• Advances in Energy Research
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• v.8 no.4
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• pp.253-264
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• 2022

This paper deals with the effects of design (active area, current density, membrane conductivity) and operating parameters (temperature, relative humidity) on the performance of hydrogen-fuelled proton exchange membrane (PEM) fuel cell. The design parameter of a PEM fuel cell with the active area of the single cell considered in this study is 25 cm² (5 × 5). The operating voltage and current density of the fuel cell were 0.7 V and 0.5 A/cm² respectively. The variations of activation voltage, ohmic voltage, and concentration voltage with respect to current density are analyzed in detail. The membrane conductivity with variable relative humidity is also analyzed. The results show that the maximum activation overpotential of the fuel cell was 0.4358 V at 0.21 A/cm² due to slow reaction kinetics. The calculated ohmic and concentrated overpotential in the fuel cell was 0.01395 V at 0.76 A/cm² and 0.027 V at 1.46 A/cm² respectively.

• Proceedings of the KSME Conference
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• 2007.05b
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• pp.2222-2227
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• 2007

Newly structured metal-supported solid oxide fuel cell was fabricated and characterized by impedance analysis and galvanodynamic experiment. Using a cermet adhesive, thin ceramic layer composed of anode(Ni/YSZ) and electrolyte(YSZ) was joined with STS430 metal support of which flow channel was fabricated. $La_{0.8}Sr_{0.2}Co_{0.4}Mn_{0.6}O_3$ perovskite oxide was used as cathode material. Single cell performance was increased and saturated at operating time to 300hours at 800$^{\circ}C$ because of cathode sintering effect. The sintering effect was reinvestigated by half cell test and exchange current density was measured as 0.005A/$cm^2$. Maximum power density of the cell was 0.09W/$cm^2$ at 800$^{\circ}C$. Numerical analysis was carried out to classify main factors influencing the single cell performances. Compared to experimental IV curve, simulated curve based on experimental parameters such as exchange current density was in good agreement.

• Transactions of the Korean hydrogen and new energy society
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• v.30 no.1
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• pp.43-48
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• 2019

This study investigates the electrochemical characteristics of the hybrid cell that combined the advantageous characteristics of Li secondary battery and supercapacitor, high energy density and high power density, respectively. Electrochemical behaviors of the hybrid cell was characterized by charge/discharge, cycle and impedance tests. The hybrid cell using Li secondary battery and supercapacitor had better discharge capacity and cycle performance than that of using Li secondary battery only. Proper design of such a hybrid cell system is expected to result in substantial benefits to the well being of the Li secondary battery. The hybrid cell involving Li secondary battery for high energy density and supercapacitor for high power density may be the possible solution for future energy storage system.

• Journal of Korean Society of Water and Wastewater
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• v.26 no.6
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• pp.883-888
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• 2012

Anode electrode is one of the most important factors in microbial fuel cell (MFC). This study was conducted to investigate the effects of mediator as methylene blue (MB) and electrode surface area on the power density of MFC with sponge and carbon nano tube (CNT) electrode (SC). The SC electrode with MB (MC) showed the maximum power density increased from 74.0 $mW/m^2$ to 143.1 $mW/m^2$. The grid shaped sponge and CNT (GSC) electrode showed the maximum power density of 209.2 $mW/m^2$ due to the increase of surface area from 88.0 to 152.0 $cm^2$. The GSC electrode with MB (GMC) revealed the maximum power density of 384.9 $mW/m^2$ which was 5.2 times higher than that obtained from the MFC with SC. Therefore MB and increase of surface area led to enhance the performance of microbial fuel cell such as power density.

• Journal of Korean Society on Water Environment
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• v.34 no.2
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• pp.210-215
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• 2018

It is difficult to count colonial cyanobacteria Microcystis cells since the thickness of colonies is constrained by amorphous mucilage, making it impossible to estimate the number of cells. Disaggregation of Microcystis colonies into single cell is needed to improve the accuracy and precision of cell density estimation of naturally collected samples. Uultrasonic treatment method is commonly used owing to the simplicity and immediacy of the procedure. However, amplitude, frequency, and duration of ultrasonic treatment also cause cell loss during the experiment. Optimal ultrasonic treatment has not been standardized yet. Therefore, the objective of this study was to investigate optimal ultrasonic treatment by analyzing cell density and colony numbers. We collected colonial Microcystis from Changnyeong-Haman weir area in Nakdong River during harmful algal boom period from September to October in 2017. Ultrasonic treatment method was applied to disrupt colonies into single cells to enumerate cell density. Among treatment conditions, results from continuously treated for 100 seconds were found to be the optimum to reduce colonies to a suspension of single cell without cell losses under high and low density of Microcystis cells. Lugol iodine fixed cells followed by sonication showed less negative impact of cell damage within the optimal treatment time (100 seconds). Furthermore, disaggregated cells treated by sonication enables microscopic observation more easily since gas vacuoles were collapsed to facilitate sedimentation of cells under the counting chamber for quantitative enumeration of buoyant Microcystis cells.

• Journal of the Korean Institute of Telematics and Electronics
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• v.26 no.6
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• pp.124-130
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• 1989

For the higher density DRAM'S, innovations in fabrication process and circuit design which have led to dramatic density improvement are discussed from the desinger's perspective. A new dynamic RAM cell called Trench Epitaxial Transistor Cell(TETC) using trench technics and SEG have been developed for use in future megabit DRAMS. Storge electrode with $n^+$-polysilicon and $n^+$-source electrode are self-contacted in TETC. With keeping the storage capacitance large enough to prevent soft errors, the cell size reduced to 30% compare with existing BSE cell by utilizing the vertical capacitor made along the isolation region.

• Proceedings of the SAREK Conference
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• 2008.11a
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• pp.9-14
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• 2008

The effects of baffles in PEM fuel cell with parallel flow channel has been simulated by using conmmercial program. The simulation has been conducted through the channel and there are four different heights of baffles, No Baffle($H_b$=0), Partially Blocked Baffle(0.25, 0.5, 0.75), Fully Blocked Baffle(1) conditions. The result shows that current density changes while placing a baffle at the various positions along the channel. Current density with a single baffle is higher than that without baffle and current density using Fully Blocked Baffle(FBB) is much higher than current density using Partially Blocked Baffle(PBB). When the baffle is closer to outlet of the channel, current density increases. It is found that pressure is related to current density. If the pressure is higher, the better performance will be expected.

• New & Renewable Energy
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• v.5 no.1
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• pp.11-17
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• 2009

To improve the performance of the anode-supported Solid Oxide Fuel Cell (SOFC) which can be operated at an intermediate temperature, the functional layer (FL) is introduced on a anode substrate. And the scandia-stabilized zirconia (ScSZ) and samaria-doped ceria (SDC) which have higher ionic conductivity and better chemical stability than yttria-stabilized zirconia (YSZ) are used as material for the anode FL with the Ni, The fabrication process of anode-supported single cell with the anode FL was established and the power density of those was evaluated. As a result, the sample with anode FL (Ni-YSZ) has higher power density than normal cell. The single cell which was composed of the FL (Ni-YSZ) and electrolyte (YSZ) showed about $550mW/cm^2$ of the maximum power density at $650^{\circ}C$ and $1430mW/cm^2$ at $750^{\circ}C$ respectively, In case of the single cell using the ScSZ and SDC as anode FL, the performance of samples decreased rapidly and those showed unstable voltage during long-term test. In case of using methane as a fuel, the cell performance with each FL decreased comparing with $H_2$ fuel. In the region of a high current density, there are large concentration polarizations.

• Proceedings of the KSME Conference
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• 2008.11b
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• pp.2834-2838
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• 2008

An free breathing proton exchange membrane fuel cell (PEMFC) was developed. This paper presents a study of the several effect on the performance of a fuel cell such as air flow rate, opening ratio, and cathode structures. Especially, an air flow rate is critical condition to improve the fuel cell performance. In this paper, we developed a synthetic jet micro air blower to supply high stoichiometric air. The synthetic jet actuation is usually generated by a traditional PZT-driven actuator, which consists of a small cylindrical cavity, orifices and PZT diaphragms. In comparison with free convection fuel cells, the forced-convection fuel cell which equipped synthetic jet micro air blower brings higher performance and stability for long term test. Also, power consumption of the synthetic jet micro air blower is under 0.3W. The results show that the maximum power density was $188mW/cm^2$ at $400mA/cm^2$. The maximum power density was higher 40% than power density of free convection fuel cell.

• Journal of Ginseng Research
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• v.16 no.2
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• pp.129-137
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• 1992

This study was carried out to investigate the localization of lipids and lipase activity with lipid staining and cytochemical technique in endosperm cells of Panax ginseng C.A. Meyer seed. In endosperm cells of indehiscent seed, protein bodies facing the umbiliform layer are different in electron density during the various degraded processes. Gradually, protein matrix near the cell wall was lysed and electron lucent inclusions appeared on umbiliform layer. The protein body with high electron density and the spherosome with low electron density were observed in endosperm cells. As a result of lipid staining, electron density of spherosome is more intense than those of the protein matrix within the protein body in endosperm cells of indehiscent seed. Free spherical spherosomes within the umbiliform layer have a high electron density. The spherical spherosomes were more electron densed and were uniform in comparison with the cytoplasmic proteinaceous granules in endosperm cells of seed with red seed coat. The major component of spherosome was determined to be lipid. Lipase activity occurs in the spherosome and near the endosperm cell wall facing the umbiliform layer. Cytochemical reaction products of lipase were observed in the spherosome membrane and in the inner regions of spherosome. After protein bodies were digested, lipase activities were observed in free spherosomes and near the cell wall of endosperm cells. Umbiliform layer composing of fibrillized wall and digested materials of the endosperm cell showed a little lipase reaction products.