Coated Carbon Nanofibers Research Articles

Tuning the High-Temperature Wetting Behavior of Metals toward Ultrafine Nanoparticles.

The interaction between metal nanoparticles (NPs) and their substrate plays a critical role in determining the particle morphology, distribution, and properties. The pronounced impact of a thin oxide coating on the dispersion of metal NPs on a carbon substrate is presented. Al2 O3 -supported Pt NPs are compared to the direct synthesis of Pt NPs on bare carbon surfaces. Pt NPs with an average size of about 2 nm and a size distribution ranging between 0.5 nm and 4.0 nm are synthesized on the Al2 O3 coated carbon nanofiber, a significant improvement compared to those directly synthesized on a bare carbon surface. First-principles modeling verifies the stronger adsorption of Pt clusters on Al2 O3 than on carbon, which attributes the formation of ultrafine Pt NPs. This strategy paves the way towards the rational design of NPs with enhanced dispersion and controlled particle size, which are promising in energy storage and electrocatalysis.

A hierarchical carbon@TiO2@MoS2 nanofibrous composite derived from cellulose substance as an anodic material for lithium-ion batteries

A filter paper derived hierarchical carbon@TiO2@MoS2 nanofibrous composite was fabricated by employing natural cellulose substance (e.g., commercial filter paper) as both scaffold and carbon source. The nanofibers of the filter paper pre-coated with an ultrathin titania-gel film were further modified with polydiallyldimethylammonium chloride (PDDA) and polysodium-p-styrenesulfonate (PSS) polyelectrolytes based on the layer-by-layer self-assemble method. Afterwards, the composite sheet was served as a host to grow MoS2 nanosheets by a hydrothermal process. Finally, the as-prepared composite sheet was carbonized in Ar atmosphere at 800 °C for 3 h to yield the carbon@TiO2@MoS2 composite. The resultant composite consists of titania thin layer coated carbon nanofibers with wrinkled MoS2 nanosheets (with a thickness of ca. 6 nm) anchored as an external coating layer on the surfaces. When evaluated as an anodic material for lithium-ion batteries, the carbon@TiO2@MoS2 composite delivered an initial discharge capacity of 1314.4 mAhh g−1 and a stable reversible capacity of 597.2 mAhh g−1 after 100 discharge/charge cycles at the current rate of 100 mA g−1, which is higher than the theoretical capacity of the as-prepared composite electrode. The enhanced electrochemical performances of this composite were benefited from its unique three-dimensional network structures, as well as the buffering effect arising from the titania-coated carbon nanofibers, which effectively alleviates the serious volume change of MoS2 and maintains the structural integrity of the electrode during the repeated lithiation/delithiation processes.

Synthesis of highly effective MnO2 coated carbon nanofibers composites as low cost counter electrode for efficient dye-sensitized solar cells

In this work, MnO2 coated carbon nanofiber (MnO2/CNF) composites have been synthesized using a combination of electrospinning and hydrothermal techniques. First, CNFs are synthesized by electrospinning, then coated them with MnO2 based on the self-limiting reaction between CNFs and KMnO4. The prepared composites of MnO2/CNFs are used as a low-cost counter electrode (CE) for dye-sensitized solar cells (DSSCs). It is found that the composite MnO2/CNFs-3, corresponding to a 100 nm thick MnO2 coating resulted in the highest catalytic activity, moreover the corresponding DSSC shows a power conversion efficiency (PCE) of 8.86%, higher than that of the Pt CE based DSSC (8.27%).

Interfacial analysis of TiO2 coated carbon nanofibers and Mg-Al alloy matrix fabricated using a liquid pressing process

Novel structures of TiC/TiAl2/carbon nanofiber (CNF) hybrid reinforcements with attached magnesium oxide (MgO) particles were successfully fabricated in the matrix of the Mg alloy AZ91 (Mg 9wt%, Al 1wt%, Zn) composite. This was done using a novel liquid pressing process, coupled with in situ reactions between titanium dioxide (TiO2)-coated CNFs and the Mg alloy. Homogeneously dispersed hybrid reinforcement with strong interfacial bonding through TiC/TiAl2, led to dramatic improvement in the mechanical properties of AZ91 alloys, with the assistance of an anchoring effect by MgO particles chemically attached to the coating layer.

Flexible High Energy Density Silicon Composite Anode for Structural Batteries

The challenges of using high capacity metallic lithium foil as an anode for high energy density lithium battery are still remaining despite many years of research efforts, due to the intrinsic problems associated with the electrodeposition of reactive light metals such as lithium. In addition, the required excess lithium (3-5 times) to satisfy the battery long cycle life, and the safety concern associated with the large format cells containing metallic lithium anode have force the battery community to search for other alternatives. Some of the alternative anodes may exceed the energy density of metallic lithium when the excess lithium is considered. We will present a new class of composite anode material for structural and conformal lithium batteries. Our new composite anode is based on an optimized free-standing silicon coated carbon nanofiber in the form of flexible thin-paper with capacity exceeding 1500Ah/kg for the electrode including the carbon fiber and the silicon, and with high capacity retention during extensive charge-discharge cycles. The electrode/electrolyte interface and the silicon/carbon interface have been engineered to minimize the initial irreversibility during lithiation and delithiation, to less than 10%. In addition, the in-plan conductivity of the free standing composite anode has been optimized for high power battery application. We will report the performances of the silicon-carbon nanofiber composite anode in half cells and in full cells against high energy density lithium-rich layered oxide, and olivine based cathodes.

Thermally stable carbon nanofibers functionalized with poly(dimethylsiloxane) for solid-phase microextraction of polycyclic aromatic hydrocarbons prior to GC analysis

The authors describe poly(dimethylsiloxane)-coated carbon nanofibers (CNF-PDMS) for solid-phase microextraction of polycyclic aromatic hydrocarbons (PAHs). The fibers were prepared by a sol–gel method and are stable at temperatures up to 350 °C, probably due to the chemical bonds between the coating and the fiber surface. The fibers can be re-used up to 180 times. The CNFs enhance the surface area of the coating compared to that of a plain PDMS fiber and, accordingly, provide higher extraction efficiency. Following thermal desorption, the PAHs were quantified by GC with FID detection. Under optimized experimental conditions, the detection limits of the method range from 5 to 20 pg mL−1, and response is linear in the 0.017 to 100 ng mL−1 range. The repeatability and reproducibility vary between 4.8 % and 8.6 %, and between 4.1 % and 10.2 %, respectively. The method was successfully utilized for the analysis of PAHs in (spiked) water samples, with satisfactory recoveries in the range of 90.1–99.9 %.

Synthesis and electrochemical performance of ruthenium oxide-coated carbon nanofibers as anode materials for lithium secondary batteries

In this study, ruthenium oxide (RuO2) coated carbon nanofibers (CNFs) were synthesized and applied as anode materials of Li secondary batteries. The CNFs were grown on Ni foam via chemical vapor deposition (CVD) method after CNFs/Ni foam was put into the 0.01M RuCl3 solution. The ruthenium oxide-coated CNFs/Ni foam was dried in a dryer at 80°C. The morphologies, compositions, and crystal quality of RuO2/CNFs/Ni foam were characterized by SEM, EDS, XRD, Raman spectroscopy, and XPS. The electrochemical characteristics of RuO2/CNFs/Ni foam as anode of Li secondary batteries were investigated using three-electrode cell. The RuO2/CNFs/Ni foam was directly employed as a working electrode without any binder, and lithium foil was used as the counter and reference electrodes. LiClO4 (1M) was employed as electrolyte and dissolved in a mixture of propylene carbonate (PC): ethylene carbonate (EC) in a 1:1 volume ratio. The galvanostatic charge/discharge cycling and cyclic voltammetry measurements were carried out at room temperature by using a battery tester. In particular, synthesized RuO2/CNFs/Ni foam showed the highest retention rate (47.4%). The initial capacity (494mAh/g) was reduced to 234mAh/g after 30 cycles.

Titanium dioxide coated carbon nanofibers as a promising reinforcement in aluminum matrix composites fabricated by liquid pressing process

Carbon-nanofiber (CNF) reinforced aluminum (Al) matrix composites were fabricated by a unique liquid pressing process. The mechanical properties of the CNF–Al composites, both with and without titanium dioxide (TiO2) coating layers on the CNF surface, have been studied. The compressive yield strength of the TiO2 coated CNF–Al composite dramatically increased (over nine times), as compared with that of an Al alloy. TiO2 coated CNFs are expected to be a highly sustainable and dispersible reinforcement for metal matrix composites (MMCs) that are fabricated by a metal melting process.

Fabrication and characterization of carbon nanofiber@mesoporous carbon core-shell composite for the Li-air battery

In this study, we successfully design and synthesize the mesoporous carbon coated carbon nanofibers (CNF@mesoCs) for the Li-air battery. The composites are fabricated via electrospinning technique and nanocasting strategy. After mesoporous carbon coating process, the composites have retained their original one-dimensional structure as pristine carbon nanofibers. Every nanofiber entangles with each other to form a three-dimensional cross-linked web structure. Because of the mesoporous carbon coating on carbon nanofibers, the surface area increases from 708m2g−1 to 2194m2g−1. We confirm that the mesoporous carbon coated on carbon nanofibers is well-graphitized by analysis of Raman spectra. The graphitized surface of CNF@mesoCs (4.638Scm−1) is believed to result in their higher electrical conductivity than that of pristine carbon nanofibers (3.0759Scm−1). Without employment of any binders and metal foams, the cathode of CNF@mesoCs exhibits high discharge capacity of 4000mAhg−1, which is much higher than that from pristine carbon nanofibers (2750mAhg−1). This work demonstrates that the fabricated CNF@mesoCs structures have a great potential to be employed as light-weight and efficient electrode for energy storage and conversion devices.

Facile preparation of Mn3O4-coated carbon nanofibers on copper foam as a high-capacity and long-life anode for lithium-ion batteries

Carbon nanofibers (CNFs) were deposited on Cu foam by a floating catalyst method, and a Mn3O4 layer was then coated onto the deposited CNFs via a hydrothermal process based on the redox reaction of carbon and potassium permanganate. The obtained architecture of Mn3O4-coated CNFs (CNFs@Mn3O4) on Cu foam was directly used as an anode for lithium-ion batteries without using any binder or conducting additive. The anode showed high reversible capacity, good cycle stability and superior rate capability. A reversible capacity of up to 1210.4 mA h g(-1) was obtained after 50 cycles at a current density of 100 mA g(-1). When the current density increased to 5000 mA g(-1), it could deliver a capacity of more than 300 mA h g(-1). The excellent electrochemical performance could be attributed to the unique morphology of the CNFs@Mn3O4 nanocomposites, which can buffer the volume change, decrease the contact resistance, shorten the ionic diffusion path and make the electron transport more efficient.

3-D Conformal Silicon/Carbon Nanofiber-Graphene Composites for Next Generation of Li Batteries

Next generation of lithium battery may use new electrode materials with significantly higher energy density to meet more demanding applications for, auto, space and marine. Silicon anode material has the highest known specific capacity, 4,200 mAh/g, more than an order of magnitude higher than the current graphite anode (372 mAh/g). We have engineered a 3-D conformal anode based on silicon anode technology with capacity exceeding 1000 mAh/g, and high capacity retention during charge-discharge cycles. The capacity retention of the composite has been optimized by engineering of support/Si interface as well as Si/electrolyte interface. Our technology includes incorporation of a nano composite of silicon coated carbon nanofiber and graphene sheets embedded in electronically conductive polymers. In this presentation we reports electron microscopy, electrochemical performance and mechanical properties of our anode composite before and after multiple electrochemical charge-discharge cycles. Applications of our new electrode in structural battery containing sulfur cathode for auto and space and marine will be discussed.

Electrochemical Characterization of a Carbon Nanofiber Electrode System Hybridized with PEDOT-PSS

In this work, electrochemical properties of a bilayer electrode system prepared from an electrically conducting polymer, poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate), PEDOT-PSS coated carbon nanofibers (CNFs), have been investigated. The CNFs were used as supports for the deposition of PEDOT-PSS by a dip-coating technique to yield a bilayer electrode system. Electrodes prepared by such a method were used in supercapacitors operating in acidic (1 M H2SO4) electrolytes. The capacitance values were estimated by voltammetry and galvanostatic techniques with a three-electrode cell configuration. Due to the CNF's graphitic structure and the presence of exterior walls with numerous edges, a high specific surface area and easily accessible electrode/electrolyte interface were obtained, thus yielding good capacitance in the bilayer active materials. The capacitance for PEDOT-PSS coated CNF bilayer electrodes ranged from 80 to 180 F/g and the fabricated materials showed good cycling performance with high stability in aqueous electrolytes. This was probably due to enhanced access to the CNFs, leading to the generation of a double layer and, ultimately, higher values of the capacitance.

Mesoporous Carbon Coated Carbon Nanofibers for Lithium-Air Battery

not Available.

Compact reactor for Fischer–Tropsch synthesis based on hierarchically structured Co catalysts: Towards better stability

A compact reactor for Fischer–Tropsch (F–T) synthesis based on hierarchically structured Co catalysts has been developed. The SiO2 coated carbon nanofiber (CNF)/carbon felt (CF) has several advantages, such as high surface area, low pressure drop, high thermal conductivity and good mass transport properties. CNFs were grown on the microfibers of CF, which greatly increased the surface area of the composite. An in situ sol–gel method has been developed to coat one thin layer of SiO2 to form CNF/CF@SiO2 core shelled tubes. The efficient 3-D thermal conductive network in the composite provided a relatively uniform temperature gradient during the F–T synthesis without adding any diluents. The prepared Co/(CNF/CF@SiO2) catalysts have higher activity and C5+ selectivity. The catalyst stability is also greatly enhanced by manipulating the Co-support interface by means of the coated SiO2 layer on CNFs. Reduction–oxidation (Redox) cycles indicate that the SiO2 layer decreases the oxidation potential of the Co nanoparticles, with enhanced catalytic stability as a result.

In Situ TEM Investigation of Congruent Phase Transition and Structural Evolution of Nanostructured Silicon/Carbon Anode for Lithium Ion Batteries

It is well-known that upon lithiation, both crystalline and amorphous Si transform to an armorphous Li(x)Si phase, which subsequently crystallizes to a (Li, Si) crystalline compound, either Li(15)Si(4) or Li(22)Si(5). Presently, the detailed atomistic mechanism of this phase transformation and the degradation process in nanostructured Si are not fully understood. Here, we report the phase transformation characteristic and microstructural evolution of a specially designed amorphous silicon (a-Si) coated carbon nanofiber (CNF) composite during the charge/discharge process using in situ transmission electron microscopy and density function theory molecular dynamic calculation. We found the crystallization of Li(15)Si(4) from amorphous Li(x)Si is a spontaneous, congruent phase transition process without phase separation or large-scale atomic motion, which is drastically different from what is expected from a classic nucleation and growth process. The a-Si layer is strongly bonded to the CNF and no spallation or cracking is observed during the early stages of cyclic charge/discharge. Reversible volume expansion/contraction upon charge/discharge is fully accommodated along the radial direction. However, with progressive cycling, damage in the form of surface roughness was gradually accumulated on the coating layer, which is believed to be the mechanism for the eventual capacity fade of the composite anode during long-term charge/discharge cycling.

탄소나노섬유/PVDF-HFP 복합재로 코팅된 부직포의 역학적 및 전기적 특성 변화

In this study, the process of preparation nonwoven with coated carbon nano fibers (CNFs) /poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) composite solution is described. The various contents of CNFs/PVDF-HFP composite coated nonwoven were prepared and characterized by morphological, mechanical, and electrical methods. Nonwovens are coated with CNFs/PVDF-HFP composite solution and decreased the pick up ratio with increasing CNFs contents in range from 0% to 16%. In the results of SEM images, it was clear that the CNFs were evenly distributed in coated nonwoven by SEM images, the existence of CNFs in coated nonwoven was confirmed regularly. The mechanical properties of various contents of CNFs/PVDF-HFP coated nonwoven were examined. The tensile linearity and compression linearity increased with increasing CNFs contents. The electrical properties of the CNFs/PVDF-HFP coated nonwoven increased with increasing CNFs contents.

Microwave absorbing hybrid composites containing Ni–Fe coated carbon nanofibers prepared by electroless plating

Microwave absorbing hybrid composites containing metal coated one-dimensional carbon nanomaterials were investigated for wider absorption bandwidth (BW) with thinner thickness. The optimally designed dielectric carbon nanofibers (CNFs)/epoxy composites had 10 dB absorbing BW of 2.8 GHz (8.8–11.6) in the X-band with the content of 3.0 wt.% (2.30 mm thickness). For the improvement of the magnetic characteristics of the fillers, Ni–Fe coated CNFs were prepared by electroless plating. The typical thickness of Ni–Fe deposited layers was about 200–300 nm. Using the prepared hybrid nanofillers, optimally designed Ni–Fe coated CNFs/epoxy composites had 10 dB absorbing BW of 3.7 GHz (8.3–12.0) in the X-band with the content of 40.0 wt.% (2.40 mm thickness). The 10 dB absorbing BW per unit thickness is about 1.54 GHz/mm. The hybrid composites showed about 26% improvement over the dielectric composites.

Hydriding/dehydriding properties of MgH 2/5 wt.% Ni coated CNFs composite

In this paper, we reported that the prepared nickel coated carbon nanofibers (NiCNFs) by electroless plating method exhibited superior catalytic effect on hydrogen absorption/desorption of magnesium (Mg). It is demonstrated that the nanocomposites of MgH 2/5 wt.% NiCNFs prepared by ball milling could absorb hydrogen very fast at low temperatures, e.g. absorb ∼6.0 wt.% hydrogen in 5 min at 473 K and ∼5.0 wt.% hydrogen in 10 min even at a temperature as low as 423 K. More importantly, the desorption of hydrogen was also significantly improved with additives of NiCNFs. Diffraction scanning calorimetry (DSC) measurement indicated that the peak desorption temperature decreased 50 K and the on-set temperature for desorption decreased 123 K. The composites also desorbed hydrogen fast, e.g. desorb 5.5 wt.% hydrogen within 20 min at 573 K. It is suggested that the new phase of Mg 2Ni, and the nano-sized dispersed distribution of Ni and carbon contributed to this significant improvement. Johnson–Mehl–Avrami (JMA) analysis illustrated that hydrogen diffusion is the rate-limiting step for hydrogen absorption/desorption.

Investigation of the electromagnetic interference shielding of titanium carbide coated nanoreinforced liquid crystalline polymer

The development and analysis of electrical and electromagnetic interference shielding effectiveness of titanium carbide (TiC)-coated carbon nanofiber (CNF) reinforced liquid crystalline polymer composites are presented. The studied samples consisted of different weight percentages (5, 10, and 15 wt %) of CNFs distributed and dispersed homogeneously within the polymeric matrix. A titanium carbide layer was deposited using pulsed laser deposition, and was conducted at room temperature, which eliminated possible thermal degradation of the polymer matrix. The effect of the thickness of the TiC layer on the electrical properties of the polymeric composites was analyzed. A synergistic behavior between the TiC coating and the polymer composite was observed for samples containing 10 wt % of NFs (within the percolation range), and the ability of the composite to shield electromagnetic interference was increased by 20–30 db.

Magnetic Properties of Ni‐Co‐B Coated Carbon Nanofibers

Continuous and uniform Ni‐Co‐B coatings were successfully deposited onto carbon nanofibers via electroless plating. SEM images of the prepared Ni‐Co‐B coated carbon nanofibers were presented. The magnetic properties of the coated carbon nanofibers were investigated. The CoSO4/(CoSO4+NiSO4) ratio in the electroless bath has obvious influence on the coercivity and residual magnetic flux density of the Ni‐Co‐B coated carbon nanofibers.