• Korean Chemical Engineering Research
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• 제56권1호
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• pp.1-5
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• 2018

본 연구에서는 고분자전해질 연료전지(PEMFC)가 실제 구동되는 고전류밀도 범위까지 임피던스를 분석해 이온전도도에 대해 연구하였다. 가스확산층(GDL)유무가 임피던스에 미치는 영향을 수소투과도 측정에 의해 간접적으로 검토하였다. 저전류 범위(<$80mA/cm^2$)에서 상대습도(RH)가 60% 이상 높을 때는 고분자 막의 수분 함량이 충분해 막의 이온전도도가 전류 변화의 영향을 받지 않았다. 그러나 RH가 낮을 때는 전류밀도가 증가하면서 수분 생성에 의해 이온전도도가 증가했다. 고전류 영역($100{\sim}800mA/cm^2$)에서 HFR (High Frequency Resistance)로 구한 막의 이온전도도 실험값과 수치해석에 의해 구한 값을 비교하였다. RH 100%에서는 실험값과 모사한 값 모두 전류 변화에 영향을 받지 않고 일정한 이온전도도를 유지함을 보였다. RH 30~70%에서는 전류밀도 증가에 따라 이온전도도가 증가하다 일정해 지는 경향을 나타냈다.

• Korean Chemical Engineering Research
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• 제52권6호
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• pp.695-700
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• 2014

고분자전해질 연료전지로 물을 전기분해하여 수소와 산소를 발생시킬 수 있다. 그러나 1.7V 이상의 높은 전압에서 수전해 반응이 일어나므로 전극과 고분자 전해질 막의 열화가 빠르게 진행된다. 수전해 과정에서 anode의 열화를 방지하기 위해 촉매로 지지체 없는 $IrO_2$를 보통 사용하는데 본 연구에서는 고분자전해질 연료전지용 Pt/C 촉매를 수전해 반응에 그대로 사용했을 때 전극과 막의 열화 현상을 분석하였다. 1.8~2.0 V 전압 범위에서 수전해 반응 후 고분자 전해질 연료전지 구동 조건에서 I-V, CV, 임피던스, LSV를 측정했다. 수전해 전압이 높을수록 전극과 막의 열화 속도가 증가하였다. 2.0 V에서 1분 동안 수전해 반응했을 때 수소 수율은 88%였고, 전극과 고분자 막이 열화되어 0.6 V에서 성능이 49% 감소하였다.

• Macromolecular Research
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• 제13권6호
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• pp.514-520
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• 2005

Composite membranes of Nafion and sulfonated poly(arylene ether sulfone) were prepared. Sulfonated poly(arylene ether sulfone)s with different degrees of sulfonation were blended with Nafion to reduce the methanol crossover. The morphology, proton conductivity and methanol permeability of the resulting composite membranes were investigated by SEM, EDAX, AC impedance spectroscopy and permeability measuring instrument. The cross­sections of the composite membranes showed a phase separated morphology. The morphology and phase separation mechanism could be controlled by varying the blend ratio and the degree of sulfonation of poly(arylene ether sulfone). These complex morphologies can be applied for reducing methanol crossover. The methanol permeability and proton conductivity of the composite membranes were lower than those of Nafion 117 membrane since the development of an ionic pathway in the blend membrane was more difficult than that in Nafion itself.

• 한국재료학회지
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• 제19권5호
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• pp.233-239
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• 2009

The electrocatalytic behavior of the PtCo catalyst supported on the multi-walled carbon nanotubes (MWNTs) has been evaluated and compared with commercial Pt/C catalyst in a polymer electrolyte membrane fuel cell(PEMFC). A PtCo/MWNTs electrocatalyst with a Pt:Co atomic ratio of 79:21 was synthesized and applied to a cathode of PEMFC. The structure and morphology of the synthesized PtCo/MWNTs electrocatalysts were characterized by X-ray diffraction and transmission electron microscopy. As a result of the X-ray studies, the crystal structure of a PtCo particle was determined to be a face-centered cubic(FCC) that was the same as the platinum structure. The particle size of PtCo in PtCo/MWNTs and Pt in Pt/C were 2.0 nm and 2.7 nm, respectively, which were calculated by Scherrer's formula from X-ray diffraction data. As a result we concluded that the specific surface activity of PtCo/MWNTs is superior to Pt/C's activity because of its smaller particle size. From the electrochemical impedance measurement, the membrane electrode assembly(MEA) fabricated with PtCo/MWNTs showed smaller anodic and cathodic activation losses than the MEA with Pt/C, although ohmic loss was the same as Pt/C. Finally, from the evaluation of cyclic voltammetry(CV), the unit cell using PtCo/MWNTs as the cathode electrocatalyst showed slightly higher fuel cell performance than the cell with a commercial Pt/C electrocatalyst.

• 한국신재생에너지학회:학술대회논문집
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• 한국신재생에너지학회 2009년도 추계학술대회 논문집
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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.

• 공업화학
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• 제32권4호
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• pp.442-448
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• 2021

고분자전해질 연료전지에서 분리판 유로 형상은 유체 공급과 물 및 열 확산, 접촉 저항 등에 영향을 주는 중요한 요소이다. 본 연구에서는 25 cm² 단위 전지를 이용하여 공기극에 구리폼을 적용한 분리판을 이용하여 연료전지 성능 평가를 수행하였다. 압력과 상대습도 조건에 대한 영향을 분극 곡선과 전기화학적 임피던스 분광법을 이용하여 분석하였다. 구리폼의 ohmic 저항이 높아 사형유로형상 보다 연료전지 성능은 낮았지만, 다공성 구조로 인한 균일한 연료 분포로 활성화 손실과 물질전달 손실이 적은 것을 확인하였다. 구리폼의 소수성이 높아 물 배출이 유리한 장점이 있지만, 저가습 조건에서는 사형유로에 비하여 전해질막 수화도가 낮은 것을 확인하였다. 다공성 금속 분리판은 균일한 압력 분포와 효과적인 수분 배출로 연료전지 성능을 개선할 수 있을 것으로 판단되며, 저항을 최소화할 수 있도록 금속폼의 물성에 대한 연구가 수행되어야 할 것이다.

• 한국신재생에너지학회:학술대회논문집
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• 한국신재생에너지학회 2010년도 춘계학술대회 초록집
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• pp.138.2-138.2
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• 2010

Scandium-doped zirconium, ScSZ-based electrolyte, provides higher oxygen conductivity than YSZ and nano-based electrolyte materials are ideal for fabricating thin film electrolyte membrane of SOFC unit cell. Moreover, it may be applied to anode and cathode as well as electrolyte as ionic conductor. In this report, nano-based ScSZ-based electrolyte powder was prepared by co-precipitation synthesis. The particle size, surface area and morphology of the powder were observed by SEM and BET. Thin film electrolyte of under $10{\mu}m$ was fabricated by tape casting and co-firing using the synthesized ScSZ-based powders, and ionic conductivity and gas permeability of electrolyte film were evaluated. Finally, the SOFC unit cell was fabricated using the anode-supported electrolyte prepared by a tape casting method and co-sintering. Electrochemical evaluations of the SOFC unit cell, including measurements such as power density and impedance, were performed and analyzed.

• 한국멀티미디어학회논문지
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• 제21권1호
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• pp.34-44
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• 2018

An early detection of intravenous (IV) infiltration is essential to minimize the injuries during infusion therapy, which is one of the most important tasks for nurses in nursing settings. We report that bioelectrical impedance analysis is useful in the early detection of infiltration at puncture sites. When infiltration was intentionally induced in the vein of a pig's posterior ear, impedance parameters (R, $X_C$, $C_m$) showed significant differences before and after infiltration. In particular, the relative resistance ($R/R_{BI}$) decreased significantly at infiltration and then slowly decreased. This indicates that the vein in pig's ear is thin and the amount of surrounding subcutaneous tissue, and hence the infiltrated solution accumulates slowly after infiltration. However, when infiltration was induced in the vein of human's forearm, the relative resistance at 20 kHz decreased gradually over time. In the $R-X_C$ graph, the positions in the case of infiltration induced in the pig' ear shifted rapidly before and after infiltration, whereas the positions in the case of infiltration induced in the human's forearm moved gradually during infiltration. Our findings suggest that the impedance parameters (R, $R/R_{BI}$, $X_C$, R vs. $X_C$, and $C_m$) are effective indicators to detect the infiltration early in a non-invasive and quantitative manners.

• 대한기계학회논문집B
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• 제38권8호
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• pp.687-693
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• 2014

본 연구에서는 휴대용 기기에 고분자 전해질막 연료전지(PEMFC)를 적용하기 위하여 상온에서 작동 시의 성능특성을 정상상태와 동적상태에서 관찰하였다. 상대습도 및 공기 화학양론비에 따른 PEMFC 성능 변화를 실험적으로 분석하였다. 또한, EIS(Electrochemical Impedance Spectroscopy)를 이용하여 내부 오믹 저항의 변화를 고찰하였다. $35^{\circ}C$ 조건에서 물질 전달률이 감소하여 $45^{\circ}C$ 조건에 비해 전압 변동이 10배 정도 크게 관찰되었으며 안정적인 작동을 위해 공기의 화학양론비를 2.5 보다 크게 유지하여야 한다. 또한 낮은 상대습도는 오믹 저항을 크게 증가시키며, 이를 감소시키기 위해 상대습도 60% 이상으로 작동하여야 한다.

• 한국수소및신에너지학회논문집
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• 제16권1호
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• pp.31-39
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• 2005

Direct methanol fuel cell (DMFC) is considered as a candidate for portable power sources, that could overcome the disadvantages of lithium battery. But in order to attain commercial viability the long term stability of the DMFC should be achieved. Understanding the long-term behavior of membrane-electrode assembly (MEA) is a prerequisite to this purpose and the optimization of the MEA is also needed. In this study we have investigated the changes in performance and electrochemical properties of the MEA during extended operation and the effects of heat treatment of MEA on the long-term performance. The MEAs have been treated in an autoclave with saturated water vapor at 120$^{\circ}C$, vacuum oven at 140$^{\circ}C$ and boiling in organic solvents. The autoclaved MEA was found to be have the best long term performance. The on-off operation mode also increased the performance probably due to effective removal of products from the electrodes. Physical and electrochemical analyses using a scanning electron microscope, impedance analyser and half-cell technique have been done to characterize the MEAs.