• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2005.07a
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• pp.461-462
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• 2005

In order to improve the efficiency of dye-sensitized solar cell (DSC), $TiO_2$ electrode screen-printed on transparent conducting oxide (TCO) substrate was sintered in variation with different temperature(350 to $550^{\circ}C$). $TiO_2$ electrode on fluorine doped tin oxide (FTO) glass was assembled with Pt counter electrode on FTO glass. I-V properties of DSC were measured under solar simulator. Also, effect of sintering temperature on surface morphology of $TiO_2$ films was investigated to understand correlation between its surface morphology and sintering temperature. Such surface morphology was observed by atomic force microscopy (AFM). From the measurement results, at sintering temperature of $500^{\circ}C$, both efficiency and fill factor of DSC were mutually complementary, enhancing highest fill factor and efficiency. Consequently, it was considered that optimum sintering temperature of $\alpha$-terpinol included $TiO_2$ paste is at $500^{\circ}C$.

• Journal of the Korean Society of Safety
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• v.30 no.1
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• pp.21-27
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• 2015

In this study, interfacial characteristics between SOFC and Ag paste as current collector was estimated in the high temperature environment. The Ag paste was used to connect the unit cell of SOFC strongly with interconnector and provide the electrical conductivity between them. To confirm electrical conductivity, Ag paste was treated in the furnace at $800^{\circ}C$ for 48 hours. The sheet resistance of Ag paste was measured to compare the resistance values before and after the heat treatment. Also, the four-point bending test was performed to measure the interfacial adhesion. The unit cell of SOFC and $SiO_2$ wafer were diced and then attached by Ag paste. The $SiO_2$ wafer had the center notch to initiate a crack from the tip of the notch. The modified stereomicroscope combined with the CCD camera and system for measuring the length was used to observe the fracture behavior. To compare the characteristics before heat treatment and after heat treatment, the specimen was exposed in the furnace at $800^{\circ}C$ for 48 hours and then the interfacial adhesion was evaluated. Finally, the interfacial adhesion energy quantitatively increases $1.78{\pm}0.07J/m^2$ to $4.9{\pm}0.87J/m^2$ between the cathode and Ag paste and also increase $2.9{\pm}0.47J/m^2$ to $5.12{\pm}1.01J/m^2$ between the anode and Ag paste through the high temperature. Therefore, it is expected that Ag paste as current collector was appropriate for improving the structural stability in the stacked SOFC system if the electrical conductivity was more increased.

• Clinical and Experimental Reproductive Medicine
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• v.25 no.3
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• pp.261-268
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• 1998

The present study was to assess the effect of ultrarapid freezing on the development of 1-cell mouse zygote using cryoprotectants, DMSO (dimethyl sulfoxide) or PROH (1,2-propanediol). We investigated the effect of the type and concentration of cryoprotectant, and of the temperature and time of prefreezing equilibration on their capacity to develop to the blastocyst stage in vitro. The concenration, the equilibration temperature, and the exposure time seemed to serve as an important factor in ultrarapid freezing of 1-cell mouse zygotes. In addition to the exposure time and the concentration of cryoprotectant appeared to playa key role in the development of the embryo. In general, the development of the embryo was more effective at $3^{\circ}C$ than $23^{\circ}C$ and 4.5 M than 3 M for 3 to 5 minutes. At $23^{\circ}C$ the development of the embryo was stimulated by DMSO while at $3^{\circ}C$ it was stimulated by PROH. Thus it has been suggested that there exists a correlation between the concentration of cryoprotectants and exposure time in the development of the embryo. In conclusion, we found that for ultrarapid freezing of mouse 1-cell embryos in DMSO, or PROH-based solution, viability shown optimum depending on the cryoprotectant, the concentration of the cryoprotectant and on the temperature and the duration of equilibration.

• Korean Chemical Engineering Research
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• v.47 no.4
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• pp.441-445
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• 2009

Effect of temperature on membrane degradation in PEMFCs was studied. After cell operation at different temperatures($60{\sim}90^{\circ}C$) under accelerating degradation conditions(OCV, anode dry, cathode RH 65%) for 144 h, cell performance decreased from 12 to 35%. The results of FER in effluent water showed that this decrease in cell performance was caused by membrane degradation by the attack of $H_2O_2$ or oxygen radicals(${\cdot}OH$, $HO_2{\cdot}$) and that resulted in increase in gas crossover for radical formation. Radical formation on the electrode was confirmed by ESR. Activation energy of 66.2 kJ/mol was obtained by Arrhenius plot used to analyze the effect of temperature on membrane degradation. Increase of cell temperature enhanced gas crossover rate, radical formation rate and membrane degradation rate.

• Journal of the Korean Electrochemical Society
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• v.11 no.1
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• pp.22-32
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• 2008

Because of an emerging importance of clean energy, fuel cells are attract more attention due to their ability to produce high efficient power without any harmful emission. Fuel cells are energy conversion device with directly convert chemical energy into electrical energy by the chemical reactions, which have potential applications in automobile, spacecraft, stationary, industrial and home appliances. Recently there are gaining demand to develop an intermediate temperature fuel cell and available proton conductors at $200{\sim}500^{\circ}C$, which promising operating temperatures range for both material science and energy conversion processes. In this paper, we have reviewed electrochemical properties and current technology of solid state proton conductors. In addition, development of intermediate temperature fuel cell using the perovskite-type solid protonic conductor is also discussed.

• 한국신재생에너지학회:학술대회논문집
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• 2009.11a
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• pp.147-148
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• 2009

The water-like ionic liquids have been widely used to enable the proton conduction in ionic liquid based membranes at high temperature and anhydrous PEFCs. In this study, we synthesized various kinds of composite membranes based on hydrocarbon polymers having good thermal and mechanical stabilities at high temperatures and ionic liquids. The composite membrane consisting of hydrocarbon polymer and ionic liquid was characterized by thermogravimetric analyzer (TGA) and impedance spectroscopy. Consequently the non-aqueous composite membranes of a variety of hydrocarbon polymer and ionic liquids have good conductivity and thermal stability at high temperature conditions.

• Journal of Digital Convergence
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• v.14 no.6
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• pp.245-251
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• 2016

A numerical model is developed to predict distributions of current density and temperature. Also the complete fuel cell performances were compared. In this study the effect of flow field design and flow direction on current density and temperature distribution as well as full cell performance. The complete three-dimensional Navier-Stokes equations were solved with convergence of electro-chemical reactions terms. In this paper, the two different flow field design were simulated, straight channel and rectangular serpentine flow channel, which is commonly used. The effect of flow direction, co-flow and counter-flow, was also analyzed. The current density and temperature is higher with abundant oxygen not fuel. Also, temperature distribution was able to be drawn by using computer simulation. In this paper, the relationship among flow pattern, flow field design and current denstity distribution.

• Journal of the Korean Society of Safety
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• v.33 no.5
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• pp.1-8
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• 2018

A fuel cell is an energy conversion device that converts a chemical energy directly into an electrical energy and has higher energy efficiency than an internal combustion engine, but solid oxide fuel cell (SOFC) consisting of brittle ceramic material remains as a major issue regarding the mechanical properties as the crack formation and propagation. In this study, the stress distribution and crack behavior around the crack tip were evaluated, due to investigated the effects of the surface crack at the operating condition of high temperature. As a result, the difference of the generated stress was insignificant at operating conditions of high temperature according to the surface crack length changes. This is because, the high stiffness interconnect has a closed structure to suppress cell deformation about thermal expansion. The stress intensity factor ratio $K_{II}/K_I$ increased as the crack depth increased, at that time the effect of $K_{II}$ is larger than that of $K_I$. Also the maximum stress intensity factor increased as the crack depth increased, but the location of crack was generated at the electrolyte/anode interface, not at the crack tip.

• Transactions of the Korean hydrogen and new energy society
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• v.18 no.4
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• pp.422-431
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• 2007

Polymer electrolyte membrane fuel cell(PEMFC) is very interesting power source due to high power density, simple construction and operation at low temperature. But it has problems such as high cost, improvement of performance and effect of temperature. These problems can be approached to be solved by using mathematical models which are useful tools for analysis and optimization of fuel cell performance and for heat and water management. In this paper, the present work is to develop an electrochemical model to examine the electrochemical process inside PEM fuel cell. A complete set of considerations of mass, momentum, species and charge is developed and solved numerically with proper account of electrochemical kinetics. When depth of gas channel becomes thinner, diffusion of reactant makes well into gas diffusion layer(GDL) and the performance increases. Although at low current region there is little voltage difference between experimental data of PEM fuel cell and numerical data. When the porosity size of gas diffusion layer for PEM fuel cell is bigger, oxygen diffusion occurs well and oxygen mass fraction appears high in catalyst layer.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.61 no.5
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• pp.705-710
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• 2012

An anti-reflection layer (AR) is used in the solar cell to improve the amount of the irradiated light, resulting in the improvement of the performance of the solar cell. In this study, the zinc oxide (ZnO) AR is applied to the dye-sensitized solar cell (DSC) by using zinc nitrate solution. The conditions such as solution concentration and sintering temperature for fabricating the ZnO AR are changed to optimize the performance of the AR. As a result, the best performance is shown when the zinc nitrate solution with 100mM concentration is used and the sintering temperature is $600^{\circ}C$. And then, the ZnO AR formed with these optimal conditions is applied to the DSC. Consequently, a DSC with a ZnO AR had an increased current density up to 13.86$mA/cm^2$ and an enhanced efficiency of 6.32%.