Research For Graphite Felt Modifacation As Advanced Electrode For Vanadium Redox Flow Battery

All vanadium redox flow battery?VRFB?is a new-type green energy storage system?ESS?,which takes unique advantage of long-cycle life,high energy efficiency and safety.VRFB is used as large-scale industrial ESS for renewable energy such as wind energy,water energy and solar energy.Electrode is regarded as one of the most important components of VRFB,because the electrode/electrolyte interface provides places for redox reaction during the charge-discharge process.Therefore,the performance of VRFB is primarily determined by the electrochemical property of electrode.Currently,the most extensively-used electrode in VRFB is PAN-graphite felts?GF?,due to its unique physique and chemical property.However,the poor kinetics reversibility of the relevant vanadium redox reaction on raw GF hinders the performance of VRFB,so various post treatments are seriously demanded.We present,two different modifications for GF and characterize the electrochemical property of prepared GFs via SEM,XPS,CV,EIS and etc.Firstly,high performance nitrogen-doped graphite felts are successfully prepared via urea hydrothermal treatment at low temperatures below 220 ^oC and is demonstrated as enhanced electrodes for vanadium redox flow batteries.Effects of urea hydrothermal treatment temperature on the nitrogen-bonding configurations are investigated.Properties of the modified graphite felts including morphology,cyclic voltammetry,X-ray photoelectron spectroscopy and cell performance of vanadium redox flow battery are characterized.Taking advantage of the increased pyridinic-N content,the prepared nitrogen-doped graphite felt presents an outstanding electrochemical performance,which exhibits 8.35%increase of energy efficiency?up to 81.32%?at a high current density of 150 mA cm^-2.In order to prepare a modified graphite felt with longer charge-discharge cycle-life and being more suitable for commercializing,carbon aerogel modified graphite felt is prepared as electrodes for vanadium redox flow batteries.Morphology and nano-porous structure of the carbon-carbon composite electrode is characterized.Properties such as cyclic voltammetry,electrochemical impedance and battery performance of the carbon-carbon composite electrodes are investigated.The results show that the specific surface area of the modified graphite felt is dramatically increased and reaches 57.16 m² g^-1,while that of the original graphite felt is only 1.13 m²g^-1.The charge transfer resistance is reduced from 1.84?to 0.21?and the energy efficiency of the unit cell equipped with the modified electrodes is increased by 32.66%at 160 mA cm^-2?increased from 57.16%to 75.83%?.