Study On Preparation And Electrochemical Performance Of Porous Carbon

Porous carbon materials are widely used on electrochemical energy storage,absorption,and catalysis,especially for efficient and clean energy storage devices owning to their excellent properties such as high specific surface area,controllable pore structure,high electrical conductivity and thermal conductivity.Recently,hierarchically porous carbon materials have attracted much attention as electrode materials due to their well-defined large pores and interconnected mesoporous and microporous structures,which can improve the electrolyte contact and utilization of specific surface area,provide more active sites and help to shorten the transmission distance of the electrolyte ions,thereby improving the specific capacity and rate performance.Meanwhile,the introduction of heteroatoms such as nitrogen in porous carbon framework can improve the wettability and stability of carbon material surface,result in many defects in the carbon atomic layer,and increase its reversible capacity as negative electrode material for lithium ion batteries.Moreover,the heteroatoms undergo a reversible redox reaction with the electrolyte,thereby providing pseudo-capacitance for supercapacitor.Therefore,in this dissertation,nitrogen-doped porous carbon materials were seclectd as the research object.Different preparation methods and raw materials were used to synthesize a series of nitrogen-doped porous carbon materials with high porosity and unique morphology.At the same time,the structure and electrochemical properties of porous carbon materials were investigated using a variety of characterization methods:1.Nitrogen-rich sandwich-like carbon nanosheets were synthesized by using glucose and guanine through a facile hydrothermal carbonization?HTC?process,followed by KOH activation.The pore structure can be controlled by adjusting the activation temperature.The resultant porous carbon has a larger specific surface area(820¹398 m² g^-1)and hierarchical porous structure with abundance micro/mesoporous.The nitrogen content of the sample activated at 600°C is 11.4 wt%,endowing it with better lithium storage performance(discharge capacity is 910 mA h g^-1 after 50 cycles at100 mA g^-1;719 mA h g^-1after 200 cycles at 500 mA g^-1)2.Nitrogen-doped porous carbon microspheres were prepared from glucose and aminourea through HTC and the following high temperature activation.The effects of different factors on the microstructure and morphology of carbon materials were studied,such as nitrogen sources,addition amounts and activator species.The prepared material has high specific surface area(1791³026 m² g^-1),uniform average pore size distribution?1.76-1.97 nm?,and microporous content exceeding 92%.As a supercapacitor electrode material,the specific capacity is as high as 390 F g^-11 at current density of 0.5 A g^-1;Evan at a high current density of 20 A g^-1,the specific capacitance remains to be 260 F g^-1.After 10 000 cycles,the specific capacitance retention rate is 90%.3.The unique rambutan-like hierarchically porous carbon microspheres were prepared through HTC and KOH activation by also using glucose as carbon source and diethylene triamine pentacetate acid with plentiful nitrogen/oxygen functional groups as raw materials.This carbon material has abundant surface functional groups,uniform pore size distribution and large specific surface area(1160¹791 m² g^-1),in which the micropore and mesoporous structure are well distributed.High specific capacitance and excellent rate performance as supercapacitor electrode materials are achieved:at current density of 0.5 A g^-1,the specific capacity is as high as 397 F g^-1;at 20 A g^-1,the specific capacity is 288 F g^-1,and the capacity retention rate can reach 95%after 10 000 cycles.4.Biomass-based porous carbon materials were prepared through activation of KOH with Guangxi's abundant natural resources,markisa husk,as carbon source and aminourea as a nitrogen source.After nitrogen source modification,the specific surface area of carbon material increased significantly.Used as a supercapacitor electrode material,the specific capacitance is 347 F g^-1 at a current density of 0.5 A g^-1,and the specific capacitance is as high as 252 F g^-1 at 20 A g^-1,and the specific capacitance retention rate is still 88%after 10 000 cycles.