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Yonghyun Lim,Soonwook Hong,Kyung-Lim Jang,Hwichul Yang,Sehoon Hwang,Taek-Soo Kim,Young Beom Kim 한국정밀공학회 2020 International Journal of Precision Engineering and Vol.7 No.1
In this study, we developed a Ni/Pt bilayer catalytic anode that has high electrochemical activity and significantly reduced Pt loading amount, for low-temperature solid oxide fuel cells (LT-SOFCs). The Ni/Pt bilayer anodes with various thicknesses of the Pt catalytic active layer were fabricated on yttria-stabilized zirconia substrates via the direct current sputtering technique, and their performances were evaluated for the LT-SOFCs. The optimal thickness of the Pt catalytic layer for the Ni/Pt bilayer was found to be 10 nm based on the results for the fuel cell performance and electrochemical impedance spectroscopy (EIS) analysis. The optimal Pt10/Ni140 anode showed a cell performance and polarization resistance very similar to those of a reference single-phase Pt anode, while having only 7% of the Pt loading amount of the reference Pt anode. For the detailed morphological analysis of the bilayer structure anode, we employed the pull-off delamination process to analyze both the surface and interface morphologies of the bilayer anodes and the interface morphology of the Ni/Pt bilayer anodes after the operating test was analyzed. The results presented herein indicate the suitability of the methodology for the morphological analysis of thin-film bilayer structures and contribute to reduce the cost of membrane electrode assembly fabrication for LT-SOFCs, thus facilitating the commercialization of these systems.
Lim, Yonghyun,Lee, Hojae,Hong, Soonwook,Kim, Young-Beom Elsevier 2019 Journal of Power Sources Vol.412 No.-
<P><B>Abstract</B></P> <P>Nickel-samaria-doped ceria (Ni-SDC) nanocomposite anodes with various compositions are fabricated by co-sputtering technique. The film compositions are effectively controlled by adjusting the applied power to the SDC target while applying a constant power to the Ni target. The microstructure, crystallinity and electrical conductivity of the deposited films are analyzed and their optimal composition is investigated based on fuel cell performance and electrochemical impedance spectroscopy (EIS) analysis. Among various deposition conditions, the lowest polarization resistance is achieved at Ni-SDC 80W condition, which is attributed to the difference in the film composition and expected reaction site densities. Thin film fuel cells with the optimal nickel cermet anode are fabricated on a nanoporous supporting structure to achieve a high cell performance and compared with noble Pt electrode. The fuel cell with the optimal nickel cermet anode yields a maximum power density of 178 mW/cm<SUP>2</SUP> and polarization resistance of 0.55 Ω cm<SUP>2</SUP> at 450 °C, which is significantly improved from the reference Pt anode cell (113 mW/cm<SUP>2</SUP> and 1.69 Ω cm<SUP>2</SUP>). Impedance analysis clearly demonstrates that the enhancement in the cell performance originates from the difference in the polarization resistance, resulting from the expanded reaction sites owing to the mixed ion electronic conducting characteristics of the nickel cermet nanocomposite anode.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Ni-SDC nanocomposite anodes are fabricated by co-sputtering method. </LI> <LI> Optimal condition of the anode is investigated based on electrochemical performance. </LI> <LI> The expanded anode reaction sites significantly enhanced the fuel cell performance. </LI> <LI> Remarkable LT-SOFC performance is reported without precious metal anode. </LI> </UL> </P>
Yonghyun Lim,Kyoungwan Park 한국물리학회 2005 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.47 No.6
Er-doped SiOx (x < 2) films were deposited in an O2-filled atmosphere using a silicon target with an Er patch in a pulsed laser deposition system. The photoluminescence intensities observed at 1.54 μm depended on the oxygen pressure during the deposition and on the post-annealing time. Er-doped SiOx light-emitting diodes were fabricated, and broad electroluminescence spectra (from 1.2 to 1.6 μm) in the infrared range were obtained above the on-current density of 2 A/cm2 under several forward-bias voltages. The electroluminescence is attributed to the defect-state transitions in the SiOx (x < 2) films and to the Er3+ intra-4f transition. An experiment was conducted to compare the visible luminescence of undoped films with that of Er-doped films. This experiment involved the separation of the Si and the SiO2 phases with silicon nanoclusters formed and embedded in the film. The electroluminescence results point to the possibility of using a silicon-based light source for optical communication devices.
임용현(Yonghyun Lim),김영범(Young-Beom Kim) Korean Society for Precision Engineering 2022 한국정밀공학회지 Vol.39 No.2
A high temperature sintering process for solid electrolyte is the main cause of the increase in manufacturing costs of SOFCs. In this study, we developed a novel flash light sintering technique as an alternative sintering process of the conventional thermal sintering process. The YSZ electrolyte films were fabricated by conventional screen-printing method and the flash light sintering process and ESB sintering aid were applied to improve the flash light sinterability of the YSZ electrolyte. In the flash light sintering process, the effect of various pulse conditions such as energy density, and pulse interval were investigated and the microstructure, crystallinity, and sintering behavior of the sintered films were analyzed to demonstrate the effectiveness of the flash light sintering process. The flash light sintered YSZ electrolyte layer was used to fabricate the anode-supported SOFCs and its functionality is successfully demonstrated with the high open circuit voltage. The significance of this study includes minimization of the process time from tens of hours to just a few seconds, thus facilitating the commercialization of SOFCs.
임용현(Yonghyun Lim),이무형(Muhyoung Lee),양영찬(Youngchan Yang),함동우(Dongwoo Ham),윤태준(Taejun Yun) 한국추진공학회 2016 한국추진공학회 학술대회논문집 Vol.2016 No.5
발전용 대형 가스터빈은 효율 증대의 목적으로 TIT(Turbine Inlet Temperature)가 점차 증가하는 추세로 개발이 진행되고 있다. 이처럼, 고온, 고압의 환경에서 터빈 블레이드의 구조 건전성을 확보하기 위해서는 가혹한 운전환경에서도 적절한 강도를 유지할 수 있는 설계가 필요하다. 일반적으로 고온, 고압의 환경에서 구동되는 부품들은 온도 증가에 따른 재료 강도저하로 파손의 우려가 높으며, 기계적, 열적 하중에 의한 손상 메커니즘 이해를 통한 구조적 건전성 확보가 요구된다. 특히, 가스터빈 터빈 블레이드는 높은 TIT로 인한 재료 강도 저하로 구조 건전성 및 내구성 저하가 많이 우려가 되는 구성품 중 하나로, 구조적 불안정성을 유발하는 원인을 개선하여 구조적 안정성 및 신뢰성을 확보할 필요가 있다. 본 논문에서는 현재 개발중인 대형 가스터빈의 핵심 구성품인 냉각 블레이드에 대한 설계 결과를 바탕으로 구조 건전성을 평가함으로써 구동 중 발생할 수 있는 파손을 미연에 방지함과 동시에 설계 개선안을 제시하여 추후 블레이드 설계에 활용할 수 있도록 하였다.
스퍼터링 기법을 통해 증착된 저온형 고체 산화물 연료전지를 위한 YSZ 박막 전해질의 증착 온도에 따른 영향 분석
임용현(Yonghyun Lim),홍순욱(Soonwook Hong),배지웅(Jiwoong Bae),김영범(Young-Beom kim) 대한기계학회 2015 대한기계학회 춘추학술대회 Vol.2015 No.11
In this study, deposition temperature effects on the crystallinity and grain morphology of sputtered yttria stabilized zirconia (YSZ) thin films have been studied. With various deposition temperature conditions, we investigated relationship between deposition temperature and crystallinity and grain morphology by X-ray diffraction (XRD) and Atomic force microscopy (AFM) respectively. With increasing deposition temperature, highly textured YSZ thin films were observed in the deposition temperature range of 500ºC. The high temperature deposited YSZ thin film electrolyte showed much higher ionic conductivity than low temperature deposited films due to influence of crystallinity in oxygen ion conduction. In respect of grain morphology, more significant changes are observed. The low temperature deposited films showed nano-granular morphology which favorable to Oxygen Reduction Reaction (ORR) for fuel cell kinetics, but the high temperature deposited film showed agglomeration of nano-grains result in comparatively few reaction sites and low cell performances. The electrochemical impedance spectroscopy (EIS) and fuel cell current-voltage behavior verified little effect of crystallinity in cell performance, but grain morphology affect more significantly in the cell performance. The low temperature deposited films showed much lower electrode impedance and higher fuel cell performance than high temperature deposited films result from difference in nano-granular morphology and grain boundary density.
Lim, Jonghoon,Lee, Haerim,Ahn, Jiwon,Kim, Jeongjun,Jang, Joonseong,Park, Yonghyun,Jeong, Birang,Yang, Heejung,Shin, Soon Shik,Yoon, Michung Elsevier 2018 Journal of Ethnopharmacology Vol.225 No.-
<P><B>Abstract</B></P> <P><B>Ethnopharmacological relevance</B></P> <P>The herbal composition Gyeongshingangjeehwan 18 (GGEx18), composed of <I>Rheum palmatum</I> L. (Polygonaceae), <I>Laminaria japonica</I> Aresch (Laminariaceae), and <I>Ephedra sinica</I> Stapf (Ephedraceae), is used as an antiobesity drug in Korean clinics. The constituents of GGEx18 have traditionally been reported to inhibit obesity and related metabolic diseases such as insulin resistance and dyslipidemia.</P> <P><B>Objective</B></P> <P>This study investigated the effects of GGEx18 on nonalcoholic fatty liver disease (NAFLD) in mice fed a high-fat diet (HFD) and the underlying cellular and molecular mechanisms involved.</P> <P><B>Methods</B></P> <P>C57BL/6 J mice were fed either a low-fat diet (LFD), an HFD, or an HFD supplemented with GGEx18 (125, 250, or 500 mg/kg of body weight/day). After 13 weeks, blood analyses, histology, immunohistochemistry, and real-time PCR were performed to assess NAFLD development in these mice.</P> <P><B>Results</B></P> <P>Mice fed an HFD had increases in body weight, epididymal adipose tissue mass, adipocyte size, and adipose expression of inflammation-related genes compared with those fed an LFD. These increases were ameliorated in mice treated with 500 mg/kg/day GGEx18 without affecting food consumption profiles. GGEx18 not only decreased serum levels of triglycerides, free fatty acids, and alanine aminotransferase, but also decreased hepatic lipid accumulation, numbers of mast cells and α-smooth muscle actin-positive cells, and collagen levels induced by an HFD. Consistent with the histological data, the hepatic expression of lipogenesis-, inflammation-, and fibrosis-related genes was lower, while hepatic fatty acid β-oxidation-related gene expression was higher, in mice receiving GGEx18 compared to mice fed only the HFD.</P> <P><B>Discussion and conclusion</B></P> <P>These results indicate that GGEx18 attenuates visceral obesity and NAFLD, in part by altering the expression of genes involved in hepatic steatosis and fibroinflammation in HFD-induced obese mice. These findings suggest that GGEx18 may be effective for preventing and treating NAFLD associated with visceral obesity.</P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>