• 한국표면공학회지
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• 제52권3호
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• pp.150-155
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• 2019

The carbon electrode was modified through manganese-catalyzed hydrogenation method for high energy density vanadium redox flow battery (VRFB). During the catalytic hydrogenation, the manganese oxide deposited at the surface of the carbon electrode stimulated the conversion reaction from carbon to methane gas. This reaction causes the penetration of the manganese and excavates a number of cavities at electrode surface, which increases the electrochemical activity by inducing additional electrochemically active site. The formation of the porous surface was confirmed by the scanning electron microscopy (SEM) images. Finally, the electrochemical performance test of the electrode with the porous surface showed lower polarization and high reversibility in the cathodic reaction compared to the conventional electrode.

• Korean Chemical Engineering Research
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• 제51권4호
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• pp.460-464
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• 2013

본 연구에서는 $LiMn_2O_4$ 제조에서 Mn 원료로 사용되는 CMD를 seed 첨가법을 사용하여 제조하고자 하였으며, Seed의 열처리 온도가 CMD 합성에 미치는 영향을 고찰하고, 그로부터 제조되는 $LiMn_2O_4$의 전기화학적 특성을 평가하고자 하였다. 제조한 시료의 물성평가는 X-선 회절 분석법(XRD), 주사전자현미경(SEM)을 통하여 실시하였다. 그 결과, $MnCO_3$를 $300^{\circ}C$ 이상의 온도에서 열처리하여 seed로 사용할 경우 ${\gamma}-MnO_2$ 상의 CMD가 얻어졌으며, 그 CMD를 LMO 제조에 사용할 경우 전기화학적 특성이 비교적 우수한 LMO가 얻어졌다.

• 한국세라믹학회지
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• 제55권5호
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• pp.498-503
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• 2018

Using the thermal ablation method, the oxidation behavior of $SiC_f/SiC$ composites was investigated in air and in the temperature range of $1,300^{\circ}C$ to $2,000^{\circ}C$. At the relatively low temperature of $1,300^{\circ}C$, passive oxidation, which formed amorphous phase, predominantly occurred in the thermal ablation test. When the oxidation temperature increased, SiO (g) and CO (g) were formed by active oxidation and the dense oxide layer changed to a porous one by vaporization of gas phases. In the higher temperature oxidation test, both active oxidation due to $SiO_2$ decomposition on the surface of the oxide layer and active/passive oxidation transition due to interfacial reaction between oxide and base materials such as SiC fiber and matrix phase simultaneously occurred. This was another cause of high temperature degradation of $SiC_f/SiC$ composites.

• 멤브레인
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• 제24권5호
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• pp.367-374
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• 2014

본 연구에서는 LSCF/GDC (20 : 80 vol%) 복합 분리막 표면에 LSC/GDC (50 : 50 vol%) 활성층을 코팅한 후 활성층의 열처리 온도, 두께, 침투법을 이용한 STF 도입이 산소투과 특성에 미치는 영향을 고찰하였다. 활성층 도입은 복합 분리막의 산소 투과 유속을 급격히 증진시켰으며 이는 활성층 성분인 LSC/GDC (50 : 50 vol%)가 전자 전도성 및 표면 산소 분해 반응을 증진시켰기 때문이었다. 활성층의 열처리 온도가 $900^{\circ}C$에서 $1000^{\circ}C$로 증가한 경우, 산소 투과 유속은 증가하였고 이는 분리막과 활성층 사이 그리고 활성층의 결정입간 접촉이 증진하여 산소이온과 전자 흐름을 증진시켰기 때문으로 설명되었다. 코팅층의 두께가 약 $10{\mu}m$에서 약 $20{\mu}m$로 증가한 경우, 산소 투과 유속은 오히려 감소하였는데 이는 코팅층의 두께가 증가할수록 기공을 통한 공기 중의 산소 유입이 어려워지기 때문으로 설명되었다. 또한, 코팅층에 침투법을 이용하여 STF를 도입한 경우가 STF를 도입하지 않은 경우 보다 높은 산소 투과 유속을 보였는데 이는 도입된 STF가 산소 분해하는 표면 반응 속도를 촉진시키기 때문이다. 본 연구로부터 LSC/GDC (50 : 50 vol%) 활성층 코팅 및 특성 제어는 LSCF/GDC (20 : 80 vol%) 복합 분리막의 산소투과 증진에 매우 중요함을 확인하였다.

• Advances in Energy Research
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• 제8권4호
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• pp.253-264
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• 2022

This paper deals with the effects of design (active area, current density, membrane conductivity) and operating parameters (temperature, relative humidity) on the performance of hydrogen-fuelled proton exchange membrane (PEM) fuel cell. The design parameter of a PEM fuel cell with the active area of the single cell considered in this study is 25 cm² (5 × 5). The operating voltage and current density of the fuel cell were 0.7 V and 0.5 A/cm² respectively. The variations of activation voltage, ohmic voltage, and concentration voltage with respect to current density are analyzed in detail. The membrane conductivity with variable relative humidity is also analyzed. The results show that the maximum activation overpotential of the fuel cell was 0.4358 V at 0.21 A/cm² due to slow reaction kinetics. The calculated ohmic and concentrated overpotential in the fuel cell was 0.01395 V at 0.76 A/cm² and 0.027 V at 1.46 A/cm² respectively.

• Applied Science and Convergence Technology
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• 제26권5호
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• pp.133-138
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• 2017

We investigated the interface defect engineering and reaction mechanism of reduced transition layer and nitride layer in the active plasma process on 4H-SiC by the plasma reaction with the rapid processing time at the room temperature. Through the combination of experiment and theoretical studies, we clearly observed that advanced active plasma process on 4H-SiC of oxidation and nitridation have improved electrical properties by the stable bond structure and decrease of the interfacial defects. In the plasma oxidation system, we showed that plasma oxide on SiC has enhanced electrical characteristics than the thermally oxidation and suppressed generation of the interface trap density. The decrease of the defect states in transition layer and stress induced leakage current (SILC) clearly showed that plasma process enhances quality of $SiO_2$ by the reduction of transition layer due to the controlled interstitial C atoms. And in another processes, the Plasma Nitridation (PN) system, we investigated the modification in bond structure in the nitride SiC surface by the rapid PN process. We observed that converted N reacted through spontaneous incorporation the SiC sub-surface, resulting in N atoms converted to C-site by the low bond energy. In particular, electrical properties exhibited that the generated trap states was suppressed with the nitrided layer. The results of active plasma oxidation and nitridation system suggest plasma processes on SiC of rapid and low temperature process, compare with the traditional gas annealing process with high temperature and long process time.

• 한국세라믹학회지
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• 제42권1호
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• pp.56-61
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• 2005

아나타제 $TiO_{2}$, 활성탄, 세라믹섬유를 포함하는 VOC 흡착과 광산화분해 특성을 동시에 갖는 내구성이 우수한 광촉매 종이를 제조하여 그 특성을 분석하였다. 광촉매 종이 제조용 슬러리 내에 함유되어 있는 $TiO_{2}$를 활성탄 및 세라믹섬유 표면에 선택적으로 결합시키기 위한 PDADMAC의 적정농도범위는 $10{\~}15ppm$이었으며, 제지방법에 의해 만들어진 광촉매 종이는 두께 0.4mm, 평량 $380g/m^{2}$을 나타내었다. 제조된 광촉매 종이는 활성탄에 의한 흡착과 $TiO_{2}$에 의한 광산화 분해 반응이 동시에 진행되어 이들 두 반응이 각각 단독으로 진행되는 VOC 제거용 소재에 비하여 아세트알에히드의 제거속도를 크게 증가시켰다. 또한 세라믹섬유-$TiO_{2}$, 활성탄-$TiO_{2}$의 선택적인 결합은 UV 조사시 $TiO_{2}$에 의한 기지내 유기물의 분해를 방지하여 내구성을 개선하는데 효과적이었다.

• 한국분말재료학회지
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• 제4권3호
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• pp.196-204
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• 1997

Joining of AIN ceramics to W and Cu by active-metal brazing method was tried with use of (Ag-Cu)-Ti alloy as insert-metal. Joints were produced under various conditions of temperature, holding time and Ti-content in (Ag-Cu) alloy Reaction and microstructural development in bonded interface were investigated through observation and analysis by SEM/EDS, EPMA and XRD. Joint strengths were measured by shear test. Bonded interface consists of two layers: an insert-metal layer of eutectic Ag- and Cu-rich phases and a reaction layer of TiN. Thickness of reaction layer increases with bonding temperature, holding time and Ti-content of insert-metal. It was confirmed that the growth of reaction layer is a diffusion-controlled process. Activation energy for this process was 260 KJ/mol which is lower than that for N diffusion in TiN. Maximum shear strength of 108 MPa and 72 MPa were obtained for AIN/W and AIN/Cu joints, respectively. Relationship between processing variables, joint strength and thickness of reaction layer was also explained.

• 한국수소및신에너지학회논문집
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• 제26권2호
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• pp.170-178
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• 2015

In this study, we carry out a study on how to improve performance of vanadium redox flow battery (VRFB) through promoting reaction rate of rate determining vanadium reaction ($[VO]^{2+}/[VO_2]^+$). In order to do that, three different carbons like Vulcan (XC-72), CMK3 and MSU-F-C are adopted as the catalysts, while their catalytic activity and reaction reversibility are evaluated using half-cell tests. Their topological images are also measured by TEM. For estimation of the VRFB performance, multiple charge-discharge curves of VRFBs including the catalysts are measured by single cell tests. As a result of that, MSU-F-C shows relatively excellent catalytic activity and reaction reversibility as well as large surface area compared to those of Vulcan (XC-72) and CMK3. Also, in terms of the performance of VRFBs including the catalysts, VRFB including MSU-F-C indicates (i) low charging/discharging overpotentials and low internal resistance, (ii) high charge/discharge capacities and (iii) high energy efficiency. These VRFB performance data are well agreed with results on catalytic activity and reaction reversibility. The reason that MSU-F-C induces superior VRFB performances is attributed to (i) its large surface area and (ii) its hydrophilic surface functional groups that mainly consist of hydroxyl bonds that are supposed to play active surface site role for facilitaing $[VO]^{2+}/[VO_2]^+$ redox reaction. Based on the above results, it is found that adoption of MSU-F-C as catalyst for VRFB results in improvement in VRFB performance by promoting the languid $[VO]^{2+}/[VO_2]^+$ redox reaction.

• Mass Spectrometry Letters
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• 제12권4호
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• pp.146-151
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• 2021

In this study, the hydrogen/deuterium (HDX) exchange mechanism of active hydrogen, nitrogen, and sulfur-containing polycyclic aromatic hydrocarbon (PAH) dissolved in toluene and deuterated methanol by atmospheric pressure photoionization (APPI) is investigated. The comparison of the data obtained using APPI suggests that aniline and benzene-1,2-dithiol contain two exchanging hydrogens. The APPI HDX that best explains the experimental findings was investigated with the use of quantum mechanical calculations. The HDX mechanism is composed of a two-step reaction: in the first step, analyte radical ion gets deuterated, and in the second step, the hydrogen transfer occurs from deuterated analyte to de-deuterated methanol to complete the exchange reaction. The suggested mechanism provides fundamentals for the HDX technique that is important for structural identification with mass spectrometry. This paper is dedicated to Professor Seung Koo Shin for his outstanding contributions in chemistry and mass spectrometry.