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Myoung Hwan Oh,
Taekyung Yu,
Seung-Ho Yu,
Byungkwon Lim,
Kyung-Tae Ko,
Marc-Georg Willinger,
Dong-Hwa Seo,
Byung Hyo Kim,
Min Gee Cho,
Jae-Hoon Park,
Kisuk Kang, Yung-Eun Sung,
Nicola Pinna,
Taeghwan Hyeon
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ABSTRACT: Galvanic replacement reactions provide a simple and versatile route for producing hollow nanostructures with controllable pore structures and compositions. However, these reactions have previously been limited to the chemical transformation of metallic nanostructures. We demonstrated galvanic replacement reactions in metal oxide nanocrystals as well. When manganese oxide (Mn3O4) nanocrystals were reacted with iron(II) perchlorate, hollow box-shaped nanocrystals of Mn3O4/γ-Fe2O3 ("nanoboxes") were produced. These nanoboxes ultimately transformed into hollow cagelike nanocrystals of γ-Fe2O3 ("nanocages"). Because of their nonequilibrium compositions and hollow structures, these nanoboxes and nanocages exhibited good performance as anode materials for lithium ion batteries. The generality of this approach was demonstrated with other metal pairs, including Co3O4/SnO2 and Mn3O4/SnO2.
Science 05/2013; 340(6135):964-968. · 31.20 Impact Factor
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ABSTRACT: The demand for lithium has greatly increased with the rapid development of rechargeable batteries. Currently, the main lithium resource is brine lakes, but the conventional lithium recovery process is time consuming, inefficient, and environmentally harmful. Rechargeable batteries have been recently used for lithium recovery, and consist of lithium iron phosphate as a cathode. These batteries feature promising selectivity between lithium and sodium, but they suffer from severe interference from coexisting magnesium ions, an essential component of brine, which has prompted further study. This study reports on a highly selective and energy-efficient lithium recovery system using a rechargeable battery that consists of a λ-MnO2 positive electrode and a chloride-capturing negative electrode. This system can be used to recover lithium from brine even in the presence of magnesium ions as well as other dissolved cations. In addition, lithium recovery from simulated brine is successfully demonstrated, consuming 1.0 W h per 1 mole of lithium recovered, using water similar to that from the artificial brine, which contains various cations (mole ratio: Na/Li ≈ 15.7, K/Li ≈ 2.2, Mg/Li ≈ 1.9).
Physical Chemistry Chemical Physics 04/2013; · 3.57 Impact Factor
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Seung Jun Hwang,
Sung Jong Yoo,
Jungho Shin,
Yong-Hun Cho,
Jong Hyun Jang,
Eunae Cho, Yung-Eun Sung,
Suk Woo Nam,
Tae-Hoon Lim,
Seung-Cheol Lee,
Soo-Kil Kim
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ABSTRACT: Core@shell electrocatalysts for fuel cells have the advantages of a high utilization of Pt and the modification of its electronic structures toward enhancement of the activities. In this study, we suggest both a theoretical background for the design of highly active and stable core@shell/C and a novel facile synthetic strategy for their preparation. Using density functional theory calculations guided by the oxygen adsorption energy and vacancy formation energy, Pd(3)Cu(1)@Pt/C was selected as the most suitable candidate for the oxygen reduction reaction in terms of its activity and stability. These predictions were experimentally verified by the surfactant-free synthesis of Pd3Cu1/C cores and the selective Pt shell formation using a Hantzsch ester as a reducing agent. In a similar fashion, Pd@Pd(4)Ir(6)/C catalyst was also designed and synthesized for the hydrogen oxidation reaction. The developed catalysts exhibited high activity, high selectivity, and 4,000 h of long-term durability at the single-cell level.
Scientific Reports 02/2013; 3:1309.
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ABSTRACT: Electrocatalysts for hydrogen oxidation reactions (HORs) are the key to renewable-energy technologies including fuel cells, hydrogen pumps, and water splitting. Despite the significant technological interest and tremendous efforts that have been made, development of hydrogen electrode catalysts with high activity at low cost remains a great challenge. Here, we report the preparation, characterization, and electrochemical properties of a hybrid material composed of Pd nanocrystals grown on spontaneously oxidized WC as a high-performance catalyst for the HOR. The Pd/WC hybrid exhibits enhanced catalytic activity compared to a carbon supported Pd (Pd/C) catalyst, making it a Pt-free, effective catalyst for the HOR. The remarkable catalytic activity arises from synergistic ligand effects between Pd and WC.
Physical Chemistry Chemical Physics 01/2013; · 3.57 Impact Factor
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ABSTRACT: We introduce a simple process to synthesize few-layered MoS(2) nanosheets supported on coaxial carbon nanotubes through an l-cysteine-assisted hydrothermal route, in which l-cysteine, a cheap and ordinary amino acid, plays a fundamental role in controlling the morphology of the hybrid material and the binder to help the growth of MoS(2) nanosheets on the surface of the carbon nanotubes. It is also demonstrated that the polypeptide formed by l-cysteine can be transformed into amorphous carbon by heat treatment under an inert atmosphere. The materials exhibit high capacity and excellent cycling performance when used as anode materials for lithium ion batteries. The specific capacity of a composite with 1 : 4 molar ratio of MoS(2) to carbon nanotubes is 736.5 mAh g(-1) after the first cycle, increased for several initial cycles, and remains at 823.4 mAh g(-1) even after 30 cycles, when cycled at a current density of 100 mA g(-1). At a very high current density of 1600 mA g(-1), the material shows a stable capacity of approximately 530 mAh g(-1) after 30 cycles. The noteworthy improvement in the electrochemical performance of the material can be attributed to their unique structure and the synergistic effects of amorphous carbon and few-layered MoS(2).
Dalton Transactions 12/2012; · 3.84 Impact Factor
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ABSTRACT: The electrocatalysts for polymer electrolyte membrane fuel cells must be designed by two equally important fundamental principles: the optimization of electrocatalytic activities as well as the long-term stability in acid mediums (<1 pH) at high potential (0.8 V). We report here a solution based approach to the preparation of Pt-based alloy with early transition metals and the realistic parameters elucidating stability and activity of Pt3M (M = Y, Zr, Ti, Ni, ion (ORR). The enhanced stability and activity of Pt-based alloy nanocatalysts in ORR and the relationship between electronic structure modification and stability were studied by experiment and DFT calculations. Stability correlates with the d-band fillings and the heat of alloy formation of Pt3M alloys, which in turn depends on the degree of the electronic perturbation due to alloying. This concept provides the realistic parameter for the rational catalyst design in Pt-based alloy system.
Journal of the American Chemical Society 11/2012; · 9.91 Impact Factor
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Tae-Yeol Jeon,
Nicola Pinna,
Sung Jong Yoo,
Docheon Ahn,
Sun Hee Choi,
Marc-Georg Willinger,
Yong-Hun Cho,
Kug-Seung Lee,
Hee-Young Park,
Seung-Ho Yu, Yung-Eun Sung
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ABSTRACT: We report a new method for deposition of Pt on a metal core to develop real electrocatalysts with significantly reduced amounts of expensive Pt as well as enhanced activity for oxygen reduction reaction. Ru and Pd have different crystal structures and modify the electronic structure of Pt to a different extent (shifts in d-band center). They were chosen as core materials to examine whether hydroquinone dissolved in ethanol can be used to deposit additional Pt atoms onto preformed core nanoparticles, and whether the modified d-character of Pt on different host metals can result in the enhanced ORR activity. The physicochemical characteristics of Pd-Pt and Ru-Pt core-shell nanoparticles are investigated. The core-shell structure was identified through a combination of experimental methods, employing electron microscopy, electrochemical measurements, and synchrotron X-ray measurements such as powder X-ray diffraction, X-ray absorption fine structure, and X-ray photoelectron spectroscopy. The hydroquinone reduction method proved to be an excellent route for the epitaxial growth of a Pt shell on the metal cores, leading to enhanced ORR activities.
Nanoscale 09/2012; 4(20):6461-9. · 5.91 Impact Factor
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ABSTRACT: In this article, we examined the feasibility of using 3,4-dihydroxy-L-phenylalanine (DOPA) as a cell adhesion molecule in serum-free cultures of anchorage-dependent mammalian cells. DOPA is a critical, functional element in mussel adhesive proteins and is known to bind strongly to various natural or synthetic materials. DOPA coating on culture plates was confirmed using X-ray photoelectron spectroscopy and energy-dispersive spectroscopy. Human dermal fibroblasts (HDFs) were cultured on DOPA-coated, fibronectin-coated, or no material-coated culture plates in serum-free medium. HDFs cultured on DOPA showed the highest cell adhesion ratio, spreading, and viability but the lowest apoptotic activity. Therefore, DOPA may be a useful cell-adhesion molecule for serum-free culture.
Biotechnology Progress 05/2012; 28(4):1055-60. · 2.34 Impact Factor
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ABSTRACT: Highly dispersed Pd nanoparticles were prepared by borohydride reduction of Pd(acac)(2) in 1,2-propanediol at an elevated temperature. They were uniformly dispersed on carbon black without significant aggregation. X-ray diffraction showed that carbons from the Pd precursor dissolved in Pd, increasing its lattice parameter. A modified reduction process was tested to remove the carbon impurities. Carbon removal greatly enhanced catalytic activity toward the oxygen reduction reaction. It also generated an inconsistency between the electronic modifications obtained from X-ray photoelectron spectroscopy and the electrochemical method. CO displacement measurements showed that the formation of Pd-C bonds decreased the work function of the surface Pd atoms.
Langmuir 02/2012; 28(7):3664-70. · 4.19 Impact Factor
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ABSTRACT: We report Pt-based alloys with early transition metals. Significant electrocatalysis occurs during oxygen reduction reaction (ORR) at the Pt-Y alloy electrodes, and the extent depends on the alloy composition. The Pt-Y alloy electrode activity is related to the d-band center position, and the lattice strain and stability for oxygen reduction reaction.
Chemical Communications 05/2011; 47(41):11414-6. · 6.17 Impact Factor
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Angewandte Chemie International Edition 03/2011; 50(10):2270-4. · 13.45 Impact Factor
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ABSTRACT: Pt overlayers were deposited on carbon-supported Ir nanoparticles with various coverages. Structural and electrochemical characterizations were performed using transmission electron microscopy (TEM), X-ray diffraction, high-resolution powder diffraction (HRPD), X-ray photoelectron spectroscopy (XPS), X-ray absorption near-edge spectroscopy (XANES), cyclic voltammetry (CV), CO stripping voltammetry, and N(2)O reduction. The surface of Ir nanoparticles was covered with Pt overlayers with thickness varying from the submonolayer scale to more than two monolayers. Surface analyses such as CV and CO stripping voltammetry indicated that the Pt overlayers were uniformly deposited on the Ir nanoparticles, and the resultant Pt overlayers exhibited gradual changes in surface characteristics toward the Pt surface as the surface coverage increased. The distinct CO stripping characteristics and the enhanced Pt utilization affected electrocatalytic activities for methanol oxidation. The electrochemical stability of the Pt overlayer was compared with a commercial carbon-supported Pt catalyst by conducting a potential cycling experiment.
Langmuir 02/2011; · 4.19 Impact Factor
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ABSTRACT: A compact BrFAFC can directly convert formate to power without hydrogen storage and poisoning effect by CO at mild temperature. We are the first to establish the performance of the BrFAFC with high power density. Furthermore, this BrFAFC can be manufactured in a simple design for use in portable fuel cells.
Chemical Communications 02/2011; 47(13):3972-4. · 6.17 Impact Factor
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ABSTRACT: Considerable efforts have been devoted to the design and synthesis of low-dimensional, nanostructured materials due to their
morphology-dependent performances. In particular, one-dimensional (1-D) TiO2 nanostructures, including nanorods (NRs), nanowires (NWs), and nanotubes (NTs), have attracted considerable interest due
to their unique characteristics. In dye-sensitized solar cell (DSSC) operation, 1-D nanostructure-based photoanodes can contribute
to rapid electron transport, ensuring efficient charge collection by the conducting substrate in competition with recombination.
Relying on the ordering of 1-D TiO2 nanomaterial, the conversion efficiency of DSSCs was affected because electron collection is determined by trapping/detrapping
events at the site of the electron traps, such as defects, surface states, grain boundaries, and self-trapping. This point
has promoted research on self-ordered, 1-D photoanodes stretched on a substrate with enhanced electron transport properties
due to their desirable features: highly decreased intercrystalline contacts and a structure with a specified directionality.
In this literature review, the preparation of various 1-D nanomaterials from disordered to ordered states and their electron
dynamics in the application of DSSCs are reviewed.
12/2010: pages 317-350;
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ABSTRACT: A physical synthesis of multilayered Pt/Ru nanorods with controllable bimetallic sites as methanol oxidation catalysts is reported for the first time. The novel nanorods were synthesized via the oblique angle deposition method, deposited prior to the formation of each individual noble metal layer, in a sequential fashion. It has been shown that the oblique angle deposition controls the morphology and electrochemical properties of the resultant nanostructures. Sequentially the multilayered nanorods comprising Pt and Ru segments exhibited superior electrocatalytic activity when compared to equivalent monometallic Pt nanorods with respect to methanol electrooxidation reaction in an acidic medium. Moreover, it has been established that the electrochemical process takes place at the Pt/Ru nanorods followed the bifunctional mechanism. The relative rates of reaction, recorded using chronoamperometry, show a linear relationship between the long-time current density and the number of Pt/Ru interfaces. Interestingly, the best catalyst for methanol oxidation was found to the surface of bimetallic Pt/Ru nanorods produced by the heat treatments via the so-called electronic effect. This reflects the fact that the ensemble effects of combined bifunctional and electronic effects via second elements could be expected in methanol oxidation reactions. Electrocatalytic activities correlate well with bimetallic pair sites and electronic properties analyzed by X-ray photoemission spectroscopy and X-ray absorption near-edge structure.
Physical Chemistry Chemical Physics 11/2010; 12(46):15240-6. · 3.57 Impact Factor
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ABSTRACT: A facile room temperature synthesis technique has been developed for Pt-Ir/C electrocatalysts for applications to low-temperature fuel cells. The prepared Pt(x)Ir(y) electrocatalyst was highly stable and active toward the oxygen reduction reaction (ORR), as well as liquid fuel oxidation reaction with high CO tolerance.
Chemical Communications 10/2010; 46(44):8401-3. · 6.17 Impact Factor
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ABSTRACT: Ru and Pt-Ru (Pt:Ru = 1:1) nanoparticles supported on carbon black were prepared by the borohydride reduction method using oleylamine as a stabilizer in an anhydrous ethanol solvent. We investigated the effect of Pt segregation to the surface of alloy nanoparticles on the methanol oxidation reaction (MOR). As-prepared Pt(1)Ru(1)/C showed a narrow size distribution and a relatively uniform particle distribution on a carbon support. However, its electrocatalytic activity toward the MOR was poor due to the high surface concentration of Ru. As duration time of heat treatment at 200 degrees C was increased up to 2 h, the surface composition of Pt atoms was increased without significant particle growth due to thermally induced segregation of Pt atoms, which were revealed by TEM images, X-ray photoelectron spectroscopy (XPS) analysis, changes in the potentials of zero total charge (pztc), and increase in the oxidation charge of "reduced CO(2)". In particular, from the combination of CO adlayer oxidation and "reduced CO(2)" oxidation charges, the increased surface concentration of Pt of alloy catalysts was relatively quantified when compared to its as-prepared state. Cyclic voltammograms in 0.1 M HClO(4) solution with 0.5 M methanol showed that Pt(1)Ru(1)/C annealed for 2 h at 200 degrees C in a flow of mixture gas of Ar and H(2) (5 vol %) had a less positive onset potential for the MOR. These results demonstrate a definitive contribution from segregation of Pt atoms to the MOR activity.
Langmuir 04/2010; 26(11):9123-9. · 4.19 Impact Factor
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ABSTRACT: Size-controlled Pt nanocatalysts embedded in TiO(2) were successfully synthesized by simultaneous dual-gun sputtering and were found to exhibit unique electronic properties depending on their size, which affected the potential of zero total charge, CO-bulk oxidation, and methanol oxidation reaction.
Chemical Communications 02/2010; 46(5):794-6. · 6.17 Impact Factor
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ABSTRACT: 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.
Chemical Communications 01/2010; 46(1):118-20. · 6.17 Impact Factor
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ABSTRACT: WO3 bilayer electrodes composed of WO3 top and bottom layers are designed for photoelectrochemical cells (PECs). The bottom layers are sputter-deposited at a high temperature (773K) that leads to large grains and suitable electrical pathways for carrier collection. The top layer is deposited at a low temperature (573K) and consists of small grains, which give rise to large electrochemical reaction sites. The bilayer electrodes give a significant enhancement in PEC performance compared with WO3 monolayer electrodes deposited at 573 or 773K, because of a combination of favourable effects.
Journal of Power Sources 01/2010; 195(16):5422-5425. · 4.95 Impact Factor
