Straight long carbon nanofibers with a large hollow core obtained by a floating reactant method show a stacking morphology of truncated conical graphene layers, which in turn exhibit a large portion of open edges on the outer surface and also in the inner channels. Through a judicious choice of oxidation conditions, nanofibers with increased active edge sites are obtained without disrupting the fiber’s morphology. A graphitization process induces a morphological change from a tubular type to a reversing saw-toothed type and the formation of loops along the inner channel of the nanofibers, accompanied by a decrease in interlayer spacing.

Mesoporous and amorphous ZnSnO3 nanocubes of ~37 nm size coated with a thin porous carbon layer have been prepared using monodisperse ZnSn(OH)6 as the active precursor and low-temperature synthesized polydopamine as the carbon precursor. The small single nanocubes cross-link with each other to form a continuous conductive framework and interconnected porous channels with macropores of 74 nm width. Because of its multi-featured nanostructure, this material exhibits greatly enhanced integration of reversible alloying/de-alloying (i.e., transformation of Li(4.4)Sn and LiZn to Sn and Zn) and conversion (i.e., oxidation of Sn and Zn to ZnSnO3) reaction processes with an extremely high capacity of 1060 mA h g(-1) for up to 100 cycles. A high reversible capacity of 650 and 380 mA h g(-1) can also be delivered at rates of 2 and 3 A g(-1), respectively. This excellent electrochemical performance is attributed to the small particle size, well-developed mesoporosity, the amorphous nature of the ZnSnO3 and the continuous conductive framework produced by the interconnected carbon layers.

Graphite nanoparticles were prepared by the heat treatment of diamond nanoparticles in the range 900-1600°C. X-ray diffraction, transmission electron microscopy ͑TEM͒ and Raman scattering studies indicate that the onset temperature of the diamond-graphite transition is around 1200°C and the complete conversion of diamond to graphite occurs at 1600°C. Based on the structural characteristics the samples are categorized into sp 3 -dominated ͑as-prepared and 900°C͒, sp 2 :sp 3 mixed-phase ͑1200 and 1400°C͒, and sp 2 -dominated systems ͑1600°C͒. The larger c-axis repeat distances and the high-resolution TEM images for the sp 2 :sp 3 mixed-phase systems denote the presence of the remnant buckling feature of the diamond ͑111͒ planes in the graphene sheets. Magnetic susceptibility and ESR studies suggest the development of itinerant--electron system from the 1200°C and higher-temperature heat-treated samples. The completely graphitized sample reveals the important role of edge-inherited nonbonding -electron states in the electronic structure. The Raman G-peak position and the orbital diamagnetism show considerable deviation from the bulk-graphite values, which is explained on the basis of charge transfer from the graphite band to the localized edge states and the resulting shifting of the Fermi level. The enhanced spin-lattice relaxation rates in the case of more graphitized samples heat-treated at 1400 and 1600°C are expected to arise from the involvement of the localized edge-state electrons. In the less-graphitized 1200°C heat-treated sample, however, the corrugated nature of the graphene planes is likely to hinder such fast-relaxation processes.

A simple and scalable method is reported for fabricating a porosity-controlled carbon nanofibers with a skin-core texture by electrospinning a selected blend of polymer solutions. Simple thermal treatment of the electrospun nanofibers from solution blends of various compositions creates suitable ultramicropores on the surface of carbon nanofibers that can accommodate many ions, removing the need for an activation step. The intrinsic properties of the electrode (e.g., nanometre-size diameter, high specific surface area, narrow pore size distribution, tuneable porosity, shallow pore depth, and good ionic accessibility) enable construction of supercapacitors with large specific capacitance (130.7 Fg -1 ), high power (100 kWkg -1 ), and energy density (15.0 Whkg -1 ).Keywords: Porosity, Skin-core, Electrospinning, Pore size distribution, Supercapacitor 3 1. Introduction Due to their high power density and long life-time, electrochemical capacitors are promising power sources for portable electronic systems and automotive applications [1][2][3]. To improve the performance of these capacitors, several approaches have been investigated (e.g., controlling the pore size distribution, introducing electroactive metallic particles or electron conducting polymers, and fabricating hybrid-type cells) [4][5][6]. Among the many types of active materials, carbon nanofibers (CNFs) are of great practical importance due to their flexibility and high aspect ratio (above 10 6 ). Moreover, to improve the energy density and ion transport within electrode materials, thin films consisting of carbon nanotubes and CNFs have been suggested as promising flexible electrodes for supercapacitors [7][8][9]. In this work, we investigated this approach for improving energy storage efficiency by narrow distribution of pore sizes, which can enhance the ionic accessibility into the pores polyacrylonitrile(PAN)/pitch-based CNFs having a skin-core structure. Further, the size of pores formed in the surface of the fiber can be controlled to an appropriate degree. Experimental FabricationThe pitch provided through condensation of the pyrolized fuel oil (PFO) with Cl 2 by Hanwha Chemical Co. Korea. The PFO used as the raw material is a heavy residual oil as by-product from naphtha cracking. The properties of the pitch used are summarized in Table 1. The concentration of pitch in THF was varied between 50 and 20 wt. %. A solution of PAN in DMF was added to pitch in THF solution achieve a PAN/pitch weight ratio of 7/3 wt.%. To produce a web, a voltage of 20 kV was applied to the positively charged capillary, and a tip-to-collector distance of 25 cm was maintained during the electrospinning process. The nanofibers were stabilized in air and carbonized at 1000 °C in a horizontal furnace under a flow of nitrogen.2.2.Characterization The CNFs were characterized by SEM (Hitachi, S-4700, Japan), TEM (using JEOL JEM-2010 FEF), and nitrogen adsorption-desorption isotherms (ASAP2010, Micromeritics Instruments Co.). The full range of pore sizes over a continuo...

Activated carbon fibers (ACF's), already used widely as absorbent materials, are now expected to be useful as new electrical and electronic materials, for their very large specific surface areas (SSA). Chemical adsorption as well as x-ray diffraction have been mainly used for characterizing the ACF structure. While TEM observations reveal the texture of ACF's, such observations have not yet yielded quantitative information about the microstructure. To promote the quantitative interpretation of the TEM images, computer image analysis is used in this work to clarify the pore structure of ACF's. The microstructures of three samples, which are all isotropic pitch-based ACF's but with different SSA values, have been investigated. Operations such as noise reduction, low frequency cut-off filtering, and binary image formation are used to clarify the pore images of the ACF's. The distribution of the ACF porosity size is clearly shown by a frequency analysis of the two-dimensional fast Fourier transform (FFT). The results suggest that TEM images include contributions from many different pore sizes. Pores in different size ranges are extracted by the inverse FFT (IFFT) operation by selecting the specific frequency range, and by-this analysis the pore structure is shown to have fractal characteristics.