Graphite–carbon nanotube composite electrodes for all vanadium redox flow battery

The voltammetric behaviors of graphite (GP) and its composites with carbon nanotube (CNT) were studied in 5 M H2SO4 + 1 M VOSO4 solution with cyclic voltammetry (CV), and the surface morphology of the composites was observed with scanning electron microscope (SEM). The results obtained from voltammetry show that the redox couples of V(IV)/V(V) and V(II)/V(III), as positive and negative electrodes of all vanadium flow liquid battery, respectively, have good reversibility but low current on the GP electrode, and the current can be improved by CNT. It is found from the observation of SEM that the CNT is dispersed evenly on the surface of sheet GP when they are mixed together. The best composition for the positive and the negative of all vanadium flow liquid battery determined by comparing voltammetric behavior of the composite electrodes with different content of CNT is 5:95 (wCNT/wGP) for both positive and negative electrodes. The activity of the composite electrode can be affected by the heat treatment of CNT. CNT treated at 200 °C gives better activity to the composite electrode.