Systhesis Of Porous Nitrogen Doped Carbon Nanomaterials And Its Application Of Energy Storage In Supercapacitor

Supercapacitors are widely used in the energy storage field due to their long cycle life,high power density and fast charge and discharge.Among them,carbon-based supercapacitors have attracted great attention because of their wide source of electrode materials,environmental-friendly,nontoxicity and excellent cyclic stability.However,carbon-based supercapacitors have lower energy density than batteries,which greatly limits its commercial application.Therefore,it is a problem worthy of our further study to improve the energy density of carbon-based supercapacitors on the basis of its high power density.As well known,carbon-based electrode materials store energy through the accumulation of electrostatic charge on the electrolyte ion and electrode.The porous structure,effective specific surface area and surface characteristics can greatly influence on the electrochemical performance of the carbon-based supercapacitors.Therefore,we can reasonably regulate the porous structure and pore size of electrode materials to provide a shortcut for the penetration and diffusion of electrolyte ions.The effective specific surface area of the carbon material is increased through designing and synthesizing unique morphology,which could provides more sites for electrolyte ion.The higher specific capacitance can be obtained by decorating the hydrophobic structure on the surface of the electrode material to improve the ion accessibility of the electrode material.Based on this,scientists are committed to develope carbon-based electrode materials with unique morphology,developed porosity and hydrophilic surface.Among them,biomass has attracted a large number of scholars due to its many advantages.For example,the precise and stable structure and channels of the biomass itself can be used as template to prepare carbon-based electrode materials with unique morphology and adjustable aperture.Based on this,we have mainly selected environmentally friendly and widely sourced biomass as the raw materials to prepare novel nano-carbon materials with unique morphologies,porous structure and surface properties for high energy density supercapacitors through activation method or template menthod.The specific contents are as follows:（1）The nitrogen-doped hierarchical porous grapheme-like carbon with coral flower structure（NCFC）has been synthesized by using MgO as template,Cellulose acetate as the carbon precursor,and urea as the nitrogen agent.The sample NCFC exhibits outstanding electrochemical performance due to the combined action of unique coral flower structure,rich nitrogen content（0.97%）,high specific surface area(937 m² g^-1)and well-developed porosity.The NCFC exhibits high specific capacitance of 333 F g^-1at the current density of 1A g^-1.Futhermore,the specific capacitance could still maintain the original value after 10000 cycles of charge and discharge.Then,the symmetrical supercapacitor has been assembled with NCFC as the positive and negative electrodes.The test data shows that the device can obtain potential window of 0-1.4V,specific capacitance of 75 F g^-1 and energy density of 21 Wh kg^-1(at the power density of 705 W kg^-1).It is surprised that two devices in series can easily light up a LED light（working voltage of 1.8 V）.（2）The nitrogen doped open bowl carbon material（HSPC-2）was synthesized with SiO₂ as template,cellulose acetate as carbon source,polyvinylpyrrolidone as modifier and nitriding agent.The sample HSPC-2 exhibits thin wall,large hollow cavity and open bowl structure with smooth surface.The electrochemical tests of HSPC-2 show that the specific capacitance is up to 245 F g^-1,when the current density is 1A g^-1.Futhermore,the symmetrical supercapacitor was assembled and tested in 1 M H₂SO₄ electrolyte.When the power density is 600 W kg^-1,the energy density is 11.2 Wh kg^-1.（3）The interconnected porous and heteroatom self-doped carbon nanosheets（PHPC-2）has been prepared by using Jackfruit nuclear as the carbon precursor containing rich nitrogen and Mg（NO₃）₂ as the activator via one-step method that carbonization,activation and nitrogen-doping occurring simultaneously.The material PHPC-2 exhibits a hierarchical porous structure composed of macropores,mesopores and micropores and high specific surface area(2621 m² g^-1).When used as electrode material,the PHPC-2 exhibits high specific capacitance 351 F g^-1 at the current density of 1 A g^-1.The specific capacitance could still maintain 97.5%of original value after10000 cycles of charge and discharge.The symmetrical supercapacitor was assembled and tested to study the real energy storage performance.It is found that the device can achieve working voltage of 1.4 V,high energy density of 16.6 wh kg^-1(at power density of 699 W kg^-1)and excellent cycle stability（the capacitance only loses 3.7%after 2000cycles）.