Study On The Preparation And Electrochemical Properties Of Porous Carbon Fiber And Their Composite Structures Based On Electrospinning

As one of the most promising energy devices,supercapacitors have attracted much attention due to possess a large number of outstanding characteristics such as charging and discharging speed,highly active and longer cycling life.This paper focus on the method of the green,fast and non-polluting to produce the porous carbon fiber structure.In this paper,the freestanding carbon fibers（CNF）structure has been prepared by electrospinning,adjusting the precursor,the method of the collection,the gas atmosphere and temperature of the thermal annealing.As a template,the zinc oxide nanoparticles would be removed to prepare porous carbon fiber structure,which could enhance the electrochemical performance of the freestanding porous carbon.In order to enhance the electrochemical properties of the manganese dioxide,it was loaded on the surface of the freestanding porous carbon structure.Even if the TiO₂ template can be incompletely removed to fabricate the porous carbonfibers,we also annealed it at the atmosphere of hydrogen,and then the manganese dioxide loaded on it to improve performance of the capacitance.（1）We get the freestanding CNF structure by adding zinc oxide nanoparticles as a template to the precursor liquid,by changing the collected method of the electrospinning.We have fabricated different morphology of freestanding porous CNF structure,by adjusting the ratio of zinc oxide and polyacrylonitrile in N,N-dimethylformamide,and then electrospun and annealing it.The formation of porous CNF’s principle is that the reaction of carbon and zinc oxide at high temperatures,polyacrylonitrile could be carbonized at the atmosphere of argon conductions under high temperature,zinc oxide reacts with carbon to produce zinc vapor and carbon monoxide,the freestanding porous CNF structure would be formed under this temperature.The best mass ratio of the zinc oxide and polyacrylonitrile is 1: 1,which can get relatively uniform distribution of the hole structure in the CNF.Even if a few of the residual zinc will be stayed in CNF after the reaction,we can further remove the residual zinc by the hydrochloric acid.We continue to add zinc acetate in the precursor fluid to get porous structure after electrospinning and annealing,which owns larger specific surface area.We have measured the electrochemical performance of the porous CNF structure,the freestanding PN-CNF structure exhibits a high capacitance value of 180 F/g at a current density of 0.2 A/g,which is about 6 times the freestanding CNFs structure.（2）The freestanding Bubble carbon fibers（B-CNFs）structure has been prepared by electrospinning,the manganese dioxide was loaded on the surface of the B-CNFs.Mainly to illustrate the formation process of the porous structure at the different temperature,we show that the zinc oxide was completely removed at 1000 ° C to prepare the freestanding B-CNFs structure.The reaction of zinc oxide and carbon at this temperature is completely removed,verify the mechanism of the reaction of zinc oxide and carbon.The manganese dioxide nanosheets was loaded on the surface of the freestanding B-CNFs structure.We have used a variety of method to test the characteristic of the freestanding B-CNFs/MnO₂,including SEM,TEM,Raman,XRD,and XPS,which shows that manganese is in the form of +4 valence by XPS testing,the MnO₂ has been loaded on the surface of the B-CNFs.The result of electrochemical test shows that the specific capacitance value of MnO₂ supported by porous CNFs is 2.1 times that of the MnO₂ supported on CNFs,which shows good electrochemical performance and cyclic stability.（3）In this chapter,we have been tried to prepare the porous carbon material by another template TiO₂,compored with the ZnO template.We test the electrochemical performance of the composite of CNFs and TiO₂ annealed at the atmosphere of hydrogen supported the MnO₂.The composite of CNFs and TiO₂ can be obtained by the method of electrospinning by adding the TiO₂ nanoparticles in the precursor liquid,annealing it at high temperature under argon atmosphere.Firstly,we tried to remove the template by the reaction of sodium hydroxide and titanium dioxide.We used the TEM to test the characterization of the freestanding porous CNFs structure after the above experiments,there also still some TiO₂ incomplete removed,which caused by a part of the TiO₂ wrapped in deeply internal in the CNFs.Secondly,when it is directly annealed at the atmosphere of hydrogen,but not to remove the template TiO₂,which make the polyacrylonitrile with high carbonation at this temperatures,the oxygen vacancy of titanium dioxide would be increased.The MnO₂ has been electrodeposited on the surface of the composite of hydrogenation of CNFs and TiO₂ composite structure has been test.Through the test,it shows that the specific capacitance of the MnO₂ loaded on the surface of the hydrogenated freestanding CNFs and TiO₂ composites structure is 2 times before hydrogenation,which shows it is a promising composite electrode structure.