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다공성 탄소층이 코팅된 하이브리드 표면 구조를 갖는 산소 환원 반응용 PtCo 합금 나노 촉매
장정희,모니카 샤르마,성후광,김순표,정남기,Jang, Jeonghee,Sharma, Monika,Sung, Hukwang,Kim, Sunpyo,Jung, Namgee 한국재료학회 2018 한국재료학회지 Vol.28 No.11
During a long-term operation of polymer electrolyte membrane fuel cells(PEMFCs), the fuel cell performance may degrade due to severe agglomeration and dissolution of metal nanoparticles in the cathode. To enhance the electrochemical durability of metal catalysts and to prevent the particle agglomeration in PEMFC operation, this paper proposes a hybrid catalyst structure composed of PtCo alloy nanoparticles encapsulated by porous carbon layers. In the hybrid catalyst structure, the dissolution and migration of PtCo nanoparticles can be effectively prevented by protective carbon shells. In addition, $O_2$ can properly penetrate the porous carbon layers and react on the active Pt surface, which ensures high catalytic activity for the oxygen reduction reaction. Although the hybrid catalyst has a much smaller active surface area due to the carbon encapsulation compared to a commercial Pt catalyst without a carbon layer, it has a much higher specific activity and significantly improved durability than the Pt catalyst. Therefore, it is expected that the designed hybrid catalyst concept will provide an interesting strategy for development of high-performance fuel cell catalysts.
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장정희(Jang Jeonghee) 한국아동청소년문학학회 2016 아동청소년문학연구 Vol.- No.18
This study conducts a comprehensive examination into the aspects of changing viewpoints of children exhibited by children"s books during the Korean Empire period. In the late Joseon Dynasty when Silhak(practical science) slowly began spreading, it was dominated by Confucian viewpoints of children where it was taught to reach adulthood by learning ‘Cheon(天)’ and ‘Dao(道).’ And this study points out that proliferation of Hangul and children’s tendency favoring books written in Korean were the pivotal elements for the formation of the viewpoints of children. Modern children’s literature in Korea is very close to ‘Korean Literature Awareness(國文意識).’ Especially, this study highly valued the Korean Empire period when the establishment of modern school was legislated including the ‘Royal Doctrine for Building State by Education(敎育立國詔書)’ by King Gojong. And many children"s textbooks published during the time were also closely looked into. At the time, Confucian viewpoints of children still remained, which led children"s book under ‘Elementary Learning’ to be the basic literature; and the concepts of ‘State(國家)’ such as ‘Gaeguk(開國)’ and ‘Independent State(獨立國)’ were enhanced. After sovereignty was taken away, the viewpoints of children also went through radical changes; and the children in the State without sovereignty emerged as a principal subject of enlightenment replacing the ‘State(國).’ It means that the declaration, “Let the young generation to be the State of Daehan,” turned feasible. And individual characteristics of children were also emphasized. During the Korean Empire period, a variety of books to read began to be developed; and while Confucian viewpoints of children still prolonged, the ‘children’ as principal subjects of modernity became more important.
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유기 리간드 제어를 통한 고분산 팔라듐 나노 촉매의 합성 및 음이온교환막 연료전지를 위한 산소 환원 반응 특성 분석
성후광,장정희,정남기,Sung, Hukwang,Sharma, Monika,Jang, Jeonghee,Jung, Namgee 한국재료학회 2018 한국재료학회지 Vol.28 No.11
In anion exchange membrane fuel cells, Pd nanoparticles are extensively studied as promising non-Pt catalysts due to their electronic structure similar to Pt. In this study, to fabricate Pd nanoparticles well dispersed on carbon support materials, we propose a synthetic strategy using mixed organic ligands with different chemical structures and functions. Simultaneously to control the Pd particle size and dispersion, a ligand mixture composed of oleylamine(OA) and trioctylphosphine(TOP) is utilized during thermal decomposition of Pd precursors. In the ligand mixture, OA serves mainly as a reducing agent rather than a stabilizer since TOP, which has a bulky structure, more strongly interacts with the Pd metal surface as a stabilizer compared to OA. The specific roles of OA and TOP in the Pd nanoparticle synthesis are studied according to the mixture composition, and the oxygen reduction reaction(ORR) activity and durability of highly-dispersed Pd nanocatalysts with different particles sizes are investigated. The results of this study confirm that the Pd nanocatalyst with large particles has high durability compared to the nanocatalyst with small Pd nanoparticles during the accelerated degradation tests although they initially indicated similar ORR performance.
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조선소의 메가블록 조립작업장을 위한 공간계획알고리즘 개발
고시근(Shiegheun Koh),장정희(Jeonghee Jang),최대원(Daewon Choi),우상복(Sangbok Woo) 대한산업공학회 2011 산업공학 Vol.24 No.1
To mitigate space restriction and to raise productivity, some shipbuilding companies use floating-docks on the sea instead of dry-docks on the land. In that case, a floating-crane that can lift very heavy objects (up to 3,600 tons) is used to handle the blocks which are the basic units in shipbuilding processes, and so, very large blocks (these are called the mega-blocks) can be used to build a ship. But, because these mega-blocks can be made only in the area near the floating-dock and beside the sea, the space is very important resource for the process. Therefore, our problem is to make an efficient spatial schedule for the mega-block assembly yard. First of all, we formulate this situation into a mathematical model and find optimal solution for a small problem using a commercial optimization software. But, the software could not give optimal solutions for practical sized problems in a reasonable time, and so we propose a GA-based heuristic algorithm. Through a numerical experiment, finally, we show that the spatial scheduling algorithm can provide a very good performance.
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