Vanadium redox flow battery is one of the most development prospect of technology because of the long cycle life, high capacity, flexible design, safe and reliable. Among many carbon materials,the carbon/graphite felt has the most application prospect.
Campared with the metal material,the graphite felt has many advantage such like: large specific surface area,good flexibility,easy to machine and install and the price is low,so it’s more suitable to be as electrode material in the vanadium redox flow battery.
Now the problem is how to improve the electrochemical activity of graphite felt.The research and development mainly bifurcated graphite felt modification and the preparation of Graphite felt composite electrode.
1) the modification of graphite felt is to improve the property through modify the surface physical structure(specific surface area, surface morphology)and chemical structure(surface functional group).
It can be devided into two types: oxygen functional groups and nitrogen functional groups.
Use nitrate to treat the carbon/graphite felt,carbon fiber,carbon sheet and graphite rod etc,the result showed that to the graphite/carbon felt and carbon fiber,the content of oxygen has a large increase,however, to the carbon sheet and graphite rod,the content of oxygen has a decrease.
The high content of oxygen does not mean high activity,some researchers believe that appropriate content of oxygen(4.0%~5.0%)is good to the reaction of vanadium battery.
Nitrogen element can change the energy level structure of carbon/graphite material,and to make it with high electrochemical activity.Compared with the oxygen functional groups,it can improve not only electrical conductivity of the material but the hydrophily.
2) the preparation of Graphite felt composite electrode is to increase the electrochemical activity through complex catalysis on the surface of the graphite felt.
The catalyst includes carbon nano-tube, grapheme and metal base(Iridium, Bismuth, Platinum alloy, Tungsten oxide etc.)