Controllable Synthesis Of Micro-nano Carbon Spheres By Cationic Surfactants And Study On Their Performance Of Supercapacitor

Energy crisis and environmental pollution have become important factors that hinder the development of today's society,and the development of new sustainable and clean energy has become an urgent problem to be solved.As a new type of electrochemical energy storage device,the supercapacitor has been widely used in production and life due to its advantages of fast charge and discharge speed,good cycle stability,low operation cost and high power density compared with lithium battery,fuel cell and solar cell.However,the low energy density is the main factor that restricts its further industrialization.The direct way to solve this problem is to develop efficient energy storage materials.Among many electrode materials,nitrogen doped mesoporous hollow carbon spheres(NMHCSs)have attracted extensive attention due to its ultra-high specific surface area,multi-dimensional interconnected pore structure and good electrochemical conductivity.However,the known synthesis methods of NMHCSs are difficult to control the microstructure and chemical composition accurately.The self-assembly morphology of surfactants is very important for the synthesis of NMHCSs with controllable structure(morphology,size,specific surface area,pore structure distribution,etc.)by soft template method.This paper aims to realize the regulation of the structure of emulsion interface microreactors by using the principle of colloid and interface chemistry,to design the structure of NMHCSs from molecular level and to build high performance supercapacitor electrode materials.The main contents of this paper are as follows:1.In the second chapter,the controllable preparation of nitrogen doped mesoporous carbon nanospheres was realized by using the assembly of Gemini cationic surfactant as the emulsion interface microreactor.The flexible linking group and two amphiphilic parts give Gemini cationic surfactants higher surface activity and smaller micelle aggregation number.A series of nitrogen doped porous carbon materials with different micro morphology(controlled size,monodisperse,uniform distribution of spherical structure and interconnected structure of internal cavities in carbon nanospheres)were synthesized by one-step sol-gel process.The prepared NMHCSs possess small and controllable particle size(30-140 nm),ultrahigh specific surface area(1215-1517 m2·g-1),large pore volume(3.22 cm3·g-1),open and interconnected mesoporous structure(5-20 nm),high proportion of heteroatom nitrogen(4.16-6.74 at.%)and oxygen(6.17-8.68 at.%).At the current density of 1 A·g-1,the specific capacity of the NMHCSs-0.6-15 based electrode material(with interconnected structure of internal cavities)in the symmetrical double-layer supercapacitor(6 M KOH as electrolyte)reaches 240 F·g-1,and at the current density of 20 A·g-1,the capacitance retention rate is 67%.2.As ordered combinations of surfactants,vesicles have not been reported in the synthesis of NMHCSs because of its unstable properties.In the third chapter,the structural design and controllable synthesis of nitrogen doped mesoporous hollow carbon spheres and core shell structured mesoporous carbon micro/nanospheres can be realized simply and accurately by nano emulsion polymerization in the microbalance system of micelles and vesicles formed by ionic liquid surfactant[C12mim]Br self-assembly.A series of carbon micro/nanospheres with controllable morphology(uniform distribution of big-sized and small-sized mesoporous hollow carbon nanospheres and momordica grosvenori-like open structured hemispheric nitrogen-doped mesoporous carbon materials with chrysanthemum-like core and ultrathin shell)were successfully prepared.The prepared NMHCSs-x-y-z and A-NMHCSs have many structural advantages,such as uniform and controllable spherical structure(55 nm-2?m),ultrahigh specific surface area(498-1906 m2·g-1),large pore volume(0.56-2.03 cm3·g-1),open and interconnected graded mesopores(4-20 nm),high proportion of heteroatom N doping(2.92-6.85 at.%).In the application of symmetrical electrochemical double-layer supercapacitor,the representative sample of A-NMHCSs shows high electrochemical specific capacity(308 F at 0.2 A·g-1),good rate performance(233 F at 20 A·g-1)and excellent long cycle stability(85%capacitance retention at 10 A·g-1 after 5000 cycles).The full-sized carbon micro/nanospheres with tunable structure are expected to be widely used in catalysis,adsorption,biomedicine and other energy storage and conversion fields.3.The synthetic methods of bowl shaped carbon nanomaterials usually require severe experimental conditions.In the fourth chapter,the double chain cationic surfactant was used as the emulsion to build the interface microreactors.The controllable synthesis of carbon nanospheres and bowl shaped carbon nanomaterials was achieved by simply adjusting the amount of surfactant and the ratio of water and ethanol in the reaction system.The carbon materials with bowl shaped structure have better electrolyte ion wettability,lower charge transfer resistance and better electrochemical conductivity.The high specific surface area(1203-1555 m2·g-1),large pore volume(1.63-1.74 cm3·g-1),open and interconnected graded mesopores(4-20 nm)and high proportion of heteroatom N-doping(6.07-7.54 at.%)of NMHCSs-x-y-z based electrode materials give the materials good electrochemical energy storage properties.In the symmetrical double electrode supercapacitor system,the specific capacity of the open bowl shaped carbon nanomaterials reaches 243 F·g-1 at the current density of 0.2 A·g-1,and the capacity retention rate reaches 72.4%(176 F·g-1)and 65.4%(159 F·g-1)at the ultrahigh current density of 10 A·g-1 and 20 A·g-1,respectively,showing high specific capacity and good rate performance.