A green approach to fabricate binder‐free S‐doped graphene oxide electrodes for vanadium redox battery

Abstract

Graphene-based electrodes have great potential for using as positive electrode material of vanadium redox flow batteries. However, production of heteroatom doped graphene oxide in classical methods had many steps and time-consuming procedure. In this work, binder-free sulfur-doped graphene oxide electrodes (S-GOEs) were obtained from graphite by the chronoamperometric method in eco-friendly media (sulphuric acid/water) and one step at room temperature. The effects of functional groups ratio on the positive electrolyte performance of vanadium redox battery was investigated via electrochemical methods such as cyclic voltammetry (CV), chrono charge-discharge, and electrochemical impedance spectroscopy (EIS). Microscopic methods were also used for investigation of the surface morphology of the modified electrodes. Detailed chemical composition of modified electrodes surfaces was investigated by X-ray photoelectron spectroscopy (XPS), Fourier transform infrared (FTIR-ATR) spectroscopy and energy-dispersive X-ray spectroscopy (EDS) techniques. CSOxC(x = 2, 3), CSO, hydroxyl, carboxyl and epoxy groups were formed on the modified electrodes during the preparation of graphene oxide based electrodes from the graphite. According to cyclic voltammetry analysis, the electrodes prepared over 3 minutes by chronoamperometric method at 1.9 V (S-GOE3) showed the best performance as a positive electrode of the vanadium redox battery. The cyclic charge-discharge test demonstrated that the discharge capacity considerably increased from 171.9 mA h to 179 mA h at 3.2 mA cm−2 discharge current density. Energy efficiency of cell was also climbing by 5% in S-GOE3 as positive electrode to bare electrode.