https://scholar.dgist.ac.kr/handle/20.500.11750/4349 2026-04-22T06:15:12Z 2026-04-22T06:15:12Z Noh, Seung Hyo Kwak, Do Hyun Lee, Juseung Kang, Joon Hee Han, Byung Chan https://scholar.dgist.ac.kr/handle/20.500.11750/13365 2025-07-25T03:31:33Z 2014-02-28T15:00:00Z

Title: First-principles calculations of the thermodynamic properties of transuranium elements in a molten salt medium Author(s): Noh, Seung Hyo; Kwak, Do Hyun; Lee, Juseung; Kang, Joon Hee; Han, Byung Chan Abstract: We utilized first-principles density-functional-theory (DFT) calculations to evaluate the thermodynamic feasibility of a pyroprocessing methodology for reducing the volume of high-level radioactive materials and recycling spent nuclear fuels. The thermodynamic properties of transuranium elements (Pu, Np and Cm) were obtained in electrochemical equilibrium with a LiCl-KCl molten salt as ionic phases and as adsorbates on a W(110) surface. To accomplish the goal, we rigorously calculated the double layer interface structures on an atomic resolution, on the thermodynamically most stable configurations on W(110) surfaces and the chemical activities of the transuranium elements for various coverages of those elements. Our results indicated that the electrodeposition process was very sensitive to the atomic level structures of Cl ions at the double-layer interface. Our studies are easily expandable to general electrochemical applications involving strong redox reactions of transition metals in non-aqueous solutions. © 2014 The Korean Physical Society.

2014-02-28T15:00:00Z Kwak, Dohyun Noh, Seunghyo Han, Byungchan https://scholar.dgist.ac.kr/handle/20.500.11750/2997 2025-07-25T02:45:08Z 2014-11-30T15:00:00Z

Title: Multi-scale computational study of the molten salt based recycling of spent nuclear fuels Author(s): Kwak, Dohyun; Noh, Seunghyo; Han, Byungchan Abstract: By applying a rigorous computational procedure combining first principles density functional theory (DFT) calculations and statistical mechanics, we acquire thermochemical properties of materials for a pyroprocessing system recycling spent nuclear fuels. Cluster expansions to DFT obtained energies parameterize atomic interaction potentials of Cl-Cl and Cl-U adsorbed on W(110) surface from a molten salt (KCL-LiCl). Using these databases of the long-range and multibody interactions, Monte Carlo simulations identify thermodynamically stable configurations of the adsorbates on the W(110) surface in grand canonical open system at T=773K. Our results indicate that Cl atoms adsorbed at the interface of the molten salt and W(110) surface substantially drive electrochemical deposition of U ions at low chemical potential of Cl. This behavior, however, stops after approximately 1/3 ML coverage of U because the atomic sites on W(110) surface are mostly blocked by adsorbed Cl, which implies that the attractive interactions of Cl-W are stronger than Cl-U as well as the repulsive interactions between U atoms are effective at these coverage ranges. We also predict the solubility limit of U ion in the molten LiCl-KCl phases at T=773K should be about 5 atomic percent, which well agrees with previous reports by experimental measurements. This study indicates that accurate characterization of the stable Cl structure at the interface is vital for understanding the fundamental mechanisms of recycling spent nuclear fuels and for screening high functional electrode materials in the pyroprocessing system. © 2014 John Wiley & Sons, Ltd.

2014-11-30T15:00:00Z Seo, Joon Kyo Khetan, Abhishek Seo, Min Ho Kim, Hasuck Han, Byungchan https://scholar.dgist.ac.kr/handle/20.500.11750/3203 2025-07-24T07:29:44Z 2013-09-14T15:00:00Z

Title: First-principles thermodynamic study of the electrochemical stability of Pt nanoparticles in fuel cell applications Author(s): Seo, Joon Kyo; Khetan, Abhishek; Seo, Min Ho; Kim, Hasuck; Han, Byungchan Abstract: The durability of Pt-based nanocatalysts in acidic media is one of the key issues hindering the development of efficient fuel cell cathodes, and the factors affecting the durability are not well-understood. In this study, first-principles calculations are used to analyze the electrochemical degradation of Pt nanoparticles. Model systems of Pt nanoparticles in different sizes are designed to calculate the dissolution potentials of these systems. Based strictly on thermodynamics, the results point toward strongly size-dependent dissolution behavior for Pt nanoparticles, the properties of which become similar to that of bulk Pt at diameters larger than 3 nm. Remarkably, the dissolution proceeds through the exposure of more (111) facets at the expense of atoms located at edges, vertices and (111) facets. The size-dependent trends in the dissolution potentials indicate that the competition between two thermodynamic factors, the cohesive energy and the surface energy, determines the dissolution pathway. Based on the findings, several characteristics are proposed that can serve in the rational design of model Pt nanocatalysts. © 2013 Elsevier B.V. All rights reserved.

2013-09-14T15:00:00Z Noh, Seung Hyo Seo, Min Ho Seo, Joon Kyo Fischer, Peter Han, Byungchan https://scholar.dgist.ac.kr/handle/20.500.11750/3301 2025-07-24T07:28:27Z 2013-08-31T15:00:00Z

Title: First principles computational study on the electrochemical stability of Pt-Co nanocatalysts Author(s): Noh, Seung Hyo; Seo, Min Ho; Seo, Joon Kyo; Fischer, Peter; Han, Byungchan Abstract: Using density functional theory (DFT) calculations, we identify the thermodynamically stable configurations of Pt-Co alloy nanoparticles of varying Co compositions and particle sizes. Our results indicate that the most thermodynamically stable structure is a shell-by-shell configuration where the Pt atom only shell and the Co only shell alternately stack and the outermost shell consists of a Pt skin layer. DFT calculations show that the structure has substantially higher dissolution potential of the outermost Pt shell compared with pure Pt nanoparticles of approximately the same size. Furthermore, our DFT calculations also propose that the shell-by-shell structure shows much better oxygen reduction reaction (ORR) activity than conventional bulk or nanoparticles of pure Pt. These novel catalyst properties can be changed when the surfaces are adsorbed with oxygen atoms via selective segregation followed by the electrochemical dissolution of the alloyed Co atoms. However, these phenomena are thermodynamically not plausible if the chemical potentials of oxygen are controlled below a certain level. Therefore, we propose that the shell-by-shell structures are promising candidates for highly functional catalysts in fuel cell applications. © 2013 The Royal Society of Chemistry.

2013-08-31T15:00:00Z