Pohang, South Korea
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Jeong H.W.,Kyungpook National University | Jeon T.H.,Pohang Accelerator Laboratory | Jang J.S.,Pohang Accelerator Laboratory | Choi W.,Pohang Accelerator Laboratory | Park H.,Kyungpook National University
Journal of Physical Chemistry C | Year: 2013

To improve the photoelectrochemical (PEC) performance of BiVO4, three different modifications (doping, heterojunction, and catalyst deposition) using earth-abundant elements are performed and their effects are compared in a 0.1 M phosphate electrolyte at pH 7 under AM1.5 light (100 mW/cm2). When a hexavalent element (Cr6+, W6+, or Mo6+) is doped at various levels, the Mo6+-doping effect is most significant at 10 atomic % with about two times higher photocurrent generation at the oxygen evolution potential (1.23 VRHE). Such enhancement is attributed to a decrease in charge transfer resistance (Rct) by donor doping, resulting in an approximate 2-fold increase in charge separation efficiency (ηsep) to about 25%. W6+ is less effective than Mo6+, whereas Cr6+ has a detrimental effect. To further improve the charge separation efficiency of Mo6+-doped BiVO4 (Mo-BiVO4), a approximate 600 nm thick WO 3 layer is deposited under a similarly thick Mo-BiVO4 layer. This binary heterojunction (WO3/Mo-BiVO4) exhibits ηsep of about 50% along with more than 3 times higher photocurrent generation. On the other hand, an oxygen evolving cobalt-phosphate (Co-Pi) catalyst electrodeposited to Mo-BiVO4 (Mo-BiVO 4/Co-Pi) enhances charge injection efficiency (ηinj) from ∼50 to ∼70% at 1.23 VRHE. These two binaries are coupled into a ternary heterojunction (WO3/Mo-BiVO4/Co-Pi) in order to improve the charge transfer efficiencies (ηsep and ηinj). The PEC performance of this ternary is significantly high with photocurrent density of about 2.4 mA/cm2 at 1.23 VRHE (corresponding to the solar-to-hydrogen efficiency of ca. 3%) due to ηsep and ηinj of ∼60 and 90%, respectively. © 2013 American Chemical Society.

Song H.-K.,Ulsan National Institute of Science and Technology | Lee K.T.,Ulsan National Institute of Science and Technology | Kim M.G.,Pohang Accelerator Laboratory | Nazar L.F.,University of Waterloo | Cho J.,Ulsan National Institute of Science and Technology
Advanced Functional Materials | Year: 2010

Diversified and extended applications of lithium-ion batteries demand the development of more enhanced materials that can be achieved by sophisticated synthetic methods. Combination of novel materials with strategic design of their shape on the nanometer scale enables a breakthrough to overcome problems experienced by present technologies. In this feature article, an overview is given of Mn-based and polyanion-based cathode materials with nanoscale features for lithium-ion batteries as materials to replace conventional bulk cathode materials. Various synthetic methods coupled with nanostructuring as well as the benefits obtained from the nanostructure are described. Strategic design of electrode materials in a nanoscale dimension provides breakthroughs in battery technologies. Enhanced cathodic materials drive advances of lithium rechargeable batteries in terms of capacity, rate capability, and cyclability. Various nanostructures such as nanoparticles, nanotubes, nanorods, nanoplates, and even the secondary structure of the primary nano-units enable promising materials for cathodes. Copyright © 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Kim T.K.,Ulsan National Institute of Science and Technology | Lee J.H.,Ulsan National Institute of Science and Technology | Moon D.,Pohang Accelerator Laboratory | Moon H.R.,Ulsan National Institute of Science and Technology
Inorganic Chemistry | Year: 2013

A luminescent lithium metal-organic framework (MOF) is constructed from the solvothermal reaction of Li+ and a well-designed organic ligand, bis(4-carboxyphenyl)-N-methylamine (H2CPMA). A Li-based MOF can detect an explosive aromatic compound containing nitro groups as an explosophore, by showing a dramatic color change with concurrent luminescence quenching in the solid state. The detection sites are proven directly through single-crystal-to-single-crystal transformations, which show strong interactions between the aromatic rings of the electron-rich CPMA2- molecules and the electron-deficient nitrobenzene. © 2012 American Chemical Society.

Egorova O.A.,Pohang University of Science and Technology | Seo H.,Pohang University of Science and Technology | Kim Y.,Pohang University of Science and Technology | Moon D.,Pohang Accelerator Laboratory | And 2 more authors.
Angewandte Chemie - International Edition | Year: 2011

Hidden nuggets of gold: Mono- and divinylgold complexes (see scheme), key intermediates in the gold-mediated cyclization reaction of N-(propargyl) benzamides, are characterized by NMR and X-ray diffraction analyses. The monovinylgold intermediates undergo proto-deauration in acetonitrile by the substrate. In aqueous media, they produce oxidized products. The divinylgold species undergo reductive elimination to produce the corresponding dimerized products. © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Shin J.W.,Pohang Accelerator Laboratory | Eom K.,Human Technology | Moon D.,Pohang Accelerator Laboratory
Journal of Synchrotron Radiation | Year: 2016

BL2D-SMC at the Pohang Light Source II is a supramolecular crystallography beamline based on a bending magnet. The beamline delivers high-flux tunable X-rays with energies from 8.3 to 20.7 keV and a 100;μm (horizontal) × 85;μm (vertical) full width at half-maximum focal spot. Experiments involving variable temperature, photo-excitation and gas sorption are supported by ancillary equipment and software in the beamline. The design of the beamline, its role and the main components are described. © 2016 International Union of Crystallography.

Choi J.-H.,Andong National University | Moon D.,Pohang Accelerator Laboratory
Journal of Molecular Structure | Year: 2014

The structure of trans-[Cr(2,2,3-tet)F2]ClO4 (2,2,3-tet = 1,4,7,11-tetraazaundecane) has been determined by single-crystal X-ray diffraction. The complex crystallizes in the space group P 1 34; of the triclinic system with two mononuclear formula units in a cell of dimensions a = 5.6741(11), b = 9.971(2), c = 13.222(3) Å, α = 73.76(3)o, β = 81.08(3) and γ = 85.12(3). The chromium(III) atom is in a slightly distorted octahedral environment coordinated by four N atoms of 2,2,3-tet and two F ligands in a mutually trans (meso RS) geometry. The mean Cr-N(2,2,3-tet) and CrF bond lengths are 2.064(9) and 1.885(7) Å, respectively. The crystal packing is stabilized by several hydrogen bonds. The 5 K sharp-line absorption spectrum and the 298 K FT-infrared and UV-visible spectra have been measured. Using the electronic transitions, a ligand field optimization has been performed to determine the metal-ligand bonding properties of the coordinated atoms. It is found that the fluoride is a strong σ- and π-donor and the nitrogen atoms of the 2,2,3-tet ligand also have strong σ-donor properties toward the chromium(III). © 2013 Elsevier B.V. All rights reserved.

Morikawa H.,Yonsei University | Hwang C.C.,Pohang Accelerator Laboratory | Yeom H.W.,Yonsei University
Physical Review B - Condensed Matter and Materials Physics | Year: 2010

We demonstrate the controllable electron doping into metallic atomic wires, indium wires self-assembled on the Si(111) surface, which feature one-dimensional (1D) band structure and temperature-driven metal-insulator transition. The electron filling of 1D metallic bands is systematically increased by alkali-metal adsorption, which, in turn, tunes the macroscopic property, that is, suppresses the metal-insulator transition. On the other hand, the dopant atoms induce a local lattice distortion without a band-gap opening, leading to a microscopic phase separation on the surface. The distinct bifunctional, electronic and structural, roles of dopants in different length scales are thus disclosed. © 2010 The American Physical Society.

Han J.-H.,Pohang Accelerator Laboratory
Nuclear Instruments and Methods in Physics Research, Section A: Accelerators, Spectrometers, Detectors and Associated Equipment | Year: 2014

As an electron beam injector of X-ray free-electron lasers (FELs), photoinjectors have been developed for the past few decades. Such an injector starting with a photocathode RF gun provides high brightness beams and therefore it is being adopted as an injector of X-ray FELs. In this paper we show how to improve photoinjector performance in terms of emittance and repetition rates by means of injector components optimization, especially with the gun. Transverse emittance at the end of an injector is reduced by optimizing the gun design, gun solenoid position, and accelerating section position. The repetition rate of an injector mainly depends on the gun. It is discussed that a repetition rate of 1 kHz at a normal-conducting S-band photoinjector is feasible by adopting a coaxial RF coupler and improving cooling-water channels surrounding the gun. © 2014 Elsevier B.V.

Kim M.G.,Pohang Accelerator Laboratory | Sim S.,The Interdisciplinary Center | Cho J.,The Interdisciplinary Center
Advanced Materials | Year: 2010

Core-shell type nanoalloys in which the Cu atoms uniformly reside as a shell around a core of Sn nanoparticles are achieved by reacting Cu(acac) 2 with tin nanoparticles. The core-shell Sn@Cu nanoparticles further demonstrate significantly improved rate capability at higher C rates than Sn@C nanoparticles. Copyright © 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Bar A.K.,Indian Institution of Science | Raghothama S.,Indian Institution of Science | Moon D.,Pohang Accelerator Laboratory | Mukherjee P.S.,Indian Institution of Science
Chemistry - A European Journal | Year: 2012

Template-assisted formation of multicomponent Pd 6 coordination prisms and formation of their self-templated triply interlocked Pd 12 analogues in the absence of an external template have been established in a single step through Pd-N/Pd-O coordination. Treatment of cis-[Pd(en)(NO 3) 2] with K 3tma and linear pillar 4,4′-bpy (en=ethylenediamine, H 3tma=benzene-1,3,5-tricarboxylic acid, 4,4′-bpy=4,4′-bipyridine) gave intercalated coordination cage [{Pd(en)} 6(bpy) 3(tma) 2] 2[NO 3] 12 (1) exclusively, whereas the same reaction in the presence of H 3tma as an aromatic guest gave a H 3tma- encapsulating non-interlocked discrete Pd 6 molecular prism [{Pd(en)} 6(bpy) 3(tma) 2(H 3tma) 2][NO 3] 6 (2). Though the same reaction using cis-[Pd(NO 3) 2(pn)] (pn=propane-1,2-diamine) instead of cis-[Pd(en)(NO 3) 2] gave triply interlocked coordination cage [{Pd(pn)} 6(bpy) 3(tma) 2] 2[NO 3] 12 (3) along with non-interlocked Pd 6 analogue [{Pd(pn)} 6(bpy) 3(tma) 2](NO 3) 6 (3′), and the presence of H 3tma as a guest gave H 3tma-encapsulating molecular prism [{Pd(pn)} 6(bpy) 3(tma) 2(H 3tma) 2][NO 3] 6 (4) exclusively. In solution, the amount of 3′ decreases as the temperature is decreased, and in the solid state 3 is the sole product. Notably, an analogous reaction using the relatively short pillar pz (pz=pyrazine) instead of 4,4′-bpy gave triply interlocked coordination cage [{Pd(pn)} 6(pz) 3(tma) 2] 2[NO 3] 12 (5) as the single product. Interestingly, the same reaction using slightly more bulky cis-[Pd(NO 3) 2(tmen)] (tmen=N,N,N′,N′-tetramethylethylene diamine) instead of cis-[Pd(NO 3) 2(pn)] gave non-interlocked [{Pd(tmen)} 6(pz) 3(tma) 2] [NO 3] 6 (6) exclusively. Complexes 1, 3, and 5 represent the first examples of template-free triply interlocked molecular prisms obtained through multicomponent self-assembly. Formation of the complexes was supported by IR and multinuclear NMR ( 1H and 13C) spectroscopy. Formation of guest-encapsulating complexes (2 and 4) was confirmed by 2D DOSY and ROESY NMR spectroscopic analyses, whereas for complexes 1, 3, 5, and 6 single-crystal X-ray diffraction techniques unambiguously confirmed their formation. The gross geometries of H 3tma-encapsulating complexes 2 and 4 were obtained by universal force field (UFF) simulations. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

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