Electrochemical characterisation of the adsorption of ferrocenemethanol on carbon nano-onion modified electrodes

Abstract The electrochemistry at glassy carbon electrodes (GCE) modified with carbon nano-onions (GCE/CNO) are not completely understood. Herein, we investigate the electrochemical behaviour of ferrocenemethanol (FcCH2OH) and [Fe(CN)6]3− at GCE/CNO and GC electrodes by cyclic voltammetry and double step chronocoulometry. The voltammetric analysis demonstrated that the electrochemical response of [Fe(CN)6]3− is a fully diffusion-controlled process, while for FcCH2OH a weak adsorption of its reduced form takes place on the GCE/CNO electrodes and in higher extension than on bare GC electrode. The surface coverage of FcCH2OH on GCE/CNO electrodes was found to be 4.3 × 10−9 mol cm−2 indicating the formation of a multi-layered structure and was 14-times greater than on GC electrodes. Laviron's lateral interaction parameter (vGθT) for adsorbed FcCH2OH molecules indicated attractive and strong repulsive interaction at GCE/CNO and GC electrodes, respectively. Double potential step chronocoulometry was used to obtain the empirical adsorption isotherms which were found to respond to the Sips model isotherm. Our results highlight the importance of considering the adsorption of the redox species to interpret the physical and kinetic parameters of these systems and could help to explain the signal enhancement observed in electrochemical CNO-based (bio)analytical systems that is commonly explained only in terms surface area and electronic properties of the CNO layer.