| Energy scarcity and environmental pollution have become two major social issues that cannot be ignored in the 21st century.Scholars have devoted themselves to finding and developing environmental-friendly renewable energy and efficient energy storage devices.Supercapacitors(Electrochemical capacitors or Faraday capacitors),which have the advantages of fast charge and discharge speed,high power density and great cycle stability,have become hotspots in the recent research.As a commonly used electrode material,carbon materials have received extensive attention because of its large specific surface area,adjustable pore structure,good electrical conductivity,wide source and low cost.However,the disadvantages of carbon materials such as lower specific capacitance and energy density have severely limited its further development and application.It is reported that doping carbon materials with nitrogen,phosphorus,oxygen,boron and other heteroatoms can effectively improve its specific capacitance and energy density.In this thesis work,three types of nitrogen-doped porous carbon materials(PNCs)were prepared and the influence of different carbonization temperatures on the morphology,structure and electrochemical properties of PNCs was studied.In addition,the practical performance of PNCs as electrode materials for supercapacitors was investigated.The main research contents and results are as followed:First,using p-phenylenediamine(PPD)and cyanuric chloride(TCT)as reactants to synthesize the covalent triazine-based microporous polymer by means of polycondensation reaction,and then carbonizing at different temperatures to prepare nitrogen doped carbon materials.The results show that the carbonization temperature has an important influence on the specific surface area,pore size distribution,nitrogen content and electrochemical performance of the electrode materials.When the carbonization temperature increases,the specific surface area and microporous volume of the samples gradually enlarge,while when the carbonization temperature is too high,they all become smaller.The sample carbonized at 900? has the highest specific surface area and microporous volume.Besides,as the carbonization temperature increases,the degree of graphitization and conductivity of the samples gradually enhance,while the nitrogen content gradually reduces.Due to the synergistic effect of specific surface area,pore size distribution,nitrogen content and conductivity of the samples,the sample obtained with the carbonization temperature of 900?(N-CTF-900)shows the highest specific capacitance of 264 F g-1 at a current density of 1 Ag-1,good rate performance and cycle stability.Second,using p-phenylenediamine(PPD)as the carbon source and nitrogen source,and hexachlorocyclotriphosphazene(HCCP)as the nitrogen source and phosphorus source to synthesize the microporous polymer by the nucleophilic replacement of-Cl groups with amino groups,and then the polymer was carbonized in a tube furnace at different temperatures to prepare the nitrogen/phosphorus co-doped porous carbon materials.The samples prepared at different carbonization temperatures all have a hierarchical porous structure,which provides a channel for the transport and storage of electrons and ions.In addition,the specific surface area and the degree of graphitization are proportional to the carbonization temperature,while the amount of nitrogen and phosphorus atoms is inversely proportional to the carbonization temperature.The sample prepared at 1000?(NP-MCP-1000)has the largest specific surface area(1785 m2 g-1),and the sample carbonized at 700?(NP-MCP-700)has the highest nitrogen and phosphorus content.The cyclic voltammetry(CV)and galvanostatic charge discharge(GCD)tests show that the sample prepared at 900?(NP-MCP-900)has the highest capacitance,great rate performance and excellent cycle stability.The specific capacitance of NP-MCP-900 is 323 F g-1 at a current density of 1 A g-1.Furthermore,the simple supercapacitor device assembled with the NP-MCP-900 sample can successfully illuminate the LED lamp,implying its good practical performance.Additionally,carbon materials doped with high content of nitrogen were prepared by carbonizing the mixture of nitrogen-rich monomer 1,2,4-triaminobenzene hydrochloride(BTD)or 1,2,4,5-tetraaminobenzene hydrochloride(TAB)and the active agent FeCl3·6H2O.During the process,FeCl3·6H2O is not only beneficial to oxidative polymerization,but also facilitates the formation of pore structure.The samples prepared at different carbonization temperatures all form hierarchical porous structure,which is conducive to electron transport and ion diffusion.The samples carbonized at 450?(PNCB-450 and PNCT-450)have the largest specific surface area and microporous volume,and the specific surface areas of PNCB-450 and PNCT-450 samples are 1335 m2 g-1 and 1139 m2 g-1,respectively.Moreover,the higher the carbonized temperature,the less nitrogen content in the carbon materials,and the samples prepared at 450?(PNCB-450 and PNCT-450)have the highest nitrogen content of 23.85%and 26.26%respectively.The increase of nitrogen content in carbon materials is beneficial to improving its specific capacitance effectively.However,the specific capacitance will be reduced when the nitrogen content is too high.Electrochemical characterization indicates that the sample carbonized at 450? has the highest specific capacitance.At a current density of 1 A g-1,the specific capacitance of PNCB-450 and PNCT-450 are 482 F g-1 and 403 F g-1,respectively.In addition,the PNCB-450 still has about 98%capacitance after 12000 cycles,indicating it possess good cycling stability.Furthermore,PNCB-450 exhibits the energy density of 9.43 Wh kg-1 and power density of 155.43 W kg-1 at a current density of 0.5 A g-1 with two-electrode cell configuration.When the simple supercapacitors assembled with PNCB-450 sample is connected with a stopwatch in series,the stopwatch can be successfully illuminated for 10 min,indicating that PNCB-450 is feasible as a supercapacitor electrode material. |
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