Min- Jung

Improved capacitance characteristics of electrospun ACFs by pore size control and vanadium catalyst

Nano-sized carbon fibers were prepared by using electrospinning, and their electrochemical properties were investigated as a possible electrode material for use as an electric double-layer capacitor (EDLC). To improve the electrode capacitance of EDLC, we implemented a three-step optimization. First, metal catalyst was introduced into the carbon fibers due to the excellent conductivity of metal. Vanadium pentoxide was used because it could be converted to vanadium for improved conductivity as the pore structure develops during the carbonization step. Vanadium catalyst was well dispersed in the carbon fibers, improving the capacitance of the electrode. Second, pore-size development was manipulated to obtain small mesopore sizes ranging from 2 to 5 nm. Through chemical activation, carbon fibers with controlled pore sizes were prepared with a high specific surface and pore volume, and their pore structure was investigated by using a BET apparatus. Finally, polyacrylonitrile was used as a carbon precursor to enrich for nitrogen content in the final product because nitrogen is known to improve electrode capacitance. Ultimately, the electrospun activated carbon fibers containing vanadium show improved functionality in charge/discharge, cyclic voltammetry, and specific capacitance compared with other samples because of an optimal combination of vanadium, nitrogen, and fixed pore structures.

Effects of surface chemical properties of activated carbon modified by amino-fluorination for electric double-layer capacitor.

The surface of phenol-based activated carbon (AC) was seriatim amino-fluorinated with solution of ammonium hydroxide and hydrofluoric acid in varying ratio to fabricate electrode materials for use in an electric double-layer capacitor (EDLC). The specific capacitance of the amino-fluorinated AC-based EDLC was measured in a 1 M H(2)SO(4) electrolyte, in which it was observed that the specific capacitances increased from 215 to 389 Fg(-1) and 119 and 250 Fg(-1) with the current densities of 0.1 and 1.0 Ag(-1), respectively, in comparison with those of an untreated AC-based EDLC when the amino-fluorination was optimized via seriatim mixed solution of 7.43 mol L(-1) ammonium hydroxide and 2.06 mol L(-1) hydrofluoric acid. This enhancement of capacitance was attributed to the synergistic effects of an increased electrochemical activity due to the formation of surface N- and F-functional groups and increased, specific surface area, and mesopore volumes, all of which resulted from the amino-fluorination of the electrode material.

An XPS Study of Oxyfluorinated Multiwalled Carbon Nano Tubes

In order to investigate functional groups on the surface of Multi-walled Carbon Nanotubes (MWCNTs) induced by oxyfluorination, XPS (X-ray photoelectron spectroscopy) analysis was carried out. All core level spectra of MWCNTs were deconvoluted to several Pseudo-Voigt functions (sum of Gaussian-Lorentzian functions). Both O1s and F1s binding energy of oxyfluorinated MWCNTs shifted high value as increment of fluorine mixing ratio. The carbon-fluorine covalent bonding concentration increased as increment of fluorine mixing ratio. The shape and intensity of OF10-MWCNTs are similar with those of as-received MWCNTs. However, the intensity and binding energies of main peak position of OF20-MWCNTs and OF30-MWCNTs were dramatically increased by oxyfluorination.

Preparation and Characterization of Electrospun TiO 2 -Activated Carbon Complex Fiber as Photocatalyst

In this study, -Activated carbon (AC) complex fibers were prepared by electrospinning for the synergetic effect of adsorption and degradation of organic pollutant. The average diameter of these fibers increased with increasing the amount of AC added, except for 1AC-TOF (AC =1/40 mass ratio). After calcinations at , long as-spun fibers were broken and their average diameter was slightly decreased. The resultant fibers after calcination had rough surface and sphere shapes like a peanut. From XRD results, it was confirmed that as-spun fibers were changed to anatase fiber after calcinations at . The prepared -AC complex fibers could remove procian blue dyes by solar light irradiation with high removal property of 94~99%. The PB dye was rapidly removed by adsorption during the initial 5 minutes. But after 5 minutes, dye removal was occurred by photodegradation. In this study, the most efficient AC/ ratio of -AC complex fibers was 5/40, showing the synergetic effect of adsorption and photodegradation. It is expected that the -AC complex fibers can be used to remove of organic pollutants in water system.

Stabilization of pitch-based carbon fibers accompanying electron beam irradiation and their mechanical properties

Carbon fibers are prepared by stabilizing pitch fibers accompanying electron beam (E-beam) irradiation. The carbon fibers pretreated by E-beam irradiation achieve a higher stabilization index than the carbon fibers that are only heat-stabilized. In addition, the carbon fibers subjected to E-beam irradiation in the stabilization step exhibit a comparable tensile strength to that of general purpose carbon fibers. The carbon fibers pretreated with an absorbed dose of 3000 kGy have a tensile strength of 0.54 GPa for a similar fiber diameter. Elemental, Fourier-transform infrared spectroscopy, and thermogravimetric analyses indicate that Ebeam irradiation is an efficient oxidation and dehydrogenation treatment for pitch fibers by showing that the intensity of the aliphatic C?H stretching and aromatic CH2 ben

Hydrogen Adsorption of PAN-based Porous Carbon Nanofibers using MgO as the Substrate

In this study, porous electrospun carbon fibers were prepared by electrospinning with PAN and , as a MgO precursor. MgO was selected as a substrate because of its chemical and thermal stability, no reaction with carbon, and ease of removal after carbonization by dissolving out in acidic solutions. was mixed with polyacrylonitrile (PAN) solution as a precursor of MgO with various weight ratios of /PAN. The average diameter of porous electrospun carbon fibers increased from 1.3 to 3 , as the to PAN weight ratio increased. During the stabilization step, was hydrolyzed to MgOHCl by heat treatment. At elevated temperature of 823 K for carbonization step, MgOHCl was decomposed to MgO. Specific surface area and pore structure of prepared electrospun carbon fibers were decided by weight ratio of /PAN. The amount of hydrogen storage increased with increase of specific surface area and micropore volume of prepared electrospun carbon fibers.

NO gas sensing ability of activated carbon fibers modified by an electron beam for improvement in the surface functional group

Activated carbon fiber (ACF) surfaces are modified using an electron beam under different aqueous solutions to improve the NO gas sensitivity of a gas sensor based on ACFs. The oxygen functional group on the ACF surface is changed, resulting in an increase of the number of non-carbonyl (-C-O-C-) groups from 32.5% for pristine ACFs to 39.53% and 41.75% for ACFs treated with hydrogen peroxide and potassium hydroxide solutions, respectively. We discover that the NO gas sensitivity of the gas sensor fabricated using the modified ACFs as an electrode material is increased, although the specific surface area of the ACFs is decreased because of the recovery of their crystal structure. This is attributed to the static electric interaction between NO gas and the non-carbonyl groups introduced onto the ACF surfaces.

Effects of e-beam irradiation on the chemical, physical, and electrochemical properties of activated carbons for electric double-layer capacitors

Activated carbons (ACs) were modified via e-beam irradiation at various doses for use as an electrode material in electric double-layer capacitors (EDLCs). The chemical compositions of the AC surfaces were largely unchanged by the e-beam irradiation. The ACs treated with the e-beam at radiation doses of 200 kGy exhibited higher nanocrystallinity than the untreated ACs. The specific surface areas and pore volumes of the e-beam irradiated ACs were also higher than those of the untreated ACs. These results were attributed to the transformation and degradation of the nanocrystallinity of the AC surfaces due to the e-beam irradiation. The specific capacitance of the ACs treated with the e-beam at radiation doses of 200 kGy increased by 24% compared with the untreated ACs, and the charge transfer resistance of the ACs was decreased by the e-beam irradiation. The enhancement of the electrochemical properties of the e-beam irradiated ACs can be attributed to an increase in their specific surface area and surface crystallinity.

Enhancement of Electrochemical Properties of Activated Carbon Fibers with Controlled Surface Structure by Electron Beam Irradiation

In this study, activated carbon fibers (ACFs) were prepared and then irradiated by electron beam (e-beam) to investigate effects of physicochemical properties of ACF surface on the electrochemical properties of ACFs according to various irradiation doses. Defects of the ACF surface were decreased and C-C (sp) bonds onto that were increased via the e-beam irradiation. The specific surface area and pore volume of the e-beam irradiated ACFs were also much higher than those of the untreated ACFs. These changes of the surface structure on ACFs were caused by formation of defects and rehybridization of carbon atoms by e-beam irradiation. The specific capacitance of the ACFs irradiated with 200 kGy increased by 39% compared with the untreated ACFs. These enhancements of the electrochemical properties in e-beam irradiated ACFs were attributed to the increase in the specific surface area and pore volume.

Preparation and Characterization of Mesophase Pitches from Petroleum Residues using Two-step Heat Treatment

>> To prepare mesophase pitches through low energy process, pyrolysis fuel oil with AlCl3 has been modified using two-step heat treatment which is heat-treated at 330°C for 3~5 h after pre-treatment at 250°C. The result of polarized optical microscope observation, mesophase is not observed in pitches carried out only pre-heat treatment. While mesophase content is significantly increased from 9% to 100% according to increasing secondary heat treatment time from 3 h to 5 h. Synthesizing of the mesophase pitch at low temperature of 330°C is attributed to decrease of viscosity of the pitches carried out first heat treatment with AlCl3. The result of Fouriertransform infrared spectroscopic analysis, it is expected that aromatization of aliphatic compounds is dominant at early secondary heat treatment, on the other hand, polycondensation reaction becomes dominant as secondary heat treatment time increases. Aromaticity and stacking height of the pitches secondary heat treated for 5 hours are more increased about 25% and 107%, respectively, than that of pitches carried out only first heat treatment.