Preparation And Electrochemical Performance Of Electrospinning Porous Nitrogen - Rich Carbon Fibers

Supercapacitors are new type of electrochemical energy storage devices between traditional capacitors and batteries, which have high capacitance, long cycle life, fast charging/discharging rate, superior power density, and low maintenance cost. With the development of the society, supercapacitors have possessed a significant amount of interest and attention due to their superior performances, they have broad application prospects including new energy vehicles, defense and aerospace, sensors, etc. Electrode materials play a crucial role in supercapacitors, and they are the key to the supercapacitors performance. Therefore, the preparation of high-performance electrode materials is a focus in the study of supercapacitors. Carbon materials have been widely used in supercapacitors because of their large surface areas-controllable pore structure and chemical stability, moreover, they are inexpensive and easy to obtain. Electrospinning offers a low cost, simple and highly effective technique to fabricate carbon nanofibers and their hybrids with tunable nanostructures.In this paper, polyacrylonitrile (PAN) was used as precursor, tripolycyanamide as source of nitrogen, and melamine resin (MF) was synthesized to dissolve in the solution. The nitrogen-rich carbon fibers were prepared by electrospinning, preoxidation and carbonization. The porous nitrogen-rich carbon fibers were obtained by chemical activation or pore forming agent added in the solution. The physical and chemical properties of fibers were characterized by SEM, XRD, XPS, nitrogen dsorption/desorption and other methods. The electrochemical properties were measured by cyclic voltammetry and galvanostatic charge/discharge test. The main results are shown as follows:Polymer fibers with different amounts of MF were fabricated by electrospinning, the doping amounts of MF were 0%,25%,50% and 75%. After preoxidation under 250℃ and carbonization at 800℃, the nitrogen-rich carbon fibers were obtained. Results show that:Fibers still can be obtained after doping MF in the solution, but with increasing of MF, fibers diameter became thicker, after carbonization the diameter was reduced. The nitrogen doped carbon fibers are amorphous graphite structure. The nitrogen content of the carbon fibers surface increased with the increasing of MF doping amount. The surface nitrogen content is 12.1% when the doping amount reach 75%。The electrochemical tests indicate that the carbon fibers with 75% MF doping amount showing the best electrochemical performance:the specific capacitance is 144F/g at the current density of 1A/g, it is much higher than the carbon fibers without MF doping. The sample also possesses a superior rate capability of 60%(85F/g) at the current density of 10A/g.PAN and MF(75)/PAN nitrogen-rich carbon fibers were soaked in KOH solution, and then activated at 800℃ for 30min to prepare porous nitrogen doped carbon fibers. Results show that: carbon fibers are still amorphous graphite structure, but graphitization degree is decreased. The surface nitrogen content of carbon fibers is reduced after activation, but the oxygen content increased slightly. The nitrogen dsorption/desorption results indicate that the surface areas of carbon fibers are extremely improved after KOH activation, the specific surface area of PAN increased to 868 m2/g and MF/PAN increased to 453 m2/g, the quantities of micropores and mesopores in fibers are also extremely increased. The electrochemical measurements indicate that activated carbon fibers have superior electrochemical performances compared to the fibers without activation. (A)MF/PAN shows an excellent electrochemical performance among these samples, the specific capacitance is 255F/g at the current density of 1A/g, and 209F/g at 10A/g, and it also possesses a superior rate capability.Polyethylene glycol (PEG) was used as pore forming agent and dissolved in the solution, porous nitrogen-rich carbon fiber (NACF) was prepared by electrospinning, preoxidation and carbonization. Results show that:PEG added will not change the element contents on the surface of the fibers; Specific surface area increased from 58m2/g to 209m2/g due to the pore formation of PEG pyrogenic decomposition. The specific capacitance of NACF prepared by pore-forming of FEG is 280F/g at the current density of 1A/g, and NACF has better electrochemical performance compared to the fiber activated by KOH.