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RISS 인기검색어
- 검색키워드
- 저자 : Hwichul Yang (검색결과 6 건)
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Hwichul Yang,Hojae Lee,Yonghyun Lim,Maria Christy,김영범 한국정밀공학회 2021 International Journal of Precision Engineering and Vol.8 No.1
Reverse electrowetting-on-dielectric (REWOD) is a novel energy harvesting technique that has been gaining considerable amount of attention owing to its high power output even with the small amount of disturbance. To enhance the output power of REWOD, the dielectric layers in the system require a high capacitance. Nevertheless, current leakage is inevitable in such high-k dielectric materials. In this work, the application of a high-k dielectric material TiO2 has been investigated along with a new leakage barrier layer Al2O3 that acts as a lamination, in order to minimize the current leakage and maximize the power output. As expected, the laminated structure with TiO2 and Al2O3 exhibited reduced current leakage and relatively high capacitance compared to the single layer of TiO2 or Al2O3, respectively. As the electrical energy is generated through the interaction of liquid droplets and the multilayered dielectric fi lm, the energy-harvesting performance displayed different behavior about current generation with respect to the top surface material that is in contact with the conductive droplet. Overall, the laminated REWOD energy harvesting system produced an enhanced power density of 15.36 mW cm −2 at a low bias voltage.
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Yang, Hwichul,Hong, Soonwook,Koo, Bongjun,Lee, Dohaeng,Kim, Young-Beom Elsevier 2017 Nano energy Vol.31 No.-
<P><B>Abstract</B></P> <P>Reverse electrowetting-on-dielectric (REWOD), which is a novel technology for energy harvesting, was demonstrated by depositing Al<SUB>2</SUB>O<SUB>3</SUB> via atomic layer deposition (ALD). Specifically, thin layers of Al<SUB>2</SUB>O<SUB>3</SUB> about 100nm-thick were successfully formed by ALD to obtain dense films with high capacitances. REWOD with the ALD Al<SUB>2</SUB>O<SUB>3</SUB> thin films exhibited high performances under low-voltage and low-excitation-frequency conditions. The maximum power density was 11mW/cm<SUP>2</SUP> with a DC bias of 24V and an external excitation frequency of 2Hz. Moreover, ALD and sputtered thin films were compared by investigating their capacitances and leakage current densities. Due to the differences between the film densities and growth methods, the ALD thin films exhibited higher capacitances and lower leakage current densities. It was also determined that the leakage current affects the REWOD energy harvesting performance. By analyzing these features, it was confirmed that ALD thin films are suitable for REWOD energy harvesting.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Highly dense ultra-thin dielectric layer was fabricated for capacitive applications. </LI> <LI> High-performance of REWOD energy harvesting was demonstrated. </LI> <LI> Superior dielectric properties were obtained using a common oxide material. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>High performance reverse electrowetting on dielectric device utilizing superior dielectric layer fabricated by atomic layer deposition.</P> <P>[DISPLAY OMISSION]</P>
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사마륨이 도핑된 세륨 옥사이드 나노 결정질 박막의 열처리 공정에 따른 표면 반응 특성 연구
양휘철(Hwichul Yang),배지웅(Jiwoong Bae),손종현(Jonghyun Son),구봉준(Bongjun Koo),김영범(Young-Beom Kim) 대한기계학회 2015 대한기계학회 춘추학술대회 Vol.2015 No.11
Surface kinetics of samarium-doped ceria (SDC) thin film have been investigated. FE-SEM image analysis is conducted to discern the grain size effect and internal effect roughly by thermal annealing. Electrode resistance of SDC surface has been measured by electrochemical impedance spectroscopy (EIS). As a result, the electrode resistance becomes larger when the annealing temperature is increased.
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Hong, Soonwook,Yang, Hwichul,Lim, Yonghyun,Prinz, Fritz B.,Kim, Young-Beom American Chemical Society 2019 ACS APPLIED MATERIALS & INTERFACES Vol.11 No.44
<P>In this Research Article, gadolinia-doped ceria (GDC), which is a highly catalyzed oxide ionic conductor, was explored to further improve oxygen surface reaction rates using a grain-controlled layer (GCL) concept. Typically, GDC materials have been used as a cathode functional layer by coating the GDC between the electrode and electrolyte to accelerate the oxygen reduction reaction (ORR). To further improve the oxygen surface kinetics of the GDC cathodic layer, we modified the grain boundary density and crystallinity developed in the GDC layer by adjusting RF power conditions during the sputtering process. This approach revealed that engineered nanograins of GDC thin films directly affected ORR kinetics by catalyzing the oxygen surface reaction rate, significantly enhancing the fuel cell performance. Using this innovative concept, the fuel cells fabricated with a GDC GCL demonstrated a peak power density of 240 mW/cm<SUP>2</SUP> at 450 °C.</P> [FIG OMISSION]</BR>
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Hong, Soonwook,Son, Jonghyun,Lim, Yonghyun,Yang, Hwichul,Prinz, Fritz B.,Kim, Young-Beom The Royal Society of Chemistry 2018 Journal of Materials Chemistry A Vol.6 No.34
<P>Scandia-stabilized zirconia (ScSZ) is employed as a cathodic functional layer onto yttria-stabilized zirconia based fuel cell systems for low-temperature solid oxide fuel cells. In order to overcome the relatively poor material properties in terms of surface reaction rate, the grain structure and the degree of crystallinity of ScSZ thin films were modified by controlling the RF power during the thin-film fabrication process <I>via</I> sputtering. The concept of grain-controlled layers (GCLs) was applied at the cathode-electrolyte interface to enhance the surface reaction rate by catalyzing the oxygen reduction reaction. By adopting this novel concept, the thin-film fuel cell fabricated with ScSZ GCLs could achieve a peak power density of 479 mW cm<SUP>−2</SUP> at 450 °C.</P>
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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.
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