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Li, Yuanyuan,Mi, Yiming,Chung, Jin Suk,Kang, Sung Gu Elsevier 2018 International journal of hydrogen energy Vol.43 No.4
<P><B>Abstract</B></P> <P>The structural stability and hydrogen release properties of M-doped KMgH<SUB>3</SUB> (M = Li, Na, Rb, or Cs) were examined using density functional theory (DFT) calculations. The reaction enthalpies (ΔH) of the four possible dehydrogenation reaction pathways were calculated using the doped structures with different phases ( P m 3 ¯ m , P<I>nma</I>, and R3<I>c</I>). The most favorable reaction pathway among these four pathways was found. Among the dopants investigated, the most promising dopant for this reaction was Li. In addition, the application of pressure was found to be useful for tuning the reaction enthalpies of the dehydrogenation reactions. Overall, the results present an efficient means of designing new promising perovskite-type hydrides for hydrogen storage.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Perovskite-type KMgH<SUB>3</SUB> is a promising candidate for hydrogen storage. </LI> <LI> The most favorable reaction pathway of dehydrogenation reactions was examined. </LI> <LI> Li was the most useful and effective dopant to release hydrogen. </LI> <LI> Pressure can be usefully employed for tuning the reaction enthalpies of dehydrogenation reactions. </LI> </UL> </P>
석탄바닥재로 제조된 결정화 유리의 물리적 특성에 미치는 Li<sub>2</sub>O 첨가 영향
엄누리,강승구,Um, Noo-Li,Kang, Seung-Gu 한국재료학회 2010 한국재료학회지 Vol.20 No.2
Glass-ceramics were fabricated by heat-treatment of glass obtained by melting a coal bottom ash with $Li_2O$ addition. The main crystal grown in the glass-ceramics, containing 10 wt% $Li_2O$, was $\beta$-spodumene solid solution, while in $Li_2O$ 20 wt% specimen was mullite, identified using XRD. The activation energy and Avrami constant for crystallization were calculated and showed that bulk crystallization behavior will be predominant, and this expectation agreed with the microstructural observations. The crystal phase grown in $Li_2O$ 10 wt% glass-ceramics had a dendrite-like shaped whereas the shape was flake-like in the 20 wt% case. The thermal expansion coefficient of the $Li_2O$ 10 wt% glass-ceramics was lower than that of the glass having the same composition, owing to the formation of a $\beta$-spodumene phase. For example, the thermal expansion coefficient of $Li_2O$ 10 wt% glass-ceramics was $20\times10^{-7}$, which is enough for application in various heat-resistance fields. But above 20 wt% $Li_2O$, the thermal coefficient expansion of glass-ceramics, on the contrary, was higher than that of the same composition glass, due to formation of mullite.
Zheng, Yongping,Song, Kyeongse,Jung, Jaepyeong,Li, Chenzhe,Heo, Yoon-Uk,Park, Min-Sik,Cho, Maenghyo,Kang, Yong-Mook,Cho, Kyeongjae American Chemical Society 2015 Chemistry of materials Vol.27 No.9
<P>Li-O-2 batteries provide high-capacity energy storage, but for aprotic Li-O-2 batteries, it is reported that the charge-discharge efficiency is ultimately limited by the crystal growth of insoluble Li2O2 on the porous cathode. Catalysts have been reported to improve the nucleation and morphology of Li2O2, which helps achieve high energy densities. We provide a new insight into the catalytic mechanism of the oxygen reduction reaction (ORR) in aprotic Li-O-2 batteries the oxygen sites on the surface play a more important role than the exposed metal sites via a study based on the density functional theory (DFT) examining alpha-MnO2 surfaces. Lithium ions from electrolytes are found to interact with the surface oxygen sites and form surface lithium sites, facilitating further growth of Li2O2. A larger number of initial growth points with uniform distribution makes Li2O2 well dispersed, forming small particles, which benefit both the ORR and oxygen evolution reactions (OER). This design concept for oxygen sites has been successfully validated by the real Li-O-2 cell experiments with alpha-MnO2 nanowire cathodes.</P>
리튬이차전지용 Li-Mn-O 계 양극활물질의 충방전 특성에 관한 연구
강탁,이선엽 대한금속재료학회(대한금속학회) 1995 대한금속·재료학회지 Vol.33 No.1
The characteristics of Li-Mn-O ternary compound was studied as a cathode active material for lithium secondary batteries. Li-Mn-O cathode active materials were prepared by the reaction of γ-MnO₂(EMD) and LiOH·H₂O at 375℃ with various molar ratios. As the contents of lithium increased, the cyclic reversihility was improved. Compound with Li/Mn=3/7 molar ratio showed the best results, considering reversibility and discharge capacity at the same time. The effects of the types of MnO₂ on the cyclic behaviour were also studied. It was shown that the channel structure of MnO₂ played important roles on the cyclic behaviour of Li-Mn-O cathode. Themodynamically, the larger the channel size, the greater the discharge capacity. The α-phase, however, which has the largest [2×2] channels showed lower lithium ion diffusivity than the γ phase having [1×2]+[1×1] channels. It was thought that this behaviour was attributed to the impurities inserted in the process of synthesis of α-MnO₂, So, as the discharge rate increased, γ-phase showed better result than α phase.
Li, Ziwei,Yang, Junghoon,Agyeman, Daniel Adjei,Park, Mihui,Tamakloe, Wilson,Yamauchi, Yusuke,Kang, Yong-Mook The Royal Society of Chemistry 2018 Journal of Materials Chemistry A Vol.6 No.22
<P>A great challenge in the application of carbon-based materials to Li-O2 batteries is to prevent the formation of carbonate-based side products, thereby extending the cycle life of Li-O2 batteries. Herein, for the first time, CNT@Ni@NiCo silicate core-shell nanocomposite is designed and used as a cathode catalyst in Li-O2 batteries. This nanocomposite shows a promising electrochemical performance with a discharge capacity of 10 046 mA h gcat<SUP>−1</SUP> and a low overpotential of 1.44 V at a current density of 200 mA gcat<SUP>−1</SUP>, and it can sustain for more than 50 cycles within the voltage range of 2-4.7 V. X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD) characterizations prove that the formation of Li2CO3 and other side products are prevented, likely due to the encapsulation of CNTs by NiCo silicates and Ni nanoparticles, which may help decompose the side products. Finally, the synergistic effects, which are contributed by the high electrical conductivity of CNTs, high surface area, the high oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) activities of NiCo silicate, and the simple decomposition of side products by Ni nanoparticles enable outstanding performance of the CNT@Ni@NiCo silicate core-shell nanocomposite as a cathode catalyst for Li-O2 batteries.</P>
Lipolysis Effect of Daucosterol Isolated from Mulberry (Morus alba) Leaves
Ke Li1(이커),Mi Lim Lee(이미림),Lu Que(루쿼),Mae Li(이매),Jum Soon Kang(강점순),Yung Hyun Choi(최영현),Kyung Mi Kim(김경미),Jae-Chul Jung(정재철),Dae Youn Hwang(황대연),Young Whan Choi(최영환) 한국생명과학회 2017 생명과학회지 Vol.27 No.12
뽕나무는 약 40여 속과 1,000여 종이 있는 것으로 알려져 있으며, 항염증, 항진정, 지사작용, 노화억제 및 신경보호작용이 있는 것으로 알려져 있다. 본 연구에서는 아시아 지역에서 전통 한약재로 사용되는 뽕 나무 잎의 지방분해 활성에 관여하고 있는 물질을 스크린하기 위하여 뽕잎 분말을 헥산, 에틸 아세테이트 및 메탄올로 순차 추출하였다. 뽕 잎의 EtOAc 추출물로부터 daucosterol이 순수분리 되었으며, 그 구조는 1H, 13C, DEPT, COSY, HSQC 및 HMBC 등의 NMR스펙트럼 분석에 의해 밝혀졌다. Daucosterol은 농도 의존적으로 지질분해 효과를 나타내었는데, 본 연구의 결과로부터 뽕나무 잎으로부터 순수분리한 daucosterol의 지분분해 활성은 다양한 질병을 치료하기 위한 천연물 소재 또는 지표성분으로서 활용이 가능할 것으로 생각된다. 그러나 보다 효율적으로 이용하기 위해서는 daucosterol의 비만에 관한 생리활성 기작에 대한 추가적인 연구가 필요할 것이다. Plants are reservoirs of naturally occurring chemical compounds and of structurally diverse bioactive molecules. The aim of this investigation was to screen for the presence of phytochemicals responsible for the lipolysis activity in mulberry (Morus alba) leaves, which are important in traditional Asian medicinal plants. Powdered mulberry leaves were extracted with hexane, ethyl acetate, and methanol. Daucosterol was isolated from the EtOAc extract of mulberry leaves, and its structure was elucidated by NMR spectral analyses. The NMR assignments for the compound were determined using 1H, 13C, DEPT, COSY, HSQC, and HMBC NMR spectral data. Daucosterol showed a concentration-dependent lipolysis activity that may impart medicinal properties that can be exploited by medical practitioners for the treatment of various diseases. However, further studies should be conducted to elucidate additional mechanisms of daucosterol.
Dispersion of carbon nanotubes in aluminum improves radiation resistance
So, Kang Pyo,Chen, Di,Kushima, Akihiro,Li, Mingda,Kim, Sangtae,Yang, Yang,Wang, Ziqiang,Park, Jong Gil,Lee, Young Hee,Gonzalez, Rafael I.,Kiwi, Miguel,Bringa, Eduardo M.,Shao, Lin,Li, Ju unknown 2016 Nano energy Vol.22 No.-
<P><B>Abstract</B></P> <P>We can mass-produce metal/carbon nanotube (CNT) composites that show improved radiation tolerance. The 0.5wt% Al+CNT composite showed improved tensile strength without reduction of tensile ductility before radiation, and reduced void/pore generation and radiation embrittlement at high displacements per atom (DPA). Under helium ion irradiation up to 72DPA, the 1D carbon nanostructures survive, while sp<SUP>2</SUP> bonded graphene transforms to sp<SUP>3</SUP> tetrahedral amorphous carbon. Self-ion (Al) irradiation converts CNTs to a metastable form of Al<SUB>4</SUB>C<SUB>3</SUB>, but still as slender 1D nanorods with prolific internal interfaces that catalyze recombination of radiation defects, reducing radiation hardening and porosity generation. The 1D fillers may also form percolating paths of “nano-chimneys” that outgas the accumulated helium and other fission gases, providing an essential solution to the gas accumulation problem.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Dispersion of CNTs showed improved tensile strength without reduction of ductility. </LI> <LI> CNTs in Al reduced void/pore generation and radiation embrittlement at high DPA. </LI> <LI> Under He ion irradiation, 1D CNTs survive, while sp<SUP>2</SUP> bond transform to sp<SUP>3</SUP> carbon. </LI> <LI> Formation of metastable 1D Al<SUB>4</SUB>C<SUB>3</SUB> from CNTs still recombine radiation defects. </LI> <LI> This nanocomposite can help improve bulk properties for nuclear applications. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>