• 한국수소및신에너지학회논문집
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• 제24권3호
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• pp.223-229
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• 2013

Polymer Electrolyte Membrane Fuel Cell (PEMFC) is a power generation system to convert chemical energy of fuels and oxidants to electricity directly by electrochemical reactions. As a catalyst support for PEMFCs, carbon black has been generally used due to its large surface area and high electrical conductivity. However, under certain circumstances (start up/shut down, fuel starvation, ice formation etc.), carbon supports are subjected to serve corrosion in the presence of water. Therefore, it would be desirable to switch carbon supports to corrosion-resistive support materials such as metal oxide. $TiO_2$ has been attractive as a support with its stability in fuel cell operation atmosphere, low cost, commercial availability, and the ease to control size and structure. However, low electrical conductivity of $TiO_2$ still inhibits its application to catalyst support for PEMFCs. In this paper, to explore feasibility of $TiO_2$ as a catalyst support for PEMFCs, $TiO_2$ nanofibers were synthesized by electrospinning and calcinated at 600, 700, 800 and $900^{\circ}C$. Effects of calcination temperature on crystal structure and electrical conductivity of electrospun $TiO_2$ nanofibers were examined. Electrical conductivity of $TiO_2$ nanofibers increased significantly with increasing calcination temperature from $600^{\circ}C$ to $700^{\circ}C$ and then increased gradually with increasing the calcination temperature from $700^{\circ}C$ to $900^{\circ}C$. It was revealed that the remarkable increase in electrical conductivity could be attributed to phase transition of $TiO_2$ nanofibers from anatase to rutile at the temperature range from $600^{\circ}C$ to $700^{\circ}C$.

• 한국세라믹학회지
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• 제43권2호
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• pp.85-91
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• 2006

Electron Beam Physical Vapor Deposition (EB-PVD) was applied to fabricate a thin film YSZ electrolyte with large area on the porous NiO-YSZ anode substrate. Microstructural and thermal stability of the as-deposited electrolyte film was investigated via SEM and XRD analysis. In order to obtain an optimized YSZ film with high stability, both temperature and surface roughness of substrate were varied. A structurally homogeneous YSZ film with large area of $12\times12\;cm^2$ and high thermal stability up to $900^{\circ}C$ was fabricated at the substrate temperature of $T_s/T_m$ higher than 0.4. The smoother surface was proved to give the better film quality. Precise control of heating and cooling rate of the anode substrate was necessary to obtain a very dense YSZ electrolyte with high thermal stability, which affords to survive after post heat treatment for fabrication a cathode layer on it as well as after long time operation of solid oxide fuel cell at high temperature.

• 한국가스학회지
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• 제22권1호
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• pp.1-8
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• 2018

수소연료전지 자동차 압력 용기에는 연료전지 스택으로 수소의 흐름을 제어하기 위해 전자 밸브가 부착되고 있다. 전자 밸브의 솔레노이드는 전기 신호에 의해 유로를 개폐하는 역할을 하며, 전원이 인가되는 시간이 경과함에 따라 온도가 상승하여 일정 온도에서 포화된다. 특히 온도의 상승은 솔레노이드의 흡인력을 감소시키므로 안정적인 수소 공급을 위해서 설계 시 포화 온도와 온도에 따른 흡인력 특성 파악이 요구된다. 본 연구에서는 솔레노이드 설계 변수에 따른 포화 온도 계산식을 제안하고 열 유동 해석을 통해 타당성을 확인하였다. 또한, 온도에 따른 흡인력 변화를 분석하기 위해 전자기장 해석을 수행하였으며 온도 특성 실험을 통해 포화 온도와 흡인력 해석 결과를 검증하였다. 포화온도는 계산식과 해석결과를 비교하였을 때 $5.3^{\circ}C$, 해석 결과와 실험 결과를 비교하였을 때 $5.9^{\circ}C$의 오차가 발생하였으며, 흡인력은 1.0 N, 최대 2.1 N의 오차가 발생하였다.

• 한국수소및신에너지학회논문집
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• 제29권1호
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• pp.11-18
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• 2018

A high efficiency integrated reforming system for improving the efficiency of the 5 kW PEMFC system used as the back up power of building was studied. The separated reforming system consisted of three parts - A steam reformer with two stage concentric circular shape, a heat exchanger type steam generator and a CO shift reactor. Temperature and steam carbon ratio (SCR) were control variables during operation. The operating conditions were optimized based on the thermal efficiency of the steam reformer as reformate gas composition changes at different temperature. In experiments, water was fully vaporized in the steam generator up to SCR 3.5 and the maximum thermal efficiency was achieved at the operating temperature around $700^{\circ}C$ in the steam reforming reactor. With the results of the separated reforming system research, we improved the shape of high efficiency integrated reformer. The performance evaluation of the integrated reformer was based on optimized operating conditions in SCR 3.5. As a result, the developed integrated reforming system maintained an efficiency of 76% and constant performance over 3,000 hours.

• 한국자동차공학회논문집
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• 제15권3호
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• pp.174-182
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• 2007

Fuel reforming technology for the fuel cell vehicles could be applied to internal combustion engine for the reduction of engine out emissions. Since syngas which is reformed from fossil fuel has hydrogen as a major component, it has abilities to enhance the combustion characteristics with wide flammability and high speed flame propagation. In this study, syngas was added to a gasoline engine to improve combustion stability and exhaust emissions of idle state. Syngas fraction is varied to 0%, 50%, 100% with various ignition timing and excess air ratio. Combustion stability, exhaust emissions, fuel consumption and exhaust gas temperature were measured to investigate the effects of syngas addition on idle performance. Results showed that syngas has ability to widely extend lean operation limit and ignition retard range with dramatical reduction of engine out emissions.

• Korean Chemical Engineering Research
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• 제57권2호
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• pp.172-176
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• 2019

저생 미생물 연료전지(BMFC)는 바다나 호수의 뻘 속에서 저생미생물이 유기물을 분해하면서 발생시키는 전기를 이용한 연료전지다. 본 연구에서는 BMFC 전극으로 카본 소재를 발수 처리한 고분자 전해질 연료전지(PEMFC)의 가스확산층(GDL)을 사용해서 성능이 높게 나오는 구동조건을 찾고자 하였다. 높은 저항 값을 갖는 외부저항을 사용했을 때 성능이 높았으며 바닷물에서 리드선의 부식에 의한 전극과 접촉저항 증가를 피해야 성능을 유지할 수 있었다. 기포 발생기를 사용해 최고출력밀도를 2배 이상 높일 수 있었고 최적 구동 온도는 $40^{\circ}C$였다.

• 한국수소및신에너지학회논문집
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• 제22권6호
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• pp.819-826
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• 2011

The proton exchange membrane fuel cell (PEMFC) is regarded as the most promising alternative power sources for unmanned aerial vehicle (UAV) due to its high energy density and silent operation. Since there are many load changes during UAV flight, thermal management is one of the important factor for the performance of PEMFC. In order to reduce the UAV weight for the stable operation of UAV, thermal management system (TMS) studied in this work does not use the fan but use the air flowing into UAV by UAV flight. In order to develop the passive type heat exchanger (HEX) for 1kW PEMFC, four types of HEXs are fabricated and their cooling performances are compared. The parametric study on the cooling performance of HEXs has performed with the variation of operating parameters such as mass flow rates and inlet temperature of air and coolant. Type 4 has the best performance in every case. This study can be helpful to achieve the optimal design of HEX for PEMFC powered UAV.

• Journal of Electrochemical Science and Technology
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• 제13권1호
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• pp.112-119
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• 2022

Molten carbonate fuel cells (MCFCs) are environmentally friendly, large-capacity power generation devices operated at approximately 650℃. If MCFCs are to be commercialized by improving their competitiveness, their cell life should be increased by operating them at lower temperatures. However, a decrease in the operating temperature causes a reduction in the cell performance because of the reduction in the electrochemical reaction rate. The cell performance can be improved by introducing a coating on the cathode of the cell. A coating with a high surface area expands the triple phase boundaries (TPBs) where the gas and electrolyte meet on the electrode surface. And the expansion of TPBs enhances the oxygen reduction reaction of the cathode. Therefore, the cell performance can be improved by increasing the reaction area, which can be achieved by coating nanosized LiCoO₂ particles on the cathode. However, although a coating improves the cell performance, a thick coating makes gas difficult to diffuse into the pore of the coating and thus reduces the cell performance. In addition, LiCoO₂-coated cathode cell exhibits stable cell performance because the coating layer maintains a uniform thickness under MCFC operating conditions. Therefore, the performance and stability of MCFCs can be improved by applying a LiCoO₂ coating with an appropriate thickness on the cathode.

• 대한금속재료학회지
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• 제49권1호
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• pp.25-31
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• 2011

Solid oxide fuel cells (SOFCs) have many attractive features for widespread applications in generation systems. Recently, stainless steels have attractive materials for metallic bipolar plate because metallic bipolar plates have many benefits compared to others such as graphite and composite bipolar plates. SOFC operates on high temperature of about $800{\sim}1000^{\circ}C$ than other fuel cell systems. Thus, many studies have attempted to reduced the operation temperature of SOFC to about $600{\sim}800^{\circ}C$, which is the intermediate temperature (IT) of SOFC. Low cost and high-temperature corrosion resistance are very important for the practical applications of SOFC in various industries. In this study, two specimens, 304 and 430 stainless steels with and without different pre-surface treatments on the surface were investigated. And, specimens were exposed at high temperature in the box furnace under oxidation atmosphere of $800^{\circ}C$. Oxidation behavior have been investigated with the materials exposed at different times (100 hrs and 400 hrs) by SEM, EDS and XRD. By increasing exposure time, the amount of metal oxide increased in the order like; STS304 < STS430 and As-received < As-polished < Sand-blast specimens.

• 한국수소및신에너지학회논문집
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• 제29권1호
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• pp.19-24
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• 2018

Fuel cells are used to generate electricity with a reformer. In particular, methanol has various advantages among the fuels for reformer. Methanol steam reformer devices can efficiently supply hydrogen to PEM fuel cell. This study investigated the optimal operation conditions of a methanol steam reforming process. For this purpose, aspen HYSYS was used for the optimization of reforming process. The optimal operating condition could be designed by setting independent variables such as temperature, pressure and steam to carbon ratio (SCR). The optimal temperature and steam to carbon ratio were $250-270^{\circ}C$ and 1.3-1.5, respectively. It is advantageous to operate at a pressure of 15-20 barg, considering the performance of the hydrogen purifier. In addition, a heat exchange network was designed to supply heat constantly to reformer through the latent heat of steam.