Preparation And Electrochemical Properties Of Graphene/Nitrogen-doped Mesoporous Carbon Composites

As a new type of energy storage device,supercapacitor has been widely studied because of its high power density,long cycle life and high rate of charge and discharge,Mesoporous carbon has become the research focus of supercapacitor electrode materials because of its large specific surface area,moderate pore size and so on.However,there are still some problems in using mesoporous carbon as electrode material,such as low energy density and large internal resistance,which seriously limits its application in the field of energy storage.Research results show that the incorporation of heteroatoms(N,P,B)can effectively improve the electrochemical properties of mesoporous carbon materials.In this thesis,the effects of nitrogen doping and graphene composite on the structure and properties of mesoporous carbon materials were studied by doping nitrogen atoms and composite graphene.The aim was to improve the electrochemical properties of mesoporous carbon materials.The main research contents and conclusions are as follows:(1)The dicyandiamide-phenolic resin(DPF)precursors were prepared by dicyandiamide as nitrogen source.Combined with block copolymer F127,nitrogen-doped mesoporous carbons(NMC-x)were prepared by solvent evaporation induced self-assembly(EISA)method.Subsequently,A-NMC-x was obtained by KOH activation.Through a variety of test methods,the results showed that nitrogen doping had a great influence on the mesoporous structure,and the excess nitrogen doping will lead to the collapse of the mesoporous structure.KOH activation could greatly enhance the specific surface area and pore volume of the mesoporous carbons,and the increments by KOH activation increases first and then decreases with the increase of nitrogen content.The optimum component A-NMC-1.0 had a specific surface area of 2828.8 m2/g,which was 2.3 times that of the nitrogen-free component.Electrochemical tests showed that the specific capacity of A-NMC-1.0 was as high as 388.0 F/g,much higher than that without nitrogen doping,and the internal resistance of sample was reduced from 1.39 ? to 0.50 ? The increase of the specific capacity was mainly caused by the increase of the specific surface area.Nitrogen doping could increase the conductivity,reduce the internal resistance value,and improve the electrochemical properties of mesoporous carbons.(2)The graphene/nitrogen doped mesoporous carbon composites(G/NMC-x)were prepared by a soft-templating strategy combined with hydrothermal polymerization process.Subsequently,A-G/NMC-x was obtained by KOH activation.This strategy involved the use of hexamethylenetetramine(HMT)as slow release source of formaldehyde,p-aminophenol as nitrogen source,ammonia as catalyst,graphene oxide(GO)prepared by the modified Hummers as raw materials,whereas F127 was used as a soft-template.Through a variety of test methods,the results showed that the addition of graphene could affect the pore structure.After the activation of KOH,the optimum component A-G/NMC-100 had a specific surface area of 3246.4 m2/g,which was 2.6 times that of the nitrogen-free sample,and was much higher than that of the graphene free component.The electrochemical tests showed that the specific capacity of A-G/NMC-100 was as high as 434.4 F/g,which was much higher than that of nitrogen-free and non-graphene components.After adding graphene,the internal resistance of N-doped mesoporous carbon decreased from 0.66 ? to 0.27 ?.The incorporation of nitrogen and composite of graphene greatly increased the specific surface area of the samples,thereby increasing the capacitance of the electric double layer,and reduced the internal resistance,increased the surface wettability,greatly improved the electrochemical properties of the mesoporous carbon materials.