• Korean Chemical Engineering Research
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• 제54권6호
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• pp.854-862
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• 2016

최근 화석연료를 대체할 친환경 신재생에너지에 대한 요구가 증가하면서 수소에너지가 미래 대체에너지원으로서 주목받고 있다. 수소를 생산하는 방법 중 수전해 기술은 에너지효율과 안정성이 뛰어난 장점이 있지만, 산소발생반응시 발생하는 높은 과전압은 여전히 단점으로 지적되고 있다. 본 연구에서는 분무열분해 공정을 통하여 Co 전구체로부터 $Co_3O_4$를 제조하였다. 또한, urea, sucrose, citric acid의 유기물첨가제를 사용하여 다양한 입자 크기와 표면형상을 가지는 $Co_3O_4$를 제조하였고, 필요에 따라 추가로 열처리를 실시하였다. 합성한 $Co_3O_4$의 물리적 특성을 분석하기 위해 X-선 회절 분석(XRD)으로 결정성을 조사하였고, 주사전자현미경(SEM)과 투과전자현미경(TEM)으로 입자형상 및 표면을 분석하였다. 질소 흡 탈착 시험을 통해 촉매의 비표면적 및 기공부피를 측정하였고, 질소도핑을 확인하기 위해 X-선 광전자 분광법(XPS)을 사용하였다. 촉매의 산소발생반응 활성을 알아보기 위해 3전극 셀에서 선형주사전위법(LSV)으로 전기화학적 거동을 분석하였다. 첨가제를 사용하지 않은 $Co_3O_4$가 가장 우수한 활성을 보였고, 이는 분무열분해법을 통하여 상대적으로 작은 입자형성과 높은 비표면적의 영향인 것으로 판단된다.

• 한국결정성장학회지
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• 제33권5호
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• pp.196-201
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• 2023

수소에너지 생산을 위한 물분해 시스템의 효율을 향상시키기 위해서는, 수소발생반응 (HER)과 산소발생반응(OER) 각각에서 촉매로 인한 전기화학적 반응에서의 높은 과전압의 감소가 수반되어야 한다. 그 중에서도 전이금속 기반의 화합물(수산화물, 황화물 등)은 현재 상용되고 있는 백금 등의 귀금속을 대체할 촉매 재료로써 주목받고 있다. 본 연구에서는, 저렴한 금속 다공성 소재인 Ni foam을 지지체로 사용하고, 수열합성 공정을 통해 β-Ni(OH)₂ 마이크로결정을 합성하고자 하였다. 또한 전기화학적 특성을 향상시키기 위하여 Fe을 도핑하여 합성된 β-Ni(OH)₂ 마이크로 결정의 형상, 결정구조 및 물분해 특성의 변화를 관찰하였으며, 상용 수전해 시스템의 촉매로서의 적용가능성을 검토하였다.

• 한국결정성장학회지
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• 제34권1호
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• pp.30-35
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• 2024

수소에너지 생산을 위한 물분해 시스템의 효율을 향상시키기 위해서는, 수소발생반응(HER)과 산소발생반응(OER) 각각에서 촉매로 인한 전기화학적 반응에서의 높은 과전압의 감소가 수반되어야 한다. 그 중에서도 전이금속 기반의 화합물들은 현재 상용되고 있는 백금 등의 귀금속을 대체할 촉매 재료로써 주목받고 있다. 본 연구에서는, 저렴한 금속 다공성 소재인 니켈폼(Ni foam)을 지지체로 사용하고, 수열합성 공정을 통해 Fe-doped β-Ni(OH)₂ 마이크로결정을 합성하였다. 또한 OER 특성을 향상시키기 위하여 Mo을 동시도핑하여 합성된 Fe-Mo co-doped β-Ni(OH)₂ 마이크로결정의 형상, 결정구조 및 수전해 특성의 변화를 관찰하였으며, 상용 수전해 시스템의 촉매로서의 적용가능성을 검토하였다.

• 한국재료학회지
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• 제33권5호
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• pp.175-188
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• 2023

Water electrolysis holds great potential as a method for producing renewable hydrogen fuel at large-scale, and to replace the fossil fuels responsible for greenhouse gases emissions and global climate change. To reduce the cost of hydrogen and make it competitive against fossil fuels, the efficiency of green hydrogen production should be maximized. This requires superior electrocatalysts to reduce the reaction energy barriers. The development of catalytic materials has mostly relied on empirical, trial-and-error methods because of the complicated, multidimensional, and dynamic nature of catalysis, requiring significant time and effort to find optimized multicomponent catalysts under a variety of reaction conditions. The ultimate goal for all researchers in the materials science and engineering field is the rational and efficient design of materials with desired performance. Discovering and understanding new catalysts with desired properties is at the heart of materials science research. This process can benefit from machine learning (ML), given the complex nature of catalytic reactions and vast range of candidate materials. This review summarizes recent achievements in catalysts discovery for the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). The basic concepts of ML algorithms and practical guides for materials scientists are also demonstrated. The challenges and strategies of applying ML are discussed, which should be collaboratively addressed by materials scientists and ML communities. The ultimate integration of ML in catalyst development is expected to accelerate the design, discovery, optimization, and interpretation of superior electrocatalysts, to realize a carbon-free ecosystem based on green hydrogen.

• 소성∙가공
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• 제7권5호
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• pp.481-488
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• 1998

The active metal brazing was applied to bond Alumina and Ni-Cr steel by Ag-Cu-Zr-Sn alloy and the interfacial microstructure and reaction mechanism were investigated. Polycrystalline monoclinic $ZrO_2$ with a very fine grain of 100-150 nm formed at the alumina grain boundary contacted with Zr segregation layer at the interface. The $ZrO_2$ layer containing the inclusions and cracks were developed at the boundary of inclusion/$ZrO_2$ due to the difference in specific volume. The development of $ZrO_2$ at the interface was successfully explained by the preferential penetration of $ZrO_2$ at the interface was successfully explained by the preferential penetration of Zr atoms a higher concentration of oxygen and a high diffusion rate of Al ions into molten brazing alloy.

• 한국분말재료학회지
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• 제8권2호
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• pp.117-123
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• 2001

Formation of pores in melt-processed $YBa_2Cu_3O_{7-x}$ (123) oxides and its effect on the microstructure were studied. Spherical pores with a size of a few tens of microns were formed due to the evolution of oxygen gas during melting of a 123 oxide. Some of pores were converted into liquid pockets by liquid filling, but others remained unfilled. The liquid pockets were converted into spherical 123 regions with a lower $Y_2BaCuO_5$ (211)density through the peritectic reaction during subsequent cooling, while the pores were entrapped into the periteictically grown 123 grains. The spherical 123 regions often consists of a residual melt due to the unbalanced peritectically reaction.

• Journal of Radiation Protection and Research
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• 제41권4호
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• pp.373-377
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• 2016

Background: Experiments with small electrochemical apparatus were previously carried out for detecting low-energy neutrinos under irradiation of reactor neutrinos and under natural neutrino environment. The experimental result indicated that the output current of reactor-neutrino irradiated detector was appreciably larger than that of natural environmental one. Usual interaction cross-sections of neutrinos are quite small, so that they do not explain the experimental result at all. Materials and Methods: To understand the experimental data, we propose that some biological products may generate AV-type scalar field B0, leading to a large interaction cross-section. The output current generation is ascribed to an electrochemical process that may be assisted by weak interaction phenomena. Dissolved oxygen concentrations in the detector solution were measured in this study, for the purpose of understanding the mechanism of the detector output current generation. Results and Discussion: It was found that the time evolution of experimental output current was mostly reproduced in simulation calculation on the basis of the measured dissolved oxygen concentration. Conclusion: We mostly explained the variation of experimental data by using the electrochemical half-cell analysis model based on the DO concentration that is consistent to the experiment.

• 한국결정성장학회지
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• 제31권2호
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• pp.96-101
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• 2021

Developing effective and earth-abundant electrocatalyst for oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) is critical for the commercialization of a water splitting system. In particular, the overpotential of the OER is relatively higher than the HER, and thus, it is considered that one of the important methods to enhance the performance of the electrocatalyst is to reduce the overpotential of the OER. We report effects of incorporation of metalloid into Ni(OH)2 microcrystal on electrocatalytic activities. In this study, Te incorporated Ni(OH)2 (��Te-Ni(OH)2) were grown on three-dimensional porous NF by a facile solvothermal method with �� = 1, 3 and 5. Homogeneous microplate structure on the NF was clearly observed for the Ni(OH)2/NF and ��Te-Ni(OH)2/NF samples. However, irregular and collapsed nanostructures were found on the surface of nickel foam when Te precursor ratio is (��) over 3. Electrocatalytic OER properties were analysed by Linear sweep voltammetry (LSV) and Electrochemical impedance spectroscopy (EIS). The amount of Te incorporation used in the electrocatalytic reaction was found to play a crucial role in improving catalytic activity. The optimum Te amount (��) introduced into the Ni(OH)2/NF was discussed with respect to their OER performance.

• 대한기계학회논문집B
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• 제36권2호
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• pp.197-204
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• 2012

본 논문에서는 공기 중에서 높은 레이저 복사 조도에 따른 효과에 의해 발생되는 금속 플라즈마의 발달 과정에 대하여 레이저 펄스가 끝나는 이후로 쉐도우그래프(Shadowgraph) 가시화 방법을 이용하여 현상을 연구하였다. 따라서 레이저에 의한 데토네이션의 발생과 이를 일으키는 연소 과정 대한 연구가 진행되었다. 본 논문의 가장 중요한 점들은 높은 레이저 에너지에 의해 삭마 된 기체 상태의 알루미늄과 공기로부터의 산소와의 화학 반응의 진행을 관측했을 뿐만 아니라, 화학 반응 최종 산화물을 X선 회절 분석법(X-Ray Diffraction)을 통해 관측한 것이다. 그리고 레이저를 통해 유도된 화학적 반응 파와 공기 중에서의 알루미늄 분진 폭발의 데토네이션과의 양적인 평가를 유도하였다. 이러한 연구는 덩어리 상태의 금속 샘플에서 공기 중의 산소를 이용하여 데토네이션을 발생시키는 새로운 방법을 제시할 것으로 여겨진다.

• 한국세라믹학회지
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• 제53권3호
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• pp.306-311
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• 2016

Li-air batteries have received much attention due to their superior theoretical energy density. However, their sluggish kinetics on the cathode side is considered the main barrier to high performance. The rational design of electrode catalysts with high activity is therefore an important challenge. To solve this issue, we performed density functional theory (DFT) calculations to analyze the adsorption behavior of the $LiO_2$ molecule, which is considered to be a key intermediate in both the Li-oxygen reduction reaction (ORR) and the evolution reaction (OER). Specifically, to use the activity descriptor approach, the $LiO_2$ adsorption energy, which has previously been demonstrated to be a reliable descriptor of the cathode reaction in Li-air batteries, was calculated on $LaB_{1-x}B^{\prime}_xO_3$(001) (B, B' = Mn, Fe, Co, and Ni, x = 0.0, 0.5). Our fast screening results showed that $LaMnO_3$, $LaMn_{0.5}Fe_{0.5}O_3$, or $LaFeO_3$ would be good candidate catalysts. We believe that our results will provide a way to more efficiently develop new cathode materials for Li-air batteries.