fully reduced complex were observed and compared with those calculated on the basis of a simple model. Reasonable agreement was obtained.