• Journal of Nuclear Fuel Cycle and Waste Technology(JNFCWT)
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• v.8 no.1
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• pp.9-17
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• 2010

The LCC (Liquid Cadmium Cathode) structure to be developed for inhibiting the formation and growth of the uranium dendrite has been known as a key part in the electrowinning process for the simultaneous recovering of uranium and TRU (TRans Uranium) elements from spent fuels. A zinc-gallium (Zn-Ga) experimental system which is able to be functional in aqueous condition and normal temperature has been set up to observe the formation and growth phenomena of the metal dendrites on liquid cathode. The growth of the zinc dendrites on the gallium cathode and the performance of the existing stirrer type and pounder type cathode structure were observed. Although the mechanical strength of the dendrites appeared to be weak in the electrolyte and easily crashed by the various cathode structures, it was difficult to effectively submerge the dendrite into the bottom of the liquid cathode. Based on the results of the aqueous phase experiments, a lab-scale electrowinning experimental apparatus which are applicable to the development of LCC srtucture for the electrowinning process was established and the performance tests of the different types of LCC structure were conducted to prohibit the uranium dendrite growth on LCC surface. The experimental results of the stirrer type LCC structures have shown that they could not effectively remove the uranium dendrites growing at the inner side of the LCC crucible and the performances of the paddle and harrow type LCC structure were similar. Therefore a mesh type LCC structure was developed to push down the uranium dendrites to the bottom of the LCC crucible growing on the LCC surface and at the inner side of the crucible. From the experimental results for the performance test of the mesh type LCC structure, the uranium was recovered over 5 wt% in cadmium without the growth of uranium dendrites. After completion of the experiments, solid precipitates of the bottom of the LCC crucible were identified as an intermetallic compound (UCd11) by the chemical analysis.

• Journal of the Korean Electrochemical Society
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• v.22 no.3
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• pp.128-137
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• 2019

A lithium is the lightest metal on the earth. It has some attractive characteristics as a negative electrode material such as a low reduction potential (-3.04 V vs. SHE) and a high theoretical capacity ($3,860mAh\;g^{-1}$). Therefore, it has been studied as a next generation anode material for high energy lithium batteries. The thin lithium electrode is required to maximize the efficiency and energy density of the battery, but the physical roll-press method has a limitation in manufacturing thin lithium. In this study, thin lithium electrode was fabricated by electrodeposition under various conditions such as compositions of electrolytes and the current density. Deposited lithium showed strong relationship between process condition and its characteristics. The concentration of electrolyte affects to the shape of deposited lithium particle. As the concentration increases, the shape of particle changes from a sharp edged long one to a rounded lump. The former shape is favorable for suppressing dendrite formation and the elec-trode shows good stripping efficiency of 92.68% (3M LiFSI in DME, $0.4mA\;cm^{-2}$). The shape of deposited particle also affected by the applied current density. When the amount of current applied gets larger the shape changes to the sharp edged long one like the case of the low concentration electrolyte. The combination of salts and solvents, 1.5M LiFSI + 1.5M LiTFSI in DME : DOL [1 : 1 vol%] (Du-Co), was applied to the electrolyte for the lithium deposition. The lithium electrode obtained from this electrolyte composition shows the best stripping efficiency (97.26%) and the stable reversibility. This is presumed to be due to the stability of the surface film induced by the Li-F component and the DOL effect of providing film flexibility.

• Journal of the Korean Electrochemical Society
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• v.6 no.2
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• pp.93-97
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• 2003

The electrode for a supercapacitor was prepared using an amorphous ruthenium oxide, which was synthesized from ruthenium trichloride hydrate$(RuO_2{\cdot}nH_2O)$. A supercapacitor was assembled with an electrode of ruthenium oxide material on a current collector of tantalum, and an electrolyte of 4.8 M sulfuric acid. The result of the AC impedance analyses on $Ta/H_2SO_4(4.8 M)/Pt$ cell showed that tantalum was stable at the potential range of $0.0\~1.1V(vs. SCE)$. Therefore, Ta film could be used the supercapacitor as a current collector. The irreversible hydrolysis in the supercapacitor occurred over ca. 1.0V(vs.SCE) when the supercapacitor was protonated to 0.5V(vs. SCE). The supercapacitor protonated to 0.5V(vs.SCE) showed good electrochemical properties when it was tested at the potential range of 1.0V in the charge-discharge test. The potential range of the electrodes including the positive and the negative electrode was varied between -0.004 and 0.995V(vs. SCE). The potential ranges of the positive and the negative electrode were $-0.004\~0.515V(vs.\;SCE)\;and\; 0.515\~0.995V(vs.\;SCE)$, respectively.

• Journal of the Korean Chemical Society
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• v.42 no.1
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• pp.122-134
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• 1998

In this review, we describe the electrochemical properties of spinel-type lithium manganese oxides $(Li_xMn_2O_4)$ and their failure modes encountered in 4 V lithium rechargable cells. The long-term cyclability (reversibility) of spinel electrodes is determined partly by the purity, size and distribution of spinel particles, and also by the microstructure of electrode plates. A proper selection of electrolytes is another important task in cyclability enhancements. In the spinel preparation, impurity formation and cation mixing should be minimized. The carbon content in composite cathodes should also be minimized to the extent where the cell polarization does not bring about adverse effects on cell performances. The binder content should be optimized on the basis of dispersion of component materials and mechanical strength of the plates. Cathodic capacity losses arising from solvent oxidation and spinel dissolution can be mitigated by using electrolytes composed of carbonates and/or fluorine-containing lithium salts. The carbon additives may be selected after a trade-off between the cell polarization in composite cathodes and the solvent oxidation on carbon surface.

• Journal of Nuclear Fuel Cycle and Waste Technology(JNFCWT)
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• v.15 no.4
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• pp.343-353
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• 2017

Processing and equipment were tailored for engineering scale fabrication of $UO_2$ porous pellets, a feed material for the electrolytic reduction process in the PRIDE (PyRoprocessing Integrated DEmonstration) facility at KAERI (Korea Atomic Energy Research Institute). The starting materials, $UO_2$ powder and pre-milled surrogate oxide powders, were proportioned to simulate the chemical composition of spent fuel (so-called Simfuel). The Simfuel powders were homogenized by mixing, compacted into a pellet shape, and finally heat treated using a tumbling mixer, rotary press, and sintering furnace. After sintering at $1450^{\circ}C$ for 24 h in $4%\;H_2-Ar$, the average bulk density of the $UO_2$ Simfuel pellets was $6.89g{\cdot}cm^{-3}$, which meets the standard of the following electrolytic reduction process. In addition, the results of a microstructural analysis demonstrated that the sintered Simfuel $UO_2$ porous pellets accurately simulate the properties of spent fuel in terms of the formation of second phases. These results provide essential information for the massive fabrication of $UO_2$ porous pellets for engineering scale pyroprocessing research.

• Korean Chemical Engineering Research
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• v.52 no.2
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• pp.247-255
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• 2014

$La_{0.8}Sr_{0.2}CuO_3$ powder with the perovskite structure was prepared as electrode catalyst using citrate method. Porous electrode was made with as-prepared catalyst, carbon as supporter and polytetrafluoroethylene (PTFE) as hydrophobic binder. As results of potentiostatic electrolysis with potential of -1.5~-2.5 V vs. Ag/AgCl in 0.1, 0.5 and 1.0 M KOH at 5 and $10^{\circ}C$ on the porous electrode, liquid products were methanol, ethanol, 2-propanol and 1, 2-butanol regardless reaction temperature, while gas products were methane, ethane and ethylene at $5^{\circ}C$, and methane, ethane and propane at $10^{\circ}C$ respectively. Optimal potentials for $CO_2$ reduction in the view of over all faradic efficiency were high values (-2.0 and -2.2 V) for gas products whereas low potential (-1.5 V) for liquid products regardless of concentration and temperature.

• Journal of the Korean Chemical Society
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• v.37 no.7
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• pp.635-641
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• 1993

Electrochemical cell, $Pt|air(PO_2=5.3{\times}10^{-3}atm)|Zr_{0.85}Ca_{0.15}O_{1.85}|air(PO_2= 0.21atm)|Pt$, has been designed to characterize the solid electrolyte and the temperature dependence of the electromotive force (EMF) has been measured in a temperature range of 600∼1000${\circ}$C. Solid electrolyte shows pure ionic conduction of the oxygen anion. The Fe-FexO, Co-CoO, Ni-NiO, and Cu2O-CuO electrodes have been prepared by mixing the 1 : 1 mole ratio of each metal and metal oxide and then by heating at 800${\circ}$C for 6 hours. Electrochemical cells, Pt│M(s), $MO(s)|Zr_{0.85}Ca_{0.15}O_{1.85}|air(PO_2=0.21atm)|Pt$, have been designed and the temperature dependence of the EMF has also been measured in the same temperature range. The changes of the thermodynamic state functions for the formation of the metal oxides are calculated from the electromotive forces and their temperature dependences. The material properties of the oxide systems are also discussed with the function changes.

• 한국신재생에너지학회:학술대회논문집
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• 2010.06a
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• pp.96.1-96.1
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• 2010

현재 태양광 시장에 진출한 대부분의 Si계열 태양전지는 복잡한 공정과 원재료 고갈, 높은 가격으로 인해 한계에 직면에 있는 상태이다. 최근 많은 연구소나 학교에서는 기존의 Si계열 태양전지를 대체할 대안으로 염료 감응형 태양전지에 대해서 높은 관심을 보이고 있으며, 그동안의 연구개발로 단위 셀 면적에서는 상용화에 근접한 효율을 확보한 상태이다. 염료 감응형 태양전지의 작동과정을 간단히 단계별로 살펴보면 나노 결정 산화물 반도체 표면에 흡착된 염료분자가 가시광선을 흡수하면 전자는 HOMO에서 LUMO로 천이하고 이 들뜬 상태의 전자는 다시 에너지 준위가 낮은 반도체 산화물의 전도띠로 주입된다. 주입된 전자는 나노 입자간 계면을 통하여 투명 전도성막으로 확산, 전달되고 산화된 염료분자는 전해질 I-에 의해 다시 환원되어 중성 분자가 된다. 그러나 표면상태 전자 중 일부는 산화된 염료와 다시 결합하거나, 전해질의 $I^{3-}$ 이온을 환원시키기도 한다. 이와 같은 과정은 암전류를 증가시키면서 반도체 전극 막의 성능을 저해하는 주원인이 된다. 전자의 재결합은 투명 전극을 통해서도 가능하기 때문에 투명 전극에 얇은 blocking layer를 도포한 후 나노 결정 산화물 반도체 전극을 제작하면 전지 특성을 향상시킬 수 있다. 본 실험에서 우리는 졸-젤 법으로 $TiO_2$ blocking layer 졸을 만들었고 간단하며 저가공정이 가능한 스크린 프린팅 방법으로 blocking layer를 형성하는 실험을 진행하였다. 전도띠 에너지가 높은 반도체 물질로 표면을 처리하면 $TiO_2$-전해질 간 계면에 에너지 장벽이 형성되어 재결합을 줄여 모든 광전특성이 향상 되었다.

• Proceedings of the Korean Vacuum Society Conference
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• 2016.02a
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• pp.412-412
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• 2016

염료감응 태양전지(dye-sensitized solar cells, DSSCs)는 식물의 광합성원리와 매우 유사한 작동원리를 갖고 있는 전지이며, 간단한 구조, 저렴한 제조단가, 친환경성 등의 등의 장점으로 인하여 많은 관심을 모으고 있다. 이러한 염료감응 태양전지는 빛을 받아들인 염료분자가 전자-홀 쌍을 생성하며 전자는 반도체 산화물을 통해 이동되고 전해질의 산화환원 과정을 통해 염료 분자가 다시 환원되는 순환메커니즘을 따르고 있다. 일반적으로 염료감응 태양전지는 밴드 갭 에너지가 큰 반도체 산화물을 포함하는 작업전극, 산화환원 반응을 통해 전자를 염료로 보내는 전해질, 환원 촉매역할을 하는 상대전극으로 구성되어 있다. 특히, 상대전극으로는 우수한 촉매특성과 높은 전도성을 갖는 백금이 가장 많이 이용되고 있지만 가격이 비싸고 요오드에 취약하기 때문에 상용화에 큰 장애물이다. 따라서, 백금을 대체하기 위해 저가의 탄소나 고분자에 대한 연구가 활발히 진행되고 있고, 그 중 탄소나노섬유(carbon nanofiber, CNFs)는 높은 표면적과 뛰어난 화학적 안정성으로 촉매효율을 증대시킬 수 있어 촉매물질로서 관심이 높아지고 있다. 본 연구에서는 상대전극에 탄소나노섬유기반 복합체를 합성하였고, 성공적으로 저가격 및 고성능의 염료감응 태양전지를 제작하였다. 이때, 지지체인 탄소나노섬유는 전기방사법을 통해 합성하였으며, 수열합성법을 이용하여 금속산화물을 담지하였다. 이렇게 제작된 탄소나노섬유-Fe2O3 복합체는 scanning electron microscopy, transmission electron microscopy, X-ray diffraction, 그리고 X-ray photoelectron spectroscopy 통해 구조적, 화학적 특성을 평가하였으며 전기화학적 특성 및 광전변환 효율을 분석하기 위해 cyclic voltammetry, electrochemical impedance spectroscopy, 그리고 solar simulator를 사용하였다. 본 학회에서 위와 관련된 더 자세한 사항에 대해 논의할 것이다.

• Proceedings of the Korean Vacuum Society Conference
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• 2015.08a
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• pp.97-97
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• 2015

전 세계적으로 화석연료의 고갈 및 환경오염 문제를 해결하기 위해 신재생에너지에 대한 관심이 급증하고 있다. 이러한 신재생에너지에는 수소 에너지, 자연 에너지(태양열, 지열 등), 바이오 매스 에너지 등이 포함된다. 이 중 수소 에너지는 지구상에 풍부하게 존재하고 있는 물과 탄화수소로부터 얻어지며, 연소 시에도 다시 물을 형성하여 오염 물질을 배출하지 않는 차세대 무공해 에너지원으로써 주목을 받고 있다. 수소 제조를 위한 공정에는 수증기 개질 공정(steam reforming), 부분 산화(partial oxidation) 및 자열개질(autothermal reforming) 등이 있으며 실제로 생산되는 대부분의 수소는 탄소/수소비(1:4)가 높은 메탄($CH_4$) 가스를 이용한 메탄 수증기 개질 공정(steam methane reforming)을 통하여 제조된다. 이 때 수소 제조의 고효율화 및 저비용화를 위해서는 반응물에 대한 높은 선택도, 고활성도 및 높은 안정성을 갖는 촉매가 반드시 필요하며, 대표적으로 Ni, Pt, Ru 등이 보고되고 있다. 이러한 촉매들은 대부분 세라믹 pellet 형태로 제작되어 왔으나 열전도도가 낮고 물리적 충격에 취약하다는 단점이 존재한다. 따라서 우리는 이러한 단점을 극복하고, 촉매의 활성을 높이기 위하여 다공성 금속 합금 폼을 촉매 지지체로 도입하였다. 또한, 다공성 금속 합금 폼 표면에 촉매의 분산 및 안정성을 향상시키기 위해 지지체와 촉매 사이에 원자층 증착법을 이용하여 inter-layer를 도입하였다. 이들의 구조, 형태, 및 표면의 화학적 상태는 주사전자현미경, EDS (energy dispersive spectroscopy)가 탑재된 주사전자현미경, X-선 회절, 및 X-선 광전자 분광법을 이용하여 규명하였다. 더하여 정전압-전류 측정법 및 유도 결합 플라즈마 분광 분석기을 이용하여 전기 화학 반응을 유도하고, 반응 후 전해질의 성분분석을 통해 촉매와 지지체 간의 안정성을 평가하였다. 따라서 본 결과들은 한국진공학회 하계정기학술대회를 통해 좀 더 자세히 논의될 것이다.