Electrochemistry on Multi-walled Carbon Nanotubes in Organic Solutions

The oxidation of ferrocene (FeCp2) to ferrocenium cation (\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$\mbox{FeCp}_{2}^{+}$\end{document}) (where Cp: cyclopentadienyl anion, \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$\mbox{C}_{5}\mbox{H}_{5}^{-}$\end{document}) was investigated by means of cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) on either a glassy carbon (GC) electrode or a film consisted of multi-walled carbon nanotubes (MWCNT) in acetone (ACE), methanol (MeOH) and ACE/MeOH binary mixtures. The half-wave potentials (E1/2), the diffusion coefficients (D) and the heterogeneous electron transfer rate constants (ks) of the redox couple \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$\mbox{FeCp}_{2}^{+/0}$\end{document} were determined. On both electrodes tested, the electron transfer process was found to be quasi-reversible and diffusion controlled in all investigated solvent mixtures. The E1/2 values were shifted toward less positive potentials with the enrichment of mixtures in MeOH, due probably to the larger Lewis basicity of the MeOH molecules. Furthermore, values of both D and ks diminish with the increase of MeOH content following the progressive increase of viscosity of the solvent medium. Among the electrodes probed, GC provides faster electrochemical process since it affords less charge-transfer resistance (Rct), and consequently, an insignificant barrier for interfacial electron transfer.