Electrochemical studies of ferrocene/ferrocenium redox couple on nitrogen-doped multi-walled carbon nanotubes in organic solvents

In present work, the oxidation of ferrocene (FeCp 2 ) to ferrocenium cation (FeCp 2 + ) was investigated on electrode consisting of nitrogen-doped multi-walled carbon nanotubes (N-MWCNTs) in acetone (ACE), acetonitrile (ACN), dichloromethane (DCM), and dimethyl sulfoxide (DMSO) in presence of n -tetrabutylammonium hexafluorophosphate (NBu 4 PF 6 ) by means of cyclic voltammetry and electrochemical impedance spectroscopy. For comparison reasons studies of FeCp 2 +/0 on glassy carbon (GC) were carried out. Parameters such as, half-wave potentials ( E 1/2 ), diffusion coefficients ( D ), heterogeneous electron-transfer rate constants ( k s ), and charge-transfer resistances ( R ct ) of FeCp 2 +/0 were determined. The electron-transfer process was found to be reversible and diffusion controlled on both electrodes in all investigated solvents. The E 1/2 values tend to shift towards less positive potentials with the increase of dipole moment and dielectric constant of solvent. Furthermore, both D and k s values tend to decrease with the progressively increase of viscosity of solvent. In addition, the k s values vary inversely with the R ct parameters indicating that the charge-transfer kinetics is strongly affected by the impedance behavior of electrode. Among the electrodes probed, the N-MWCNTs-based film provides faster electrochemical process since it affords insignificant barrier for interfacial electron transfer. The lower limit of detection ( LOD ) estimated for N-MWCNTs (0.6 × 10 –6 –3.6 × 10 –6 mol∙L −1 ) and GC (1.8 × 10 –6 –6.2 × 10 –6 mol∙L −1 ) towards FeCp 2 +/0 was found to be strongly tied to the diffusion coefficient of redox system in different solvents.