Research On The High-performance Graphite Felt Of Vanadium Flow Batteries

Vanadium flow battery（VFB）is a fast going and promising system for large-scale stationary energy storage because of its advantages such as long lifespan,easy to scale and flexible operation.However,drawbacks such as low power density and narrow temperature window caused by poor catalytic activity of graphite felt（GF）electrodes limit its worldwide application.Fabricating novel electrodes with high power density and wide operating temperature is critical to promote the practical application of VFB for all-climate energy storage.In this paper,graphite felt was modified by two methods,making holes in the surface of graphite felt fiber and loading bismuth catalyst respectively,to obtain graphite felt electrode with high electrochemical activity,high power density and wide temperature adaptability.We take a well-controlled method to prepare holey-engineered porous graphite felt（PGF）electrodes,in which nanosized pores are evenly distributed on the microscale graphite fibers of the graphite felt.Owing to its excellent electrolyte wettability and greatly enhanced surface area,the as-prepared PGF electrode exhibits high electrochemical activity towards VO²⁺/VO₂⁺and V²⁺/V³⁺redox couples.As a result,the VFB single cell assembled with PGF electrodes demonstrates outstanding rate performance under current density up to300 mA cm^-2.The resulting PGF electrode also exhibits superior long-term stability over3000 charging-discharging cycles at a high current density of 150 mA cm^-2,and have higher energy efficiency and electrochemical stability during wide temperature adaptability from-20°C to 60°C.Bismuth,as a low-cost,no-toxic and high-activity electrocatalyst,is used to modify the thermal activated GF（TGF）via a facile hydrothermal method for obtaining Bi/TGF electrode.Bismuth can effectively inhibit the side reaction of hydrogen evolution in wide temperature range,while promoting the V²⁺/V³⁺redox reaction.As a result,the VFB assembled with Bi/TGF as negative electrode demonstrates higher energy efficiency and discharge capacity than those of TGF in rate performance tests.At the current density of150 mA cm^-2,the energy efficiency of Bi/TGF is 78.9%.In addition,the Bi/TGF maintains long-term stability over 600 charging/discharging cycles at a high current density.Moreover,it also shows excellent temperature adaptability from-10℃ to 50℃ and high stability and durability for life test at the temperature of 50℃.