Structural Design Of Porous Carbon And Its Performance In Supercapacitor

The increasingly consume of traditional fossil fuels such as coal,oil,natural gas drives people to develop renewable clean energy and corresponding energy storage devices.New electrochemical energy storage devices,including supercapacitors,lithium batteries and solar cells have emerged,which are indispensable in modern society.Among these energy storage devices,supercapacitors have become a hotspot of research deriving from their fast charge/discharge process,wide range of operating temperature,long cycle life and high power density.Electrode materials are the key factor for the performance of supercapacitors,among which porous carbon has become one of the most widely used electrode materials due to the adjustable surface area,multi-dimensional complex pore structure,good conductivity and low cost.However,the limited capacity of traditional porous carbon materials such as graphite and activated carbon has greatly hindered the application of electrochemical supercapacitors.Accordingly,it is in urgent need of developing advanced carbon materials(high specific surface area,optimized pore distribution,heteroatom doping,surface defect,etc.)to improve the performance of supercapacitors.This paper aims to design porous carbon materials with controllable microstructure via simple,efficient and green methods for high energy density and power density supercapacitors.The main contents of this paper are list as follows:1.In the third chapter,the nitrogen-doped and mesoporous-dominated hollow carbon nanospheres(NMHCS)with the unique "interpenetration twin" structure was synthesized via the one-step "sol-gel" method by choosing phenolic-resin as the carbon source,tetrapropyl orthosilicate(TPOS)as the silicon source and cetyltrimethyl ammonium bromide(CTAB)as the soft template.The silicon dioxide provides a stable skeleton structure and restrictive nano-space for the hollow nanospheres,which effectively hinders the contraction and collapse of structure during the carbonization process.After etching of silicon,NMHCS with open skeleton structure was obtained,as well as precisely controllable size(50-500 nm),adjustable pore volume(1.23-2.56 cm-3·g-1)and high specific surface area(1526-1824 m2·g).The supercapacitor performance of NMHCS shows obviously increase with the decreasing of the materials size.The specific capacitance of NMHCS-5 reaches to 178 F·g-1 at 1 A·g-1,and maintained 132 F·g-1 at 20 A·g-1 in 6 M KOH,the retention rate of which reached to 74%.Besides energy storage devices,the NMHCS could also be utilized in photoelectric material,adsorbing materials and many other fields.2.Although NMHCS own the advantages of high surface area,large pore volume and nitrogen doping,the complex preparation process,low yield,secondary pollution in removing silicon dioxide and the mismatch between mesoporous size and electrolyte ion radius impede their electrochemical application.Accordingly,a high efficiency,green and scalable method was designed for the preparation of microporous-dominated porous carbon nanosheets with a little amount of micropores in Chapter 4.By selecting rice as raw materials,the precursor is converted into puffed rice with a honeycomb-like structure composed of thin sheets via the explosion-induced "puffing effect".The honeycomb-like macrostructure effectively prevents the cross-linking tendency towards the adjacent nanosheets during activation process,and tunable micro/mesoporous structures with ultrahigh specific surface areas(SBET)are successfully designed by alkali activation.The highest SBET of 3326 m2·g-1 with optimized proportion of small-mesopores is achieved at 850?.The rice-derived porous N-doped carbon nanosheets(NCS-850)are used as the active electrode materials for supercapacitors.It exhibites high specific capacitance specifically of 218 F·g-1 at 80 A·g-1 in 6 M KOH and a high-energy density of 104 Wh·kg-1(53 Wh·L-1)in the ionic liquid electrolytes.3.Traditional theory believes that only the mesoporous could store a large amount of ions/charges and rapidly transfer them.The favorable supercapacitor performance of NCS-X indicates that micropores could also play a similar role of the mesopores.In order to further explore the effect of micropore on the performance of electrochemical,afully microporous-dominated material was designed in Chapter 5.Utilizing the "inner heating"mechanism of microwave and the "puffing effect" from rapid heating,the nubby maize grain turned into materials with an interconnected honeycomb-like porous structure composed of carbon flakes.The following alkali activation method enabled the as-prepared products(PCF-X)to possess optimized porous structures for electrochemical energy-storage devices,such as multilayer flake-like structures,ultrahigh specific surface area(SBET:3301 m2·g-1),and a high content of micropores(micropore surface area of 95%,especially the optimized sub-nanopores with the size of 0.69 nm)that can increase the specific capacitance.The ion desolvation process of "micropore effect" caused by unique porous structure significantly improved the capacitance and energy density of supercapacitor.The as-obtained sample displayed excellent specific capacitance of 286 F·g-1 at 90 A·g-1 for supercapacitors.Moreover,the unique porous structure demonstrated an ideal way to improve the volumetric energy density performance.A high energy density of 103 Wh·kg-1(53 Wh·L-1)has been obtained in the case of ionic liquid electrolyte,which may satisfy the urgent requirements of a primary power source for electric vehicles.