Characteristics of Carbon Nanotube-graphite Composite Electrodes for Vanadium Redox Flow Battery

Electrodes were prepared by mixture of graphite powder(GP) and multi-walled carbon nanotubes(MWNT) at various ratios for all-vanadium redox flow battery.In this studies,the surface morphologies of the composite electrodes were characterized by scanning electron microscope(SEM),and electrochemical behaviors were investigated by cyclic voltammograms,impedance spectroscope and charge-discharge technique.SEM observation shows that the electrode surface roughness increases after adding MWNT to GP.The research results indicate that the MWNT added into GP can provide good electron conductive network between the GP particles,which results in a shorter current conducting pathway in the sheet GP and also a lower internal resistance for the electrodes.The best composition for the positive electrode of all-vanadium redox flow battery(VRB) with different content of MWNT is 15wt%.The current efficiency of VRB using 15wt% MWNT-GP composite electrode is above 93% and the voltage efficiency decrease with current densities increasing under current densities of 20-80 mA/cm2.The improvement in the electrochemical activity of 15wt% MWNT-GP composite electrode is ascribed to the decrease in the total resistivity of vanadium ions adsorption and desorption from MWNT-GP composite electrode and the charge transfer resistivity of MWNT-GP electrode at the electrolyte/electrode interface.