• Proceedings of the KIEE Conference
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• 2007.07a
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• pp.1271-1272
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• 2007

Experimental results regarding to the structural properties of carbon nanotubes (CNTs) and the field-emission characteristics of CNT-coated tungsten (W) tips are presented. CNTs are successfully grown on conical-type W-tips by inductively coupled plasma-chemical vapor deposition (ICP-CVD) with or without inserting a TiN-buffer layer prior to the formation of Ni catalysts. For all the CNTs grown, their nanostructures, morphologies, and crystalline structures are analyzed by FESEM, HRTEM, and Raman spectroscopy. Furthermore, the emission properties of CNT-based field-emitters are characterized to estimate the maximum current density and the threshold voltage. The results obtained in this study indicate that the emission current level of the CNT-emitter without using a TiN buffer is desirable for the application of micro-focused x-ray systems.

• Applied Chemistry for Engineering
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• v.25 no.1
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• pp.78-83
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• 2014

In this research, we evaluated the performance and characteristics of carbon supported PtM (M = Ni and Y) alloy catalysts (PtM/Cs) synthesized by a modified polyol method. With the PtM/Cs employed as a catalyst for the oxygen reduction reaction (ORR) of cathodes in proton exchange membrane fuel cells (PEMFCs), their catalytic and ORR activities and electrical performance were investigated and compared with those of commercial Pt/C. Their particle sizes, particle distributions and electrochemically active surface areas (EAS) were measured by TEM and cyclic voltammetry (CV), while their ORR activity and electrical performance were explored using linear sweeping voltammetries with rotating disk electrodes and rotating ring-disk electrodes as well as PEMFC single cell tests. TEM and CV measurements show that PtM/Cs have the compatible particle size and EAS with Pt/C. When it comes to ORR activity, PtM/C showed the equivalent or better half-wave potential, kinetic current density, transferred electron number per oxygen molecule and $H_2O_2$ production(%) to or than commerical Pt/C. Based on results gained by the three electrode tests, when the PEMFC single cell tests were carried out, the current density measured at 0.6 V and maximum power density of PEMFC single cell adopting PtM/C catalysts were better than those adopting Pt/C catalyst. It is therefore concluded that PtM/C catalysts synthesized by modified polyol can result in the equivalent or better ORR catalytic capability and PEMFC performance to or than commercial Pt/C catalyst.

• 한국신재생에너지학회:학술대회논문집
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• 2010.06a
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• pp.223.2-223.2
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• 2010

용융탄산염 연료전지(MCFC)는 $650^{\circ}C$에서 작동하는 고온형 연료전지 시스템이다. 이 시스템은 천연가스 등을 개질하여 생산된 수소를 바로 전기로 생산할 수 있는 시스템으로 열효율이 높으며, 현재 대체 발전시스템으로 각광을 받고 있다. MCFC는 개질방식에 따라 내부개질 방식과 외부개질 방식이 있다. 내부개질 방식은 수소를 생산하는 개질기가 스택내부에 장착된 형식으로 천연가스를 스택내부에서 개질하여 바로 전기를 생산하는 방식이다. 이 내부개질반응에 사용되는 촉매로는 알루미나에 담지된 니켈(Ni) 계열촉매이 주로 쓰이고 있다. 또한 내부개질촉매의 형태는 작은 원주형의 촉매형태로 성형되어 사용된다. 이 성형된 촉매의 크기가 바로 내부개질 스택의 크기를 결정하는 중요한 요소이다. 그래서 촉매의 크기는 되도록이면 작게 성형하는 것이 중요하다. 그러나 촉매의 크기가 너무 작으면 촉매를 성형하는데 큰 어려움이 생기게 된다. 본 연구에서는 니켈 촉매를 공침법이 아닌 균일용액침전법을 이용하여 제조하였으며, 이 촉매를 이용하여 지름이 약 2 mm 이하로 촉매를 압출성형하는 방법을 연구하였다. 먼저 요소(urea)를 이용한 균일용액침전법으로 촉매를 제조하였다. 최적의 촉매 합성조건을 살펴보기 위해서, 반응 온도를 80, 85, 90, 95, $100^{\circ}C$로 변화 시키면서 제조된 촉매의 특성을 살펴보았다. 그리고 촉매의 적절한 니켈 양을 알아보기 위해서 니켈의 양을 30, 40, 50, 60, 70 wt%로 변화 시켰으며, 조촉매로 사용되는 MgO 양을 5, 10, 15, 20 wt%로 변화 시켜서 제조된 촉매의 특성을 살펴보았다. 물성을 비교하기 위해서, X-선 회절분석(XRD) 및 TPR, 물리화학흡착을 하였다. 그 결과 침전반응온도가 $80^{\circ}C$에서 촉매가 가장 좋은 물성을 보였으며, 우수한 개질성능을 보였다. 그리고 촉매 활성물질인 니켈의 함량은 50 wt% 정도가 가장 적절한 함량이었으며, MgO의 함량이 15 wt%일 때 가장 우수한 물성과 개질 성능을 보여주었다. 이 촉매들은 공침법으로 제조된 상용촉매와 비교하였을 때, 보다 우수한 물성과 개질성능 보였다. 그래서 이 촉매를 균일침전법을 이용하여 대량으로 제조한 다음 압출성형 방법을 이용하여 촉매를 원주형으로 제조하였다. 먼저 제조된 촉매는 별도의 분쇄작업(볼밀 혹은 제트밀)을 거치지 않아도 입자사이즈가 약 $4{\mu}m$ 수준이 나오도록 촉매 제조조건을 조절 하였다. 그리고 소량의 Methyl cellulose(MC) 바이더와 물만 사용하여 촉매를 혼합한 다음 스크류 압출기를 이용하여 촉매를 성형하였다. 이 촉매는 지름이 약 2 mm 이하로 제조할 수 있었으며, 기계적 강도는 타정기로 성형한 상용촉매보다 우수하였다. 그리고 촉매 성능 또한 상용촉매와 비교하였을 때, 우수한 성능 보였다. MCFC용 내부개질 촉매로 균일용액침전법을 사용한 촉매가 적합하다고 판단되며, 압출성형에도 적합하다고 판단되었다.

• Journal of Korean Society of Environmental Engineers
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• v.39 no.2
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• pp.82-88
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• 2017

MET (Microbial Electrochemical Technology), such as MFC (Microbial Fuel Cell) and MEC (Microbial Electrolysis Cell), is a promising technology for producing sustainable biogas from an anaerobic digester (AD). At current stage, however, the most likely limiting factors, large internal resistances, should be overcome for successful scale up of this technology. Various researchers reported that application of electrode materials containing high current density, increase of ion strength and conductivity, configuration of electrode are good methods for minimizing internal resistances. Recently, stainless steel is receiving great attention because of not only high performance and durability but also low cost. Therefore, in this study, we evaluate electrochemical characteristics and biogas production rate using various electrode materials and configuration (graphite carbon coated with catalysts ($GC-C_M$) or not (GC), stainless steel mesh (SUS-M) and plate (SUS-P)). As the results, current densities of $GC-C_M$, GC, SUS-P, SUS-M were 2.03, 1.36, 1.04, $1.13A/m^2$, respectively. Methane yields of $GC-C_M$, GC, SUS-P, SUS-M were 0.27, 0.14, 0.19, 0.21 $L-CH_4/g-COD_{rem}$., respectively. Stainless steel shows high current density and methane yield, which are similar as graphite carbon coated with catalysts.

• Clean Technology
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• v.20 no.3
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• pp.269-276
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• 2014

This study was aimed to develop catalytic system for the dry-based reduction of oxidized mercury ($Hg^{2+}$) to elemental mercury ($Hg^0$) which is one of the most important components comprising mercury continuous emission monitoring system (Hg-CEMS). Based on the standard potential in oxidation-reduction reaction, transition metals including Fe, Cu, Ni and Co were selected as possible candidates for catalyst proceeding spontaneous reduction of $Hg^{2+}$ into $Hg^0$. These transition metal catalysts revealed high activity for reduction of $Hg^{2+}$ into $Hg^0$ in the absence of oxygen in reactant gases. However, their activities were greatly decreased in the presence of oxygen, which was attributed to the transformation of transition metals by oxygen to the corresponding transition metal oxides with less catalytic activity for the reduction of oxidized mercury. Hydrogen supplied to the reactant gases significantly enhanced $Hg^{2+}$ reduction activity even in the presence of oxygen. It might be due to occurrence of combustion reaction between $H_2$ and $O_2$ causing the consumption of $O_2$ at such high reaction temperature at which oxidized mercury reduction reaction took place. Because the system showed high activity for $Hg^{2+}$ reduction to $Hg^0$, which was compatible to that of wet-chemistry technology using $SnCl_2$ solution, the catalytic reduction system of Fe catalyst with the supply of $H_2$ could be employed as a commercial system for the reduction of oxidized mercury to elemental mercury.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2009.06a
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• pp.440-440
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• 2009

Semiconductor nanowires offer exciting possibilities as components of solar cells and have already found applications as active elements in organic, dye-sensitized, quantum-dot sensitized, liquid-junction, and inorganic solid-state devices. Among many semiconductors, silicon is by far the dominant material used for worldwide photovoltaic energy conversion and solar cell manufacture. For silicon wire to be used for solar device, well aligned wire arrays need to be fabricated vertically or horizontally. Macroscopic silicon wire arrays suitable for photovoltaic applications have been commonly grown by the vapor-liquid-solid (VLS) process using metal catalysts such as Au, Ni, Pt, Cu. In the case, the impurity issues inside wire originated from metal catalyst are inevitable, leading to lowering the efficiency of solar cell. To escape from the problem, the wires of purity of wafer are the best for high efficiency of photovoltaic device. The fabrication of wire arrays by the electrochemical etching of silicon wafer with photolithography can solve the contamination of metal catalyst. In this presentation, we introduce silicon wire arrays by electrochemical etching method and then fabrication methods of radial p-n junction wire array solar cell and the various merits compared with conventional silicon solar cells.

• Journal of the Korean Applied Science and Technology
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• v.20 no.3
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• pp.212-220
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• 2003

Electrical properties of carbon filler/PVdF [poly(vinylidene fluoride)] composite were investigated as a funtion of carbon filler/PVdF ratio in the range of 0.2${\sim}$0.5. Three kinds of comercialzied conductive carbon blacks such as Hiblack 41Y, KE300J, and KE600J, and carbon nanofibers prepared by the catalytic chemical vapor deposition of $C_2H_4$ over Ni-Cu catalysts were used as the carbon fillers. The electrical conductivity of carbon filler/PVdF composites were in the range of 0.65 to 13.5 S/cm depending the fillers' electrical conductivity ranging from 5.6 to 23.1 S/cm. Among the carbon fillers used, the KE600J carbon black showed the highest conductivity both in the composite and filler itself because of its high degree of graphitization due to the high-temperature thermal treatment and its high surface area due to the activation treatment.

• Journal of the Korean Applied Science and Technology
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• v.21 no.2
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• pp.174-181
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• 2004

Multi-walled carbon nanotubes (CNTs) were prepared by thermal chemical vapor deposition (CVD) and microwave plasma chemical vapor deposition (MPCVD) using various combination of binary catalysts with four transition metals such as Fe, Co, Cu, and Ni. In the preparation of CNTs from acetylene precursor by thermal CVD, the CNTs with very high yield of 43.6 % was produced over $Fe-Co/Al_2O_3$. The highest yield of CNTs was obtained with the catalyst reduced for 3 hr and the yield was decreased with increasing reduction time to 5 hr, due to the formation of $FeAl_2O_4$ metal-aluminate. On the other hand, the CNTs prepared by acethylene plasma CVD had more straight, smaller diameter, and larger aspect ratio(L/D) than those prepared by thermal CVD, although their yield had lower value of 27.7%. The degree of graphitization of CNTs measured by $I_d/I_g$ value and thermal degradation temperature were 1.04 and $602^{\circ}C$, respectively.

• Korean Journal of Materials Research
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• v.11 no.8
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• pp.703-707
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• 2001

The effects of chromium addition on the catalytic activity of Raney nickel in alkaline fuel cell (AFC) have been studied. When the catalysts are prepared from various contents of chromium, the electrochemical characteristics shows the highest mass activity of 3.588 A/g. Operating temperature and electrolyte concentration of half cell were $80^{\circ}C$ and 6N KOH, respectively. With the addition of chromium, the particle size is diminished from 12.11 $\mu\textrm{m}$ to 11.07 $\mu\textrm{m}$ and the decrease of particle size contributes to the enlargement of the specific surface area from 0.653 $\m^2$/g to 0.685$\m^2$/g. The residual aluminium contents of Raney nickel surface are considerably influenced by the particle size and chromium acts as sintering inhibitor.

• Journal of Environmental Science International
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• v.25 no.4
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• pp.517-524
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• 2016

In order to treat groundwater containing high levels of nitrate, nitrate reduction by nano sized zero-valent iron (nZVI) was studied using batch experiments. Compared to nitrate removal efficiencies at different mass ratios of $nitrate/Fe^0$, the removal efficiency at the mass ratio of 0.02% was the highest(54.59%). To enhance nitrate removal efficiency, surface modification of nZVI was performed using metallic catalysis such as Pd, Ni and Cu. Nitrate removal efficiency by Cu-nZVI (at $catalyst/Fe^0$ mass ratio of 0.1%) was 66.34%. It showed that the removal efficiency of Cu-nZVI was greater than that of the other catalysts. The observed rate constant ($k_{obs}$) of nitrate reduction by Cu-nZVI was estimated to $0.7501min^{-1}$ at the Cu/Fe mass ratio of 0.1%. On the other hand, TEM images showed that the average particle sizes of synthetic nZVI and Cu-nZVI were 40~60 and 80~100 nm, respectively. The results imply that catalyst effects may be more important than particle size effects in the enhancement of nitrate reduction by nZVI.