The Design And Preparation Of 3D Porous Carbon Materials And Their Performance As Electrode Materials Of Supercapacitors

Due to the advantages of high power density,short charge time and long cycle life,supercapacitors have excellent promising application in the areas of consumer electronics,new energy automobiles,the reforming of smart power grids and are the focus of energy device.It is worth noting that the capacitance,energy density and power density of supercapacitors are closely depending on the electrochemical properties of electrode materials.Comparing with low dimensional carbon materials,three-dimensional(3D)porous carbon not only have abundant pores and large specific surface area,but also have 3D continuous carbon conductive network,which can be directly used as electrode material and served as effective supporting skeleton of pseudo-capacitive materials.Therefore,3D porous carbon materials are great candidates for high performance supercapacitor electrode materials and their design and preparation have attracted much researchers' attention.This thesis,mainly concentrate on 3D porous carbon materials,have demonstrated that the preparation of 3D porous carbon materials with different pores,and the attempts to improving electrochemical performance of electrode by preparing C/MnO2 composites and surface functionalization.The main research contents and conclusions are as follows:(1)3D oporous carbon frameworks were prepared by a simple carbonization process which of PVA used as carbon precursor and NaCl used as template.The morphology and structure of 3D carbon frameworks have been studied.Furthermore,MnO2 materials were in-situ grown on the surface of 3D macroporous carbon frameworks.C/MnO2 composites with various nano-morphologies and crystalline structures have obtained by using the strong oxidation of KMnO4.When the as-prepared composites were employed as electrode materials of supercapacitor,their electrochemical performance has been systematically studied.The experimental results indicate that 3D porous carbon can supply conductive supporting path for MnO2 which accelerates the transportation of electrons and diffusion of ions,while the nano-morphologies with high surface area of MnO2 are helpful to increasing contact area with electrolyte and resulting a high capacitance of composites.Besides,the birnessite MnO2 can provide more pseudo-capacitance than ?-MnO2.Thus,the C/MnO2 composite with connected nanosheets on the basis of 3D carbon frameworks exhibits the best electrochemical performance,showing a high capacitance of 132 F/g at the current density of 0.5 A/g and nearly maintain 116 F/g at 2 A/g without obviously decay after 1000 charge/discharge cycles.(2)The nitrogen and oxygen co-doped porous carbon nanofibers(CNFs)network was obtained by electrospinning technology followed a carbonization and a removing template process which using SnCl2 as template and PAN as carbon precursor/nitrogen resource.The sample is self-supporting and can be directly served as electrode showing a good application prospect in developing high performance supercapacitors.Notably,in three-electrode system,the electrode shows a high capacitance of 233.1 F/g at 0.2 A/g,and displays a capacitance of 130.2 F/g when the current density increases to 14 A/g.After 4000 charge/discharge cycles,it still remains the initial capacitance of 90.17%.Such an outstanding electrochemical performance can be attributed to the unique structure and morphology of electrode material: The porous CNFs construct a continuous conductive network which is beneficial to decreasing electrode resistance and promoting the transport of electrons and the diffusion of electrolyte ions.The abundant pores greatly increase specific surface area of CNFs,contributing a large double layer capacitance.Moreover,the existence of nitrogen and oxygen functional groups can not only improve conductivity and wettability of CNFs,but also increase many electrochemical active sites which produce additional pseudocapacitance.Therefore,after the symmetry supercapacitor is assembled with porous CNFs,it obtains a high capacitance of 37 F/g at 0.2 A/g and a high energy density of 5.14 Wh/kg.And the porous CNFs/Co(OH)2 asymmetry supercapacitor achieves a higher capacitance of 87.1 F/g at 0.5 A/g and exhibits a maximum energy density of 27.2 Wh/kg.