Preparation Of Nitrogen-doped Carbon-based Materials And Their Application In Supercapacitors

With the increasing demand of energy and environment for sustainable development,many countries in the world have invested a lot of resources to develophigh-performance,low-costandenvironmentally-friendly electrochemical devices,including fuel cells,lithium-ion batteries and supercapacitors.Supercapacitors?also known as electrochemical capacitors?include electrochemical double-layer capacitors that depend on the charge storage of ion adsorption,and pseudo-capacitors that are based on charge storage involving fast surface redox reactions.The energy storage capacity of supercapacitors is several orders of magnitude higher than that of traditional dielectric capacitors,but much lower than that of secondary batteries.They usually have high power density,long period stability and high security,so they are of considerable value in applications requiring high power output or fast energy collection.Although supercapacitors have many advantages,their performances depend heavily on the electrode materials.Starting from the charge storage mechanism and the latest research progress of supercapacitors,the preparation of carbon materials or their composite electrode materials and their applications in supercapacitors are studied in this paper.It mainly includes the following aspects:Firstly,the preparation and application of new nitrogen doped graphene aerogels were studied.Starting from the nitrogen doping and drying methods of aerogels,the method of preparing nitrogen doped graphene aerogels through natural drying with plant extracts was discussed.The excellent properties of graphene aerogels and the application of nitrogen doped graphene aerogels in supercapacitors were studied.The results show that the prepared samples have a recoverable compressive strain of about 95%and an actual volume retention of about 95.64%.More importantly,when used as a supercapacitor electrode material,the nitrogen doped graphene aerogel prepared by this way has 371 F g^-1(Electrolyte:1M KOH;Current density:1 A g^-1)and about 54.978%(Current density:1⁵0 A g^-1)super high rate performance.Owing to graphene aerogels not only have their own excellent properties,they can also serve as carriers of various metals and their oxygen/sulfide nanoparticles.On the basis of the first work,three-dimensional blocks of CoS₂@MoS₂-NG were prepared.The sample has a specific capacitance of 198 F g^-1(Electrolyte:1M KOH;Current density:1 A g^-1)when it is used as electrode material of supercapacitor.Although it is a pseudocapacitance mechanism,the capacitance remains 96.97%after 1000 cycles.In addition to graphene and other carbon materials,traditional activated carbon materials still have tremendous development potential in supercapacitor electrode materials.Nitrogen-doped cigarette butt active carbon is prepared from common cigarette butt waste.The experimental results show that the sample exhibits a specific capacitance of 330.1 F g^-1(Electrolyte:1M KOH;Current density:0.5 A g^-1).It also has a long cycle life?93.48%after 10000cycles?.Wood has a natural hierarchical porous structure.As a result,nitrogen-doped wood-derived carbon was prepared by one-step method to achieve low cost without destroying its graded pore structure.When used as an electrode,it has a specific capacitance of 211 F g^-1(Electrolyte:1M KOH;Current density:1 A g^-1),57.35%rate performance(current density from 1 to 50 A g^-1),and excellent cycle life?93.24%after 7500 cycles?.In a word,the application of graphene materials,composites and traditional activated carbon materials in supercapacitor electrodes is discussed in this paper.The results show that after certain chemical modificationt,they all exhibit excellent electrochemical properties and show great potential in the field of commercial supercapacitor electrode materials.