Preparation And Properties Study Of Electrode Materials For VRFB

The vanadium redox flow battery(VRFB)is a potential effective means of solving energy problems due to its long service life,great charge-discharge capacity,high safety and low cost.To establish VRFB,the key issue is to explore the electrode material with excellent performances.Because the electrodes of VRFB is only the reaction place not involving the redox reaction process,the most methods how to enhance the electrochemical activity of the electrode is to improve the catalytic performance of the electrode material by increasing the surface area of the electrode and the numbers of oxygen-containing functional groups on it.Therefore,we prepared high performance modified graphite felt electrode and graphene composite electrode material by the simple and efficient hydrothermal method and the physical adsorption method.The results show that the prepared electrode materials improve the electrochemical activity,promote the catalytic converting activity of VZ2+/VO2+and increase the coulombic efficiency.The content of oxygen-containing functional groups was increased significantly and the catalytic activity on VO2+/VO2+ was improved after the graphite felt is pretreated.For the graphite felt modified by the reduced graphene oxide(rGO/GF)electrode,the graphene sheets attached to the surface of the graphite felt fibers provide a larger specific surface area and reactive sites for the redox reaction.Compared with the GF-blank electrode at the same scanning rate,the rGO/GF electrode has a higher peak current,a lower peak potential,better good catalytic activity and reversibility.Moreover,due to the superconductivity of the reduced graphene oxide,the charge transfer resistance was reduced to about 9.2Ω and the coulombic efficiency was improved by about 6.9%due to the superconductivity of graphene.For the electrode modified with CeO2(CeO2/GF),the catalytic activity of the electrode is obviously improved,and the electrode charge transfer resistance is reduced to about 19.3 Ω and coulombic efficiency is increased by about 5%owing to CeO2 enduing more oxygen-containing functional groups to the electrode.The foamed nickel prepared by the optimized graded electroplating process(①2.5A dm-2 pre-plating for 5min,②continuous plating for 15min at 1.4A dm-2)showed a dense and uniform crystal morphology and a smaller charge transfer resistance,it can be used as a matrix for the foamed nickel and graphene(NF/G)integrated electrodes in vanadium battery.The ion diffusion resistance of the 3DG electrode is lower than that of NF/G electrode,and the charge transfer impedance of the 3DG is reduced to about 13.5 Ωfrom 66.1Ωof NF/G electrode.The 3DG electrode has a higher charging potential platform,a lower discharge potential platform,a smaller electrode polarization,a better reversibilitythan the NF/G electrode.The coulombic efficiency of the 3DG electrode being about 78.0%.Finally,during the hydrothermal reaction of urea,ferrous oxalate and graphene oxide,Fe2+undergoes redox reaction with graphene oxide and forms the ferric oxide and grapheme(Fe2O3/N/G)electrode.The absorption peaks belonging to C-N and C=N in the FTIR spectrum indicates that nitrogen from urea was effectively doped into the graphene structure in the hydrothermal reaction.Nitrogen optimizes the catalytic activity of the electrode,improves the charge mobility of the electrode,improves the charge transfer and mass transfer process,and improve the electrochemical performance of the electrode as well.The Fe2O3/N/G electrode has good catalytic activity and reversibility.After being doped with nitrogen,the electrode dropped its charge transfer resistance from 133.2Ωto 45.9Ω,reduced its ion diffusion resistance,improved its coulombic efficiency to about 82.5%.