Carbon Nanofiber Mats Research Articles

Efficient polysulfide trapping enabled by a polymer adsorbent in lithium-sulfur batteries

Lithium-sulfur (Li-S) batteries have been viewed as promising candidates for next-generation high-energy rechargeable batteries due to their high theoretical energy density. However, their practical application is severely impeded by the notorious shuttle effect of soluble polysulfides. Herein, a nature polymer of konjac glucomannan (KGM) was adopted as polysulfide-adsorbing agent by coating on carbon nanofiber (CNF) mats for polysulfide-trapping interlayers in Li-S batteries. A uniform coating method was developed by improving the wettability of CNFs to aqueous solutions using ethanol as a co-solvent of water. It is revealed that not only the KGM polymer itself but also the coating quality is critical to prevent polysulfide diffusion. With the improved coating quality and the strong chemisorption of KGM, the shuttle effect was effectively suppressed and excellent electrochemical performance was demonstrated with a high reversible capacity of 1286 mAh g−1 at 0.2C, good cycling stability with a capacity retention of 84% after 400 cycles at 1C and high rate capability. Our findings provide a facile way to address the shuttle behavior of Li-S batteries using low-cost and environmental friendly materials, which are very promising for large-scale energy storage applications.

A Feasible Way to Produce Carbon Nanofiber by Electrospinning from Sugarcane Bagasse.

Recently, the nanofiber materials derived from natural polymers instead of petroleum-based polymers by electrospinning have aroused a great deal of interests. The lignocellulosic biomass could not be electrospun into nanofiber directly due to its poor solubility. Here, sugarcane bagasse (SCB) was subjected to the homogeneous esterification with different anhydrides, and the corresponding esterified products (SCB-A) were obtained. It was found that the bead-free and uniform nanofibers were obtained via electrospinning even when the mass fraction of acetylated SCB was 70%. According to the thermogravimetric analyses, the addition of SCB-A could improve the thermal stability of the electrospun composite nanofibers. More importantly, in contrast to the pure polyacrylonitrile (PAN) based carbon nanofiber, the SCB-A based carbon nanofibers had higher electrical conductivity and the surface N element content. In addition, the superfine carbon nanofiber mats with minimum average diameter of 117.0 ± 13.7 nm derived from SCB-A were obtained, which results in a larger Brunauer–Emmett–Teller (BET) surface area than pure PAN based carbon nanofiber. These results demonstrated that the combination of the homogeneous esterification and electrospinning could be a feasible and potential way to produce the bio-based carbon nanofibers directly from lignocellulosic without component separation.

Increased Mechanical Properties of Carbon Nanofiber Mats for Possible Medical Applications

Carbon fibers belong to the materials of high interest in medical application due to their good mechanical properties and because they are chemically inert at room temperature. Carbon nanofiber mats, which can be produced by electrospinning diverse precursor polymers, followed by thermal stabilization and carbonization, are under investigation as possible substrates for cell growth, especially for possible 3D cell growth applications in tissue engineering. However, such carbon nanofiber mats may be too brittle to serve as a reliable substrate. Here we report on a simple method of creating highly robust carbon nanofiber mats by using electrospun polyacrylonitrile/ZnO nanofiber mats as substrates. We show that the ZnO-blended polyacrylonitrile (PAN) nanofiber mats have significantly increased fiber diameters, resulting in enhanced mechanical properties and thus supporting tissue engineering applications.

Electrodeposition of nickel on electrospun carbon nanofiber mat electrode for electrochemical sensing of glucose

In this study, a novel non-enzymatic glucose sensor was successfully produced using nickel electrodeposition on an oil free carbon nanofiber (CNF) mat prepared by electrospinning method. The as-prepared Ni/CNF mat electrode was studied by means of scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD). The characterization results showed that not only was nickel coating electrodeposited on the CNF mat but also the nickel coating was uniformly deposited on the CNF mat electrode. The electrochemical properties of Ni/CNF mat were evaluated using cyclic voltammetry (CV) and amperometry measurements. It was found that the Ni/CNF mat electrode had good electrocatalytic activity toward the oxidation of glucose and demonstrated a wide linear range of 0.002–5 mM, a low detection limit of 0.57 µM, a rapid response time (2 s), a high selectivity with no interference from other oxidable species, good reproducibility and long-term stability. Moreover, the prepared sensor was used to identify glucose in real sample species. Therefore, Ni/CNF mat electrode due to good analytical performance, cost effective and simple preparation method can be proposed as a promising sensor for non-enzymatic glucose detection.

Carbon nanofibers as thick electrodes for aqueous supercapacitors

Abstract Flexible and thick carbon nanofiber (CNF) electrodes are developed for symmetric supercapacitor application. Free-standing CNF mats with diameter of 335 ± 60 nm are produced via solution blowing technique and the microstructure and porosity are analyzed. The electrochemical performances of CNF are firstly investigated by determining the maximum operating voltage window in aqueous electrolytes with various pH. Then, CNF electrodes with high mass loading and thicknesses up to 1.2 mm are used for symmetric supercapacitor cells with 6 M KOH solution as an electrolyte. It is found that electrodes with mass loading of 25 mg/cm2 can be cycled up to 10,000 cycles without capacity loss, at current of 2 A/g and 1.4 V cut-off voltage. While electrodes with higher mass loading retain 85% of their capacity. Post-mortem analysis shows that the capacity loss of the thicker electrodes is a result of decreased ion diffusion during cycling. The lower ion diffusion appears due to crystal-like products formed as a result of side reactions with the electrolyte.

Ultrafine Titanium Nitride Sheath Decorated Carbon Nanofiber Network Enabling Stable Lithium Metal Anodes

AbstractNonuniform local electric field and few nucleation sites on the reactive interface tend to cause detrimental lithium (Li) dendrites, which incur severe safety hazards and hamper the practical application of Li metal anodes in batteries. Herein, a carbon nanofiber (CNF) mat decorated with ultrafine titanium nitride (TiN) nanoparticles (CNF‐TiN) as both current collector and host material is reported for Li metal anodes. Uniform Li deposition is achieved by a synergetic effect of lithiophilic TiN and 3D CNF configuration with a highly conductive network. Theoretical calculations reveal that Li prefers to be adsorbed onto the TiN sheath with a low diffusion energy barrier, leading to controllable nucleation sites and dendrite‐free Li deposits. Moreover, the pseudocapacitive behavior of TiN identified through kinetics analysis is favorable for ultrafast Li+ storage and the charge transfer process, especially under a high plating/stripping rate. The CNF‐TiN‐modified Li anodes deliver lower nucleation overpotential for Li plating and superior electrochemical performance under a large current density (200 cycles at 3 mA cm−2) and high capacity (100 cycles with 6 mAh cm−2), as well as a long‐running lifespan (>600 h). The CNF‐TiN‐based full cells using lithium iron phosphate and sulfur cathodes exhibit excellent cycling stability.

Investigation on the Performance Improvement of Polyacrylonitrile-Derived Flexible Electrospun Carbon Nanofiber Mats

Polyacrylonitrile (PAN)-derived carbon nanofiber mats were fabricated using electrospinning and further carbonization. Scanning electron microscopy (SEM), X-ray diffraction (XRD) and electrochemical characterization were used to investigate the effects of precursor concentration, thermal stabilization and carbonization temperature, addition of multi-walled carbon nanotubes (MWCNTs), activation of nitric acid and sulfuric acid on the morphologies, conductivity, flexibility and electrochemical properties of the fabricated carbon nanofiber mats. The results reveal that the carbon nanofiber mats with uniform fiber diameter of 200 nm and sheet resistance of 154 Ω/sq could be achieved with a PAN mass fraction of 12 wt% and a thermal stabilization and carbonization temperature of 270 °C and 900 °C, respectively. Due to the good conductivity and high strength of the MWCNTs, the sheet resistance of the carbon nanofiber mats decreases to around 60 Ω/sq by adding MWCNTs to precursor, and the mats exhibit excellent bend and fold flexibility. The electrochemical performance of the co-spun carbon nanofiber mats could be further improved by the activation treatment of acids, and the maximum specific capacitance of the carbon mat reaches 113.5 F/g at a current density of 0.1 mA/cm2 in the case of 1:3 HNO3:H2SO4. The investigation provides a reference for improving the performance of spun carbon nanofiber mats, which can be used as the electrodes or current collectors to further load other active materials in the applications of energy storage devices.

Controlling the Three-Phase Boundary in Na-Oxygen Batteries: The Synergy of Carbon Nanofibers and Ionic Liquid.

A series of electrospun binder-free carbon nanofiber (CNF) mats have been studied as air cathodes for Na-oxygen batteries using a pyrrolidinium-based electrolyte and compared with the commercial air cathode Toray 090. A tenfold increase in the discharge capacity is attained when using CNFs in comparison with Toray 090, affording a discharge capacity of 1.53 mAh cm-2 at a high discharge rate of 0.63 mA cm-2 . The good specific discharge and charge capacities of these CNFs are determined by the void space and the highly accessible surface of the carbon fiber. Furthermore, a threefold increase has been attained in terms of specific capacity by controlling the flooding of the air cathode and hence the location of the three-phase boundary within the CNF mat. The enhancement in performance has been correlated to the morphology, composition, distribution, and location of the discharge products. Sodium superoxide and peroxide were identified as the discharge products and, more importantly, the common side reaction discharge products, which are known to be detrimental to battery performance (including sodium fluoride, sodium hydroxide, and formate), were not observed, exemplifying the stability of the pyrrolidinium-based electrolyte and these binder-free CNF air cathodes.

Pt Nanorods-Decorated Macroporous Carbon Nanofiber Free-Standing Cathodes for High-Performance Li-O2 Battery

Controlling the pore structure of cathodes has a strong influence on the performance of Li-O2 battery. In the present study, macroporous carbon nanofiber (MCNF) mats are successfully fabricated through an electrospinning and templating methods using cross-linked polystyrene particles. Additionally, Pt nanorods are grown on the surface of the MCNF (PtNR-MCNF) as catalysts for Li/O2 reactions. As-prepared PtNR-MCNF has interconnected macropores along the MCNF interior and abundant surface openings. Those macropores are also connected to larger pores between individual MCNF through the orifices on the MCNF surface, rendering a hierarchical porous structure. Owing to the highly porous structure, Li-O2 cells using the PtNR-MCNF cathodes achieved a specific capacity of approximately 7,000 mAh/gc and even more at a current density of 200 mA/gc. In particular, the Li-O2 cell using the PtNR-MCNF cathode exhibited higher electrochemical performance in terms of rate capability, energy efficiency, and cycle stability. This study demonstrates that the growth of PtNRs resulted in the formation of poorly crystalized Li2O2, which significantly reduced the overpotentials, both during the discharge and the charge. Additionally, it contributed to the considerably prolonged cycle life of the Li-O2 cell using the PtNR-MCNF (468 cycles) compared to the cell using the MCNF cathode (272 cycles) with a limiting capacity of 1,000 mAh/gc at a current density of 500 mA/gc.

Binder free carbon nanofiber electrodes derived from polyacrylonitrile-lignin blends for high performance supercapacitors

Lignin was blended with polyacrylonitrile (PAN) in different ratios and fabricated into carbon nanofiber electrodes by electrospinning followed by thermal stabilization, carbonization and subsequent activation by CO2 of the carbonized mats. These carbon fiber electrodes exhibit high surface area, high mesoporosity, high graphitic content and high electrical conductivity. Activated carbon nanofiber mats derived from PAN:Lignin 70:30 blends display a surface area of 2370 m2 g−1 with 0.635 cm3 g−1 mesopore volume. These results are due to the selective partial removal of carbonized lignin during the activation step. Coin cell supercapacitors employing these electrodes exhibit 128 Fg−1 specific capacitance, 59 Wh kg−1 energy density and a 15 kW kg−1 power density when operated at 3.5 V using an ionic liquid electrolyte. Since lignin is an inexpensive, abundant, and green polymer, incorporating it into carbon blends enhances the scalability of such materials in energy storage applications.

Impact of Thermal Oxidative Stabilization on the Performance of Lignin-Based Carbon Nanofiber Mats.

Lignin is a renewable biopolymer considered as a potential precursor for low-cost carbon materials. Thermal oxidative stabilization (TOS) is an important processing step to maintain fiber geometry during carbonization, yet the impact of TOS on the properties of lignin-based carbon materials has not been clearly identified in the literature. Yield, change in fiber diameter/distribution, elemental composition, and mechanical properties were explored for both stabilized and carbonized lignin fibers. Vibrational spectroscopy and solid-state 13C nuclear magnetic resonance spectroscopy were used to analyze the changes in lignin molecular structure after exposure to various heating conditions during the TOS steps. Further, studies were focused on the effects of TOS conditions on the resulting carbon structure of fiber mats through Raman spectroscopy measurements and electrical conductivity analysis. Although TOS conditions influenced the properties of the oxidized lignin fiber mats, properties of the carbonized samples were invariant to the TOS procedures used in this study over most of the conditions. As a result, there was flexibility for the parameters (time and temperature) in the TOS process when conditioning softwood lignin materials for carbon fibers.

Electrical Properties and Electromagnetic Interference Shielding Effectiveness of Interlayered Systems Composed by Carbon Nanotube Filled Carbon Nanofiber Mats and Polymer Composites.

The demand for multifunctional requirements in aerospace, military, automobile, sports, and energy applications has encouraged the investigation of new composite materials. This study focuses on the development of multiwall carbon nanotube (MWCNT) filled polypropylene composites and carbon nanofiber composite mats. The developed systems were then used to prepare interlayered composites that exhibited improved electrical conductivity and electromagnetic interference (EMI) shielding efficiency. MWCNT-carbon nanofiber composite mats were developed by centrifugally spinning mixtures of MWCNT suspended in aqueous poly(vinyl alcohol) solutions. The developed nanofibers were then dehydrated under sulfuric acid vapors and then heat treated. Interlayered samples were fabricated using a nanoreinforced polypropylene composite as a matrix and then filled with carbon fiber composite mats. The in-plane and through-plane electrical conductivity of an eight-layered flexible carbon composite (0.65 mm thick) were shown to be 6.1 and 3.0 × 10−2 S·cm−1, respectively. The EMI shielding effectiveness at 900 MHz increased from 17 dB for the one-layered composite to 52 dB for the eight-layered composite. It was found that the reflection of the electromagnetic waves was the dominating mechanism for EMI shielding in the developed materials. This study opens up new opportunities for the fabrication of novel lightweight materials that are to be used in communication systems.

Hybrid multi-scale thermoplastic composites reinforced with interleaved nanofiber mats using in-situ polymerization of cyclic butylene terephthalate

Abstract Mechanically flexible electrospun carbon and glass nanofiber mats (i.e., ECNF-mats and EGNF-mats) were prepared by electrospinning followed by thermal treatments; subsequently, a technique was applied to fabricate two types of multi-scale thermoplastic composites, involving infiltration of molten cyclic butylene terephthalate (CBT) followed by in-situ polymerization under compression. For the first composite type, eight conventional carbon fabrics were interleaved with seven ECNF-mats. For the second composite type, eight conventional glass fabrics were interleaved with seven EGNF-mats. Compared to the values acquired from the corresponding control samples without nanofiber mats, the interlaminar shear strength, flexural strength, flexural modulus, and work of fracture acquired from the hybrid multi-scale composite containing ECNF-mats were increased by 32%, 25%, 19%, and 33%, respectively; while the values acquired from the hybrid multi-scale composite containing EGNF-mats were increased by 66%, 43%, 17%, and 64%, respectively. Furthermore, the enhancements of out-of-plane properties were not at the expense of in-plane tensile strength or modulus. The study indicated that the employed fabrication technique could be adopted as an efficient approach to produce polybutylene terephthalate (PBT) thermoplastic composites through in-situ polymerization of CBT oligomer; and the ECNF-mats and EGNF-mats could be utilized as innovative reinforcement fillers for enhancing the performance of structural thermoplastic composites.

The Construction of Fe-Compounds Doped Porous Carbon Nanofiber and Carbon Nanotube Composite Material by One-Step Carbonization and CVD for Li-Ion Capacitor

In this paper, the Fe-Compounds (FeF2 and Fe2O3) doping porous carbon nanofiber & carbon nanotube (FeCD-PCNF&CNT) composite material is firstly prepared by electro-blown spinning followed by pretreatment and one-step carbonization & chemical vapor deposition (CVD) processes. The CNTs are uniformly growing on the PCNF skeleton which deeply increased specific surface area (from 334.066 to 743.402 m2 g−1) and enhanced electrical conductivity (from 42.22 to 149.48 S cm−1) comparing to those of PCNF, and large number of hierarchical-pores are existed. In addition, the Fe-Compounds are uniformly distributed on the PCNF skeleton which provided numerous active sites. The obtained FeCD-PCNF&CNT as an anode material for Li-ion capacitors exhibited high energy density and power density (76.1 Wh kg−1 at 0.075 kW kg−1, 15.4 Wh kg−1 at 7.5 kW kg−1), which had broad application prospect in the energy storage field. Moreover, the composite materials with special structure and excellent properties may realize the other applications in the fields of adsorption, water treatment, etc., and the prepared method has a great industrialization potentiality.

Catalyst-free large-scale synthesis of composite SiC@SiO2/carbon nanofiber mats by blow-spinning

A robust photocatalytic composite SiC/SiO2 nanofiber/carbon nanofiber mat is prepared via blow-spinning followed by calcination in absence of metal catalysts.

Morphological study of stabilization and carbonization of polyacrylonitrile/TiO2 nanofiber mats

Polyacrylonitrile belongs to the most often used precursors for carbon fibers. Using electrospinning, polyacrylonitrile nanofiber mats can be prepared and afterwards stabilized and carbonized to prepare carbon nanofiber mats which, by adding other materials, will be useful for several applications. One of these materials is TiO2, which has photocatalytic properties and can thus be used as a photocatalyst for photodegradation of dyes. Here, we report on a detailed study of electrospinning, stabilization, and carbonization of electrospun polyacrylonitrile/TiO2 mats with varying TiO2 content. Depending on the amount of TiO2 in the nanofibers, the fiber morphology changes strongly, indicating an upper limit for the preparation of carbon/TiO2 nanofibers with smooth surface, but offering an even increased inner surface of the rougher carbon/TiO2 nanofibers with increased TiO2 content due to better maintenance of the fibrous structure during stabilization.

Aerosolization and characterization of carbon nanotube and nanofiber materials: Relationship between aerosol properties and bulk density

Potential inhalation of fibrous carbon nanomaterials depends on the manufacturing/handling process and their tendency for air dispersion. Because of the large variety of carbon nanotube and nanofiber (CNT and CNF) products, with varying physical and chemical properties, characterization of these materials and their associated exposure risks is challenging. In this study, we aerosolized different types of CNT and CNF materials using an acoustic generator (AG) and characterized their aerodynamic and physical properties. The generation characteristics of the AG for the different CNT and CNF materials were investigated by measuring aerosol number concentrations and its decay properties with time. Airborne particle properties such as mobility and aerodynamic diameters were measured using mobility and aerodynamic particle sizers. The bulk and effective densities of the powder and aerosol were obtained by measuring the mass and volume of the bulk material and aerosol particles, where effective density was calculated by a tandem mobility-mass technique. The relationship between the aerosol properties (i.e., particle size, concentration, and dustiness) and bulk density of the material was also investigated to understand the potential for dispersion in air. The results showed that the aerosol concentration decay for each nanomaterial has a unique time constant, and that the rate of decay is positively correlated with the bulk density of the powder: the lower the bulk density, the slower the concentration decay. The aerodynamic diameter increased with increasing bulk density, while the mobility diameter showed the opposite trend. In general, bulk density is smaller than the particle effective density, and the effective density tends to approach the bulk density as particle size increases. Also, the bulk density of the fibrous nanomaterials tested in this study showed a reasonable correlation with dustiness data obtained from both our measurements and the literature, which was relatively weak for non-fibrous powders. This study indicates that more loosely agglomerated CNT powders, with lower bulk densities, would be more readily dispersed, and the dispersed particles remain airborne for longer periods. Depending on particle size, such materials can pose higher exposure risks due to their ease of dispersion and longer residence times.

Flexible and binder-free electrospun Co3O4 nanoparticles/carbon composite nanofiber mats as negative electrodes for sodium-ion batteries

Transition metal oxides applied as anode material for sodium-ion batteries have been widely investigated due to their high specific capacity, especially for Co3O4-related nanomaterials. However, its intrinsic low electronic conductivity and the aggregation phenomenon of commercial Co3O4 nanoparticles result in a low initially coulombic efficiency and the fading of cycle performance. In this paper, commercial Co3O4 nanoparticles/carbon composite nanofiber mats were synthesized by sol–gel electrospinning. When directly applied, such flexible negative electrodes as sodium-ion batteries, revealed high specific capacity and excellent rate performance simultaneously, which are not only attributed to the high electronic conductivity of carbon nanofiber mats that could enhance the ionic and electronic transport property, but also attributed to its three-dimensional fibrous network that could prevent the aggregation of commercial Co3O4 nanoparticles. Such a flexible, binder-free and high electronic conductivity negative electrode enables promising applications for large-scale energy storage and conversion.

Fixing PAN Nanofiber Mats during Stabilization for Carbonization and Creating Novel Metal/Carbon Composites.

Polyacrylonitrile (PAN) is one of the materials most often used for carbonization. PAN nanofiber mats, created by electrospinning, are an especially interesting source to gain carbon nanofibers. A well-known problem in this process is fixing the PAN nanofiber mats during the stabilization process which is necessary to avoid contraction of the fibers, correlated with an undesired increase in the diameter and undesired bending. Fixing this issue typically results in breaks in the nanofiber mats if the tension is too high, or it is not strong enough to keep the fibers as straight as in the original state. This article suggests a novel method to overcome this problem by electrospinning on an aluminum substrate on which the nanofiber mat adheres rigidly, stabilizing the composite and carbonizing afterwards either with or without the aluminum substrate to gain either a pure carbon nanofiber mat or a metal/carbon composite.

Preparation, characterization and performance of an electrospun carbon nanofiber mat applied in hexavalent chromium removal from aqueous solution.

Hexavalent chromium, Cr(VI), a highly toxic oxyanion known as a carcinogen and mutagen, is an issue of concern due to its adverse impact on human health. Therefore, development of effective technologies and/or materials for Cr(VI) removal from water has been of great interest for researchers. In this study, an electrospun carbon nanofiber (CNF) mat was prepared via electrospinning polyacrylonitrile (PAN), followed by thermal pre-oxidation and carbonization. Scanning electron microscopy (SEM) observation showed that the fiber diameter of the CNF with carbonization temperature of 950°C (CNF950) was about 266 nm. Potentiometric titration analysis demonstrated that the point of zero charge pH (pHpzc) of CNF950 was around 7.93. CNF950 demonstrated high adsorption capacity and fast adsorption kinetics for Cr(VI) at pH < 3. Langmuir isotherm calculations showed that the maximum adsorption capacity of Cr(VI) on CNF950 was 118.8 mg/g at pH 2. The adsorption isotherm of Cr(VI) on CNF950 was well described by the Redlich-Peterson model, revealing that Cr(VI) adsorption was the result of a combination of monolayer and multilayer adsorption, depending on the initial Cr(VI) concentration. Solution pH greatly affected Cr(VI) adsorption onto CNF950 due to the electrostatic interaction, and the adsorption capacity was relatively high when pH was below 3. X-ray photoelectron spectroscopy (XPS) analysis revealed that the removal of Cr(VI) might be the result of a combination of redox reaction and electrostatic adsorption. The adsorption-saturated CNF950 could be regenerated by NaOH solution. This study extends the potential applicability of electrospun CNF mats for Cr(VI)-contaminated water purification.