Fabrication And Properties Of Carbon/Tin Based Nanofibrous Materials Via Electrospinning

In this paper, porous carbon nanofibers(CNFs) membrane, porous tin oxide(SnO2) nanofibers membrane and carbon-tin based composite nanofibers membrane were successfully fabricated by a dual-opposite-spinneret electrospinning technique combined with calcination treatment, using polyacrylonitrile(PAN), SnCl4·5H2O as precursors, and polyvinyl pyrrolidone(PVP) as spinning additive, respectively. For nanofibers membranes, morphology observation, structure characterization, wettability analysis and electrochemical capacitive tests were investigated by optical microscope, scanning electron microscopy(SEM), thermo-gravimetric analysis(TGA), Fourier transform infrared spectroscopy(FTIR), Raman spectra, X-ray diffraction(XRD), contact angle meter and autolab-electrochemical workstation.PAN with 53000 weight-average molecular weight has good spinnability within the electrospinning parameters, namely, mass fraction of about (12～14)%, viscosity of about (600～1200) mPa/s, velocity of about (0.1～1.0) mL/h, electric field intensity of (1.2～1.6) kV/cm, the distance between two spinnerets of approximately 15.00 cm. The effect of preoxidation temperature, heating rate and heating medium on the preoxidized structural transformation of PAN was discussed by FTIR and TGA. The optimized parameters are as the following that preoxidation temperature is 290℃, heating rate 3℃/min, preoxidation time 80 min, and oxidation medium air. The influence of carbonization temperature on the structure of CNFs membrane was studied by FTIR, Raman and XRD, which makes it clear that with the increase of carbonization temperature, the graphite-like layer structure in CNFs becomes more compact and ordered, the space between graphite layers decreases and graphite-like structure size gradually increases. The wettability tests reveal the changing rule of contact angle in the three stages of PAN nanofiber membrane, preoxidation membrane, and carbonization membrane.SEM was used to reveal the surface morphology and size of SnO2 nanofibers. The effect of calcination temperature on crystalline size was studied by X-ray diffraction. The influence of calcination temperature on the molecular structure, thermal stability and phase structure of nanofibers membrane was studied using FTIR, TGA-DTA and Raman spectra. The results show that the PVP/SnCl4 nanofibers with the average diameter of about 640.87nm could be stably and continuously electrospun when the distance between two spinnerets is 15.0cm, the electric field strength ranges from 1.1kV/cm to 1.4kV/cm, the flow rate of micro-injection pump is 0.5 mL/h and viscosity ranges from 1500 mPa/s to 3300 mPa/s. It concluded that smooth PVP/SnCl4 nanofibers membrane calcined at 900℃ presents a tetragonal, rutile crystal structure type with a grain size about 12.27 nm and hydrophilicity.In this work, we used a new approach to fabricate side-by-side carbon-tin based composite nanofibers via a dual-opposite-spinneret electrospinning followed by thermal treatment. FTIR, TGA, FE-SEM and EDX were applied to investigate surface structural changes and micromorphology of the as-prepared composite nanofibers membranes before and after calcination. Contact Angle tests show that wettability of the composite nanofibers membranes after calcination dramatically changes from hydrophilic material into hydrophobic one. The influences of carbonization temperature and scanning speed on the electrochemical capacitance of unactivated CNFs membrane and carbon-tin based composite nanofibrous membrane were examined by electrochemical workstation.The results show that the higher the carbonization temperature is, the higher the graphitization degree of carbon fiber structure becomes, leading to be better electrical conductivity and capacitance characteristic. The influence of scan rate on the capacitive depends mainly on the diffusion rate of anion and cation in electrolyte and the active area on the surface of membrane electrodes. At current density of 20mA/g, the specific capacitances of the unactivated CNFs membrane and carbon-tin based composite nanofibers membrane after carbonization at 900℃ are about 46.1 F/g and 53.7 F/g, the values of ESR are 220 Ω,223 Ω, respectively. It can be seen that bicomponent carbon-tin based composite can synergistically improve the capacitance characteristic of CNFs membrane. After carbonization at 1100℃, the specific capacitance of carbon-tin based composite nanofibrous membrane is about 83.3 F/g, and the value of ESR 82Ω. After carbonization at high temperature, the conductivity of the composite membrane turns out to be better, the value of ESR lowers, and the specific capacitance increases significantly.