Graphite Nanofibers Research Articles

Single layer nano graphene platelets derived from graphite nanofibres.

Solutions of calibrated nanographenides (negatively charged nanographenes) are obtained by dissolution of graphite nanofibre intercalation compounds (GNFICs). Deposits show homogeneous unfolded nanographene platelets of 1 to 2 layers thickness and 10 nm lateral size, evidenced by atomic force microscopy and Raman spectroscopy. Upon oxidation, nanographenide solutions exhibit strong photoluminescence.

The carbon deposits formed by reaction of a series of red mud samples with methanol

Magnetic carbon materials were prepared by the catalytic growth of graphitic carbon and carbon nanofibers using methanol as carbon source with a series of red mud wastes from different sources.

Cumulative effect of transition metals on nitrogen and fluorine co-doped graphite nanofibers: an efficient and highly durable non-precious metal catalyst for the oxygen reduction reaction.

Nitrogen and fluorine co-doped graphite nanofibers (N/F-GNF) and their cumulative effect with Fe and Co have been developed as an alternative non-precious metal catalyst for efficient oxygen reduction reaction (ORR) in acidic media. The synergistic effect between the doped hetero atoms and the co-ordinated Fe and Co towards ORR activity and durability of the catalyst is deeply investigated. A high ORR onset potential comparable with commercial Pt/C catalyst is observed with the Fe-Co/NF-GNF catalyst, which indicates that this catalyst is a potential alternative to Pt/C. A fivefold increase in mass activity is achieved by the Fe-Co/NF-GNF catalyst compared to the simple N/F-GNF catalyst, which endorses the significant role of transition metal atoms in enhancing ORR activity. The advanced Fe-Co/NF-GNF catalyst also exhibits complete tolerance to CH3OH and CO. The Fe-Co/NF-GNF catalyst also exhibits excellent durability towards the ORR with only a 10 mV negative shift in its half wave potential after a 10 000 repeated potential cycling test, whereas in the case of a commercial Pt/C catalyst there was an ∼110 mV negative shift under similar environmental conditions. More stringent corrosive test cycles were also performed by maintaining the cell as high as 1.4 V with a later decrease to 0.6 V vs. RHE for 300 cycles, which showed the excellent durability of the Fe-Co/NF-GNF catalyst in comparison with the Pt/C catalyst. XPS analysis of the Fe-Co/NF-GNF catalyst presents the ORR active chemical states of N (pyridinic-N and graphitic-N) and F (semi-ionic-F) and the co-ordinated sites of Fe and Co species with the dopants. The excellent performance and durability of the Fe-Co/NF-GNF catalyst is due to the synergistic effect between the hetero atoms dopants (N and F) and strong co-ordinating bonds of M-N-C, which protect the graphene layers around the metallic species and greatly mitigates the leaching of Co and Fe during the long term cycling test. The high activity and long term durability of the Fe-Co/NF-GNF catalyst make it a promising ORR electrocatalyst for the fuel cell cathode reaction.

Nanocomposite membranes of sulfonated poly(phthalalizinone ether ketone)–sulfonated graphite nanofibers as electrolytes for direct methanol fuel cells

Polymer nanocomposite membranes are prepared by the dispersion of sulfonated graphite nanofibers (SGNF) in the sulfonated poly(phthalazinone ether ketone) (SPPEK) matrix.

A timesaving, low-cost, high-yield method for the synthesis of ultrasmall uniform graphene oxide nanosheets and their application in surfactants

Graphene oxide nanosheets (GONSs) with a lateral size less than 100 nm have attracted more and more attention for their wide range of potential applications, from bionanotechnology and nanobiomedicine to surfactants. However, at present GONSs are commonly prepared from graphite nanofibers or graphite nanopowders which are both expensive. Here, a timesaving, low-cost, high-yield method is proposed for preparing ultrasmall uniform GONSs with an average lateral size of ∼30 nm, utilizing common graphite powder as the raw material in the absence of a strong acid. The obtained GONSs are able to disperse single-walled carbon nanotubes (SWCNTs) effectively, and the dispersion could withstand high-speed centrifugation. Consequently, GONSs could indeed serve as a superior surfactant for the dispersion of SWCNTs, and the dispersion could be further applied in electronics, as the GONSs may be further reduced to reduced GONSs or graphene nanosheets.

Co-Embedded Graphitic Porous Carbon Nanofibers for Pt-Free Counter Electrode in Dye-Sensitized Solar Cells

Co-embedded graphitic porous carbon nanofibers(Co-GPCNFs) are synthesized by using an electrospinning method. Their morphological, structural, electrochemical, and photovoltaic properties are investigated. To obtain the optimum condition of Co-GPCNFs for dye-sensitized solar cells(DSSCs), the amount of cobalt precursor in an electrospinning solutuion are controlled to be 0 wt%(conventional CNFs), 1 wt%(sample A), and 3 wt%(sample B). Among them, sample B exhibited a high degree of graphitization and porous structure compared to conventional CNFs and sample A, which result in the performance improvement of DSSCs. Therefore, sample B showed a high current density(JSC, ) and excellent power conversion efficiency(PCE, 5.33 %) than those of conventional CNFs(, 3.78 %). This result can be explained by combined effects of the increased contact area between the electrode and elecytolyte caused by improved porosity and the increased conductivity caused by the formation of a high degree of graphitization. Thus, the Co-GPCNFs may be used as a promising alternative of Pt-free counter electrode in DSSCs.

Expanded graphitic materials prepared from micro- and nanometric precursors as anodes for sodium-ion batteries

A series of expanded graphitic materials are prepared from two different precursors: micrometric synthetic graphite and graphitized carbon nanofibers, and tested as anodes for sodium-ion batteries. The materials preparation involves the oxidation of the precursors followed by partial thermal reduction. Overall, the expanded synthetic graphite materials show better electrochemical performance as anode than the expanded graphite nanofibers, providing higher specific capacity, leading to lower capacity losses in the first discharge-charge cycle and exhibiting outstanding cycling stability. Specific capacities of ∼150mAhg−1 at 37mAg−1 and ∼110mAhg−1 at 100mAg−1 are attained, and up to 50% of the initial capacity at 19mAg−1 is kept at 372mAg−1. Unexpectedly, higher capacity losses are measured for the nanostructured electrodes by progressively increasing the current density. These differences are attributed to the lower surface area and porosity of expanded synthetic graphite materials which favors the formation of thinner and more stable SEI, thus reducing the electrode resistance and enhancing the accessibility of Na+ ions to surface oxygen-containing functional groups with the consequent increase of the surface capacity which was found to be the main contribution to the total specific capacity.

Mechanism and Energetics of the Unique Spillover Effect Manifestation, Relevance to the Efficient Hydrogen Storage in Graphite Nanofibers

The “thermodynamic forces” and energetics of intercalation of H2 nanophase of a high density into carbon-based nanostructures are considered. The hydrogen self-compression effect, at the expense of the free energy of association of the penetrating hydrogen atoms to the “captured” hydrogen molecules, is shown. The mechanisms of the extraordinary manifestation of both the hydrogen spillover effect, and the Kurdjumov-like effect are discussed.

Catalytic Pyrolysis of Oil Palm Frond (OPF) Using Graphite Nanofiber (GNF) As Catalysts

Catalytic Pyrolysis of Oil Palm Frond (OPF) Using Graphite Nanofiber (GNF) As Catalysts

Anchoring Mechanism of ZnO Nanoparticles on Graphitic Carbon Nanofiber Surfaces through a Modified Co-Precipitation Method to Improve Interfacial Contact and Photocatalytic Performance.

A facile three-step co-precipitation method is developed to synthesize graphitic carbon nanofibers (CNFs) decorated with ZnO nanoparticles (NPs). By interchanging intermediate steps of the reaction processes, two kinds of nanohybrids are fabricated with stark morphological and physicochemical differences. The morphologies differ because of the different chemical environments of the NP/nanocluster formation. The hybrid with larger and non-uniform ZnO nanocluster size is formed in liquid phase and resulted in considerable interfacial defects that deteriorate the charge-transfer properties. The hybrid with smaller and uniform ZnO NPs was formed in a dry solid phase and produced near-defect-free interfaces, leading to efficient charge transfer for superior photocatalytic performance. The results broaden the understanding of the anchoring/bonding mechanism in ZnO/CNF hybrid formation and may facilitate further development of more effective exfoliation strategies for the preparation of high-performance composites/hybrids.

Deoxyribonucleic acid directed metallization of platinum nanoparticles on graphite nanofibers as a durable oxygen reduction catalyst for polymer electrolyte fuel cells

Effective surface functionalization to the hydrophobic graphite nanofibers (GNF) is performed with the biomolecule, namely deoxy-ribo-nucleic-acid (DNA) via π–π interactions. Pt nanoparticles are impregnated on GNF–DNA composite by ethylene glycol reduction method (Pt/GNF–DNA) and its effect on electro catalytic activity for oxygen reduction reaction (ORR) is systemically studied. Excellent dispersion of Pt nanoparticles over GNF–DNA surfaces with no evidence on particle aggregation is a remarkable achievement in this study. This result in higher electro chemical surface area of the catalyst, enhanced ORR behavior with significant enhancement in mass activity. The catalyst is validated in H2–O2 polymer electrolyte fuel cell (PEFC) and a peak power density of 675 mW cm−2 is achieved at a load current density of 1320 mA cm−2 with a minimal catalyst loading of 0.1 mg cm−2 at a cell temperature of 70 °C and 2 bar absolute pressure. Repeated potential cycling up to 10000 cycles in acidic media is also performed for this catalyst and found excellent stability with only 60 mV drop in the ORR half wave potential. The superior behavior of Pt/GNF–DNA catalyst is credited to the robust fibrous structure of GNF and its effective surface functionalization process via π–π interaction.

Detecting the Genesis of a High-Performance Carbon-Supported Pd Sulfide Nanophase and Its Evolution in the Hydrogenation of Butadiene

A new procedure for preparation of palladium sulfide nanoparticles, which are deposited and anchored over highly graphitized carbon nanofibers, is presented. The preparation method is based on the use of PdSO4 as metal precursor or alternatively in the previous functionalization of the carbon surfaces with sulfonic groups by treatment with fuming sulfuric acid. Using an in situ high-energy X-ray diffraction technique, in both cases it is demonstrated that during the reduction treatment, the initially present palladium hydride is transformed into a palladium sulfide (Pd4S). The catalytic properties of these materials have been tested in the gas-phase butadiene partial reduction to butenes. Although metallic palladium nanoparticles supported in the same carbon fibers produce butane as the principal product, the supported Pd4S nanocrystals mainly yield different isomers of butenes independently of the conversion level. Furthermore, applying the same X-ray diffraction method reveals that this catalytic phase is stable during reaction.

Carbon nanofibers synthesized by pyrolysis of chloroform and ethanol mixture

Platelet graphite nanofibers (PGNFs) and turbostratic carbon nanofibers (TSCNFs) were synthesized by the pyrolysis of 3 and 10 vol% chloroform in ethanol, respectively, in the presence of Ni catalyst at 700 °C. Auger electron spectrometry analysis reveals that the participation of chloroform in the synthesis led to Ni–Cl bonding on the surface of the catalysts, resulting in a relatively poor crystalline layer and a coarse surface. Furthermore, the Ni–Cl compound affected the melting point and mobility of Ni, changing the morphology and geometrical shape of Ni particles. A low amount of chlorine in the catalyst led to the formation of smaller catalyst particles with a flat surface, resulting in graphene nanosheets stacked perpendicular to the fiber axis, which became PGNFs. In contrast, a high amount of chlorine in the catalyst led to the aggregation of the catalyst and thus the formation of large catalyst particles with a rough surface, resulting in the random stacking of graphene nanosheets, which became TSCNFs. The participation of chlorine was found to be important in the synthesis of the PGNFs and TSCNFs.

Dilatometric Study of the Electrochemical Intercalation of Bis(trifluoromethanesulfonyl) Imide and Hexafluorophosphate Anions into Carbon-Based Positive Electrodes

“Dual-ion cells” are electrochemical energy storage devices that employ graphitic carbons as positive electrode material. The electrolyte in this cell system does not only behave as a charge carrier but also as active material.[1] The negative electrode in the dual-ion system can be built up by typical anode materials for lithium ion cells such as lithium metal, lithium titanate (Li4Ti5O12, LTO) or graphite.[2] During charging, the anions of the electrolyte are intercalated into the layered structure of the graphite positive electrode, while the lithium ions of the electrolyte deposit on the surface of the metallic lithium negative electrode. The gallery height expansion for graphite positive electrodes by bis(trifluoromethanesulfonyl) imide (TFSI-) intercalation is around 140%[3] and 130% if hexafluorophosphate (PF6-) is intercalated.[4] On discharge, both ions are stripped/de-intercalated and solvated again in the electrolyte. Furthermore several carbon materials like graphite, carbon black or carbon nanofibers are applied as conductive additives in high voltage cathodes. At potentials above 4.5 V vs. Li/Li+, major problems are related to electrolyte degradation and to anion and solvent co-intercalation. Co-intercalation can lead to the destruction of the carbon structure (exfoliation) and therefore to continuous electrolyte degradation.[5,6] The method of electrochemical dilatometry has been used since the 1970s to investigate the height change of layered host compounds when a guest molecule or ion is inserted.[7] The Li+ intercalation into different types of graphite or the BF4-intercalation into carbons are two examples that were already investigated using the electrochemical dilatometer (ECD-1), which was developed by Hahn et al.[8,9] The complete electrode height change or the electrode height change per cycle can be calculated. An illustration of the ECD-1 cell core is presented in Figure 1. In this work, we report the intercalation of TFSI- and PF6 - anions into graphitic and carbon black-based positive electrodes from an ionic liquid-based and organic solvent-based electrolyte using LiTFSI and LiPF6 as the conductive salts. Furthermore, we investigated the influence of two electrode binders, namely sodium-carboxymethyl cellulose (CMC) and poly(vinylidene diflouride) (PVdF) on the electrochemical intercalation/de-intercalation behavior of the electrode. Especially, the influence of the electrode binder on the electrode expansion behavior and the electrode material stability are discussed. Additionally, the influence of a constant voltage step at the upper cut-off potential and the influence of a higher operation temperature of 60 °C on the electrode expansion are discussed. Figure 1: Illustration of the in-situelectrochemical dilatometer cell (ECD-1 (EL-Cell GmbH)). 1: Metal membrane; 2: Working electrode (WE); 3: Glass T-frit; 4: Metallic lithium (CE); 5: CE plunger; 6: Sensor tip; 7: Spacer disc; 8: RE with metallic lithium on top.

Graphite with Different Structures as Catalysts for Counter Electrodes in Dye-sensitized Solar Cells

Three graphite materials with different structures, including graphite nanofiber (GNF), graphite nanosheet (GNS), and graphite nanoball (GNB), were used as the catalytic films on the counter electrodes (CEs) of dye–sensitized solar cells (DSSCs). Compared to GNF and GNS, GNB not only provides a higher degree of defects in the sp2 plane structure but also possesses aboundant hydroxyl functional groups as the electro-catalytic active sites for I3− reduction; thereby, the intrinsic heterogeneous rate constant (k0) and effective electro-catalytic surface area (Ae) of GNB-based CE are both higher than the values of GNF-based and GNS-based CEs. The GNB-based DSSC with showed the power conversion efficiency (η) of 7.88%, while those GNF-based and GNS-based DSSCs showed η’s of 3.60% and 2.99%, respectively. Moreover, it is also observed that the η of the GNB-based DSSC (7.88%) is quite close to that of a Pt-based DSSC (η=8.38%); this implies that the GNB can become a potential candidate to replace the expensive Pt, owing to its low-cost.

Nanocomposite coatings on cotton and silk fibers for enhanced electrical conductivity

Electrically conducting carbon nanofillers like liquid exfoliated graphite (EG), nanographite (NG), carbon nanotube (CNT) and carbon nanofiber (CNF) were dispersed in thermoplastic polyurethane (TPU) matrix. HRTEM images and SAED patterns confirmed exfoliation of graphite and good dispersion of all nanofillers. The polymer dispersions were used to develop nanocomposite coatings on cotton yarn and silk fibers. These nanocomposite coated fibers showed significant improvements in electrical conductivity. Current-voltage (IV) plots indicated linearity for most of the nanocomposite coated fibers. Among the nanofillers, CNF and CNT have strong potential to impart stable conductivity on such fibers. The electrical conductivity of 10 wt% CNF based nanocomposite coated cotton yarn was 2 S/m; while it was more than 12 S/m for silk filament. 2 wt% CNT dispersed nanocomposite coating on silk also showed very good conductivity of 11 S/m. The large void fraction in coated cotton yarn (~12 %) is attributed for such difference in electrical conductivity. Hence, staple yarns are not suitable to develop such nanocomposite coated fibers. Both the resistance and impedance tests were carried out at different test lengths up to 5 cm and resistance and impedance (at 100 Hz, 120 Hz and 1 kHz) per cm was calculated with variable test length. As variations in test results were not very high it can be concluded that the uniformity in electrical conductivity is achieved through these coatings.

A Bamboo-Inspired Nanostructure Design for Flexible, Foldable, and Twistable Energy Storage Devices.

Flexible energy storage devices are critical components for emerging flexible electronics. Electrode design is key in the development of all-solid-state supercapacitors with superior electrochemical performances and mechanical durability. Herein, we propose a bamboo-like graphitic carbon nanofiber with a well-balanced macro-, meso-, and microporosity, enabling excellent mechanical flexibility, foldability, and electrochemical performances. Our design is inspired by the structure of bamboos, where a periodic distribution of interior holes along the length and graded pore structure at the cross section not only enhance their stability under different mechanical deformation conditions but also provide a high surface area accessible to the electrolyte and low ion-transport resistance. The prepared nanofiber network electrode recovers its initial state easily after 3-folded manipulation. The mechanically robust membrane is explored as a free-standing electrode for a flexible all-solid-state supercapacitor. Without the need for extra support, the volumetric energy and power densities based on the whole device are greatly improved compared to the state-of-the-art devices. Even under continuous dynamic operations of forceful bending (90°) and twisting (180°), the as-designed device still exhibits stable electrochemical performances with 100% capacitance retention. Such a unique supercapacitor holds great promise for high-performance flexible electronics.

Nitrogen and fluorine co-doped graphite nanofibers as high durable oxygen reduction catalyst in acidic media for polymer electrolyte fuel cells

Nitrogen and fluorine co-doped graphite nanofibers (N–F/GNFs) were synthesized using melamine and ammonium fluoride as precursors, respectively, for use as metal-free catalysts for oxygen reduction reaction (ORR). The N–F/GNF catalyst undergoes structural transformation resulting in wrinkled graphene structures with many open-edge sites when F is doped into N/GNF. The developed catalyst has no effect on CH3OH or CO, which makes it highly desirable as a metal-free electrocatalyst for the ORR. The developed catalyst was subjected to 20,000 repeated potential cycles, no degradation of ORR activity was observed in acidic media. X-ray photoelectron spectroscopy analysis of the N–F/GNF catalyst reveals the presence of active pyridine and graphitic type N with highly active semi-ionic C–F bond in the graphitic structure. First-principles density functional theory calculations further support the formation of graphene structures from the GNF with the interlayer distance increasing from 3.9 to 5.1Å. The Bader charge analysis predicts the site specificity of F doping in N-doped GNF. This N–F/GNF catalyst delivers a peak power density of 165mWcm−2 at a load current density of 850mAcm−2 in a H2/O2 polymer electrolyte fuel cell, as a nonmetallic electrocatalyst in acidic media.

One-pot synthesis of graphene oxide sheets and graphene oxide quantum dots from graphite nanofibers

A one-pot synthesis of graphene oxide (GO) sheets and GO quantum dots using graphite nanofibers (GNF) as starting material is reported. Two types of GNF starting materials, namely herringbone and platelet structures, were used. HRTEM revealed that platelet GNF produces quantum dots typically less than 10 nm in size while herringbone GNF produces relatively larger GO sheets. SAED patterns indicate that the produced GO sheets have a hexagonal crystal structure. UV–Vis, PL, XPS, and Raman show salient differences between the produced GO nanostructures which correlate well with the morphological analysis. Unlike the GO sheets, the GO quantum dots are photoluminescent. The difference in PL properties was attributed to the higher oxygen content in GO quantum dots which were shown by XPS. The results offer a new insight to the importance of starting material in the synthesis of graphene nanostructures.

Ultrathin graphitic C3N4 nanofibers: Hydrolysis-driven top-down rapid synthesis and application as a novel fluorosensor for rapid, sensitive, and selective detection of Fe3+

Ultrathin graphitic C3N4 (g-C3N4) nanofibers about 5–10nm in diameters have been rapidly prepared via alkali-catalyzed hydrolysis of bulk g-C3N4 in concentrated alkaline aqueous solution. The morphologies of the g-C3N4 nanostructures can be facilely controlled by varying reaction time, and a scissoring mechanism is proposed to explain the formation process involved. The g-C3N4 nanofibers can serve as a novel fluorosensor for rapid Fe3+ detection with high sensitivity and selectivity.