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        • Rationally engineered surface properties of carbon nanofibers for the enhanced supercapacitive performance of binary metal oxide nanosheets

          Kim, Ji Hoon,Kim, Chang Hyo,Yoon, Hyeonseok,Youm, Je Sung,Jung, Yong Chae,Bunker, Christopher E.,Kim, Yoong Ahm,Yang, Kap Seung The Royal Society of Chemistry 2015 Journal of Materials Chemistry A Vol.3 No.39

          <▼1><P>Electrochemically active binary metal oxide nanosheets on the surface of electrically conductive and porous carbon nanofibers exhibited a high pseudo-capacitive performance.</P></▼1><▼2><P>The hybridization of an electrochemically active metal oxide with electrically conductive carbon nanofibers (CNFs) has been utilized as a solution to overcome the energy density limitation of carbon-based supercapacitors as well as the poor cyclic stability of metal oxides. Herein, we have demonstrated the growth of binary metal oxide nanosheets on the engineered surface of CNFs to fully exploit their electrochemical activity. Metal oxide nanosheets were observed to grow vertically from the surface of CNFs. The high structural toughness of the CNF–metal oxide composite under strong sonication indicated strong interfacial binding strength between the metal oxide and the CNFs. The rationally designed porous CNFs presented a high specific surface area and showed high capacity for adsorbing metal ions, where the active edge sites acted as anchoring sites for the nucleation of metal oxides, thereby leading to the formation of a well dispersed and thin layer structure of binary metal oxide nanosheets. Excellent electrochemical performance (<I>e.g.</I>, specific capacitance of 2894.70 F g<SUP>−1</SUP> and energy density of 403.28 W h kg<SUP>−1</SUP>) was observed for these binary metal oxide nanosheets, which can be attributed to the large increase in the accessible surface area of the electrochemically active metal oxide nanosheets due to their homogeneous distribution on porous CNFs, as well as the efficient charge transfer from the metal oxide to the CNFs facilitated the improvement in the performance.</P></▼2>

        • SCISCIESCOPUS

          Single-walled carbon nanotube-mediated physical gelation of binary polymer blends: An efficient route to versatile porous carbon electrode materials

          Kim, Yukyung,Kim, Saerona,Noh, Seonmyeong,Kim, Semin,Park, Geunsu,Le, Thanh-Hai,Han, Hyunwoo,Kim, Yoong Ahm,Yoon, Hyeonseok Elsevier 2018 CHEMICAL ENGINEERING JOURNAL -LAUSANNE- Vol.353 No.-

          <P><B>Abstract</B></P> <P>A non-covalent approach to prepare nanotube-containing gels was developed based on the physical gelation of two polymers, polyvinyl alcohol (PVA) and polyacrylonitrile (PAN), with different microphase behaviors in water/dimethyl sulfoxide (DMSO) mixture. Single-walled carbon nanotubes (SWNTs) were incorporated into the binary-polymer/binary-solvent system to alter the physical gelation behavior and, in turn, to achieve unique physicochemical characteristics of the resulting gels. SWNTs were wrapped with PVA, which extended the binary polymer system to a ternary polymer system consisting of PVA bound to SWNTs, free PVA, and PAN. It was observed that the SWNT/PVA/PAN ensembles gelled with appropriate amounts of water in DMSO and the gelation behavior was reversible. The amounts of water and SWNT were determined to be key parameters affecting the formation of the gels. The SWNT/PVA/PAN gels were successfully converted to carbonaceous gels via heat treatment in an inert atmosphere, which can be extended to several applications such as electrode materials. The macroporous carbonaceous gels were further functionalized via manganese deposition followed by potassium hydroxide activation, which yielded excellent cell performance in a neutral electrolyte with the energy density of 9.6–24.8 Wh kg<SUP>−1</SUP> and power density of 8.0–0.1 kW kg<SUP>−1</SUP>.</P> <P><B>Highlights</B></P> <P> <UL> <LI> The effect of co-nonsolvents on the microstructure of the gel was demonstrated. </LI> <LI> The SWNT-mediated physical gelation of binary polymer blends were reported. </LI> <LI> Physically cross-linked gels were converted to versatile electrode materials. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

        • Defect-Assisted Heavily and Substitutionally Boron-Doped Thin Multiwalled Carbon Nanotubes Using High-Temperature Thermal Diffusion

          Kim, Yoong Ahm,Aoki, Shunta,Fujisawa, Kazunori,Ko, Yong-Il,Yang, Kap-Seung,Yang, Cheol-Min,Jung, Yong Chae,Hayashi, Takuya,Endo, Morinobu,Terrones, Mauricio,Dresselhaus, Mildred S. American Chemical Society 2014 The Journal of Physical Chemistry Part C Vol.118 No.8

          <P>Carbon nanotubes have shown great potential as conductive fillers in various composites, macro-assembled fibers, and transparent conductive films due to their superior electrical conductivity. Here, we present an effective defect engineering strategy for improving the intrinsic electrical conductivity of nanotube assemblies by thermally incorporating a large number of boron atoms into substitutional positions within the hexagonal framework of the tubes. It was confirmed that the defects introduced after vacuum ultraviolet and nitrogen plasma treatments facilitate the incorporation of a large number of boron atoms (ca. 0.496 atomic %) occupying the trigonal sites on the tube sidewalls during the boron doping process, thus eventually increasing the electrical conductivity of the carbon nanotube film. Our approach provides a potential solution for the industrial use of macro-structured nanotube assemblies, where properties, such as high electrical conductance, high transparency, and lightweight, are extremely important.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/jpccck/2014/jpccck.2014.118.issue-8/jp410732r/production/images/medium/jp-2013-10732r_0006.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/jp410732r'>ACS Electronic Supporting Info</A></P>

        • SCIESCOPUSKCI등재

          Double-walled carbon nanotubes: synthesis, structural characterization, and application

          Kim, Yoong Ahm,Yang, Kap-Seung,Muramatsu, Hiroyuki,Hayashi, Takuya,Endo, Morinobu,Terrones, Mauricio,Dresselhaus, Mildred S. 한국탄소학회 2014 Carbon Letters Vol.15 No.2

          Double walled carbon nanotubes (DWCNTs) are considered an ideal model for studying the coupling interactions between different concentric shells in multi-walled CNTs. Due to their intrinsic coaxial structures they are mechanically, thermally, and structurally more stable than single walled CNTs. Geometrically, owing to the buffer-like function of the outer tubes in DWCNTs, the inner tubes exhibit exciting transport and optical properties that lend them promise in the fabrication of field-effect transistors, stable field emitters, and lithium ion batteries. In addition, by utilizing the outer tube chemistry, DWCNTs can be useful for anchoring semiconducting quantum dots and also as effective multifunctional fillers in producing tough, conductive transparent polymer films. The inner tubes meanwhile preserve their excitonic transitions. This article reviews the synthesis of DWCNTs, their electronic structure, transport, and mechanical properties, and their potential uses.

        • SCIESCOPUSKCI등재

          Effect of low processing rate on homogeneous microstructural evolution of polyacrylonitrile‑based carbon fibers

          Doo‑Won Kim,Dae Ho Kim,Sung Ryong Kim,Bo‑Hye Kim,Yun Hyuk Bang,Duck Joo Yang,Go Bong Choi,Yoong Ahm Kim,Kap Seung Yang 한국탄소학회 2019 Carbon Letters Vol.29 No.5

          This study demonstrates that low processing rate for producing polyacrylonitrile (PAN)-based carbon fiber is a critical to obtain a homogeneous radial microstructure with high resistance to oxidation, thereby resulting in their improved mechanical strength. The dry-jet wet spun PAN organic fibers were processed (e.g., stabilized and then carbonized) utilizing two different rates; one is 1.6 times longer than the other. The effect of processing rate on the microstructural evolutions of carbon fibers was analyzed by scanning electron microscopy after slow etching in air, as well as Raman mapping after graphitization. The rapidly processed fiber exhibited the multilayered radial structure, which is caused by the radial direction stretching of the extrusion in the spinning. In case of the slowly processed fiber, the layered radial structure formed in the spinning process was changed into a more homogeneous radial microstructure. The slowly processed fibers showed higher oxidation resistance, higher mechanical properties, and higher crystallinity than the rapidly processed one. Raman mapping confirmed that the microstructure developed during spinning was sustained even though fiber was thermally treated up to 2800 °C.

        • KCI등재

          Effects of electromagnetic irradiation on low-molecular-weight fraction of fluidized catalytic cracking decant oil for synthesis of pitch precursor

          Doo Won Kim,Kyu-Kwan Im,Hee Jou Kim,DONG-HUN LEE,Yoong Ahm Kim,Jisu Choi,Kap Seung Yang 한국공업화학회 2020 Journal of Industrial and Engineering Chemistry Vol.82 No.-

          We examined the effects of different energies of electromagnetic irradiation on the molecular sizeincrease in the low-molecular-weight fraction offluidized catalytic cracking decant oil (LMFD), whichwas fractionated from the originalfluidized catalytic cracking decant oil. Microwave (MW) radiation wasemployed as a relatively low-energy source, and an electron beam (EB) was employed as a high-energysource. Variations in viscosity, color, molecular weight, and functional groups of the LMFD wereexamined before and after irradiation to illuminate the LMFD reaction mechanism. The viscosityincreased from 43.17 cP for LMFD to 3978 cP after 3 h of MW irradiation (MW3h) and to 1136 cP after1000 kGy EB irradiation (EB1000). The reddish-brown color of the LMFD changed to black for the MW3hsample, whereas the EB1000 sample changed to a dark brown. As evaluated by matrix-assisted laserdesorption ionization time-of-flight mass spectrometry, the molecular weights of the MW-irradiatedsamples increased more than those of the EB samples. The results can be related to the activation energiesfor radical formation and recombination. MW irradiation is considered to have an effective energy sourcefor both radical formation and recombination, whereas EB irradiation exhibits an energy too high forradical recombination.

        • SCIESCOPUS

          Electrochemical Characteristics of Solid Polymer Electrode Fabricated with Low IrO<sub>2</sub> Loading for Water Electrolysis

          Ban, Hee-Jung,Kim, Min Young,Kim, Dahye,Lim, Jinsub,Kim, Tae Won,Jeong, Chaehwan,Kim, Yoong-Ahm,Kim, Ho-Sung The Korean Electrochemical Society 2019 Journal of electrochemical science and technology Vol.10 No.1

          To maximize the oxygen evolution reaction (OER) in the electrolysis of water, nano-grade $IrO_2$ powder with a low specific surface was prepared as a catalyst for a solid polymer electrolyte (SPE) system, and a membrane electrode assembly (MEA) was prepared with a catalyst loading as low as $2mg\;cm^{-2}$ or less. The $IrO_2$ catalyst was composed of heterogeneous particles with particle sizes ranging from 20 to 70 nm, having a specific surface area of $3.8m^2g^{-1}$. The anode catalyst layer of about $5{\mu}m$ thickness was coated on the membrane (Nafion 117) for the MEA by the decal method. Scanning electron microscopy (SEM) and electrochemical impedance spectroscopy (EIS) confirmed strong adhesion at the interface between the membrane and the catalyst electrode. Although the loading of the $IrO_2$ catalyst was as low as $1.1-1.7mg\;cm^{-2}$, the SPE cell delivered a voltage of 1.88-1.93 V at a current density of $1A\;cm^{-2}$ and operating temperature of $80^{\circ}C$. That is, it was observed that the over-potential of the cell for the oxygen evolution reaction (OER) decreased with increasing $IrO_2$ catalyst loading. The electrochemical stability of the MEA was investigated in the electrolysis of water at a current density of $1A\;cm^{-2}$ for a short time. A voltage of ~2.0 V was maintained without any remarkable deterioration of the MEA characteristics.

        • SCISCIESCOPUS

          Pore engineering of nanoporous carbon nanofibers toward enhanced supercapacitor performance

          Kim, Chang Hyo,Yang, Cheol-Min,Kim, Yoong Ahm,Yang, Kap Seung Elsevier BV * North-Holland 2019 Applied Surface Science Vol.497 No.-

          <P><B>Abstract</B></P> <P>Porous carbon nanofibers (PCNFs) were prepared from electrospinning both without and with a pore generating inorganic material. Next, they were activated with different activation media (N<SUB>2</SUB>, H<SUB>2</SUB>O, or CO<SUB>2</SUB>). The pore size was tailored from 0.64 to 0.81 nm under various activation conditions, and the specific surface area ranged from 404 to 1624 m<SUP>2</SUP>·g<SUP>−1</SUP>. To determine the charging mechanism of the supercapacitor in an aqueous electrolyte, the normalized capacitance was calculated, and it was compared with the adsorption behavior of the solvent, H<SUB>2</SUB>O, separately. The normalized capacitance showed a trend similar to that of H<SUB>2</SUB>O adsorption at a low relative pressure (<I>P</I>/<I>P</I> <SUB> <I>0</I> </SUB> = 0.1), which was expected to be driven by the filler–pore wall interaction, indicating that the ions were strongly solvated by the solvent, H<SUB>2</SUB>O. The highest normalized capacitance value (32 μF·cm<SUP>−2</SUP> at 1 mA·cm<SUP>−2</SUP>) was achieved from PCNFs having a pore size of 0.64 nm, similar to the electrolyte solvated ion sizes. It was observed that both the capacitance and H<SUB>2</SUB>O adsorption were achieved near the pore size of 0.64 nm and at a high functionality. It was understood that the adsorption of the solvated ions was primarily driven by the interaction of the solvent, H<SUB>2</SUB>O, with the surface functional groups.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Finely tuned porous carbon nanofibers (PCNFs) with pore size of 0.64–0.81 nm are prepared. </LI> <LI> Capacitive behavior and H<SUB>2</SUB>O adsorption property of the PCNFs are evaluated. </LI> <LI> High normalized capacitance is achieved from pore size similar to solvated ion sizes. </LI> <LI> Suitable pore size and high surface functionality are key factors for supercapacitor application. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

        • Enhanced Thermal Conductivity of Individual Polymeric Nanofiber Incorporated with Boron Nitride Nanotubes

          Kim, Dukeun,You, Myungil,Seol, Jae Hun,Ha, Sumin,Kim, Yoong Ahm American Chemical Society 2017 The Journal of Physical Chemistry Part C Vol.121 No.12

          <P>Thermal conductivity of individual polyvinylpyrrolidone (PVP) nanofibers embedding boron nitride nanotube (BNNT) fillers has been measured. The PVP nanofibers were electrospun on suspended microdevices in order to better understand the effect of BNNT fillers on the thermal conductivity of polymeric nanofibers. Various material characterization methods provided evidence that ketone group in the PVP interacted with the surface of BNNTs via strong intermolecular forces, thereby resulting in an effective heat transfer between the polymer matrix and BNNTs. The individual PVP nanofiber containing 30 wt % of BNNTs exhibited approximately 2-fold higher thermal conductivity than that of the bulk PVP.</P>

        • Synthesis and Characterization of Porous Carbon Nanofibers with Hollow Cores Through the Thermal Treatment of Electrospun Copolymeric Nanofiber Webs

          Kim, Chan,Jeong, Young Il,Ngoc, Bui Thi Nhu,Yang, Kap Seung,Kojima, Masahito,Kim, Yoong Ahm,Endo, Morinobu,Lee, Jae-Wook WILEY-VCH Verlag 2007 Small Vol.3 No.1

          <B>Graphic Abstract</B> <P>Porous, fibrous carbon nanofibers containing hollow cores (see image) are fabricated by electrospinning two immiscible polymer solutions followed by thermal treatment at 1000 °C in an inert atmosphere. This new type of carbon nanofibers has controlled porosity combined with a low density and expected high electrical and mechanical properties due to an interlinked fiber morphology, and may be utilized as an efficient electromagnetic shielding material. <img src='wiley_img/16136810-2007-3-1-SMLL200600243-content.gif' alt='wiley_img/16136810-2007-3-1-SMLL200600243-content'> </P>

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