• Proceedings of the Korean Vacuum Society Conference
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• 2010.08a
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• pp.161-161
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• 2010

n-type 반도체 특성을 띄는 $SnO_2$ 나노선은 가스 센서, 투명 소자, 태양광 전지 등으로 널리 사용되고 있다. 본 연구에서는 화학기상증착법으로 성장한 $SnO_2$ 나노선으로 폴리이미드 (PMDA-ODA: PI) 박막을 게이트 절연막으로 이용한 전계효과트랜지스터를 플렉서블 기판에 제작하고 전기적 특성을 분석하였다. 전자 전달 특성 곡선으로부터 n-형의 반도체 특성을 확인하였으며, 대부분의 산화금속 나노선에서와 같이 매우 큰 전기적 히스테리시스가 관찰되었다. 산화금속계통 나노선 소자의 히스테리시스는 나노선 표면에 산소 및 물 분자가 흡착되어 생기는 전자 갇힘 현상이 가장 큰 원인으로 알려져 있는데, 이러한 히스테리시스를 조절하거나 없애는 것은 소자의 특성 향상에 있어 매우 중요하다. 한편 PI 절연막에는 느린 분극 현상을 만드는 OH 반응기가 존재하기 때문에 나노선과는 반대 방향의 히스테리시스를 보일 것으로 예상된다. 본 연구에서는 제작된 $SnO_2$ 나노선 FET에서 PI 게이트 절연막의 경화 정도에 따른 히스테리시스를 조사하였다. FT-IR 측정에 따르면, PI 필름에 존재하는 OH 반응기는 PI를 경화시킴에 따라 감소하였으며 전기적인 히스테리시스도 감소하였다. 따라서, 절연막을 경화시키지 않았을 때는 PI 내부에 다량의 OH 반응기가 존재하여, PI의 히스테리시스가 나노선 히스테리시스보다 더 크게 작용하여, 전체적으로는 PI의 특성인 반시계 (counterclockwise) 방향의 히스테리시스를 나타내었다. 한편, 절연막을 완전히 경화시키면, OH 반응기는 대부분 사라지고 나노선의 히스테리시스만 발현되어 소자는 시계방향의 히스테리시스를 보였다. 이러한 실험결과를 통해, PI 박막을 $250^{\circ}C$ 에서 약 7분간 경화시켰을 때 나노선과 절연막의 히스테리시스가 가장 이상적으로 상쇄되어 전체적으로 히스테리시스가 매우 작아진 것을 관찰할 수 있었다. 이는 향후 나노선 FET의 안정적인 응용에 매우 유용한 결과로 활용될 것으로 예측된다.

• Journal of the Korean Electrochemical Society
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• v.6 no.1
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• pp.36-40
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• 2003

Freezing of water in a polymer electrolyte membrane fuel cell (PEMFC) may cause severe problems in driving a fuel cell vehicle during the winter time. Characteristics of PEMFC which suffered low temperatures below zero degree was examined with the thermal cycles from 80 to $-10^{\circ}C$. With the thermal cycles, the cell performance was degraded due to the phase transformation and volume changes of water. Effects of freezing of water in PEMFC on the electrode structure and polarization resistance were examined by BET analysis, cyclic voltammetry, and AC impedance spectroscopy.

• Applied Chemistry for Engineering
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• v.7 no.3
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• pp.473-480
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• 1996

Synthesis of n-perfluorooctanesulfonyl fluoride(n-PFOSF), which is valuable precursor perfluoro-chemicals, was studied by electrochemical fluorination(ECF). Of prime concern was to investigate the cyclic voltamograms of Ni electrode in anhydrous hydrogen fluoride(AHF) with and without the reactants and to measure fluorine evolution potential. In a batch cell, chronoampherometric electrolysis and various chemical analysis such as GC, GC/MS and IR were used to understand the amphere change of electrode and the reaction paths. Fluorine equilibrium potential was found to be about 2.8V(vs. $Cu/CuF_2$) from the cyclic voltammograms and decay curves of anode potential in AHF. In batch processes, the ECF proceeded in two distinguished steps. The first step proceeded electrochemically and the second one chemically. Under 7V(vs. $Cu/CuF_2$), amount of crude products was proportional to the applied anode potential. Above 7V(vs. $Cu/CuF_2$), it had a hundred percentage with weight ratio of reactants and productivity of PFOSF was almost constant.

• Applied Chemistry for Engineering
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• v.31 no.5
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• pp.568-574
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• 2020

Gas diffusion layer (GDL) is one of the main components of PEMFC as a pathway of reactants from a flow field to an electrode, water transport in reverse direction, heat management and structural support of MEA. In this study, the effect of GDL on fuel cell performance was investigated for commercial products such as 39BC and JNT30-A3. Polarization curve measurements were performed at different flow rates and relative humidity conditions using 25 ㎠ unit cell. The parameters on operating conditions were calculated using an empirical equation. The electrical resistance increased as the GDL PTFE content increased. The crack of microporous layer had influence on the concentration loss as water pathway. In addition, the ohmic resistance increased as the relative humidity decreased, but decreased as the current density increased due to water formation. Curve fitting analysis using the empirical equation model was applied to identify the tendency of performance parameters on operating conditions for the gas diffusion layer.

• Journal of the Korean Ceramic Society
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• v.38 no.10
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• pp.948-952
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• 2001

PZT thick films were fabricated on alumina substrates by a screen printing method. They were sintered at $750^{\circ}C{\sim}1050^{\circ}C$ for 1 h under air or Pb atmosphere. Pyrochlore was observed as a second phase in PZT thick films sintered in air at temperatures of $950^{\circ}C$ and higher. PZT thick films sintered under Pb atmosphere showed denser microstructure, higher dielectric constant, and better-developed P-E hysteresis curve than the films sintered in air. PZT thick films sintered at $900^{\circ}C$ under Pb atmosphere showed the typical ferroelectric hysteresis with remanent polarization of $29.8{\mu}C/cm^2$ and coercive field of 48.4 kV/cm.

• Journal of Hydrogen and New Energy
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• v.25 no.1
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• pp.28-38
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• 2014

The organic-inorganic composite membrane in polymer exchange membrane fuel cells (PEMFCs) have several fascinating technological advantages such as a proton conductivity, thermal stability and mechanical properties. As the inorganic filler, silicon carbide (SiC) fiber have been used in various fields due to its unique properties such as thermal stability, conductivity, and tensile strength. In this study, composite membrane was successfully fabricated by modified-silicon carbide fiber. Modified process, as a novel process in SiC, takes reaction by phosphoric acid after oxidation process (generated homogeniusly $SiO_2$ layer on SiC fiber). The mechanical property which was conducted by tensile test of the 5wt% modified-$SiO_2@SiCf$ composite membrane was better than that of Aquivion casting membrane as well as ion cxchange capacity(IEC) and proton conductivity. In addition, the single cell performance was observed that the 5wt% modified-$SiO_2@SiCf$ composite membrane was approximately $0.2A/cm^2$ higher than that of a Aquivion casting electrolyte membrane and electrochemical impedance was improved with the charge transfer resistance and membrane resistance.

• Journal of the Korea Convergence Society
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• v.9 no.11
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• pp.285-290
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• 2018

The steel has been used in modern industry, car maker and electric appliance. The steel have some problem, specially corrosion problem. To solve corrosion problem, Zn electrodeposit on steel have been adapted. Recently, The modern industry asks to increase corrosion resistance. Naturally, Increasing corrosion resistance increases the thickness of Zn electrodeposit. But increasing thickness of Zn electrodeposit has some problems. In making part, There are some crack. This crack cause to decrease corrosion resistance. To solve this problem, it is interested in Zn Based alloy electrodeposit such as Zn-Cr. Here, the influence of the electrolytic conditions on the composition of the alloy plating in the chloride bath was investigated. The results are explained by the cathode overvoltage curve of Cr and Zn. As the current density of the cathode increases, Zn content of electrodeposit decrease and Cr content of electrodeposit increase. As the temperature of the electrolyte increases, Zn content of electrodeposit decrease and Cr content of electrodeposit increase.

• Applied Chemistry for Engineering
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• v.32 no.4
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• pp.442-448
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• 2021

Flow field is an important parameter for polymer electrolyte membrane fuel cell (PEMFC) performance to have an effect on the reactant supply, heat and water diffusion, and contact resistance. In this study, PEMFC performance was investigated using Cu foam flow field at the cathode of 25 cm² unit cell. Polarization curve and electrochemical impedance spectroscopy were performed at different pressure and relative humidity conditions. The Cu foam showed lower cell performance than that of serpentine type due to its high ohmic resistance, but lower activation and concentration loss due to the even reactant distribution of porous structure. Cu foam has the advantage of effective water transport because of its hydrophobicity. However, it showed low membrane hydration at low humidity condition. The metal foam flow field could improve fuel cell performance with a uniform pressure distribution and effective water management, so future research on the properties of metal foam should be conducted to reduce electrical resistance of bipolar plate.

• Applied Chemistry for Engineering
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• v.32 no.1
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• pp.68-74
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• 2021

Gas diffusion layer (GDL) compression is important parameter of polymer electrolyte membrane fuel cell (PEMFC) performance to have an effect on contact resistance, reactants transfer to electrode, water content in membrane and electrode assembly (MEA). In this study, the effect of GDL compression on fuel cell performance was investigated for commercial products, JNT20-A3. Polarization curve and electrochemical impedance spectroscopy was performed at different relative humidity and compression ratio using electrode area of 25 ㎠ unit cell. The contact resistance was reduced to 8, 30 mΩ·㎠ and membrane hydration was increased as GDL compression increase from 18.6% to 38.1% at relative humidity of 100 and 25%, respectively. It was identified through ohmic resistance change at relative humidity conditions that as GDL compression increased, water back-diffusion from cathode and electrolyte membrane hydration was increased because GDL porosity was decreased.

• Applied Chemistry for Engineering
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• v.34 no.1
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• pp.9-14
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• 2023

In this work, we developed a Nafion polymer-coated impedance sensor with two gold electrode configurations to measure the ion concentration in solution samples. The gold electrodes were fabricated through the sputtering process, followed by surface modification using Nafion polymer. The resulting sensors enable the prevention of the polarization phenomenon on the electrode surface, resulting in stable measurement of electrochemical signals. Spectroscopy and scanning electron microscopy measurements revealed that the thin film of Nafion was coated uniformly onto the surface of the gold electrode. The Nafion-coated sensor exhibited more stable impedance signals than the conventional gold electrode. It showed a highly reliable calibration curve (R² = 0.983) of the impedance sensor using a standard sodium chloride solution. In addition, a comparison experiment between the impedance sensor and a commercial conductivity sensor was performed to measure the ion concentration of artificial tears, showing similar results for the two sensors.