Acid treatment is an oxidation process to graphite felt. Usually using concentrated sulfuric acid, nitric acid, potassium dichromate to modify the graphite felt.put the graphite felt into concentrated sulfuric acid and under boiling situation for 5h,then make it as electrode material for vanadium redox flow battery,it could make the energy efficiency increase to about 90%.the result of testing shows that after the treatment of concentrated sulfuric acid,it can reduce the electric resistance of the electrode material,and the electrochemical property of the graphite felt can increase with the concentration of the sulfuric acid.the number of the active group on the surface of graphite felt have an obvious increase.

　　Some researchs showed that the graphite felt under the mixed acid and boiling situation can increase the hydrophily.make a comparison between the activation graphite felt and non activation graphite felt,the activation one can be soaked soon,but the non activation graphite felt can not be soaked lasting for many days.

　　After observation with the SEM,we could find that there are several little partical adhere the surface of the graphite felt,and after acid treatment,the partical disappeared,and the surface become smooth.

　　After the acid treatment to the carbon/graphite felt,the number of O atoms increase.the corrosion effect of the acid obviously increase the specific surface area.it found that,the graphite felt electric resistance of mixed acid is higher than only sulfuric acid.

　　There are a lot of ways to activate the graphite felt,but few articals to describe the difference and influence between the different ways.

　　Used in the vanadium redox flow battery,is one of the most useful application of carbon felt/graphite felt.If other materials are used in the vanadium redox flow battery,something will happen,like: the electric current density of vanadium redox flow battery is very low,only about 20mA/cm2 or even lower,but the vanadium redox flow battery with carbon felt/graphite felt can be about 80mA/cm2,and at the same time,the service life of the carbon plate used as bipolar plate is very short and it will lead to the service life of vanadium redox flow battery is very short.

　　So the vanadium battery system must use the carbon felt/graphite felt as electrode materials.

　　The electrode material which is used in the vadadium system divided into two types,one is graphite felt,and another one is carbon felt.To the graphite felt,the baking temperature is higher,and the degree of graphitization is also higher,accordingly,the graphite felt has a higher cost and price than carbon felt.

　　The felt used for electrode material in the vanadium battery mainly divided into PAN base and RAYON base,the rayon ones are more expensive than the PAN ones,but the property of vanadium battery depends on the design of the battery system.

　　Among so many carbon electrode materials ,the graphite felt holds greatest promise. The structure cross section as below:

　　PAN base graphite felt is the first choice to be used in the vanadium redox flow battery,but it still has some disadvantage such as the hydrophilic property can not meet the battery requirement,and the chemical activity can not make it ether. So the research and development of PAN carbon/graphite felt is more and more important.