Catalysis Of Functional Modification On The Surface Of Graphite Felt For V(?)/V(?) Species

The most common electrode material of vanadium flow batteries(VFB)is graphite felts.However,the commercial graphite felts(GF)has poor electrical conductivity,hydrophilicity and electrochemical property.To solve this problem,the in-situ doping of the surface of GF was carried out by three different methods.And the three modified electrodes were used for positive at static VFB.The experimental results are as follows:The CoP catalyst was prepared by direct heat treatment of Co-based zeolitic imidazolate framework(ZIF-67)followed by phosphidation.CoP modified graphite felts(GF-CoP)was obtained by depositing CoP onto GF surface.Cyclic voltammetry(CV)results confirmed that the peak potential separation on GF-CoP is smaller than that GF electrode at the V(?)/V(?)cathodic reaction.Battery performance testing results confirmed that the capacity of the cell using GF-CoP electrode was about 32.7 mA h larger than that of GF electrode,and the voltage efficiency(VE)was about 5.9% higher than that using GF electrode at 100 mA cm-2,respectively.Thiourea can react with carboxylic acid(COOH)on the surface of GF to form thiourea grafted graphite felts(TG-GF).The results showed that both electrochemical activity and reversibility of the modified electrode toward V(?)/V(?)redox reaction were improved.Compared with cell without grafted GF electrode,the cell using TG-GF electrode display higher discharge capacity and energy efficiency,particularly at high current density.The glycine was grafted onto the surface of GF by aminating reaction to form glycine grafted graphite felts(G-GF).The CV showed that the peak potential separation decreased by 231 m V compared with no-grafted GF electrode at the V(?)/V(?)cathodic reaction.Battery performance testing results confirmed that the initial capacity and VE of G-GF based cell increased by 33.4 mA h and 6%,compared with those of no-grafted GF based cell at 100 mA cm-2,respectively.