Preparation And Electrochemical Properties Of MOFs/Conductive Polymer Composites

Metal organic framework(MOFs)is a kind of porous material with network structure and rich redox active sites,which determines its great theoretical electrochemical capacity.However,the poor conductivity and stability of MOFs restrict its application in the field of energy storage.On the basis of obtaining stable MOFs material Ni-BTC,the conductivity of MOFs is improved by compositing conductive polymer.This work provides experimental and theoretical reference for the application of MOFs in electrochemical energy storage materials.The main research work are as follows:(1)The influence of hydrothermal time and other process parameters on the properties of Ni-BTC was studied.The results show that with the increase of hydrothermal time,the Ni-BTC shows the largest specific capacity in 18 h.The results of SEM and adsorption isotherm show that in the hydrothermal reaction,the basic macrostructure is firstly constructed,and the subsequent Ni-BTC grows in this pore structure,and the collapse of porous structure was observed after increasing of hydrothermal time.The electrochemical study shows that the specific capacity of Ni-BTC prepared by hydrothermal method is 677.59 F/g(1 A/g),and the coulomb efficiency is 82%.Further study shows that the environmental humidity has a certain influence on the electrochemical stability of Ni-BTC.EDS and XRD tests indicate that water molecules adsorb on the surface of Ni-BTC,resulting in the decrease of specific surface area,specific capacity,rate performance and coulomb efficiency to some extent.(2)In order to improve the environmental stability of Ni-BTC,the hydrophobic material 2,2-dimethyl-4,4-bipyridine was added in the hydrothermal preparation process to obtain the modified Ni-BTC.Through the FTIR and XRD characterization of the modified Ni-BTC,it shows that the hydrophobic group has been successfully introduced into the Ni-BTC.The results of EDS,XRD and BET showed that the molecular structure,element composition and specific surface area did not change significantly after long time exposure of Ni-BTC to air,indicating the stability of the material.The electrochemical test shows that the specific capacity of the modified Ni-BTC is 505.92 F/g,and the coulomb efficiency is 82%.The specific capacity of Ni-BTC decreases with the introduction of this hydrophobic material,and the equivalent series resistance(ESR)of electrode material increases slightly due to the insulation of hydrophobic material.(3)In order to improve the conductivity of Ni-BTC,the as-prepared and hydrophobically modified Ni-BTC were compounded with conducting polymer poly(3,4-ethylenedioxothiophene)(PEDOT),and the molar ratio of 3,4-ethylenedioxothiophene(EDOT)monomer to Ni-BTC was optimized to explore the influence of the composite ratio of EDOT to Ni-BTC on the electrochemical properties of the composite.The results of SEM and FTIR showed that PEDOT and Ni-BTC were successfully compounded.The electrochemical test shows that with the increase of the composite ratio of Ni-BTC and PEDOT,the electrochemical capacity of the composite increases first and then decreases.When the molar ratio of Ni-BTC and PEDOT is close to 2:1,the specific capacity of Ni-BTC @ PEDOT is 744.33 F/g,and the coulomb efficiency is 83%.The specific capacity of modified Ni-BTC@PEDOT is 550.41 F/g,and the coulomb efficiency is 83%.Furthermore,the symmetrical supercapacitor was assembled by using the composite as the electrode materials.The results show that the energy storage ability and stability of the device are promising as energy storage applications.