Boron-doped Carbon Fiber And Optimization Of Its Electrochemical Performance

Carbon materials are widely used in the fields of energy conversion and energy storage devices due to their rich sources,simple synthesis methods,and low prices.Among them,carbon fiber materials stand out among the many carbon materials because of their unique one-dimensional structure,good electrical conductivity,thermal conductivity,and corrosion resistance,and have attracted widespread attention.However,the performance of unmodified carbon fiber in energy conversion and energy storage devices is not satisfactory.Therefore,this paper uses high-voltage electrospinning technology to synthesize a series of carbon fiber materials.The fine adjustment of fiber diameter is achieved by controlling the precursor concentration,voltage,flow rate and other parameters.Carbon fibers with different boron doping concentrations were prepared using tributyl borate as boron source,and the effects of boron doping concentration on wettability,conductivity,specific surface area and other parameters closely related to electrochemical performance were investigated.Finally,the practical application effect of carbon fiber as an electrode active material in energy conversion and energy storage devices such as supercapacitors,oxygen reduction systems,and photocapacitors is explored.The experimental results obtained are as follows:(1)The study found that the diameter of carbon fiber can be adjusted by voltage.As the voltage applied to the polymer solution increases,the electrostatic force of the system increases,and the droplet splitting ability increases accordingly.The fiber diameter gradually decreases.By controlling the voltage,the synthesis is successful.A carbon fiber material with a diameter between 200 nm and 300 nm is used.At the same time,carbon fiber materials with different boron doping concentrations were prepared.(2)In the three-electrode system of supercapacitors,the energy storage effect of fiber materials in lithium electrolyte(1 mol L^-1 acidic Li₂SO₄,1 mol L^-1 neutral Li₂SO₄,1 mol L^-1 Li OH)was investigated.The study found that the carbon fiber electrode material exhibits the highest electrochemical performance in the acidic Li₂SO₄ solution.When the current density is 1 A g^-1,the discharge specific capacity of the carbon fiber without boron is 144.41 F g^-1.The discharge specific capacity of boron-doped carbon fiber is higher than that of undoped electrode materials.When the addition amount of tributyl borate is 5.00 m L,the discharge specific capacity is the largest,reaching 280.23 F g^-1,which doubles the performance.In addition,after10,000 cycles of cycle stability test,the specific capacitance retention rate is 93.98%.Because the introduction of boron element,the boron produces charge polarization to adjacent carbon atoms,which breaks the neutral condition of the electrode material,and can also use the spatial network structure of the fiber material to promote the rapid movement of electrons,thus realizing the electrode the energy density and power density of materials are improved.(3)In the oxygen reduction(ORR)system,several boron-doped carbon fiber electrode materials all show better ORR characteristics than carbon fiber.Under the same conditions,the half-wave potential of the carbon fiber system is 452.93 m V(vs.RHE).When the amount of tributyl borate added is 5.00 m L,the half-wave potential reaches the maximum value of 609.22 m V(vs.RHE)in the system.The reaction is a two-electron and four-electron mixing process,and the hydrogen peroxide yield is the lowest.(4)In the self-charging integrated photocapacitor device with dye-sensitized solar cells as the energy conversion part and supercapacitors as the energy storage part,carbon fiber materials also exhibit high electrochemical performance.In dye-sensitized solar cells,when carbon fiber is used as the counter electrode,the cell efficiency is only 1.19%;Boron doping can significantly improve the catalytic activity of carbon fiber electrodes.When the added amount of tributyl borate is 5.00 m L and7.50 m L,the battery efficiency reaches 2.38 and 2.49%,respectively;In a solid supercapacitor with a symmetrical structure,when the added amount of tributyl borate is 5.00 m L,the discharge specific capacity of the capacitor reaches 41.15 F g^-1,which is significantly higher than the undoped capacitor capacity of 24.79 F g^-1.In addition,the boron-doped electrode also shows high stability in capacitor devices.After 2000cycles of charge and discharge,the capacity retention rate is 84.20%.Finally,the prepared fiber electrode material is used to assemble the photo-capacitor,and the integrated device is photo-charged,and then it is discharged at a constant current of0.10 A g^-1 in a dark environment,and the discharge time can be as long as 60 s.In summary,this thesis prepared a series of carbon fiber materials,explored the influence of precursor concentration,flow rate,voltage and other experimental conditions on fiber diameter,and modified the carbon fiber materials by boron doping,which proved that element doping is one An effective way to improve the electrochemical performance of carbon fiber electrodes.Finally,the application effects of carbon fiber in supercapacitors,ORR systems,and optical capacitors were initially explored.The research results have certain reference value for the development of cheap and efficient electrode materials for supercapacitors,fuel cells,and photocapacitors.