Study On The Construction And Properties Of Nitrogen Doped Porous Carbon-Based Supercapacitors

At the beginning of the 21st century,with the developed of science and technology,a large number of new types of equipment emerged.Nowadays,it is urgent to find a way to improve the operation time and environment of such advanced devices.Therefore,the development of new type energy devices have become an urgent need.Supercapacitors?SC?stand out among numerous new type energy devices due to its advantages of both high power density and excellent cycle performance.However,compared with other novel energy storage devices,the disadvantage of low energy density for SC has become a serious problem.Therefore,how to increasing the energy density without sacrificing the power density of SC has become the focus and difficulty on its study.As a branch of SCs,the study of Carbon-based capacitors has a long development history.Mostly,it possesses both ultra-high specific surface area and extremely fast charge/discharge efficiency.And also the low cost of raw materials makes it suitable for industrial production.However,the electrostatic energy storage mechanism makes it difficult to reach a high energy density.In order to obtain a higher energy density,numerous studies has focus on the basic energy storage mechanism,such as enhancing the hetero atom doping content or increasing the specific surface area,which has been proved an effect way for fabrication of high performance carbon-based supercapacitor.In recent years,scientists has found a phenomenon that"the capacitance can get the optimal energy density when the electrolyte ions match the pore size in the porous carbon material."The publication of this research has aroused widespread concern in the scientific research community.Inspired by this,this paper was firstly explored the carbon storage methods and preparation methods in the first chapter.Then,in the second and third chapters,an appropriate carbon source has been selected to explore and fabricate porous carbon material with a monodisperse pore size.The three researches are as followed:Part 1:Use the squid bone as the precursor,and then explored appropriate activator and activation conditions to convert it into hierarchically porous carbon material with specific surface area at around 2,070 cm² g^-1.Under the optimal process condition,the high N?6.0%?and O?18.9%?doping combined with its high specific surface area makes KSPC-800 possess excellent electrochemical performance.Then,the KSPC-800 performed a highest specific capacitance of 581 F g^-1 at a current density of 1 A g^-1,which is about twice that of conventional commercial activated carbon(100²50 F g^-1).The KSPC-800 retained a specific capacitance of 336 F g^-1,even at a current densities at 10 A g^-1,performing a good rate performance.In addition,the KSPC also performed excellent cycling stability with 90%capacitance retention after10,000 cycles.The simple preparation process and ultra-high electrochemical performance of KSPC-800 make it excellent in industrialization and commercialization.Part 2:The main idea of part 2 is the design of an monodisperse microporous carbon material.A supramolecular compound,named cucurbit[6]uril,is used as the carbon source.The cucurbit[6]uril?CB[6]?,a pumpkin-shaped supramolecule with a cavity diameter of⁶.0?,provides a promising opportunity for the design of narrow-disperse sub-nanoporous carbon electrodes.After the exploration of the carbonization conditions,we successfully prepared a cucurbit[6]uril deribed carbon material decorated with a large number of sub-nanopores.The as prepared carbon material was assembled into a supercapacitor with a pure ionic liquid?1-methyl-3-methylimidazolium tetrafluoroborate?as electrolyte which have a cation/anion diameter at 0.56/0.34 nm.By virtue of the matching effect of the pore size and the ions,the as prepared carbon material exhibits an exceptionally excellent electrochemical performance at a low specific surface area(684 cm² g^-1).The PAA-C-800 based symmetrical capacitor possesses a maximum energy density of 82.9 Wh kg^-1 at a power density of 187.2 W kg^-1,indicating an excellent electrochemical performance of the PAA-C-800.In addition,due to the high nitrogen content of the carbon source,the material possesses a nitrogen doping ratio up to?9.2%?,which improves the electrochemical performance of the PAA-C-800.The systematic research shows that:1)the doping of nitrogen atoms can effectively improve the conductivity of the material and provide additional pseudocapacitance,2)when the electrolyte diameters are close to the pore sizes of the electrode,the energy storage capacity can rich a maximum,making the material an excellent capacitance performance.The porous nitrogen-doped carbon material designed by the system successfully prepared supercapacitors with high energy density and broke through the limitations of traditional preparation methods,which provided a new research idea for the research of carbon supercapacitors.Part 3:This Part also uses CB[6]as a carbon source to fabricate sub-nanopores.However,unlike Part 2,this part directly coordinates CB[6]with barium to form a supramolecular polymer?SPCC-6?at room temperature,and then self-pyrolysis the SPCC-6 at a high temperature.The SPCC-6 was self-pyrolysised and carbonized in a tubular furnace under Ar atmosphere at temperature?X??to form the cucurbituril carbon materials?CBC-Xs?.During the carbonization process,the coordination bonds of Ba ion with C=O group on the port of CB[6]cavity were broken,and the hat of CB[6]cavity was opened,leaving a great number of sub-nanopores?size⁰.59 nm?in the CBC-Xs.Meanwhile,some CB[6]cavities collapsed and connected with each other to form micropores and mesopores.By changing the self-pyrolysis temperature to adjust the heteroatom doping rate and pore size distribution of the material,whose influence on the electrochemical performance can be explored.Similarly,the material was assembled into a symmetric supercapacitor using pure ionic liquid?MMIMBF₄?as the electrolyte.The capacitors possess a maximum energy density of 104 Wh kg^-1 with a 91%capacitance retention after 8,000 cycles,demonstrating an excellent electrochemical performance.In summary,the results provide new vision for the study of energy storage mechanism of EDLC and of the development of sub-nanopore novel materials.