• Title/Summary/Keyword: GNFS

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Influence of Chemical Activation of Carbon Supports on Electrochemical Behaviors of Pt-Ru Nanoparticle for Fuel cells (연료전지 백금-루테늄 나노입자의 전기화학적 거동에 대한 탄소지지체의 활성화 효과)

  • Kim, Byung-Ju;Park, Soo-Jin
    • 한국신재생에너지학회:학술대회논문집
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    • 2011.05a
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    • pp.93.2-93.2
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    • 2011
  • In this work, graphite nanofibers (GNFs) were prepared for using catalyst supports in fuel cells. The GNFs were chemically activated to obtain high surface area and small pore diameter with different potassium hydroxide (KOH) amounts, i.e., 0, 1, 3, 4, and 5 g as an activating agent. And then Pt-Ru was deposited onto activated GNFs (A-GNFs) by chemical reduction method. The characteristics of Pt-Ru catalysts deposited onto A-GNFs were determined by specific surface area and pore size analyzer, X-ray diffraction (XRD), transmission electron microscopy (TEM), and inductive coupled plasma-mass spectrometer (ICP-MS). The electrochemical properties of Pt-Ru/A-GNFs catalysts were also analyzed by cyclic voltammetry (CV) experiments. From the results, the A-GNFs carbon supports activated with 4 g of KOH (A4g-GNFs) showed that the highest specific surface areas. In addition, the A4g-GNFs led to uniform dispersion of Pt-Ru onto A4g-GNFs, resulting in the enhancement of electrochemical activity of Pt-Ru catalysts.

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Effect of Chemical Activation on Electrochemical behaviors of Ni-loaded Graphite Nanofibers (화학적 활성화에 따른 Ni 담지된 흑연나노섬유의 전기화학적 거동)

  • Yoo, Hye-Min;Park, Soo-Jin
    • 한국신재생에너지학회:학술대회논문집
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    • 2011.05a
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    • pp.159.2-159.2
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    • 2011
  • In this study, we prepared the activated graphite nanofibers (A-GNFs) via chemical activation with KOH reagent. The effect of A-GNFs on the surface and textural properties of Ni-loaded graphite nanofibers (Ni/GNFs) was investigated by X-ray diffraction (XRD), transmission electron microscope (TEM), and Brunauer-Emmett-Teller (BET). The textural properties of samples were investigated by $N_2$/77K adsorption isotherms. The electrochemical performances were investigated by cyclic voltammetry. As a results, the electrochemical performances of Ni/GNFs were improved with usage of A-GNFs. This could be interpreted by the high specific surface area and large total pore volume of the A-GNFs.

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Effect of Heat Treatment on CO2 Adsorption of Ammonized Graphite Nanofibers

  • Meng, Long-Yue;Cho, Ki-Sook;Park, Soo-Jin
    • Carbon letters
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    • v.11 no.1
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    • pp.34-37
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    • 2010
  • In this work, graphite nanofibers (GNFs) were prepared by ammonia and heat treatment at temperatures up to $1000^{\circ}C$ to improve its $CO_2$ adsorption capacity. The effects of the heat treatment on the textural properties and surface chemistry of the GNFs were investigated by $N_2$ adsorption isotherms, XRD, and elemental analysis. We found that the chemical properties of GNFs were significantly changed after the ammonia treatment. Mainly amine groups were formed on the GNF surfaces such as lactam groups, pyrrole and pyridines. The GNFs treated at $500^{\circ}C$ showed highest $CO_2$ adsorption capacity of 26.9 mg/g at 273 K in this system.

Effect of KOH Activation on Electrochemical Behaviors of Graphite Nanofibers (KOH 활성화 효과에 의한 흑연나노섬유의 전기화학적 거동)

  • Yoo, Hye-Min;Min, Byung-Gak;Lee, Kyu-Hwan;Byun, Joon-Hyung;Park, Soo-Jin
    • Polymer(Korea)
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    • v.36 no.3
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    • pp.321-325
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    • 2012
  • In this work, we prepared the activated graphite nanofibers (A-GNFs) via chemical activation with KOH/GNFs ratios in a range of 0 to 5. The effect of KOH activation was studied in the surface and pore properties of the samples for electrochemical performance. The surface properties of A-GNFs were characterized by XRD and SEM measurements. The textural properties of the A-GNFs were investigated by $N_2$/77 K adsorption isotherms using Brunauer-Emmett-Teller (BET) equation. Their electrochemical behaviors were investigated by cyclic voltammetry and galvanostatic charge-discharge performance. From the results, electrochemical performances of the A-GNFs were improved with increasing the ratio of KOH reagent. It was found that specific surface area and total pore volume of the A-GNFs were increased by KOH activation.

Effect of Graphite Nanofibers Addition on the Electrochemical Behaviors of Platinum Nanoparticles Deposited on Activated Carbons (활성탄소에 담지된 백금나노입자의 전기화학적 거동에 대한 그라파이트 나노섬유 첨가효과)

  • Jo, Wonbin;Oh, Misoon;Kim, Juhyun;Kim, Seok
    • Korean Chemical Engineering Research
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    • v.48 no.6
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    • pp.673-678
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    • 2010
  • In the present study, mixed carbon-supported platinum(Pt) nanoparticles were prepared by a chemical reduction method of Pt precursor solution on two types of carbon materials such as activated carbons(ACs) and graphite nanofibers(GNFs). Average crystalline sizes and loading levels of Pt metal particles could be controlled by changing a content of GNFs. The highest electroactivity for methanol oxidation was obtained by preparing the carbon supports having 15 wt% GNFs. Furthermore, with an increase of GNFs content from 0% to 15%, an electrical conductivity was changed from $10^{-4}S/cm$ to $10^{-1}S/cm$. By an introduction of 10 wt% GNFs additive, the electroactivity of platinum particles was enhanced, but was saturated in the case of 15 wt% GNFs contents. This was related with the fact that the electroactivity change was dependent on the electrical conductivity of mixed carbon supports and Pt particle deposition content or deposition morphology.

KOH-activated graphite nanofibers as CO2 adsorbents

  • Yuan, Hui;Meng, Long-Yue;Park, Soo-Jin
    • Carbon letters
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    • v.19
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    • pp.99-103
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    • 2016
  • Porous carbons have attracted much attention for their novel application in gas storage. In this study, porous graphite nano-fiber (PGNFs)-based graphite nano fibers (GNFs) were prepared by KOH activation to act as adsorbents. The GNFs were activated with KOH by changing the GNF/KOH weight ratio from 0 through 5 at 900℃. The effects of the GNF/KOH weight ratios on the pore structures were also addressed with scanning electron microscope and N2 adsorption/desorption measurements. We found that the activated GNFs exhibited a gradual increase of CO2 adsorption capacity at CK-3 and then decreased to CK-5, as determined by CO2 adsorption isotherms. CK-3 had the narrowest micropore size distribution (0.6–0.78 nm) among the treated GNFs. Therefore, KOH activation was not only a significant method for developing a suitable pore-size distribution for gas adsorption, but also increased CO2 adsorption capacity as well. The study indicated that the sample prepared with a weight ratio of ‘3’ showed the best CO2 adsorption capacity (70.8 mg/g) as determined by CO2 adsorption isotherms at 298 K and 1 bar.

Electro-catalytic Performance of PtRu Catalysts Supported on Urea-treated MWNTs for Methanol Oxidation

  • Park, Jeong-Min;Park, Soo-Jin
    • 한국신재생에너지학회:학술대회논문집
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    • 2009.11a
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    • pp.159-159
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    • 2009
  • In this work, nitrogen and oxygen functionalities was introduced to the graphite nanofibers (GNFs) and their effect on electrocatalytic performance of the GNF supports for direct methanol fuel cells (DMFCs) was invesigated. The nitrogen and oxygen groups were introduced through the urea treatments and acid treatment, respectively. And, PtRu catalysts deposited on modified GNFs were prepared by a chemical reduction method. The catalysts were characterized by means of elemental analysis, nitrogen adsorption, and X-ray photoelectron spetroscopy (XPS). The structure and morphological characteristics of the catalysts were characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM). As a result, the Pt-Ru nanoparticles were impregnated on GNFs with good formation in 3-5 nm. And, the cyclic voltammograms for methanol oxidation revealed that the methanol oxidation peak varied depending on changes of surface functional groups. It was thus considered that the PtRu deposition was related to the reduction of PtRu and surface characteristics of the carbon supports. The changes of surface functional groups were related to PtRu reduction, significantly affect the methanol oxidation activity of anode electrocatalysts in DMFCs.

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Efficient Optimization Method for Polynomial Selection (다항식 선택을 위한 효율적인 최적화 기법)

  • Kim, Suhri;Kwon, Heetaek;Lee, Yongseong;Chang, Nam Su;Yoon, Kisoon;Kim, Chang Han;Park, Young-Ho;Hong, Seokhie
    • Journal of the Korea Institute of Information Security & Cryptology
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    • v.26 no.3
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    • pp.631-643
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    • 2016
  • Currently, General Number Field Sieve(GNFS) is known as the most efficient way for factoring large numbers. CADO-NFS is an open software based on GNFS, that was used to factor RSA-704. Polynomial selection in CADO-NFS can be divided into two stages - polynomial selection, and optimization of selected polynomial. However, optimization of selected polynomial in CADO-NFS is an immense procedure which takes 90% of time in total polynomial selection. In this paper, we introduce modification of optimization stage in CADO-NFS. We implemented precomputation table and modified optimization algorithm to reduce redundant calculation for faster optimization. As a result, we select same polynomial as CADO-NFS, with approximately 40% decrease in time.

Enhanced Polynomial Selection Method for GNFS (GNFS를 위한 향상된 다항식 선택 기법)

  • Kim, Suhri;Kwon, Jihoon;Cho, Sungmin;Chang, Nam Su;Yoon, Kisoon;Han, Chang;Park, Young-Ho;Hong, Seokhie
    • Journal of the Korea Institute of Information Security & Cryptology
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    • v.26 no.5
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    • pp.1121-1130
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    • 2016
  • RSA cryptosystem is one of the most widely used public key cryptosystem. The security of RSA cryptosystem is based on hardness of factoring large number and hence there are ongoing attempt to factor RSA modulus. General Number Field Sieve (GNFS) is currently the fastest known method for factoring large numbers so that CADO-NFS - publicly well-known software that was used to factor RSA-704 - is also based on GNFS. However, one disadvantage is that CADO-NFS could not always select the optimal polynomial for given parameters. In this paper, we analyze CADO-NFS's polynomial selection stage. We propose modified polynomial selection using Chinese Remainder Theorem and Euclidean Distance. In this way, we can always select polynomial better than original version of CADO-NFS and expected to use for factoring RSA-1024.

ON NONLINEAR POLYNOMIAL SELECTION AND GEOMETRIC PROGRESSION (MOD N) FOR NUMBER FIELD SIEVE

  • Cho, Gook Hwa;Koo, Namhun;Kwon, Soonhak
    • Bulletin of the Korean Mathematical Society
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    • v.53 no.1
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    • pp.1-20
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    • 2016
  • The general number field sieve (GNFS) is asymptotically the fastest known factoring algorithm. One of the most important steps of GNFS is to select a good polynomial pair. A standard way of polynomial selection (being used in factoring RSA challenge numbers) is to select a nonlinear polynomial for algebraic sieving and a linear polynomial for rational sieving. There is another method called a nonlinear method which selects two polynomials of the same degree greater than one. In this paper, we generalize Montgomery's method [12] using geometric progression (GP) (mod N) to construct a pair of nonlinear polynomials. We also introduce GP of length d + k with $1{\leq}k{\leq}d-1$ and show that we can construct polynomials of degree d having common root (mod N), where the number of such polynomials and the size of the coefficients can be precisely determined.