• Bulletin of the Korean Chemical Society
• /
• 제34권6호
• /
• pp.1763-1770
• /
• 2013

A series of the block copolymers were successfully synthesized from post-sulfonated hydrophilic and hydrophobic macromers via three-step copolymerization. The degrees of sulfonation (DS) of the copolymers (10%, 30%, or 50%) were controlled by changing the molar ratio of the hydrophilic and hydrophobic parts. The resulting block copolymers were characterized by $^1H$ NMR and other technologies. The membranes were successfully cast using dimethyl sulfoxide (DMSO) solution at $100^{\circ}C$. The copolymers were characterized to confirm chemical structure by $^1H$ NMR and FT-IR. Thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) demonstrated that all sulfonated block copolymers exhibited good thermal stability with an initial weight loss at temperatures above $240^{\circ}C$. The membranes showed acceptable ion exchange capacity (IEC) and water uptake values in accordance with DS. The maximum proton conductivity was 184 mS $cm^{-1}$ in block copolymer-50 at $60^{\circ}C$ and 100% relative humidity, while the conductivity of Nifion-115 was 160 mS $cm^{-1}$ under the same measurement conditions. AFM images of the block copolymer membranes showed well separated the hydrophilic and hydrophobic domains. From the observed results it is that the prepared block membranes can be considered as suitable polymer electrolyte membranes for the application of polymer electrolyte membrane fuel cells (PEMFC).

• 한국수소및신에너지학회논문집
• /
• 제29권1호
• /
• pp.41-55
• /
• 2018

General polymer electrolyte fuel cell (PEMFC) operates at less than $80^{\circ}C$. Therefore liquid phase water resulting from electrochemical reaction accumulates and floods the cell which in turn increases the mass transfer loss. To prevent the flooding, it is common to employ serpentine flow channel, which can efficiently export liquid phase water to the outlet. The major drawback of utilizing serpentine flow channel is the large pressure drop that happens between the inlet and outlet. On the other hand, in the high temperature polymer electrolyte fuel cell (HT-PEMFC), since the operating temperature is 130 to $180^{\circ}C$, the generated water is in the state of gas, so the flooding phenomenon is not taken into consideration. In HT-PEMFCs parallel flow channel with lower pressure drop between the inlet and outlet is employed therefore, in order to circulate hydrogen and air in the cell less pumping power is required. In this study we analyzed HT-PEMFC's different flow channels by parallel computation using previously developed 3-D isothermal model. All the flow channels had an active area of $25cm^2$. Also, we numerically compared the performance of HT-PEMFC parallel flow channel with different manifold area and Rib interval against the original serpentine flow channel. Results of the analysis are shown in the form of three-dimensional contour polarization curves, flow characteristics in the channel, current density distribution in the Membrane, overpotential distribution in the catalyst layer, and hydrogen and oxygen concentration distribution. As a result, the performance of a real area fuel cell was predicted.

• 대한수의학회지
• /
• 제60권3호
• /
• pp.133-137
• /
• 2020

Diarrhea is the most common cause of death in calves, and remains a major health challenge. Although there are many studies on the related pathogens, the understanding of the clinicopathological changes is limited. This study aimed to identify the pathogens and observe the clinicopathological changes in electrolytes and acute phase proteins (APPs) associated with diarrhea. Blood samples and fecal samples were collected from 141 calves for the determination of APPs, electrolyte and acid-base status and identification of enteropathogens, respectively. Single or co-infections with enteropathogens, including virus (bovine viral diarrhea virus, coronavirus, and rotavirus), Eimeria, Cryptosporidium, and Escherichia coli K99 were detected in both non-diarrheic and diarrheic calves. Levels of APPs such as serum amyloid A, haptoglobin and fibrinogen were comparable between diarrheic and non-diarrheic calves. Hypoglycemia, high blood urea, electrolytes and acid-base imbalance (hyponatremia, hypochloremia, and decreased bicarbonate), and strong ion difference (SID) acidosis showed a significant association in diarrheic calves (p < 0.01). Particularly, significant hyponatremia, bicarbonate loss, SID acidosis, hypoglycemia, and elevated blood urea nitrogen were found in rotavirus-infected calves. Monitoring the clinicopathological parameters of APPs and electrolyte levels could be vital in the clinical management of diarrheic calves.

• 전기화학회지
• /
• 제25권2호
• /
• pp.51-68
• /
• 2022

리튬금속전지는 높은 에너지 밀도를 구현시킬 수 있음에도 불구하고, 단락, 낮은 쿨롱 효율, 용량 손실, 사이클 성능 감소 등의 문제를 초래하는 덴드라이트 성장을 억제시키는 기술은 아직 학술연구 단계에 머물러 있다. 본 논문에서는 최근까지 발표된 리튬금속전극에서 덴드라이트 성장을 억제시킬 수 있는 방법을 4가지로 분류하여 분석해보았다. 즉, 리튬금속전극의 부피 팽창에 대응할 수 있는 유연한 SEI (solid electrolyte interface) 층, 덴드라이트 성장을 물리적으로 억제시킬 수 있는 SEI 지지층, 균일한 리튬 확산을 유도하여 리튬 성장을 조절하는 SHES (self-healing electrostatic shield) 메커니즘, 그리고 리튬의 균일한 전착을 유도하는 마이크로패터닝 등에 대해 연구된 사례들의 장단점을 분석하여, 리튬금속전극의 실용화 연구에 도움을 주고자 한다.

• Korean Chemical Engineering Research
• /
• 제57권6호
• /
• pp.847-852
• /
• 2019

본 연구에서는 퀴노잘린(quinoxaline)과 페로시아나이드(ferrocyanide)를 활물질로 활용한 알칼리 전해질 기반 수계 유기 레독스 흐름전지에 대해 다양한 첨가제를 적용하여 성능을 비교하는 실험을 진행하였다. 퀴노잘린(quinoxaline)의 경우 염화칼륨(KCl) 전해질보다는 수산화칼륨(KOH) 전해질에서의 레독스 전위(-0.97 V)가 더 작은 위치에 있으며, 이에 따라 KOH 전해질에 대해 페로시아나이드와 조합을 이루었을 때, 셀 전압 값은 1.3 V로 높게 나타났다. 상용 양이온 교환막 중 하나인 Nafion 117 멤브레인을 사용하였을 때, 퀴노잘린(quinoxaline)의 부반응 현상을 반전지 상에서 관찰할 수 있었으며, 이에 따라 충방전 자체가 잘 되지 않는 문제점이 있다. 따라서, 문제점이 되는 퀴노잘린(quinoxaline)의 부반응을 해결하기 위해 친전자체와 친핵체 중 하나인 포타슘설페이트($K_2SO_4$)와 포타슘아이오다이드(KI)를 사용하였으며, 포타슘아이오다이드(KI)를 사용하였을 때, 용량 손실율 측면에서 포타슘 아이오다이드(KI)를 첨가제로 넣지 않았을 때($0.29Ah{\cdot}L^{-1}per\;cycle$) 보다 더 낮은 용량 손실율($0.21Ah{\cdot}L^{-1}per\;cycle$)로 더 높은 용량 유지율을 보였다.

• 한국수소및신에너지학회논문집
• /
• 제21권6호
• /
• pp.533-539
• /
• 2010

Ni-YSZ supported button cells were prepared by spray-coating YSZ and screen-printing YSZ-LSM powder as an electrolyte and oxygen electrode on Ni-YSZ cermet disks. In order to identify the polarization loss mechanism in high temperature electrolysis current-voltage characteristics coupled with electrochemical impedance spectroscopy were investigated as a function of temperature, current load, and the humidity. The effects of the different current collectors of platinum and silver for oxygen electrodes were compared. With Ag current collector two polarization losses were distinguished. The high frequency component was attributed to the Ni-YSZ cermet which was less susceptible to temperature variation but increasing in loss with humidity. The lower frequency component was attributed to the LSM electrode. Platinum current collector led to a much lower polarization loss.

• 대한기계학회논문집B
• /
• 제33권8호
• /
• pp.604-612
• /
• 2009

Water management has been recognized as a crucial factor for achieving better performance and stability in polymer electrolyte membrane fuel cells (PEMFCs). Proper water management should provide favorable water conditions, including the local humidity, membrane water content, and liquid water saturation in PEMFCs, thereby leading to more uniform electrochemical reaction and current generation. In this study, computational fluid dynamics (CFD) simulation was conducted to investigate the effects of the cathode relative humidity (RH) on the performance of a 3 by $3\;cm^2$ PEMFC with serpentine flow fields. The CFD results showed that the best performance of the PEMFC was obtained for the cathode RH of 80%, but the performance variation was small for the cathode RH range of $60{\sim}100%$. However, the loss of the PEMFC performance was significant when the cathode RH was reduced below 40%. The reason for such performance variation was investigated through the detailed inspection of ohmic loss, activation and concentration overpotential, and water and current distributions.

• Bulletin of the Korean Chemical Society
• /
• 제32권11호
• /
• pp.3952-3958
• /
• 2011

The effect of sintering temperature on the electrochemical property of $LiMn_2O_4$ was investigated. Results showed that the particle size was increased at higher sintering temperatures while the initial capacity was decreased after high temperature sintering. Capacity fading, on the other hand, was suppressed at lower sintering temperatures since the sintering at higher temperatures (${\geq}800^{\circ}C$) increased the Mn ions with a lower oxidation state ($Mn^{+3}$), which induced structural instability during cycling due to dissolution of Mn ions into the electrolyte. In particular, $LiMn_2O_4$ sintered above $830^{\circ}C$ showed severe capacity fading (capacity loss was 38% of initial capacity) by lower coulombic efficiency due to the abnormally increased particle size.

• Journal of Chest Surgery
• /
• 제11권4호
• /
• pp.422-427
• /
• 1978

Alterations in the serum and urine potassium were studied in twenty patients who underwent open heart surgery in National Medical Center during the period from Jan.1978 to June 1978. There were twelve cases congenital heart disease and eight acquired heart disease. Rigg-Kyvsgaad mark IV roller pump and Polystan bubble oxygenator were used in all patients. Hemodilution was carried out by priming the oxygenator with Hartmann`s solution. Measurements were made of the serum electrolyte, gas analysis and twenty four hour urine electrolytes. During the bypass, the serum potassium decreased Significantly from 4.2?.47 to 3.6?. 72 mEq. per liter. [p<0.05] Fifty seven miliequivalant of potassium chloride were added during operation-urine potassium was higher in the diuretic group than in the non diuretic group. Plasma potassium level in the diuretic group was more significantly reduced than nondiuretic group. In this series large amount of urine potassium loss was noted on the day of operation, the first and second post operative day.

• 대한약리학회지
• /
• 제5권1호
• /
• pp.29-33
• /
• 1969

The effects of Ginseng saponin on respiration and $Na^+$, $K^+$ content of rat cerebral cortex slices were investigated to determine the action of Ginseng saponin on brain cortex at cellular level. There are many reports for the study of Ginseng on central stimulatory action in experimental animals. The electrical stimulation of slices of cortex causes a loss of potassium. And the respiration is needed to maintain a supply of energy for active cation transport. The reduction in $Qo_2$ is a consequence of primary cessation of active cation transport. Ginseng saponin stimulated respiration which was depressed by Morphine. But there was no significant change of electrolyte. It is suggested that the Ginseng saponin act rather on metabolic process than neural excitatory mechanism in vitro.