Graphite Nanofibers Research Articles

Flexible, Highly Graphitized Carbon Aerogels Based on Bacterial Cellulose/Lignin: Catalyst‐Free Synthesis and its Application in Energy Storage Devices

Currently, most carbon aerogels are based on carbon nanotubes (CNTs) or graphene, which are produced through a catalyst‐assisted chemical vapor deposition method. Biomass based organic aerogels and carbon aerogels, featuring low cost, high scalability, and small environmental footprint, represent an important new research direction in (carbon) aerogel development. Cellulose and lignin are the two most abundant natural polymers in the world, and the aerogels based on them are very promising. Classic silicon aerogels and available organic resorcinol–formaldehyde (RF) or lignin–resorcinol–formaldehyde (LRF) aerogels are brittle and fragile; toughening of the aerogels is highly desired to expand their applications. This study reports the first attempt to toughen the intrinsically brittle LRF aerogel and carbon aerogel using bacterial cellulose. The facile process is catalyst‐free and cost‐effective. The toughened carbon aerogels, consisting of blackberry‐like, core–shell structured, and highly graphitized carbon nanofibers, are able to undergo at least 20% reversible compressive deformation. Due to their unique nanostructure and large mesopore population, the carbon materials exhibit an areal capacitance higher than most of the reported values in the literature. This property makes them suitable candidates for flexible solid‐state energy storage devices. Besides energy storage, the conductive interconnected nanoporous structure can also find applications in oil/water separation, catalyst supports, sensors, and so forth.

Facile and gram-scale synthesis of metal-free catalysts: toward realistic applications for fuel cells.

Although numerous reports on nonprecious metal catalysts for replacing expensive Pt-based catalysts have been published, few of these studies have demonstrated their practical application in fuel cells. In this work, we report graphitic carbon nitride and carbon nanofiber hybrid materials synthesized by a facile and gram-scale method via liquid-based reactions, without the use of toxic materials or a high pressure-high temperature reactor, for use as fuel cell cathodes. The resulting materials exhibited remarkable methanol tolerance, selectivity, and stability even without a metal dopant. Furthermore, these completely metal-free catalysts exhibited outstanding performance as cathode materials in an actual fuel cell device: a membrane electrode assembly with both acidic and alkaline polymer electrolytes. The fabrication method and remarkable performance of the single cell produced in this study represent progressive steps toward the realistic application of metal-free cathode electrocatalysts in fuel cells.

Graphene Oxide Thin Films: Influence of Chemical Structure and Deposition Methodology

We synthesized graphene oxide sheets of different functionalization by oxidation of two different starting materials, graphite and GANF nanofibers, followed by purification based on alkaline washing. The chemical structure of graphene oxide materials was determined by X-ray photoelectron spectroscopy (XPS), and the nanoplatelets were characterized by ζ potential and dynamic light scattering (DLS) measurements. The XPS results indicated that the chemical structure depends on the starting material. Two different deposition methodologies, Langmuir-Blodgett (LB) and Langmuir-Schaefer (LS), were employed to build the graphene oxide thin films. The film morphology was analyzed by scanning electron microscopy (SEM). The SEM images allow us to conclude that the LB methodology provides the highest coverage. This coverage is almost independent of the chemical composition of sheets. Conversely, the coverage obtained by the LS methodology increases with the percentage of C-O groups attached to sheets. Surface-pressure isotherms of these materials were interpreted according to the Volmer model.

Research progress on fibrous carbon materials as anode materials for lithium ion batteries

Fibrous carbon materials have a variety of dimensions and structures. However, these materials were earlier restricted for use as anode materials for lithium ion batteries due to their cost and performance. With the development of nanotechnology, some modified and new forms of carbon fibers have emerged, which show good performance as anode materials. This paper reviews recent domestic and foreign research progress on fibrous carbon materials as anode materials. The electrochemical performance and prospective use of graphite fibers, carbon fibers and carbon nanofibers for this purpose are summarized. Research has ranged from non-graphitized to graphitized carbon fibers, from micron to nanometer diameter, and has focused on the parameters of their preparation to the design of their microstructure. Fibrous carbon materials are likely to be important alternatives for carbon anode materials in the future based on their high capacity, high rate capability, low cost and ease of industrialization. [New Carbon Materials 2015, 30(1): 1–11]

Electrical and mechanical properties of RFID chip joints assembled on flexible substrates

Purpose – The purpose of this paper is to examine electrical and mechanical properties of radio frequency identification (RFID) chip joints assembled on a flexible substrate and made from isotropic conductive adhesives (ICAs) reinforced with graphene nanoplatelets (GPNs) or graphite nanofibers (GFNs). Design/methodology/approach – The ICAs reinforced with GPNs or GFNs were prepared and screen printed on a test pattern to investigate resistance and thickness of these adhesive layers. Differential Scanning Calorimetry (DSC) was performed to assess a curing behaviour of the prepared ICAs. Then, RFID chips were mounted with the prepared ICAs to the pattern of silver tracks prepared on foil. Shear test was carried out to evaluate mechanical durability of the created chip joints, and resistance measurements were carried out to evaluate electrical properties of the tested ICAs. Findings – The 0.5 per cent (by weight) addition of GFNs or GPNs to the ICA improved shear force values of the assembled RFID chip joints, whereas resistance of these modified adhesives increased. The DSC analysis showed that a processing temperature of the tested adhesives may range from 80 to 170°C with different curing times. It revealed a crucial influence of curing time and temperature on electrical and mechanical properties of the tested chip joints. When the chip pads were cured for too long (i.e. 60 minutes), it resulted in a resistance increase and shear force decrease of the chip joints. In turn, the increase of curing temperature from 80 to 120°C entailed improvement of electrical and mechanical properties of the assembled chips. It was also found that a failure location changed from the chip – adhesive interface towards the adhesive – substrate one when the curing temperature and time were increased. Research limitations/implications – Further investigations are required to examine changes thoroughly in the adhesive reinforced with GFNs after a growth of curing time. It could also be worth studying electrical and mechanical properties of the conductive adhesive with a different amount of GFNs or GPNs. Practical implications – The tested conductive adhesive reinforced with GFNs or GPNs can be applied in the production of RFID tags because it may enhance the mechanical properties of tags fabricated on flexible substrates. Originality/value – Influence of GFNs and GPNs on the electrical and mechanical properties of commercial ICAs was investigated. These properties were also examined depending on a curing time and temperature. New conductive materials were proposed and tested for a chip assembly process in fabrication of RFID tags on flexible substrates.

English

Herein, results of thermodynamic analysis of some theoretical and experimental [thermal desorption (TDS), scanning tunneling microscopy (STM), scanning tunneling spectroscopy (STS), high-resolution electron energy loss spectroscopy/low-energy electron diffraction (HREELS/LEED), photoelectron spectroscopy (PES), angle-resolved photoemission spectroscopy (ARPES), Raman spectroscopy and others] data on “reversible” hydrogenation and dehydrogenation of some graphene-layer-nanostructures are presented. In the framework of the formal kinetics and the approximation of the first order rate reaction, some thermodynamic quantities for the reaction of hydrogen sorption (the reaction rate constant, the reaction activation energy, the per-exponential factor of the reaction rate constant) have been determined. Some models and characteristics of hydrogen chemisorption on graphite (on the basal and edge planes) have been used for interpretation of the obtained quantities, with the aim of revealing the atomic mechanisms of hydrogenation and dehydrogenation of different graphene-layer-systems. The cases of both non-diffusion rate limiting kinetics and diffusion rate limiting kinetics are considered. Some open questions and perspectives remain in solving the actual problem in effective hydrogen on-board storage; using the graphite nanofibers (GNFs) is also considered.   Key words: Epitaxial and membrane graphenes, other graphene-layer-systems, hydrogenation-dehydrogenation, thermodynamic characteristics, atomic mechanisms, the hydrogen on-board efficient storage problem.&nbsp

Increasing the reversibility of Li–O2 batteries with caterpillar structured α–MnO2/N–GNF bifunctional electrocatalysts

The high performance of α–MnO2/NGNF catalyzed air cathode for Li–O2 battery is reported in this article. The α–MnO2 nanorods are successfully grown on highly conductive nitrogen doped graphite nanofibers with caterpillar like morphology by a simple hydrothermal technique. The as–prepared α–MnO2/N–GNF catalyst exhibits better electrocatalytic performance in terms of oxygen reduction and evolution reactions in the air cathode exhibiting comparatively low overpotential. In addition to the low overpotential, α–MnO2/NGNF catalyzed Li–O2 battery also show high capacity, reversibility and rate capability. The combined effect of α–MnO2 and N–GNF for facilitating electrochemical reactions between Li and O2 is described for improving energy and columbic efficiency of Li–O2 battery.

Superplastic deformation and energy dissipation mechanism in surface-bonded carbon nanofibers

Molecular dynamics simulations are used to understand the role of surface C–C bonds formed by heat treatment on plastic deformation and fracture mechanisms in cone-stacked carbon nanofibers. The simulations predict that the surface bond density linearly relates to the heat treatment temperature. As the surface bond density increases, it is found that tensile strength and ductile fracture energy in carbon nanofibers rise dramatically by more than 65% and 622%, respectively; hence unveiling a regime of superplastic deformation that is unmatched by standard carbon nanotubes and graphitic nanofibers. We demonstrate that both strengthening and superplasticity effects are enabled by the occurrence of surface bond-induced fiber splaying processes that can effectively resist interlayer sliding and crack propagation during deformation. The findings of this computational study have important implications for designing flaw-tolerant nanocomposite systems.

Synthesis and Antibacterial Activity of Antibiotic‐Functionalized Graphite Nanofibers

Surface functionalization of nanomaterials is an area of current investigation that supports the development of new biomaterials for applications in biology and medicine. Herein we describe the synthesis, characterization, and antibacterial properties of the first examples of antibiotic‐labeled graphitic carbon nanofibers (GCNFs) covalently functionalized with aminoglycoside and quinolone antibiotics. Ruthenium tetroxide oxidation of herringbone GCNFs gave higher amounts of surface carboxyl groups than previous methods. These carboxyl groups served as sites of attachment for antibiotics by acyl substitution. Bioassay of these novel, functionalized GCNFs using serial dilution and optical density methods demonstrated that antibiotic‐labeled GCNFs possess significant antibacterial activity against Pseudomonas aeruginosa. The activity we observe for aminoglycoside‐functionalized GCNFs suggests a membranolytic mechanism of action.

Visible-light responsive electrospun nanofibers based on polyacrylonitrile-dispersed graphitic carbon nitride

A visible-light responsive photocatalyst, polyacrylonitrile-dispersed graphitic carbon nitride nanofibers (g-C3N4/PAN nanofibers), was synthesized by electrospinning.

Enhanced electrochemical performance of Li3V2(PO4)3 structurally converted from LiVOPO4 by graphite nanofiber addition

In this work, the structural conversion of LiVOPO4 to Li3V2(PO4)3 due to the addition of graphene nanofiber (GNF) was investigated, and the resulting materials were found to exhibit enhanced capacity and cyclability. First, LiVOPO4 was synthesized using a solid-state method followed by annealing at 900°C for 12h under nitrogen atmosphere. Then, the conversion from the triclinic LiVOPO4 structure to the monoclinic Li3V2(PO4)3 structure due to the GNF addition was observed. No impurity peak was observed in the X-ray diffraction patterns of LiVOPO4 or Li3V2(PO4)3, and the structural conversion caused no defects to form in the resulting Li3V2(PO4)3 crystallite. Field emission-scanning electron microscope studies clearly demonstrate that larger corroded-structure-like particles formed which were mixed with GNF. This provided both a large active area and fast transport of lithium ions, which afforded enough active sites for simultaneous intercalation of many lithium ions, leading to improved electrochemical properties of the material. Compared with LiVOPO4, the Li3V2(PO4)3–GNF showed better properties, such as an improved lithium ion diffusion coefficient, improved cyclability, and smaller impedance. Furthermore, the optimized Li3V2(PO4)3–GNF (7%) battery showed the best discharge capacity of 181mAhg−1 at 0.1C and lithium ion diffusion coefficient of 6.01×10−9cm2s−1.

Enhanced Reaction Kinetic of Fe3O4-graphite Nanofiber Composite Electrode for Lithium Ion Batteries

A -graphite nanofiber composite for use as an anode material was successfully synthesized by calcining and graphite nanofiber (GNF) together in a atmosphere. Using this -GNF composite in a lithium ion battery resulted in a higher lithium storage capacity than that obtained using -graphite (-G). The -GNF (10 wt%) electrode exhibited a higher lithium ion diffusion coefficient () than did the -G (10%) (). At a current density of , the -GNF (10 wt%) anode showed a higher reversible capacity () than did the -G (10%) anode (). Moreover, the electrodes showed good cycling performance without the addition of a conductive material.

Oxygen-assisted low-pressure chemical vapor deposition for the low-temperature direct growth of graphitic nanofibers on fluorine-doped tin oxide glass as a counter electrode for dye-sensitized solar cell

In this paper, we report an oxygen-assisted low-pressure chemical vapor deposition (LPCVD) method for the direct growth of graphitic nanofibers (GNFs) on a fluorine-doped tin oxide (FTO) glass substrate at a low temperature (550 °C). By adding moderate concentrations of oxygen in a gas mixture of argon, ethylene, and hydrogen during LPCVD, an extremely dense GNF forest can be obtained on a nickel-coated FTO glass substrate. Though this process, the graphitic nanofibers are grown homogenously on a large area of FTO glass. It was observed that oxygen-assisted LPCVD leads to the direct growth of high-quality GNFs as a counter electrode for dye-sensitized solar cells (DSSCs). In combination with an N719 dye-sensitized TiO2 working electrode and an iodine-based electrolyte, the DSSC with a GNF counter electrode showed a power conversion efficiency of 5.51% under AM 1.5 (100 mW cm−2) illumination, which approached that of the DSSC with a Pt counter electrode (5.44%). The results demonstrated that our directly grown GNFs could be promising candidates for counter electrodes to achieve high performance in DSSCs.

Stacking fault induced tunnel barrier in platelet graphite nanofiber

A correlation study using image inspection and electrical characterization of platelet graphite nanofiber devices is conducted. Close transmission electron microscopy and diffraction pattern inspection reveal layers with inflection angles appearing in otherwise perfectly stacked graphene platelets, separating nanofibers into two domains. Electrical measurement gives a stability diagram consisting of alternating small-large Coulomb blockade diamonds, suggesting that there are two charging islands coupled together through a tunnel junction. Based on these two findings, we propose that a stacking fault can behave as a tunnel barrier for conducting electrons and is responsible for the observed double-island single electron transistor characteristics.

Spine-like nanostructured carbon interconnected by graphene for high-performance supercapacitors.

Recent studies on supercapacitors have focused on the development of hierarchical nanostructured carbons by combining two-dimensional graphene and other conductive sp2 carbons, which differ in dimensionality, to improve their electrochemical performance. Herein, we report a strategy for synthesizing a hierarchical graphene-based carbon material, which we shall refer to as spine-like nanostructured carbon, from a one-dimensional graphitic carbon nanofiber by controlling the local graphene/graphitic structure via an expanding process and a co-solvent exfoliation method. Spine-like nanostructured carbon has a unique hierarchical structure of partially exfoliated graphitic blocks interconnected by thin graphene sheets in the same manner as in the case of ligaments. Owing to the exposed graphene layers and interconnected sp2 carbon structure, this hierarchical nanostructured carbon possesses a large, electrochemically accessible surface area with high electrical conductivity and exhibits high electrochemical performance.

Graphene quantum dots derived from platelet graphite nanofibers by liquid-phase exfoliation

Graphene quantum dots (GQDs) were formed by liquid-phase exfoliation in an ultrasonic bath using platelet graphite nanofibers (PGNFs) as the raw material and dimethyl sulfoxide (DMSO) as the exfoliation agent. PGNFs, carbon fibers with graphene nanosheets stacked perpendicular along the fiber axis, were sectioned layer by DMSO for 3h with ultrasonic assistance to create GQDs. The diameters of the derived GQDs were in the range of 10–30nm and fewer than five graphene layers were formed. X-ray photoelectron spectroscopy analysis revealed that no functional groups were grafted onto the GQDs during the process, indicating that the synthetic route produced high-quality GQDs.

Ionic liquid-assisted synthesis of Pt nanoparticles onto exfoliated graphite nanoplatelets for fuel cells.

Exfoliated graphite nanoplatelets (GnP) has been investigated as an electrocatalyst support for fuel cell applications. GnP-supported Pt catalysts were synthesized by a microwave process in the presence of room temperature ionic liquids (RTILs). Thermal-oxidation resistance of GnP and GnP-supported Pt catalysts was studied by thermogravimetric analysis and compared with a variety of other carbon nanostructures: carbon black, graphite nanofiber, single- and multiwalled carbon nanotubes. GnP showed the best thermal-oxidative stability. The results obtained from X-ray diffraction, X-ray photoelectron spectroscopy, electrochemical testing, scanning and transmission electron microscopy showed that the RTIL synthesis method resulted in size reduction of Pt nanoparticle, improvement of Pt dispersion on GnP, and identification of the relationships between the mean size of Pt particles with increasing RTIL content. The interaction of Pt particles-GnP is stronger than that of a commercial Pt-CB, and the Pt/GnP catalysts prepared by this method have excellent electrocatalytic activity and stability for methanol oxidation.

Tunable Thermal Transport in Phase Change Materials Using Inverse Micellar Templating and Nanofillers

We report extremely large tunable thermal conductivity (k) in alkanes using inverse micellar templating and nanofillers. The thermal properties of n-hexadecane containing inverse micelles of different volume fractions (ϕ) have been studied during freezing and melting. The k enhancement between the solid and liquid phase in the presence of oleic acid, dioctyl sodium sulfosuccinate, and sorbitan oleate inverse micelles (size ∼1.5–6 nm) are found to be 185, 119, and 111%, respectively. Unlike the conventional nanofluids, the k enhancement in micellar templated alkanes is perfectly reversible under repeated thermal cycling owing to the monodispersity and nonaggregating nature of micelles. Our results suggest that during the first-order phase transition, the inverse micelles with highly packed linear chain surfactant are pushed to the intercrystal boundaries of alkanes, thereby reducing the interfacial thermal resistance. The k contrasts in surface modified graphite nanofibers and multiwalled carbon nanotube i...

Roles of nitric acid treatment on PtRu catalyst supported on graphite nanofibers and their methanol electro-oxidation behaviors

In the present study, the effect of chemical treatment on graphite nanofiber supports (GNFs) with various concentrations of nitric acid was investigated for methanol electro-oxidation. To optimize the electrocatalytic activity, PtRu catalysts were deposited on GNF supports by the impregnation method. The surface and structural properties of the GNF supports were characterized by X-ray photoelectron spectroscopy (XPS), elemental analysis (EA), and X-ray diffraction (XRD). The morphology of the catalysts was characterized by transmission electron microscopy (TEM). The electrocatalytic activity of PtRu/GNF catalysts was investigated by cyclic voltammetry. Oxygen functional groups were introduced on the GNF supports by the addition of nitric acid. Increasing the concentration of nitric acid caused a subsequent increase in the presence of oxygen functional groups, which resulted in smaller catalyst particle size and a higher loading of the catalyst. The electrocatalytic activity of the catalysts for methanol oxidation was also improved with these treatments. Consequently, it was found that chemical treatments could influence the surface properties of the carbon supports, resulting in enhanced electrocatalytic activity of the catalysts for direct methanol fuel cells (DMFCs).

Adsorption Behavior of Perfluorinated Sulfonic Acid Ionomer on Highly Graphitized Carbon Nanofibers and Their Thermal Stabilities

A systematic adsorption study of perfluorinated sulfonic acid Nafion ionomer on ribbon-type highly graphitized carbon nanofibers (CNFs) was carried out using fluorine-19 nuclear magnetic resonance spectroscopy. On the basis of the values obtained for the equilibrium constant (Keq , derived from Langmuir isotherm), the ionomer has varying affinities for CNFs (Keq between 5 and 22) as compared to Vulcan (Keq = 18), depending on surface treatments. However, the interactions are most likely governed by different adsorption mechanisms depending on hydrophilicity/hydrophobicity of the adsorbent carbon. The ionomer is probably adsorbed via the polar sulfonic group on hydrophilic Vulcan, whereas it is adsorbed primarily via hydrophobic −CF2– backbone on the highly hydrophobic pristine CNFs. Ionomer adsorption behavior is gradually altered from apolar to polar group adsorption for the acid-modified CNFs of decreasing hydrophobicity. This is indicated by the initial decrease and then increase in the value of Keq with the increasing strength of the acid treatment. The corresponding carbon–ionomer composite also showed varying thermal stability depending on Nafion orientation. The specific maximum surface coverage (ΓSmax) of the CNFs is 1 order of magnitude higher than that of Vulcan. The large discrepancy is due to the fact that the ionomers are inaccessible to the internal surface area of Vulcan with high microporosity.