In recent years, all-vanadium redox flow battery (VRFB) has been paid much attention as a new type of battery for energy storage. Researchers have been focusing much on activation of carbon electrodes used for the key material in VRFB. The carbon electrode, such as carbon felts and graphite felts, are widely used as electrode for VRFB due to their low cost and high performance. The electrochemical activation and reversibility towards V(Ⅴ)/V(Ⅳ) and V(Ⅲ)/V(Ⅱ) redox reactions can be significantly improved after increasing the oxygen and nitrogen functional groups on the surface of carbon electrodes or introducing all kinds of catalysts by activation treatment, which can improve the overall performance of VRFB and further accelerate its commercialization process. The research progress in various common activation methods including oxidation activation, doping activation and carbon nanocatalysts activation, are summarized in this paper. The further research and prospect on carbon electrodes in VRFB are also presented.

Contents
1 Introduction
2 Carbon electrodes
3 Active of carbon electrodes
3.1 Oxidation activation method
3.2 Doping activation method
3.3 Carbon nanocatalysts activation method
3.4 Other activation methods
4 Outlook