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Electrical Conductivity Behavior of Chemically Surface Modified MWNTs in Epoxy Matrix Composites
Joohyuk Park,Abu Bakar Bin Sulong 대한기계학회 2006 대한기계학회 춘추학술대회 Vol.2006 No.6
Few attempt to study the effects of chemical surface modification carbon nanotubes (CNTs) to the electrical conductivity nanocomposites instead to increase dispersion and interfacial bonding strength between CNTs and polymer matrix. Therefore, the electrical conductivity of two type’s chemical surface modified (carboxylated and octadecylated) multi-walled carbon nanotubes (MWNTs), non ionic surfactant additive MWNTs and as produced MWNTs reinforced epoxy nanocomposites are investigated by as function of MWNTs concentration. As-produced MWNTs and surfactant additive MWNTs nanocomposites resulted higher electrical conductivity at low loading concentration. However, chemically surface modified MWNTs significantly decreased the electrical conductivity of epoxy nanocomposite. Therefore, it can be deduced that the chemically surface modified MWNTs are not suitable electrical applications.
공침법을 통한 나노로드 형태의 니켈계 양극 소재 개발에 관한 연구
박주혁 ( Joohyuk Park ) 한국전기전자재료학회 2024 전기전자재료학회논문지 Vol.37 No.2
Ni-rich cathode materials have been developed as the most promising candidates for next-generation cathode materials for lithium-ion batteries because of their high capacity and energy density. In particular, the electrochemical performance of lithium-ion batteries could be enhanced by increasing the contents of nickel ion. However, there are still limitations, such as low structural stability, cation mixing, low capacity retention and poor rate capability. Herein, we have successfully developed the nanorod-type Ni-rich cathode materials by using co-precipitation method. Particularly, the nanorod-type primary particles of LiNi<sub>0.7</sub>Co<sub>0.15</sub>Mn<sub>0.15</sub>O<sub>2</sub> could facilitate the electron transfer because of their longitudinal morphology. Moreover, there were holes at the center of secondary particles, resulting in high permeability of the electrolyte. Lithium-ion batteries using the prepared nanorod-type LiNi<sub>0.7</sub>Co<sub>0.15</sub>Mn<sub>0.15</sub>O<sub>2</sub> achieved highly improved electrochemical performance with a superior rate capability during battery cycling.
Park, Joohyuk,Risch, Marcel,Nam, Gyutae,Park, Minjoon,Shin, Tae Joo,Park, Suhyeon,Kim, Min Gyu,Shao-Horn, Yang,Cho, Jaephil Royal Society of Chemistry 2017 ENERGY AND ENVIRONMENTAL SCIENCE Vol.10 No.1
<P>Oxygen reduction reaction (ORR) or oxygen evolution reaction (OER) electrocatalysts including carbon-, non-precious metal-, metal alloy-, metal oxide-, and carbide/nitride-based materials are of great importance for energy conversion and storage technologies. Among them, metal oxides (<I>e.g.</I>, perovskite and pyrochlore) are known to be promising candidates as electrocatalysts. Nevertheless, the intrinsic catalytic activities of pyrochlore oxides are still poorly understood because of the formation of undesirable phases derived from the synthesis processes. Herein, we present highly pure single crystalline pyrochlore nanoparticles with metallic conduction (Pb2Ru2O6.5) as an efficient bi-functional oxygen electrocatalyst. Notably, it has been experimentally shown that the covalency of Ru-O bonds affects the ORR and OER activities by comparing the X-ray absorption near edge structure (XANES) spectra of the metallic Pb2Ru2O6.5and insulating Sm2Ru2O7for the first time. Moreover, we followed the interatomic distance changes of Ru-O bonds using<I>in situ</I>X-ray absorption spectroscopy (XAS) to investigate the structural stabilities of the pyrochlore catalysts during electrocatalysis. The highly efficient metallic Pb2Ru2O6.5exhibited outstanding bi-functional catalytic activities and stabilities for both ORR and OER in aqueous Zn-air batteries.</P>
Park, Joohyuk,Park, Minjoon,Nam, Gyutae,Kim, Min Gyu,Cho, Jaephil American Chemical Society 2017 NANO LETTERS Vol.17 No.6
<P>Zn-air batteries suffer from the slow kinetics of oxygen reduction reaction (ORR) and/or oxygen evolution reaction (OER). Thus, the bifunctional electrocatalysts are required for the practical application of rechargeable Zn-air batteries. In terms of the catalytic activity and structural stability, pyrochlore oxides (A(2)[B(2-x)A(x)]O7-y) have emerged as promising candidates. However, a limited use of A-site cations (e.g., lead or bismuth cations) of reported pyrochlore catalysts have hampered broad understanding of their catalytic effect and structure. More seriously, the catalytic origin of the pyrochlore structure was not clearly revealed yet. Here, we report the new nano crystalline yttrium ruthenate (Y-2[Ru2-xYx]O7-y) with pyrochlore structure. The prepared pyrochlore oxide demonstrates comparable catalytic activities in both ORR. and OER, compared to that of previously reported metal oxide-based catalysts such as perovskite oxides. Notably, we first find that the catalytic activity of the Y-2[Ru2-xYx]O7-y is associated with the oxidations and corresponding changes of geometric local structures of yttrium and ruthenium ions during electrocatalysis, which were investigated by in situ X-ray absorption spectroscopy (XAS) in real-time. Zn-air batteries using the prepared pyrochlore oxide achieve highly enhanced charge and discharge performance with a stable potential retention for 200 cycles.</P>
기능화된 다중벽 탄소나노튜브 복합재료의 제조 및 물성 평가에 대한 연구
박주혁(Joohyuk Park),김태구(Taegoo Kim) 대한기계학회 2004 대한기계학회 춘추학술대회 Vol.2004 No.4
Chemically modified multiwalled carbon nanotubes with acids were incorporated into a epoxy matrix by in situ polymerization process, to improve the transfer of mechanical load through chemical bonds, which were demonstrated by infrared spectroscopy. And the mechanical properties of epoxy/carbon nanotube composites were measured to investigate the role of carbon nanotubes. The epoxy/carbon nanotube composites shows higher tensile strength and wear resistance than existing epoxy, with 1 or 2 wt. % addition of functionalized carbon nanotubes. The tensile strength with 7 wt. % carbon nanotibes is increased by a 28% and the wear resistance in exceptionally increased by an outstanding 100 times.
Multibody-FE Coupling을 이용한 정면 북미NCAP 조수석 승객상해 예측기법 연구
이주혁(JooHyuk Lee),최장훈(JangHoon Choi),이강욱(KangWook Lee) 한국자동차공학회 2011 한국자동차공학회 학술대회 및 전시회 Vol.2011 No.11
National Highway Traffic Safety Administration (NHTSA) enhanced the New Car Assessment Program (NCAP) rating program. The previous rating program was based on the combined chance of serious injury to the head and chest. Now, the new program includes all of the Federal Motor Vehicle Safety Standard (FMVSS) No. 208 body regions like head, neck, chest, and femur. The new program also uses a different crash test dummy (Hybrid III 5th%ile female dummy) in the frontal passenger side. In this paper, a comparative study on the femur load was accomplished to meet reliability and effectiveness.