Functionalized single-walled carbon nanotubes with enhanced electrocatalytic activity for Br-/Br3- redox reactions in vanadium bromide redox flow batteries

Pristine graphite, multi-walled carbon nanotubes (MWCNTs), singe-walled carbon nanotubes (SWCNTs), and functionalized SWCNTs with large numbers of oxygen-containing groups (FSWCNTs) have been used as electrocatalysts for the Br-/Br3- redox couple reactions in the positive half-cell of the vanadium bromide redox battery. The structure, composition, and electrochemical properties were characterized by scanning electron microscopy, transmission electron microscopy, X-ray diffraction, Raman spectroscopy, X-ray photoelectron spectroscopy, cyclic voltammetry, and electrochemical impedance spectroscopy. The electrochemical activity of the FSWCNTs-modified electrodes for the Br-/Br3- redox couple reactions is greatly increased relative to graphite and other carbon nanotube-modified electrodes and the electrochemical kinetics of the redox reactions are in the order of FSWCNTs > SWCNTs > MWCNTs > graphite. This result suggests that the oxygen functional groups significantly facilitate the electron transfer processes, by providing active sites for the reactions and enhancing the effective electrode area.