Graphene oxide-carbon nanotubes hybrid co-electrodeposited on graphite sheet as an excellent electrocatalytic material for [VO]2+/[VO2]+ redox reaction in VRFBs

Abstract

A highly effective GO-CNT/graphite sheet as electrochemical active material for [VO]2+/[VO2]+ redox pairs in vanadium redox flow battery (VRFB) has been developed. The modified sheet was fabricated by co-electrochemical reduction of functionalized carbon nanotubes (fCNTs) and graphene oxide (GO) on graphite sheet. The structures and electrochemical properties of GO-CNT/graphite sheet were studied by scanning electron microscopy, transmission electron microscopy, contact angle measurement, Fourier-transform infrared spectroscopy, Raman spectroscopy, cyclic voltammetry, electrochemical impedance spectroscopy, and chronoamperometry (CHA). The morphology studies showed that GO-CNTs hybrid has been uniformly deposited on the surface of graphite sheets. Electrochemical measurements are carried out in a three-electrode half-cell to characterize the electrochemical properties of the GO-CNT/graphite sheet towards the VO2+/VO2+ redox reactions. Results showed that the GO-CNT/graphite electrode exhibits high peak current density and low charge-transfer resistance towards the [VO]2+/[VO2]+ redox reactions compared to bare graphite sheet, confirming good electrocatalytic activity and kinetic reversibility of the modified electrode. The enhanced electrochemical activity can be attributed to the synergetic catalytic effect of GO-CNTs and the large numbers of oxygen-containing functional groups on the GO-CNTs hybrid which can provide more active sites to catalyze the [VO]2+/[VO2]+ redox reactions.