Electrochemical performance of graphene oxide modified graphite felt as a positive electrode in all-iron redox flow batteries

Abstract

In this study, we demonstrate that coating a layer of graphene oxide (GO) onto graphite felts (GF) by electrostatic spraying can substantially increase the performance of all-iron redox flow batteries (IRFBs). Graphite felts are extensively used as electrodes but they do not have the desired electrochemical properties. GO has good electrochemical features. Hence, GO was synthesized from graphite powder and applied onto graphite felts. Chemical and structural features of the bare graphite felt electrode (BGF), thermally treated graphite felt electrode (TTGF), and graphene oxide modified graphite felt electrode (GOMGF) were characterized using X-Ray Diffraction (XRD), Scanning Electron Microscopy (SEM), Energy Dispersive X-Ray Analysis (EDX), Transmission Electron Microscopy (TEM), Raman Spectroscopy (RS), X-Ray Photoelectron Spectroscopy (XPS) and Brunauer–Emmett–Teller (BET) surface area analysis. Similarly, the electrochemical performance was evaluated using Cyclic Voltammetry (CV), Electrochemical Impedance Spectroscopy (EIS), Tafel analysis and charge–discharge experiments. The Charge–discharge experiments were performed at 1 to 5 mgcm−2 weight of GO on the modified graphite felt electrode and varying the current densities from 10 to 40 mAcm−2. The coulombic efficiency (ηC) and energy efficiency (ηE) of the cell determined at 20 mAcm−2 for 4 mgcm−2-GOMGF electrodes were found to be 64.61% and 50.27%, respectively. Among the three different types of electrodes, the GOMGF electrode showed better electrocatalytic performance mainly due to the excellent conducting network of the defective edges of oxygen on the surface of layered flakes of the GO. After twenty cycles, the average ηC and ηE of the cell using a 4 mgcm−2-GOMGF electrode were found to be 62.06% and 42.02%, respectively.