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Park, Taehyun,Chang, Ikwhang,Cha, Suk Won American Scientific Publishers 2013 Journal of Nanoscience and Nanotechnology Vol.13 No.12
<P>Triple phase boundaries (TPBs) where electrode, electrolyte, and reactant meet altogether were augmented in thin film solid oxide fuel cell when Pt cathode was deposited on yttrium-doped barium zirconate electrolyte (BZY) via sputter. The augmented TPBs were observed to exist as three-dimensional structures, which is different from what are known to exist as two-dimensional planes or interfaces, by using energy dispersive spectroscopy (EDS). The permeating phenomenon of sputtered Pt into BZY was found to depend on dc sputtering power. Polarization curves showed increasing tendency of maximum powers in accordance with increasing thickness of Pt cathode and spectra of ac impedances showed decreasing tendency of faradaic resistances. If TPBs were located as an interfacial structure between electrode and electrolyte, oxygen could not diffuse well into TPBs, causing radius of semicircle in impedance spectra to decrease. The results are violating this expectation. As a result, as long as charge transfer resistance is a function of temperature, reactant concentration, activation barrier and TPB length, TPB must be only a factor to affect the results in this experiment.</P>
A rollable ultra-light polymer electrolyte membrane fuel cell
Park, Taehyun,Kang, Yun Sik,Jang, Segeun,Cha, Suk Won,Choi, Mansoo,Yoo, Sung Jong Nature Publishing Group 2017 NPG Asia Materials Vol.9 No.-
<P>We have developed a highly flexible, ultra-light and thin polymer electrolyte membrane fuel cell that can be used as a portable power source for flexible electronics. To achieve such flexibility and ultra-lightness, we fabricated a thin flow-field plate using a thermal imprinting process and combined it with a laser-machined metal current collector. The air-breathing fuel cell, with a thickness of 0.992 mm and a weight of 2.23 g, demonstrated a total power of 508 mW and a performance degradation of <10% after severe bending fatigue (200 repeated bends). This high power per weight (0.228 W g(-1)) and robust bending durability have never been observed before. The highly flexible architecture enabled the operation of the fuel cell in an S-shape or even in a rolled-up state without any significant performance loss. We have fabricated a cylindrical planar stack of 10 fuel cells and successfully carried out its outdoor operation to demonstrate its practical applications in various fields.</P>
Park, Taehyun,Lee, Yoon Ho,Cho, Gu Young,Ji, Sanghoon,Park, Joonho,Chang, Ikwhang,Cha, Suk Won Elsevier 2015 THIN SOLID FILMS - Vol.584 No.-
<P><B>Abstract</B></P> <P>Sputtered gadolinia-doped ceria (GDC) film was introduced as the cathodic interlayer between an yttria-stabilized zirconia (YSZ) pellet and a Pt cathode in solid oxide fuel cells (SOFCs). The fuel cells with none, 50, 100 and 150nm thick GDC interlayers were fabricated to investigate the effect of the thickness of the GDC interlayer. The performances of the SOFCs with the 100 and 150nm thick GDC interlayers operated at 450°C showed the highest performance. Through electrochemical impedance analysis, it was visualized that the GDC interlayer significantly reduced the faradaic resistance of the SOFC. The degradation of the performance from the increased ohmic resistance by adding the GDC interlayer was negligible. From the topographical images scanned by atomic force microscope, it was observed that the 50nm thick GDC interlayer did not perfectly cover the surface of the YSZ pellet, resulting in incomplete performance enhancement by the sputtered GDC.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Gadolinia-doped ceria was used as a cathodic interlayer in solid oxide fuel cells. </LI> <LI> Sputter was used to deposit gadolinia-doped ceria. </LI> <LI> Gadolinia-doped ceria interlayer improved the electrochemical performance. </LI> <LI> 100nm or thicker gadolinia-doped ceria showed a full functionality as interlayer. </LI> </UL> </P>
Park, Taehyun,Chang, Ikwhang,Jung, Ju Hae,Lee, Ha Beom,Ko, Seung Hwan,O'Hayre, Ryan,Yoo, Sung Jong,Cha, Suk Won Elsevier 2017 ENERGY Vol.134 No.-
<P><B>Abstract</B></P> <P>This work investigates the effect of assembly pressure on the performance of a bendable polymer electrolyte fuel cell based on silver nanowire current collectors. We define assembly pressure as the compressive stress exerted by the bendable fuel cell flow structure on the membrane electrode assembly. The performance of the bendable fuel cell increases with increasing assembly pressure while the corresponding ohmic and charge transfer resistances of the fuel cell decrease. While in certain circumstances bending can increase fuel cell performance because it increases the assembly pressure internally exerted on the MEA, we also find that deformation of the flow structures upon bending the fuel cell can negatively affect performance due to non-uniform disruptions in the distribution of reactants. We extract the key electrochemical parameters that are most sensitive to assembly pressure and develop a simulation model for bendable fuel cells using these parameters. This model is validated against the experimental data of here and previous studies, thereby showing the feasibility of engineering the bendable fuel cells for various demands.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Bendable polymer electrolyte fuel cell was fabricated using silver nanowires. </LI> <LI> Effect of assembly pressure on bendable fuel cell was investigated experimentally. </LI> <LI> Causes of performance loss by bending in bendable fuel cell were figured out. </LI> <LI> Simulation model of bendable fuel cell was established based on experimental data. </LI> <LI> Simulation model predicts performances of other bendable fuel cells in literatures. </LI> </UL> </P>
Fabrication and Application of Micro Polymer Chip Platform for Rare Cell Sample Preparation
Taehyun Park 한국융합학회 2018 한국융합학회논문지 Vol.9 No.3
본 논문에서는 정확한 수의 희귀 세포 포집 및 이송을 위한 마이크로 폴리머 칩 플랫폼의 디자인과 제작, 그리고 프로토콜을 소개하고 있다. 본 플랫폼과 프로토콜은 기존의 통계학적인 샘플 준비 방법인 희석(Dilution)의 한계와 고가이며 형광염색이 요구되는 유세포분석기(Fluorescence activated cell sorter)의 단점을 극복하였다. 타켓 세포를 선택적으로 쉽고 간단하게 채집할 수 있으며 채집되는 세포의 수는 시각적으로 검증되므로 매우 정확한 방법이다. 또한, 채집된 세포들은 마이크로 챔버 등의 원하는 곳으로 세포의 손실 없이 이송 또는 주입 시킬 수 있다. 본 연구는 암진단 등을 목적으로 하는 칩 속의 실험실(Lab on a chip) 등에 필요한 희귀 세포 샘플 준비를 위해 활용 될 수 있을 뿐만 아니라 세포분석을 위한 싱글/더블/다수 세포 샘플의 준비에도 활용 가능하다. 본 논문에서 제시하는 세포 채집 플랫폼과 프로토콜을 검증하기 위해 5개의 인간 암세포(MCF-7)를 채집한 뒤 세포계수기(Hemocytometer) 안으로 주입시켜 세포의 수를 확인하였다. In this paper, a new micro polymer chip platform and protocol were developed for rare cell sample preparation. The proposed platform and protocol overcome the current limitation of the dilution method which is based on statistics and the FACS method which expensive and requires fluorescence staining. It allows collecting exact number of target cells simply and selectively because the cells are visually confirmed during the collecting process. The collected cells can be transported or spiked into a desired locations, such as a microchamber, without cell loss. This research may applicable not only to a rare cell sample preparation for Lab on a Chip cancer diagnosis, but also to a single/double/multiple cell sample preparation for a cell analysis field. To verify this platform and protocol, five human breast cancer cells (MCF-7) were collected and transported into a hemocytometer chamber.
Park, Taehyun,Chang, Ikwhang,Lee, Jinhwan,Ko, Seung Hwan,Cha, Suk Won The Electrochemical Society 2014 ECS Transactions Vol.64 No.3
<P>Performance variation of flexible fuel cell based on polydimethylsiloxane coated with Ag nanowires percolation network for current collection was characterized as torsion on it increases. Maximum power densities of flexible fuel cell at no torsion and 0 degree of torsion were 16.8 and 10.9 mW/cm<SUP>2</SUP>, respectively, showing decreasing tendency of power density as torsion increases. By measuring electrochemical impedances, it was found that cause for decreased electrochemical performance was increased ohmic and faradaic resistances. In addition, inhomogeneous distribution of hydrogen and air in fuel cell caused by torsion contributed to decrease of faradaic resistance and resulting electrical performance. From solid-mechanical model of finite element analysis, generated internal stress by torsion was not severe and the decreased performance was not the effect of contact resistance, which was already reported in our previous study. </P>