Graphite Nanofibers Research Articles

A comparison of three carbon nanoforms as catalyst supports for the oxygen reduction reaction

Defective graphene nanosheets (GNSs), single-walled carbon nanotubes (SWCNTs), and herringbone graphite nanofibres (GNFs) were used as Pd3Pt1 catalyst supports for an oxygen reduction reaction (ORR). Raman spectroscopy and cyclic voltammetry analyses revealed oxygen-containing functional groups and physical defects on the surfaces of the SWCNTs, GNFs, and synthesised GNSs. Mass-transfer-corrected Tafel diagrams obtained in an O2-saturated electrolyte showed that the SWCNTs with a high curvature allowed for more surface Pt atoms; thus, these Pd3Pt1 catalysts are the first SWCNT system to promote the ORR. These catalysts, however, were slower than the GNS-supported catalysts after 0.875V (vs. SCE; saturated calomel electrode). In terms of the kinetic current density, the highest mass activity was found for the Pd3Pt1/GNS composites. Additionally, according to rotating-ring disk electrode (RRDE) measurements, the H2O production efficiencies for the Pd3Pt1/GNS, Pd3Pt1/SWCNT, and Pd3Pt1/GNF systems were 70.35%, 66.7%, and 9.58%, respectively. Among these carbon supports, Pd3Pt1 on GNS showed the greatest efficiency and durability for producing H2O via an approximate four-electron pathway; this efficiency was ascribed to metal-support interaction.

Thermal conductivity predictions of composites containing percolated networks of uniform cylindrical inclusions

A theoretical approach is introduced that enables the prediction of the effective thermal conductivity of a composite containing a thermally insulating matrix and percolated networks of highly-conducting cylindrical inclusions. This theory is applicable for all inclusion sizes but is applied here for nanocomposites. The theory is based on first determining the effective thermal conductivity of a percolated inclusion backbone, followed by the introduction of spherical matrix regions within the backbone. The methodology presented here provides a prediction of the percolation threshold that is in good agreement with other studies, a simple expression to estimate the composite thermal conductivity where conduction through the matrix is ignored, and a straightforward iterative methodology for predicting the composite thermal conductivity when matrix conduction is included. In addition, the method provides a means to estimate the inclusion thermal conductivity, inclusion-inclusion contact conductance, and the thermal boundary resistance (TBR) based on macroscopic experimental measurements of the composite thermal conductivity for various inclusion volume fractions. Application of the method to existing carbon nanotube (CNT) and graphite nanofiber (GNF) composite experimental measurements provides predictions of these three parameters with some agreement with other studies, where more robustness is seen in predicting interfacial resistances than inclusion thermal conductivity.

Assessment of electromechanical properties of screen printed polymer nanopastes

Abstract Printed electronics has provided different printing techniques as environmentally friendly and cost-effective manufacturing methods of electronic components. The printed items can be produced on low cost, different types of flexible substrates, even when their surface is corrugated. This opens a new application range of printed electronics and makes them competitive with traditionally manufactured electronics. However, it is necessary to investigate new materials to continue the rapid progress in printed electronics. In our study, the electromechanical properties of polymer nanopastes consisted of carbon nanotubes and graphite platelet nanofibers mixed with a conductive polymer poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) were investigated. Their microstructure and the layer morphology were observed using a scanning electron microscope and an optical microscope. The thickness and average roughness of the layers printed on the foil and paper were determined with a contact profilometer. The mechanical durability of the screen printed layers was verified in a cyclic bending test. The highest mechanical durability was exhibited by the polymer pastes containing carbon nanotubes.

Thermal conductivity predictions of herringbone graphite nanofibers using molecular dynamics simulations

Non-equilibrium molecular dynamics (NEMD) simulations are used to investigate the thermal conductivity of herringbone graphite nanofibers (GNFs) at room temperature by breaking down the axial and transverse conductivity values into intralayer and interlayer components. The optimized Tersoff potential is used to account for intralayer carbon-carbon interactions while the Lennard-Jones potential is used to model the interlayer carbon-carbon interactions. The intralayer thermal conductivity of the graphene layers near room temperature is calculated for different crease angles and number of layers using NEMD with a constant applied heat flux. The edge effect on a layer's thermal conductivity is investigated by computing the thermal conductivity values in both zigzag and armchair directions of the heat flow. The interlayer thermal conductivity is also predicted by imposing hot and cold Nosé-Hoover thermostats on two layers. The limiting case of a 90° crease angle is used to compare the results with those of single-layer graphene and few-layer graphene. The axial and transverse thermal conductivities are then calculated using standard trigonometric conversions of the calculated intralayer and interlayer thermal conductivities, along with calculations of few-layer graphene without a crease. The results show a large influence of the crease angle on the intralayer thermal conductivity, and the saturation of thermal conductivity occurs when number of layers is more than three. The axial thermal conductivity, transverse thermal conductivity in the crease direction, and transverse thermal conductivity normal to the crease for the case of a five-layer herringbone GNF with a 45° crease angle are calculated to be 27 W∕m K, 263 W∕m K, and 1500 W∕m K, respectively, where the axial thermal conductivity is in good agreement with experimental measurements.

Graphitization behavior of carbon nanofibers derived from bacteria cellulose

Bacteria cellulose was prepared from nata de coco which is composed of pure cellulose nanofibers. The nanofibers were dispersed in ethanol or distilled water and were stirred and then filtered to obtain paper-like sheets. The diameters of the nanofibers were in the range of 30 to 60 nm. The sheets were carbonized and then heat-treated at temperatures between 2400 and 3200 °C in a high purity Ar flow under atmospheric pressure, and the texture and structure of the heat-treated sheets were investigated. Cellulose-based carbon materials are known to be one of the nongraphitizing carbons. However, graphitization of the carbon sheets was observed as a result of the heat treatment, and was especially apparent for those from the nanofibers dispersed in ethanol. The development of a graphite structure in the carbon nanofibers of the sheets seems to be attributed to graphitization on the surface of nongraphitizing carbon, and the surface graphitization seems to extend to the inside of the carbon nanofibers with very thin diameters of 30–60 nm. The graphitization degree of the 3200 °C-treated sheet derived from the nanofibers dispersed in ethanol was nearly comparable to that for a commercial graphite nanofiber powder VGCF ® . However, the improvement in structural perfection with heat treatment for the carbon sheets was less remarkable in comparison with that for typical graphitizing carbons. The limited graphitization behavior of the heat-treated sheets may be attributed to their heterogeneous structure. [TANSO 2012 (No. 255), 225–230.]

Influence of KOH-activated graphite nanofibers on the electrochemical behavior of Pt–Ru nanoparticle catalysts for fuel cells

Graphite nanofibers (GNFs) were activated chemically by a heat treatment at between 700 and 1000°C. The GNFs were used as carbon supports for Pt–Ru nanoparticles in fuel cells. The surface, structural, and textural characteristics of the carbon supports and Pt–Ru/KOH-activated GNFs catalysts were characterized by X-ray photoelectron spectroscopy, X-ray diffraction, and surface area analyzer, respectively. The electrochemical activity was examined by cyclic voltammetry. The results showed that the concentration of oxygen functional groups and the specific surface area of the carbon supports increased with increasing activation temperature up to 900°C, whereas the mean Pt–Ru nanoparticle size decreased due to an improvement in the dispersibility of the Pt–Ru/KOH-activated GNFs catalysts. From the results, it was found that the electrochemical activities of the Pt–Ru/KOH-activated GNFs catalysts were improved by the larger active surface area available due to an increase in the number of oxygen functional groups and specific surface area, resulting in the enhanced electrochemical activity for use in fuel cells.

Comparative Study of Carbon Ionic Liquid Electrodes Based on Different Carbon Allotropes as Conductive Phase

Different carbon ionic liquid electrodes were constructed from several kinds of carbon allotropes such as multi-walled carbon nanotubes, single-walled carbon nanotubes, graphite, fullerene and carbon nanofiber by using 30wt% of the ionic liquid, n-octylpyridinium hexafluorophosphate as a binder. Some physical characteristics and electrochemical responses of electrodes in Fe(CN)6 3− and some important biological compounds (i.e., ascorbic acid, dopamine, uric acid and guanine) were compared. The obtained results demonstrate that fullerene and carbon nanofiber, as conductive phases, show the worst responses compared to other carbon allotropes. The activation on electrode surfaces was also investigated. The results showed that activation of electrode surface, merely affects the multi-walled carbon nanotubes ionic liquid electrode. Moreover, our observations support the idea that the presence of ionic liquid has a critical role in physical and electrochemical characteristics of carbon ionic liquid electrodes such as good mechanical stability, repeatability, high electroactive surface areas and antifouling effects toward some important biomolecules.

Developing green photochemical approaches towards the synthesis of carbon nanofiber- and graphene-supported silver nanoparticles and their use in the catalytic reduction of 4-nitrophenol

A green, photochemical approach for the liquid-phase synthesis of carbon nanomaterial-supported silver nanoparticles is proposed. The method is based on irradiating a colloidal dispersion containing the carbon nanomaterial, a metal precursor and an environmentally friendly reducing agent (bioreductant) with UV light at room temperature. Two representative carbon materials have been used, namely platelet-type graphite nanofibers and graphene oxide. The experimental conditions that afford the photochemical growth of the nanoparticles on each carbon support are also investigated and discussed. In addition, the resulting carbon–silver nanoparticle hybrids are demonstrated to be notably effective catalysts for the reduction of 4-nitrophenol to 4-aminophenol with NaBH4. Particularly, the graphene oxide-based samples were seen to exhibit exceptional catalytic activity towards such reaction. Finally, it is also shown that with a suitable choice of bioreductant the present UV approach can afford highly reduced graphene oxide samples comparable to those attained with well-known, efficient chemical reductants (e. g., hydrazine at ∼100 °C), thus constituting an attractive room temperature alternative to such reduction methods.

Chlorine Effect on the Formation of Carbon Nanofibers

Platelet graphite nanofibers (GNFs) and turbostratic carbon nanofibers (CNFs) are synthesized by the thermal evaporation and decomposition of a polymer-based mixture at 700 degrees C using Ni as a catalyst. The mixture consists of poly(ethylene glycol) (PEG), serving as the carbon source, and hydrochloric acid solution (HCl(aq)), serving as the promoter/additive for the growth of CNFs. High-purity zigzag-shaped platelet GNFs form with 10 wt% HCl(aq) as an additive in the PEG. The diameters of the platelet GNFs are in the range of 40-60 nm, with lengths of a few micrometers. High-resolution transmission electron microscopy images indicate a high degree of graphitization and well ordered graphene layers along the fiber axis. In contrast, high-purity turbostratic CNFs form with 20 wt% HCl(aq) in the PEG. The diameter and length of the turbostratic CNFs are 20-40 nm and a few micrometers, respectively. The participation of HCl in the thermal process leads to the formation of Ni-Cl compounds. The amount of chlorine affects the shape of the Ni catalyst, which determines the type of CNF formed.

An ionic liquid-assisted method for splitting carbon nanotubes to produce graphene nano-ribbons by microwave radiation

An ionic liquid-assisted splitting method for the production of graphene nano-ribbons from multi-wall or single wall carbon nanotubes was developed using microwave irradiation as an external energy source. Graphene nano-ribbons with a high aspect ratio can be produced by the ionic liquid assisted splitting action under microwave radiation. The technique involves neither oxidation with strong acids nor reduction with hydrazine and is a fast, simple, one-step procedure. Also, the present method can be extended to split and expand tubular graphite nanofibers. Our simple approach will make a new route for splitting carbon nanomaterials to form graphene nanoribbions in the hundred nanometers.

Bridge effect of silver nanoparticles on electrochemical performance of graphite nanofiber/polyaniline for supercapacitor

In this work, silver (Ag) nanoparticles were deposited onto graphite nanofibers (GNFs) by chemical reduction while polyaniline-coated Ag-GNFs (Ag-GNFs/PANI) were prepared by in situ polymerization. The effect of the Ag nanoparticles intercalated in composite interface on the electrochemical performances, such as CV curve, charge–discharge behaviors, and specific capacitance of the GNFs/PANI was investigated. It was found that nano-sized Ag particles could be uniformly deposited onto the GNFs and that Ag-GNFs were successfully coated by PANI via in situ polymerization. According to the charge–discharge curves, the highest specific capacitance (212F/g) of the Ag-GNFs/PANI was obtained at a scan rate of 0.1A/g, as compared to 153F/g for GNFs/PANI and 80F/g for PANI. This indicated that the Ag nanoparticles that were deposited onto the GNFs led to a bridge effect between GNFs and PANI to improve the charge transfer, which resulted in the enhanced electrochemical performances of the composites due to a synergistic effect.

Entangled Germanium Nanowires and Graphite Nanofibers for the Anode of Lithium-Ion Batteries

High performance negative electrode materials for lithium-ion batteries were fabricated using germanium nanowire (GeNW) and graphite nanofiber (GNF) composites prepared by a low-pressure chemical vapor deposition (CVD) method. The promising high power rate anode material GeNWs were grown on the surface of a GNF bundle to mutually form the entangled structure. The high contact area between the GeNWs and GNFs enabled electrons to be efficiently transported and the GeNWs entwined with GNFs minimized the degradation of the electrochemical characteristics. These composite materials for the anode of lithium-ion batteries showed a very constant high specific capacity of ∼1,200 mAh g−1 with little decline of the cycling performance while the rate capability was significantly improved.

Discovery of effective solvents for platelet-type graphite nanofibers

The dispersibility of platelet-type graphite nanofibers (PGNFs), an archetype of carbon material with a surface dominated by graphitic edge planes, has been measured in 28 solvents and rationalized on the basis of solvent surface tension and Hansen solubility parameters. Successful solvents possess surface tensions of ∼25–35mJm−2 and substantial values of the hydrogen-bonding Hansen parameter (δH∼14–16MPa1/2), and many of them are alcohols, such as 1-butanol, ethanol or cyclohexanol. Such result is mainly attributed to the fact that the PGNF edge planes are decorated with oxygen functional groups. The dispersion behavior of the nanofibers could be changed to that typically exhibited by carbon nanotubes and graphene by means of a high temperature annealing that converted their surface edge planes to curved basal planes.

Synthesis of polystyrene nanoparticles “armoured” with nanodimensional graphene oxide sheets by miniemulsion polymerization

AbstractPolystyrene particles “armoured” with nanosized graphene oxide (GO) sheets have been prepared by aqueous miniemulsion polymerization of styrene, exploiting the amphiphilic properties of GO in the absence of conventional surfactants. The nanoscale GO sheets were prepared from graphite nanofibers of diameter approximately 100 nm based on a novel procedure, thus effectively ensuring the absence of larger sheets. Polymerization proceeded to high conversion with minor coagulation, with final number‐average particle diameters of approximately 500 nm, but relatively broad particle size distributions. Scanning electron microscopy analysis revealed particles with a textured surface, consistent with the expected morphology. Interestingly, analysis of GO sheets recovered from the polymerization revealed that the GO sheets are partially reduced during the polymerization—approximately 50% of the initial carboxyl groups of the GO were lost, consistent with some loss in colloidal stability at high conversion. The overall approach offers a convenient and attractive synthetic route to novel graphene‐based polymeric nanostructures. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013

Electrochemical Performance of Lithium Iron Phosphate by Adding Graphite Nanofiber for Lithium Ion Batteries

Olivine type <TEX>$LiFePO_4$</TEX> cathode material was synthesized by solid-state reaction method including one-step heat treatment. To improve the electrochemical characteristics, graphite nanofiber (GNF) was added into <TEX>$LiFePO_4$</TEX> cathode material. The structure and morphological performance of <TEX>$LiFePO_4$</TEX> were investigated by X-ray diffraction (XRD); and a field emission-scanning electron microscope (FE-SEM). The synthesized <TEX>$LiFePO_4$</TEX> has an olivine structure with no impurity, and the average particle size of <TEX>$LiFePO_4$</TEX> is about 200~300 nm. With graphite nanofiber added, the discharge capacity increased from 113.43 mAh/g to 155.63 mAh/g at a current density of 0.1 <TEX>$mA/cm^2$</TEX>. The resistance was also significantly decreased by the added graphite nanofiber.

Toward facile synthesizing of diamond nanostructures via nanotechnological approach: Lonsdaleite carbon nanofibers by electrospinning

Low cost synthesis of the diamond is a dream for the scientists. In this study, different forms of carbon were obtained due to utilizing of different cobalt-based catalytic materials in the graphitization of poly(vinyl alcohol) (PVA) electrospun nanofibers. The utilized cobalt-based catalysts were cobalt acetate tetrahydrate (CoAc), cobalt NPs, and CoAc/palladium NPs. Calcination in argon atmosphere of the polymeric nanofibers containing the aforementioned catalytic materials led to obtain different products. High yield and good nanofibrous morphology were obtained in case of CoAc-containing nanofibers, however cobalt nanoparticles destroyed the nanofibrous morphology and revealed low yield. Interestingly, diamond-like lonsdaleite carbon nanofibers were produced when CoAc–Pd NPs catalytic system was utilized; however normal graphite powder and nanofibers were obtained when Co NPs and CoAc have been used, respectively. The obtained Co-graphite and Co–Pd–lonsdaleite nanofibers could be also synthesized in the form of thin films supported on graphite disks when polyacrylonitrile disks were used as collectors. Calcination of the obtained disks with the attached electrospun nanofibers produced well affixed Co-graphite and Co–Pd–lonsdaleite nanofibers on graphite disks. Electrical properties study of the obtained films indicated that the Co–Pd–lonsdaleite nanofibers behave as semiconductor while Co-graphite nanofibers show ohmic conductivity. Magnetically, Pd has a negative impact on the magnetic properties of the cobalt.

Adsorption of Four Representative Biological Compounds onto Graphite Nanofibers

The present study investigates the adsorption of four compounds important in carbon adsorption hemoperfusion. Graphite nanofibers (GNFs) having different carbon plane orientations have structural features that make them potentially attractive in this application compared to activated carbon. Generally, adsorption capacity increased in the order of ribbon > herringbone > platelet fiber types. All fibers were poor adsorbents for creatinine. Herringbone and platelet fibers had sorption capacities less than 25% of activated carbon for all adsorbates on a mass basis. Except for vitamin B12, behavior of ribbon fibers was similar; vitamin B12 adsorption was nearly 50% greater than activated carbon on a mass basis. In contrast, on the basis of surface area, all of the fibers were comparable to or outperformed activated carbon for the adsorption of all adsorbates. This suggests that in addition to BET surface area, interactions between adsorbate and exposed basal planes in carbon are important in determining adsor...

Preparation and characterization of nanoporous carbons from thermoplastic acrylic resin for an electric double layer capacitor

An electric double layer capacitor (EDLC) is an electrochemical capacitor with relatively high energy density. The energy density is typically a thousand of times greater than that of conventional electrolytic capacitors. The electrode of EDLC differs from a traditional capacitor in being composed of a porous conductor, such as activated carbons with a huge specific surface area, which accumulates the charges on the thin layer of electrode/electrolyte interface via an electrostatic force or non Faradic effect. Therefore, various types of porous carbons, such as carbon aerogel, carbon fibers, graphite nanofibers, mesoporous carbons, carbon nanotubes, and graphene, are used widely as electrodes materials in EDLC devices on account of their high specific surface area, chemical and thermal stability, relatively low cost, and nature friendly. Porous carbons are usually obtained via the carbonization of precursors of a natural or synthetic origin, followed by activation. There are a range of precursors and processes to prepare porous carbons. Recently, the template method is considered to be an efficient method for preparing nanoporous carbons. Normally, in the template method, the template is be dissolved out by strong acids after carbonization making large scale production difficult despite, pores with a specific size being obtained easily. Various kinds of micro-/ meso-porous carbons have been widely prepared using a range of templates, including zeolites, mesoporous silica, metal-organic framework, and alkali metals (MgO, TiO2, and Ni(OH)2). 9-13

KOH 활성화 효과에 의한 흑연나노섬유의 전기화학적 거동

In this work, we prepared the activated graphite nanofibers (A-GNFs) via chemical activation with KOH/GNFs ratios in a range of 0 to 5. The effect of KOH activation was studied in the surface and pore properties of the samples for electrochemical performance. The surface properties of A-GNFs were characterized by XRD and SEM measurements. The textural properties of the A-GNFs were investigated by /77 K adsorption isotherms using Brunauer-Emmett-Teller (BET) equation. Their electrochemical behaviors were investigated by cyclic voltammetry and galvanostatic charge-discharge performance. From the results, electrochemical performances of the A-GNFs were improved with increasing the ratio of KOH reagent. It was found that specific surface area and total pore volume of the A-GNFs were increased by KOH activation.

Quantification of the Impact of Embedded Graphite Nanofibers on the Transient Thermal Response of Paraffin Phase Change Material Exposed to High Heat Fluxes

Paraffin phase change material (PCM) is enhanced with suspended graphite nanofibers at high loading levels. The loading levels reach in excess of 10% by weight. The thermal effects of the nanofiber loading level, the PCM module design, and the applied power density on the transient thermal response of the system are examined. A strong effect of nanofiber loading level on thermal performance is found, including a suppression of Rayleigh-Benard convection currents at high loading levels. Increases in nanofiber loading level also result in lowered heating rates and greater thermal control of the heated base. Increases in power density are found to result in higher heating rates, and increases in mass lead to lower operating temperatures. The design of the module is found to have a strong effect on thermal performance.