In-Situ Encapsulation of Nickel Particles in Electrospun Carbon Nanofibers and the Resultant Electrochemical Performance

Flexible, superhydrophobic and multifunctional carbon nanofiber hybrid membranes for high performance light driven actuators

Recently, a series of super-hydrophobic materials have been prepared and efforts have been made to further expand their applications, especially in electronics and smart actuators. However, it remains challenging to develop light weight, flexible and super-hydrophobic materials integrating multifunctionalities such as superior photothermal conversion, corrosion resistance, and controllable actuation. Herein, a superhydrophobic and multi-responsive carbon nanofiber (CNF) hybrid membrane with an outstanding photo-thermal effect is fabricated by electrospinning the mixture of polyacrylonitrile and nickel acetylacetonate, followed by two step heat treatment and subsequent fluorination. The superhydrophobic CNF hybrid membrane with outstanding anti-corrosion and self-cleaning performance can float on the water surface spontaneously, thus effectively reducing the motion resistance. The light driven actuation with controllable movement can be achieved by adjusting the laser irradiated location, in which the localized absorption of light is transformed into thermal energy, and hence an imbalanced surface tension is created. The multifunctional hybrid membrane also opens up an arena of applications such as freestanding flexible electronics, drug delivery, and environmental protection.

Chemical and Morphological Transition of Poly(acrylonitrile)/Poly(vinylidene Fluoride) Blend Nanofibers during Oxidative Stabilization and Incipient Carbonization

Thermally stabilized and subsequently carbonized nanofibers are a promising material for many technical applications in fields such as tissue engineering or energy storage. They can be obtained from a variety of different polymer precursors via electrospinning. While some methods have been tested for post-carbonization doping of nanofibers with the desired ingredients, very little is known about carbonization of blend nanofibers from two or more polymeric precursors. In this paper, we report on the preparation, thermal treatment and resulting properties of poly(acrylonitrile) (PAN)/poly(vinylidene fluoride) (PVDF) blend nanofibers produced by wire-based electrospinning of binary polymer solutions. Using a wide variety of spectroscopic, microscopic and thermal characterization methods, the chemical and morphological transition during oxidative stabilization (280 °C) and incipient carbonization (500 °C) was thoroughly investigated. Both PAN and PVDF precursor polymers were detected and analyzed qualitatively and quantitatively during all stages of thermal treatment. Compared to pure PAN nanofibers, the blend nanofibers showed increased fiber diameters, strong reduction of undesired morphological changes during oxidative stabilization and increased conductivity after carbonization.

Electrocatalytic N-Doped Graphitic Nanofiber - Metal/Metal Oxide Nanoparticle Composites

Carbon-based nanocomposites have shown promising results in replacing commercial Pt/C as high-performance, low cost, nonprecious metal-based oxygen reduction reaction (ORR) catalysts. Developing unique nanostructures of active components (e.g., metal oxides) and carbon materials is essential for their application in next generation electrode materials for fuel cells and metal-air batteries. Herein, a general approach for the production of 1D porous nitrogen-doped graphitic carbon fibers embedded with active ORR components, (M/MO_x , i.e., metal or metal oxide nanoparticles) using a facile two-step electrospinning and annealing process is reported. Metal nanoparticles/nanoclusters nucleate within the polymer nanofibers and subsequently catalyze graphitization of the surrounding polymer matrix and following oxidation, create an interconnected graphite-metal oxide framework with large pore channels, considerable active sites, and high specific surface area. The metal/metal oxide@N-doped graphitic carbon fibers, especially Co₃ O₄ , exhibit comparable ORR catalytic activity but superior stability and methanol tolerance versus Pt in alkaline solutions, which can be ascribed to the synergistic chemical coupling effects between Co₃ O₄ and robust 1D porous structures composed of interconnected N-doped graphitic nanocarbon rings. This finding provides a novel insight into the design of functional electrocatalysts using electrospun carbon nanomaterials for their application in energy storage and conversion fields.

Copper Nanoparticle-Incorporated Carbon Fibers as Free-Standing Anodes for Lithium-Ion Batteries

Copper-incorporated carbon fibers (Cu/CF) as free-standing anodes for lithium-ion batteries are prepared by electrospinning technique following with calcination at 600, 700, and 800 °C. The structural properties of materials are characterized by X-ray diffraction (XRD), Raman, thermogravimetry (TGA), scanning electron microscopy (SEM), transmission electron microscope (TEM), and energy dispersive X-ray spectrometry (EDS). It is found that the Cu/CF composites have smooth, regular, and long fibrous morphologies with Cu nanoparticles uniformly dispersed in the carbon fibers. As free-standing anodes, the unique structural Cu/CF composites show stable and high reversible capacities, together with remarkable rate and cycling capabilities in Li-ion batteries. The Cu/CF calcined at 800 °C (Cu/CF-800) has the highest charge/discharge capacities, long-term stable cycling performance, and excellent rate performance; for instance, the Cu/CF-800 anode shows reversible charge/discharge capacities of around 800 mAh g(-1) at a current density of 100 mA g(-1) with stable cycling performance for more than 250 cycles; even when the current density increases to 2 A g(-1), the Cu/CF-800 anode can still deliver a capacity of 300 mAh g(-1). This excellent electrochemical performance is attributed to the special 1D structure of Cu/CF composites, the enhanced electrical conductivity, and more Li(+) active positions by Cu nanoinclusion.

Influence of oxygen on nitrogen-doped carbon nanofiber growth directly on nichrome foil

The synthesis of various nitrogen-doped (N-doped) carbon nanostructures has been significantly explored as an alternative material for energy storage and metal-free catalytic applications. Here, we reveal a direct growth technique of N-doped carbon nanofibers (CNFs) on flexible nichrome (NiCr) foil using melamine as a solid precursor. Highly reactive Cr plays a critical role in the nanofiber growth process on the metal alloy foil in an atmospheric pressure chemical vapor deposition (APCVD) process. Oxidation of Cr occurs in the presence of oxygen impurities, where Ni nanoparticles are formed on the surface and assist the growth of nanofibers. Energy-dispersive x-ray spectroscopy (EDXS) and x-ray photoelectron spectroscopy (XPS) clearly show the transformation process of the NiCr foil surface with annealing in the presence of oxygen impurities. The structural change of NiCr foil assists one-dimensional (1D) CNF growth, rather than the lateral two-dimensional (2D) growth. The incorporation of distinctive graphitic and pyridinic nitrogen in the graphene lattice are observed in the synthesized nanofiber, owing to better nitrogen solubility. Our finding shows an effective approach for the synthesis of highly N-doped carbon nanostructures directly on Cr-based metal alloys for various applications.

Flexible NiO-Graphene-Carbon Fiber Mats Containing Multifunctional Graphene for High Stability and High Specific Capacity Lithium-Ion Storage

An electrode's conductivity, ion diffusion rate, and flexibility are critical factors in determining its performance in a lithium-ion battery. In this study, NiO-carbon fibers were modified with multifunctional graphene sheets, resulting in flexible mats. These mats displayed high conductivities, and the transformation of active NiO to inert Ni(0) was effectively prevented at relatively low annealing temperatures in the presence of graphene. The mats were also highly flexible and contained large gaps for the rapid diffusion of ions, because of the addition of graphene sheets. The flexible NiO-graphene-carbon fiber mats achieved a reversible capacity of 750 mA h/g after 350 cycles at a current density of 500 mA/g as the binder-free anodes of lithium-ion batteries. The mats' rate capacities were also higher than those of either the NiO-carbon fibers or the graphene-carbon fibers. This work should provide a new route toward improving the mechanical properties, conductivities, and stabilities of mats using multifunctional graphene.

Coaxial carbon nanofiber/NiO core–shell nanocables as anodes for lithium ion batteries

The CNF/NiO core–shell nanocables are prepared by electrospinning and electrophoretic deposition. The CNF/NiO nanocables deliver a high reversible capacity of 825 mA h g⁻¹ at 200 mA g⁻¹ after 50 charge–discharge cycles without showing obvious decay.

Chemically anchored NiOx–carbon composite fibers for Li-ion batteries with long cycle-life and enhanced capacity

NiO_x nanoparticles are chemically anchored on carbon fiber networks to obtain binder-free anodes with high properties for Li⁺ storage.

Controlling SEI formation on SnSb-porous carbon nanofibers for improved Na ion storage

Porous carbon nanofiber (CNF)-supported tin-antimony (SnSb) alloys are synthesized and applied as a sodium-ion battery anode. The chemistry and morphology of the solid electrolyte interphase (SEI) film and its correlation with the electrode performance are studied. The addition of fluoroethylene carbonate (FEC) in the electrolyte significantly reduces electrolyte decomposition and creates a very thin and uniform SEI layer on the cycled electrode surface, which an promote the kinetics of Na-ion migration/transportation, leading to excellent electrochemical performance.

Maghemite nanoparticles on electrospun CNFs template as prospective lithium-ion battery anode

In this work, maghemite (γ-Fe2O3) nanoparticles were uniformly coated on carbon nanofibers (CNFs) by a hybrid synthesis procedure combining an electrospinning technique and hydrothermal method. Polyacrylonitrile nanofibers fabricated by the electrospinning technique serve as a robust support for iron oxide precursors during the hydrothermal process and successfully limit the aggregation of nanoparticles at the following carbonization step. The best materials were optimized under a carbonization condition of 600 °C for 12 h. X-ray diffraction and electron microscopy studies confirm the formation of a maghemite structure standing on the surface of CNFs. The average size of γ-Fe2O3 nanoparticles is below 100 nm, whereas CNFs are ∼150 nm in diameter. In comparison with aggregated bare iron oxide nanoparticles, the as-prepared carbon-maghemite nanofibers exhibit a higher surface area and greatly improved electrochemical performance (>830 mAh g(-1) at 50 mA g(-1) for 40 cycles and high rate capacity up to 5 A g(-1) in the voltage range of 0.005-3 V vs Li). The greatly enhanced electrochemical performance is attributed to the unique one-dimensional nanostructure and the limited aggregation of nanoparticles.

CoO-carbon nanofiber networks prepared by electrospinning as binder-free anode materials for lithium-ion batteries with enhanced properties

CoOx-carbon nanofiber networks were prepared from cobalt(ii) acetate and polyacrylonitrile by an electrospinning method followed by thermal treatment. The XPS results demonstrated that the cobalt compound in CoOx-carbon obtained at 650 °C was CoO rather than Co or Co3O4. The CoO nanoparticles with diameters of about 8 nm were homogeneously distributed in the matrix of the nanofibers with diameters of 200 nm. As binder-free anodes for lithium-ion batteries, the discharge capacities of such CoO-carbon (CoO-C) composite nanofiber networks increased with the pyrolysis and annealing temperature, and the highest value was 633 mA h g(-1) after 52 cycles at a current density of 0.1 A g(-1) when the CoO-C was obtained at 650 °C. In addition, the rate capacities of the CoO-C obtained at 650 °C were found to be higher than that of the sample annealed at a lower temperature and pure carbon nanofiber networks annealed at 650 °C. The improved properties of CoO-C nanofiber networks were ascribed to nanofibers as the framework to keep the structural stability, and favorable mass and charge transport. The present study may provide a new strategy for the synthesis of binder-free anodes for lithium-ion batteries with excellent properties.

Fabrication of Electrospun Si/Carbon Composite Nanofibers as Anodes Materials for Lithium-Ion Batteries

Si/carbon nanofibers (Si/CNFs) composite used as the anode materials of lithium-ion battery have been prepared via electrospinning and calcinations treatment. Hydrofluoric acid is used to remove surface oxides of Si particles. SEM observation indicates that silicon particles are uniformly embedded in the carbon nanofibers. X-ray diffraction (XRD), energy dispersive x-ray spectroscopy (EDX) and Raman scattering have been used to analysis the composition and phase of the composite materials. The first reversible capacity of the Si/CNFs composite is 1004 mAh/g, and 390 mAh/g has been remained after 100 cycles. Such Si/CNFs composite could be a promising anode material in lithium ion batteries.

Carbon nanofibers prepared via electrospinning

Carbon nanofibers prepared via electrospinning and following carbonization are summarized by focusing on the structure and properties in relation to their applications, after a brief review of electrospinning of some polymers. Carbon precursors, pore structure control, improvement in electrical conductivity,and metal loading into carbon nanofibers via electrospinning are discussed from the viewpoint of structure and texture control of carbon.