• Journal of the Korean Electrochemical Society
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• v.12 no.1
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• pp.81-87
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• 2009

An indium-tin oxide (ITO) coated spinel manganese oxide (${LiMn_2}{O_4}$, LMO) is prepared and its high-temperature ($55^{\circ}C$) cycle performance and rate capability are examined. A severe electrolyte decomposition and film deposition is observed on the un-coated ${LiMn_2}{O_4}$ cathode, which leads to a significant electrode polarization and capacity fading. Such an electrode polarization is, however, greatly reduced for the ITO-coated (> 2 mol%) LMO cathode, which leads to an improved cycle performance. This can be rationalized by a suppression of electrolyte decomposition, which is in turn indebted to a decrease in the direct contact area between LMO and electrolyte. The suppression of film deposition on the ITO-coated LMO cathode is confirmed by infra-red spectroscopy. The rate capability is also improved by the surface coating, which may be resulted from a suppression of resistive film deposition and high electric conductivity of ITO itself.

• Journal of Bio-Environment Control
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• v.19 no.4
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• pp.343-350
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• 2010

This study was conducted to investigate the effect of harvest seasons on quality and microbial population at different steps of production chain of fresh-cut iceberg lettuce. Iceberg lettuces harvested in May, June, July, October, and December were processed following industrial practices, and stored at $5^{\circ}C$ for 9 days. For microbial measurement, samples were taken from each of the following steps: harvest, transport, pretreatment, cutting, 1st-washing, 2nd-washing, and day 3, 6, and 9 of storage. Iceberg lettuce cultivated in protect house and harvested in May and October showed higher $CO_2$ levels in the packages and electrolyte leakages than lettuce harvested in June, July and December. Microbial population of raw materials harvested in July was highest (6.76 log), and microbial growth rate during storage was highest in samples harvested in May. Lettuce harvested in June had better quality and microbial safety compared to other lettuces. Although lettuce harvested in October and December had less microbial population in either raw materials or processed products, those samples had inferior quality due to off-odor development and severe browning. Therefore, it is required to maintain quality and ensure microbial safety to distribute fresh-cut lettuce with high quality and safety throughout the year.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.35 no.6
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• pp.585-592
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• 2011

The enhancement of the cold-start capability of polymer electrolyte fuel cells is of great importance in terms of the durability and reliability of fuel-cell vehicles. In this study, vanadium oxide films deposited onto the flat surface of metallic bipolar plates were synthesized to investigate the feasibility of their use as an efficient self-heating source to expedite the temperature rise during startup at subzero temperatures. Samples were prepared through the dip-coating technique using the hydrolytic sol-gel route, and the chemical compositions and microstructures of the films were characterized by X-ray diffraction, X-ray photoelectron spectroscopy, and field-emission scanning electron microscopy. In addition, the electrical resistance hysteresis loop of the films was measured over a temperature range from -20 to $80^{\circ}C$ using a four-terminal technique. Experimentally, it was found that the thermal energy (Joule heating) resulting from self-heating of the films was sufficient to provide the substantial amount of energy required for thawing at subzero temperatures.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.35 no.6
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• pp.649-656
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• 2011

A model for the numerical simulation of lithium-ion batteries (LIBs) is developed for use in battery cell design, with a view to improving the performances of such batteries. The model uses Newman-type electrochemical and transfer $theories^{(1,2)}$ to describe the behavior of the lithium-ion cell, together with the Levenberg-Marquardt optimization scheme to estimate the performance or design parameters in nonlinear problems. The mathematical model can provide an insight into the mechanism of LIB behavior during the charging/discharging process, and can therefore help to predict cell performance. Furthermore, by means of least-squares fitting to experimental discharge curves measured at room temperature, we were able to obtain the values of transport and kinetic parameters that are usually difficult to measure. By comparing the calculated data with the life-test discharge curves (SB LiMotive cell), we found that the capacity fade is strongly dependent on the decrease in the reaction area of active materials in the anode and cathode, as well as on the electrolyte diffusivity.

• Polymer(Korea)
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• v.33 no.4
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• pp.377-383
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• 2009

Ionic polymer-metal composite (IPMC) actuator generates bending actuation via ion/water flux to the cathode side under an electric field. Polyelectrolytes in IPMC should possess high water-retention capability, proton conductivity, and Young's modulus. In this study. for endowing IPMCs with these properties, Nafion-alumina composite membranes containing $\alpha$- or $\gamma$-aluminas of $4{\sim}8$ wt% were prepared. Mechanical moduli of Nafion-alumina composite membranes were $7{\sim}3$ MPa higher than that of Nafion, with the slight decrease in proton conductivity. At DC 3 V. the actuation performance of the Nafion-$\alpha$-alumina (8 wt%)-IPMC was superior to that of the typical Nafion-IPMC. exhibiting 2.7 times the displacement with an enhanced blocking force. The enhanced actuation performance with the Nafion-$\alpha$-alumina composite membranes was attributed to the higher proton conductivity, the elevated ion/water flux, and the lower interfacial electric resistance of platinum electrodes and membrane, compared with those containing $\gamma$-alumina.

• Korean Chemical Engineering Research
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• v.61 no.2
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• pp.189-195
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• 2023

As a PEMFC (Polymer Exchange Membrane Fuel Cell) cathode catalyst, Pt-Co/C has recently been widely used because of its improved durability. In a fuel cell, electrodes and electrolytes have a close influence on each other in terms of performance and durability. The effect on the electrochemical durability of the electrolyte membrane when Pt-Co/C was replaced in the Pt/C electrode catalyst was studied. The durability of Pt-Co/C MEA (Membrane Electrode Assembly) was higher than that of Pt/C MEA in the electrochemical accelerated degradation process of PEMFC membrane. As a result of analyzing the FER (Fluorine Emission Rate) and hydrogen permeability, it was shown that the degradation rate of the membrane of Pt-Co/C MEA was lower than that of Pt/C MEA. In the OCV (Open Circuit Voltage) holding process, the rate of decrease of the active area of the Pt-Co/C electrode was lower than that of the Pt/C electrode, and the amount of Pt deposited on the membrane was smaller in Pt-Co/C MEA than in Pt/C MEA. Pt inside the polymer membrane deteriorates the membrane by generating radicals, so the degradation rate of the membrane of Pt/C MEA with a high Pt deposition rate was higher than Pt-Co/C MEA. When the Pt-Co/C catalyst was used, the electrode durability was improved, and the amount of Pt deposited on the membrane was also reduced, thereby improving the electrochemical durability of the membrane.

• Journal of the Korean Electrochemical Society
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• v.16 no.1
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• pp.39-45
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• 2013

The water management is one of the key issues in low operating temperature proton exchange membrane fuel cells (PEMFCs). The gas diffusion layer (GDL) allows the reactant gases flow to the reaction sites of the catalyst layer (CL). At high current density, generated water forms droplets because the normal operating temperature is $60{\sim}80^{\circ}C$. If liquid water is not evacuated properly, the pores in the GDL will be blocked and the performance will be reduced severely. In this study, the microchannel GDL was proposed to solve the flooding problem. The liquid water transport through 3-D constructed conventional GDL and microchannel GDL was analyzed varying air velocity, water velocity, and contact angle. The simulation results showed that the liquid water was evacuated rapidly through the microchannel GDL because of the lower flow resistance. Therefore, the microchannel GDL was efficient to remove liquid water in the GDL and gas channels.

• 한국신재생에너지학회:학술대회논문집
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• 2010.06a
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• pp.130.2-130.2
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• 2010

한전 전력연구원에서는 2009년 12월부터 125 kW급 용융탄산염 연료전지 발전시스템의 성능평가를 위한 운전이 진행되고 있다. 현재 진행 중인 "250 kW급 열병합 용융탄산염 연료전지 Proto Type개발" 과제의 최종시작품인 250 kW급 발전시스템은 125 kW급 MCFC 스택 2기로 설계되어, 125 kW급 시스템의 시험운전은 매우 중요한 기술적 성과가 될 것이다. 현재 125 kW급 MCFC 스택은 10,000 $cm^2$의 유효전극면적을 갖는 단위전지들로 구성되었으며, 적층 스택의 온도 및 농도분포의 최적화를 위해 내부 매니폴드 및 Co-flow Type 열교환기 기반의 분리판을 개발 적용하였다. 연료극의 전극 구성은 Ni-Al alloy로, 공기극의 전극 구성은 Lithiated-NiO로 이루어졌다. 그리고 매트릭스는 ${\alpha}-LiAlO_2$로 제작되었고, 전해질은 Li과 K Carbonate가 68 : 32 비율로 섞인 용융염을 사용하였다. 본 125 kW급 용융탄산염 연료전지 시스템의 운전평가는 고적층 스택의 온도 및 농도 분포를 확인하고, 최적화된 스택 운전 조건을 도출하는 것을 그 목적으로 하고 있다. 125kW급 스택 1기의 규모의 주변기기 시스템은 외부개질기, 촉매연소기, 이젝터, 고온순환 블로어 및 공기블로어 등으로 이루어져 있다. 고온형 연료전지 시스템에서 연료극과 공기극의 균일한 온도 및 압력 확보는 매우 중요하며, 이를 위하여 외부개질기 및 촉매연소기 연동을 통한 온도편차를 최소화하고, 기존 고온용 순환 블로어 대신 이젝터를 개발 도입하여 압력균형을 조절하였다. 125kW급 MCFC 시스템은 2009년 12월부터 전처리 운전을 시작하여 2010년 1월 말부터 PCS로 전기를 생산하고 있다. 평균전압 0.83V에서 100kW의 출력을 기록하였으며, 피크부하 120 kW, 누적출력량 30 MWh를 초과달성하였다.

• Membrane Journal
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• v.26 no.1
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• pp.1-13
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• 2016

Fuel cells are regarded as a representative energy source expected to replace fossil fuels particularly used in internal combustion engines. One of the most important components is polymer electrolyte membranes (PEMs) acting as a proton conducting barrier to prevent fuel gas crossover. Since water channels act as proton pathways through PEMs, many researchers have been focused on the 'good phase-separation of hydrophilic moiety' which ensures high water retention under low humidity enough to keep the water channel for good proton conduction. Here, we summarized the strategies which have been adopted to synthesize sulfonated PEMs having high proton conductivities even under low humidified conditions, and hope this review will be helpful to design high performance hydrocarbon PEMs.

• Korean Chemical Engineering Research
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• v.54 no.6
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• pp.847-853
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• 2016

Here has been examined a 3-dimensional computational fluid dynamics (CFD) modeling in order to investigate the performance analysis of proton exchange membrane (PEM) fuel cells with serpentine flow fields. The present CFD model considers the isothermal transport phenomena in a fuel cell involving mass, momentum transport, electrode kinetics, and potential fields. Co-current flow patterns for a PEMFC are considered for various geometries in the single straight cell. Current density distribution from the calculated distribution of oxygen and hydrogen mass fractions has been determined, where the activation overpotential has been also calculated within anode and cathode. CFD results showed that profiles differ from those simulations subjected to each the calculated activation overpotential. It is interesting that the present serpentine flow field shows the specific distribution of current density with respect to the aspect ratio of depth to width and the ratio of reaction area for various serpentine geometries. Simulation results were considered reasonable with the other CFD results reported in literature and global comparisons of the PEMFC model.