57 research outputs found
Performance evaluation of La0.8Sr0.2CoO3 in catalytic decomposition of hydrogen peroxide
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Searching Alloying Elemetnes to accelerate Nitriding Process on Cu: A Combined DFT and CALPHAD Study
No full textA Screening of Transition Metal Nitrides with Dopants as Electrocatalysts for Oxygen Reduction Reaction
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Hierarchical analysis of alloying element effects on gas nitriding rate of Fe alloys: A DFT, microkinetic and kMC study
No full textNitriding is the most widely employed thermochemical surface treatment to enhance the mechanical properties of steel. Specifically, gas nitriding, which is a low-temperature process for efficiently producing high-performance steels, has a disadvantage in that it consumes a large amount of time. To enhance the nitriding rate, we studied the surface alloying of iron (Fe) and its effect on ammonia (NH3) nitriding of Fe using a hierarchical protocol with density functional theory (DFT)-based microkinetics and real-time simulations. First, we considered the NH3 decomposition and nitrogen (N) diffusion mechanism on clean and alloyed (Fe-X) Fe (100) surfaces using DFT. In this study, the alloying elements including transition metals and period Ill to VI elements in the periodic table were considered for DFT-based computational screening. For the candidate Fe-X systems selected to improve the nitriding rate in the previous step, we calculated all the energy barriers for every elementary reaction step by varying the alloying elements and performed microkinetic analysis using those kinetic energy barriers to determine their influence on the nitriding rate. After adding consideration of thermodynamic factors, selected candidate alloys were subjected to detailed DFT calculations of the nitriding mechanism with N coverage, and based on these results, a kinetic Monte Carlo (kMC) simulation was performed to reconfirm the results under the actual nitriding process conditions. Through a hierarchical protocol, we performed a theoretical analysis and simulation of the effects of alloying elements on the nitriding rate that were not explained experimentally and suggested the best alloying element with the improved nitriding rate. (C) 2019 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
A study of catalytic decomposition for hydrogen peroxide gas generator
No full text학위논문(석사) - 한국과학기술원 : 항공우주공학전공, 2005.2, [ x, 78 p. ]한국과학기술원 : 항공우주공학전공
Tin sulfide modified separator as an efficient polysulfide trapper for stable cycling performance in Li–S batteries
No full textLithium–sulfur batteries (Li–S) are considered the most promising systems for next-generation energy storage devices due to their high theoretical energy density and relatively low cost. However, the practical applications of Li–S batteries are hindered by the poor electronic conductivity of sulfur and capacity degradation resulting from the shuttle effect of lithium polysulfides (LiPSs). Herein, we demonstrate use of a tin-sulfide (SnS2) modified separator to facilitate the redox reaction involving LiPS intermediates and realize improved electrochemical performance in a Li–S battery. Density functional theory (DFT) calculations revealed that SnS2 exhibits a strong affinity with LiPSs and induces a rapid conversion of trapped polysulfides. As a result, Li–S batteries with a SnS2-modified separator exhibited an enhanced specific capacity of 1300 mA h g−1 at 0.2C (corresponding to a high areal capacity of 4.03 mA h cm−2), which was maintained at 1040 mA h g−1 after 150 cycles. Furthermore, an excellent rate capability is achieved with a capacity of 700 mA h g−1 (2.17 mA h cm−2) at 5C. Additionally, the modified separator exhibited excellent cycling performance up to 500 cycles at 2C, with a low capacity decay rate of 0.0710% per cycle. The excellent performance of the sulfur electrode is mainly attributed to the incorporation of the SnS2 coating layer on the separator, which effectively confines polysulfides via both chemical and physical interaction and rapidly improves lithium ion diffusion. Moreover, the SnS2 coating layer greatly improves sulfur utilization and efficiently accelerates the kinetic conversion of trapped polysulfides.
Alloy design of Al-Ni for fast hydrogen generation via hydrolysis in an alkaline solution
No full text학위논문(석사) - 한국과학기술원 : 신소재공학과, 2009. 8., [ x, 68 p. ]화석연료고갈과 환경오염으로 인하여 많은 과학자들은 새로운 에너지 자원이나 에너지 변환 및 생성하는 소자에 대하여 많은 연구를 하고 있다. 수소는 친환경적이면서 재생 가능함 등 여러 혜택을 누리게 함으로 미래 에너지원으로 적합하다. 그러나 수소가 에너지원으로써 널리 이용되기 위해서는 수소 생산 및 저장하는 분야에 많은 기술적인 진전이 요구된다. 금속이 가수분해하는 동안 발생하는 수소를 축출하는 방법은 온보드로 수소를 발생 및 생산하는 방법 중 하나다. 이 분야로는 알루미늄이 적합한 금속으로 여겨지고 있다. 그 동안 고속 가수분해를 목적으로 하는 알루미늄 합금 설계에 대한 연구가 많이 진행되어 왔는데 이는 주로 분말형태 알루미늄을 이용한 연구들이었다. 분말로 제조한 알루미늄합금은 벌크형의 알루미늄 합금보다 빠른 가수분해를 일으켜 더 높은 수소발생속도를 얻게 할 수 있지만 가격, 저장문제, 위험성 등 여러 문제를 낳는다. 본 연구에서는 벌크형의 알루미늄을 이용하여 Ni함량이 다른 몇 가지 Al-Ni합금을 전통적인 방법으로 주조로 제조하여 각각의 미세조직을 분석하였다. 그리고 Ni함량, NaOH농도, 반응환경의 온도와 같은 조건들이 가수분해에 미치는 영향을 조사하여 가수분해에 있어서 최적의 조건들을 제시하였다. 또한 합금에 냉간압연과 어닐링과 같은 추가적인 가공을 했을 때 이들의 미세조직 및 수소발생양상에 미치는 영향 또한 조사하였다.한국과학기술원 : 신소재공학과
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