Preparation and Electrochemical Properties of Graphene‐Modified Electrodes for All‐Vanadium Redox Flow Batteries

Abstract

The electrochemical properties of graphene make it an attractive material for use in a range of devices. We herein describe the simple preparation of graphene-modified graphite (GMG) composite electrodes by hybridization with graphite for all-vanadium redox flow batteries (VRB). The cyclic voltammetry (CV) results revealed that the use of GMG composite electrodes with an optimal graphene loading content (3 wt%) allowed remarkable improvements in terms of both the reversibility and the current density, which was up to 30 % higher than that of the pristine graphite electrode, and that an electrode of this type shows considerable potential for use in VRBs. , and the allvanadium redox flow battery (VRB). The last system is one of the more promising, thanks to its high storage capacity, its long life-cycle, its reliability and its high energy conversion efficiency [6][7]. The performance of the electrode of the VRB is still a key factor in the determination of the overall performance of the cell. The two redox couples of VO 2 + /VO 2 + and V 2 + /V 3 + are used for the positive and negative half-cell reactions, respectively. In comparison with the negative electrode, the positive redox couple of VO 2 + /VO 2 + sustains a relatively leisurely dynamic reaction, due to the rearrangement of the coordination structures of the vanadium ions [8], resulting in a significant influence on the performance of the cell. This rearrangement consists in the transfer of electrons, the exchange of protons, and the formation of a number of intermediate complexes, according to the pH of the electrolyte and the electrical potential [9]; hence, it is the positive half-cell reaction of the VRB that determines the electrochemical kinetic limitation. In consequence, the evolution of the electrodes plays an important role in the storage of energy. Various carbonaceous materials have been widely reported to have been used for the electrodes of VRBs, including polyacrylonitrile (PAN)-based graphite felt [10], carbon black [11], and carbon fiber [12].Graphene is a two dimensional (2-D) graphitic material in which the sp 2 -hybridized carbon atoms are arranged in a honeycomb lattice with a thickness of one atom. It has generated extensive scientific interest in a variety of technological fields [13,14]. In previous studies, a number of different authors have described the exceptional mechanical [15] [18], which may promote a higher rate of ionic adsorption, and may thereby enhance the electrochemical properties of any redox system in which it is used. Furthermore, the foregoing properties imply that graphene may be expected to be an excellent filler in graphite, thereby forming composite graphene-graphite electrodes. We herein describe the preparation of graphene-modified graphite (GMG) composite electrodes with various weight ratios of graphene to graphite. The electrochemical behavior and surface morphology of all samples were assessed using cyclic voltammetry (CV) and field-emission scanning electron microscopy (FE-SEM). We found that t...

A technology review of electrodes and reaction mechanisms in vanadium redox flow batteries

“…Xie et al highlighted research on improving the VO 2 + /VO 2+ redox reaction by employing a composite electrode composed of graphite and graphene in various compositions. 102 Compared to a graphite electrode, the graphite-graphene composite electrode with graphene as a filler showed noticeable reactivity in VRFB catholyte. In their research, the best electrochemical reactivity was obtained from the composite electrode containing 3 wt% graphene.…”

Graphene‐Based Nanocomposites for Energy Storage

“…Graphene promotes a higher rate of ionic adsorption and thereby, enhances electrochemical properties in a VRFB system . For example, graphene‐based materials obtained from thermally reduced graphite oxides are used as active electrodes in the positive half‐cell of VRFB with outstanding electrochemical performance in terms of peak current densities and reversibility .…”

Electrocatalysis at Electrodes for Vanadium Redox Flow Batteries

“…These structural-morphological details became most obvious in a comparative study of carbon felt and polymer-bonded activated carbon as electrode materials with cobalt impregnations. Graphene-modified graphite with PVDF as a binder was prepared by Tsai et al [438] and deposited on a platinum support. An optimum content of 3 wt.% yielding significant peak current increases of the positive electrode was found.…”