Preparation And Electrochemical Properties Of Functionalized Carbon Materials

With the rapid development of industrialization,the sharp rise of energy demand and the serious shortage of supply have led to structural contradictions.At the same time,traditional fossil fuels also cause a lot of environmental pollution in the process of production and use.Therefore,people pay more and more attention to energy related research.Since modern times,supercapacitors have been regarded as potential energy storage devices because of their advantages such as fast charge discharge rate,long cycle life,high power density and environmental friendliness.In particular,carbon materials show excellent electrochemical performance as electrode materials,but due to its relatively low energy density,it has limited its wide application.Therefore,the main research topic of this paper is to prepare functional carbon materials as electrode materials,in order to improve the electrochemical performance of supercapacitors.The specific contents are as follows:In the first part,we describe a simple and economical method to prepare functionalized graphene sheet/carbon nanotube(G/CNTs-200)electrode materials by chemical oxidation at lower temperatures.The G/CNTs-200 material is composed of one-dimensional carbon nanotubes as a continuous conductive network matrix and functionalized graphene sheets,forming a three-dimensional network composite structure.This unique structure provides the electrode material with a high specific surface area and abundant oxygen-containing functional groups.Through electrochemical tests,the specific capacity of the G/CNTs-200 electrode material at the current density of 0.5 A/g was 202 F/g,which was more than 5 times higher than the specific capacitance(40 F/g)of pure carbon nanotubes reported in the literature.It is worth noting that in the electrolyte environment of 6 mol/L KOH.The symmetrical supercapacitor was assembled with G/CNTs-200 as a positive and negative electrode material.Through electrochemical tests in 1 mol/L Na2SO4 electrolyte,the device showed excellent electrochemical stability and was able to provide 11.7 Wh/kg energy density.Therefore,it has a good prospect to design and assemble high performance supercapacitor electrode materials based on carbon nanotubes.In the second part,the functionalized graphene nanosheet/carbon nanotube network(G/CNTs)material prepared in the first part is used as the conductive substrate of the composite material,because it provides a high surface area and a large number of oxygen functional groups in the structure,which can provide nucleation sites for metal oxides and promote nanalization of metal oxide particles.Therefore,in this part,G/CNTs/Fe2O3 and G/CNTs/MnO2 composites were prepared by hydrothermal method as the negative and positive electrodes of asymmetric supercapacitors.Due to the high coupling of nanoscale Fe2O3 and MnO2 with the conductive base,the electron and electrolyte ions can be transferred in the whole electrode,which has been proved to have good electrochemical performance by electrochemical test.In the 1 mol/L Li2SO4 electrolyte solution of the three-electrode system,the maximum specific capacitance of the G/CNTs/Fe2O3-150 electrode composites display a specific capacitance of 258 F/g at 1 A/g.The maximum specific capacitance of the G/CNTs/MnO2 positive electrode at 1 A/g is 264 F/g.An asymmetric supercapacitor had a voltage window of 2V,showing superior energy density of 43.2Wh/kg,good times and good cyclic stability.The third part,we explore A simple,direct pyrolysis step 3D interconnected porous carbon,potassium gluconate preparation of porous carbon materials and doping of experiment scheme,end product as A total sulfur nitrogen doped porous carbon materials(NSHPC),because of its unique pore structure,interconnected ion diffusion channels and higher content of nitrogen and sulfur atoms were mixed.After the electrochemical testing,the specific capacitance of the electrode material is 320 F/g at the current density of 0.5 A/g,and at the current density of 50 A/g,the specific capacity still reaches 200 F/g.After 10,000 cycles,the specific capacity can still maintain 99.3%of the initial capacitance,indicating that the material has good multiplier performance and electrochemical stability.In addition,in order to further improve the energy density,the super capacitor assembly NSHPC materials as anode materials and porous carbon/manganese dioxide(HPC-700/MnO2)composites as anode asymmetric supercapacitor,the device when power density is 666.7 W/kg can provide larger energy density,good electrochemical stability.The experimental results show that the method of hetero-atom doping can provide reference for the large-scale production of high performance supercapacitors in the future.