Modification Of Graphite Felt Electrodes For Vanadium Redox Flowbattery

All-vanadium redox flow battery(VRB) is a new green battery with advantages of high efficiency, long life,high safety and reliability. It can be used as large-scale energy storage devices for wind energy, hydro energy, solar energy, as well as backup power system.Poor hydrophilicity and electrochemical activity lead to the Polyacrylonitrile-based(PAN) graphite felt to be modified in order to be better applied in vanadium battery. Ce O2 has oxygen storage function and rapid oxygen vacancy diffusion capacity, and it is the most active rare earth oxide catalytic material.Taking into account of the excellent performance of Ce O2, an ethanol and sol-gel method is used to modify graphite felt with Ce O2 to improve its electrochemical activity. The electrochemical methods such as cyclic voltammetry、AC impedance and battery test, with the physical methods of XRD、SEM and so on are used to the characterization of modified graphite felt. The optimized preparation process shows that the best reaction time is 60 min, and the heat treatment atmosphere is in air by using ethanol solution method. Furthermore, the optimized sol concentration and p H in sol-gel method is also obtained. Coulombic efficiency of VRB battery with modified graphite felt can reach up to 95%, and the energy efficiency is close to 90%.Surface deposition is another method of modifing graphite felt to introduce a catalytically active metal on the surface of graphite felt. Ion-exchange method is used to introduce manganese, cobalt and nicke on graphite felt surface. The modified graphite felts are tested with physical and electrochemical methods. Results show that the functional groups on the surface of the graphite felt change, and the hydrophilicity as well as electrochemical activity of graphite felt is improved. Battery test showed that the coulomb efficiency can reach up to 90%.Finally, reaction reversibility and rate-determining step of the modified graphite felt electrod are studied with cyclic voltammetry and AC impedance methods. Furthermore, reaction mechanism on positive electrode of Ce O2 modifed graphite felt is also disussed.