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Kim, Hyun Gyu,Kim, Riyul,Kim, Soohyun,Choi, Chanyong,Kim, Bugi,Guim, Hwanuk,Kim, Hee-Tak Elsevier 2018 Journal of industrial and engineering chemistry Vol.60 No.-
<P><B>Abstract</B></P> <P>There is an increasing need to develop an alternative to Nafion membrane in order to reduce the cost of vanadium redox flow batteries. Pore-filled composite membranes based on Nafion is one way to reduce the amount of costly material, however its chronic problem is low conductivity and water uptake ability. We suggest a novel approach to enhance the conductivity and water uptake by incorporating propylene carbonate to modulate water channel morphologies in Nafion directly. We present a pore-filled type Nafion composite membrane to prove the effect of PC addition. Small-angle X-ray scattering and simulation results are suggested for further understanding.</P>
Kim, Soohyun,Yuk, Seongmin,Kim, Hyun Gyu,Choi, Chanyong,Kim, Riyul,Lee, Jang Yong,Hong, Young Taik,Kim, Hee-Tak The Royal Society of Chemistry 2017 Journal of materials chemistry. A, Materials for e Vol.5 No.33
<▼1><P>A hydrocarbon/Nafion bilayer membrane is fabricated using a three-dimensionally interlocked interfacial layer for improved cycling durability of VRFBs.</P></▼1><▼2><P>Hydrocarbon (HC) membranes have not been successfully employed for vanadium redox flow batteries (VRFBs) due to their severe chemical degradation by highly oxidative VO2<SUP>+</SUP> ions in the positive electrolyte. Protective coating of chemically stable Nafion ionomers on HC membranes can retard the degradation, but how to achieve strong interfacial adhesion of the two layers without losing proton conductivity presents a challenge. Here, we report a sulfonated poly(arylene ether sulfone) (SPAES)/Nafion bilayer membrane (S/N membrane), the interface of which is mechanically fastened by a three-dimensionally interlocked interfacial layer (3-D IIL). The 3-D IIL, which features a ball and socket joint structure, strongly binds the two chemically dissimilar membranes and thus does not generate additional interfacial resistance for proton conduction. As a result, the VRFB with the S/N membrane achieves higher coulombic and energy efficiencies than that with Nafion 115. Moreover, it can operate more than 200 cycles in contrast to a sudden membrane failure after 110 cycles for the cell with a pristine SPAES membrane, demonstrating the efficacy of this approach.</P></▼2>
A review of vanadium electrolytes for vanadium redox flow batteries
Choi, Chanyong,Kim, Soohyun,Kim, Riyul,Choi, Yunsuk,Kim, Soowhan,Jung, Ho-young,Yang, Jung Hoon,Kim, Hee-Tak Elsevier 2017 RENEWABLE & SUSTAINABLE ENERGY REVIEWS Vol.69 No.-
<P><B>Abstract</B></P> <P>There is increasing interest in vanadium redox flow batteries (VRFBs) for large scale-energy storage systems. Vanadium electrolytes which function as both the electrolyte and active material are highly important in terms of cost and performance. Although vanadium electrolyte technologies have notably evolved during the last few decades, they should be improved further towards higher vanadium solubility, stability and electrochemical performance for the design of energy-dense, reliable and cost-effective VRFBs. This timely review summarizes the vanadium electrolyte technologies including their synthesis, electrochemical performances, thermal stabilities, and spectroscopic characterizations and highlights the current issues in VRFB electrolyte development. The challenges that must be confronted to further develop vanadium electrolytes may stimulate more researchers to push them forward.</P>
김동기(Dongki Kim),김원태(Wontae Kim),김기열(Kiyoul Kim),김찬영(Chanyong Kim),강신재(Shinjae Kang) 한국자동차공학회 2009 한국자동차공학회 지부 학술대회 논문집 Vol.2009 No.10
Materials design and processing development proposed in this research, aims at contributing to low price wear resistant automobile diesel engine parts. Dense bonding layer products were fabricated by solid diffusion bonding method. The hardness and TRS values obtained were 88HRA and 120㎏/㎟, respectively. Finally, teamwork consisting of company, university and research center will give them a chance of learning, processing, theory and applications in machine parts and will help domestic automobile industries internationally competitive.
A highly conducting graphene film with dual-side molecular n-doping.
Kim, Youngsoo,Park, Jaesung,Kang, Junmo,Yoo, Je Min,Choi, Kyoungjun,Kim, Eun Sun,Choi, Jae-Boong,Hwang, Chanyong,Novoselov, K S,Hong, Byung Hee RSC Pub 2014 Nanoscale Vol.6 No.16
<P>Doping is an efficient way to engineer the conductivity and the work function of graphene, which is, however, limited to wet-chemical doping or metal deposition particularly for n-doping, Here, we report a simple method of modulating the electrical conductivity of graphene by dual-side molecular n-doping with diethylenetriamine (DETA) on the top and amine-functionalized self-assembled monolayers (SAMs) at the bottom. The resulting charge carrier density of graphene is as high as -1.7 10(13) cm(-2), and the sheet resistance is as low as 86 39 ω sq(-1), which is believed to be the lowest sheet resistance of monolayer graphene reported so far. This facile dual-side n-doping strategy would be very useful to optimize the performance of various graphene-based electronic devices.</P>
Kim, Soohyun,Choi, Junghoon,Choi, Chanyong,Heo, Jiyun,Kim, Dae Woo,Lee, Jang Yong,Hong, Young Taik,Jung, Hee-Tae,Kim, Hee-Tak American Chemical Society 2018 NANO LETTERS Vol.18 No.6
<P>The laminated structure of graphene oxide (GO) membranes provides exceptional ion-separation properties due to the regular interlayer spacing (<I>d</I>) between laminate layers. However, a larger effective pore size of the laminate immersed in water (∼11.1 Å) than the hydrated diameter of vanadium ions (>6.0 Å) prevents its use in vanadium redox-flow batteries (VRFB). In this work, we report an ion-selective graphene oxide framework (GOF) with a <I>d</I> tuned by cross-linking the GO nanosheets. Its effective pore size (∼5.9 Å) excludes vanadium ions by size but allows proton conduction. The GOF membrane is employed as a protective layer to address the poor chemical stability of sulfonated poly(arylene ether sulfone) (SPAES) membranes against VO<SUB>2</SUB><SUP>+</SUP> in VRFB. By effectively blocking vanadium ions, the GOF/SPAES membrane exhibits vanadium-ion permeability 4.2 times lower and a durability 5 times longer than that of the pristine SPAES membrane. Moreover, the VRFB with the GOF/SPAES membrane achieves an energy efficiency of 89% at 80 mA cm<SUP>-2</SUP> and a capacity retention of 88% even after 400 cycles, far exceeding results for Nafion 115 and demonstrating its practical applicability for VRFB.</P> [FIG OMISSION]</BR>
Antiferromagnetic coupling of van der Waals ferromagnetic Fe<sub>3</sub>GeTe<sub>2</sub>
Kim, Dongseuk,Park, Sijin,Lee, Jinhwan,Yoon, Jungbum,Joo, Sungjung,Kim, Taeyueb,Min, Kil-joon,Park, Seung-Young,Kim, Changsoo,Moon, Kyoung-Woong,Lee, Changgu,Hong, Jisang,Hwang, Chanyong IOP Pub 2019 Nanotechnology Vol.30 No.24
<P>Among two-dimensional (2D) layered van der Waals materials, ferromagnetic 2D materials can be useful for compact low-power spintronic applications. One promising candidate material is Fe<SUB>3</SUB>GeTe<SUB>2</SUB> (FGT), which has a strong perpendicular magnetic anisotropy and relatively high Curie temperature. In this study, we confirmed that an oxide layer (O-FGT) naturally forms on top of exfoliated FGT and that an antiferromagnetic coupling (AFC) exists between FGT and O-FGT layers. From a first-principles calculation, oxide formation at the interface of each layer induces an AFC between the layers. An AFC causes a tailed hysteresis loop, where two-magnetization reversal curves are included, and a negative remanence magnetization at a certain temperature range.</P>