Graphite Nanofibers Research Articles

High thermoelectric performance of graphite nanofibers.

Graphite nanofibers (GNFs) have been demonstrated to be a promising material for hydrogen storage and heat management in electronic devices. Here, by means of first-principles and transport simulations, we show that GNFs can also be an excellent material for thermoelectric applications thanks to the interlayer weak van der Waals interaction that induces low thermal conductance and a step-like shape in the electronic transmission with mini-gaps, which are necessary ingredients to achieve high thermoelectric performance. This study unveils that the platelet form of GNFs in which graphite layers are perpendicular to the fiber axis can exhibit outstanding thermoelectric properties with a figure of merit ZT reaching 3.55 in a 0.5 nm diameter fiber and 1.1 in a 1.1 nm diameter one. Interestingly, by introducing 14C isotope doping, ZT can even be enhanced up to more than 5, and more than 8 if we include the effect of finite phonon mean free path, which demonstrates the amazing thermoelectric potential of GNFs.

Synthesis and photocatalytic properties of graphitic carbon nitride nanofibers using porous anodic alumina templates

In the present study, we describe an effective method for the synthesis of Graphitic carbon nitride (GCN) nanostructures using porous anodic alumina (AAO) membrane as template by simple thermal condensation of cyanamide. Synthesized nanostructure was fully analysed by various techniques to detect its crystalline nature, morphology, luminescent properties followed by the evaluation of its photocatalytic activity in the degradation of Methylene blue dye. Structural analysis of synthesized GCNNF was systematically carried out using x-ray powder diffraction (XRD) and scanning electron microscope (SEM), and. The results confirmed the growth of GCN inside the nanochannels of anodic alumina templates. Luminescent properties of GCNNF were studied using photoluminescence (PL) spectroscopy. PL analysis showed the presence of a strong emission peak in the wavelength range of 350–600 nm in blue region. GCNNF displays higher photocatalytic performance in the photodegradation of methylene blue compare to the bulk GCN.Highlights1. In the present paper, we report the synthesis of graphitic carbon nitride nanofibers (GCNNF) using porous anodic aluminium oxide membranes as templates through thermal condensation of cyanamide at 500 °C.2. The synthesis of Graphitic carbon nitride nanofibers using porous andic alumina template is the efficient approach for increasing crystallinity and surface area.3. The high surface area of graphitic carbon nitride nanofibers has a good impact on novel optical and photocatalytic properties of the bulkGCN.4. AAO templating of GCN is one of the versatile method to produce tailorable GCN nanostructures with higher surface area and less number of structural defects.5. Towards photocatalytic degradation of dyes, the tuning of physical properties is very essential thing hence we are succeeded in achieving better catalytic performance of GCN nanostructures by making use of AAO templates.

Coaxial Carbon/MnO2 Hollow Nanofibers as Sulfur Hosts for High-Performance Lithium-Sulfur Batteries.

Lithium-sulfur (Li-S) batteries have recently attracted a large amount of attention as promising candidates for next-generation high-power energy storage devices because of their high theoretical capacity and energy density. However, the shuttle effect of polysulfides and poor conductivity of sulfur are still vital issues that constrain their specific capacity and cyclic stability. Here, we design coaxial MnO2 -graphitic carbon hollow nanofibers as sulfur hosts for high-performance lithium-sulfur batteries. The hollow C/MnO2 coaxial nanofibers are synthesized via electrospinning and carbonization of the carbon nanofibers (CNFs), followed by an in situ redox reaction to grow MnO2 nanosheets on the surface of CNFs. The inner graphitic carbon layer not only maintains intimate contact with sulfur and outer MnO2 shell to significantly increase the overall electrical conductivity but also acts as a protective layer to prevent dissolution of polysulfides. The outer MnO2 nanosheets restrain the shuttle effect greatly through chemisorption and redox reaction. Therefore, the robust S@C/MnO2 nanofiber cathode delivers an extraordinary rate capability and excellent cycling stability with a capacity decay rate of 0.044 and 0.051 % per cycle after 1000 cycles at 1.0 C and 2.0 C, respectively. Our present work brings forward a new facile and efficient strategy for the functionalization of inorganic metal oxide on graphitic carbons as sulfur hosts for high performance Li-S batteries.

Electrical and piezoresistive sensing capacities of cement paste with multi-walled carbon nanotubes

This study examined the feasibility of using multi-walled carbon nanotubes (MWCNTs) in cement paste for piezoresistive sensors. Two types of MWCNTs with different carbon content (>90% and >99%) were incorporated into cement paste at 1% by weight of binder (1wt%). Plain cement paste and cement composites including 1wt% graphite nanofiber (GNF) and graphene (G) were also considered for comparisons of the electrical conductivity. The test results indicate that the MWCNTs more effectively improved the conductivity of the cement paste than GNF and G. In addition, composites with MWCNTs with lower flowability had less resistivity than those with higher flowability. The size effect in electrical resistivity was observed in the cement pastes with and without the carbon-based nanomaterials, but it was mitigated by incorporating MWCNTs in the cement paste. The stresses and strains under cyclic compression and monotonic tension were well simulated by the measured fraction change in the resistivity of the composites with 1wt% MWCNTs. The gauge factor (GF) for the composites with 1wt% MWCNTs was higher than that of commercially available strain gauges, and it was affected by the loading condition: a higher GF obtained under compression than under tension.

Enhanced hydrogen storage in graphitic carbon micro-nanofibers at moderate temperature and pressure: Synergistic interaction of asymmetrically-dispersed nickel-ceria nanoparticles

Nickel (Ni) and ceria (CeO2) nanoparticles (NPs) containing microporous and graphitic carbon nanofiber (CNF)-activated carbon microfiber (ACF)-based adsorbent was prepared as an efficient hydrogen (H2) storage material at 200 °C and 1 bar. The prepared NiCeO2-ACF/CNF was tested for the H2 storage capacity under batch (static) as well as dynamic (flow) conditions, and the amounts of H2 adsorbed were measured to be approximately the same. In its multiple roles, Ni NP served as the chemical vapor deposition catalyst to grow the CNFs on ACF, besides enhancing H2 adsorption via the spillover mechanism, and decreasing the reduction temperature of CeO2. The experimental data corroborated the positive effects of the synergistic interaction between the Ni and CeO2 NPs and the graphitic characteristics of the CNFs on H2 adsorption. Although CeO2 induced irreversibility in H2 adsorption on NiCeO2-ACF/CNF, the adsorbent was completely regenerated at 300 °C and 1 bar, indicating the developed H2 storage-regeneration process in this study to be effective, practical, and energy efficient.

Epitaxial Growth of Urchin‐Like CoSe2 Nanorods from Electrospun Co‐Embedded Porous Carbon Nanofibers and Their Superior Lithium Storage Properties

AbstractA facile synthesis of porous graphitic carbon nanofibers (CNFs) with encapsulated Co nanoparticles (denote as Co@CNFs) via electrospinning and subsequent annealing is reported. The in situ generated Co nanoparticles (NPs) promote the CNF graphitization under a low temperature of 700 °C, which simultaneously results in the porous structure of the Co@CNFs with a large surface area (416 m2 g−1). Furthermore, urchin‐like CoSe2 nanorods are epitaxially grown from the Co@CNFs via a facile hydrothermal selenation, in which the embedded Co NPs serve as directing seeds and sacrificial Co‐source, and CoSe2 nanorods are rooted into the CNFs (denote as CoSe2@CNFs). When used as anode materials for lithium ion batteries, the CoSe2@CNFs demonstrate superior lithium storage properties, delivering a high reversible capacity of 1405 mA h g−1 after 300 cycles at a current density of 200 mA g−1. The enhanced lithium storage performance can be attributed to the novel hybrid structure, namely, the porous and graphitic CNFs can not only facilitate the charge/ion transfer but also buffer the volume changes of the electrode during lithiation/delithiation processes. More importantly, a general strategy is provided to graphitize amorphous carbon materials via the use of in situ generated transition metal nanoparticles as catalyst.

High-Performance Supercapacitors Based on Graphitic Nanofibers/Nickel Sulfide Composite Electrodes

Fossil fuel depletion, environmental pollution, and global warming have attracted interest in developing green and replaceable energy storage devices. Among various energy storage devices, supercapacitors (SCs) have been widely recognized in a wide range of applications in energy storage over the past decade, such as electric vehicles, mobile electronic devices, large industrial equipment, memory backup systems, and military devices. It is due to their unique properties including high power capability, long cycle lifetime, and fast charge/discharge rate.In this work, nickel sulfide (Ni3S2) nanosheets were growth on the surface of graphitic-nanofibres (GNFs) by using pulse-reversal (PR) electrodeposition method. Compared to the pristine Ni3S2 electrode with discharged capacitance of 461 F g-1, the GNFs@ Ni3S2 electrode revealed a higher capacitance of 635 F g-1 at the same charge-discharge current density of 0.5 mA cm-2. The GNFs@ Ni3S2 electrode still retained 79% of the capacitance at 0.5 mA cm-2 when it was charged/discharged at 4 mAcm-2. Furthermore, the GNFs@ Ni3S2 electrode showed great electrochemical stability. For instance, the GNFs@ Ni3S2 electrode displayed 90% of initial capacitance after the consecutive 200 cycles charged/discharged at current density of 0.5 mAcm-2.

A combination of CoO and Co nanoparticles supported on electrospun carbon nanofibers as highly stable air electrodes

Bifunctional materials able to catalyze both the oxygen reduction (ORR) and the oxygen evolution (OER) reactions in alkaline media are still a challenge for the progress of energy conversion and storage devices such as metal-air batteries or unitized regenerative fuel cells. In this work, carbon nanofibers synthesized by electrospinning are modified with a combination of cobalt oxide and metallic cobalt (CoO-Co/CNF) and studied as a bifunctional air electrode for metal-air batteries. The performance of CoO-Co/CNF for both reactions is compared with state-of-the-art catalysts such as Pt/C and IrO2. The combination of cobalt oxide and metallic cobalt, finely distributed on the surface of graphitic carbon nanofibers, leads to a bifunctional catalyst with a half-wave potential for the ORR slightly better than Pt/C and a reversibility (ΔEOER-ORR) of 809 mV. The stability of CoO-Co/CNF is assessed by means of different stress tests: polarizations at high electrochemical potentials (2 V vs. RHE), rapid charge-discharge cycles at ±80 mA cm−2 and long durability tests by charging for 12 h at 60 mA cm−2 and discharging for 8 h at −80 mA cm−2. CoO-Co/CNF shows a remarkable stability, maintaining, at least, an 82% of its performance for the ORR after the stress tests, even when cycled for more than 100 h.

Characterization of Activated Carbon from Eggshell Membranes Prepared Using Sodium Acetate and Zinc Metal Activation

The eggshell membranes of ducks and hens were carbonized or activated with 4 wt% sodium acetate or zinc at 400-600°C. The carbonized or activated products were characterized by SEM-EDS, TEM, FTIR and XRD. It was found that the suitable activation temperature for eggshell membranes is 500°C with 30.03-35.26% yield. The activation performance of CH3COONa for eggshell membrane activated carbon production was higher than that of Zn metal. The CO3-2, Ca-O, C=C, Na-O and C-O functional groups have been formed on the surface of eggshell membrane activated carbon materials during both CH3COONa and Zn activation. Furthermore, CaO, MgO, Na2O and ZnO have also accumulated on eggshell membrane activated carbon materials with high content and regular dispersion. It was shown that the particles on the duck eggshell membrane activated carbon formed with Zn had weaker attachment on the surface than for duck eggshell membrane activated carbon formed with CH3COONa at same temperature. The XRD and TEM results revealed that the eggshell membrane activated carbons consist of an amorphous carbon matrix with some disordered graphite carbon matrix, spherical particles and nanofiber.

Ag Nanoparticles Drop-Casting Modification of Screen-Printed Electrodes for the Simultaneous Voltammetric Determination of Cu(II) and Pb(II).

A new silver nanoparticle modified screen-printed electrode was developed and applied to the simultaneous determination of Pb(II) and Cu(II). Two different types of silver nanoparticles with different shapes and sizes, Ag nanoseeds and Ag nanoprisms, were microscopically characterized and three different carbon substrates, graphite, graphene and carbon nanofibers, were tested. The best analytical performance was achieved for the combination of Ag nanoseeds with a carbon nanofiber modified screen-printed electrode. The resulting sensor allowed the simultaneous determination of Pb(II) and Cu(II) at trace levels and its applicability to natural samples was successfully tested with a groundwater certified reference material, presenting high reproducibility and trueness.

Fine front side metallisation by stretching the dispensed silver paste filament with graphite nanofibres

The miniaturization of finger electrodes is an area of active research in the crystalline silicon solar cell industry, and diverse trials have been conducted with various printing techniques, including stencil, laser, aerosol jet, inkjet, electrohydrodynamic jet, and dispensing printing. Among these techniques, dispensing printing is regarded as promising due to its superior capability to construct fine finger electrodes with a high aspect ratio and homogeneity by single-pass printing without direct contact with the solar cell wafer. However, its requirements of a small nozzle, short stand-off distance between the nozzle and the solar cell, and specially formulated highly viscous silver paste with a high yield stress raise the issues of nozzle clogging, nozzle breakage by colliding with the solar cell, and the challenges of developing a dispensing printer that can accommodate high pneumatic pressures. In this study, a robust resolution of the aforementioned issues is proposed using graphite nanofibres. The small addition of graphite nanofibres to conventional silver paste greatly enhances the elongational property of silver paste. By stretching the silver paste filament with the enhanced elongational property, the diameter of the silver paste filament is reduced and a finger width of 47.7µm was achieved, which is finer by 21.4µm than the finger width achieved using paste without the graphite nanofibres. Moreover, the stable construction of finger electrodes is enabled with graphite nanofibres at a stand-off distance as far as 1mm and a printing speed as fast as 100mm/s. The resulting cell efficiency with graphite nanofibres is higher by +0.22%p (average) and +0.30%p (median) than those obtained without graphite nanofibres.

Electrical Properties of Cement-Based Composites with Carbon Nanotubes, Graphene, and Graphite Nanofibers

This study was conducted to evaluate the effect of the carbon-based nanomaterial type on the electrical properties of cement paste. Three different nanomaterials, multi-walled carbon nanotubes (MWCNTs), graphite nanofibers (GNFs), and graphene (G), were incorporated into the cement paste at a volume fraction of 1%. The self-sensing capacity of the cement composites was also investigated by comparing the compressive stress/strain behaviors by evaluating the fractional change of resistivity (FCR). The electrical resistivity of the plain cement paste was slightly reduced by adding 1 vol % GNFs and G, whereas a significant decrease of the resistivity was achieved by adding 1 vol % MWCNTs. At an identical volume fraction of 1%, the composites with MWCNTs provided the best self-sensing capacity with insignificant noise, followed by the composites containing GNFs and G. Therefore, the addition of MWCNTs was considered to be the most effective to improve the self-sensing capacity of the cement paste. Finally, the composites with 1 vol % MWCNTs exhibited a gauge factor of 113.2, which is much higher than commercially available strain gauges.

Development of structurally stable electrospun carbon nanofibers from polyvinyl alcohol

Continuous carbon nanofibers are of great interest in research nowadays due to their outstanding properties. But synthesis of cost effective, stable and straight carbon nanofibers from low cost polymeric precursor is still a challenge. In this direction, in the present study efforts are made to prepare stable and straight carbon nanofibers from low cost polyvinyl alcohol (PVA). The PVA nanofibers are drawn by electrospinning technique from the solution of PVA and stabilization of nanofibers was carried out in the presence of iodine vapors for different time interval with applying the load. The stabilized nanofibers were carbonized at 1000 °C and semi-graphitized at 2200 °C. The resultant nanofibers were characterized by analytical and spectroscopic techniques. The microscopic study reveals that there is not much difference in stabilized, carbonized and semi graphitized nanofiber diameter, derived from PVA nanofiber stabilized with the application of load. The XRD and TEM study reveals the presence of amorphous as well as crystalline phases in semi graphitized nanofibers with different interlayer spacing. The higher value of electrical conductivity obtained as a consequence of alignment of carbon layer in the case of nanofiber stabilized with applying load and further increases in conductivity due to crystallinity and decreases in sp3 content.

Graphitic carbon nitride nanofibers in seaweed-like architecture for gas chromatographic separations

Seaweed-like graphitic carbon nitride (g-C3N4) has a unique porous architecture composed of interlocking g-C3N4 nanofibers (NF-C3N4) with much higher surface area than bulk g-C3N4 and shows good potential in separation science. This work investigated the separation performance of NF-C3N4 as stationary phase for capillary gas chromatographic (GC) separations. The NF-C3N4 column exhibits weak polarity and high column efficiency of 4728 plates/m for n-dodecane. Importantly, it displays good separation performance for a wide range of analytes and shows different retention behaviors from the bulk g-C3N4 column and commercial HP-5MS column with 5% phenylpolysiloxane. Particularly, it shows high resolving capability for both aliphatic and aromatic isomers. In addition, NF-C3N4 column has high thermal stability up to 280°C and good separation repeatability with relative standard deviation (RSD) values in the range of 0.29–0.61% for intra-day, 0.56–1.1% for inter-day and 2.0–4.9% for between-column, respectively. Moreover, it was applied for the determination of isomer impurities in real samples, showing good potential in GC applications.

Electro-graphitization and exfoliation of graphene on carbon nanofibers

We present electrical current assisted graphitization as an alternative to conventional high temperature annealing of carbon nanofibers. In-situ experiments were performed on individual vapor grown carbon nanofibers inside a transmission electron microscope to measure the changes in resistance as a function of current density while observing the microstructural changes in real time. About 1000 times decrease in resistivity was measured at current density below 106 A/cm2. Further increase in current density leads to the uniform exfoliation of mostly bi-layer graphene flakes from the skin of the graphitic nanofibers, which leads to further reduction of the electrical resistance. The uniformity of the graphene flake growth over the nanofiber surface area achieved in this study is difficult to achieve with conventional approaches. Further experiments on networked nanofibers suggest that the graphene can remarkably reduce the electrical Kapitza resistance of the nanofiber junctions. The demonstrated processing of such hierarchical nanostructured fibers lead to high surface area and high conductivity carbon nanofibers that can impact flexible electrodes in electrochemical energy conversion or high specific strength composites applications.

A Catalytic Etching-Wetting-Dewetting Mechanism in the Formation of Hollow Graphitic Carbon Fiber

Summary Hollow graphitic carbon nanofibers (HGCNFs) have great promise for many important applications, such as catalysis, sensors, energy conversion, gas storage, and electronic devices. Here, we report a catalytic etching-wetting-dewetting mechanism in synthesizing HGCNFs with both hollow spherical-like and tunnel-like pores. With in situ transmission electron microscope imaging, we show that the spherical pores are formed by the evaporation of encapsulated Ni on the surface of amorphous carbon nanofiber and that hollow tunnels are developed through continuous etching of the amorphous carbon under catalysis of Ni nanoparticles. Theoretical calculations and simulations reveal that continuous tunnel etching is driven by the wetting-to-dewetting transition of the Ni-tunnel wall interaction during the catalytic graphitization of the amorphous carbon wall. In a typical application, we demonstrate that the synthesized HGCNFs, with a capacity about three times higher than that of their non-hollow counterparts, are excellent potential candidates for CO 2 capture.

The coaxial nanostructure of ruthenium oxide thin films coated onto the vertically grown graphitic nanofibers for electrochemical supercapacitor

In this work, the coaxial nanostructure of ruthenium oxide (RuOx) thin films coated onto the surface of the vertical graphitic nanofibers (GNFs) was developed and employed as electrodes for electrochemical supercapacitor. The vertically aligned GNFs were directly grown on the fluorine doped tin oxide glass via the chemical vapor deposition, and the RuOx thin films were prepared by an easy cyclic voltammetric electrochemical deposition. The morphologies and nanostructures of the coaxial-nanostructure RuOx/GNFs were investigated by the field emission gun scanning electron microscopy and the high-resolution transmission electron microscopy, respectively. Raman spectrum was used to examine the characteristic features of the RuOx/GNFs. The electrochemical properties were examined by cyclic voltammetry, galvanostatic charge-discharge, and electrochemical impedance spectra. The directly grown GNFs not only played the attractive template that offered a large surface area to promote the loading of RuOx for enhancing electrochemical activity, but also provided a high-speed pathway that promoted charge transport and transfer. The macroporous structure of the vertically coaxial-nanostructure RuOx/GNFs avoided the self-aggregation, thus allowed the electrolyte can easily diffuse through the open space between them to enhance the electrochemical performance. The electrochemical measurements revealed that the excellent charge storage properties of the RuOx/GNFs can be obtained, the good electrochemical performance was attributed to the unique macroporous structure and the coaxial nanostructure of RuOx/GNFs.

Graphitic carbon nanofiber growth from catalytic-metal organic frameworks & their electrochemical double layer properties

Electrochemical utilization of catalyst particles significantly increases the capacitance of catalytic MOF-derived graphitic carbon-nanofibers.

The effect of Ni(i)–N active sites on the photocatalytic H2O2 production ability over nickel doped graphitic carbon nitride nanofibers

This work provides a strategy to improve the photocatalytic H2O2 production ability by embedding Ni(i)–N sites into the g-C3N4 lattice.

Comparative Study of H-ZSM 5 Zeolite and Graphite Nanofiber (GNF) in Catalytic Pyrolysis of Oil Palm Fronds (OPF)

In keeping an eye on the goal of a sustainable chemical and energy industry, bio-oil produced from biomass fast pyrolysis liquefaction has aroused great interests and attentions among various stakeholders. In present paper, carbon based catalyst, Graphite Nanofiber (GNF) was employed to investigate and evaluate its potential in thermal pyrolysis of Oil Palm Frond (OPF). The pyrolysis was carried out in a semi batch reactor which was externally heated by an electrical vertical split tube furnace. 15g of OFP biomass with 1.5g of catalysts is thermally decomposed at two distinct temperatures of 573K and 773K, producing a solid char residue and a liquefied vapour product after passing through a condenser. Comparative study of both catalyst performances in thermal pyrolysis of OPF was conducted in term of selectivity and conversion. Between Zeolite ZSM-5 and GNF, GNF catalysts achieved a better conversion performance in transforming a total of 66.57 wt% and 72.40 wt% of biomass into vapour and liquid products at 573K and 773K respectively. On the other hand, H-ZSM 5 Zeolite catalyst yields the highest selectivity of 64.33 wt% toward condensable vapour components at 773K with a remarkably high bio-oil yield of 45.71 wt%. Such superior results strengthened the fact of H-ZSM 5 Zeolite catalysts being the more effective catalyst than GNF in catalytic pyrolysis of OPF.
 Keywords: Catalytic Pyrolysis, Oil Palm Fronds, Bio-Oil, Graphite Nanofiber, H-ZSM 5 Zeolite