Surface Modification of Carbon-Based Electrodes for Vanadium Redox Flow Batteries

The vanadium redox flow battery (VRFB) is one of the promising large-scale energy storage technologies. The electrode is one of the key components of the VRFB, and its design has an important effect on its electrochemical redox kinetics and battery performance. The ideal VRFB electrode material has high catalytic activity, good conductivity, and high stability. Carbon-based electrodes are the most commonly used electrode materials for VRFBs. However, its reaction kinetics and catalytic active sites are low. This paper summarizes the methods of carbon-based electrode modification of the electrochemical performance in VRFBs. Three representative methods including metal/metal oxide modification, nonmetal atom modification, and defect engineering for graphite felt in VRFBs are generally reviewed. First, metal and metal oxides have high catalytic activity, which can enhance the chemical reaction process of vanadium ions and greatly improve the reversibility of the redox reaction of vanadium ions. Then, nonmetal atom modification can generally improve the hydrophilicity of carbon-based electrodes, enhance the adsorption/desorption capacity of vanadium ions, and improve the reaction kinetics. Moreover, defect engineering can lead to the formation of the micropore structure on the surface and increase the specific surface area of the material, thus generating more redox reaction active sites. Finally, the development direction of electrode modification in VRFBs is prospected, and it is expected that this review will provide useful insights into the development of VRFBs.