Preparation And Electrochemical Properties Of Nitrogen-doped Porous Carbon Materials

Carbon materials become the most commonly employed for electrode materials because of its easily obtained,good conductivity,large surface area and good stability.However,the energy density of carbon materials is low because it is mainly through the electric double layer capacitor for energy storage.Therefore,how to improve the energy density of electrode materials become the highlights for researchers.It is well known that the energy can be calculated according to the equation:E=1/2CV2.So it is possible to improve the energy density of the electrode material by increasing the voltage window or specific capacitance.In this thesis,gelatin was used as the carbon source,the nitrogen content was modified by urea as nitrogen source,the specific surface area was increased by SiO₂ as template,and then further loaded with 2,5-methoxy-1,4-benzoquinone（DMQ）material to increase the specific capacitance separately.Transmission electron microscope（TEM）,scanning electron microscopy（SEM）,X-Ray Diffraction（XRD）and Raman spectroscopy（Raman）methods were used as the main characterization methods to observe the morphology,structure and other properties of the carbon material.The electrochemical properties and stability of the carbon material involved in supercapacitors were studied through electrochemical methods.The main results are as follows:（1）The nitrogen-doped mesoporous carbon nanofibers（N-m-CNFs）were synthesized by "in situ" nitrogen incorporation method using gelatin as carbon source and urea as nitrogen source.The effects of urea template,incorporation and calcination temperature on the morphology properties,structure and electrochemical performance of the N-m-CNFs were studied.The electrochemical properties of the N-m-CNFs were measured by using three-electrode system and 1 M H2SO4 as the electrolyte.The results show that the carbon material is fibrous and the nitrogen content is up to 14.632%after urea incorporation.The specific capacitance of the N-m-CNFs can reach 230.9 F g^-1 at the current density of 1 A g^-1,much larger than the carbon which non-urea added(86.9 F g^-1),and having better cyclic stability.（2）Nitrogen-doped porous carbon sheet（N-p-CSs）with uniform pore size was obtained by template method using gelatin as carbon and nitrogen source and SiO₂ as template.By regulating the particle size of SiO₂,the pore size and specific surface area of the porous carbon sheet material could be altered.And the effect of different calcination temperature on the morphology,structure and electrochemical properties of the synthesized carbon were studied.The results show that the capacitance of the N-p-CSs prepared with SiO₂ particles is obviously higher than the pure carbon which non-SiO₂ added.Among them,the specific capacitance of the N-p-CSs,which synthesized by 20 nm SiO₂ as template,is 252.3 F g^-1 at the current density of 1 A g^-1.（3）The DMQ @ N-p-CSs composites were prepared by loading the DMQ on the surface of the N-p-CSs through the hydrothermal method,which using the N-p-CSs prepared in the second part as the substrate.The influences of different DMQ loading content on the morphology and structure of the synthesized composites were characterized,and the electrochemical properties of the different synthesized composites were tested respectively.The experimental results show that the DMQ @N-p-CSs composite prepared by the DMQ and N-p-CSs weight ratio of 1:1,has better cycle performance and the highest specific capacitance.At a current density of 1 A g^-1,the specific capacitance can reach 356.4 F g^-1,and having 98.6%of the initial specific capacitance after 10000 cycles.