Electrospun Carbon Nanofiber Mats Research Articles

Controlled Alignment of Carbon Black Nanoparticles in Electrospun Carbon Nanofibers for Flexible Films.

Carbon nanofiber (CNF) films or mats have great conductivity and thermal stability and are widely used in different technological processes. Among all the fabrication methods, electrospinning is a simple yet effective technique for preparing CNF mats, but the electrospun CNF mats are often brittle. Here, we report a feasible protocol by which to control the alignment of carbon black nanoparticles (CB NPs) within CNF to enhance the flexibility. The CB NPs (~45 nm) are treated with non-ionic surfactant Triton-X 100 (TX) prior to being blended with a solution containing poly(vinyl butyral) and polyacrylonitrile, followed by electrospinning and then carbonization. The optimized CB-TX@CNF mat has a boosted elongation from 2.25% of pure CNF to 2.49%. On the contrary, the untreated CB loaded in CNF displayed a lower elongation of 1.85% because of the aggregated CB spots created weak joints. The controlled and uniform dispersion of CB NPs helped to scatter the applied bending force in the softness test. This feasible protocol paves the way for using these facile surface-treated CB NPs as a commercial reinforcement for producing flexible CNF films.

Conformal CVD of WO3−x on electrospun carbon nanofiber mats assisted by Joule heating

This article presents a novel technique for building carbon nanofiber composites using chemical vapor deposition (CVD) assisted by Joule heating. The heating of electrospun carbon nanofibers mats, induced by the passing of an electric current through the resistive mat and the associated Joule heating, is studied using infrared thermography. The standard deviation of the resulting temperature field is smaller than 5% of its average value, a result explained by the homogeneous and two-dimensional nature of the mat, as well as by the dominance of radiative heat transport over thermal conduction. A thermal model is developed to correlate the imposed electrical dissipation and the temperature of the mat, a key variable in CVD. Joule heating is used to decompose W(CO)6 and deposit a coating of WO3−x on all carbon nanofibers without the need of annealing. The coating is conformal, uniform along the nanofiber and across the mat, and its thickness is controlled with the voltage difference applied across the mat. Because of the wide range of temperatures that can be imposed and the variety of precursors that can be employed, CVD assisted by Joule heating is a promising method for developing new carbon composites.

High‐Performance All‐Solid‐State Supercapacitor Electrode Materials Using Freestanding Electrospun Carbon Nanofiber Mats of Polyacrylonitrile and Novolac Blends

AbstractHerein, this paper reports a facile method to prepare electrospun carbon nanofiber mats (ECNFMs) with high specific surface area and interconnected structure using polyacrylonitrile (PAN) as a precursor and novolac resin (NOC) as a polymer sacrificial pore‐making agent. Without additional treatment, the prepared ECNFMs have a highly porous structure because NOC decomposes in a wider temperature range than most polymer activators. The NOC content in the PAN nanofibers shows important effects on porosity. The BET specific surface area of ECNFMs reaches a maximum of 1468 m2 g−1 when the precursor nanofibers contained 30 wt% NOC (ECNFM‐3) after carbonization at 1000 °C. The supercapacitor device from ECNFM‐3 electrode and all‐solid‐state electrolyte shows excellent cycling durability and high specific capacitance: ≈99.72% capacitance retention after 10 000 charge/discharge cycles and ≈320 mF cm−2 at 0.25 mA cm−2. Furthermore, it shows a large energy density of ≈11.1 Wh cm−2 under the power density of 500 mW m−2. Activation of carbon nanofibers simply by the addition of NOC into precursor nanofibers can offer a handy way to prepare ECNFMs for high‐performance all‐solid‐state supercapacitors and other potential applications.

Flexible Cross-Linked Electrospun Carbon Nanofiber Mats Derived from Pitch as Dual-Functional Materials for Supercapacitors

Freestanding and binder-free electrospun carbon nanofiber mats with a cross-linked structure (CLCF) were fabricated by using pitch as the precursor. The cross-linked structure can be tuned easily b...

Deposition Behavior of Polyaniline on Carbon Nanofibers by Oxidative Chemical Vapor Deposition.

Oxidative chemical vapor deposition (oCVD) offers unique advantages as a liquid-free processing technique in synthesizing and integrating conducting polymers, including polyaniline (PANI), by enabling conformal coatings onto nanostructured substrates, like carbon nanofibers. With relatively thick nanofiber mats, the challenge is to ensure uniform coating thickness through the porous substrates. Here, the substrate temperature during oCVD is found to be a primary factor influencing PANI coating uniformity. Coating uniformity is enhanced by operating at a higher substrate temperature, where monomer adsorption is believed to be limiting relative to intrinsic reaction kinetics. Also, a higher substrate temperature leads to significantly less PANI oligomers and more PANI in the emeraldine oxidation state. A systematic study of oCVD kinetics with substrate temperature shows a reaction-limited regime at lower substrate temperatures with an activation energy of 12.0 kJ/mol, which is believed to be controlled by the self-catalyzed PANI polymerization reaction that transitions at higher substrate temperatures above 90 °C to an adsorption-limited regime as indicated by a negative activation energy of -18.8 kJ/mol. Overall, by operating within an adsorption-limited oCVD regime, more uniform oCVD PANI coatings on electrospun carbon nanofiber mats have been achieved.

High performance electrospun carbon nanofiber mats derived from flax lignin

Flax (Linum usitatissimum) is an abundant source of natural fiber that is industrially cultivated globally for the production of linen as well as for linseed oil. Flax shives isolated from these operations represent a significant source of underutilized biomass. This study reports a novel method to delignify flax shives, describes the characteristics of the isolated flax lignin, and the properties of carbonized fiber derived from the lignin. Knife-milled flax straw was pretreated using a glycerol thermal process that permitted the fractionation of lignin via solvent extraction. The resulting lignin was characterized for its thermal properties, chemical structure, and molecular weight using differential scanning calorimetry, 31P nuclear magnetic resonance (NMR) spectroscopy, Fourier transform infrared (FTIR) spectroscopy, and gel permeation chromatography. Additionally, the isolated lignin was transformed into continuous nanofiber mats by electrospinning, using blends of lignin and differing concentrations of polyethylene oxide (PEO). The addition of PEO as a co-processing polymer facilitated the production of uniform nanofibers without defects, such as beading. As-spun nanofiber mats were thermally stabilized in an oxygen environment and subsequently carbonized at 1000 °C. The ensuing nanofiber mats had similar mechanical properties to carbon nanofiber mats spun from softwood kraft lignin, and outperformed those derived from organosolv processed hardwoods.

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.

Surface-Limited Platinum Electrodeposition on Highly Ordered Pyrolytic Graphite

Recently we reported an overpotential electrodeposition method to deposit contiguous Pt nanoplatelets/thin films directly onto the surface of self-standing electrospun carbon nanofiber mats, leading to Carbon Nanofibrous Electrodes (NFEs) [1]. We demonstrated the high electrocatalytic activity and improved stability over high-potential prolonged cycling compared to conventional Pt nanoparticles on carbon. In order to study more in detail the Pt growth and the morphology of the obtained Pt surfaces as a function of the experimental parameters, we investigated such surface-limited electrodeposition employing Highly Ordered Pyrolytic Graphite (HOPG) as a model surface.We studied Pt deposition on HOPG by contact-mode AFM imaging. Pt interconnected particles and Pt networks can be grown directly onto the substrate at high overpotential as a function of the deposition time, with no significant variation in thickness and size of the connected particles. A progressive coverage of the substrate surface is clearly present, eventually leading to the formation of Pt thin islands below 2 nm in thickness. We also show by TEM analysis that Pt(111) facets are preferentially deposited and grown on the substrate.We studied the deposition mechanism at high overpotential. We will show that the Pt deposition is not diffusion-limited and that it overlaps with other processes. We will discuss the effects of these other processes (H2 evolution on Pt and HOPG) on the Pt deposition. Additional indications can be derived from computer simulations (e.g. DigiElch®) that approximate the experimental conditions. The rate constants used for the simulations were obtained experimentally and their variation with HOPG surface preparation will also be presented.In this work we will present our advances towards understanding the nature of this surface-limited electrodeposition. The morphological and structural characterization of these Pt features on HOPG will be presented and discussed, along with some early insights on their growth mechanism.[1] G. Ercolano, F. Farina, S. Cavaliere, D.J. Jones, J. Rozière, J. Mater. Chem. A 5 (2017) 3974-3980.

Mechanically flexible electrospun carbon nanofiber mats derived from biochar and polyacrylonitrile

Mechanically flexible electrospun carbon nanofiber (ECNF) mats were prepared by electrospinning mixtures containing hydrothermal liquefaction (HTL) derived biochar and polyacrylonitrile (PAN) into precursor nanofiber mats followed by stabilization in air and then carbonization in argon. The resulting ECNF mats well retained the overall morphological structures of their precursors (i.e., biochar/PAN composite nanofiber mats), and the carbon nanofibers showed the enlarged specific surface area upon the increase of biochar loading amount in precursor nanofibers. The ECNFs (4/10), which were derived from composite nanofibers with the biochar/PAN weight ratio being 4/10, had the fiber diameters of ∼350nm and the BET specific surface area of 30.12m2·g−1; and these ECNF mats exhibited the highest gravimetric capacitance of 37.60F·g−1 at the current density of 500mA·g−1. Hence, the prepared ECNF mats could potentially be utilized for energy related (e.g., supercapacitor) applications.

Electrospun lignin-derived carbon nanofiber mats surface-decorated with MnO2 nanowhiskers as binder-free supercapacitor electrodes with high performance

Abstract The aim of this study is to explore innovative materials for the development of next-generation supercapacitor electrodes. The hypothesis is that, upon the surface-decoration with appropriate amount of MnO 2 nanowhiskers, freestanding and highly graphitic electrospun carbon nanofiber (ECNF) mats (with fiber diameters of ∼200 nm and BET specific surface areas of ∼583 m 2 g −1 ) derived from a natural product of lignin would be binder-free supercapacitor electrodes with high performance. To test the hypothesis, the ECNF mats have been prepared first; thereafter, the acquired ECNF mats have been surface-decorated with varied amounts of MnO 2 nanowhiskers to prepare three types of ECNF/MnO 2 mats. The morphological and structural properties of ECNF and ECNF/MnO 2 mats are characterized by SEM, TEM and XRD, the weight percentages of MnO 2 nanowhiskers in three ECNF/MnO 2 mats are determined by thermal gravimetric analysis; while the electrochemical performance of each mat/electrode is evaluated by cyclic voltammetry, galvanostatic charge/discharge method, and electrochemical impedance spectroscopy. This study reveals that, all of the three ECNF/MnO 2 mats/electrodes have significantly enhanced electrochemical performances compared to the ECNF mat/electrode; while the ECNF/MnO 2 (1:1) mat/electrode exhibits the highest gravimetric capacitance of 83.3 F g −1 , energy density of 84.3 W h kg −1 , and power density of 5.72 kW kg −1 .

WSe2 and W(SexS1−x)2 nanoflakes grown on carbon nanofibers for the electrocatalytic hydrogen evolution reaction

Triangular W(SexS1−x)2 nanoflakes uniformly dispersed on the surface of electrospun carbon nanofiber mats were synthesized. The hybrid catalyst mats were directly used as hydrogen evolution cathodes and exhibit excellent HER performances.

Lignin-derived electrospun carbon nanofiber mats with supercritically deposited Ag nanoparticles for oxygen reduction reaction in alkaline fuel cells

Ag nanoparticles (AgNPs) (11, 15, and 25wt.%) were deposited on the surface of the freestanding and mechanically flexible mats consisting of lignin-derived electrospun carbon nanofibers (ECNFs) by the supercritical CO2 method followed by the thermal treated at 180°C. The electrochemical activity of Ag/ECNFs electrocatalyst systems towards oxygen reduction reaction (ORR) was studied in 0.1M KOH aqueous solution using the rotating disk/rotating ring disk electrode (RDE/RRDE) technique. The SEM, TEM, and XRD results indicated that, the spherical AgNPs were uniformly distributed on the ECNF surface with sizes in the range of 2-10nm. The electrocatalytic results revealed that, all of the Ag/ECNFs systems exhibited high activity in ORR and demonstrated close-to-theoretical four-electron pathway. In particular, the mass activity of 15wt.% Ag/ECNFs system was the highest (119mAmg−1), exceeding that of HiSPEC 4100™ commercial Pt/C catalyst (98mAmg−1). This study suggested that the lignin-derived ECNF mats surface-deposited with AgNPs would be promising as cost-effective and highly efficient electrocatalyst for ORR in alkaline fuel cells.

Fabrication and mechanical properties of hybrid multi-scale epoxy composites reinforced with conventional carbon fiber fabrics surface-attached with electrospun carbon nanofiber mats

This paper reports the fabrication and mechanical properties of hybrid multi-scale epoxy composites reinforced with conventional carbon fiber (CF) fabrics surface-attached with electrospun carbon nanofiber (ECN) mats. The ECNs were prepared via thermal treatments of polyacrylonitrile copolymer nanofibers, which were produced by the electrospinning technique and collected as overlaid mats on the T300 CF fabrics. The ECN-CF fabrics/mats were used as innovative reinforcement fillers for the fabrication of hybrid multi-scale composites (with SC-15 epoxy resin) through the composite-manufacturing technique of vacuum assisted resin transfer molding. Three-point bending test and short-beam shear test were carried out to evaluate the strengthening/toughening effects of ECNs on mechanical properties of the novel composites. The results indicated that out-of-plane mechanical properties of the ECN-CF/epoxy composites were considerably higher than the control sample of traditional CF/epoxy composites.

Hybrid multi-scale epoxy composite made of conventional carbon fiber fabrics with interlaminar regions containing electrospun carbon nanofiber mats

Herein we report the development and evaluation of hybrid multi-scale epoxy composite made of conventional carbon fiber fabrics with interlaminar regions containing mats of electrospun carbon nanofibers (ECNs). The results indicated that (1) the interlaminar shear strength and flexural properties of hybrid multi-scale composite were substantially higher than those of control/comparison composite without ECNs; in particular, the interlaminar shear strength was higher by ∼86%; and (2) the electrical conductivities in both in-plane and out-of-plane directions were enhanced through incorporation of ECNs, while the enhancement of out-of-plane conductivity (∼150%) was much larger than that of in-plane conductivity (∼20%). To validate the data reduction procedure, a new shear stress formula was formulated for composite laminates, which took into account the effect of layup and inter-layers. The study suggested that ECNs could be utilized for the development of high-performance composites, particularly with the improved out-of-plan properties ( e.g., interlaminar shear strength).