Electrochemical oxidation of ascorbic acid mediated by a carbon nanotubes/Li+ modified graphite electrode

Carbon nanotube (CNT) paste, consisting of multiwalled CNT and nujul, was mechanically attached to the surface of a basal plane pyrolitic graphite electrode (BPPGE) and this used as a working electrode. The CNT/BPPGE electrode was found to be able to mediate the oxidation process of ascorbic acid (AA) during cyclic voltammetry, especially in the presence of Li⁺. The oxidation current of AA was found to increase about 3-6 fold compared to the bare BPPGE. The oxidative current of AA was found to be irreversible and diffusion controlled. Current magnitude was largely influenced by concentration, electrolyte, scan rate and rotation speed. Based on the surface charge determined by chronocoulometry, CNT/BPPGE appears more conductive in the presence of Li⁺ dopant. Diffusion coefficient of 1.22×10^-7 cm²/s and kinetic rate constant of 4.07×10^-3 s^-1 for the oxidation of ascorbic acid were determined using hydrodynamic voltammetry.