| In this paper, Melamine/polyacrylonitrile/DMF emulsion spinning system was successfully prepared, using melamine as modifier, and polyacrylonitrile (PAN) as precursors. Melamine modified polyacrylonitrile nanofiber membranes were successfully fabricated by electrospinning technique. Nitrogen doped porous carbon nanofiber (CNF), were further successfully synthetized with calcination treatment Furthermore, hydrothermal method was used to produce Ni(0H)2/CNF binary composite electrode materials The structure and morphology of these above materials above were tested by a series of characterization methods. The electrochemical capacitor performance of nitrogen doped porous carbon nanofiber and Ni(OH)2/CNF binary composite materials were studied. Wettability analysis and tensile properties of the organic composite membrane were investigated by contact angle meter and electronic universal tensile testing machine. The main work includes the following aspects:Firstly, We study the properties of spinning solution and electrostatic spinning process parameters which have the impacts on morphology of the nanofibers. The electrospinning parameters, namely, mass fraction of about 8-14%, viscosity of about 600-1600 mPa.s, velocity of about 0.50-1.00 mL/h, electric field intensity of 1.00-1.33 kV/cm, were finalized from fiber’s microstructure which can be observed by optical microscope. Fiber membrane’s tensile testing showed that the lower the levels of melamine, and the greater the viscosity of the spinning solution the larger the tensile strength. The hydrophilic and hydrophobic properties of the organic nanofiber membrane were changed owing to the addition of melamineSecondly, pre-oxidation process parameters including, heating rate 3℃/min, pre-oxidation temperature 290℃, holding time 90 min, were confirmed by analyzing pre-oxidation mechanism, TGA curves, and optical images. The influence of pre-oxidation temperature on the molecular structure, thermal stability and phase structure of nanofibers membrane was studied using FTIR, TGA-DTA and Raman spectra. SEM was used to reveal the surface morphology and size of nitrogen doping carbon nanofibers. XPS, XRD, N2 adsorption/desorption and organic element analyzer were applied to investigate structural changes and micromorphology of the as-prepared composite nanofibers membranes after carbonization. The results show these carbon nanofibers have relatively high-level nitrogen doping (up to 14.25%) and inter-connected nanofibrous morphology with a well-developed porous structure including micropores, mesopores and macropores by melamine doping. Carbon nanofiber with high-level nitrogen content and porous structure has excellent electrochemical performance. Without activation, the carbon nanofibers have high specific capacitance up to 194 F/g at a current density of 0.05 A/g. Cycling evolution shows that specific capacitance retained approximately 99.20% of initial capacitance after 1000 cycles at a current density of 2 A/g, indicating an excellent electrochemical performance.Lastly, we research the relationship between the electrochemical capacitance performance of the composite materials and different hydrothermal reaction time, reaction temperature, different substrate materials and different pretreatment of the substrate materials. According to the electrochemical capacitance performance, we determine the appropriate hydrothermal reaction conditions. Based on optimal conditions of hydrothermal process, we successfully prepared binary composite electrode material with different carbon nanofiber content by controlling the feed ratio. The effects of carbon nanofiber content on the electrochemical properties of the composite electrode material were studied. The results show the conductive properties and structural stability of these composite electrode materials achieve significant improvement with the increase of carbon nanofiber content. The composite electrode material has high specific capacitance up to 1820.02F/g at a current density of 0.50 A/g. |
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