Single-Entity “Nano-Catalysis”: Carbon Nanotubes and the VO2+/VO2+Redox Reaction

Cyclic voltammetry and single-entity electrochemistry (aka "nano-impacts") are used to evaluate the electrocatalysis of the VO2+/VO2+ redox couple by means of bamboo-like multiwalled carbon nanotubes particularly in comparison with the kinetics seen at carbon macro-electrodes. The individual nanotubes are shown to accelerate the reaction in the oxidative direction but to retard it in the reductive direction! The asymmetry is explained in terms of the multistep nature of the electrode reaction and the relative sequence of electron transfer and chemical steps. When an ensemble of nanotubes is drop-casted onto a glassy carbon electrode, an electrochemically nearly reversible response is seen and understood in terms of the changed mass transport regime under which the reaction occurs.