Synthesis of activated graphite felt using consecutive post-treatments for vanadium redox flow batteries

A new consecutive post-treatment for activating graphite felt electrodes is developed for use in vanadium redox flow batteries (VRFBs). Graphite felt is treated by thermal oxidation under air followed by thermal annealing with melamine as the nitrogen source. The physical and electrochemical analyses demonstrate that the oxygen-containing groups facilitates nitrogen doping in the carbon framework. A higher nitrogen content and pyridinic-N are observed when nitrogen is doped on the oxidized graphite surface using melamine compared to the content of pristine graphite felt. As a result, the treated graphite felt (GFO+N) exhibits outstanding electrochemical performance in VRFBs. It exhibits a 203% and 31% increased discharge capacity at a current density of 150 mA cm^-2 comparted to pristine graphite felt and oxidized graphite felt, respectively. The improved performance is ascribed to the high nitrogen content and active nitrogen groups generated on the graphite felt, which improve the fast electrochemical kinetics of the vanadium redox reaction.