Preparation Of Nitrogen-doped Porous Carbon Material And Application For Supercapacitors

As a new energy storage device,supercapacitors have the advantages of traditional capacitors and rechargeable batteries to deliver high power and high energy storage in short time.The electrode material is a key factor in determining the specific capacitance and energy storage density of the supercapacitor.Carbon is one of the most widely used electrode material in supercapacitors.In this study,a series of porous N-doped carbon materials with different pore structures were prepared by template method or biomass was used as carbon source to prepare carbons.The pore structure,surface species and chemical composition of carbons were characterized.The capacitive performances of carbon materials were studied by using KOH or Li2SO4 as electrolyte.The effects of pore structure and surface chemical morphology on capacitive performance were investigated.The main studies are as follows:1.N-doped hierarchically micro-and mesoporous carbons with superior performance in supercapacitorsA series of N-doped carbons with hierarchically micro-and mesoporous structure were prepared by using silica nanoparticles as the template,ethylenediamine(EDA)and CCl4 as carbon and nitrogen sources,and potassium hydroxide(KOH)as the activation agent.It was found that the nitrogen-doped carbon(NC)without being activated shows lower capacitive performance due to the low surface area(287 m2 g-1)while the carbon activated at 800 oC(NC800)shows the best capacitive performance and the capacitance can reach up to 417 F g-1 at a current density of 0.5 A g-1 due to the ultra-high surface area(3056 m2g-1),large mesopores(~3 nm)and the proper nitrogen content.The large surface area is beneficial to the double-layer capacitance while the nitrogen content attributes to the pseudocapacitance.The larger mesopores and micropores are in favor of the decrease of mass transfer resistance.After 5000 cycles at a current density of 3 A g-1,the capacitance of NC800 can still maintain 97.6% of original capacitance.The energy density can reach up to 11.2 Wh Kg-1 at the power density of 125.1 W Kg-1.2.Facile preparation of seaweed-like Carbons with Ultrahigh Nitrogen Content using Mg O as hard template and activation agent with superior performance in supercapacitorsPorous nitrogen-doped carbon materials were prepared by using magnesia as template and ethylenediamine(EDA)and carbon tetrachloride(CCl4)as carbon and nitrogen sources.By changing the carbonization temperature,a series of porous nitrogen-doped carbon materials with different nitrogen contents can be controllably synthesized.The three-electrode test results showed that the M600 has the highest specific capacitance of 535 F g-1 at a current density of 0.5 A g-1 in a 6 M KOH solution.The M600 was assembled into a symmetric supercapacitor and tested in two electrolytes,6 M KOH and 2 M Li2SO4,showing excellent performance.At 5 A g-1,after 10000 cycles,the capacitance remained at 98.2% and 96%.Among them,the voltage window in 2 M Li2SO4 electrolyte can be widened to 0-1.8 V,the energy density can reach 41.6 Wh Kg-1,and the corresponding power density is 225 W Kg-1.This is attributed to the increase of the wettability of the surface of the carbon material after the introduction of nitrogen atoms into the carbon skeleton,the high nitrogen content and the high specific surface area and the mesoporous structure contribute to the increase in the pseudocapacitance of the carbon material.3.N-Doped Carbons with Hierarchically Micro-and Mesoporous Structure Derived from Sawdust for High Performance SupercapacitorsA series of nitrogen-doped carbons were prepared by using biomass waste sawdust as carbon source for supercapacitors.A new nitrogen-doping strategy was proposed to introduce nitrogen element into carbons by using ethylenediamine and carbon as nitrogen source through the polymerization reaction on sawdust under moderate conditions.The raw carbons were further activated with KOH to improve the surface area to increase the electric double layer capacitance while the heteroatoms can improve the pseudocapacitance.The prepared carbons were characterized with different techniques and the electrochemical performances were tested.It was found that the nitrogen-doped carbons activated with a KOH to carbon mass ratio of 5(NC600-800-5)has the largest specific surface area(1674 m2 g-1)and moderate nitrogen content(2.88 wt%).Compared with the carbon without introduction of nitrogen element(C600-800-5),the capacitive performances of nitrogen-doped carbons were greatly improved,which may be due to the increase of pseudocapacitance and the improvement of wettability introduced by nitrogen element.The largest specific capacitance,367 F g-1,was reached at 0.5 A g-1 in 6 M KOH solution while the specific capacitance of C600-800-5 is only 279 F g-1.After 10,000 cycles at 3 A g-1,the specific capacitance can keep 96.7% of the initial value,suggesting the excellent cycling performance.The energy density can reach 8.7 Wh Kg-1 at a power density of 251.6 W Kg-1.Thus,it is proved that the nitrogen-doping strategy is effective and the introduction of nitrogen element to carbons is particularly important to the improvement of the electrochemical performances.