Turbostratic graphite nanofibres from electrospun solutions of PAN in dimethylsulphoxide

Structural Reconstruction via Carbon Nanotube Spatially Confined Metal Catalysis: A Morphology-Controlled Approach to Convert Polycyclic Aromatic Hydrocarbon into Carbon Nanofibers for Highly Active Anodes in Li-Ion Batteries

By a carbon nanotube (CNT) spatially confined metal-catalyzed structural reconstruction, carbon nanofibers (CNFs) with a hollow, hollow-solid, solid graphite core, and CNT shell are prepared using nitrogen heterocycle (NHC) and polycyclic aromatic hydrocarbon (PAH) as carbon sources. The formation mechanism of CNFs with oriented graphene layers and enlarged intergraphene spacing is studied by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, and selected area electron diffraction analysis. It revealed that this one-dimensional nanoconfined metal-catalyzed carbon rearrangement is totally different from the reported spatially localized metal-catalyzed graphitization of electrospun polymer and nanocasted carbohydrate nanofibers, as the graphene orientation, cavity volume, and interlayer distance of CNFs can be controlled by the carbon concentration-related competitive metal-catalyzed tip growth of latitudinal and longitudinal graphene layers from NHC and PAH. The unique CNF structure renders good electronic/ionic conductivity, abundant Li+ storage interlayer gaps, and robust mechanical durability, resulting in outstanding electrochemical properties as anodes in lithium-ion batteries. The optimum CNF anode delivers a stable discharge capacity of 475 mA h g-1 at 0.1 C, an extraordinary rate capability of 303 mA h g-1 at 5 C, and a remarkable long-term cycling stability of 378 mA h g-1 after 600 cycles at 1 C. This 1D nanoconfined metal catalysis synthesis could be useful for the development of efficient CNF anodes in many electrochemical reactions with a potential for industrial applications.

Atmospheric Pressure Plasma-Jet Treatment of PAN-Nonwovens—Carbonization of Nanofiber Electrodes

Carbon nanofibers are produced from dielectric polymer precursors such as polyacrylonitrile (PAN). Carbonized nanofiber nonwovens show high surface area and good electrical conductivity, rendering these fiber materials interesting for application as electrodes in batteries, fuel cells, and supercapacitors. However, thermal processing is slow and costly, which is why new processing techniques have been explored for carbon fiber tows. Alternatives for the conversion of PAN-precursors into carbon fiber nonwovens are scarce. Here, we utilize an atmospheric pressure plasma jet to conduct carbonization of stabilized PAN nanofiber nonwovens. We explore the influence of various processing parameters on the conductivity and degree of carbonization of the converted nanofiber material. The precursor fibers are converted by plasma-jet treatment to carbon fiber nonwovens within seconds, by which they develop a rough surface making subsequent surface activation processes obsolete. The resulting carbon nanofiber nonwovens are applied as supercapacitor electrodes and examined by cyclic voltammetry and impedance spectroscopy. Nonwovens that are carbonized within 60 s show capacitances of up to 5 F g−1.

The carbonization of polyacrylonitrile-derived electrospun carbon nanofibers studied by in situ transmission electron microscopy

The carbonization of polyacrylonitrile (PAN) nanofibers is observed in situ up to 1000 °C by transmission electron microscopy (TEM).

Solvent-fractionated sugar cane bagasse lignin: structural characteristics and electro-spinnability

Lignin is one of the most abundant macromolecules on Earth. Lignins are obtained as by-products from the paper industry and used mostly as fuel. Their diverse composition has limited the development of high added-value applications: however, because of their abundance and sustainable origin, there is a growing interest in using lignins as a raw material and as a replacement for oil derivatives. In order to use lignins in bio-refineries, several processes must be studied and standardized. Lignin fractionation using solvents is a promising process. In this study, lignin from sugar cane bagasse (L1) was fractionated with solvents, and the fractions were characterized to evaluate structural aspects relevant for the production of fibers. L1 was extracted into four fractions with toluene (E1), ethanol (E2), methanol (E3), and dimethyl sulfoxide (DMSO, E4). Fractions E2, E3, and E4, showed only slightly different molar masses and molar mass distribution, but have relevant differences in their structural characteristics and processability. The ethanol extract (E2) provided lignins with a more flexible structure, and electro-spinning resulted in the production of nanofibers with diameters between 60 and 120 nm; the methanol fraction (E3) produced nanospheres with diameters between 90 and 350 nm; the DMSO fraction (E4) covered only a surface with electro-spray. These results show the possibility of developing high added-value applications using fractions of lignin from distinct biomasses or from their combination.

Graphene nanoribbons hybridized carbon nanofibers: remarkably enhanced graphitization and conductivity, and excellent performance as support material for fuel cell catalysts

High electronic conductivity of the support material and uniform distribution of the catalyst nanoparticles (NPs) are extremely desirable for electrocatalysts. In this paper, we present our recent progress on electrocatalysts for fuel cells with simultaneously improved conductivity of the supporting carbon nanofibers (CNFs) and distribution of platinum (Pt) NPs through facile incorporation of graphene nanoribbons (GNRs). Briefly, GNRs were obtained by the cutting and unzipping of multiwalled carbon nanotubes (MWCNTs) and subsequent thermal reduction and were first used as novel nanofillers in CNFs towards high performance support material for electrocatalysis. Through electrospinning and carbonization processes, GNR embedded carbon nanofibers (G-CNFs) with greatly enhanced graphitization and electronic conductivity were synthesized. Chemical deposition of Pt NPs onto G-CNFs generated a new Pt-G-CNF hybrid catalyst, with homogeneously distributed Pt NPs of ∼3 nm. Compared to Pt-CNF (Pt on pristine CNFs) and Pt-M-CNF (Pt on MWCNT embedded CNFs), Pt-G-CNF hybrids exhibit significantly improved electrochemically active surface area (ECSA), better CO tolerance for electro-oxidation of methanol and higher electrochemical stability, testifying G-CNFs are promising support materials for high performance electrocatalysts for fuel cells.

Extraordinary improvement of the graphitic structure of continuous carbon nanofibers templated with double wall carbon nanotubes

Carbon nanotubes are being widely studied as a reinforcing element in high-performance composites and fibers at high volume fractions. However, problems with nanotube processing, alignment, and non-optimal stress transfer between the nanotubes and surrounding matrix have so far prevented full utilization of their superb mechanical properties in composites. Here, we present an alternative use of carbon nanotubes, at a very small concentration, as a templating agent for the formation of graphitic structure in fibers. Continuous carbon nanofibers (CNF) were manufactured by electrospinning from polyacrylonitrile (PAN) with 1.2% of double wall nanotubes (DWNT). Nanofibers were oxidized and carbonized at temperatures from 600 °C to 1850 °C. Structural analyses revealed significant improvements in graphitic structure and crystal orientation in the templated CNFs, with the largest improvements observed at lower carbonization temperatures. In situ pull-out experiments showed good interfacial bonding between the DWNT bundles and the surrounding templated carbon matrix. Molecular Dynamics (MD) simulations of templated carbonization confirmed oriented graphitic growth and provided insight into mechanisms of carbonization initiation. The obtained results indicate that global templating of the graphitic structure in fine CNFs can be achieved at very small concentrations of well-dispersed DWNTs. The outcomes reveal a simple and inexpensive route to manufacture continuous CNFs with improved structure and properties for a variety of mechanical and functional applications. The demonstrated improvement of graphitic order at low carbonization temperatures in the absence of stretch shows potential as a promising new manufacturing technology for next generation carbon fibers.