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Jung D.-R.,Research Center for Energy Conversion And Storage | Kim J.,Research Center for Energy Conversion And Storage | Park B.,Research Center for Energy Conversion And Storage
Applied Physics Letters | Year: 2010

This study examined the effects of surface-passivation on the photoluminescence (PL) properties of ZnS:Mn nanoparticles treated by ultraviolet (UV) irradiation with oxygen bubbling. Compared to the pristine Mn-doped zinc-sulfide nanocrystals (quantum efficiency: ∼16%), the UV-irradiated ZnS:Mn showed significantly enhanced luminescence properties (quantum efficiency: ∼35%). The photoinduced surface passivation was characterized by X-ray diffraction, X-ray photoelectron spectroscopy, and time-resolved PL. The optimum thickness of the passivation layer for the quantum efficiency was examined considering the nanocrystal size, local strain, and radiative/nonradiative recombination rates. © 2010 American Institute of Physics.


Choi I.,Research Center for Energy Conversion And Storage | Ahn S.H.,Research Center for Energy Conversion And Storage | Kim J.J.,Research Center for Energy Conversion And Storage | Kwon O.J.,Incheon National University
Applied Catalysis B: Environmental | Year: 2011

High over-potential induced by the irreversibility of oxygen reduction reaction (ORR) in polymer electrolyte membrane fuel cell (PEMFC) causes low cell performance. In order to overcome such a problem, many research groups have been studying to enhance the catalytic activity of platinum in fuel cell. In this regard, Ptshell-Pdcore (Pt/Pd/C) nanoparticle was prepared by electrochemical method in this study. The home-made Pd/C was surrounded by Cu as a result of electroless deposition (ELD) which was followed by displacement reaction with Pt. X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD) were applied to identify metallic composition. Transmission electron microscope (TEM) was adopted to image the catalysts. Besides, the catalytic properties were investigated using rotating disk electrode (RDE). The results indicated that the kinetics of electrochemically-prepared Pt/Pd/C catalyst for O2 reduction was superior to conventional Pt/C catalyst and the feasibility of electroless deposition in fabricating electro-catalyst was confirmed through the formation of Cu ad-layer. © 2010 Elsevier B.V.


Park C.-M.,Research Center for Energy Conversion And Storage | Sohn H.-J.,Research Center for Energy Conversion And Storage
Advanced Materials | Year: 2010

The new concept of quasi-intercalation and the method of facile amorphization are demonstrated for layered orthorhombic ZnSb, orthorhombic-black P and rhombohedral-grey As. These anode materials showed excellent electrochemical properties. Application of this concept and method in layered materials will be a breakthrough for realization and mass production of next generation lithium ion batteries. © 2010 WILEY-VCH Verlag GmbH & Co. KGaA.


Liu L.,Research Center for Energy Conversion And Storage | Wang F.-Y.,Research Center for Energy Conversion And Storage | Shao G.-S.,Research Center for Energy Conversion And Storage | Yuan Z.-Y.,Research Center for Energy Conversion And Storage
Carbon | Year: 2010

Low-temperature autoclaving has been demonstrated to synthesize monolithic carbon materials with an ordered mesostructure by using triblock copolymer F127 as template, and resorcinol/formaldehyde resol as carbon precursor under acidic conditions. Transmission electron microscopy, small angle X-ray scattering, Fourier transform infrared spectroscopy and nitrogen adsorption measurements show that the crack-free carbon monoliths have a 2-D hexagonal pore system, a uniform pore size of ∼5.0 nm and a high surface area of ∼675 m2 g-1. The macroscopic morphology can be tuned by changing the diameter of the autoclave. The influence of the synthesis conditions including the autoclaving treatment time and the molar ratio of formaldehyde (F) to resorcinol (R) are discussed. It is found that while the F/R molar ratio ≤2 and the autoclaving treatment time ≥2 d, highly ordered mesoporous carbon monoliths can be obtained. In comparison, monolithic mesoporous carbon materials prepared through an evaporation-induced self-assembly strategy are partly cracked with a disordered wormhole-like mesostructure, suggesting that low-temperature autoclaving is an efficient way to prepare crack-free monolithic carbon materials with an ordered mesostructure. © 2010 Elsevier Ltd. All rights reserved.


Park C.-M.,Lawrence Berkeley National Laboratory | Kim J.-H.,National Renewable Energy Laboratory | Kim H.,Samsung | Sohn H.-J.,Research Center for Energy Conversion And Storage
Chemical Society Reviews | Year: 2010

Research to develop alternative electrode materials with high energy densities in Li-ion batteries has been actively pursued to satisfy the power demands for electronic devices and hybrid electric vehicles. This critical review focuses on anode materials composed of Group IV and V elements with their composites including Ag and Mg metals as well as transition metal oxides which have been intensively investigated. This critical review is devoted mainly to their electrochemical performances and reaction mechanisms (313 references). © 2010 The Royal Society of Chemistry.


Park C.-M.,Research Center for Energy Conversion And Storage | Sohn H.-J.,Research Center for Energy Conversion And Storage
Electrochimica Acta | Year: 2010

Intermetallic FeSb2 and CrSb2 and their nanocomposites (FeSb2/C and Sb/Cr3C2/C) were prepared using solid-state routes, such as heat-treatment and high-energy mechanical milling, in order to enhance the electrochemical properties of Sb. These electrodes were tested as anode materials for rechargeable Li-ion batteries. The reaction mechanism of intermetallic FeSb2 and CrSb2 was investigated using ex situ X-ray diffraction and high resolution transmission electron microscopy. The FeSb2/C and Sb/Cr3C2/C nanocomposite electrodes exhibited greatly enhanced electrochemical behaviors compared to the FeSb2 and CrSb2 electrodes. Additionally, the Sb/Cr3C2/C nanocomposite electrode showed a better electrochemical performance than the FeSb2/C nanocomposite electrode. © 2010 Elsevier Ltd. All rights reserved.


Piao Y.,Seoul National University | Piao Y.,Korea Advanced Institute of Science and Technology | Kim H.S.,Research Center for Energy Conversion And Storage | Sung Y.-E.,Research Center for Energy Conversion And Storage | Hyeon T.,Seoul National University
Chemical Communications | Year: 2010

A simple and scalable process was developed for the synthesis of highly crystalline magnetite nanocrystals embedded in a carbon matrix using low cost starting materials; the resulting nanocomposite showed a very high specific capacity of 863 mA hg-1 in the initial cycle and high capacity retention of 90% after 30 cycles. © 2010 The Royal Society of Chemistry.


Jung H.,Research Center for Energy Conversion And Storage | Park C.-M.,Kumoh National Institute of Technology | Sohn H.-J.,Research Center for Energy Conversion And Storage
Electrochimica Acta | Year: 2011

Bi2S3 and Bi2S3/C nanocomposites prepared by high-energy mechanical milling were evaluated as electrode materials in lithium secondary batteries. For a Bi2S 3/C nanocomposite, Bi2S3 nanocrystallites were well distributed in an amorphous carbon matrix. The reaction mechanism of the Bi2S3/C electrode was also examined during the first cycle. The Bi2S3/C nanocomposite anode showed superior electrochemical performance (ca. 500 mAh g-1 and 85% of the capacity retention over 100 cycles). © 2010 Elsevier Ltd.


Park C.-M.,Research Center for Energy Conversion And Storage | Sohn H.-J.,Research Center for Energy Conversion And Storage
Journal of the Electrochemical Society | Year: 2010

Intermetallic TiSb2 and Sb/TiC/C nanocomposites were prepared by alloying and dealloying reactions, respectively, and their potential as anode materials for rechargeable Li-ion batteries was investigated. The Sb/TiC/C nanocomposite was composed of nanocrystalline Sb and TiC, which were distributed uniformly in an amorphous carbon matrix. The reaction mechanism of intermetallic TiSb2 with Li was examined by ex situ X-ray diffraction and high resolution transmission electron microscopy. The Sb/TiC/C nanocomposite exhibited good electrochemical performance, such as a high initial coulombic efficiency of 87% and a long cycle retention of 83% after 100 cycles. © 2009 The Electrochemical Society.


Lim D.-H.,Research Center for Energy Conversion And Storage | Lee W.-D.,Research Center for Energy Conversion And Storage | Choi D.-H.,Research Center for Energy Conversion And Storage | Lee H.-I.,Research Center for Energy Conversion And Storage
Applied Catalysis B: Environmental | Year: 2010

An effective method is developed for preparing highly dispersed CeO2 nanoparticles on a Pt/C catalyst synthesized by a continuous two-step process as a cathode material in low-temperature fuel cell. The XRD patterns of the 20Pt-10CeO2/C catalyst reveal that both crystalline Pt and CeO2 phases coexist. The HR-TEM images show that Pt and CeO2 nanoparticles have average particle sizes of approximately 3.4 nm and 4.2 nm, respectively, with quite a narrow distribution between 3 nm and 5 nm. Based on the analysis of the polarization curves for the ORR, the optimum proportion of CeO2 into the 20Pt/C catalyst is 10 wt%. In the ORR and single cell tests, the 20Pt-10CeO2/C catalyst shows higher performance than the commercial 20Pt/C catalyst, owing to the oxygen storage capacity of CeO2 and its ability to exchange oxygen rapidly with oxygen in the buffer. In the accelerated stability tests, the 20Pt-10CeO2/C catalyst has a better durability compared to the commercial 20Pt/C catalyst due to the existence of CeO2, which prevents the agglomeration and dissolution of Pt nanoparticles on the carbon support, extending the life of the catalyst. © 2009 Elsevier B.V. All rights reserved.

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