A novel textile-like carbon wrapping for high-performance silicon anodes in lithium-ion batteries

Kim, Jong Min,Guccini, Valentina,Kim, Dongwon,Oh, Jiseop,Park, Seungman,Jeon, Youngmoo,Hwang, Taejin,Salazar-Alvarez, German,Piao, Yuanzhe The Royal Society of Chemistry 2018 Journal of Materials Chemistry A Vol.6 No.26

<P>Carbon coating is essential for active materials in electrochemical applications that are often insulators or poor conductors. A conventional conformal carbon coating can hinder the ion diffusion to and from the active material and form an isolated conducting network. Especially, active materials with very large volume expansion, <I>e.g.</I>, silicon, can destroy the carbon coating during lithiation, which makes conformal carbon coating inappropriate. This paper presents a novel textile-like carbon wrapping that provides efficient electron and ion diffusion paths <I>via</I> a wide-range carbon network and pores. The textile-like carbon wrapping can reduce the electrical contact loss during cycling through the wide-range carbon network, which makes it a suitable carbon coating for materials that undergo volume expansion. A textile-like carbon-wrapped silicon is formed by pyrolysis of a dried suspension of silicon nanoparticles mixed with enzymatically hydrolyzed cellulose nanofibers. It shows excellent electrochemical performance compared to a conformal carbon-coated silicon. It exhibits a reversible specific capacity of 680 mA h g<SUP>−1</SUP> at 8.0 A g<SUP>−1</SUP> and shows excellent cycling stability (capacity retention of 94.5% after 500 cycles at 2.0 A g<SUP>−1</SUP>) with high Si content (95.71 wt%). Therefore, this novel textile-like carbon wrapping can be utilized in many electrochemical applications instead of the conventional carbon coating, especially for active materials that undergo large volume expansion.</P>

Novel two-step activation of biomass-derived carbon for highly sensitive electrochemical determination of acetaminophen

Kim, Dongwon,Kim, Jong Min,Jeon, Youngmoo,Lee, Jeongyeon,Oh, Jiseop,Hooch Antink, Wytse,Kim, Daekyu,Piao, Yuanzhe Elsevier 2018 Sensors and actuators. B, Chemical Vol.259 No.-

<P><B>Abstract</B></P> <P>The determination of the concentration of acetaminophen (AC) in the human body is of significant importance to carefully monitor and regular drug safety and public health. However, most conventional methods are insufficient due to their time-consuming, expensive and complicated nature. In this study, we report a novel two-step activation of biomass-derived carbon for the electrochemical determination of AC. The electrode material is prepared by a two-step activation process, which involves the initial activation of kelp powder with ZnCl<SUB>2</SUB>, followed by an activation step with KOH. The activation procedure greatly increased the overall pore volume and specific surface area. The characterizations of ZnCl<SUB>2</SUB>-KOH activated kelp carbon (ZKAKC) were conducted with scanning electron microscopy (SEM), transmission electron microscopy (TEM), Raman spectroscopy, Brunauer-Emmett-Teller (BET) surface area analysis, and electrochemical impedance spectroscopy (EIS). The electrochemical characterization of ZKAKC was performed with cyclic voltammetry (CV) analysis of potassium ferricyanide. The sensing ability of ZKAKC/GCE toward acetaminophen was conducted using CV analysis and differential pulse voltammetry (DPV). The modified electrode showed high sensitivity, selectivity and a good detection limit for the determination acetaminophen with the detection limit of 0.004 μM. Also, the modified electrode showed good result toward acetaminophen even in the presence of ascorbic acid and dopamine with the detection limit of 0.007 μM. For the evaluation of sensing ability as an actual electrochemical sensor, a real sample test was conducted. The electrochemical performance was enhanced due to the increased physical and electrochemical surface area, which occurred during the two-step activation process. This approach for producing activated carbon is crucial for future development and can be applied to different carbon source materials.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Activated carbon was prepared with a novel two-step activation process. </LI> <LI> Kelp is used as source material for the biomass-derived activated carbon. </LI> <LI> The modified electrode was used for the electrochemical determination of acetaminophen. </LI> <LI> High sensitivity toward acetaminophen and a low detection limit were achieved. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

Fabrication and characterization of powder metallurgy tantalum components prepared by high compaction pressure technique

Kim, Youngmoo,Lee, Dongju,Hwang, Jaewon,Ryu, Ho Jin,Hong, Soon Hyung Elsevier 2016 Materials characterization Vol.114 No.-

<P><B>Abstract</B></P> <P>The present study has investigated the consolidation behaviors of tantalum powders during compaction and sintering, and the characteristics of sintered components. For die compaction, the densification behaviors of the powders are simulated by finite element analyses based on the yield function proposed by Shima and Oyane. Accordingly, the green density distribution for coarser particles is predicted to be more uniform because they exhibits higher initial relative tap density owing to lower interparticle friction. It is also found that cold isostatic pressing is capable of producing higher dense compacts compared to the die pressing. However, unlike the compaction behavior, the sintered density of smaller particles is found to be higher than those of coarser ones owing to their higher specific surface area. The maximum sintered density was found to be 0.96 of theoretical density where smaller particles were pressed isostatically at 400MPa followed by sintering at 2000°C. Moreover, the effects of processing conditions on grain size and texture were also investigated. The average grain size of the sintered specimen is 30.29μm and its texture is less than 2 times random intensity. Consequently, it is concluded that the higher pressure compaction technique is beneficial to produce high dense and texture-free tantalum components compared to hot pressing and spark plasma sintering.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Higher Ta density is obtained from higher pressure and sintering temperature. </LI> <LI> High compaction method enables P/M Ta to achieve the density of 16.00g·cm<SUP>−3</SUP>. </LI> <LI> A P/M Ta component with fine microstructure and random orientation is developed. </LI> </UL> </P>

Solid-state sintering mechanism of blended elemental Ti-6Al-4V powders

Kim, Youngmoo,Song, Young-Beom,Lee, Sung Ho The Korean Powder Metallurgy Institute 2018 한국분말재료학회지 (KPMI) Vol.25 No.2

The objective of this study is to reveal the sintering mechanism of mixed Ti-6Al-4V powders considering the densification and the homogenization between Ti and Al/V particles. It is found that the addition of master alloy particles into Ti enhances densification by the migration of Al into the Ti matrix prior to the self-diffusion of Ti. However, as Ti particles become coarser, sintering of the powders appears to be retarded due to slower inter-diffusion of the particles due to the reduced surface energies of Ti. Such phenomena are confirmed by a series of dilatometry tests and microstructural analyses in respect to the sintering temperature. Furthermore, the results are also consistent with the predicted activation energies for sintering. The energies are found to have decreased from 299.35 to $135.48kJ{\cdot}mol^{-1}$ by adding the Al/V particles because the activation energy for the diffusion of Al in ${\alpha}-Ti$ ($77kJ{\cdot}mol^{-1}$) is much lower than that of the self-diffusion of ${\alpha}-Ti$. The coarser Ti powders increase the energies from 135.48 to $181.16kJ{\cdot}mol^{-1}$ because the specific surface areas of Ti decrease.

Zeolitic imidazolate frameworks derived novel polyhedral shaped hollow Co-B-O@Co₃O₄ electrocatalyst for oxygen evolution reaction

Kim, Dongwon,Kim, Daekyu,Jeon, Youngmoo,Li, Yong,Lee, Jeongyeon,Kang, Jeongmin,Lee, Lawrence Yoon Suk,Piao, Yuanzhe Elsevier 2019 ELECTROCHIMICA ACTA Vol.299 No.-

<P><B>Abstract</B></P> <P>The development of highly effective and low-cost non-noble metal electrochemical catalysts for oxygen evolution reactions (OER) is a major challenge for overall water splitting and rechargeable metal-air batteries. In this study, we develop a novel hollow cobalt-borate modified cobalt oxide composite (denoted by Co-B-O@Co<SUB>3</SUB>O<SUB>4</SUB>) catalyst derived from zeolitic imidazolate framework-67 (ZIF-67) for electrochemical OER. The Co-B-O@Co<SUB>3</SUB>O<SUB>4</SUB> was easily synthesized via pyrolysis of ZIF-67 in Ar and air to produce hollow Co<SUB>3</SUB>O<SUB>4</SUB> (denoted by h-Co<SUB>3</SUB>O<SUB>4</SUB>), followed by simple NaBH<SUB>4</SUB> treatment at ambient temperature for 4 h. The unique polyhedral morphology was well preserved during the NaBH<SUB>4</SUB> treatment. Benefiting from its structural and compositional merit, the as-synthesized Co-B-O@Co<SUB>3</SUB>O<SUB>4</SUB> exhibit excellent electrocatalytic activity and long-term stability for OER. Also, we conducted the OER test using a Co-B-O@Co<SUB>3</SUB>O<SUB>4</SUB> catalyst in a neutral pH environment for further investigation. Our study can provide an insight into catalyst modification step to enhance the overall performance while keeping its physical structure simultaneously. using metal-organic framework for the electrochemical catalyst thus can be recognized as a method for producing a highly active, long-term working and novel engineered electrocatalyst for OER applications.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Co-B-O@Co<SUB>3</SUB>O<SUB>4</SUB> was prepared using calcination-NaBH<SUB>4</SUB> treatment strategy with a facile and energy efficient method. </LI> <LI> A distinctive polyhedral morphology of Co-B-O@Co<SUB>3</SUB>O<SUB>4</SUB> was well preserved after the NaBH<SUB>4</SUB> treatment of its precursor material. </LI> <LI> Co-B-O@Co<SUB>3</SUB>O<SUB>4</SUB> was employed for the electrochemical oxygen evolution reaction. </LI> <LI> Co-B-O@Co<SUB>3</SUB>O<SUB>4</SUB> showed excellent catalytic performance and long-term durability for oxygen evolution reaction in basic media. </LI> </UL> </P>

전기 도금 법으로 제조된 Cu 박막 구조물의 탄성계수와 미세조직과의 연관성 연구

김영무(Youngmoo Kim),한준희(Jun-Hee Hahn),이창승(Chang Seung Lee),박준협(Jun-Hyub Park),홍순형(Soon Hyung Hong) 대한기계학회 2003 대한기계학회 춘추학술대회 Vol.2003 No.8

This paper reports on the manufacturing, surface morphology and Young's modulus of Cu thin films used as MEMS (micro-electro-mechanical systems) devices. Nanoindentation test and microcantilever bending test were performed to evaluate the mechanical properties, especially Young's modulus of these thin films. Cu thin film specimens were produced by MEMS fabrication techniques such as sputtering, electrochemical deposition, lithography and silicon bulk micromachining. Surface morphologies of specimens were measured by atomic force microscopy (AFM). Young's moduli of Cu electrodeposited films were decreased with increasing the thickness of specimens. From these results, it was shown that Young's modulus of Cu thin films had anisotropy with crystal orientations. Elastic moduli were varied with the thickness of thin film due to the texture of Cu thin films. Young's modulus of Cu thin films can be predicted by using two methods. One is to use the elastic modulus of single crystal and the information of distribution of crystal orientation, Voigt model. The other is to calculate it from load-deflection curves computed with ABAQUS. The theoretical estimation of elastic modulus using texture analysis showed good agreement with the results of nanoindentation test. But in computational modeling, Young's moduli were different from the results of bending test with isotropic and anisotropic Cu beams having (001) texture.

외상성 슬관절 손상 환자의 보행분석

나영무 ( Youngmoo Na ),( Youngbae Kim ),( Youngjin Kim ),( Jaehyung Sa ),( Youngkyung Kim ) 국군의무사령부 1994 대한군진의학학술지 Vol.25 No.1

A study on entomopathogenic nematode symbiotic bacteria in Korea

Namjun Chung,Seongmo Koo,Youngjoon Kim,Geungon Kim,Dajeong Son,Youngmoo Choo,Yeojin Kim,Gilsang Jeong 한국응용곤충학회 2022 한국응용곤충학회 학술대회논문집 Vol.2022 No.10

흉막삼출에서 흉수내 Adenosine Deaminase와 콜레스테롤의 감별 진단적 의의

김수성,권영무 동국대학교 경주대학 2000 東國論集 Vol.19 No.-

Pleural fluid can be divided into transudate and exudate, and the cause of it should be identified for the treatment. Pleural protein, glucose, and LDH were frequently used for differentiation. Recently, several laboratory tests including ADA(Adenosine deaminase) and cholesterol has been used for differentiation of pleural fluid. The ADA and cholesterol in the patients who were treated in the Department of Thoracic and Cardiovascular Suregry of Dongguk University Kyungju Hospital and Pohang Sunlin Hospital were studied. The patients were divided into four groups, group Ⅰ for transudate, group Ⅱ for malignant exudate, group Ⅲ for tuberculous exudate, and group Ⅳ for other inflammatory exudate. Statistical analysis was done by using repeated measures analysis of variance (ANOVA) and Kruskal-Wallis one-way ANOVA in the SPSS 8.0. The WBC count and glucose level were the good tests for the differentiation of pleural fluid, but the LDH level resulted in the borderline. The pleural ADA and cholesterol level were significantly different(p<0.05) between groups. So, these tests were thought to be good predictors for the differentiation of exudate.

下顎洞에 發生한 智齒의 症例

金守經,黃渶武 대한치과의사학회 1989 대한치과의사학회지 Vol.10 No.3