Papers by Keyword: Carbon Nanofiber

Abstract: This study aims to synthesize, purify, and modify magnetic carbon nanofibers (Mag-CNF) into hydrophilic carbon material. The synthesis method was carried out by chemical vapor deposition (CVD) using the catalyst from Incolloy at 800°C with argon, nitrogen, hydrogen, and acetylene gases. The purification of Mag-CNF was then conducted by dissolving Mag-CNF with toluene and ethanol, followed by vacuum annealing. The hydrophilization of Mag-CNF was further performed by adding amine groups via reacting Mag-CNF with ethylene diamine, NaNO₂, and H₂SO₄. The successfully prepared Mag-CNF has characteristics of tubular tube bundles consisting of carbon nanofibers with an average diameter of 100-120 nm. The X-ray diffraction (XRD) profile shows the characteristics of carbon, iron, iron oxide, and iron carbide. The Raman spectra show the existence of D, G, and G' bands corresponding to the characteristics of carbon nanomaterials. The magnetic property characterization using a vibration sample magnetometer (VSM) shows the synthesized product as ferrimagnetic materials. The modification results show the addition of hydrophilic groups to Mag-CNF, such as O–H and N–H groups, as analyzed in Fourier Transform Infrared (FTIR) spectra. The successful hydrophilization was also visually confirmed using a dispersion test in water, showing that Mag-CNF has better dispersion after surface modification.

Abstract: A novel electrocatalyst has been developed based on polypyrol-carbon nanofiber (PPy-CNF) support material to increase the stability of Pt/ PPy-CNF/GDL electrocatalyst in direct methanol fuel cell (DMFC). A novel conducting polymer (PPy)-CNF nanocomposites was prepared by a solution dispersion technique and used to support platinum nanoparticles. For preparation of catalyst ink, 20 wt.% Pt/PPy-CNF electrocatalyst with a platinum loading of 0.4 mg cm^-2 was prepared by ethylene glycol (EG) method. Physical and electrochemical properties were analyzed by X-ray diffraction (XRD), Fourier transform infrared (FTIR), scanning electron microscopy (SEM), transmission electron microscopy (TEM) imaging and cyclic voltammetry (CV) experiments. FTIR results prove the existence of PPy in the support. SEM images showed that the one–dimensional CNFs were efficaciously covered by PPy. The TEM characterization revealed that the fine Pt nanoparticles prepared by polyol method were dispersed on the surface of the electrocatalyst successfully. XRD patterns also revealed that the mean size of Pt crystal nanoparticles was about 3.69, 6.51 and 2.91 nm for Pt/PPy-CNF, Pt/CNF and Pt/C electrocatalyst respectively. The size of the PPy on carbon paper has been measured in the range of 35-40nm by AFM. Based on the electrochemical properties and acceleration tests evaluated by cyclic voltammetry measurements and Chronoamperometric experiments it was found that the as prepared Pt/PPy-CNF/GDL electrode exhibited a comparable electrochemical surface are (ECSA), MOR activity and so stability (in the presence of methanol) with respect to the Pt/CNF /GDL and Pt/C/GDL commercial one. A rather significant reduction in the peak potential of methanol electro-oxidation from 0.69V for Pt/C/GDL to 0.76V for Pt/PPy-CNF/GDL electrode indicates that an increase in the activity for MOR is achieved by replacing the C by PPy-CNF. The corresponding ECSA values for the Pt/PPy-CNF/GDL, Pt/CNF/GDL and Pt/C/GDL electrodes were 108.69, 53.93 and 17.98 m²g^-1 respectively.

Abstract: The need for the development of renewable energy harvesting and storage devices is on the front as the world is facing an environmental crisis due to the consumption of gallons of fossil fuels. One of the promising solutions on which many researchers are concentrating is supercapacitor as it possesses high energy and power density. Current literature study focusing on developments already had in the field of manufacturing of supercapacitors using different precursors, testing conditions, fiber dimensions, and their performance analysis. Most of the studies found that Polyacrylonitrile (PAN) based electrospun carbon fiber webs is a potential electrode material for supercapacitors. The information gathered in this article is about the electrospinning technique, Surface and electrochemical characterization methods, and recent advances in their performance are highlighted. Also, enhancement in electrochemical performance through optimization of electrospinning parameter, a precursor modification by the addition of active materials (such as carbon nanotubes, metal oxides, and catalysts), heat and surface treatment followed, and optimum fibrous structures are summarized.

Abstract: Pressure-sensitive conductive material is used for various pressure sensors consists of a polymer nanocomposite with carbon nanotubes (VGCF). And the resistance in it were changed by adding applied load. Recently, carbon nanotubes (VGCF) has drawn attention as a function filler that imparts various functions to a resin, including electrical properties. In polycarbonate (PC) composite with VGCF, the resistance decreases with increase in applied load. And increase of the addition amount of VGCF was enhanced the mechanical properties and electronic properties. In addition, this conclusion suggested that strain of PC/VGCF caused reducing the resistance. Therefore, changing matrix is predictably effective on electrical properties in pressure-conductive materials. In the present study, we used various matrix had different elastic modulus. The addition amount of VGCF was 12.5% volume rate. We made silicone/VGCF and polyethylene (PE)/VGCF and polycarbonate (PC)/VGCF by twin screw extruder and injection moldings. To clarify the influence of elastic modulus of matrix on conductivity of VGCF dispersed plastic matrix composites. The experimental results showed that conductive property of pressure-sensitive conductive materials is related to elastic modulus of them.

Abstract: Carbon nanofibers (CNFs) have been successfully prepared by using electrospinning at various flowrates, and were formed from polyvinyl alcohol (PVA) and activated carbon (700-1400 m²/g) as electrodes on capacitive deionization. Before being furthermore deposited into electrodes, characterization was carried out on CNFs by using SEM. Cyclic voltammetry analysis was also performed to determine the electrolysis mechanism of the electrodes. The best results in removing salt reaching 70% were achieved by capacitive deionization systems with the smallest diameter size of CNFs, at a voltage of 1.5 V. The CNFs formed by electrospinning have potential to be used as excellent capacitive deionization electrodes for the desalination process.

Abstract: The objective of this research is to evaluate the temperature dependent strengthening mechanism of 0.5 wt.% carbon nanofiber reinforced glass fiber/epoxy (CNF-GE) as a function of environmental temperature. Flexural response of the CNF-GE composite has been studied at 30°C, 70°C and 110°C temperatures and compared over control glass fiber/epoxy (GE) composite. When flexural test was conducted at room temperature, CNF-GE composite exhibited about 29% improvement in strength, over control GE composite. With increase in environmental temperature, the extent of strength enhancement continued to decrease and at 110°C, the strength of the CNF-GE composite was found to be about 12% lower than control GE composite. Visco-elastic properties of CNF-GE and control GE composites have also been studied in the temperature range of 40 to 200°C.

Abstract: Carbon nanofibers (CNFs) were grown in situ on porous glass at different temperatures and times using a Ni acetate catalyst and CH₄/N₂ as a carbon source. The porous glass was obtained by acid leaching of phase separated borosilicate glass, which generates a broad size distribution of mesopores (≈20 nm). Subsequent impregnation with Ni acetate reduces the pore size to ≈ 4 nm but also creates new micropores, thus increasing the surface area. During thermal treatment the surface area decreases as temperature rises, mainly due to shrinkage of the glassy matrix; however new pores are created at ≈ 70 nm (mainly at 600 oC) associated to the generation of CNFs on the glass surface, indicating this temperature offers the best conditions. The CNFs grow inside and fill in the micro-mesopores in the porous glass. They do not grow at 500 oC as the Ni acetate is not transformed into metallic Ni. Ni deactivation occurs at temperatures over 700 oC, thus reducing the formation of CNFs. At 1000 oC the degradation of CH₄ leads to a thickening of the CNFs. The thermal degradation of the CNFs occurs in two steps, the first (360-416oC) corresponding to CNFs grown on the glass surface and the second (518-649oC) to CNFs grown inside the glass pores. Treatment times over 2 h lead to the deactivation of Ni, pore shrinkage and hence lower CNF yields.

Abstract: In the present study, the effects of different parameters of needleless electrospinning systems on polyacrylonitrile (PAN) nanofibers morphology and diameter were studied. The electric field profile at the surface of the spinneret and electrospinning zone was evaluated by Finite Element Method. The PAN nanofibers were used as the precursor to fabricate carbon nanofibers. Scanning electron microscope (SEM), X-ray diffraction and Raman spectroscopy were used for electrospun nanofibers analysis. The results of electric field analysis indicated, in the spinning direction, the electric field was concentrated at the surface of the spinneret and decayed rapidly toward the surface of the collector. Increasing polymer solution concentration from 7.00 to 11.00 wt.% resulted increasing nanofibers diameter form 77.76 ± 19.44 to 202.42 ± 36.85. The results of X-ray diffraction and Raman spectroscopy show that heat treatments could convert needleless electrospun PAN nanofibers to carbon nanofibers.

Abstract: In this work, Carbon Nanofiber mates (CNF) were fabricated by carbonization of electrospun non-conducting PolyAcryloNitrile (PAN) and PAN/PolyvinylAlcohol (PVA) nanofiber mates at 1100°C. PAN acts as a carbon source while PVA acts as a scarifying material to create porosity which leads to increase the accessible surface area. Two types of samples have been produced, carbon nanofiber mate (CNF) and Porous carbon nanofiber mate (P-CNF). The samples were first characterized by XRD, FTIR and SEM then examined as novel electrodes for supercapacitor applications. The specific capacitance (SC) results of the CNFs based on electrospun PAN mate and P-CNF based on electrospun PAN/PVA mate precursors, were 170 and 202 Fgm^-1 respectively. The porous structure of P-CNF mate not only increased SC but also increased the capacitive retention and cyclic stability at discharging current density three times higher than that applied in case of CNFs. These results confirm that the tailored P-CNFs have potential for lightweight and durable flexible supercapacitor applications.

Abstract: This work was focused on improving machining performance of reaction-bonded silicon carbide (RB-SiC) ceramic material using an electrical discharge machine (EDM) with the aid of surfactant. The changes of material removal rate, electrode wear ratio and surface roughness were investigated under two different surfactants, namely Span 20 and Span 80. The surfactant was mixed with carbon nanofiber (CNF) and EDM oil prior to the experiment. Then, the mixture was homogenized in an ultrasonic homogenizer for 35 minutes. In order to investigate the effect of surfactant, different weight percentages which is 0.4wt%, 0.6wt% and 0.8wt% of surfactant were used. The experimental results show that with the addition of Span 20 and Span 80, the electrode wear ratio was decreased with the increased of surfactants weight percentage. Surface finish also can be improved by adding surfactant in the dielectric fluid. The lowest surface roughness was achieved at a surfactant weight percentage of 0.4wt%. The optimum weight percentage for obtaining the highest material removal rate (MRR) was 0.6wt% for both surfactants. In comparison, CNF added with surfactant Span 80 was more effective to improve the machining efficiency of RB-SiC compared to surfactant Span 20, at the optimum weight percentage 0.6wt%.