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Atomistic Simulation of Hydrogen Diffusion at Tilt Grain Boundaries in Vanadium
심재혁,고원석,Jin-Yoo Suh,이영수,이병주 대한금속·재료학회 2013 METALS AND MATERIALS International Vol.19 No.6
Molecular dynamics simulations of hydrogen diffusion at Σ3 and Σ5 tilt grain boundaries in bcc vanadium (V) have been performed based on modified embedded-atom method interatomic potentials. The calculated diffusivity at the grain boundaries is lower than the calculated bulk diffusivity in a temperature range between 473 and 1473 K, although the difference between the grain boundary and bulk diffusivities decreases with increasing temperature. Compared with that of the other directions, the mean square displacement of an interstitial hydrogen atom at the Σ3 boundary is relatively small in the direction normal to the boundary, leading to two dimensional motion. Molecular statics simulations show that there is strong attraction between the hydrogen atom and these grain boundaries in V, which implies that the role of grain boundaries is to act as trap sites rather than to provide fast diffusion paths of hydrogen atoms in V.
Controlling Fe-based active sites of pyro-synthesized Fe-N-C oxygen reduction electrocatalyst
심재혁,김미주,이국승,성영은 한국공업화학회 2020 한국공업화학회 연구논문 초록집 Vol.2020 No.-
Efficient and sustainable oxygen reduction reaction (ORR) catalysts have been required to replace commercial platinum-based catalysts in many energy conversion/storage system including metal-air batteries and fuel cells. Fe-based catalysts have captured attention due to its high activity and availability. However, the role of two active sites, Fe-N bonding and Fe covered with carbon layer (Fe@C), in Fe-based catalysts were ambiguous due to the difficulty in controlling these active sites during synthesis. In this study, Fe-N-C electrocatalysts were prepared using pyrosynthesis and controlling the Fe/C ratio, resulting in adequate Fe-N/Fe@C ratio. In single cell test of Zn-air batteries and anion exchange membrane fuel cells, the Fe-N-C electrocatalysts exhibit excellent performance, based on its superior ORR activity when compared to the previously reported transition metal-based catalysts. This work provides efficient strategies to design high-performance catalysts for ORR.
심재혁,김미주,박지은,성영은 한국공업화학회 2020 한국공업화학회 연구논문 초록집 Vol.2020 No.-
Sustainable and available air cathode electrocatalysts are of importance for energy conversion/storage devices including fuel cells and metal-air batteries. In this study, porous S,N-co-doped carbon materials are produced via pyrolysis of bamboo and thiourea and exhibit adequate micro/mesoporosity and sufficient active site. Therefore, the S,N-co-doped bamboo carbons (SNBCs) present high activities comparable to those of commercial Pt/C catalysts. In single cell test of anion exchange membrane fuel cells and Zn-air batteries, SNBCs exhibit high performances, attributed to their intrinsic activities as well as well-developed secondary pore structure in the catalyst layer. Thus, this work demonstrates a green strategy for the design of high performance and sustainable ORR catalysts for practical applications.
심재혁,김미주,성영은,이국승 한국공업화학회 2020 한국공업화학회 연구논문 초록집 Vol.2020 No.-
The efficiency of the fuel cell depends on how well the oxygen reduction reaction (ORR) occurs at the cathode. The solution to making its slow reactions faster is to use effective catalysts. Platinum exhibits the highest activity, and, however, is recommended to reduce its use or replace it with other materials due to its scarcity and high prices. In this study, we tried to develop a non-precious metal catalyst for ORR reaction using MOF (Metal Organic Framework). The structure, morphology, and electrochemical performance of Fe-MOF were examined and the transition metal Ni, which can be expected to improve the catalytic activity, was added to the Fe-MOF synthesis method to confirm the shape and structure. The electrochemical performance of nanosize FeNi-MOF-HT is higher than that of Fe-MOF-HT. Due to the high degree of graphitization and its maintained structure, FeNi-MOF heat-treated at 700°C and 800°C show excellent performance.
Resistive Switching Characteristics of TiO2 Thin Films with Different Electrodes
심재혁,Quanli Hu,박미라,Yawar Abbas,강치중,김재완,윤태식 한국물리학회 2015 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.67 No.5
Resistive switching behaviors in metal oxides have been mentioned for several decades. TiO2 is still a well-known material for resistive switching memory devices. The resistive switching characteristics of TiO2 thin films with different top electrodes were investigated. The devices had typical bipolar resistive switching behaviors. The resistance changed from a high-resistance state (low-resistance state) to a low-resistance state (high-resistance state) under positive (negative) sweeping voltage. The interface between the top electrode and the oxide layer could affect the resistive switching behaviors. The electrical properties of Metal/TiO2/Pt devices with different top electrodes showed different switching characteristics. The conduction mechanism of the devices was also investigated. In the low-resistance state, ohmic conduction was dominant. The conduction mechanism exhibited ohmic conduction at low voltages and space-charge-limited-conduction at high voltages in the devices of Cu/TiO2/Pt, Ni/TiO2/Pt and Al/TiO2/Pt, respectively. For Ta/TiO2/Pt Schottky conduction also played an important role.
심재혁,이승철,Sim, Jae-Hyeok,Lee, Seung-Cheol 재료연구소 2010 機械와 材料 Vol.22 No.2
전산 모사 기술은 재료의 물리 화학적 현상을 규명하고 재료의 물성을 예측하는 측면에서 새로운 재료를 개발하기 위한 효율적인 방법론으로 자리를 잡아가고 있다. 철강 재료는 다양한 합금 원소를 포함하고 있고 복잡한 상변태 및 자성 거동을 나타내 전산 모사 기술의 가장 적용하기 어려운 재료로 인식되어 왔으나, 최근 컴퓨터 기술의 발전과 새로운 전산 모사 방법론의 개발에 힘입어 전산 모사 기법의 적용 사례가 늘고 있다. 이 글에서는 철강 재료에 대한 전산 모사의 연구 동향을 기술하고 여러 적용 사례에 대하여 소개하고자 한다.
심재혁,백현만 한국뇌신경과학회 2021 Experimental Neurobiology Vol.30 No.5
Historically, studies have extensively examined the basal ganglia in Parkinson’s disease for specific characteristics that can be observed with medical imaging. One particular methodology used for detecting changes that occur in Parkinson’s disease brains is diffusion tensor imaging, which yields diffusion indices such as fractional anisotropy and radial diffusivity that have been shown to correlate with axonal damage. In this study, we compare the diffusion measures of basal ganglia structures (with substantia nigra divided into subregions, pars compacta, and pars reticula), as well as the diffusion measures of the diffusion tracts that pass through each pair of basal ganglia structures to see if significant differences in diffusion measures can be observed in structures or tracts in newly diagnosed Parkinson’s disease patients. Additionally, we include the ventral tegmental area, a structure connected to various basal ganglia structures affected by dopaminergic neuronal loss and have historically shown significant alterations in Parkinson’s disease, in our analysis. We found significant fractional anisotropy differences in the putamen, and in the diffusion tracts that pass through pairs of both substantia nigra subregions, subthalamic nucleus, parabrachial pigmental nucleus, ventral tegmental area. Additionally, we found significant radial diffusivity differences in diffusion tracts that pass through the parabrachial nucleus, putamen, both substantia nigra subregions, and globus pallidus externa. We were able to find significant diffusion measure differences in structures and diffusion tracts, potentially due to compensatory mechanisms in response to dopaminergic neuronal loss that occurs in newly diagnosed Parkinson’s disease patients.