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Sample records for ag pd pt

  1. EXAFS Studies of Bimetallic Ag-Pt and Ag-Pd Nanorods

    SciTech Connect

    Lahiri, D.; Chattopadhyay, S.; Bunker, B.A.; Doudna, C.M.; Bertino, M.F.; Blum, F.; Tokuhiro, A.; Terry, J.

    2008-10-30

    Nanoparticles of Ag-Pt and Ag-Pd with high aspect ratios were synthesized using a radiolysis method. Gamma rays at dose rates below 0.5 kGy/h were used for irradiation. The nanoparticles were characterized by transmission electron microscopy (TEM), optical absorption spectroscopy and x-ray Absorption Fine Structure (XAFS) spectroscopy. Bright field micrographs show that Ag-Pt nanowires are composed of large particles with diameters ranging from 20-30 nm and joined by filaments of diameter between 2-5 nm. The Ag-Pd nanowires have diameters of 20-25 nm and lengths of 1.5 {micro}m. For XAFS measurements, the Pt L3 edge (11.564 keV), Ag K-edge (25.514 keV) and Pd K-edge (24.350 keV) were excited to determine the local structure around the respective atoms in the cluster. The Ag-Pt particles were found to possess a distinct core-shell structure with Pt in the core surrounded by Ag shell, with no indication of alloy formation. However, nanorods of Ag-Pd have formed an alloy for all the alloy compositions.

  2. Genetic Pd, Pt, Au, Ag, and Rh mineralogy in Noril'sk sulfide ores

    NASA Astrophysics Data System (ADS)

    Spiridonov, E. M.; Kulagov, E. A.; Serova, A. A.; Kulikova, I. M.; Korotaeva, N. N.; Sereda, E. V.; Tushentsova, I. N.; Belyakov, S. N.; Zhukov, N. N.

    2015-09-01

    The undeformed ore-bearing intrusions of the Noril'sk ore field (NOF) cut through volcanic rocks of the Late Permian-Early Triassic trap association folded in brachysynclines. Due to the nonuniform load on the roof of intrusive bodies, most sulfide melts were squeezed, up to the tops of ore-bearing intrusions; readily fusible Ni-Fe-Cu sulfide melts were almost completely squeezed. In our opinion, not only one but two stages of mineralization developed at the Noril'sk deposits: (i) syntrap magmatic and (ii) epigenetic post-trap metamorphic-hydrothermal. All platinum-group minerals (PGM) and minerals of gold are metasomatic in the Noril'sk ores. They replaced sulfide solid solutions and exsolution structures. All types of PGM and Au minerals occur in the ores, varying in composition from pyrrhotite to chalcopyrite, talnakhite, mooihoekite, and rich in galena; they are localized in the inner and outer contact zones and differ only in the quantitative proportions of ore minerals. The aureoles of PGM and Au-Ag minerals are wider than the contours of sulfide bodies and coincide with halos of fluid impact on orebodies and adjacent host rocks. The pneumatolytic PGM and Au-Ag minerals are correlated in abundance with the dimensions of sulfide bodies. Their amounts are maximal in veins of late fusible ore composed of eutectic PbS ss and iss intergrowths, as well as at their contacts. The Pd and Pt contents in eutectic sulfide ores of NOF are the world's highest. In the process of noble-metal mineral formation, the fluids supply Pd, Pt, Au, As, Sb, Sn, Bi, and a part of Te, whereas Fe, Ni, Cu, Pb, Ag, Rh, a part of Te and Pd are leached from the replaced sulfide minerals. The pneumatolytic PGM of the early stage comprises Pd and Pt intermetallic compounds enriched in Au along with Pd-Pt-Fe-Ni-Cu-Sn-Pb(As) and (Pd,Pt,Au)(Sn,Sb,Bi,Te,As) solid solutions. Pneumatolytic PGM and Au minerals of the middle stage are products of solid-phase transformation and recrystallization of

  3. Trimetallic nanostructures: the case of AgPd/Pt multiply twinned nanoparticles

    PubMed Central

    Khanal, Subarna; Bhattarai, Nabraj; Velázquez-Salazar, J. Jesús; Bahena, Daniel; Soldano, German; Ponce, Arturo; Mariscal, Marcelo M.; Mejía-Rosales, Sergio; José-Yacamán, Miguel

    2013-01-01

    We report the synthesis, structural characterization, and atomistic simulations of AgPd/Pt trimetallic (TM) nanoparticles. Two types of structure were synthesized using a relatively facile chemical method: multiply twinned core-shell, and hollow particles. The nanoparticles were small in size, with an average diameter of 11 nm and a narrow distribution, and their characterization by aberration corrected scanning transmission electron microscopy allowed us to probe the structure of the particles at atomistic level. In some nanoparticles, the formation of a hollow structure was also observed, that facilitates the alloying of Ag and Pt in the shell region and the segregation of Ag atoms in the surface, affecting the catalytic activity and stability. We also investigated the growth mechanism of the nanoparticles using grand canonical Monte Carlo simulations, and we have found that Pt regions grow at overpotentials on the AgPd nanoalloys, forming 3D islands at the early stages of the deposition process. We found very good agreement between the simulated structures and those observed experimentally. PMID:24165796

  4. Nanocatalyst superior to Pt for oxygen reduction reactions: the case of core/shell Ag(Au)/CuPd nanoparticles.

    PubMed

    Guo, Shaojun; Zhang, Xu; Zhu, Wenlei; He, Kai; Su, Dong; Mendoza-Garcia, Adriana; Ho, Sally Fae; Lu, Gang; Sun, Shouheng

    2014-10-22

    Controlling the electronic structure and surface strain of a nanoparticle catalyst has become an important strategy to tune and to optimize its catalytic efficiency for a chemical reaction. Using density functional theory (DFT) calculations, we predicted that core/shell M/CuPd (M = Ag, Au) NPs with a 0.8 or 1.2 nm CuPd2 shell have similar but optimal surface strain and composition and may surpass Pt in catalyzing oxygen reduction reactions. We synthesized monodisperse M/CuPd NPs by the coreduction of palladium acetylacetonate and copper acetylacetonate in the presence of Ag (or Au) nanoparticles with controlled shell thicknesses of 0.4, 0.75, and 1.1 nm and CuPd compositions and evaluated their catalysis for the oxygen reduction reaction in 0.1 M KOH solution. As predicted, our Ag/Cu37Pd63 and Au/Cu40Pd60 catalysts with 0.75 and 1.1 nm shells were more efficient catalysts than the commercial Pt catalyst (Fuel Cells Store), with their mass activity reaching 0.20 A/mg of noble metal at -0.1 V vs Ag/AgCl (4 M KCl); this was over 3 times higher than that (0.06 A/mg Pt) from the commercial Pt. These Ag(Au)/CuPd nanoparticles are promising non-Pt catalysts for oxygen reduction reactions. PMID:25279704

  5. Global optimization of bimetallic cluster structures. II. Size-matched Ag-Pd, Ag-Au, and Pd-Pt systems.

    PubMed

    Rossi, Giulia; Ferrando, Riccardo; Rapallo, Arnaldo; Fortunelli, Alessandro; Curley, Benjamin C; Lloyd, Lesley D; Johnston, Roy L

    2005-05-15

    Genetic algorithm global optimization of Ag-Pd, Ag-Au, and Pd-Pt clusters is performed. The 34- and 38-atom clusters are optimized for all compositions. The atom-atom interactions are modeled by a semiempirical potential. All three systems are characterized by a small size mismatch and a weak tendency of the larger atoms to segregate at the surface of the smaller ones. As a result, the global minimum structures exhibit a larger mixing than in Ag-Cu and Ag-Ni clusters. Polyicosahedral structures present generally favorable energetic configurations, even though they are less favorable than in the case of the size-mismatched systems. A comparison between all the systems studied here and in the previous paper (on size-mismatched systems) is presented.

  6. Beet juice utilization: Expeditious green synthesis of nobel metal nanoparticles (Ag, Au, Pt, and Pd) using microwaves

    EPA Science Inventory

    Metal nanoparticles of Ag, Au, Pt, and Pd were prepared in aqueous solutions via a rapid microwave-assisted green method using beet juice, an abundant sugar-rich agricultural produce, served as both a reducing and a capping reagent. The Ag nanoparticles with capping prepared by b...

  7. Effect of Ag addition to L1{sub 0} FePt and L1{sub 0} FePd films grown by molecular beam epitaxy

    SciTech Connect

    Tokuoka, Y.; Seto, Y.; Kato, T.; Iwata, S.

    2014-05-07

    L1{sub 0} ordered FePt-Ag (5 nm) and FePd-Ag (5 nm) films were grown on MgO (001) substrate at temperatures of 250–400 °C by using molecular beam epitaxy method, and their crystal and surface structures, perpendicular magnetic anisotropies and Curie temperatures were investigated. In the case of FePt-Ag, Ag addition with the amount of 10–20 at. % was effective to promote L1{sub 0} ordering and granular growth, resulting in the increase of the perpendicular magnetic anisotropy and coercivity of the FePt-Ag films. On the other hand, in the case of FePd-Ag, Ag addition changed the surface morphology from island to continuous film associated with the reductions of its coercivity and perpendicular anisotropy. The variations of lattice constants and Curie temperature with Ag addition were significantly different between FePt-Ag and FePd-Ag. For FePd-Ag, the c and a axes lattice spacings and Curie temperature gradually changed with increasing Ag content, while they unchanged for FePt-Ag. These results suggest the possibility of the formation of FePdAg alloy in FePd-Ag, while Ag segregation in FePt-Ag.

  8. Thermomodulation spectra of high-energy interband transitions in Cu, Pd, Ag, Pt, and Au

    SciTech Connect

    Olson, C.G.; Lynch, D.W.; Rosei, R.

    1980-07-15

    Thermotransmission and thermoreflectance spectra were obtained for Cu, Pd, Ag, Pt, and Au in the 10 --30 eV spectral region. Structures due to transitions from the Fermi level to high-density bands 15 eV above the Fermi level were identified in Pt. All metals showed structures arising from interband transitions between the d bands and the same flat bands, 15--20 eV above the Fermi energy. Attempts to fit to interband critical points in Au revealed over 40 possible critical points in the region of these structures, most of them near the Brillouin-zone centers. Systematic trends in the series of metals make the qualitative identification of the structures more secure, and no energy shifts of calculated energy bands are required. The observed widths of structures are sometimes much narrower than the widths of free-electron-like bands at comparable energies.

  9. Thermomodulation spectra of high-energy interband transitions in Cu, Pd, Ag, Pt, and Au

    SciTech Connect

    Olson, C.G.; Lynch, D.W.; Rosei, R.

    1980-05-01

    Many f.c.c. metals exhibit a rise in the reflectance at about 18 eV, leading to a broad peak. Thermomodulation spectra in this region reveal a richly-structured spectra. We have made thermotransmission measurements on unsupported thin films of Cu, Pd, Ag, and Au, and thermoreflectance measurements on Pt in the 15 to 30 eV spectral region. The temperature-modulated transmittance spectrum can be shown to be simply -d..delta mu.., the sample thickness multiplied by the negative of the temperature-induced change in the absorption coefficient. No data treatment is necessary. For Pt the thermoreflectance spectra were Kramers-Kronig analyzed to get ..delta mu... The data obtained for these metals are given. The spectra do not change appreciably when the ambient temperature is changed.

  10. Ultra-thin L1{sub 0}-FePt for perpendicular anisotropy L1{sub 0}-FePt/Ag/[Co/Pd]{sub 30} pseudo spin valves

    SciTech Connect

    Ho, Pin; Chow, Gan Moog; Chen, Jing-Sheng; Han, Guchang; He, Kaihua

    2014-05-07

    Perpendicular anisotropy L1{sub 0}-FePt/Ag/[Co/Pd]{sub 30} pseudo spin valves (PSVs) with ultra-thin L1{sub 0}-FePt alloy free layer possessing high anisotropy and thermal stability have been fabricated and studied. The thickness of the L1{sub 0}-FePt layer was varied between 2 and 4 nm. The PSV became increasingly decoupled with reduced L1{sub 0}-FePt thickness due to the larger difference between the coercivity of the L1{sub 0}-FePt and [Co/Pd]{sub 30} films. The PSV with an ultra-thin L1{sub 0}-FePt free layer of 2 nm displayed a high K{sub u} of 2.21 × 10{sup 7} ergs/cm{sup 3}, high thermal stability of 84 and a largest giant magnetoresistance of 0.54%.

  11. Nanoparticles of Ag with a Pt and Pd rich surface supported on carbon as a new catalyst for the oxygen electroreduction reaction (ORR) in acid electrolytes: Part 1

    NASA Astrophysics Data System (ADS)

    Pech-Pech, I. E.; Gervasio, Dominic F.; Godínez-Garcia, A.; Solorza-Feria, O.; Pérez-Robles, J. F.

    2015-02-01

    Silver (Ag) nanoparticles enriched with platinum (Pt) and palladium (Pd) on their surfaces (Ag@Pt0.1Pd0.1) are supported on Vulcan XC-72 carbon (C) to form a new catalyst (Ag@Pt0.1Pd0.1/C) for the oxygen reduction reaction (ORR) in acid electrolytes. This catalyst is prepared in one pot by reducing Ag and then Pt and Pd metal salts with sodium borohydride in the presence of trisodium citrate then adding XC-72 while applying intense ultrasound. The metallic Ag@Pt0.1Pd0.1 nanoparticles contain 2 weight percent of Pt, are spherical and have an average size less than 10 nm as determined by X-ray diffraction (XRD) and transmission electron microscopy (TEM). At the ORR potentials, Ag nanoparticles on carbon (Ag/C) rapidly lose Ag by dissolution and show no more catalytic activity for the ORR than the carbon support, whereas Ag@Pt0.1Pd0.1/C is a stable catalyst and exhibits 1.4 and 1.6 fold greater specific activity, also 3.6 and 2.8 fold greater mass activity for ORR in 0.5 M H2SO4 solution than comparable Pt/C and Pt0.5Pd0.5/C catalysts with the same Pt loading as determined for thin-films of these catalysts on a rotating-disk electrode (TF-RDE). Using silver nanoparticles increases Pt utilization and therefore decreases Pt-loading and cost of a catalyst for a proton exchange membrane fuel cell (PEMFC) electrode.

  12. Continuous syntheses of Pd@Pt and Cu@Ag core-shell nanoparticles using microwave-assisted core particle formation coupled with galvanic metal displacement.

    PubMed

    Miyakawa, Masato; Hiyoshi, Norihito; Nishioka, Masateru; Koda, Hidekazu; Sato, Koichi; Miyazawa, Akira; Suzuki, Toshishige M

    2014-08-01

    Continuous synthesis of Pd@Pt and Cu@Ag core-shell nanoparticles was performed using flow processes including microwave-assisted Pd (or Cu) core-nanoparticle formation followed by galvanic displacement with a Pt (or Ag) shell. The core-shell structure and the nanoparticle size were confirmed using high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) observation and EDS elemental mapping. The Pd@Pt nanoparticles with a particle size of 6.5 ± 0.6 nm and a Pt shell thickness of ca. 0.25 nm were synthesized with appreciably high Pd concentration (Pd 100 mM). This shell thickness corresponds to one atomic layer thickness of Pt encapsulating the Pd core metal. The particle size of core Pd was controlled by tuning the initial concentrations of Na2[PdCl4] and PVP. Core-shell Cu@Ag nanoparticles with a particle size of 90 ± 35 nm and an Ag shell thickness of ca. 3.5 nm were obtained using similar sequential reactions. Oxidation of the Cu core was suppressed by the coating of Cu nanoparticles with the Ag shell. PMID:24948122

  13. M-Au/TiO2 (M = Ag, Pd, and Pt) nanophotocatalyst for overall solar water splitting: role of interfaces.

    PubMed

    Melvin, Ambrose A; Illath, Kavya; Das, Tanmay; Raja, Thirumalaiswamy; Bhattacharyya, Somnath; Gopinath, Chinnakonda S

    2015-08-28

    M-Au/TiO2 (M = Ag, Pd, Pt) composites were prepared through a facile one-pot photodeposition synthesis and evaluated for solar water splitting (SWS) with and without a sacrificial agent. The M-Au combination exhibits a dominant role in augmenting the H2 generation activity by forming a bi-metallic system. Degussa P25 was used as a TiO2 substrate to photodeposit Au followed by Au + M (M = Ag/Pd/Pt). The SWS activity of the M-Au/TiO2 was determined through photocatalytic H2 production in the presence of methanol as a sacrificial agent under one sun conditions with an AM1.5 filter. The highest H2 yield was observed for Pt0.5-Au1/TiO2 and was around 1.3 ± 0.07 mmol h(-1) g(-1), with an apparent quantum yield (AQY) of 6.4%. Pt0.5-Au1/TiO2 also demonstrated the same activity for 25 cycles of five hours each for 125 h. Critically, the same Pt0.5-Au1/TiO2 catalyst was active in overall SWS (OSWS) without any sacrificial agent, with an AQY = 0.8%. The amount of Au and/or Pt was varied to obtain the optimum composition and it was found that the Pt0.5-Au1/TiO2 composition exhibits the best activity. Detailed characterization by physico-chemical, spectral and microscopy measurements was carried out to obtain an in-depth understanding of the origin of the photocatalytic activity of Pt0.5-Au1/TiO2. These in-depth studies show that gold interacts predominantly with oxygen vacancies present on titania surfaces, and Pt preferentially interacts with gold for an effective electron-hole pair separation at Pt-Au interfaces and electron storage in metal particles. The Pt in Pt0.5-Au1/TiO2 is electronically and catalytically different from the Pt in Pt/TiO2 and it is predicted that the former suppresses the oxygen reduction reaction. PMID:26199221

  14. M-Au/TiO2 (M = Ag, Pd, and Pt) nanophotocatalyst for overall solar water splitting: role of interfaces

    NASA Astrophysics Data System (ADS)

    Melvin, Ambrose A.; Illath, Kavya; Das, Tanmay; Raja, Thirumalaiswamy; Bhattacharyya, Somnath; Gopinath, Chinnakonda S.

    2015-08-01

    M-Au/TiO2 (M = Ag, Pd, Pt) composites were prepared through a facile one-pot photodeposition synthesis and evaluated for solar water splitting (SWS) with and without a sacrificial agent. The M-Au combination exhibits a dominant role in augmenting the H2 generation activity by forming a bi-metallic system. Degussa P25 was used as a TiO2 substrate to photodeposit Au followed by Au + M (M = Ag/Pd/Pt). The SWS activity of the M-Au/TiO2 was determined through photocatalytic H2 production in the presence of methanol as a sacrificial agent under one sun conditions with an AM1.5 filter. The highest H2 yield was observed for Pt0.5-Au1/TiO2 and was around 1.3 +/- 0.07 mmol h-1 g-1, with an apparent quantum yield (AQY) of 6.4%. Pt0.5-Au1/TiO2 also demonstrated the same activity for 25 cycles of five hours each for 125 h. Critically, the same Pt0.5-Au1/TiO2 catalyst was active in overall SWS (OSWS) without any sacrificial agent, with an AQY = 0.8%. The amount of Au and/or Pt was varied to obtain the optimum composition and it was found that the Pt0.5-Au1/TiO2 composition exhibits the best activity. Detailed characterization by physico-chemical, spectral and microscopy measurements was carried out to obtain an in-depth understanding of the origin of the photocatalytic activity of Pt0.5-Au1/TiO2. These in-depth studies show that gold interacts predominantly with oxygen vacancies present on titania surfaces, and Pt preferentially interacts with gold for an effective electron-hole pair separation at Pt-Au interfaces and electron storage in metal particles. The Pt in Pt0.5-Au1/TiO2 is electronically and catalytically different from the Pt in Pt/TiO2 and it is predicted that the former suppresses the oxygen reduction reaction.M-Au/TiO2 (M = Ag, Pd, Pt) composites were prepared through a facile one-pot photodeposition synthesis and evaluated for solar water splitting (SWS) with and without a sacrificial agent. The M-Au combination exhibits a dominant role in augmenting the H2

  15. DFT study of the adsorption properties of single Pt, Pd, Ag, In and Sn on the γ-Al2O3 (1 1 0) surface

    NASA Astrophysics Data System (ADS)

    Gao, Hongwei

    2016-07-01

    GGA/PW91 exchange-correlation functional within periodic density functional theory (DFT) has been used to investigate the adsorption properties of different metal atoms (Pt, Pd, Ag, Sn and In) on the O-terminated and Al-terminated γ-Al2O3 (1 1 0) surface. The predicted adsorption energies follow the order Sn > In > Ag > Pd > Pt. It is found that O-bridge position is the most favorable site for single Pt, Pd, Ag, Sn and In adsorption on the O-terminated γ-Al2O3 (1 1 0) surface. It is found that the most favorable site on the Al-terminated γ-Al2O3 (1 1 0) surface is O-top position.

  16. The growth, structure, and thermal stability of vapor deposited ultra-thin metal films: Rh on Ag(100), Au on Pd(110), and Pt on Pd(110)

    SciTech Connect

    Schmitz, P.

    1990-09-21

    The growth, structure, and thermal stability of ultra-thin metal films (Rh on Ag(100); Au on Pd(110) and Pt on Pd(110)) is investigated using surface sensitive techniques. The three systems studied present a variety of differing characteristics which can contribute to the growth mode, two-dimensional structure, and thermal stability of the films. The main factors contributing to the differing properties of the three systems presented here are: (1) the different substrate morphologies; (2) the differences in surface free energies between the overlayer and the substrate; (3) the degree of lattice mismatch for a particular system; and (4) the extent of miscibility of the two metals. 200 refs., 38 figs.

  17. Monolayer magnetism of 3d transition metals in Ag, Au, Pd, and Pt hosts: Systematics of local moment variation

    NASA Astrophysics Data System (ADS)

    McHenry, M. E.; MacLaren, J. M.; Clougherty, D. P.

    1991-11-01

    Electronic and magnetic properties of T/Aun, T/Agn (T=Cr, Mn, Fe, Co, and Ni), Fe/Pdn and Fe/Ptn multilayers and sandwiches have been computed using the layer Korringa-Kohn-Rostoker (LKKR) band-structure technique. Enhanced (as compared with bulk) 2D T magnetism is observed in all Cr, Mn, and Fe/host configurations, consistent with weak coupling between Cr, Mn, and Fe d bands and those of the noble metal (NM) hosts and consequently d bandwidths which are exceeded by the exchange splitting. Fe and Cr moments vary systematically with the number of mediating Ag or Au planes and the Fermi energy of the system. These systematics are explained by considering the variation of the Fermi energy (EF) with composition as well as constraints of charge neutrality and strong (single-band) ferromagnetism. For Fe in Pt and Pd hosts, d-d hybridization leads to a nearly invariant Fe moment as a function of the number of mediating Pd or Pt planes but with large induced moments on the host.

  18. Proposed power-function N-body potential for the fcc structured metals Ag, Au, Cu, Ni, Pd, and Pt

    SciTech Connect

    Li, J. H.; Kong, Y.; Guo, H. B.; Liang, S. H.; Liu, B. X.

    2007-09-01

    We propose, for the fcc structured Ag, Au, Cu, Ni, Pd, and Pt metals, an N-body potential with a simple power-function form, which significantly simplifies the fitting procedure and computation. The proposed potentials are able to correctly reproduce the lattice constants, cohesion energies, elastic constants, relative stabilities of different structures, formation energies of vacancy, and surface energies. In addition, the thermal properties, such as melting points and heat capacities, etc., are also satisfactorily determined from the proposed potentials. Moreover, the proposed potential is applied to calculate the trigonal and tetragonal paths between the fcc and bcc structures, and the calculated paths match well with those obtained from the first principles calculations.

  19. Synthesis, characterization of Ag(I), Pd(II) and Pt(II) complexes of a triazine-3-thione and their interactions with bovine serum albumin.

    PubMed

    Zhang, Xiuying; Li, Shuyan; Yang, Lin; Fan, Changqing

    2007-11-01

    Ag(I), Pd(II) and Pt(II) complexes of 5-methoxy-5,6-diphenyl-4,5-dihydro-2H-[1,2,4]triazine-3-thione (LH(2)OCH(3)) have been synthesized and characterized by elemental analysis, molar conductance, (1)H NMR, IR spectra, UV spectra and thermal analysis (TG-DTA). The components of the three complexes are [Ag(C(15)H(10)N(3)S)](6), Pd(C(15)H(10)N(3)S)(2) and Pt(C(15)H(10)N(3)S)(2).C(3)H(6)O.2H(2)O, respectively. All the complexes are nonelectrolyte and have high thermodynamic stability. The ligand may act as bidentate NS donor for Pd(II) and Pt(II) complexes, while it seems to be bidentate NS bridging via sulphur atom for Ag(I) complex. A planar quadrangular structure is proposed for Pd(II) and Pt(II) complexes and Ag(I) complex may be a hexanuclear cluster. Their interactions with bovine serum albumin (BSA) are investigated using steady state fluorescence technology. It is observed that all of them can quench the intrinsic fluorescence of BSA through static quenching procedure. The binding constants (K(A)) at different temperatures, thermodynamic parameters enthalpy changes (DeltaH) and entropy changes (DeltaS) between BSA and the compounds are calculated. Based on the values of DeltaH and DeltaS, it is judged that the main acting force of PtL(2).C(3)H(6)O.2H(2)O with BSA may be electrostatic interaction, and for the LH(2)OCH(3), Ag(6)L(6) and PdL(2), hydrophobic and electrostatic interactions may be involved in their binding processes.

  20. Distribution of Precious Metals (Ag, Au, Pd, Pt, and Rh) Between Copper Matte and Iron Silicate Slag

    NASA Astrophysics Data System (ADS)

    Avarmaa, Katri; Johto, Hannu; Taskinen, Pekka

    2016-02-01

    The distributions of precious metals (Ag, Au, Pd, Pt, and Rh) between copper matte and silica-saturated iron silicate slag were determined at 1523 K to 1623 K (1250 °C to 1350 °C), in controlled CO-CO2-SO2-Ar gas mixtures. The experiments were done in silica crucibles and a fixed partial pressure of sulfur dioxide for matte grades of 55, 65, and 75 wt pct Cu. High-temperature equilibration/quenching/electron probe X-ray microanalysis technique was used to obtain compositions of the equilibrated matte and slag. The technique was applied for the first time to the distributions of precious metals in simulated flash smelting conditions. The resolution of electron probe microanalysis became critical as the detection limits were insufficient to measure reliably the precious metals concentrations (except silver) in the slag. The distribution coefficient of silver, L m/s[Ag] = [wt pctAg in matte]/(wt pctAg in slag), was found to be between 200 and 300, which agrees well with the latest studies in the literature. For other precious metals, the minimum values of distribution coefficients were determined according to the detection limits in the slag. The values obtained were for gold and platinum >250, for palladium >1000, and for rhodium >900. The distribution coefficients of palladium, although locating above distribution coefficient of the detection limit, formed a clear dependency with a good repeatability as a function of the matte grade. It increased along with matte grade and was approximately 1000 at 50 pct Cu and 2000 to 3000 at 70 pct Cu. The precious metals replace metal in the matte structure and they are present as sulfides in the copper matte.

  1. Absorption and scattering of light by Pt, Pd, Ag, and Au nanodisks: absolute cross sections and branching ratios.

    PubMed

    Langhammer, Christoph; Kasemo, Bengt; Zorić, Igor

    2007-05-21

    Localized surface plasmons (LSPs) of metallic nanoparticles decay either radiatively or via an electron-hole pair cascade. In this work, the authors have experimentally and theoretically explored the branching ratio of the radiative and nonradiative LSP decay channels for nanodisks of Ag, Au, Pt, and Pd, with diameters D ranging from 38 to 530 nm and height h=20 nm, supported on a fused silica substrate. The branching ratio for the two plasmon decay channels was obtained by measuring the absorption and scattering cross sections as a function of photon energy. The former was obtained from measured extinction and scattering coefficients, using an integrating sphere detector combined with particle density measurements obtained from scanning electron microscopy images of the nanoparticles. Partly angle-resolved measurements of the scattered light allowed the authors to clearly identify contributions from dipolar and higher plasmonic modes to the extinction, scattering, and absorption cross sections. Based on these experiments they find that absorption dominates the total scattering cross section in all the examined cases for small metallic nanodisks (D<100 nm). For D>100 nm absorption still dominates for Pt and Pd nanodisks, while scattering dominates for Au and Ag. A theoretical approach, where the metal disks are approximated as oblate spheroids, is used to account for the trends in the measured cross sections. The field problem is solved in the electrostatic limit. The spheroid is treated as an induced dipole for which the dipolar polarizability is calculated based on spheroid geometry and the (bulk) dielectric response function of the metal the spheroid consists of and the dielectric medium surrounding it. One might expect this model to be inappropriate for disks with D>100 nm since effects due to the retardation of the incoming field across the metallic nanodisk and contributions from higher plasmonic modes are neglected. However, this model describes quite well

  2. The germanides ScTGe (T = Co, Ni, Cu, Ru, Rh, Pd, Ag, Ir, Pt, Au) - Structure and 45Sc solid state NMR spectroscopy

    NASA Astrophysics Data System (ADS)

    Heying, Birgit; Haverkamp, Sandra; Rodewald, Ute Ch; Eckert, Hellmut; Peter, Sebastian C.; Pöttgen, Rainer

    2015-01-01

    The germanides ScTGe (T = Co, Ni, Cu, Ru, Rh, Pd, Ag, Ir, Pt, Au) were obtained in X-ray pure form by arc-melting of the elements. The structures of the members with T = Co, Ni, Cu, Rh, Pd, Ag, Ir, and Pt were refined on the basis of single crystal X-ray diffractometer data. The germanides with T = Cu, Ru, Pd, Ag crystallize with the hexagonal ZrNiAl type structure, space group P 6 bar 2m and those with T = Co, Ni, Rh, Ir, Pt adopt the orthorhombic TiNiSi type. ScAuGe is isotypic with NdPtSb. All germanides exhibit single scandium sites. A simple systematization of the structure type according to the valence electron concentration is not possible. The 45Sc solid state NMR parameters (Knight shifts and nuclear electric quadrupole coupling constants) of those members crystallizing in the TiNiSi structure show systematic trends as a function of valence electron concentration number. Furthermore, within each T-group the Knight shift decreases with increasing atomic number; this correlation also includes previously published results on the isotypic silicide family. The 45Sc quadrupolar interaction tensor components are generally well-reproduced by quantum mechanical electric field gradient calculations using the WIEN2k code.

  3. Copper-based alloys, crystallographic and crystallochemical parameters of alloys in binary systems Cu-Me (Me=Co, Rh, Ir, Cu, Ag, Au, Ni, Pd, Pt)

    NASA Astrophysics Data System (ADS)

    Porobova, Svetlana; Markova, Tat'jana; Klopotov, Vladimir; Klopotov, Anatoliy; Loskutov, Oleg; Vlasov, Viktor

    2016-01-01

    The article presents the results of the analysis of phase equilibrium of ordered phases in binary systems based on copper Cu- Me (where Me - Co, Rh, Ir, Ag, Au, Ni, Pd, Pt) to find correlations of crystallochemical and crystallographic factors. It is established that the packing index in disordered solid solutions in binary systems based on copper is close to the value of 0.74 against the background of an insignificant deviation of atomic volumes from the Zen's law.

  4. Photochemical synthesis of noble metal (Ag, Pd, Au, Pt) on graphene/ZnO multihybrid nanoarchitectures as electrocatalysis for H2O2 reduction.

    PubMed

    Gu, Hui; Yang, Yan; Tian, Jixiang; Shi, Guoyue

    2013-07-24

    For the first time, a series of noble metal (Ag, Au, Pd, and Pt) nanoparticles (NPs) based on new functional graphene were successfully achieved via UV-assisted photocatalytic reduction by ZnO nanorods. The whole preparation strategy for constructing noble metal deposited graphene sheets/ZnO (GS/ZnO) was elucidated in detail in this work. First, graphene oxide based two-dimensional carbon nanostructures served as a support to disperse ZnO nanorods through a hydrothermal route. The ZnO nanorods were self-assembled onto the surface of graphene sheets, forming GS/ZnO nanocomposite, and the graphene oxide was reduced, yielding reduced graphene sheets in this synthetic procedure. Second, the GS/ZnO films were further employed as supporting materials for the dispersion of metal nanoparticles. Photogenerated electrons from UV-irradiated ZnO were transported across GS to stepwise and respectively reduce v μL metal ions (Ag(+), Pd(2+), AuCl4(-), PtCl6(2-), 20 mg/mL) into metal (Ag, Pd, Au, Pt) NPs at a location distinct from the ZnO anchored site, forming five graphene-based hybrid nanocomposites designated as GS/ZnO, GS/ZnO@Agv, GS/ZnO@Pdv, GS/ZnO@Auv, GS/ZnO@Ptv, respectively. The obtained mutihybrid nanoarchitectured materials were clearly characterized by transmission electron microscopy (TEM) and X-ray diffraction (XRD). According to the diameters and distribution, the four metal NPs on GS/ZnO were divided into two categories: Ag&Au and Pd&Pt. Their difference was rooted in the rival abilities of gathering electron between graphene and different metal islands in the photochemical reduction process. The electrochemical behaviors of the five resultant hybrid nanocomposites were investigated in H2O2 as well as in potassium ferricyanide (Fe(CN)6(3-/4-)) and displayed distinct electrocatalytic activity. PMID:23790187

  5. Electronic structures of an epitaxial graphene monolayer on SiC(0001) after metal intercalation (metal = Al, Ag, Au, Pt, and Pd): A first-principles study

    NASA Astrophysics Data System (ADS)

    Hsu, Chia-Hsiu; Lin, Wen-Huan; Ozolins, Vidvuds; Chuang, Feng-Chuan

    2012-02-01

    The atomic structures and electronic properties of metal-intercalated (metal = Al, Ag, Au, Pt, and Pd) graphene monolayers on SiC(0001) were investigated using first-principles calculations. The unique Dirac cone of graphene near the K point reappeared as the graphite layer was intercalated by these metals at a coverage of 3/8 ML. Furthermore, our results show that metal intercalation leads to n-type doping of graphene. The bands contributed from graphene exhibit small splitting after intercalation, whereas the bands contributed from the intercalated metal layer have significant Rashba spin-orbit splittings in all cases except Al.

  6. General synthesis of noble metal (Au, Ag, Pd, Pt) nanocrystal modified MoS2 nanosheets and the enhanced catalytic activity of Pd-MoS2 for methanol oxidation.

    PubMed

    Yuwen, Lihui; Xu, Fei; Xue, Bing; Luo, Zhimin; Zhang, Qi; Bao, Biqing; Su, Shao; Weng, Lixing; Huang, Wei; Wang, Lianhui

    2014-06-01

    A general and facile method for water-dispersed noble metal (Au, Ag, Pd, Pt) nanocrystal modified MoS2 nanosheets (NM-MoS2 NSs) has been developed. By using sodium carboxymethyl cellulose as a stabilizer, well-dispersed NM-MoS2 NSs with homogeneously deposited noble metal nanocrystals (NM NCs) can be synthesized in aqueous solutions. Due to the transition from the semiconducting 2H phase to the metallic 1T phase, the chemically exfoliated MoS2 (ce-MoS2) NSs have improved electrochemical activity. The partially metallic nature of the ce-MoS2 NSs and the catalytic activity of the NM NCs synergistically make NM-MoS2 NSs a potential electrochemical catalyst. For the first time, Pd-MoS2 NSs were used as an electrocatalyst for methanol oxidation in alkaline media. The results showed that Pd-MoS2 NSs have enhanced catalytic activity with 2.8-fold anodic peak current mass density compared to a commercial Pd/C catalyst, suggesting potential for application in direct methanol fuel cells (DMFCs).

  7. Pd-Ag Membrane Coupled to a Two-Zone Fluidized Bed Reactor (TZFBR) for Propane Dehydrogenation on a Pt-Sn/MgAl2O4 Catalyst

    PubMed Central

    Medrano, José-Antonio; Julián, Ignacio; Herguido, Javier; Menéndez, Miguel

    2013-01-01

    Several reactor configurations have been tested for catalytic propane dehydrogenation employing Pt-Sn/MgAl2O4 as a catalyst. Pd-Ag alloy membranes coupled to the multifunctional Two-Zone Fluidized Bed Reactor (TZFBR) provide an improvement in propane conversion by hydrogen removal from the reaction bed through the inorganic membrane in addition to in situ catalyst regeneration. Twofold process intensification is thereby achieved when compared to the use of traditional fluidized bed reactors (FBR), where coke formation and thermodynamic equilibrium represent important process limitations. Experiments were carried out at 500–575 °C and with catalyst mass to molar flow of fed propane ratios between 15.1 and 35.2 g min mmol−1, employing three different reactor configurations: FBR, TZFBR and TZFBR + Membrane (TZFBR + MB). The results in the FBR showed catalyst deactivation, which was faster at high temperatures. In contrast, by employing the TZFBR with the optimum regenerative agent flow (diluted oxygen), the process activity was sustained throughout the time on stream. The TZFBR + MB showed promising results in catalytic propane dehydrogenation, displacing the reaction towards higher propylene production and giving the best results among the different reactor configurations studied. Furthermore, the results obtained in this study were better than those reported on conventional reactors. PMID:24958620

  8. Pd-Ag Membrane Coupled to a Two-Zone Fluidized Bed Reactor (TZFBR) for Propane Dehydrogenation on a Pt-Sn/MgAl2O4 Catalyst.

    PubMed

    Medrano, José-Antonio; Julián, Ignacio; Herguido, Javier; Menéndez, Miguel

    2013-01-01

    Several reactor configurations have been tested for catalytic propane dehydrogenation employing Pt-Sn/MgAl2O4 as a catalyst. Pd-Ag alloy membranes coupled to the multifunctional Two-Zone Fluidized Bed Reactor (TZFBR) provide an improvement in propane conversion by hydrogen removal from the reaction bed through the inorganic membrane in addition to in situ catalyst regeneration. Twofold process intensification is thereby achieved when compared to the use of traditional fluidized bed reactors (FBR), where coke formation and thermodynamic equilibrium represent important process limitations. Experiments were carried out at 500-575 °C and with catalyst mass to molar flow of fed propane ratios between 15.1 and 35.2 g min mmol-1, employing three different reactor configurations: FBR, TZFBR and TZFBR + Membrane (TZFBR + MB). The results in the FBR showed catalyst deactivation, which was faster at high temperatures. In contrast, by employing the TZFBR with the optimum regenerative agent flow (diluted oxygen), the process activity was sustained throughout the time on stream. The TZFBR + MB showed promising results in catalytic propane dehydrogenation, displacing the reaction towards higher propylene production and giving the best results among the different reactor configurations studied. Furthermore, the results obtained in this study were better than those reported on conventional reactors. PMID:24958620

  9. Cage-bell Pt-Pd nanostructures with enhanced catalytic properties and superior methanol tolerance for oxygen reduction reaction

    PubMed Central

    Chen, Dong; Ye, Feng; Liu, Hui; Yang, Jun

    2016-01-01

    Precisely tailoring the structure and fully making use of the components of nanoparticles are effective to enhance their catalytic performance for a given reaction. We herein demonstrate the design of cage-bell structured Pt-Pd nanoparticles, where a Pd shell is deliberately selected to enhance the catalytic property and methanol tolerance of Pt for oxygen reduction reaction. This strategy starts with the synthesis of core-shell Pt@Ag nanoparticles, followed by galvanic replacement reaction between the Ag shell and Pd2+ ions to form core-shell-shell Pt@Ag@Ag-Pd nanoparticles with a Pt core and double shells composed of Ag at inner and alloy Ag-Pd at outer, respectively. Then, the core-shell-shell templates are agitated with saturated NaCl solution to eliminate the Ag component from the double shells, leading to the formation of bimetallic Pt-Pd nanoparticles with a cage-bell structure, defined as a movable Pt core enclosed by a porous Pd shell, which show enhanced catalytic activity for oxygen reduction compared with that of the Pt seeds due to the additional catalysis from Pd shell. In addition, owing to the different diffusion behavior of methanol and oxygen molecules in the porous Pd shell, the Pt-Pd cage-bell nanostructures also exhibit superior methanol tolerant property in catalyzing the oxygen reduction. PMID:27079897

  10. Cage-bell Pt-Pd nanostructures with enhanced catalytic properties and superior methanol tolerance for oxygen reduction reaction.

    PubMed

    Chen, Dong; Ye, Feng; Liu, Hui; Yang, Jun

    2016-01-01

    Precisely tailoring the structure and fully making use of the components of nanoparticles are effective to enhance their catalytic performance for a given reaction. We herein demonstrate the design of cage-bell structured Pt-Pd nanoparticles, where a Pd shell is deliberately selected to enhance the catalytic property and methanol tolerance of Pt for oxygen reduction reaction. This strategy starts with the synthesis of core-shell Pt@Ag nanoparticles, followed by galvanic replacement reaction between the Ag shell and Pd(2+) ions to form core-shell-shell Pt@Ag@Ag-Pd nanoparticles with a Pt core and double shells composed of Ag at inner and alloy Ag-Pd at outer, respectively. Then, the core-shell-shell templates are agitated with saturated NaCl solution to eliminate the Ag component from the double shells, leading to the formation of bimetallic Pt-Pd nanoparticles with a cage-bell structure, defined as a movable Pt core enclosed by a porous Pd shell, which show enhanced catalytic activity for oxygen reduction compared with that of the Pt seeds due to the additional catalysis from Pd shell. In addition, owing to the different diffusion behavior of methanol and oxygen molecules in the porous Pd shell, the Pt-Pd cage-bell nanostructures also exhibit superior methanol tolerant property in catalyzing the oxygen reduction. PMID:27079897

  11. Cage-bell Pt-Pd nanostructures with enhanced catalytic properties and superior methanol tolerance for oxygen reduction reaction

    NASA Astrophysics Data System (ADS)

    Chen, Dong; Ye, Feng; Liu, Hui; Yang, Jun

    2016-04-01

    Precisely tailoring the structure and fully making use of the components of nanoparticles are effective to enhance their catalytic performance for a given reaction. We herein demonstrate the design of cage-bell structured Pt-Pd nanoparticles, where a Pd shell is deliberately selected to enhance the catalytic property and methanol tolerance of Pt for oxygen reduction reaction. This strategy starts with the synthesis of core-shell Pt@Ag nanoparticles, followed by galvanic replacement reaction between the Ag shell and Pd2+ ions to form core-shell-shell Pt@Ag@Ag-Pd nanoparticles with a Pt core and double shells composed of Ag at inner and alloy Ag-Pd at outer, respectively. Then, the core-shell-shell templates are agitated with saturated NaCl solution to eliminate the Ag component from the double shells, leading to the formation of bimetallic Pt-Pd nanoparticles with a cage-bell structure, defined as a movable Pt core enclosed by a porous Pd shell, which show enhanced catalytic activity for oxygen reduction compared with that of the Pt seeds due to the additional catalysis from Pd shell. In addition, owing to the different diffusion behavior of methanol and oxygen molecules in the porous Pd shell, the Pt-Pd cage-bell nanostructures also exhibit superior methanol tolerant property in catalyzing the oxygen reduction.

  12. Facile synthesis of Pt-Pd alloy nanocages and Pt nanorings by templating with Pd nanoplates

    DOE PAGES

    Wang, Xue; Luo, Ming; Huang, Hongwen; Chi, Miaofang; Howe, Jane; Xie, Zhaoxiong; Xia, Younan

    2016-09-06

    We report a facile method for the synthesis of Pt-Pd nanocages and Pt nanorings by conformally coating Pd nanoplates with Pt-based shells using polyol- and water-based protocols, respectively, followed by selective removal of the Pd cores. For the polyol-based system, Pd nanoplates were conformally coated with Pt-Pd alloy shells due to the use of a high reaction temperature of 200 °C and a slow injection rate for the Pt precursor. In comparison, Pt shells were formed on Pd nanoplates (with a larger thickness on the side face than on the top/bottom face) in the water-based system due to the usemore » of a low reaction temperature of 80 °C and the presence of twin boundaries on the side face. As such, the Pd@Pt nanoplates prepared using the polyol- and water-based protocols evolved into Pt-Pd nanocages and Pt nanorings, respectively, when the Pd templates in the cores were selectively removed by wet etching. As a result, the wall thickness of the nanocages and the ridge thickness of the nanorings could be reduced down to 1.1 nm and 1.8 nm, respectively, without breaking the hollow structures.« less

  13. Pd surface and Pt subsurface segregation in Pt1-c Pd c nanoalloys

    NASA Astrophysics Data System (ADS)

    De Clercq, A.; Giorgio, S.; Mottet, C.

    2016-02-01

    The structure and chemical arrangement of Pt1-c Pd c nanoalloys with the icosahedral and face centered cubic symmetry are studied using Monte Carlo simulations with a tight binding interatomic potential fitted to density-functional theory calculations. Pd surface segregation from the lowest to the highest coordinated sites is predicted by the theory together with a Pt enrichment at the subsurface, whatever the structure and the size of the nanoparticles, and which subsists when increasing the temperature. The onion-shell chemical configuration is found for both symmetries and is initiated from the Pd surface segregation. It is amplified in the icosahedral symmetry and small sizes but when considering larger sizes, the oscillating segregation profile occurs near the surface on about three to four shells whatever the structure. Pd segregation results from the significant lower cohesive energy of Pd as compared to Pt and the weak ordering tendency leads to the Pt subsurface segregation. The very weak size mismatch does not prevent the bigger atoms (Pt) from occupying subsurface sites which are in compression whereas the smaller ones (Pd) occupy the central site of the icosahedra where the compression is an order of magnitude higher.

  14. Pd surface and Pt subsurface segregation in Pt1-c Pd c nanoalloys.

    PubMed

    De Clercq, A; Giorgio, S; Mottet, C

    2016-02-17

    The structure and chemical arrangement of Pt1-c Pd c nanoalloys with the icosahedral and face centered cubic symmetry are studied using Monte Carlo simulations with a tight binding interatomic potential fitted to density-functional theory calculations. Pd surface segregation from the lowest to the highest coordinated sites is predicted by the theory together with a Pt enrichment at the subsurface, whatever the structure and the size of the nanoparticles, and which subsists when increasing the temperature. The onion-shell chemical configuration is found for both symmetries and is initiated from the Pd surface segregation. It is amplified in the icosahedral symmetry and small sizes but when considering larger sizes, the oscillating segregation profile occurs near the surface on about three to four shells whatever the structure. Pd segregation results from the significant lower cohesive energy of Pd as compared to Pt and the weak ordering tendency leads to the Pt subsurface segregation. The very weak size mismatch does not prevent the bigger atoms (Pt) from occupying subsurface sites which are in compression whereas the smaller ones (Pd) occupy the central site of the icosahedra where the compression is an order of magnitude higher. PMID:26795206

  15. Heterostructured Au/Pd-M (M = Au, Pd, Pt) nanoparticles with compartmentalized composition, morphology, and electrocatalytic activity.

    PubMed

    Lutz, Patrick S; Bae, In-Tae; Maye, Mathew M

    2015-10-14

    The synthesis, processing, and galvanic exchange of three heterostructured nanoparticle systems is described. The surface accessibility and redox potential of a Au/Pd-Ag dumbbell nanoparticle, where a Au/Pd core/shell region, and a silver region make up the domains, was used to prepare the new nanostructures with controlled composition, morphology, and microstructure. Results indicate that the silver domain was particularly susceptible to galvanic displacement, and was exchanged to Au/Pd-M (M = Au, Pd, Pt). Interestingly, the dumbbell morphology remained after exchange, and the silver region was transformed to hollow, parachute, or concentric domains respectively. The morphology and microstructure change was visualized via TEM and HRTEM, and the composition changes were probed via STEM-EDS imaging and XPS. The electrocatalytic activity of the Au/Pd-M towards methanol oxidation was studied, with results indicating that the Au/Pd-Pt nanoparticles had high activity attributed to the porous nature of the platinum domains. PMID:26351824

  16. Why are the 3d-5d compounds CuAu and NiPt stable, whereas the 3d-4d compounds CuAg and NiPd are not

    NASA Astrophysics Data System (ADS)

    Wang, L. G.; Zunger, Alex

    2003-03-01

    We show that the existence of stable, ordered 3d-5d intermetallics CuAu and NiPt, as opposed to the unstable 3d-4d isovalent analogs CuAg and NiPd, results from relativity. First, in shrinking the equilibrium volume of the 5d element, relativity reduces the atomic size mismatch with respect to the 3d element, thus lowering the elastic packing strain. Second, in lowering the energy of the bonding 6s,p bands and raising the energy of the 5d band, relativity enhances (diminishes) the occupation of the bonding (antibonding) bands. The raising of the energy of the 5d band also brings it closer to the energy of the 3d band, improving the 3d-5d bonding.

  17. Electrical properties of thin-film structures formed by pulsed laser deposition of Au, Ag, Cu, Pd, Pt, W, Zr metals on n-6H-SiC crystal

    SciTech Connect

    Romanov, R. I.; Zuev, V. V.; Fominskii, V. Yu. Demin, M. V.; Grigoriev, V. V.

    2010-09-15

    Diode structures with ideality factors of 1.28-2.14 and potential barriers from 0.58 to 0.62 eV on the semiconductor side were formed by pulsed laser deposition of Au, Ag, Cu, Pd, Pt, W, and Zr metal films on n-6H-SiC crystal without epitaxial layer preparation. A high density of surface acceptor and donor states was formed at the metal-semiconductor interface during deposition of the laser-induced atomic flux, which violated the correlation between the potential barrier height and metal work function. The barrier heights determined from characteristic currents and capacitance measurements were in quite good agreement. For the used low-resistance semiconductor and contact elements, the sizes of majority carrier (electron) depletion regions were determined as 26-60 nm.

  18. Superconductivity in Pd, Ir, and Pt chalcogenide

    NASA Astrophysics Data System (ADS)

    Oh, Yoon Seok; Yang, Junjie; Choi, Y. J.; Hogan, A.; Horibe, Y.; Cheong, S.-W.

    2012-02-01

    Large spin-orbit coupling in materials with heavy chalcogens can result in unique quantum states or functional properties such as topological insulator, giant thermoelectric power, and superconductivity. When materials contain heavy cations in addition to heavy chalcogens, spin-orbit coupling can be further enhanced. For these reasons, we have studied the superconductivity of Pd, Ir, and Pt tellurides and selenides. In the exploration of these chalcogenides, we have focused on the competition between superconductivity and charge density wave that is associated with superlattice reflections.

  19. Monodispersed bimetallic PdAg nanoparticles with twinned structures: Formation and enhancement for the methanol oxidation

    PubMed Central

    Yin, Zhen; Zhang, Yining; Chen, Kai; Li, Jing; Li, Wenjing; Tang, Pei; Zhao, Huabo; Zhu, Qingjun; Bao, Xinhe; Ma, Ding

    2014-01-01

    Monodispersed bimetallic PdAg nanoparticles can be fabricated through the emulsion-assisted ethylene glycol (EG) ternary system. Different compositions of bimetallic PdAg nanoparticles, Pd80Ag20, Pd65Ag35 and Pd46Ag54 can be obtained via adjusting the reaction parameters. For the formation process of the bimetallic PdAg nanoparticles, there have two-stage growth processes: firstly, nucleation and growth of the primary nanoclusters; secondly, formation of the secondary nanoparticles with the size-selection and relax process via the coalescence or aggregation of the primary nanoclusters. The as-prepared PdAg can be supported on the carbon black without any post-treatment, which exhibited high electro-oxidation activity towards methanol oxidation under alkaline media. More importantly, carbon-supported Pd80Ag20 nanoparticles reveal distinctly superior activities for the methanol oxidation, even if compared with commercial Pt/C electro-catalyst. It is concluded that the enhanced activity is dependant on the unique twinning structure with heterogeneous phase due to the dominating coalescence growth in EG ternary system. PMID:24608736

  20. Adsorption of molecular hydrogen on Pd(Pt) decorated graphene

    NASA Astrophysics Data System (ADS)

    Adhikari, Narayan; Khaniya, Asim; Lamichhane, Saran; Pantha, Nurapati

    2015-03-01

    We have performed the first-principles based Density Functional Theory (DFT) calculations to study the stability, geometrical structures, and electronic properties of a Pd(Pt) atom adsorbed graphene to investigate the possibility of using Pd(Pt) decorated graphene as energy storage materials with reference to pristine graphene. The London dispersion forces have been incorporated by the DFT-D2 levels of calculations implemented in Quantum Espresso packages. Our findings show that Pd and Pt both adsorb on graphene at Bridge site. The electronic structures of Pd(Pt) adsorbed graphene possesses band gap opening due to breaking of the symmetry of graphene. Further we have studied the adsorption of moelcular hydrogen ((H 2) n , n = 1-7) on the Pd(Pt)-graphene system. The adatom Pd(Pt) enhances the binding energy per hydrogen molecule in Pd(Pt)-graphene system in comparison to that in the pristine graphene. The binding energy per hydrogen molecule of the adatom-graphene system decreases as the number of H 2 molecules increases and finally it saturates to 0.15 eV (0.16 eV) per hydrogen molecule for Pd-graphene (Pt-graphene) systems respectively. ICTP-NET 56/TWAS.

  1. The role of charge transfer in the oxidation state change of Ce atoms in the TM13-CeO2(111) systems (TM = Pd, Ag, Pt, Au): a DFT + U investigation.

    PubMed

    Tereshchuk, Polina; Freire, Rafael L H; Ungureanu, Crina G; Seminovski, Yohanna; Kiejna, Adam; Da Silva, Juarez L F

    2015-05-28

    Despite extensive studies of transition metal (TM) clusters supported on ceria (CeO2), fundamental issues such as the role of the TM atoms in the change in the oxidation state of Ce atoms are still not well understood. In this work, we report a theoretical investigation based on static and ab initio molecular dynamics density functional theory calculations of the interaction of 13-atom TM clusters (TM = Pd, Ag, Pt, Au) with the unreduced CeO2(111) surface represented by a large surface unit cell and employing Hubbard corrections for the strong on-site Coulomb correlation in the Ce f-electrons. We found that the TM13 clusters form pyramidal-like structures on CeO2(111) in the lowest energy configurations with the following stacking sequence, TM/TM4/TM8/CeO2(111), while TM13 adopts two-dimensional structures at high energy structures. TM13 induces a change in the oxidation state of few Ce atoms (3 of 16) located in the topmost Ce layer from Ce(IV) (itinerant Ce f-states) to Ce(III) (localized Ce f-states). There is a charge flow from the TM atoms to the CeO2(111) surface, which can be explained by the electronegativity difference between the TM (Pd, Ag, Pt, Au) and O atoms, however, the charge is not uniformly distributed on the topmost O layer due to the pressure induced by the TM13 clusters on the underlying O ions, which yields a decrease in the ionic charge of the O ions located below the cluster and an increase in the remaining O ions. Due to the charge flow mainly from the TM8-layer to the topmost O-layer, the charge cannot flow from the Ce(IV) atoms to the O atoms with the same magnitude as in the clean CeO2(111) surface. Consequently, the effective cationic charge decreases mainly for the Ce atoms that have a bond with the O atoms not located below the cluster, and hence, those Ce atoms change their oxidation state from IV to III. This increases the size of the Ce(III) compared with the Ce(IV) cations, which builds-in a strain within the topmost Ce layer, and

  2. Spectroscopy and electronic structure of jet-cooled NiPd and PdPt

    NASA Astrophysics Data System (ADS)

    Taylor, Scott; Spain, Eileen M.; Morse, Michael D.

    1990-03-01

    Resonant two-photon ionization spectroscopy of jet-cooled NiPd and PdPt has revealed a dense vibronic spectrum for NiPd and a much more sparse spectrum for PdPt. Four vibrational progressions have been identified for NiPd, and three have been located for PdPt. High resolution investigations of NiPd have established a ground state bond length of r″0 =2.242±0.005 Å with Ω″=2. The observed spectra have been used to bracket the ionization potentials, giving IP(NiPd)=7.18±0.76 eV and IP(PdPt)=8.27±0.38 eV. In contrast to previous work on Ni2, NiPt, and Pt2, no abrupt onset of rapid predissociation is observed for either NiPd or PdPt. A discussion of this result in terms of the expected potential energy curves for the palladium-containing diatomics is presented, which when combined with the frequencies of the highest energy vibronic bands observed yields estimates of D0(NiPd)≊1.46 eV and D0(PdPt)≊1.98 eV. The lack of observable vibronic transitions in Pd2 above 11 375 cm-1 places D0(Pd2) below 1.41 eV, in agreement with Knudsen effusion mass spectrometry. Finally a comparison of the platinum group dimers and the coinage metal dimers is given, demonstrating the increasing importance of d-orbital contributions to the bonding in the platinum group dimers as one moves down the periodic table. The anomalous behavior of the palladium-containing diatomics is also discussed in terms of the highly stable 4d105s0, 1S0 ground state of atomic palladium.

  3. Why are the 3d-5d compounds CuAu and NiPt stable, whereas the 3d-4d compounds CuAg and NiPd are not*

    NASA Astrophysics Data System (ADS)

    Wang, Ligen; Zunger, Alex

    2003-03-01

    Experiments indicate that the 3d-5d compounds CuAu and NiPt have negative formation enthalpies (ΔH < 0), and thus form stable ordered compounds, whereas the analogous isovalent 3d-4d compounds CuAg and NiPd, made of elements from the same columns in the periodic table, have positive formation enthalpies (ΔH > 0) and thus phase-separate. We explain this long standing puzzle according to the relativistic effect and show, via first-principles calculations, that in binary compounds of late 3d-5d intermetallics, the inter-sublattice 3d-5d coupling is dominant. First, in shrinking the equilibrium volume of the 5d element, relativity reduces the atomic size-mismatch with respect to the 3d element, thus lowering the elastic packing strain. Second, in lowering the energy of the bonding 6s,p bands and raising the energy of the 5d band, relativity enhances (diminishes) the occupation of the bonding (antibonding) bands. The raising of the energy of the 5d band also brings it closer to the energy of the 3d band, improving the 3d-5d bonding. * Supported by DOE-SC-BES-DMS

  4. Heterostructured Au/Pd-M (M = Au, Pd, Pt) nanoparticles with compartmentalized composition, morphology, and electrocatalytic activity

    NASA Astrophysics Data System (ADS)

    Lutz, Patrick S.; Bae, In-Tae; Maye, Mathew M.

    2015-09-01

    The synthesis, processing, and galvanic exchange of three heterostructured nanoparticle systems is described. The surface accessibility and redox potential of a Au/Pd-Ag dumbbell nanoparticle, where a Au/Pd core/shell region, and a silver region make up the domains, was used to prepare the new nanostructures with controlled composition, morphology, and microstructure. Results indicate that the silver domain was particularly susceptible to galvanic displacement, and was exchanged to Au/Pd-M (M = Au, Pd, Pt). Interestingly, the dumbbell morphology remained after exchange, and the silver region was transformed to hollow, parachute, or concentric domains respectively. The morphology and microstructure change was visualized via TEM and HRTEM, and the composition changes were probed via STEM-EDS imaging and XPS. The electrocatalytic activity of the Au/Pd-M towards methanol oxidation was studied, with results indicating that the Au/Pd-Pt nanoparticles had high activity attributed to the porous nature of the platinum domains.The synthesis, processing, and galvanic exchange of three heterostructured nanoparticle systems is described. The surface accessibility and redox potential of a Au/Pd-Ag dumbbell nanoparticle, where a Au/Pd core/shell region, and a silver region make up the domains, was used to prepare the new nanostructures with controlled composition, morphology, and microstructure. Results indicate that the silver domain was particularly susceptible to galvanic displacement, and was exchanged to Au/Pd-M (M = Au, Pd, Pt). Interestingly, the dumbbell morphology remained after exchange, and the silver region was transformed to hollow, parachute, or concentric domains respectively. The morphology and microstructure change was visualized via TEM and HRTEM, and the composition changes were probed via STEM-EDS imaging and XPS. The electrocatalytic activity of the Au/Pd-M towards methanol oxidation was studied, with results indicating that the Au/Pd-Pt nanoparticles had

  5. Microstructure and electronic behavior of PtPd@Pt core-shell nanowires

    SciTech Connect

    Han, Wei-Qiang; Su, Dong; Murphy, Michael; Ward, Matthew; Sham, Tsun-Kong; Wu, Lijun; Zhu, Yimei; Hu, Yongfeng; Aoki, Toshihiro

    2010-07-19

    PtPd{at}Pt core-shell ultrathin nanowires were prepared using a one-step phase-transfer approach. The diameters of the nanowires range from 2 to 3 nm, and their lengths are up to hundreds of nanometers. Line scanning electron energy loss spectra showed that PtPd bimetallic nanowires have a core-shell structure, with a PtPd alloy core and a Pt monolayer shell. X-ray absorption near edge structure (XANES) spectra reveal that a strong Pt-Pd interaction exists in this nanowire system in that there is PtPd alloying and/or interfacial interaction. Extended x-ray absorption fine structures (EXAFS) further confirms the PtPd@Pt core-shell structure. The bimetallic nanowires were determined to be face-centered cubic structures. The long-chain organic molecules of n-dodecyl trimethylammonium bromide and octadecylamine, used as surfactants during synthesis, were clearly observed using aberration-corrected TEM operated at 80 KV. The interaction of Pt and surfactants was also revealed by EXAFS.

  6. High-performance core-shell PdPt@Pt/C catalysts via decorating PdPt alloy cores with Pt

    NASA Astrophysics Data System (ADS)

    Wu, Yan-Ni; Liao, Shi-Jun; Liang, Zhen-Xing; Yang, Li-Jun; Wang, Rong-Fang

    A core-shell structured low-Pt catalyst, PdPt@Pt/C, with high performance towards both methanol anodic oxidation and oxygen cathodic reduction, as well as in a single hydrogen/air fuel cell, is prepared by a novel two-step colloidal approach. For the anodic oxidation of methanol, the catalyst shows three times higher activity than commercial Tanaka 50 wt% Pt/C catalyst; furthermore, the ratio of forward current I f to backward current I b is high up to 1.04, whereas for general platinum catalysts the ratio is only ca. 0.70, indicating that this PdPt@Pt/C catalyst has high activity towards methanol anodic oxidation and good tolerance to the intermediates of methanol oxidation. The catalyst is characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS). The core-shell structure of the catalyst is revealed by XRD and TEM, and is also supported by underpotential deposition of hydrogen (UPDH). The high performance of the PdPt@Pt/C catalyst may make it a promising and competitive low-Pt catalyst for hydrogen fueled polymer electrolyte membrane fuel cell (PEMFC) or direct methanol fuel cell (DMFC) applications.

  7. Interaction of CO with PtxAg1-x/Pt(111) surface alloys: More than dilution by Ag atoms

    NASA Astrophysics Data System (ADS)

    Schüttler, K. M.; Mancera, L. A.; Diemant, T.; Groß, A.; Behm, R. J.

    2016-08-01

    We have investigated CO adsorption on structurally well-defined PtxAg1-x/Pt(111) surface alloys, combining temperature-programmed desorption (TPD) and infrared reflection absorption spectroscopy (IRRAS) as well as density functional theory (DFT) based calculations. This is part of a systematic approach including previous studies of CO adsorption on closely related Pt(111)- and Pd(111)-based surface alloys. Following changes in the adsorption properties with increasing Ag content and correlating them with structural changes allow us to assign desorption features to specific adsorption sites/ensembles identified in previous scanning tunneling microscopy (STM) measurements, and thus to identify and separate contributions from different effects such as geometric ensemble effects and electronic ligand/strain effects. DFT calculations give further insight into the nature of the metal-CO bond on these bimetallic sites. Most prominently, the growth of a new CO desorption feature at higher temperature (~ 550 K) in the TPD spectra of Ag-rich surface alloys, which is unique for the group of Pt(111)- and Pd(111)-based surface alloys, is attributed to CO adsorption on Pt atoms surrounded by a Ag-rich neighborhood. Adsorption on these sites manifests in an IR band down-shifted to significantly lower wave number. Systematic comparison of the present results with previous findings for CO adsorption on the related Pt(111)- and Pd(111)-based surface alloys gains a detailed insight into general trends in the adsorption behavior of bimetallic surfaces.

  8. Mesoporous Trimetallic PtPdRu Spheres as Superior Electrocatalysts.

    PubMed

    Jiang, Bo; Ataee-Esfahani, Hamed; Li, Cuiling; Alshehri, Saad M; Ahamad, Tansir; Henzie, Joel; Yamauchi, Yusuke

    2016-05-17

    Mesoporous Trimetallic PtPdRu Spheres with well-defined spherical morphology and uniformly sized pores were synthesized in an aqueous solution using ascorbic acid as the reducing agent and triblock copolymer F127 as the pore directing agent. These mesoporous PtPdRu spheres exhibited enhanced electrocatalytic activity compared to commercial Pt black, resulting in a ∼4.9 times improvement in mass activity for the methanol oxidation reaction. The excellent electrocatalytic activity and stability are due to the unique mesoporous architecture and electronic landscape between different elements. PMID:27072776

  9. A pathway for the growth of core-shell Pt-Pd nanoparticles

    SciTech Connect

    Narula, Chaitanya Kumar; Yang, Xiaofan; Li, Chen; Pennycook, Stephen J; Lupini, Andrew R

    2015-10-12

    In this study, the aging of both Pt-Pd nanoparticles and core-shell Pt-Pd nanoparticles has been reported to result in alloying of Pt with Pd. In comparison to monometallic Pt catalysts, the growth of Pd-Pt bimetallics is slower; however, the mechanism of growth of particles and the mechanism by which Pd improves the hydrothermal durability of bimetallic Pd-Pt particles remains uncertain. In our work on hydrothermal aging of core-shell Pt-Pd nanoparticles, synthesized by solution methods, with varying Pd:Pt ratio of 1:4, 1:1, and 4:1, we compare the growth of core-shell Pt-Pd nanoparticles and find that particles grow by migrating and joining together. The unique feature of the observed growth is that Pd shells from both particles open up and join, allowing the cores to merge. At high temperatures, alloying occurs in good agreement with reports by other workers.

  10. Anion-exchange separation of Pt and Pd using perchloric and hydrochloric acid solutions

    USGS Publications Warehouse

    Petrie, R.K.; Morgan, J.W.

    1982-01-01

    On Biorad Ag-1X8 anion-exchange resin (200-400 mesh), Pd and Pt may be separated from one another by elution with 0.2M HClO4, and 5M HClO4, respectively. If present, Au may be retained by making the elutriants 0.003M in HCl. Alternatively, reduction by H2SO3 enables elution of Pt2+ with 6M HCl before recovery of Pd2+ with 0.2M HClO4??Ir4+ is reduced to Ir3+ by H2SO3 and may be eluted ahead of Pt2+ by 2M HCl. ?? 1982 Akade??miai Kiado??.

  11. Adsorbate-Induced Segregation in a PdAg Membrane Model System: Pd3Ag(1 1 1)

    SciTech Connect

    Svenum, I. H.; Herron, Jeffrey A.; Mavrikakis, Manos; Venvik, H. J.

    2012-10-15

    Thin PdAg alloy membranes with 20–25% Ag are being developed for hydrogen separation technology. Despite many investigations on such membranes as well as representative experimental and theoretical model systems, unresolved issues remain concerning the effect of the alloy surface structure and composition on adsorption and vice versa. Therefore, the interaction between hydrogen, carbon monoxide or oxygen with the surface of a PdAg model alloy was studied using periodic self-consistent density functional theory (DFT-GGA) calculations. In particular, the adsorption structure, coverage dependence and possible adsorption-induced segregation phenomena were addressed using Pd3Ag(1 1 1) model surfaces with varying degrees of surface segregation. In agreement with previous experimental and theoretical investigations, we predict Ag surface termination to be energetically favorable in vacuum. The segregation of Ag is then reversed upon adsorption of H, CO or O. For these adsorbates, the binding is strongest on Pd three-fold hollow sites, and hence complete Pd termination is favored at high coverage of H or CO, while 25% Ag may remain under oxygen because of the lower O-saturation coverage. CO adsorption provides a somewhat stronger driving force for Pd segregation when compared to H, and this may have implications with respect to permeation properties of PdAg alloy surfaces. Our predictions for high coverage are particularly relevant in underlining the importance of segregation phenomena to the hydrogen transport properties of thin PdAg alloy membranes.

  12. Groundstates in AgPd using cluster expansion methods

    NASA Astrophysics Data System (ADS)

    Nelson, Lance; Hart, Gus

    2010-03-01

    Palladium alloys have applications in electronics, catalysis, hydrogen storage, and jewelry. The appearance of ordered phases can improve the materials properties for some applications. We present a study of the Ag-Pd system, which is of current interest in electronics and jewelry. We use a model Hamiltonian to quickly search large sets of derivative superstructures for ground states. The model Hamiltonian allows us to perform Monte Carlo simulations to determine transition temperatures. Previous predictions show two unusual ground states: L11, which has only been observed in Cu-Pt, and a new structure (never observed in any other system) with a 1:3 stoichiometry (dubbed L13). We find that L13 is actually unstable. We also predict the ordering temperature for the L11 phase.

  13. Ion beam mixing in Ag-Pd alloys

    NASA Astrophysics Data System (ADS)

    Klatt, J. L.; Averback, R. S.; Peak, David

    1989-09-01

    Ion beam mixing during 750 keV Kr+ irradiation at 80 K was measured on a series of Ag-Pd alloys using Au marker atoms. The mixing in pure Ag was the greatest and it decreased monotonically with increasing Pd content, being a factor of 10 higher in pure Ag than in pure Pd. This large difference in mixing cannot be explained by the difference in cohesion energy between Ag and Pd in the thermodynamic model of ion beam mixing proposed by Johnson et al. [W. L. Johnson, Y. T. Cheng, M. Van Rossum, and M-A. Nicolet, Nucl. Instrum. Methods B 7/8, 657 (1985)]. An alternative model based on local melting in the cascade is shown to account for the ion beam mixing results in Ag and Pd.

  14. Shape-directional growth of Pt and Pd nanoparticles.

    PubMed

    Leong, G Jeremy; Ebnonnasir, Abbas; Schulze, Maxwell C; Strand, Matthew B; Ngo, Chilan; Maloney, David; Frisco, Sarah L; Dinh, Huyen N; Pivovar, Bryan; Gilmer, George H; Kodambaka, Suneel; Ciobanu, Cristian V; Richards, Ryan M

    2014-10-01

    The design and synthesis of shape-directed nanoscale noble metal particles have attracted much attention due to their enhanced catalytic properties and the opportunities to study fundamental aspects of nanoscale systems. As such, numerous methods have been developed to synthesize crystals with tunable shapes, sizes, and facets by adding foreign species that promote or restrict growth on specific sites. Many hypotheses regarding how and why certain species direct growth have been put forward, however there has been no consensus on a unifying mechanism of nanocrystal growth. Herein, we develop and demonstrate the capabilities of a mathematical growth model for predicting metal nanoparticle shapes by studying a well known procedure that employs AgNO3 to produce {111} faceted Pt nanocrystals. The insight gained about the role of auxiliary species is then utilized to predict the shape of Pd nanocrystals and to corroborate other shape-directing syntheses reported in literature. The fundamental understanding obtained herein by combining modeling with experimentation is a step toward computationally guided syntheses and, in principle, applicable to predictive design of the growth of crystalline solids at all length scales (nano to bulk).

  15. Hollow raspberry-like PdAg alloy nanospheres: High electrocatalytic activity for ethanol oxidation in alkaline media

    NASA Astrophysics Data System (ADS)

    Peng, Cheng; Hu, Yongli; Liu, Mingrui; Zheng, Yixiong

    2015-03-01

    Palladium-silver (PdAg) alloy nanospheres with unique structure were prepared using a one-pot procedure based on the galvanic replacement reaction. Their electrocatalytic activity for ethanol oxidation in alkaline media was evaluated. The morphology and crystal structure of the samples were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray diffraction (XRD). Electrochemical characterization techniques, including cyclic voltammetry (CV) and chronoamperometry (CA) measurements were used to analyze the electrochemical performance of the PdAg alloy nanospheres. The SEM and TEM images showed that the PdAg alloy nanospheres exhibit a hierarchical nanostructure with hollow interiors and porous walls. Compared to the commercial Pd/C catalyst, the as-prepared PdAg alloy nanospheres exhibit superior electrocatalytic activity and stability towards ethanol electro-oxidation in alkaline media, showing its potential as a new non-Pt electro-catalyst for direct alcohol fuel cells (DAFCs).

  16. Study of coordination environments around Pd and Pt in a Pd-core Pt-shell nanoparticle during heating

    NASA Astrophysics Data System (ADS)

    Nishimura, Y. F.; Hamaguchi, T.; Yamaguchi, S.; Takagi, H.; Dohmae, K.; Nonaka, T.; Nagai, Y.

    2016-05-01

    Local coordination environments around Pd and Pt in a Pd-core Pt-shell nanoparticle (NP) at temperatures ranging from 473 to 873 K was evaluated by utilizing in situ XAFS measurement technique to investigate the temperature range in which a core-shell structure is preserved. The core-shell structure was considered to be kept up to 673 K and start to change at about 773 K. Heating to 873 K accelerated atomic mixing in the core-shell NPs. Catalytic properties of the present Pd-core Pt-shell NP are available in the stoichiometric C3H6-O2 atmosphere at temperatures less than 773 K at most.

  17. Pt skin on Pd-Co-Zn/C ternary nanoparticles with enhanced Pt efficiency toward ORR

    NASA Astrophysics Data System (ADS)

    Xiao, Weiping; Zhu, Jing; Han, Lili; Liu, Sufen; Wang, Jie; Wu, Zexing; Lei, Wen; Xuan, Cuijuan; Xin, Huolin L.; Wang, Deli

    2016-08-01

    Exploring highly active, stable and relatively low-cost nanomaterials for the oxygen reduction reaction (ORR) is of vital importance for the commercialization of proton exchange membrane fuel cells (PEMFCs). Herein, a highly active, durable, carbon supported, and monolayer Pt coated Pd-Co-Zn nanoparticle is synthesized via a simple impregnation-reduction method, followed by spontaneous displacement of Pt. By tuning the atomic ratios, we obtain the composition-activity volcano curve for the Pd-Co-Zn nanoparticles and determined that Pd : Co : Zn = 8 : 1 : 1 is the optimal composition. Compared with pure Pd/C, the Pd8CoZn/C nanoparticles show a substantial enhancement in both the catalytic activity and the durability toward the ORR. Moreover, the durability and activity are further enhanced by forming a Pt skin on Pd8CoZn/C nanocatalysts. Interestingly, after 10 000 potential cycles in N2-saturated 0.1 M HClO4 solution, Pd8CoZn@Pt/C shows improved mass activity (2.62 A mg-1Pt) and specific activity (4.76 A m-2total), which are about 1.4 and 4.4 times higher than the initial values, and 37.4 and 5.5 times higher than those of Pt/C catalysts, respectively. After accelerated stability testing in O2-saturated 0.1 M HClO4 solution for 30 000 potential cycles, the half-wave potential negatively shifts about 6 mV. The results show that the Pt skin plays an important role in enhancing the activity as well as preventing degradation.Exploring highly active, stable and relatively low-cost nanomaterials for the oxygen reduction reaction (ORR) is of vital importance for the commercialization of proton exchange membrane fuel cells (PEMFCs). Herein, a highly active, durable, carbon supported, and monolayer Pt coated Pd-Co-Zn nanoparticle is synthesized via a simple impregnation-reduction method, followed by spontaneous displacement of Pt. By tuning the atomic ratios, we obtain the composition-activity volcano curve for the Pd-Co-Zn nanoparticles and determined that Pd : Co : Zn = 8

  18. A photoemission study of Pd ultrathin films on Pt(111)

    SciTech Connect

    Mun, Bongjin Simon; Lee, Choongman; Stamenkovic, Vojislav; Markovic, Nenad M.; Ross Jr., Philip N.

    2005-05-11

    The origin of surface core-level shift (SCLS) of Pd thin films on Pt(111) substrate is investigated. At sub-monolayer coverage of Pd thin films, the splitting of Pd 3d core level peaks indicate the contribution of both initial and final-state of photo-ionization processes while there is almost no change on valence band (VB) spectra. When the coverage of Pd reaches to single monolayer, the final-state relaxation effect on the Pd 3d vanishes and only the initial-state effect, a negative SCLS, is present. Also, the VB spectrum at Pd monolayer films shows a clear band narrowing, that is the origin of the negative SCLS at monolayer coverage. As the Pd coverage is increased to more than monolayer thickness, the Pd 3d peaks start to show the surface layer contribution from second and third layers, positive SCLS, and the VB spectrum shows even narrower band width, possibly due to the formation of surface states and strained effect of Pd adlayers on top of the first pseudomorphic layer.

  19. Shape and Composition Effects on Photocatalytic Hydrogen Production for Pt-Pd Alloy Cocatalysts.

    PubMed

    Luo, Muhua; Lu, Pan; Yao, Weifeng; Huang, Cunping; Xu, Qunjie; Wu, Qiang; Kuwahara, Yasutaka; Yamashita, Hiromi

    2016-08-17

    The shape and composition effects of platinum-palladium (Pt-Pd) alloy nanoparticle cocatalysts on visible-light photocatalytic hydrogen evolution from an aqueous ammonium sulphite solution have been reported and discussed. The activity of Pt-Pd nanoparticles loaded Pt-Pd/CdS photocatalysts are affected based on both the Pt-Pd alloy nanoparticles' shape and their compositions. In this research, two shapes of Pt-Pd nanoparticles have been studied. One is Pt-Pd nanocubes enclosed by {100} crystal planes and the other is nano-octahedra covered with {111} crystal facets. Results show that the photocatalytic turnover frequency (TOF), defined as moles of hydrogen produced per surface mole of Pt-Pd metal atom per second, for Pt-Pd nanocubes/CdS (Pt-Pd NCs/CdS) photocatalyst can be 3.4 times more effective than Pt-Pd nano-octahedra/CdS (Pt-Pd NOTa/CdS) nanocomposite photocatalyst. Along with the shape effect, the atomic ratio of Pt to Pd can also impact the efficiency of Pt-Pd/CdS photocatalysts. When the Pt to Pd atomic ratio changes from 1:0 to about 2:1, the rate of hydrogen production increases from 900 μmol/h for Pt NCs/CdS catalyst to 1837 μmol/h for Pt-Pd (2:1) NCs/CdS photocatalyst-a 104% rate increase. This result suggests that the 33 mol % of more expensive Pt can be replaced with less costly Pd, resulting in a more than 100% hydrogen production rate increase. The finding of this research will lead to the research and development of highly effective catalysts for photocatalytic hydrogen production using solar photonic energy. PMID:27439590

  20. Pt skin on Pd-Co-Zn/C ternary nanoparticles with enhanced Pt efficiency toward ORR.

    PubMed

    Xiao, Weiping; Zhu, Jing; Han, Lili; Liu, Sufen; Wang, Jie; Wu, Zexing; Lei, Wen; Xuan, Cuijuan; Xin, Huolin L; Wang, Deli

    2016-08-21

    Exploring highly active, stable and relatively low-cost nanomaterials for the oxygen reduction reaction (ORR) is of vital importance for the commercialization of proton exchange membrane fuel cells (PEMFCs). Herein, a highly active, durable, carbon supported, and monolayer Pt coated Pd-Co-Zn nanoparticle is synthesized via a simple impregnation-reduction method, followed by spontaneous displacement of Pt. By tuning the atomic ratios, we obtain the composition-activity volcano curve for the Pd-Co-Zn nanoparticles and determined that Pd : Co : Zn = 8 : 1 : 1 is the optimal composition. Compared with pure Pd/C, the Pd8CoZn/C nanoparticles show a substantial enhancement in both the catalytic activity and the durability toward the ORR. Moreover, the durability and activity are further enhanced by forming a Pt skin on Pd8CoZn/C nanocatalysts. Interestingly, after 10 000 potential cycles in N2-saturated 0.1 M HClO4 solution, Pd8CoZn@Pt/C shows improved mass activity (2.62 A mg(-1)Pt) and specific activity (4.76 A m(-2)total), which are about 1.4 and 4.4 times higher than the initial values, and 37.4 and 5.5 times higher than those of Pt/C catalysts, respectively. After accelerated stability testing in O2-saturated 0.1 M HClO4 solution for 30 000 potential cycles, the half-wave potential negatively shifts about 6 mV. The results show that the Pt skin plays an important role in enhancing the activity as well as preventing degradation. PMID:27445114

  1. Isomerization and hydrocracking of heptane over bimetallic bifunctional PtPd/H-Beta and PtPd/USY zeolite catalysts

    SciTech Connect

    Blomsma, E.; Martens, J.A.; Jacobs, P.A.

    1997-01-15

    Bifunctional catalysts are prepared by loading NH{sub 4}-Beta zeolites with platinum, palladium, and platinum-palladium metal combinations via cation exchange and incipient wetness impregnation with Pt(NH{sub 3}){sub 4}Cl{sub 2} and Pd(NH{sub 3}){sub 4}Cl{sub 2} complexes, followed by calcination and reduction. In comparison to the Pt and Pd loaded acid zeolites, the bimetallic Pd-Pt zeolites are found to be more active and selective in the isomerization of heptane. The noble metal phases are characterized with temperature programmed reduction and hydrogen chemisorption. The dispersion of platinum is significantly improved in presence of as little as 20 mole% of palladium. The improved Pt dispersion leads to a better intimacy and balance of the acid and hydrogenation-dehydrogenation functions in these bi-functional catalysts and suppression of undesirable hydrogenolysis and dimerization-cracking activity. On Pt/USY zeolite, the addition of palladium has similar beneficial effects on the catalytic performances. 34 refs., 4 figs., 3 tabs.

  2. Investigation of the structure of a Ag/Pd/Ag( 1 1 1 ) trilayer by means of electronic spectroscopies

    NASA Astrophysics Data System (ADS)

    Dumont, J.; Ghijsen, J.; Sporken, R.

    2002-06-01

    The growth of the Ag/Pd/Ag system has been studied by X-ray photoelectron spectroscopy and low energy electron diffraction. No chemical reaction or interdiffusion was observed between the Pd and Ag layers. The growth of the Pd interlayer follows the Frank Van der Merwe mode but is not pseudomorphic on the Ag(1 1 1) substrate. The growth of the top Ag layer on the Pd interlayer is pseudomorphic and layer by layer but contains around 12% of voids.

  3. Synthesis of bimetallic Pt-Pd core-shell nanocrystals and their high electrocatalytic activity modulated by Pd shell thickness.

    PubMed

    Li, Yujing; Wang, Zhi Wei; Chiu, Chin-Yi; Ruan, Lingyan; Yang, Wenbing; Yang, Yang; Palmer, Richard E; Huang, Yu

    2012-02-01

    Bimetallic Pt-Pd core-shell nanocrystals (NCs) are synthesized through a two-step process with controlled Pd thickness from sub-monolayer to multiple atomic layers. The oxygen reduction reaction (ORR) catalytic activity and methanol oxidation reactivity of the core-shell NCs for fuel cell applications in alkaline solution are systematically studied and compared based on different Pd thickness. It is found that the Pd shell helps to reduce the over-potential of ORR by up to 50 mV when compared to commercial Pd black, while generating up to 3-fold higher kinetic current density. The carbon monoxide poisoning test shows that the bimetallic NCs are more resistant to the CO poisoning than Pt NCs and Pt black. It is also demonstrated that the bimetallic Pt-Pd core-shell NCs can enhance the current density of the methanol oxidation reaction, lowering the over-potential by 35 mV with respect to the Pt core NCs. Further investigation reveals that the Pd/Pt ratio of 1/3, which corresponds to nearly monolayer Pd deposition on Pt core NCs, gives the highest oxidation current density and lowest over-potential. This study shows for the first time the systematic investigation of effects of Pd atomic shells on Pt-Pd bimetallic nanocatalysts, providing valuable guidelines for designing high-performance catalysts for fuel cell applications. PMID:22159178

  4. Thermodynamic modeling of Pt-Al and Pd-Al

    NASA Astrophysics Data System (ADS)

    Carr, Derek

    2011-03-01

    Pure platinum and pure palladium are too soft for typical jewelry applications. Adding small amounts of other metals can significantly increase their performance. However, international hallmarking standards require the alloys to be 95% pure by weight. How does one achieve significant improvements in performance adding only small amounts (5 wt-%) of other metals? Significant improvements are possible even with small additions if precipitate hardening can be induced. Using a combination of first-principles, cluster expansion, and Monte Carlo modeling, we have identified new Pt-rich/Pd-rich phases in Pt-Al and Pd-Al that should be useful in precipitate hardening. Thermodynamical modeling indicates that the phases are experimentally feasible (not kinetically inhibited).

  5. Deactivation Mechanisms of Pt/Pd-based Diesel Oxidation Catalysts

    SciTech Connect

    Wiebenga, Michelle H.; Kim, Chang H.; Schmieg, Steven J.; Oh, Se H.; Brown, David B.; Kim, Do Heui; Lee, Jong H.; Peden, Charles HF

    2012-04-30

    Currently precious metal-based diesel oxidation catalysts (DOC) containing platinum (Pt) and palladium (Pd) are most commonly used for the oxidation of hydrocarbon and NO in diesel exhaust hydrocarbon oxidation. The present work has been carried out to investigate the deactivation mechanisms of the DOC from its real-world vehicle operation by coupling its catalytic activity measurements with surface characterization including x-ray diffraction, transmission electron microscopy, and x-ray photoelectron spectroscopy. A production Pt-Pd DOC was obtained after being aged on a vehicle driven for 135,000 miles in order to study its deactivation behavior. The performance of the vehicle-aged part was correlated with that of the simulated hydrothermal lab aged sample assuming that Pt-Pd sintering plays a major role in irreversible catalyst deactivation. In addition to the hydrothermal sintering, the deterioration of hydrocarbon and NO oxidation performance was caused by surface poisoning. The role of the various aging factors in determining long-term performance in mobile applications will be discussed.

  6. Pd-Pt Bimetallic Nanodendrites with High Activity for Oxygen Reduction

    SciTech Connect

    Lim, B.; Tao, J.; Jiang, M.; Camargo, P.H.C.; Cho, E.C.; Lu, X.; Zhu, Y.; Xia, Y.

    2009-06-05

    Controlling the morphology of Pt nanostructures can provide a great opportunity to improve their catalytic properties and increase their activity on a mass basis. We synthesized Pd-Pt bimetallic nanodendrites consisting of a dense array of Pt branches on a Pd core by reducing K{sub 2}PtCl{sub 4} with L-ascorbic acid in the presence of uniform Pd nanocrystal seeds in an aqueous solution. The Pt branches supported on faceted Pd nanocrystals exhibited relatively large surface areas and particularly active facets toward the oxygen reduction reaction (ORR), the rate-determining step in a proton-exchange membrane fuel cell. The Pd-Pt nanodendrites were two and a half times more active on the basis of equivalent Pt mass for the ORR than the state-of-the-art Pt/C catalyst and five times more active than the first-generation supportless Pt-black catalyst.

  7. High-temperature oxidation of Pt-45Pd-10Rh

    SciTech Connect

    Graham, G.W.; Potter, T.J.; Weber, W.H.; Gandhi, H.S.

    1988-06-01

    The surfaces of Pt-45Pd-10Rh foils oxidized over the range 875-1075 K in a 20% O/sub 2/-Ar mixture at atmospheric pressure were examined by Auger electron, X-ray photoelectron, and Raman spectroscopy. The composition of the oxide formed on the surface was found to vary with temperature from predominantly PdO at 875 K to PdRhO/sub 2/ at 1075 K. Only a few atomic percent Pt was observed, present in both the metallic and (apparently) + 1 oxidation states at 875 K and in the metallic state at 1075 K. The formation of PdRhO/sub 2/ (and no Rh/sub 2/O/sub 3/) at 1075 K was found to persist upon reoxidation following a low-temperature reduction cycle in which the increased Rh concentration on the surface was retained. An oxidation-induced Rh enrichment of the surface of the alloy foil beyond 50 at.% does not appear likely within the temperature/pressure regime investigated.

  8. Large faceted Pd nanocrystals supported small Pt nanoparticles as highly durable electrocatalysts for oxygen reduction

    NASA Astrophysics Data System (ADS)

    Zhang, Geng; Lu, Wangting; Cao, Longsheng; Qin, Xiaoping; Ding, Fei; Tang, Shun; Shao, Zhi-Gang; Yi, Baolian

    2016-09-01

    The reduction of Pt content together with the improvement of the durability of the catalyst for oxygen reduction reaction (ORR) is required to the large-scale commercialization of proton exchange membrane fuel cells. In this work, a novel ORR catalyst consisting of large Pd nanocrystal as the core with small Pt nanoparticles supported on the Pd core is prepared by a facile one-step synthesis method. The Pd substrate is presented in the form of well-defined cuboctahedrons and icosahedrons. The type of metal precursors and Pt/Pd molar ratio are important factors to obtain this Pd-supporting-Pt structure. The Pd2-s-Pt1 catalyst with a nominal Pt/Pd atomic ratio at 1/2 shows improved ORR activity: its mass specific activity and area specific activity is 2.5 and 3.5 times that of commercial Pt/C, respectively. More importantly, the Pd2-s-Pt1 catalyst demonstrates outstanding durability against potential cycling which can be ascribed to the slow dissolution of Pd core and the structure transformation from Pd@Pt to hollow PdPt alloyed nanocages. This exciting result provides a new pathway to the design of ORR catalyst with excellent durability.

  9. Monodispersed bimetallic PdAg nanoparticles with twinned structures: formation and enhancement for the methanol oxidation.

    PubMed

    Yin, Zhen; Zhang, Yining; Chen, Kai; Li, Jing; Li, Wenjing; Tang, Pei; Zhao, Huabo; Zhu, Qingjun; Bao, Xinhe; Ma, Ding

    2014-01-01

    Monodispersed bimetallic PdAg nanoparticles can be fabricated through the emulsion-assisted ethylene glycol (EG) ternary system. Different compositions of bimetallic PdAg nanoparticles, Pd₈₀Ag₂₀, Pd₆₅Ag₃₅ and Pd₄₆Ag₅₄ can be obtained via adjusting the reaction parameters. For the formation process of the bimetallic PdAg nanoparticles, there have two-stage growth processes: firstly, nucleation and growth of the primary nanoclusters; secondly, formation of the secondary nanoparticles with the size-selection and relax process via the coalescence or aggregation of the primary nanoclusters. The as-prepared PdAg can be supported on the carbon black without any post-treatment, which exhibited high electro-oxidation activity towards methanol oxidation under alkaline media. More importantly, carbon-supported Pd₈₀Ag₂₀ nanoparticles reveal distinctly superior activities for the methanol oxidation, even if compared with commercial Pt/C electro-catalyst. It is concluded that the enhanced activity is dependant on the unique twinning structure with heterogeneous phase due to the dominating coalescence growth in EG ternary system. PMID:24608736

  10. Enhanced electrocatalytic performance of Pt monolayer on nanoporous PdCu alloy for oxygen reduction

    NASA Astrophysics Data System (ADS)

    Hou, Linxi; Qiu, Huajun

    2012-10-01

    By selectively dealloying Al from PdxCu20-xAl80 ternary alloys in 1.0 M NaOH solution, nanoporous PdCu (np-PdCu) alloys with different Pd:Cu ratios are obtained. By a mild electrochemical dealloying treatment, the np-PdCu alloys are facilely converted into np-PdCu near-surface alloys with a nearly pure-Pd surface and PdCu alloy core. The np-PdCu near-surface alloys are then used as substrates to fabricate core-shell catalysts with a Pt monolayer as shell and np-PdCu as core by a Cu-underpotential deposition-Pt displacement strategy. Electrochemical measurements demonstrate that the Pt monolayer on np-Pd1Cu1 (Pt/np-Pd1Cu1) exhibits the highest Pt surface-specific activity towards oxygen reduction, which is ˜5.8-fold that of state-of-the-art Pt/C catalyst. The Pt/np-Pd1Cu1 also shows much enhanced stability with ˜78% active surface retained after 10,000 cycles (0.6-1.2 V vs. RHE). Under the same condition, the active surface of Pt/C drops to ˜28%.

  11. Localized Pd Overgrowth on Cubic Pt Nanocrystals for Enhanced Electrocatalytic Oxidation of Formic Acid

    SciTech Connect

    Lee, H.; Habas, S.E.; Somorjai, G.A.; Yang, P.

    2008-03-20

    Binary Pt/Pd nanoparticles were synthesized by localized overgrowth of Pd on cubic Pt seeds for the investigation of electrocatalytic formic acid oxidation. The binary particles exhibited much less self-poisoning and a lower activation energy relative to Pt nanocubes, consistent with the single crystal study.

  12. Certification of Pd and Pt single spikes and application to the quantification of Pt and Pd in automotive exhaust emissions

    NASA Astrophysics Data System (ADS)

    Vogl, Jochen; Meyer, Christian; Noordmann, Janine; Rienitz, Olaf; Geilert, Sonja

    2014-05-01

    Numerous epidemiological studies show the effect of increased ambient pollution. Therefore measurement networks for air quality have been installed worldwide and legislation requires the monitoring of air pollution. Besides monitoring it is also important to be able to identify, to quantify and finally to regulate the emission of distinct sources in order to improve the quality of life. Automotive vehicles are a major source of environmental pollution especially through contaminants such as CO, NOX, SOX and hydrocarbons which derive from petrol combustion, while for example Platinum Group Elements (PGE) can be present from catalytic converters. The release of PGE into the environment, however, may be damaging in terms of public health, ecological and economic interests. In order to reliably assess the risks from PGEs, traceable and thus comparable data on the release rates of PGE from automotive catalysers are needed. As no Certified Reference Materials (CRM) are available for such samples the development of analytical procedures enabling SI-traceable results will be challenging. Therefore reference procedures for Pd and Pt in automotive exhaust emissions based on isotope dilution mass spectrometry (IDMS) have been developed and applied to specifically sampled automotive exhaust emissions. Due to the commonly known advantages, IDMS often is applied for quantification PGEs, as is the case within this work. The main reasons here are the required accuracy and the low PGE mass fractions in the sample. In order to perform IDMS analysis the analyte element must be available in an isotopically enriched form as so-called spike material or solution thereof, which is mixed with the sample. Unfortunately, no certified PGE spike solutions are available yet. To fill this gap two single PGE spikes, one 106Pd and one 194Pt spike, have been produced and characterized. The selection of the isotopes, the production of the solutions and the ampoulation will be described in this

  13. A pathway for the growth of core-shell Pt-Pd nanoparticles

    DOE PAGES

    Narula, Chaitanya Kumar; Yang, Xiaofan; Li, Chen; Pennycook, Stephen J; Lupini, Andrew R

    2015-10-12

    In this study, the aging of both Pt-Pd nanoparticles and core-shell Pt-Pd nanoparticles has been reported to result in alloying of Pt with Pd. In comparison to monometallic Pt catalysts, the growth of Pd-Pt bimetallics is slower; however, the mechanism of growth of particles and the mechanism by which Pd improves the hydrothermal durability of bimetallic Pd-Pt particles remains uncertain. In our work on hydrothermal aging of core-shell Pt-Pd nanoparticles, synthesized by solution methods, with varying Pd:Pt ratio of 1:4, 1:1, and 4:1, we compare the growth of core-shell Pt-Pd nanoparticles and find that particles grow by migrating and joiningmore » together. The unique feature of the observed growth is that Pd shells from both particles open up and join, allowing the cores to merge. At high temperatures, alloying occurs in good agreement with reports by other workers.« less

  14. Synthesis, characterization and antibacterial activity of polyaniline/Pt-Pd nanocomposite.

    PubMed

    Boomi, Pandi; Prabu, Halliah Gurumallesh; Mathiyarasu, Jayaraman

    2014-01-24

    Pt colloid and Pt-Pd colloid, pristine polyaniline, polyaniline/Pt nanocomposite and polyaniline/Pt-Pd nanocomposite were synthesized by simple chemical method. They were characterized by UV-Vis, FT-IR, XRD, TGA, SEM, HR-SEM and HR-TEM with EDAX techniques. The results proved that there is a strong interaction between metal nanoparticles (Pt-Pd) and polyaniline chains. This interaction creates changes in the backbone chain of polyaniline/Pt-Pd nanocomposite when compared to pristine polyaniline. The synthesized materials were evaluated for antibacterial activity, minimal inhibitory concentration and minimal bactericidal concentration. The results indicated that the nanocomposites exhibited improved antibacterial activity when compared to pristine polyaniline and individual metal colloids. This is the first report on the chemical synthesis of polyaniline/Pt-Pd nanocomposite, which exhibits antibacterial activity at micro molar concentration levels.

  15. Synthesis of bimetallic Pt-Pd core-shell nanocrystals and their high electrocatalytic activity modulated by Pd shell thickness

    NASA Astrophysics Data System (ADS)

    Li, Yujing; Wang, Zhi Wei; Chiu, Chin-Yi; Ruan, Lingyan; Yang, Wenbing; Yang, Yang; Palmer, Richard E.; Huang, Yu

    2012-01-01

    Bimetallic Pt-Pd core-shell nanocrystals (NCs) are synthesized through a two-step process with controlled Pd thickness from sub-monolayer to multiple atomic layers. The oxygen reduction reaction (ORR) catalytic activity and methanol oxidation reactivity of the core-shell NCs for fuel cell applications in alkaline solution are systematically studied and compared based on different Pd thickness. It is found that the Pd shell helps to reduce the over-potential of ORR by up to 50mV when compared to commercial Pd black, while generating up to 3-fold higher kinetic current density. The carbon monoxide poisoning test shows that the bimetallic NCs are more resistant to the CO poisoning than Pt NCs and Pt black. It is also demonstrated that the bimetallic Pt-Pd core-shell NCs can enhance the current density of the methanol oxidation reaction, lowering the over-potential by 35 mV with respect to the Pt core NCs. Further investigation reveals that the Pd/Pt ratio of 1/3, which corresponds to nearly monolayer Pd deposition on Pt core NCs, gives the highest oxidation current density and lowest over-potential. This study shows for the first time the systematic investigation of effects of Pd atomic shells on Pt-Pd bimetallic nanocatalysts, providing valuable guidelines for designing high-performance catalysts for fuel cell applications.Bimetallic Pt-Pd core-shell nanocrystals (NCs) are synthesized through a two-step process with controlled Pd thickness from sub-monolayer to multiple atomic layers. The oxygen reduction reaction (ORR) catalytic activity and methanol oxidation reactivity of the core-shell NCs for fuel cell applications in alkaline solution are systematically studied and compared based on different Pd thickness. It is found that the Pd shell helps to reduce the over-potential of ORR by up to 50mV when compared to commercial Pd black, while generating up to 3-fold higher kinetic current density. The carbon monoxide poisoning test shows that the bimetallic NCs are more

  16. Enhanced hydrogenation and reduced lattice distortion in size selected Pd-Ag and Pd-Cu alloy nanoparticles

    SciTech Connect

    Sengar, Saurabh K.; Mehta, B. R.; Kulriya, P. K.; Khan, S. A.

    2013-10-21

    Important correlation between valence band spectra and hydrogenation properties in Pd alloy nanoparticles is established by studying the properties of size selected and monocrystalline Pd, Ag, Cu, Pd-Ag, and Pd-Cu nanoparticles. The X-ray photoelectron spectroscopy and elastic recoil detection analysis show that size induced Pd4d centroid shift is related to enhanced hydrogenation with H/Pd ratio of 0.57 and 0.49 in Pd-Ag and Pd-Cu nanoparticles in comparison to reported bulk values of 0.2 and 0.1, respectively. Pd-alloy nanoparticles show lower hydrogen induced lattice distortion. The reduced distortion and higher hydrogen reactivity of Pd-alloy nanoparticles is important for numerous hydrogen related applications.

  17. Low-energy electron diffraction investigation of epitaxial growth: Pt and Pd on Pd(100)

    SciTech Connect

    Flynn-Sanders, D.

    1990-09-21

    We investigate the epitaxial growth of Pt and Pd and Pd(100) via spot profile analysis using conventional low-energy electron diffraction (LEED). We resolve a central-spike and diffuse component in the spot profiles, reflecting the layer-occupations and pair-correlations, respectively. Kinetic limitations inhibit layer-by-layer growth at low temperatures. Our data suggest diffusion switches on at ca. 150 K for Pt and ca. 170 K for Pd indicating activation barriers to surface diffusion of ca. 10 and ca. 13 kcal/mol, respectively. To clarify the role of diffusion in determining the resulting film morphology, we develop a growth model that incorporates the adsorption-site requirement and predicts intensity oscillations. We present a new procedure to experimentally determine out-of-phase scattering conditions. At these energies, ring-structure is evident in the profiles during Pd growth between ca. 200 and 400 K. We report ring intensity oscillations as a function of coverage, which demonstrate the filling of individual layers.

  18. Improved catalytic performance of Pd nanowires for ethanol oxidation by monolayer of Pt

    NASA Astrophysics Data System (ADS)

    Huang, Zhongyuan; Zhou, Haihui; Chang, Yiwen; Fu, Chaopeng; Zeng, Fanyan; Kuang, Yafei

    2013-10-01

    Pd nanowires with diameter of 10-20 nm and length of several micrometers were prepared and monolayer of Pt was deposited on the Pd nanowires by using copper underpotential deposition and subsequent replacement of Cu by Pt. The products were characterized by using scanning electron microscopy, transmission electron microscopy, X-ray photoelectron spectroscopy and energy spectrum analysis. The electrocatalytic performance of PdPt nanowires was studied by cyclic voltammetry and chronoamperometry. Electrochemical results show that the monolayer of Pt can improve not only the activity of Pd nanowires but also the stability for ethanol oxidation in alkaline medium.

  19. Controllable galvanic synthesis of triangular Ag-Pd alloy nanoframes for efficient electrocatalytic methanol oxidation.

    PubMed

    Xu, Lin; Luo, Zhimin; Fan, Zhanxi; Yu, Sijia; Chen, Junze; Liao, Yusen; Xue, Can

    2015-06-01

    Triangular Ag-Pd alloy nanoframes were successfully synthesized through galvanic replacement by using Ag nanoprisms as sacrificial templates. The ridge thickness of the Ag-Pd alloy nanoframes could be readily tuned by adjusting the amount of the Pd source during the reaction. These obtained triangular Ag-Pd alloy nanoframes exhibit superior electrocatalytic activity for the methanol oxidation reaction as compared with the commercial Pd/C catalyst due to the alloyed Ag-Pd composition as well as the hollow-framed structures. This work would be highly impactful in the rational design of future bimetallic alloy nanostructures with high catalytic activity for fuel cell systems.

  20. Pt-content-controlled synthesis of Pd nanohollows/Pt nanorods core/shell composites with enhanced electrocatalytic activities for the methanol oxidation reaction

    NASA Astrophysics Data System (ADS)

    Lai, Shiqin; Fu, Chenglin; Chen, Yongxiang; Yu, Xiang; Lai, Xuandi; Ye, Cui; Hu, Jianqiang

    2015-01-01

    Pd nanohollows/Pt nanorods (PdNHs/PtNRs) core/shell composites have been synthesized by a multistep crystalline growth method, in which Pt NRs grow on the exterior surface of hollow Pd nanospheres in order. Moreover, the size and quantity of the Pt NRs in the PdNHs/PtNRs can be easily tailored and thus ameliorate Pt utilization efficiency through varying H2PtCl6 concentrations. By comparing with Pt NPs and commercial Pt/C (JM), the PdNHs/PtNRs prepared using 2.50 mL 0.02 M H2PtCl6 have larger surface area, better anti-CO poisoning ability and more excellent catalytic performance. Moreover, the catalytic properties of the PdNHs/PtNRs can be well tunable by modifying the Pt contents. Our studies indicate that the PdNHs/PtNRs prepared using 2.50 mL 0.02 M H2PtCl6, in which Pd NHs are nearly completely covered with Pt NRs, have the largest surface area, best antitoxic ability and most excellent catalytic performance, indicative of high Pt utilization efficiency of the PdNHs/PtNRs relative to Pt/C (JM), Pt NPs and other PdNHs/PtNRs prepared using other H2PtCl6 concentrations. Therefore, the strategy to the size and content control of the PdNHs/PtNRs nanocomposites can facilitate optimized design of Pt-based catalysts for direct methanol fuel cells.

  1. Highly Active Carbon Supported Pd-Ag Nanofacets Catalysts for Hydrogen Production from HCOOH.

    PubMed

    Wang, Wenhui; He, Ting; Liu, Xuehua; He, Weina; Cong, Hengjiang; Shen, Yangbin; Yan, Liuming; Zhang, Xuetong; Zhang, Jinping; Zhou, Xiaochun

    2016-08-17

    Hydrogen is regarded as a future sustainable and clean energy carrier. Formic acid is a safe and sustainable hydrogen storage medium with many advantages, including high hydrogen content, nontoxicity, and low cost. In this work, a series of highly active catalysts for hydrogen production from formic acid are successfully synthesized by controllably depositing Pd onto Ag nanoplates with different Ag nanofacets, such as Ag{111}, Ag{100}, and the nanofacet on hexagonal close packing Ag crystal (Ag{hcp}). Then, the Pd-Ag nanoplate catalysts are supported on Vulcan XC-72 carbon black to prevent the aggregation of the catalysts. The research reveals that the high activity is attributed to the formation of Pd-Ag alloy nanofacets, such as Pd-Ag{111}, Pd-Ag{100}, and Pd-Ag{hcp}. The activity order of these Pd-decorated Ag nanofacets is Pd-Ag{hcp} > Pd-Ag{111} > Pd-Ag{100}. Particularly, the activity of Pd-Ag{hcp} is up to an extremely high value, i.e., TOF{hcp} = 19 000 ± 1630 h(-1) at 90 °C (lower limit value), which is more than 800 times higher than our previous quasi-spherical Pd-Ag alloy nanocatalyst. The initial activity of Pd-Ag{hcp} even reaches (3.13 ± 0.19) × 10(6) h(-1) at 90 °C. This research not only presents highly active catalysts for hydrogen generation but also shows that the facet on the hcp Ag crystal can act as a potentially highly active catalyst. PMID:27454194

  2. Highly Active Carbon Supported Pd-Ag Nanofacets Catalysts for Hydrogen Production from HCOOH.

    PubMed

    Wang, Wenhui; He, Ting; Liu, Xuehua; He, Weina; Cong, Hengjiang; Shen, Yangbin; Yan, Liuming; Zhang, Xuetong; Zhang, Jinping; Zhou, Xiaochun

    2016-08-17

    Hydrogen is regarded as a future sustainable and clean energy carrier. Formic acid is a safe and sustainable hydrogen storage medium with many advantages, including high hydrogen content, nontoxicity, and low cost. In this work, a series of highly active catalysts for hydrogen production from formic acid are successfully synthesized by controllably depositing Pd onto Ag nanoplates with different Ag nanofacets, such as Ag{111}, Ag{100}, and the nanofacet on hexagonal close packing Ag crystal (Ag{hcp}). Then, the Pd-Ag nanoplate catalysts are supported on Vulcan XC-72 carbon black to prevent the aggregation of the catalysts. The research reveals that the high activity is attributed to the formation of Pd-Ag alloy nanofacets, such as Pd-Ag{111}, Pd-Ag{100}, and Pd-Ag{hcp}. The activity order of these Pd-decorated Ag nanofacets is Pd-Ag{hcp} > Pd-Ag{111} > Pd-Ag{100}. Particularly, the activity of Pd-Ag{hcp} is up to an extremely high value, i.e., TOF{hcp} = 19 000 ± 1630 h(-1) at 90 °C (lower limit value), which is more than 800 times higher than our previous quasi-spherical Pd-Ag alloy nanocatalyst. The initial activity of Pd-Ag{hcp} even reaches (3.13 ± 0.19) × 10(6) h(-1) at 90 °C. This research not only presents highly active catalysts for hydrogen generation but also shows that the facet on the hcp Ag crystal can act as a potentially highly active catalyst.

  3. Characterization of Na+- beta-Zeolite Supported Pd and Pd Ag Bimetallic Catalysts using EXAFS, TEM and Flow Reactor

    SciTech Connect

    Huang,W.; Lobo, R.; Chen, J.

    2008-01-01

    Flow reactor studies of the selective hydrogenation of acetylene in the presence of ethylene have been performed on Na+ exchanged {beta}-zeolite supported Pd, Ag and PdAg catalysts, as an extension of our previous batch reactor studies [W. Huang, J.R. McCormick, R.F. Lobo, J.G. Chen, J. Catal. 246 (2007) 40-51]. Results from flow reactor studies show that the PdAg/Na+-{beta}-zeolite bimetallic catalyst has lower activity than Pd/Na+-{beta}-zeolite monometallic catalyst, while Ag/Na+-{beta}-zeolite does not show any activity for acetylene hydrogenation. However, the selectivity for the PdAg bimetallic catalyst is much higher than that for either the Pd catalyst or Ag catalyst. The selectivity to byproduct (ethane) is greatly inhibited on the PdAg bimetallic catalyst as well. The results from the current flow reactor studies confirmed the pervious results from batch reactor studies [W. Huang, J.R. McCormick, R.F. Lobo, J.G. Chen, J. Catal. 246 (2007) 40-51]. In addition, we used transmission electron microscope (TEM), extended X-ray absorption fine structure (EXAFS), and FTIR of CO adsorption to confirm the formation of Pd-Ag bimetallic alloy in the PdAg/Na+-{beta}-zeolite catalyst.

  4. Segregated Pt on Pd nanotubes for enhanced oxygen reduction activity in alkaline electrolyte.

    PubMed

    St John, Samuel; Atkinson, Robert W; Dyck, Ondrej; Sun, Cheng-Jun; Zawodzinski, Thomas A; Papandrew, Alexander B

    2015-12-01

    Nanoscaled Pt domains were integrated with Pd nanotubes via vapor deposition to yield a highly active electrocatalyst for the oxygen reduction reaction (ORR) in alkaline media. The surface-area-normalized ORR activity of these bi-metallic Pt-on-Pd nanotubes (PtPdNTs) was nearly 6× the corresponding carbon-supported Pt nanoparticle (Pt/C) activity at 0.9 V vs. RHE (1.5 vs. 0.24 mA cmmetal(-2), respectively). Furthermore, the high specific activity of the PtPdNTs was achieved without sacrificing mass-normalized activity, which is more than twice that of Pt/C (0.333 A mgPtPdNT(-1)vs. 0.141 A mgPt/C(-1)) and also greater than that of Pd/C (0.221 A mgPd/C(-1)). We attribute the enhancements in specific and mass activity to modifications of the segregated Pt electronic structure and to nanoscale porosity, respectively. PMID:26553367

  5. Triangular Ag-Pd alloy nanoprisms: rational synthesis with high-efficiency for electrocatalytic oxygen reduction

    NASA Astrophysics Data System (ADS)

    Xu, Lin; Luo, Zhimin; Fan, Zhanxi; Zhang, Xiao; Tan, Chaoliang; Li, Hai; Zhang, Hua; Xue, Can

    2014-09-01

    We report the generation of triangular Ag-Pd alloy nanoprisms through a rationally designed synthetic strategy based on silver nanoprisms as sacrificial templates. The galvanic replacement between Ag nanoprisms and H2PdCl4 along with co-reduction of Ag+/Pd2+ is responsible for the formation of final prismatic Ag-Pd alloy nanostructures. Significantly, these Ag-Pd alloy nanoprisms exhibited superior electrocatalytic activity for the oxygen reduction reaction (ORR) as compared with the commercial Pd/C catalyst. Such a high catalytic activity is attributed to not only the alloyed Ag-Pd composition but also the dominant {111} facets of the triangular Ag-Pd nanoprisms. This work demonstrates the rational design of bimetallic alloy nanostructures with control of selective crystal facets that are critical to achieve high catalytic activity for fuel cell systems.We report the generation of triangular Ag-Pd alloy nanoprisms through a rationally designed synthetic strategy based on silver nanoprisms as sacrificial templates. The galvanic replacement between Ag nanoprisms and H2PdCl4 along with co-reduction of Ag+/Pd2+ is responsible for the formation of final prismatic Ag-Pd alloy nanostructures. Significantly, these Ag-Pd alloy nanoprisms exhibited superior electrocatalytic activity for the oxygen reduction reaction (ORR) as compared with the commercial Pd/C catalyst. Such a high catalytic activity is attributed to not only the alloyed Ag-Pd composition but also the dominant {111} facets of the triangular Ag-Pd nanoprisms. This work demonstrates the rational design of bimetallic alloy nanostructures with control of selective crystal facets that are critical to achieve high catalytic activity for fuel cell systems. Electronic supplementary information (ESI) available. See DOI: 10.1039/c4nr03600j

  6. Desorption of oxygen from alloyed Ag/Pt(111)

    SciTech Connect

    Jankowski, Maciej; Wormeester, Herbert Zandvliet, Harold J. W.; Poelsema, Bene

    2014-06-21

    We have investigated the interaction of oxygen with the Ag/Pt(111) surface alloy by thermal desorption spectroscopy (TDS). The surface alloy was formed during the deposition of sub-monolayer amounts of silver on Pt(111) at 800 K and subsequent cooling to 300 K. The low-temperature phase of the surface alloy is composed of nanometer-sized silver rich stripes, embedded within platinum-rich domains, which were characterized with spot profile analysis low energy electron diffraction. The TDS measurements show that oxygen adsorption is blocked on Ag sites: the saturation coverage of oxygen decreases with increasing Ag coverage. Also, the activation energy for desorption (E{sub des}) decreases with Ag coverage. The analysis of the desorption spectra from clean Pt(111) shows a linear decay of E{sub des} with oxygen coverage, which indicates repulsive interactions between the adsorbed oxygen atoms. In contrast, adsorption on alloyed Ag/Pt(111) leads to an attractive interaction between adsorbed oxygen atoms.

  7. Understanding the structural properties and thermal stabilities of Au-Pd-Pt trimetallic clusters

    NASA Astrophysics Data System (ADS)

    Zhao, Zheng; Li, Mingjiang; Cheng, Daojian; Zhu, Jiqin

    2014-09-01

    In this work, surface segregation phenomena of Au-Pd-Pt trimetallic clusters are investigated by using semi-grand Monte Carlo simulations based on the Gupta potential. It is found that Au atoms are systematically segregated on the surface of the Au-Pd-Pt clusters (6-24 at.% higher than the overall Au concentration), due to the competition among the surface energies of Au, Pd, and Pt. The melting properties of Au-Pd-Pt trimetallic clusters with different composition and size are investigated by using molecular dynamics simulations, based on the same Gupta potential. It is found that the Au-Pd-Pt trimetallic cluster with the highest melting point corresponds to the one with the most stable structure. In addition, linear decrease in cluster melting point with the inverse cluster diameter is predicted for both pure and trimetallic clusters, which is well-known as the Pawlow's law.

  8. Synthesis of Pd9Ru@Pt nanoparticles for oxygen reduction reaction in acidic electrolytes

    NASA Astrophysics Data System (ADS)

    Sun, Yu; Hsieh, Yu-Chi; Chang, Li-Chung; Wu, Pu-Wei; Lee, Jyh-Fu

    2015-03-01

    Nanoparticles of PdRu, Pd3Ru, and Pd9Ru are synthesized and impregnated on carbon black via a wet chemical reflux process. X-ray diffraction patterns of the as-synthesized samples, PdxRu/C (x = 1/3/9), suggest successful formation of alloy without presence of individual Pd and Ru nanoparticles. Images from transmission electron microscope confirm irregularly-shaped nanoparticles with average size below 3 nm. Analysis from extended X-ray absorption fine structure on both Pd and Ru K-edge absorption profiles indicate the Ru atoms are enriched on the surface of PdxRu/C. Among these samples, the Pd9Ru/C exhibits the strongest electrocatalytic activity for oxygen reduction reaction (ORR) in an oxygen-saturated 0.1 M aqueous HClO4 solution. Subsequently, the Pd9Ru/C undergoes Cu under potential deposition, followed by a galvanic displacement reaction to deposit a Pt monolayer on the Pd9Ru surface (Pd9Ru@Pt). The Pd9Ru@Pt reveals better ORR performance than that of Pt, reaching a mass activity of 0.38 mA μg-1Pt, as compared to that of commercially available Pt nanoparticles (0.107 mA μg-1Pt). The mechanisms responsible for the ORR enhancement are attributed to the combined effects of lattice strain and ligand interaction. In addition, this core-shell Pd9Ru@Pt electrocatalyst represents a substantial reduction in the amount of Pt consumption and raw material cost.

  9. Tailoring Silica-alumina Supported Pt-Pd As Poison Tolerant Catalyst For Aromatics Hydrogenation

    SciTech Connect

    Yu, Yanzhe; Gutierrez, Oliver Y.; Haller, Gary L.; Colby, Robert J.; Kabius, Bernd C.; Rob van Veen, J. A.; Jentys, Andreas; Lercher, Johannes A.

    2013-08-01

    The tailoring of the physicochemical and catalytic properties of mono- and bimetallic Pt-Pd catalysts supported on amorphous silica-alumina is studied. Electron energy loss spectroscopy and extended X-ray absorption fine structure analyses indicated that bimetallic Pt-Pd and relatively large monometallic Pd particles were formed, whereas the X-ray absorption near edge structure provided direct evidence for the electronic deficiency of the Pt atoms. The heterogeneous distribution of metal particles was also shown by high resolution transmission electron microscopy. The average structure of the bimetallic particles (Pt-rich core and Pd-rich shell) and the presence of Pd particles led to surface Pd enrichment, which was independently shown by IR spectra of adsorbed CO. The specific metal distribution, average size, and surface composition of the Pt-Pd particles depend to a large extent on the metal precursors. In the presence of NH3 ligands, Pt-Pd particles with a fairly homogeneous bulk and surface metal distribution were formed. Also high Lewis acid site concentration of the carrier leads to more homogeneous bimetallic particles. All catalysts were active for the hydrogenation of tetralin in the absence and presence of quinoline and dibenzothiophene (DBT). Monometallic Pt catalysts had the highest hydrogenation activity in poison-free and quinoline-containing feed. When DBT was present, bimetallic Pt-Pd catalysts with the most homogenous metal distribution showed the highest activity. The higher resistance of bimetallic catalysts towards sulfur poisoning compared to their monometallic Pt counterparts results from the weakened metal-sulfur bond on the electron deficient Pt atoms. Thus, increasing the fraction of electron deficient Pt on the surface of the bimetallic particles increases the efficiency of the catalyst in the presence of sulfur.

  10. Ti-Ag-Pd alloy with good mechanical properties and high potential for biological applications.

    PubMed

    Zadorozhnyy, V Yu; Shi, X; Gorshenkov, M V; Kozak, D S; Wada, T; Louzguine-Luzgin, D V; Inoue, A; Kato, H

    2016-01-01

    Ti-based alloys containing Ag were produced by tilt-casting method and their properties were studied. Even in its as-cast state, Ti94Ag3Pd3 showed relatively high tensile properties, good electrochemical behavior, and good biocompatibility. The relatively good mechanical properties of the as-cast α-Ti-type Ti94Ag3Pd3 alloy (tensile strength up to 850 MPa and elongation of ~10%) can be explained by its severely deformed, fine crystalline structure. The high biocompatibility of Ti94Ag3Pd3 can be explained by the Ag-Pd interaction, which inhibits the release of Ag ions from the surface. Ag, in combination with Pd has no toxic effects and demonstrates useful antimicrobial properties. The Ti94Ag3Pd3 alloy shows a good potential to be applied as a biomedical implant alloy. PMID:27122177

  11. Ti-Ag-Pd alloy with good mechanical properties and high potential for biological applications

    NASA Astrophysics Data System (ADS)

    Zadorozhnyy, V. Yu.; Shi, X.; Gorshenkov, M. V.; Kozak, D. S.; Wada, T.; Louzguine-Luzgin, D. V.; Inoue, A.; Kato, H.

    2016-04-01

    Ti-based alloys containing Ag were produced by tilt-casting method and their properties were studied. Even in its as-cast state, Ti94Ag3Pd3 showed relatively high tensile properties, good electrochemical behavior, and good biocompatibility. The relatively good mechanical properties of the as-cast α-Ti-type Ti94Ag3Pd3 alloy (tensile strength up to 850 MPa and elongation of ~10%) can be explained by its severely deformed, fine crystalline structure. The high biocompatibility of Ti94Ag3Pd3 can be explained by the Ag-Pd interaction, which inhibits the release of Ag ions from the surface. Ag, in combination with Pd has no toxic effects and demonstrates useful antimicrobial properties. The Ti94Ag3Pd3 alloy shows a good potential to be applied as a biomedical implant alloy.

  12. Carbon-supported Pd-Pt cathode electrocatalysts for proton exchange membrane fuel cells

    NASA Astrophysics Data System (ADS)

    Tang, Yongfu; Zhang, Huamin; Zhong, Hexiang; Xu, Ting; Jin, Hong

    A series of carbon-supported Pd-Pt alloy (Pd-Pt/C) catalysts for oxygen reduction reaction (ORR) with low-platinum content are synthesized via a modified sodium borohydride reduction method. The structure of as-prepared catalysts is characterized by powder X-ray diffraction (XRD) and transmission electron microscope (TEM) measurements. The prepared Pd-Pt/C catalysts with alloy form show face-centered-cubic (FCC) structure. The metal particles of Pd-Pt/C catalysts with mean size of around 4-5 nm are uniformly dispersed on the carbon support. The electrocatalytic activities for ORR of these catalysts are investigated by rotating disk electrode (RDE), cyclic voltammetry (CV), single cell measurements and electrochemical impedance spectra (EIS) measurements. The results suggest that the electrocatalytic activities of Pd-Pt/C catalysts with low platinum are comparable to that of the commercial Pt/C with the same metal loading. The maximum power density of MEA with a Pd-Pt/C catalyst, the Pd/Pt mass ratio of which is 7:3, is about 1040 mW cm -2.

  13. Synthesis and phase transition of self-assembled FePd and FePdPt nanoparticles

    NASA Astrophysics Data System (ADS)

    Kang, Shishou; Jia, Zhiyong; Nikles, David E.; Harrell, J. W.

    2004-06-01

    Fe54Pd46 nanoparticles were prepared by the simultaneous chemical reduction of palladium acetylacetonate and iron chloride. The particle size can be tunable from 2 to 10 nm by controlling the amount of surfactants. Similarly, Fe50PdxPt50-x (x=8, 15, 25) nanoparticles were prepared by the simultaneous reduction of palladium acetylacetonate, platinum acetylacetonate, and iron chloride. The average diameter for the Fe50PdxPt50-x particles was always 3.5 nm and independent of the amount of surfactants. Films of the particles were cast onto silicon wafers from hydrocarbon dispersion. The coercivity of Fe54Pd46 nanoparticles increases with annealing temperature up to 550 °C, indicating fcc to fct phase transition. After further increasing the annealing temperature, the coercivity of the Fe54Pd46 nanoparticles decreased, suggesting the formation of a soft magnetic phase. This new phase (Fe3Pd) was confirmed from x-ray diffraction measurements. For Fe50PdxPt50-x nanoparticles, the coercivity increases to more than 10 kOe with annealing temperature up to 650 °C (x=8). With increasing Pd content, the coercivity of the Fe50PdxPt50-x nanoparticles decreased, as expected since the anisotropy energy of bulk FePd material is only one third of that of bulk FePt.

  14. Size and alloying induced shift in core and valence bands of Pd-Ag and Pd-Cu nanoparticles

    SciTech Connect

    Sengar, Saurabh K.; Mehta, B. R.; Govind

    2014-03-28

    In this report, X-ray photoelectron spectroscopy studies have been carried out on Pd, Ag, Cu, Pd-Ag, and Pd-Cu nanoparticles having identical sizes corresponding to mobility equivalent diameters of 60, 40, and 20 nm. The nanoparticles were prepared by the gas phase synthesis method. The effect of size on valence and core levels in metal and alloy nanoparticles has been studied by comparing the values to those with the 60 nm nanoparticles. The effect of alloying has been investigated by comparing the valence and core level binding energies of Pd-Cu and Pd-Ag alloy nanoparticles with the corresponding values for Pd, Ag, and Cu nanoparticles of identical sizes. These effects have been explained in terms of size induced lattice contractions, alloying induced charge transfer, and hybridization effects. The observation of alloying and size induced binding energy shifts in bimetallic nanoparticles is important from the point of view of hydrogen reactivity.

  15. Synthesis of Pt-Pd bimetallic nanoparticles anchored on graphene for highly active methanol electro-oxidation

    NASA Astrophysics Data System (ADS)

    Zhang, Yuting; Chang, Gang; Shu, Honghui; Oyama, Munetaka; Liu, Xiong; He, Yunbin

    2014-09-01

    A simple, one-step reduction route was employed to synthesize bimetallic Pt-Pd nanoparticles (Pt-PdNPs) supported on graphene (G) sheets, in which the reduction of graphite oxide and metal precursor was carried out simultaneously using ascorbic acid as a soft reductant. The morphology and structure of Pt-PdNPs/G composites were characterized using X-ray diffraction, Transmission Electron Microscopy, Field Emission Scanning Electron Microscopy and X-ray Photoelectron Spectroscopy analysis. The results show that Pt-Pd bimetallic nanoparticles were successfully synthesized and evenly anchored on the graphene sheets. Electrochemical experiments, including cyclic voltammetry and chronoamperometric measurements, were performed to investigate the electrochemical and electrocatalytic properties of the Pt-PdNPs/G composites. It was found that Pt-PdNPs/G composites show better electrocatalytic activity and stability towards the electro-oxidation of methanol than its counterparts such as composites composed of graphene-supported monometallic nanoparticles (PtNPs/G, PdNPs/G) and free-standing (Pt-PdNPs) and Vulcan-supported bimetallic Pt-Pd nanoparticles (Pt-PdNPs/V). The results could be attributed to the synergetic effects of the Pt-Pd nanoparticles and the enhanced electron transfer of graphene. The electrocatalytic activity of Pt-PdNPs/G changed with the Pd content in the Pt-Pd alloy, and the best performance was achieved with a Pt-Pd ratio of 1/3 in an alkaline environment. Our study indicates the potential use of Pt-PdNPs/G as new anode catalyst materials for direct methanol fuel cells.

  16. Isolation and structural characterization of a silver-platinum nanocluster, Ag4Pt2(DMSA)4

    NASA Astrophysics Data System (ADS)

    Pedicini, Anthony; Reber, Arthur; Biltek, Scott; Sen, Ayusman; Khanna, Shiv

    2015-03-01

    Cluster assembled materials offer an attractive prospect of making nanoscale materials with tunable characteristics. Here, we report the synthesis, isolation, and characterization of the ligand-protected bimetallic cluster, Ag4Pt2(DMSA)4 (DMSA =meso-2,3,-dimercaptosuccinic acid) and its analogue, Ag4Pd2(DMSA)4. The procedure is similar to the one employed previously for the synthesis of Ag4Ni4(DMSA)4. Theoretical studies show that the Pt and Ni atoms are square planar in configuration. Furthermore, the dependence on the optical spectrum due to congener replacement of the transition metal is highlighted. Since the crystal field splitting of 5d orbitals is typically larger than that for 3d orbitals, we show the Pt-based cluster has an optical spectrum that is significantly blue shifted as compared to the Ni-based cluster. This work was supported by an Air Force Office of Scientific Research (AFOSR) Basic Research Initiative Grant FA9550-12-1-0481.

  17. Intermartensitic Transformation and Enhanced Exchange Bias in Pd (Pt) -doped Ni-Mn-Sn alloys.

    PubMed

    Dong, S Y; Chen, J Y; Han, Z D; Fang, Y; Zhang, L; Zhang, C L; Qian, B; Jiang, X F

    2016-01-01

    In this work, we studied the phase transitions and exchange bias of Ni50-xMn36Sn14Tx (T = Pd, Pt; x = 0, 1, 2, 3) alloys. An intermartensitic transition (IMT), not observed in Ni50Mn36Sn14 alloy, was induced by the proper application of negative chemical pressure by Pd(Pt) doping in Ni50-xMn36Sn14Tx (T = Pd, Pt) alloys. IMT weakened and was suppressed with the increase of applied field; it also disappeared with further increase of Pd(Pt) content (x = 3 for Pd and x = 2 for Pt). Another striking result is that exchange bias effect, ascribed to the percolating ferromagnetic domains coexisting with spin glass phase, is notably enhanced by nonmagnetic Pd(Pt) addition. The increase of unidirectional anisotropy by the addition of Pd(Pt) impurities with strong spin-orbit coupling was explained by Dzyaloshinsky-Moriya interactions in spin glass phase. PMID:27170057

  18. Intermartensitic Transformation and Enhanced Exchange Bias in Pd (Pt) -doped Ni-Mn-Sn alloys

    PubMed Central

    Dong, S. Y.; Chen, J. Y.; Han, Z. D.; Fang, Y.; Zhang, L.; Zhang, C. L.; Qian, B.; Jiang, X. F.

    2016-01-01

    In this work, we studied the phase transitions and exchange bias of Ni50−xMn36Sn14Tx (T = Pd, Pt; x = 0, 1, 2, 3) alloys. An intermartensitic transition (IMT), not observed in Ni50Mn36Sn14 alloy, was induced by the proper application of negative chemical pressure by Pd(Pt) doping in Ni50−xMn36Sn14Tx (T = Pd, Pt) alloys. IMT weakened and was suppressed with the increase of applied field; it also disappeared with further increase of Pd(Pt) content (x = 3 for Pd and x = 2 for Pt). Another striking result is that exchange bias effect, ascribed to the percolating ferromagnetic domains coexisting with spin glass phase, is notably enhanced by nonmagnetic Pd(Pt) addition. The increase of unidirectional anisotropy by the addition of Pd(Pt) impurities with strong spin-orbit coupling was explained by Dzyaloshinsky-Moriya interactions in spin glass phase. PMID:27170057

  19. Structures of small Pd Pt bimetallic clusters by Monte Carlo simulation

    NASA Astrophysics Data System (ADS)

    Cheng, Daojian; Huang, Shiping; Wang, Wenchuan

    2006-11-01

    Segregation phenomena of Pd-Pt bimetallic clusters with icosahedral and decahedral structures are investigated by using Monte Carlo method based on the second-moment approximation of the tight-binding (TB-SMA) potentials. The simulation results indicate that the Pd atoms generally lie on the surface of the smaller clusters. The three-shell onion-like structures are observed in 55-atom Pd-Pt bimetallic clusters, in which a single Pd atom is located in the center, and the Pt atoms are in the middle shell, while the Pd atoms are enriched on the surface. With the increase of Pd mole fraction in 55-atom Pd-Pt bimetallic clusters, the Pd atoms occupy the vertices of clusters first, then edge and center sites, and finally the interior shell. It is noticed that some decahedral structures can be transformed into the icosahedron-like structure at 300 and 500 K. Comparisons are made with previous experiments and theoretical studies of Pd-Pt bimetallic clusters.

  20. CO adsorption and kinetics on well-characterized Pd films on Pt(111) in alkaline solutions

    SciTech Connect

    Arenz, M.; Stamenkovic, V.; Wandelt, K.; Ross, P.N.; Markovic, N.M.

    2002-01-01

    The electrochemistry of CO on a bare Pt(111) electrode as well as a Pt(111) electrode modified with pseudomorphic thin palladium films has been studied in alkaline solution by means of Fourier transform infrared (FTIR) spectroscopy. First Pd films were prepared and well characterized in UHV and subsequently transferred into the electrochemical cell for the registration of the voltammetric profiles. The charge corresponding to the formation of underpotentially deposited hydrogen (H{sub upd}) on these Pt(111)-xPd surfaces was established in sulfuric acid solution as a function of x (0 {le} x {le} 1 Pd monolayer (ML)). All subsequent measurements were then performed on electrochemically deposited palladium films using the above H{sub upd}-charge vs. Pd coverage relationship to evaluate the amount of electrochemically deposited palladium. FTIR spectra for CO adsorbed on one monolayer and a submonolayer coverage are compared to those of the unmodified Pt(111) surface, all surfaces having identical 2D lattice structures. Infrared absorption bands of CO bound on either Pt(111) or Pt(111)-1ML Pd are clearly distinguished. Spectra of CO adsorbed on Pd submonolayers show characteristic features of both CO bound to Pt and to Pd, indicating that on Pt(111)-xPd surfaces there is no coupling between Pt-CO{sub ad} and Pd-CO{sub ad} molecules. The kinetics of CO oxidation on these surfaces is determined either by rotating disk electrode (RDE) measurements or by FTIR spectroscopy, monitoring the CO{sub 3}{sup 2-} production. The oxidation of CO{sub ad} on Pt(111) and on Pd modified platinum surfaces starts at the same potential, ca. at 0.2 V. The oxidation rate is, however, considerably lower on the Pt(111)-xPd surfaces than on the Pt(111) surface. The kinetics of CO oxidation appears to be determined by the nature of adsorbed hydroxyl anions (OH{sub ad}), which are more strongly (less active) adsorbed on the highly oxophilic Pd atoms.

  1. Ag on Pt(111): Changes in Electronic and CO Adsorption Properties upon PtAg/Pt(111) Monolayer Surface Alloy Formation.

    PubMed

    Diemant, Thomas; Schüttler, Konstantin M; Behm, R Jürgen

    2015-10-01

    The electronic and chemical (adsorption) properties of bimetallic Ag/Pt(111) surfaces and their modification upon surface alloy formation, that is, during intermixing of Ag and Pt atoms in the top atomic layer upon annealing, were studied by X-ray photoelectron spectroscopy (XPS) and, using CO as probe molecule, by temperature-programmed desorption (TPD) and infrared reflection absorption spectroscopy (IRRAS), respectively. The surface alloys are prepared by deposition of sub-monolayer Ag amounts on a Pt(111) surface at room temperature, leading to extended Ag monolayer islands on the substrate, and subsequent annealing of these surfaces. Surface alloy formation starts at ≈600-650 K, which is evidenced by core-level shifts (CLSs) of the Ag(3d5/2 ) signal. A distinct change of the CO adsorption properties is observed when going to the intermixed PtAg surface alloys. Most prominently, we find the growth of a new desorption feature at higher temperature (≈550 K) in the TPD spectra upon surface alloy formation. This goes along with a shift of the COad -related IR bands to lower wave number. Surface alloy formation is almost completed after heating to 700 K.

  2. Simultaneous tunable structure and composition of PtAg alloyed nanocrystals as superior catalysts.

    PubMed

    Fang, Caihong; Zhao, Jun; Zhao, Guili; Kuai, Long; Geng, Baoyou

    2016-08-11

    PtAg alloyed nanostructural catalysts were firstly prepared by co-reduction of AgNO3 and H2PtCl6 precursors in growth solution using a seed-mediated method. By simply changing the molar ratio of the metal precursors, the morphologies of the porous alloyed nanocrystals can be tuned from multipetals to multioctahedra. Simultaneously, the alloy composition can be varied from Pt76Ag24 to Pt66Ag34. The catalytic properties of the prepared PtAg alloyed nanocrystals with a tunable structure and composition were tentatively examined by choosing the reduction of 4-nitrophenol with NaBH4. The reaction rate normalized to the concentration of catalysts was calculated to be 318.9 s(-1) mol(-1) L and 277.4 s(-1) mol(-1) L for Pt70Ag30 and Pt66Ag34 porous catalysts, which is much higher than the pure Pt catalysts. Moreover, PtAg nanostructures can also serve as efficient electrocatalysts toward the methanol oxidation reaction, especially for Pt70Ag30 and Pt66Ag34 porous nanocrystals. The electrocatalytic activity and the durability were both highly enhanced compared to the commercial Pt/C catalyst. In addition, we also investigated the enhancement mechanism.

  3. Comparison of Pt and Pd catalysts for hydrogen pump separation from reformate

    NASA Astrophysics Data System (ADS)

    Wu, Xuemei; Benziger, Jay; He, Gaohong

    2012-11-01

    Hydrogen recovery from CO2/H2 reformate mixtures by selective electrochemical pumping was compared from carbon supported Pt and Pd catalysts. Catalyst coated membranes were prepared by air-brushing a suspension of commercially available 20 wt% Pt/C or 20 wt% Pd/C catalysts and solubilized Nafion in methanol onto Nafion 115 membranes. Electrochemical activity and separation efficiency for the different catalyst layer formulations were evaluated by cyclic voltammetry, polarization and potentiostatic hydrogen pumping. The effective membrane-electrode-assembly (MEA) resistance increased due to dilution of H2 by CO2; the effective MEA resistance was greater for Pd/C catalysts than for Pt/C catalysts. CO2 adsorbed more strongly to Pd catalysts than Pt catalysts reducing the electrochemical active surface area available for hydrogen oxidation/reduction. Pd/C catalysts had an energy efficiency for hydrogen recovery from reformate mixtures approximately 80% that of Pt catalysts. Because Pd is ten times less costly than Pt the results presented here suggest that Pd/C catalysts would be a promising candidate for hydrogen pumps to recover H2 from reformate mixtures.

  4. Pt/Pd electrocatalyst electrons for fuel cells

    DOEpatents

    Stonehart, P.

    1981-11-03

    This invention relates to improved electrochemical cells and to novel electrodes for use therein. In particular, the present invention comprises a fuel cell used primarily for the consumption of impure hydrogen fuels containing carbon monoxide or carbonaceous fuels where the electrode in contact with the fuel is not substantially poisoned by carbon monoxide. The anode of the fuel cell comprises a Pd/Pt alloy supported on a graphitized or partially graphitized carbon material. Fuel cells which comprise as essential elements a fuel electrode, an oxidizing electrode, and an electrolyte between said electrodes are devices for the direct production of electricity through the electrochemical combustion of a fuel and oxidant. These devices are recognized for their high efficiency as energy conversion units, since unlike conventional combustion engines, they are not subject to the limitations of the Carnot heat cycle. It is the primary object of the present invention to provide an electrode having high electrochemical activity for an electrochemical cell. It is another object of the present invention to provide an electrode having an electro-catalyst which is highly resistant to the corrosive environment of an electrochemical cell.

  5. Cluster Expansion for Pt/Pd-Al binary alloys

    NASA Astrophysics Data System (ADS)

    Carr, Derek

    2010-10-01

    Pure platinum and pure palladium are too soft for typical jewelry applications. Adding small amounts of other metals can significantly increase their performance. However, international hallmarking standards require the alloys to be 95% pure by weight. How does one achieve significant improvements in performance adding only small amounts (5 wt-%) of other metals? Significant improvements are possible with small additions when the added element forms an ordered array in the Pt/Pd matrix. Our task is to identify, among an infinite set of possibilities, arrangements that are stable and which will form easily. One solution is to use a cluster expansion. A cluster expansion is a fast method which can calculate the energy of all candidate crystal superstructures. Using the cluster expansion, we identify the ``ground states,'' the atomic arrangements that are the most stable. After the ground states are identified, Monte Carlo simulations are used to predict the order-disorder transition temperatures. The transition temperatures indicate the feasibility of making the ordered alloys in the laboratory.

  6. Spin pumping damping and magnetic proximity effect in Pd and Pt spin-sink layers

    NASA Astrophysics Data System (ADS)

    Caminale, M.; Ghosh, A.; Auffret, S.; Ebels, U.; Ollefs, K.; Wilhelm, F.; Rogalev, A.; Bailey, W. E.

    2016-07-01

    We investigated the spin pumping damping contributed by paramagnetic layers (Pd, Pt) in both direct and indirect contact with ferromagnetic Ni81Fe19 films. We find a nearly linear dependence of the interface-related Gilbert damping enhancement Δ α on the heavy-metal spin-sink layer thicknesses tN in direct-contact Ni81Fe19 /(Pd, Pt) junctions, whereas an exponential dependence is observed when Ni81Fe19 and (Pd, Pt) are separated by 3 nm Cu. We attribute the quasilinear thickness dependence to the presence of induced moments in Pt, Pd near the interface with Ni81Fe19 , quantified using x-ray magnetic circular dichroism measurements. Our results show that the scattering of pure spin current is configuration-dependent in these systems and cannot be described by a single characteristic length.

  7. Drift and inhomogeneity of Pt/Pd thermocouples exposed to around 1500 °C

    NASA Astrophysics Data System (ADS)

    Ogura, H.; Izuchi, M.; Tamba, J.; Arai, M.

    2013-09-01

    To investigate the thermoelectric stability of Pt/Pd thermocouples at around 1500 °C which is the upper application limit of Pt/Pd thermocouples, a large-sized Pd-C eutectic-point (1492 °C) cell was constructed and employed to examine the drift and inhomogeneity of four thermocouples. The drift of the Pt/Pd thermocouples during exposure was measured in-situ by repeating the realization of the Pd-C eutectic point. The inhomogeneity was examined several times during the drift measurement by moving the thermocouple slowly from full immersion position to 200 mm upwards while a melting plateau was progressing. In addition, to investigate the cause of the drift and inhomogeneity, thermocouples were scanned in a water heat-pipe furnace at 140 °C before and after the exposure at around 1500 °C.

  8. Impurity scattering effect in Pd-doped superconductor SrPt3P

    NASA Astrophysics Data System (ADS)

    Hu, Kang-Kang; Gao, Bo; Ji, Qiu-Cheng; Ma, Yong-Hui; Zhang, Hui; Mu, Gang; Huang, Fu-Qiang; Cai, Chuan-Bing; Xie, Xiao-Ming

    2016-08-01

    We present a systematic study of the impurity scattering effect induced by Pd dopants in the superconductor SrPt3P. Using a solid-state reaction method, we fabricated the Pd-doped superconductor Sr(Pt1- x Pd x )3P.We found that the residual resistivity ρ 0 increases quickly with Pd doping, whereas the residual resistance ratio (RRR) displays a dramatic reduction. In addition, both the nonlinear field-dependent behavior of the Hall resistivity ρ xy and the strong temperature dependence of the Hall coefficient R H at low temperature are suppressed by Pd doping. All the experimental results can be explained by an increase in scattering by impurities induced by doping. Our results suggest that the Pt position is very crucial to the carrier conduction in the present system.

  9. Structural and Electronic Transformations of Pt/C, Pd@Pt(1 ML)/C and Pd@Pt(2 ML)/C Cathode Catalysts in Polymer Electrolyte Fuel Cells during Potential-step Operating Processes Characterized by In-situ Time-resolved XAFS

    NASA Astrophysics Data System (ADS)

    Nagamatsu, Shin-ichi; Takao, Shinobu; Samjeské, Gabor; Nagasawa, Kensaku; Sekizawa, Oki; Kaneko, Takuma; Higashi, Kotaro; Uruga, Tomoya; Gayen, Sirshendu; Velaga, Srihari; Saniyal, Milan K.; Iwasawa, Yasuhiro

    2016-06-01

    The dynamic structural and electronic transformations of Pt/C, Pd@Pt(1 ML)/C, Pd@Pt(2 ML)/C cathode catalysts in polymer electrolyte fuel cells (PEFCs) during the potential-step operating processes between 0.4 and 1.4 VRHE (potential vs RHE) were characterized by in-situ (operando) time-resolved Pt LIII-edge quick-XAFS at 100 ms time-resolution. Potential-dependent surface structures and oxidation states of Pt, Pd@Pt(1 ML) and Pd@Pt(2 ML) nanoparticles on carbon at 0.4 and 1.4 VRHE were also analyzed by in-situ Pt LIII-edge and Pd K-edge quick-XAFS. The Pt, Pd@Pt(1 ML) and Pd@Pt(2 ML) nanoparticle surfaces were restructured and disordered at 1.4 VRHE, which were induced by strong Pt-O bonds as well as alloying effects. The rate constants for the changes of Pt valence, CN(Pt-Pt), CN(Pt-Pd) and CN(Pt-O) (CN: coordination number) in the potential-step operating processes were also determined and discussed in relation to the origin of oxygen reduction reaction (ORR) activities of the Pt/C, Pd@Pt(1 ML)/C and Pd@Pt(2 ML)/C cathode catalysts.

  10. Contact Resistance of Ti-Si-C-Ag and Ti-Si-C-Ag-Pd Nanocomposite Coatings

    NASA Astrophysics Data System (ADS)

    Sarius, N. G.; Lauridsen, J.; Lewin, E.; Jansson, U.; Högberg, H.; Öberg, Å.; Sarova, G.; Staperfeld, G.; Leisner, P.; Eklund, P.; Hultman, L.

    2012-03-01

    Ti-Si-C-Ag-Pd and Ti-Si-C-Ag nanocomposite coatings were deposited by direct-current magnetron sputtering on Cu substrates with an electroplated Ni layer. Analytical electron microscopy, x-ray diffraction, and x-ray photoelectron spectroscopy show that the nanocomposites consist of TiC, Ag:Pd, and amorphous SiC. The contact resistance of these coatings against a spherical Au-Co surface was measured for applied contact forces up to 5 N. Ti-Si-C-Ag-Pd coatings with Ag:Pd top coating had ~10 times lower contact resistance at contact forces below 1 N (~10 mΩ at ~0.1 N), and 2 to 3 times lower for contact forces around 5 N (<1 mΩ at 5 N), compared with the Ti-Si-C-Ag coating.

  11. Selective biosorption behavior of Escherichia coli biomass toward Pd(II) in Pt(IV)-Pd(II) binary solution.

    PubMed

    Kim, Sok; Song, Myung-Hee; Wei, Wei; Yun, Yeoung-Sang

    2015-01-01

    This study reports a new finding that the industrial waste biomass of Escherichia coli is capable of selective binding of Pd(II) in the Pd(II)-Pt(IV) bimetal solution. Batch sorption experiments with E. coli were carried out at different initial metal concentrations in single and bimetal systems. In the single metal systems, the maximum sorption capacities of E. coli for Pt(IV) and Pd(II) were found to be 45.65 ± 2.04 and 38.87 ± 2.08 mg/g, respectively. Meanwhile, in the bimetal system, the maximum sorption capacities for Pd(II) and Pt(IV) were 33.16 ± 1.53 and 7.32 ± 0.29 mg/g, respectively, which corresponded to 4.53 times of selective adsorption toward Pd(II). In order to understand the underlying reason, ion exchange resins (TP214 and Amberjet 4200) with different amine types were compared with the E. coli biomass. As a result, it was found that the sorbents containing primary amine groups could selectively adsorb Pd(II) more easily in the binary mixture.

  12. Effects of the PdO nanoflake support on electrocatalytic activity of Pt nanoparticles toward methanol oxidation in acidic solutions

    NASA Astrophysics Data System (ADS)

    Chen, Chung-Shou; Pan, Fu-Ming

    2012-06-01

    We prepared PdO nanoflake thin films on carbon cloths by reactive sputtering deposition, and studied electrocatalytic performance of Pt nanoparticles electrodeposited on the PdO thin film in methanol oxidation reaction (MOR) in acidic media. The PdO nanoflake thin film exhibits a cyclic voltamperometric (CV) behavior similar to metallic Pd electrodes because a metallic Pd surface layer is formed on the PdO thin film electrode under the CV measurement condition. The nanoflake morphology of the PdO electrode provides a large surface area for Pt nanoparticle loading, resulting in a large electrochemical active surface area (ESA). The Pt/PdO electrode has a high electrocatalytic activity toward MOR, and the good electrocatalytic performance of the Pt/PdO electrode is ascribed to a high CO tolerance and the large ESA. We suggest that the high CO tolerance of the catalyst on the Pt/PdO electrode is a result of the synergism of the bifunctional mechanism and the electronic effect. XPS analyses indicate that negative charge transfer occurs from the PdO support to the Pt nanoparticles, indicating the presence of the electronic effect. Pt nanoparticles on the PdO support can greatly alleviate the nanoflake damage during the CV measurement, which results from anodic dissolution of metal Pd from the PdO support in acidic media.

  13. The mechanism of Ag top layer on the coercivity enhancement of FePt thin films

    SciTech Connect

    Zhao, Z.L.; Ding, J.; Yi, J.B.; Chen, J.S.; Zeng, J.H.; Wang, J.P.

    2005-05-15

    The magnetic properties of the FePt thin films with a Ag top layer prepared by magnetron sputtering have been studied. With 4 nm Ag layer deposited right after the deposition of FePt layer, the ordering temperature of the L1{sub 0} FePt phase decreased to 350 deg. C or below. X-ray photoelectron spectroscopy results indicate that Ag has diffused into the FePt layer when Ag was deposited at 350 deg. C, while Ag remains on the top of the FePt when Ag was deposited at room temperature. The Ag top layer deposited at 350 deg. C was also found to protect the FePt layer from oxidation.

  14. Pt-Decorated PdCo@Pd/C Core-Shell Nanoparticles with Enhanced Stability and Electrocatalytic Activity for the Oxygen Reduction Reaction

    SciTech Connect

    Wang, Deli; Xin, Huolin L.; Yu, Yingchao; Wang, Hongsen; Rus, Eric; Muller, David A.; Abruña, Héctor D.

    2010-11-24

    A simple method for the preparation of PdCo@Pd core-shell nanoparticles supported on carbon based on an adsorbate-induced surface segregation effect has been developed. The stability of these PdCo@Pd nanoparticles and their electrocatalytic activity for the oxygen reduction reaction (ORR) were enhanced by decoration with a small amount of Pt deposited via a spontaneous displacement reaction. The facile method described herein is suitable for large-scale, lower-cost production and significantly lowers the Pt loading and thus the cost. The as-prepared PdCo@Pd and Pd-decorated PdCo@Pd nanocatalysts have a higher methanol tolerance than Pt/C in the ORR and are promising cathode catalysts for fuel cell applications.

  15. Gram-Scale-Synthesized Pd2Co-Supported Pt Monolayer Electrocatalysts for Oxygen Reduction Reaction

    SciTech Connect

    Zhou, W.; Sasaki, K; Su, D; Zhu, Y; Wang, J; Adzic, R

    2010-01-01

    Gram-scale synthesis of Pt{sub ML} electrocatalysts with a well-defined core-shell structure has been carried out using method involving galvanic displacement of an underpotential deposition Cu layer. The Pt shell thickness can be controlled by stepwise deposition. The Pt{at}Pd{sub 2}Co/C nanoparticles were characterized by X-ray powder diffraction, aberration-corrected scanning transmission electron microscopy, high-resolution energy-loss spectrometry, and in situ X-ray absorption spectroscopy. A complete Pt shell of 0.6 nm on a Pd{sub 2}Co core has been confirmed. The Pt{at}Pd{sub 2}Co/C core-shell electrocatalysts showed a very high activity for the oxygen reduction reaction; the Pt mass and specific activity were 0.72 A mg{sub Pt}{sup -1} and 0.5 mA cm{sup -2}, respectively (3.5 and 2.5 times higher than the corresponding values for commercial Pt catalysts), at 0.9 V in 0.1 M HClO{sub 4} at room temperature. In an accelerated potential cycling test, a loss in active surface area and a decrease in catalytic activity for gram-scale-synthesized Pt{sub ML} catalysts were also determined.

  16. Millimeter thick ionic polymer membrane-based IPMCs with bimetallic Pd-Pt electrodes

    NASA Astrophysics Data System (ADS)

    Palmre, Viljar; Kim, Sung Jun; Kim, Kwang

    2011-04-01

    Ionic polymer metal composites (IPMC) are a low-voltage driven Electroactive Polymers (EAP) that can be used as actuators or sensors. This paper presents a comparative study of millimeter thick ionic polymer membrane-based IPMCs with high-performance Pd-Pt electrodes and conventional Pt electrodes. IPMCs assembled with different electrodes are characterized in terms of electromechanical, -chemical and mechanolelectrical properties. The SEM and energy dispersive X-ray (EDS) analysis are used to investigate the distribution of deposited electrode metals in the cross-section of Pd-Pt IPMCs. The study shows that IPMCs assembled with millimeter thick ionic polymer membranes and bimetallic Pd-Pt electrodes are superior in mechanoelectrical sensing and, also, show considerably higher blocking forces compared to the conventional type of IPMCs. Blocking forces more than 30 grams are measured under 4V DC. However, the actuation response is slower than conventional IPMCs having approximately 0.2-0.3 mm thickness.

  17. Cyclometalated heteronuclear Pt/Ag and Pt/Tl complexes: a structural and photophysical study.

    PubMed

    Jamali, Sirous; Ghazfar, Reza; Lalinde, Elena; Jamshidi, Zahra; Samouei, Hamidreza; Shahsavari, Hamid R; Moreno, M Teresa; Escudero-Adán, Eduardo; Benet-Buchholz, Jordi; Milic, Dalibor

    2014-01-21

    To investigate the factors influencing the luminescent properties of polymetallic cycloplatinated complexes a detailed study of the photophysical and structural properties of the heteronuclear complexes [Pt2Me2(bhq)2(μ-dppy)2Ag2(μ-acetone)](BF4)2, 2, [PtMe(bhq)(dppy)Tl]PF6, 3, and [Pt2Me2(bhq)2(dppy)2Tl]PF6, 4, [bhq = benzo[h]quinoline, dppy = 2-(diphenylphosphino)pyridine] was conducted. Complexes 3 and 4 synthesized by the reaction of [PtMe(bhq)(dppy)], 1, with TlPF6 (1 or 1/2 equiv.) and stabilized by unsupported Pt-Tl bonds as revealed by multinuclear NMR spectroscopy and confirmed by X-ray crystallography for 3. DFT calculations for the previously reported butterfly Pt2Ag2 cluster 2 reveal that in the optimized geometry the bridging acetone molecule is removed and the metal core displays a planar-shaped geometry in which according to a QTAIM calculation and natural bond orbital (NBO) analysis the Ag···Ag metallophilic interaction is strengthened. In contrast to the precursor 1, which is only emissive in glassy solutions ((3)MLCT 485 nm), all 2-4 heteropolynuclear complexes display intense emissions in the solid state and in glassy solutions. Time-dependent density functional theory (TD-DFT) is used to elucidate the origin of the electronic transitions in the heteronuclear complexes 2 and 3. The low energy absorption and intense orange emission for cluster 2 (solid 77 K and glass) are attributed to metal-metal to ligand charge transfer (MM'LCT) with a minor L'LCT contribution. For 3 and 4 two different bands are developed: the high energy band (602-630 nm) observed for 4 at 77 K (solid, glass) and in diluted glasses for 3 is ascribed to emission from discrete Pt2Tl units of mixed (3)L'LCT/(3)LM'CT origin. However, the low energy band (670-690 nm) observed at room temperature (solid) for both complexes and also in concentrated glasses for 3 is assigned to (3)ππ excited states arising from intermolecular interactions. PMID:24165802

  18. Magnetic phase diagram in CePd 1- xAg x

    NASA Astrophysics Data System (ADS)

    Besnus, M. J.; Godart, C.; Kappler, J. P.; Sereni, J.

    1994-04-01

    Magnetic susceptibility, high field magnetization and specific heat measurements are presented on CePd 1- xAg x for 0 ≤ x ≤ 0.175. The strong effect of Pd substitution by Ag stresses the instability of the compound towards noble metals solutes or electron-like impurities.

  19. Evaluation of bimetallic catalyst PtAg/C as a glucose-tolerant oxygen reduction cathode

    NASA Astrophysics Data System (ADS)

    Guerra-Balcázar, M.; Cuevas-Muñiz, F. M.; Álvarez-Contreras, L.; Arriaga, L. G.; Ledesma-García, J.

    2012-01-01

    PtAg/C nanoparticles were synthesized by chemical reduction and evaluated for the oxygen reduction reaction (ORR) in the absence and presence of glucose. PtAg/C catalyst formed onion-like layered structures, which are uniformly distributed on the support. PtAg/C showed activity comparable to that of Pt/C ETEK for ORR. Further, the catalyst exhibited high selectivity for ORR in the presence of glucose. PtAg/C was evaluated as cathode in a microfluidic fuel cell operated with high concentration of glucose (100 mM) as fuel. The results demonstrated that the use of PtAg/C as cathode electrode achieved higher selectivity and better performance compared with Pt/C catalyst.

  20. Synthesis and electrocatalytic properties of PtBi nanoplatelets and PdBi nanowires

    NASA Astrophysics Data System (ADS)

    Liao, Hanbin; Zhu, Jinghan; Hou, Yanglong

    2013-12-01

    We have demonstrated a one-pot, facile and rapid strategy to synthesize novel PtBi nanoplatelets (NPLs) and PdBi nanowires (NWs) with controlled shape, size, and composition in the presence of oleylamine (OAm) and NH4Br. In contrast to the conventional face centered cubic (fcc) structure of Pt-based NPs, PtBi possesses a chemically ordered intermetallic hexagonal close packed (hcp) structure. Using this uniaxial crystal structural character of PtBi, we succeed in synthesizing two-dimensional (2-D) PtBi NPLs. Significantly, the electrochemical studies indicate that the as-prepared 2-D PtBi NPLs exhibit enhanced electrocatalytic activity toward formic acid and methanol oxidation with larger oxidation current density, higher tolerance to CO poisoning, and more negative onset potential in comparison with the commercial Pt/C catalyst. This is attributed to the addition of second metal Bi. In addition, to the best of our knowledge, this is the first time that synthesis of one-dimensional (1-D) PdBi alloy NWs has been reported. The as-synthesized 1-D PdBi bimetallic NWs may find promising potential applications in various fields, such as fuel cells, electrochemical sensors, and organocatalysis.We have demonstrated a one-pot, facile and rapid strategy to synthesize novel PtBi nanoplatelets (NPLs) and PdBi nanowires (NWs) with controlled shape, size, and composition in the presence of oleylamine (OAm) and NH4Br. In contrast to the conventional face centered cubic (fcc) structure of Pt-based NPs, PtBi possesses a chemically ordered intermetallic hexagonal close packed (hcp) structure. Using this uniaxial crystal structural character of PtBi, we succeed in synthesizing two-dimensional (2-D) PtBi NPLs. Significantly, the electrochemical studies indicate that the as-prepared 2-D PtBi NPLs exhibit enhanced electrocatalytic activity toward formic acid and methanol oxidation with larger oxidation current density, higher tolerance to CO poisoning, and more negative onset potential

  1. Preparation of PdAg and PdAu nanoparticle-loaded carbon black catalysts and their electrocatalytic activity for the glycerol oxidation reaction in alkaline medium

    NASA Astrophysics Data System (ADS)

    Lam, Binh Thi Xuan; Chiku, Masanobu; Higuchi, Eiji; Inoue, Hiroshi

    2015-11-01

    PdAg and PdAu alloy nanoparticle catalysts for the glycerol oxidation reaction (GOR) were prepared at room temperature by a wet method. The molar ratio of the precursors controlled the bulk composition of the PdAg and PdAu alloys, and their surface composition was Ag-enriched and Pd-enriched, respectively. On PdAg-loaded carbon black (PdAg/CB) electrodes, the onset potential of GOR was 0.10-0.15 V more negative than on the Pd/CB electrode due to the electronic effect. The ratio of GOR peak current densities in the backward and forward sweeps of CVs (ib/if) was smaller because of the improved tolerance to the poisoning species. The ratio of the GOR current density at 60 and 5 min (i60/i5) for the PdAg/CB electrodes was higher for more negative potentials than the Pd/CB electrode. In contrast, the PdAu-loaded CB (PdAu/CB) electrodes had an onset potential of GOR similar to the Pd/CB electrode and a higher GOR peak current density owing to the bi-functional effect. However, the ib/if ratio was higher for PdAu/CB because of the increase in ib as the Pd surface was recovered, and the i60/i5 ratio was higher for more positive potentials, similar to the Pd/CB electrode.

  2. PdCuPt Nanocrystals with Multibranches for Enzyme-Free Glucose Detection.

    PubMed

    Fu, Shaofang; Zhu, Chengzhou; Song, Junhua; Engelhard, Mark; Xia, Haibing; Du, Dan; Lin, Yuehe

    2016-08-31

    By carefully controlling the synthesis condition, branched PtCu bimetallic templates were synthesized in aqueous solution. After the galvanic replacement reaction between PtCu templates and the Pt precursors, PdCuPt trimetallic nanocrystals with branched structures were obtained. Owing to the open structure and the optimized composition, the electrochemical experimental results reveal that the PdCuPt trimetallic nanocrystals possess high electrocatalytic activity, selectivity and stability for the oxidation of glucose in alkaline solution. In detail, a detection limit of 1.29 μM and a sensitivity of 378 μA/mM/cm(2) are achieved. The good electrocatalytic performance should be attributed to the unique branched nanostructure as well as the synergistic effect among metals. The superior catalytic properties suggest that these nanocrystals are promising for enzyme-free detection of glucose. PMID:27494365

  3. Size-dependent adhesion energy of shape-selected Pd and Pt nanoparticles

    NASA Astrophysics Data System (ADS)

    Ahmadi, M.; Behafarid, F.; Cuenya, B. Roldan

    2016-06-01

    Thermodynamically stable shape-selected Pt and Pd nanoparticles (NPs) were synthesized via inverse micelle encapsulation and a subsequent thermal treatment in vacuum above 1000 °C. The majority of the Pd NPs imaged via scanning tunneling microscopy (STM) had a truncated octahedron shape with (111) top and interfacial facets, while the Pt NPs were found to adopt a variety of shapes. For NPs of identical shape for both material systems, the NP-support adhesion energy calculated based on STM data was found to be size-dependent, with large NPs (e.g. ~6 nm) having lower adhesion energies than smaller NPs (e.g. ~1 nm). This phenomenon was rationalized based on support-induced strain that for larger NPs favors the formation of lattice dislocations at the interface rather than a lattice distortion that may propagate through the smaller NPs. In addition, identically prepared Pt NPs of the same shape were found to display a lower adhesion energy compared to Pd NPs. While in both cases, a transition from a lattice distortion to interface dislocations is expected to occur with increasing NP size, the higher elastic energy in Pt leads to a lower transition size, which in turn lowers the adhesion energy of Pt NPs compared to Pd.Thermodynamically stable shape-selected Pt and Pd nanoparticles (NPs) were synthesized via inverse micelle encapsulation and a subsequent thermal treatment in vacuum above 1000 °C. The majority of the Pd NPs imaged via scanning tunneling microscopy (STM) had a truncated octahedron shape with (111) top and interfacial facets, while the Pt NPs were found to adopt a variety of shapes. For NPs of identical shape for both material systems, the NP-support adhesion energy calculated based on STM data was found to be size-dependent, with large NPs (e.g. ~6 nm) having lower adhesion energies than smaller NPs (e.g. ~1 nm). This phenomenon was rationalized based on support-induced strain that for larger NPs favors the formation of lattice dislocations at the

  4. [Atomic emission spectrometry determination of Au, Pt and Pd after separation and enrichment by hyperbranched polymer].

    PubMed

    Li, Hui-Zhi; Zhai, Dian-Tang; Shou, Chong-Qi; Zhao, Shu-Ying; Wei, Qin

    2006-09-01

    The present paper shows that the trace amount of gold, platinum and palladium in hydrochloric acid solution can be concentrated by hyperbranched polymer. The new reagent has a rapid adsorption rate and big concentrating capacity. The determination of trace Au, Pt and Pd in sample using carbon powder and strontium carbonate as buffer was carried out by atomic emission spectrometry(AES). Zirconium was selected as internal standard line. The sample was directly loaded into ordinary electrode. The method is simple, rapid and accurate. The condition of determination, and factors of influence were studied. The analysis line of Au, Pt and Pd is 312.3, 306.5 and 311.4 nm respectively. The internal standard line of Zr is 310.7 nm. The linear range of the determination of Au, Pt and Pd is 0-0. 20%, 0-0. 40% and 0-0. 20% respectively. The detection limit of Au, Pt and Pd is 0.010%, 0.0030% and 0.0030% respectively. The method has been applied to the determination of Au, Pt and Pd with satisfactory results.

  5. Hydrogen sensitivity of Pt-Pd/rho-CaFe/sub 2/O/sub 4/ diode

    SciTech Connect

    Matsumoto, Y.; Hombo, J. . Faculty of Engineering); Yoshikawa, T.; Sato, E. . Faculty of Engineering)

    1989-03-01

    Hydrogen sensitivity of the current at the Pt-Pd/rho-CaFe/sub 2/O/sub 4/ diode has been studied and compared with that of the Pt-Pd/eta-TiO/sub 2/ diode. The current decreased by H/sub 2/-on in air, but was not recovered by H/sub 2/-off at room temperature. The latter result is different from that for the Pt-Pd/TiO/sub 2/ diode, indicating a mechanism other than the change of the work function of the metal is involved. The Schottky barrier was estimated from activation energy and photocurrent measurements. A surface state mechanism for the H/sub 2/ response of the Pt-Pd/CaFe/sub 2/O/sub 4/ diode is proposed. In this case, the Pt-Pd acts as the catalyst for the reaction of H/sub 2/ with surface states. This mechanism is important for the diode type gas sensor using the semiconductors which show the Fermi level pinning.

  6. Mixed-phase Pd-Pt bimetallic alloy on graphene oxide with high activity for electrocatalytic applications

    NASA Astrophysics Data System (ADS)

    Khan, Majid; Yousaf, Ammar Bin; Chen, Mingming; Wei, Chengsha; Wu, Xibo; Huang, Ningdong; Qi, Zeming; Li, Liangbin

    2015-05-01

    Bimetallic PdPt alloy nanoparticles on graphene oxide (GO) have been prepared by a simple and facile chemical route, in which the reduction of metal precursors is carried out using CO as a reductant. Structural and morphological characterizations of GO/PdPt composites are performed using X-ray diffraction, X-ray photoelectron spectroscopy analysis and transmission electron microscopy. It is found that PdPt bimetallic nanoparticles are successfully synthesized and uniformly attached on the graphene sheets. The electrocatalytic and electrochemical properties of GO/PdPt composites including methanol oxidation reaction (MOR), oxygen reduction reaction (ORR) and methanol tolerant oxygen reduction reaction (MTORR) are studied in HClO4 aqueous solution. A significant improvement in the electrocatalytic activities is observed by increasing the atomic ratio of Pt in PdPt bimetallic alloys compared to the freestanding Pd nanoparticles on GO. The prepared GO/PdPt composites with an (Pd:Pt) atomic ratio of 40:60 exhibits higher methanol oxidation activity, higher specific ORR activity and better tolerance to CO poisoning. The results can be attributed to the collective effects of the PdPt nanoparticles and the enhanced electron transfer of graphene.

  7. Local density of unoccupied states in ion-beam-mixed Pd-Ag alloys

    SciTech Connect

    Chae, K.H.; Jung, S.M.; Lee, Y.S.; Whang, C.N.; Jeon, Y.; Croft, M.; Sills, D.; Ansari, P.H.; Mack, K.

    1996-04-01

    X-ray absorption spectroscopy (XAS) measurements have been used to probe the electronic structure of ion-beam-mixed (IBM) Pd-Ag thin films with bulk alloys being studied for comparison. Pd {ital L}{sub 3} and Ag {ital L}{sub 3} absorption edges for pure Pd, Ag, and Pd{sub 1{minus}{ital x}}Ag{sub {ital x}} alloys are discussed. Structural information from both x-ray diffraction and the XAS fine structure oscillations are discussed. The observed decrease of the white-line feature strength, at the Pd {ital L}{sub 3} edge, indicates that the local density of unoccupied Pd 4{ital d} states declines upon alloying with Ag in a manner similar to that observed in previous bulk studies. However, while the Pd {ital d}-hole count decreases monotonically for bulk alloys, in the IBM alloys it saturates at higher levels in the Ag-rich materials. This disparity is interpreted on the basis of a modified charge transfer due to structural differences in the IBM alloys. The Ag {ital L}{sub 3} near-edge region is largely unchanged in these alloys, indicating that the charge transferred away from the Ag site is dominantly of {ital non}-{ital d} type. Our experimental results are discussed in the context of recent electronic structure calculations and of previous work on this alloy system. {copyright} {ital 1996 The American Physical Society.}

  8. Core-shell Au@Pd nanoparticles with enhanced catalytic activity for oxygen reduction reaction via core-shell Au@Ag/Pd constructions

    PubMed Central

    Chen, Dong; Li, Chengyin; Liu, Hui; Ye, Feng; Yang, Jun

    2015-01-01

    Core-shell nanoparticles often exhibit improved catalytic properties due to the lattice strain created in these core-shell particles. Herein, we demonstrate the synthesis of core-shell Au@Pd nanoparticles from their core-shell Au@Ag/Pd parents. This strategy begins with the preparation of core-shell Au@Ag nanoparticles in an organic solvent. Then, the pure Ag shells are converted into the shells made of Ag/Pd alloy by galvanic replacement reaction between the Ag shells and Pd2+ precursors. Subsequently, the Ag component is removed from the alloy shell using saturated NaCl solution to form core-shell Au@Pd nanoparticles with an Au core and a Pd shell. In comparison with the core-shell Au@Pd nanoparticles upon directly depositing Pd shell on the Au seeds and commercial Pd/C catalysts, the core-shell Au@Pd nanoparticles via their core-shell Au@Ag/Pd templates display superior activity and durability in catalyzing oxygen reduction reaction, mainly due to the larger lattice tensile effect in Pd shell induced by the Au core and Ag removal. PMID:26144550

  9. Phase stability and magnetism in NiPt and NiPd alloys

    NASA Astrophysics Data System (ADS)

    Paudyal, Durga; Mookerjee, Abhijit

    2004-08-01

    We show that the differences in stability of 3d-5d NiPt and 3d-4d NiPd alloys arise mainly due to relativistic corrections. The magnetic properties of disordered NiPd and NiPt alloys also differ due to these corrections, which lead to increase in the separation between the s-d bands of 5d elements in these alloys. For the magnetic case we also analyse the results in terms of splitting of majority and minority spin d band centres of the 3d elements. We further examine the effect of relativistic corrections to the pair energies and order-disorder transition temperatures in these alloys. The magnetic moments and Curie temperatures have also been studied along with the short range ordering/segregation effects in NiPt/NiPd alloys.

  10. The role of Pd in the transport of Ag in SiC

    NASA Astrophysics Data System (ADS)

    Olivier, E. J.; Neethling, J. H.

    2013-01-01

    This paper presents results in support of a newly proposed transport mechanism to account for the release of Ag from intact TRISO particles during HTR reactor operation. The study reveals that the migration of Ag in polycrystalline SiC can occur in association with Pd, a relatively high yield metallic fission product. The migration takes place primarily along grain boundary routes, seen in the form of distinct Pd, Ag and Si containing nodules. Pd is known to rapidly migrate to the SiC and iPyC interface within TRISO particles during operation. It has been shown to chemically corrode the SiC to form palladium silicides. These palladium silicides are found present along SiC grain boundaries in nodule like form. It is suggested that Ag penetrates these nodules together with the palladium silicide, to form a Pd, Ag and Si solution capable of migrating along SiC grain boundaries over time.

  11. PdPt catalyst synthesized using a gas aggregation source and magnetron sputtering for fuel cell electrodes

    NASA Astrophysics Data System (ADS)

    Caillard, A.; Cuynet, S.; Lecas, T.; Andreazza, P.; Mikikian, M.; Thomann, A.-L.; Brault, P.

    2015-12-01

    PdPt catalysts with different morphologies and atomic ratios have been synthesized on native SiO2/Si and on proton exchange membranes. The combination of the gas aggregation source and magnetron sputtering techniques allows the formation of quasi core-shell Pd0.97Pt0.03@Pt nanoclusters. Transmission electron microscopy and grazing incidence wide-angle x-ray scattering measurements of the Pd-rich core reveal a mean diameter of 4 nm and a face-centered cubic structure. The Pt shell around half of the Pd-rich core is formed by magnetron sputtering, and increases the nanocluster diameter (up to 10 nm) and the overall Pt content (up to 85%). Membranes coated by the PdPt core catalyst and PdPt@Pt catalyst (resulting in the formation of catalyst-coated membranes) are incorporated into fuel cells and their electrical characteristics are measured. The association of the two deposition techniques results in the formation of quasi core-shell PdPt@Pt nanoclusters, improving the start-up step of the fuel cell.

  12. Geometric structures of thin film: Pt on Pd(110) and NiO on Ni(100)

    SciTech Connect

    Warren, O.L.

    1993-07-01

    This thesis is divided into 3 papers: dynamical low-energy electron- diffraction investigation of lateral displacements in topmost layer of Pd(110); determination of (1{times}1) and (1{times}2) structures of Pt thin films on Pd(110) by dynamical low-energy electron-diffraction analysis; and structural determination of a NiO(111) film on Ni(100) by dynamical low-energy electron-diffraction analysis.

  13. Effects of Ag addition on FePt L1{sub 0} ordering transition: A direct observation of ordering transition and Ag segregation in FePtAg alloy films

    SciTech Connect

    Wang, Lei; Yu, Youxing; Gao, Tenghua

    2015-12-21

    FePt and (FePt){sub 91.2}Ag{sub 8.8} alloy films were deposited by magnetron sputtering. The average coercivity of (FePt){sub 91.2}Ag{sub 8.8} films reaches 8.51 × 10{sup 5} A/m, which is 0.63 × 10{sup 5} A/m higher than that of the corresponding FePt films. Ag addition effectively promotes the FePt L1{sub 0} ordering transition at a relatively low annealing temperature of 400 °C. The promotion mechanism was investigated by using in situ high-resolution transmission electron microscopy (HRTEM) and ex situ X-ray absorption fine structure (XAFS). The concurrence of ordering transition and Ag segregation in FePtAg alloy films was first observed by using in situ heating HRTEM. The time-resolved evolution reveals more details on the role of Ag addition in FePt low-temperature ordering. Ex situ XAFS results further confirm that Ag replaces Fe sites in the as-deposited films and segregates from FePt-Ag solid solution phase through annealing at elevated temperatures. The segregation of Ag atoms leaves vacancies in the grain. The vacancy formation is believed to accelerate the diffusion of Fe and Pt atoms, which is critical for the L1{sub 0} ordering transition.

  14. Reactions of Pd(II) and Pt(II) Complexes With Tetraethylthiouram Disulfide

    PubMed Central

    Cervantes, G.; Molins, E.; Miravitlles, C.

    1997-01-01

    The reactions of tetraethylthiouram disulfide (DTS), an inhibitor of the nephrotoxicity of Pt(II) drugs, an efficient agent in the treatment of chronic alcoholism, in the treatment of HIV infections, AIDS and heavy metal toxicity, and a fungicide and herbicide, with K2[PtCl4], in ratio 1:1 and 1:2, gave the compounds [PtCl2DTS] and [Pt(S2CNEt2)2] respectively. The reaction of the complexes K2[PdCl4], Pd(AcO)2 and [PdCl2(PhCN)2], where PhCN = Benzonitrile, with tetraethylthiouram disulfide in ratio 1:1 or 1:2, yielded orange crystals identified as [Pd(S2CNEt2)2]. The crystals were suitable for study by X-ray diffraction. The -S-S- bridge in the tetraethylthiouram disulfude molecule was broken and the two molecules of the thiocarbamate derivative were bound to the Pd(II) by the equivalents sulfur atoms. All the compounds were characterized by IR, 1H and 13C NMR spectroscopies. PMID:18475812

  15. Pt@Pd(x)Cu(y)/C core-shell electrocatalysts for oxygen reduction reaction in fuel cells.

    PubMed

    Cochell, T; Manthiram, A

    2012-01-17

    A series of carbon-supported core-shell nanoparticles with Pd(x)Cu(y)-rich cores and Pt-rich shells (Pt@Pd(x)Cu(y)/C) has been synthesized by a polyol reduction of the precursors followed by heat treatment to obtain the Pd(x)Cu(y)/C (1 ≤ x ≤ 3 and 0 ≤ y ≤ 5) cores and the galvanic displacement of Pd(x)Cu(y) with [PtCl(4)](2-) to form the Pt shell. The nanoparticles have also been investigated with respect to the oxygen reduction reaction (ORR) in proton-exchange-membrane fuel cells (PEMFCs). X-ray diffraction (XRD) analysis suggests that the cores are highly alloyed and that the galvanic displacement results in a certain amount of alloying between Pt and the underlying Pd(x)Cu(y) alloy core. Transmission electron microscopy (TEM) images show that the Pt@Pd(x)Cu(y)/C catalysts (where y > 0) have mean particle sizes of <8 nm. Compositional analysis by energy-dispersive X-ray spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS) clearly shows Pt enrichment in the near-surface region of the nanoparticles. Cyclic voltammograms show a positive shift of as much as 40 mV for the onset of Pt-OH formation in the Pt@Pd(x)Cu(y)/C electrocatalysts compared to that in Pt/C. Rotating disk electrode (RDE) measurements of Pt@PdCu(5)/C show an increase in the Pt mass activity by 3.5-fold and noble metal activity by 2.5-fold compared to that of Pt/C. The activity enhancements in RDE and PEMFC measurements are believed to be a result of the delay in the onset of Pt-OH formation.

  16. Ag-Pt alloy nanoparticles with the compositions in the miscibility gap

    SciTech Connect

    Peng Zhenmeng; Yang Hong

    2008-07-15

    Silver platinum binary alloys with compositions between about Ag{sub 2}Pt{sub 98} and Ag{sub 95}Pt{sub 5} at <{approx} 400 deg. C have largely not been observed in bulk due to the large immiscibility between these two metals. We present in this paper that Ag-Pt alloy nanostructures can be made in a broad composition range. The formation of Ag-Pt nanostructures is studied by powder X-ray diffraction (PXRD) and energy-dispersive X-ray (EDX). Our results indicate that lattice parameter changes almost linearly with composition in these Ag-Pt nanomaterials. In another word, lattice parameter and composition relationship follows the Vegard's law, which is a strong indication for the formation of metal alloys. Our transmission electron microscopy (TEM) study shows that the silver-rich Ag-Pt alloy nanostructures have spherical shape, while the platinum-rich ones possess wire-like morphology. The stability and crystal phase are investigated by annealing the alloy nanostructures directly or on carbon supports. - Graphical abstract: While platinum and silver cannot form a solid solution with the composition between about Ag{sub 2}Pt{sub 98} and Ag{sub 95}Pt{sub 5} at 400 deg. C or below in bulk form, alloy particles and wires can be made within this miscibility gap at the nanometer scale.

  17. Morphology, dimension, and composition dependence of thermodynamically preferred atomic arrangements in Ag-Pt nanoalloys.

    PubMed

    Deng, Lei; Deng, Huiqiu; Xiao, Shifang; Tang, Jianfeng; Hu, Wangyu

    2013-01-01

    The present article is on Metropolis Monte Carlo simulations coupled with semiempirical potentials to obtain the thermodynamically preferred configurations of Ag-Pt nanoalloys. The effects of particle size, morphology or alloy composition on the surface segregation and the chemical ordering patterns were investigated. Surface segregation of Ag is observed in all Ag-Pt nanoalloys. Such segregation develops quickly as the increase of particle sizes or global Ag composition. Generally, Ag surface enrichment is more apparent for more open particles except for large sized icosahedron (ICO) nanoalloys. The most energetically favorable chemical ordering patterns gradually evolve from Pt-core/Ag-shell to onion-like structures when the global Ag composition increases. Due to the site preference of Ag segregation, the presence of partly alloyed facets and Ag blocked vertices or edges at low global Ag compositions can modify the electronic and geometric structures on the nanoalloys' surface. The coupling between Pt and Ag sites is a topic of particular interest for catalysis. The detailed atomistic understanding of atomic arrangements in Ag-Pt nanoalloys is essential to intelligently design robust and active nanocatalysts with a low cost. PMID:24015590

  18. Efficient solvent-free hydrogenation of ketones over flame-prepared bimetallic Pt-Pd/ZrO(2) catalysts.

    PubMed

    Jiang, Yijiao; Büchel, Robert; Huang, Jun; Krumeich, Frank; Pratsinis, Sotiris E; Baiker, Alfons

    2012-07-01

    Named and flamed: Bimetallic Pt-Pd/ZrO(2) catalysts with different Pt/Pd atomic ratios and high dispersion of the metal nanoparticles are prepared by a single-step flame-spray pyrolysis. The catalysts show excellent activity and tunable product selectivity for the solvent-free hydrogenation of the ketone model compounds cyclopentanone and acetophenone. PMID:22674738

  19. Pd@Pt Core–Shell Nanoparticles with Branched Dandelion-like Morphology as Highly Efficient Catalysts for Olefin Reduction

    EPA Science Inventory

    A facile synthesis based on the addition of ascorbic acid to a mixture of Na2PdCl4, K2PtCl6, and Pluronic P123 results in highly branched core–shell nanoparticles (NPs) with a micro–mesoporous dandelion-like morphology comprising Pd core and Pt shell. The slow reduction kinetics ...

  20. Structures and energetics of 98 atom Pd-Pt nanoalloys: potential stability of the Leary tetrahedron for bimetallic nanoparticles.

    PubMed

    Paz-Borbón, Lauro Oliver; Mortimer-Jones, Thomas V; Johnston, Roy L; Posada-Amarillas, Alvaro; Barcaro, Giovanni; Fortunelli, Alessandro

    2007-10-14

    The energetics of 98 atom bimetallic Pd-Pt clusters are studied using a combination of: a genetic algorithm technique (to explore vast areas of the configurational space); a basin-hopping atom-exchange routine (to search for lowest-energy homotops at fixed composition); and a shell optimisation approach (to search for high symmetry isomers). The interatomic interactions between Pd and Pt are modelled by the Gupta many-body empirical potential. For most compositions, the putative global minima are found to have structures based on defective Marks decahedra, but in the composition range from Pd46Pt52 to Pd63Pt35, the Leary tetrahedron (LT)--a structure previously identified for 98 atom Lennard-Jones clusters--is consistently found as the most stable structure. Based on the excess energy stability criterion, Pd56Pt42 represents the most stable cluster across the entire composition range. This structure, a Td-symmetry LT, exhibits multi-layer segregation with an innermost core of Pd atoms, an intermediate layer of Pt atoms and an outermost Pd surface shell (Pd-Pt-Pd). The stability of the Leary tetrahedron is compared against other low-energy competing structural motifs: the Marks decahedron (Dh-M), a "quasi" tetrahedron (a closed-packed structure) and two other closed-packed structures. The stability of LT structures is rationalized in terms of their spherical shape and the large number of nearest neighbours.

  1. Stellated Ag-Pt bimetallic nanoparticles: An effective platform for catalytic activity tuning

    PubMed Central

    Liu, Hui; Ye, Feng; Yao, Qiaofeng; Cao, Hongbin; Xie, Jianping; Lee, Jim Yang; Yang, Jun

    2014-01-01

    The usefulness of Pt-based nanomaterials for catalysis can be greatly enhanced by coupling morphology engineering to the strategic presence of a second or even third metal. Here we demonstrate the design and preparation of stellated Ag-Pt bimetallic nanoparticles where significant activity difference between the methanol oxidation reaction (MOR) and the oxygen reduction reaction (ORR) may be realized by relegating Ag to the core or by hollowing out the core. In particular the stellated Pt surface, with an abundance of steps, edges, corner atoms, and {111} facets, is highly effective for the ORR but is ineffective for MOR. MOR activity is only observed in the presence of a Ag core through electronic coupling to the stellated Pt shell. The bimetallic Ag-Pt stellates therefore demonstrate the feasibility of tuning a Pt surface for two very different structure sensitive catalytic reactions. Stellated bimetallics may therefore be an effective platform for highly tunable catalyst designs. PMID:24495979

  2. Bimetallic PdAg nanoparticle arrays from monolayer films of diblock copolymer micelles

    NASA Astrophysics Data System (ADS)

    Ehret, E.; Beyou, E.; Mamontov, G. V.; Bugrova, T. A.; Prakash, S.; Aouine, M.; Domenichini, B.; Cadete Santos Aires, F. J.

    2015-07-01

    The self-assembly technique provides a highly efficient route to generate well-ordered structures on a nanometer scale. In this paper, well-ordered arrays of PdAg alloy nanoparticles on flat substrates with narrow distributions of particle size (6-7 nm) and interparticle spacing (about 60 nm) were synthesized by the block copolymer micelle approach. A home-made PS-b-P4VP diblock copolymer was prepared to obtain a micellar structure in toluene. Pd and Ag salts were then successfully loaded in the micellar core of the PS-b-P4VP copolymer. A self-assembled monolayer of the loaded micelles was obtained by dipping the flat substrate in the solution. At this stage, the core of the micelles was still loaded with the metal precursor rather than with a metal. Physical and chemical reducing methods were used to reduce the metal salts embedded in the P4VP core into PdAg nanoparticles. HRTEM and EDX indicated that Pd-rich PdAg alloy nanoparticles were synthesized by chemical or physical reduction; UV-visible spectroscopy observations confirmed that metallic PdAg nanoparticles were quickly formed after chemical reduction; XPS measurements revealed that the PdAg alloy nanoparticles were in a metallic state after a short time of exposure to O2 plasma and after hydrazine reduction.

  3. Synthesis of Pd9Ru@Pt nanoparticles for oxygen reduction reaction in acidic electrolytes

    DOE PAGES

    Sun, Yu; Hsieh, Yu -Chi; Chang, Li -Chung; Wu, Pu -Wei; Lee, Jyh -Fu

    2014-11-22

    Nanoparticles of PdRu, Pd₃Ru, and Pd₉Ru are synthesized and impregnated on carbon black via a wet chemical reflux process. X-ray diffraction patterns of the as-synthesized samples, PdxRu/C (x=1/3/9), suggest succesful formation of alloy without presence of individual Pd and Ru nanoparticles. Images from transmission electron microscope confirm irregularly-shaped nanoparticles with average size below 3 nm. Analysis from extended X-ray absorption fine structure on both Pd and Ru K-edge absorption profiles indicate the Ru atoms are enriched on the surface of PdxRu/C. Among these samples, the Pd₉Ru/C exhibits the strongest electrocatalytic activity for oxygen reduction reaction (ORR) in an oxygen-saturated 0.1more » M aqueous HClO₄ solution. Subsequently, the Pd₉Ru/C undegoes Cu under potential deposition, followed by a galvanic displacement reaction to deposit a Pt monolayer on the Pd₉Ru surface (Pd₉Ru@Pt). The Pd₉Ru@Pt reveals better ORR performance than that of Pt, reaching a mass activity of 0.38 mA μg⁻¹ Pt, as compared to that of commercially available Pt nanoparticles (0.107 mA μg⁻¹ Pt). Thus, the mechanisms responsible for the ORR enhancement are attributed to the combined effects of lattice strain and ligand interaction. In addition, this core-shell Pd₉Ru@Pt electrocatalyst represents a substantial reduction in the amount of Pt consumption and raw material cost.« less

  4. Relating adatom emission to improved durability of Pt-Pd diesel oxidation catalysts

    DOE PAGES

    Johns, Tyne Richele; Goeke, Ronald S.; Ashbacher, Valerie; Thune, Peter C.; Niemantsverdriet, J. W.; Kiefer, Boris; Kim, Chang H.; Balogh, Michael P.; Datye, Abhaya K.

    2015-06-05

    Sintering of nanoparticles is an important contributor to loss of activity in heterogeneous catalysts, such as those used for controlling harmful emissions from automobiles. But mechanistic details, such as the rates of atom emission or the nature of the mobile species, remain poorly understood. Herein we report a novel approach that allows direct measurement of atom emission from nanoparticles. We use model catalyst samples and a novel reactor that allows the same region of the sample to be observed after short-term heat treatments (seconds) under conditions relevant to diesel oxidation catalysts (DOCs). Monometallic Pd is very stable and does notmore » sinter when heated in air (T ≤ 800 °C). Pt sinters readily in air, and at high temperatures (≥800 °C) mobile Pt species emitted to the vapor phase cause the formation of large, faceted particles. In Pt–Pd nanoparticles, Pd slows the rate of emission of atoms to the vapor phase due to the formation of an alloy. However, the role of Pd in Pt DOCs in air is quite complex: at low temperatures, Pt enhances the rate of Pd sintering (which otherwise would be stable as an oxide), while at higher temperature Pd helps to slow the rate of Pt sintering. DFT calculations show that the barrier for atom emission to the vapor phase is much greater than the barrier for emitting atoms to the support. Thus, vapor-phase transport becomes significant only at high temperatures while diffusion of adatoms on the support dominates at lower temperatures.« less

  5. Relating adatom emission to improved durability of Pt-Pd diesel oxidation catalysts

    SciTech Connect

    Johns, Tyne Richele; Goeke, Ronald S.; Ashbacher, Valerie; Thune, Peter C.; Niemantsverdriet, J. W.; Kiefer, Boris; Kim, Chang H.; Balogh, Michael P.; Datye, Abhaya K.

    2015-06-05

    Sintering of nanoparticles is an important contributor to loss of activity in heterogeneous catalysts, such as those used for controlling harmful emissions from automobiles. But mechanistic details, such as the rates of atom emission or the nature of the mobile species, remain poorly understood. Herein we report a novel approach that allows direct measurement of atom emission from nanoparticles. We use model catalyst samples and a novel reactor that allows the same region of the sample to be observed after short-term heat treatments (seconds) under conditions relevant to diesel oxidation catalysts (DOCs). Monometallic Pd is very stable and does not sinter when heated in air (T ≤ 800 °C). Pt sinters readily in air, and at high temperatures (≥800 °C) mobile Pt species emitted to the vapor phase cause the formation of large, faceted particles. In Pt–Pd nanoparticles, Pd slows the rate of emission of atoms to the vapor phase due to the formation of an alloy. However, the role of Pd in Pt DOCs in air is quite complex: at low temperatures, Pt enhances the rate of Pd sintering (which otherwise would be stable as an oxide), while at higher temperature Pd helps to slow the rate of Pt sintering. DFT calculations show that the barrier for atom emission to the vapor phase is much greater than the barrier for emitting atoms to the support. Thus, vapor-phase transport becomes significant only at high temperatures while diffusion of adatoms on the support dominates at lower temperatures.

  6. The synthesis of Pt/Ag bimetallic nanoparticles using a successive solution plasma process.

    PubMed

    Kim, Sung Min; Lee, Sang Yul; Lee, Min Hyung; Kim, Jung Wan

    2014-12-01

    A successive solution plasma process was developed for the synthesis of Pt/Ag bimetallic nanoparticles. Ag nanoparticles were made first by applying a high voltage of bipolar pulsed DC to anode and cathode electrodes composed of Ag rods. The solution containing Ag nanoparticles was discharged successively using Pt electrodes. The joule heating and electrolysis between electrodes generated vapors, and solution plasma was sustained due to progressive ionization and excitation in the vapor phase. The maximum current and voltage breakdown was observed at approximately 8.9 A and 900 V with an interval of 25 μs, which indicated that an intense solution plasma was sustained continuously. The Pt-on-Ag heterogeneous nanostructures formed, and finally, the Ag nanoparticles were completely covered by Pt nanoparticles after a discharge duration of 1,200 s. PMID:25970983

  7. Mechanism of coercivity enhancement by Ag addition in FePt-C granular films for heat assisted magnetic recording media

    SciTech Connect

    Varaprasad, B. S. D. Ch. S.; Takahashi, Y. K. Wang, J.; Hono, K.; Ina, T.; Nakamura, T.; Ueno, W.; Nitta, K.; Uruga, T.

    2014-06-02

    We investigated the Ag distribution in a FePtAg-C granular film that is under consideration for a heat assisted magnetic recording medium by aberration-corrected scanning transmission electron microscope-energy dispersive X-ray spectroscopy and X-ray absorption fine structure. Ag is rejected from the core of FePt grains during the deposition, forming Ag-enriched shell surrounding L1{sub 0}-ordered FePt grains. Since Ag has no solubility in both Fe and Pt, the rejection of Ag induces atomic diffusions thereby enhancing the kinetics of the L1{sub 0}-order in the FePt grains.

  8. Nanoporous PtAg and PtCu alloys with hollow ligaments for enhanced electrocatalysis and glucose biosensing.

    PubMed

    Xu, Caixia; Liu, Yunqing; Su, Fa; Liu, Aihua; Qiu, Huajun

    2011-09-15

    Nanoporous silver (NPS) and copper (NPC) obtained by dealloying AgAl and CuAl alloys, respectively, were used as both three-dimensional templates and reducing agents for the fabrication of nanoporous PtAg (NPS-Pt) and PtCu (NPC-Pt) alloys with hollow ligaments by a simple galvanic replacement reaction with H(2)PtCl(6). Electron microscopy and X-ray diffraction characterizations demonstrate that NPS and NPC with similar ligament sizes (30-50 nm) have different effects on the formed hollow nanostructures. For NPS-Pt, the shell of the hollow ligament is seamless. However, the shell of NPC-Pt is comprised of small pores and alloy nanoparticles with a size of ∼3 nm. The as-prepared NPS-Pt and NPC-Pt exhibit remarkably improved electrocatalytic activities towards the oxidation of ethanol and H(2)O(2) compared with state-of-the-art Pt/C catalyst, and can be used for sensitive electrochemical sensing applications. The hierarchical nanoporous structure also provides a good microenvironment for enzymes. After immobilization of glucose oxidase (GOx), the enzyme modified nanoporous electrode can sensitively detect glucose in a wide linear range (0.6-20 mM). PMID:21778046

  9. Crystal structure and physical properties of new Ca2TGe3 (T = Pd and Pt) germanides

    NASA Astrophysics Data System (ADS)

    Klimczuk, T.; Xie, Weiwei; Winiarski, M. J.; Kozioł, R.; Litzbarski, L. S.; Luo, Huixia; Cava, R. J.

    2016-11-01

    The crystallographic, electronic transport and thermal properties of Ca2PdGe3 and Ca2PtGe3 are reported. The compounds crystalize in an ordered variant of the AlB2 crystal structure, in space group P6/mmm, with the lattice parameters a = 8.4876(4) Å/8.4503(5) Å and c = 4.1911(3) Å/4.2302(3) Å for Ca2PdGe3 and Ca2PtGe3, respectively. The resistivity data exhibit metallic behavior with residual-resistivity-ratios (RRR) of 13 for Ca2PdGe3 and 6.5 for Ca2PtGe3. No superconducting transition is observed down to 0.4 K. Specific heat studies reveal similar values of the Debye temperatures and Sommerfeld coefficients: ΘD = 298 K, γ = 4.1 mJ mol-1 K-2 and ΘD = 305 K, γ = 3.2 mJ mol-1 K-2 for Ca2PdGe3 and Ca2PtGe3, respectively. The low value of γ is in agreement with the electronic structure calculations.

  10. Electronic and magnetic properties of X-doped (X=Ni, Pd, Pt) WS2 monolayer

    NASA Astrophysics Data System (ADS)

    Zhao, Xu; Xia, Congxin; Dai, Xianqi; Wang, Tianxing; Chen, Peng; Tian, Liang

    2016-09-01

    We investigate the electronic and magnetic properties of X-doped (X=Ni, Pd, Pt) WS2 monolayer using the first-principles methods based on density functional theory. The results show that WS2 monolayer doped by Ni, Pd and Pt is ferromagnetic. The impurity states near the Fermi level depend highly on the atomic size and electronegativity. For different X-doped WS2, the formation energy is lower under S-rich conditions, which indicates that it is energy favorable and relatively easier to incorporate X atom into WS2 under S-rich experimental conditions. Moreover, Ni-doped system owns the lowest formation energy compared with other atoms under S-rich experimental condition. Our studies predict X-doped (X=Ni, Pd, Pt) WS2 monolayers to be candidates for thin dilute magnetic semiconductors. Ni-doped WS2 has relatively wide half-metallic gap. So Ni-doped WS2 is the most ideal for spin injection among Ni, Pd, and Pt, which is important for application in semiconductor spintronics.

  11. Green synthesis of noble nanometals (Au, Pt, Pd) using glycerol under microwave irradiation conditions

    EPA Science Inventory

    A newer application of glycerol in the field of nanomaterials synthesis has been developed from both the economic and environmental points of view. Glycerol can act as a reducing agent for the fabrication of noble nanometals, such as Au, Pt, and Pd, under microwave irradiation. T...

  12. Electrochemistry of cholesterol biosensor based on a novel Pt-Pd bimetallic nanoparticle decorated graphene catalyst.

    PubMed

    Cao, Shurui; Zhang, Lei; Chai, Yaqin; Yuan, Ruo

    2013-05-15

    A new electrochemical biosensor with enhanced sensitivity was developed for detection of cholesterol by using platinum-palladium-chitosan-graphene hybrid nanocomposites (PtPd-CS-GS) functionalized glassy carbon electrode (GCE). An electrodeposition method was applied to form PtPd nanoparticles-doped chitosan-graphene hybrid nanocomposites (PtPd-CS-GS), which were characterized by scanning electron microscopy (SEM) and electrochemical methods. The presence of the PtPd-CS-GS nanocomposites not only accelerated direct electron transfer from the redox enzyme to the electrode surface, but also enhanced the immobilized amount of cholesterol oxidase (ChOx). Under optimal conditions, the fabricated biosensor exhibited wide linear ranges of responses to cholesterol in the concentration ranges of 2.2×10(-6) to 5.2×10(-4)M, the limit of detection was 0.75 μM (S/N=3). The response time was less than 7s and the Michaelis-Menten constant (Km(app)) was found as 0.11 mM. In addition, the biosensor also exhibited excellent reproducibility and stability. Along with these attractive features, the biosensor also displayed very high specificity to cholesterol with complete elimination of interference from UA, AA, and glucose. PMID:23618155

  13. Shaped Pd-Ni-Pt core-sandwich-shell nanoparticles: influence of Ni sandwich layers on catalytic electrooxidations.

    PubMed

    Sneed, Brian T; Young, Allison P; Jalalpoor, Daniel; Golden, Matthew C; Mao, Shunjia; Jiang, Ying; Wang, Yong; Tsung, Chia-Kuang

    2014-07-22

    Shape-controlled metal nanoparticles (NPs) interfacing Pt and nonprecious metals (M) are highly active energy conversion electrocatalysts; however, there are still few routes to shaped M-Pt core-shell NPs and fewer studies on the geometric effects of shape and strain on catalysis by such structures. Here, well-defined cubic multilayered Pd-Ni-Pt sandwich NPs are synthesized as a model platform to study the effects of the nonprecious metal below the shaped Pt surface. The combination of shaped Pd substrates and mild reduction conditions directs the Ni and Pt overgrowth in an oriented, layer-by-layer fashion. Exposing a majority of Pt(100) facets, the catalytic performance in formic acid and methanol electro-oxidations (FOR and MOR) is assessed for two different Ni layer thicknesses and two different particle sizes of the ternary sandwich NPs. The strain imparted to the Pt shell layer by the introduction of the Ni sandwich layer (Ni-Pt lattice mismatch of ∼11%) results in higher specific initial activities compared to core-shell Pd-Pt bimetallic NPs in alkaline MOR. The trends in activity are the same for FOR and MOR electrocatalysis in acidic electrolyte. However, restructuring in acidic conditions suggests a more complex catalytic behavior from changes in composition. Notably, we also show that cubic quaternary Au-Pd-Ni-Pt multishelled NPs, and Pd-Ni-Pt nanooctahedra can be generated by the method, the latter of which hold promise as potentially highly active oxygen reduction catalysts.

  14. Physical properties of FePt nanocomposite doped with Ag atoms: First-principles study

    NASA Astrophysics Data System (ADS)

    Jia, Yong-Fei; Shu, Xiao-Lin; Xie, Yong; Chen, Zi-Yu

    2014-07-01

    L10 FePt nanocomposite with high magnetocrystalline anisotropy energy has been extensively investigated in the fields of ultra-high density magnetic recording media. However, the order—disorder transition temperature of the nanocomposite is higher than 600 °C, which is a disadvantage for the use of the material due to the sustained growth of FePt grain under the temperature. To address the problem, addition of Ag atoms has been proposed, but the magnetic properties of the doped system are still unclear so far. Here in this paper, we use first-principles method to study the lattice parameters, formation energy, electronic structure, atomic magnetic moment and order—disorder transition temperature of L10 FePt with Ag atom doping. The results show that the formation energy of a Ag atom substituting for a Pt site is 1.309 eV, which is lower than that of substituting for an Fe site 1.346 eV. The formation energy of substituting for the two nearest Pt sites is 2.560 eV lower than that of substituting for the further sites 2.621 eV, which indicates that Ag dopants tend to segregate L10 FePt. The special quasirandom structures (SQSs) for the pure FePt and the FePt doped with two Ag atoms at the stable Pt sites show that the order—disorder transition temperatures are 1377 °C and 600 °C, respectively, suggesting that the transition temperature can be reduced with Ag atom, and therefore the FePt grain growth is suppressed. The saturation magnetizations of the pure FePt and the two Ag atoms doped FePt are 1083 emu/cc and 1062 emu/cc, respectively, indicating that the magnetic property of the doped system is almost unchanged.

  15. The effect of specific chloride adsorption on the electrochemicalbehavior of ultrathin Pd films deposited on Pt(111) in acidsolution

    SciTech Connect

    arenz@thch.uni-bonn.de

    2002-10-01

    The electrochemical behavior of thin Pd films supported on a Pt(111) electrode is investigated by cyclic voltammetry (CV) and in-situ Fourier transform infrared (FTIR) spectroscopy. It is demonstrated that in perchloric acid solution underpotential deposition of hydrogen (H{sub upd}) and hydroxyl adsorption (OH{sub ad}) is in strong competition with the adsorption of Cl- anions, the latter being present as a trace impurity in HClO{sub 4}. The interaction of Cl- with Pd is rather strong, controlling the adsorption of H{sub upd} and OH{sub ad} as well as the kinetic rate of CO oxidation. The microscopic insight (the binding sites) of the adsorbed CO (CO{sub ad}) and the rate of CO oxidation (established from CO2 production) on Pt(111) modified with a (sub)monolayer of Pd is elucidated by means of Fourier infrared (FTIR) spectroscopy. The appearance of both the characteristic Pt(111)-CO{sub ad} and Pt(111)1 ML Pd-CO{sub ad} stretching bands on a Pt(111) surface covered by 0.5 ML Pd confirms previous findings that the Pd atoms agglomerate into islands and that the bare Pt areas and the Pd islands behave according to their own surface chemistry. The systematic increase of the Pd surface coverage results in a gradual change in the catalytic properties of Pt(111)-xPd electrodes towards CO oxidation, from those characteristic of bare Pt(111) to those which are characteristic for Pt(111) covered with 1 ML of Pd.

  16. Transition voltages of vacuum-spaced and molecular junctions with Ag and Pt electrodes

    SciTech Connect

    Wu, Kunlin; Bai, Meilin; Hou, Shimin; Sanvito, Stefano

    2014-07-07

    The transition voltage of vacuum-spaced and molecular junctions constructed with Ag and Pt electrodes is investigated by non-equilibrium Green's function formalism combined with density functional theory. Our calculations show that, similarly to the case of Au-vacuum-Au previously studied, the transition voltages of Ag and Pt metal-vacuum-metal junctions with atomic protrusions on the electrode surface are determined by the local density of states of the p-type atomic orbitals of the protrusion. Since the energy position of the Pt 6p atomic orbitals is higher than that of the 5p/6p of Ag and Au, the transition voltage of Pt-vacuum-Pt junctions is larger than that of both Ag-vacuum-Ag and Au-vacuum-Au junctions. When one moves to analyzing asymmetric molecular junctions constructed with biphenyl thiol as central molecule, then the transition voltage is found to depend on the specific bonding site for the sulfur atom in the thiol group. In particular agreement with experiments, where the largest transition voltage is found for Ag and the smallest for Pt, is obtained when one assumes S binding at the hollow-bridge site on the Ag/Au(111) surface and at the adatom site on the Pt(111) one. This demonstrates the critical role played by the linker-electrode binding geometry in determining the transition voltage of devices made of conjugated thiol molecules.

  17. L10 ordered phase formation in FePt, FePd, CoPt, and CoPd alloy thin films epitaxially grown on MgO(001) single-crystal substrates

    NASA Astrophysics Data System (ADS)

    Ohtake, Mitsuru; Ouchi, Shouhei; Kirino, Fumiyoshi; Futamoto, Masaaki

    2012-04-01

    The FePt, FePd, CoPt, and CoPd epitaxial thin films are prepared on MgO(001) single-crystal substrates by ultrahigh vacuum RF magnetron sputtering. The effects of the magnetic material and the substrate temperature on the film growth, the film structure, and the magnetic properties are investigated. The L10 ordered phase formation is observed for FePt, FePd, and CoPt films prepared at temperatures higher than 200, 400, and 600 °C, respectively, whereas that is not recognized for CoPd films. The L10-FePd(001) single-crystal films with the c-axis normal to the substrate surface are formed, whereas the FePt and CoPt epitaxial films include L10(100) crystals whose c-axis is parallel to the substrate surface, in addition to the L10(001) crystals. Upon increasing the substrate temperature, the ordering degree increases. A higher ordering parameter is observed in the order of FePd > FePt > CoPt. The magnetic properties are influenced by the crystal structure, the crystallographic orientation of the L10 crystal, and the ordering degree.

  18. Component conversion from pure Au nanorods to multiblock Ag-Au-Ag nanorods assisted by Pt nanoframe templates

    NASA Astrophysics Data System (ADS)

    Lee, Sangji; Jang, Hee-Jeong; Jang, Ho Young; Kim, Seong Kyu; Park, Sungho

    2016-06-01

    We developed a new method for synthesizing multiblock Ag-Au-Ag nanorods using Pt nanoframes that had been deposited on the edges of Au nanorod seeds. As a function of Au etching time, the length of the Au nanorod decreased symmetrically starting from the two ends, leading to the formation of empty inner space at the ends. Subsequent reduction of Ag ions could be selectively performed in the inner space confined by Pt nanoframes and the resulting Ag-Au-Ag nanorods exhibited characteristic LSPR modes originating from each block component (in a transverse direction) and SPR coupling (in a longitudinal direction). The high quality of the resulting multiblock nanorods enabled observation of the longitudinal quadrupole mode that was induced by Ag-Au SPR coupling in a long axis. The mode exhibited high sensitivity in accordance with the change in the surrounding media, demonstrating great potential for sensor applications.We developed a new method for synthesizing multiblock Ag-Au-Ag nanorods using Pt nanoframes that had been deposited on the edges of Au nanorod seeds. As a function of Au etching time, the length of the Au nanorod decreased symmetrically starting from the two ends, leading to the formation of empty inner space at the ends. Subsequent reduction of Ag ions could be selectively performed in the inner space confined by Pt nanoframes and the resulting Ag-Au-Ag nanorods exhibited characteristic LSPR modes originating from each block component (in a transverse direction) and SPR coupling (in a longitudinal direction). The high quality of the resulting multiblock nanorods enabled observation of the longitudinal quadrupole mode that was induced by Ag-Au SPR coupling in a long axis. The mode exhibited high sensitivity in accordance with the change in the surrounding media, demonstrating great potential for sensor applications. Electronic supplementary information (ESI) available. See DOI: 10.1039/c6nr03484e

  19. Facile synthesis of Pt-Pd@Silicon nanostructure as an advanced electrocatalyst for direct methanol fuel cells

    NASA Astrophysics Data System (ADS)

    Ensafi, Ali A.; Jafari-Asl, M.; Rezaei, B.; Abarghoui, M. Mokhtari; Farrokhpour, H.

    2015-05-01

    In this work, platinum-palladium (Pt-Pd) is assembled in-situ on the surface of porous silicon flour (PSiF) through chemical reduction of PtCl62-/PdCl42- and oxidation of the precursor solution SiF64-. The components and the morphological properties of the Pt-Pd on PSiF is investigated by means of transmission electron microscopy, energy dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy, and X-ray diffraction techniques. In the next stage, screen printed graphene electrode (SPGE) is prepared by electro-reduction of exfoliated graphene oxide at the surface of a screen printed carbon electrode (SPCE), which is subsequently characterized by FT-IR, Raman spectroscopy, FE-SEM, and electrochemical methods. Finally, a combination of Pt-Pd@PSi nanostructure and SPGE is used for the electro-oxidation of methanol in direct methanol fuel cell. The electrochemical results demonstrate that the Pt-Pd@PSiF-SPGE exhibits an excellent electrocatalytic activity for methanol oxidation. In addition, the electron transfer kinetic of methanol oxidation on Pt-Pd@PSiF-SPGE is investigated by electrochemical impedance spectroscopy. The results showed that the surface of Pt-Pd@PSiF-SPGE is not affected (poisoned) by intermediate products such as CO.

  20. Annealing effect of ultrathin Ag films on Ni/Pt(111)

    SciTech Connect

    Su, C.W.; Yo, H.Y.; Chen, Y.J.; Shern, C.S.

    2005-06-15

    The epitaxial growth and alloy formation of Ag-capped layer on Ni/Pt(111) surface were investigated using Auger electron spectroscopy, ultraviolet photoelectron spectroscopy, and low-energy electron diffraction. The growth of Ag on one ML Ni/Pt(111) transforms from layer-by-layer mode into three-dimensional island mode after the growth of one atomic monolayer of Ag. The starting temperature for the alloy formation of Ni-Pt is dependent of the thickness of Ni films. The interface compositions after the high-temperature annealing were studied with the depth-profile analysis of Ar ion sputtering.

  1. Crystallinity-induced shape evolution of Pt-Ag nanosheets from branched nanocrystals.

    PubMed

    Mahmood, Azhar; Saleem, Faisal; Lin, Haifeng; Ni, Bing; Wang, Xun

    2016-08-18

    Crystallinity offers countless opportunities for the controlled synthesis of multimetallic 2D and 3D nanomaterials. Herein we have successfully synthesized 2D Pt-Ag ultrathin nanosheets through the oxidative etching of twin seeds and 3D Pt-Ag-Cu tetrapods via altering the crystallinity through the incorporation of copper into the Pt-Ag alloy. A better electrocatalytic activity is obtained for the oxidation of formic acid which is 3.8 times higher than that of a commercial platinum catalyst as the stepped surface atom densities are higher on the nanosheets. PMID:27494004

  2. High-activity PtRuPd/C catalyst for direct dimethyl ether fuel cells.

    PubMed

    Li, Qing; Wen, Xiaodong; Wu, Gang; Chung, Hoon T; Gao, Rui; Zelenay, Piotr

    2015-06-22

    Dimethyl ether (DME) has been considered as a promising alternative fuel for direct-feed fuel cells but lack of an efficient DME oxidation electrocatalyst has remained the challenge for the commercialization of the direct DME fuel cell. The commonly studied binary PtRu catalyst shows much lower activity in DME than methanol oxidation. In this work, guided by density functional theory (DFT) calculation, a ternary carbon-supported PtRuPd catalyst was designed and synthesized for DME electrooxidation. DFT calculations indicated that Pd in the ternary PtRuPd catalyst is capable of significantly decreasing the activation energy of the CO and CH bond scission during the oxidation process. As evidenced by both electrochemical measurements in an aqueous electrolyte and polymer-electrolyte fuel cell testing, the ternary catalyst shows much higher activity (two-fold enhancement at 0.5 V in fuel cells) than the state-of-the-art binary Pt50 Ru50 /C catalyst (HiSPEC 12100).

  3. First principles investigation of the activity of thin film Pt, Pd and Au surface alloys for oxygen reduction.

    PubMed

    Tripkovic, Vladimir; Hansen, Heine Anton; Rossmeisl, Jan; Vegge, Tejs

    2015-05-01

    Further advances in fuel cell technologies are hampered by kinetic limitations associated with the sluggish cathodic oxygen reduction reaction. We have investigated a range of different formulations of binary and ternary Pt, Pd and Au thin films as electrocatalysts for oxygen reduction. The most active binary thin films are near-surface alloys of Pt with subsurface Pd and certain PdAu and PtAu thin films with surface and/or subsurface Au. The most active ternary thin films are with pure metal Pt or Pd skins with some degree of Au in the surface and/or subsurface layer and the near-surface alloys of Au with mixed Pt-Pd skins. The activity of the binary and ternary catalysts is explained through weakening of the OH binding energy caused by solute elements. However, given the low alloy formation energies it may be difficult to tune and retain the composition under operating conditions. This is particularly challenging for alloys containing Au due to a high propensity of Au to segregate to the surface. We also show that once Au is on the surface it will diffuse to defect sites, explaining why small amounts of Au retard dissolution of Pt nanoparticles. For the PtPd thin films there is no pronounced driving force for surface segregation, diffusion to defects or surface self-assembling. On the basis of stability and activity analysis we conclude that the near surface alloy of Pd in Pt and some PdAu binary and PtPdAu ternary thin films with a controlled amount of Au are the best catalysts for oxygen reduction. PMID:25865333

  4. Polarization-sensitive photocurrent in the resistive Ag/Pd films

    NASA Astrophysics Data System (ADS)

    Saushin, A. S.; Zonov, R. G.; Mikheev, K. G.; Shamshetdinov, R. R.; Mikheev, G. M.

    2016-08-01

    We report on the observation of helicity dependent photocurrent of the 20 μm thick silver-palladium (Ag/Pd) films manufactured by the thick-film technology. The transverse photocurrent is observed at oblique incidence of laser radiation with different wavelengths in the spectral range of 266 - 2100 nm. At the wavelength range of 532 - 2100 nm the polarity of the transverse photocurrent is positive (negative) for the left- (right-) circular polarized beam. We show that action of high temperature on the films in vacuum results in the decrease of longitudinal photocurrent due to the reduction of PdO content. The photon drag effect is suggested to be the origin of the polarization-sensitive photocurrent in the Ag/Pd films. The obtained results show that the Ag/Pd resistive films may be of interest for polarization- sensitive measurements.

  5. Interdiffusion and stress development in single-crystalline Pd/Ag bilayers

    NASA Astrophysics Data System (ADS)

    Noah, Martin A.; Flötotto, David; Wang, Zumin; Mittemeijer, Eric J.

    2016-04-01

    Interdiffusion and stress evolution in single-crystalline Pd/single-crystalline Ag thin films were investigated by Auger electron spectroscopy sputter-depth profiling and in-situ X-ray diffraction, respectively. The concentration-dependent chemical diffusion coefficient, as well as the impurity diffusion coefficient of Ag in Pd could be determined in the low temperature range of 356 °C-455 °C. As a consequence of the similarity of the strong concentration-dependences of the intrinsic diffusion coefficients, the chemical diffusion coefficient varies only over three orders of magnitude over the whole composition range, despite the large difference of six orders of magnitude of the self-diffusion coefficients of Ag in Ag and Pd in Pd. It is shown that the Darken-Manning treatment should be adopted for interpretation of the experimental data; the Nernst-Planck treatment yielded physically unreasonable results. Apart from the development of compressive thermal stress, the development of stress in both sublayers separately could be ascribed to compositional stress (tensile in the Ag sublayer and compressive in the Pd sublayer) and dominant relaxation processes, especially in the Ag sublayer. The effect of these internal stresses on the values determined for the diffusion coefficients is shown to be negligible.

  6. Magnetic and Fermi Surface Properties of Ferromagnets EuPd2 and EuPt2

    NASA Astrophysics Data System (ADS)

    Nakamura, Ai; Akamine, Hiromu; Ashitomi, Yousuke; Honda, Fuminori; Aoki, Dai; Takeuchi, Tetsuya; Matsubayashi, Kazuyuki; Uwatoko, Yoshiya; Tatetsu, Yasutomi; Maehira, Takahiro; Hedo, Masato; Nakama, Takao; Ōnuki, Yoshichika

    2016-08-01

    We succeeded in growing single crystals of the ferromagnets EuPd2 and EuPt2 with the Laves-type cubic structure by the Bridgman method, namely, heating constituting materials in a Mo crucible up to a high temperature of about 1500 °C. The ferromagnetic properties of EuPd2 and EuPt2 with Curie temperatures of 74 and 100 K, respectively, were confirmed from the results of electrical resistivity, specific heat, and magnetization measurements. The ordered moment is 7 μB/Eu, revealing the Eu-divalent ferromagnetism. The present Eu-divalent electronic state is found to be robust against high pressures of up to 8 GPa and is not changed into the Eu-trivalent state. We also carried out de Haas-van Alphen (dHvA) experiments for EuPd2. The detected dHvA branches in EuPd2 are well explained by the relativistic linearized augmented plane wave (RLAPW) energy band calculations for SrPd2, revealing a closed hole Fermi surface and compensated four closed electron Fermi surfaces.

  7. Coordination chemistry of cyclopropenylidene-stabilized phosphenium cations: synthesis and reactivity of Pd and Pt complexes.

    PubMed

    Kozma, Agnes; Deden, Tobias; Carreras, Javier; Wille, Christian; Petuškova, Jekaterina; Rust, Jörg; Alcarazo, Manuel

    2014-02-17

    A straightforward synthesis of cyclopropenylidene-stabilized phosphenium cations 1 a-g through the reaction of [(iPr2N)2C3(+)Cl]BF4 with secondary phosphines is described. Their donor ability was evaluated by analysis of the CO stretching frequency in Rh complexes [RhCl(CO)L2](BF4)2 and electrochemical methods. The cyclopropenium ring induces a phosphite-type behavior that can be tuned by the other two substituents attached to the phosphorus atom. Despite of the positive charge that they bear, phosphenium cations 1 a-g still act as two-electron donor ligands, forming adducts with Pd(II) and Pt(II) precursors. Conversely, in the presence of Pd(0) species, an oxidative insertion of the Pd atom into the Ccarbene-phosphorus bond takes place, providing dimeric structures in which each Pd atom is bonded to a cyclopropenyl carbene while two dialkyl/diaryl phosphide ligands serve as bridges between the two Pd centers. The catalytic performance of the resulting library of Pt(II) complexes was tested; all of the cationic phosphines accelerated the prototype 6-endo-dig cyclization of 2-ethynyl-1,1'-biphenyl to afford pentahelicene. The best ligand 1 g was used in the synthesis of two natural products, chrysotoxene and epimedoicarisoside A.

  8. Study of Ag-Pd bimetallic nanoparticles modified glassy carbon electrode for detection of L-cysteine

    NASA Astrophysics Data System (ADS)

    Murugavelu, M.; Karthikeyan, B.

    2014-11-01

    Ag-Pd bimetallic nanoparticles (Ag-Pd BNPs) as an enhanced sensing material with improved electronic transmission rates in the electrochemical sensing of L-cysteine (L-cys) has been reported. The morphology of Ag-Pd BNPs was characterized with X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM) and cyclic voltammetry (CV). Oxidation of L-cys on Ag-Pd BNPs is investigated in detail by discussing the effect of the structure and from the electrocatalytic oxidation of L-cys. We found that the Ag-Pd BNPs exhibited high electrocatalytic activity towards L-cys oxidation in neutral condition and could be used for the development of nonenzymatic L-cys sensor. Based on the efficient catalytic ability of Ag-Pd BNPs, the fabricated biosensor exhibited a wide linear range of responses to the L-cys with the concentration detection limit of nearly down to 2 mM with fast response time.

  9. Density functional theory study of structural, electronic, and thermal properties of Pt, Pd, Rh, Ir, Os and PtPd X (X = Ir, Os, and Rh) alloys

    NASA Astrophysics Data System (ADS)

    Shabbir, Ahmed; Muhammad, Zafar; M, Shakil; M, A. Choudhary

    2016-03-01

    The structural, electronic, mechanical, and thermal properties of Pt, Pd, Rh, Ir, Os metals and their alloys PtPdX (X = Ir, Os and Rh) are studied systematically using ab initio density functional theory. The groundstate properties such as lattice constant and bulk modulus are calculated to find the equilibrium atomic position for stable alloys. The electronic band structure and density of states are calculated to study the electronic behavior of metals on making their alloys. The electronic properties substantiate the metallic behavior for all studied materials. The firstprinciples density functional perturbation theory as implemented in quasi-harmonic approximation is used for the calculations of thermal properties. We have calculated the thermal properties such as the Debye temperature, vibrational energy, entropy and constant-volume specific heat. The calculated properties are compared with the previously reported experimental and theoretical data for metals and are found to be in good agreement. Calculated results for alloys could not be compared because there is no data available in the literature with such alloy composition.

  10. Improving Electrocatalysts for O2 Reduction by Fine-Tuning the Pt-Support Interaction: Pt Monolayer on the Surfaces of a Pd3Fe(111) Single-Crystal Alloy

    SciTech Connect

    Zhou, W.P.; Yang, X.; Vukmirovic, M.B.; Koel, B.E.; Jiao, J.; Peng, G.; Mavrikakis, M.; Adzic, R.R.

    2009-09-09

    We improved the effectiveness of Pt monolayer electrocatalysts for the oxygen-reduction reaction (ORR) using a novel approach to fine-tuning the Pt monolayer interaction with its support, exemplified by an annealed Pd{sub 3}Fe(111) single-crystal alloy support having a segregated Pd layer. Low-energy ion scattering and low-energy electron diffraction studies revealed that a segregated Pd layer, with the same structure as Pd (111), is formed on the surface of high-temperature-annealed Pd{sub 3}Fe(111). This Pd layer is considerably more active than Pd(111); its ORR kinetics is comparable to that of a Pt(111) surface. The enhanced catalytic activity of the segregated Pd layer compared to that of bulk Pd apparently reflects the modification of Pd surface's electronic properties by underlying Fe. The Pd{sub 3}Fe(111) suffers a large loss in ORR activity when the subsurface Fe is depleted by potential cycling (i.e., repeated excursions to high potentials in acid solutions). The Pd{sub 3}Fe(111) surface is an excellent substrate for a Pt monolayer ORR catalyst, as verified by its enhanced ORR kinetics on PT{sub ML}/Pd/Pd{sub 3}Fe(111). Our density functional theory studies suggest that the observed enhancement of ORR activity originates mainly from the destabilization of OH binding and the decreased Pt-OH coverage on the Pt/Pd/Pd{sub 3}Fe(111) surface. The activity of Pt{sub ML}/Pd(111) and Pt(111) is limited by OH removal, whereas the activity of Pt{sub ML}/Pd/Pd{sub 3}Fe(111) is limited by the O-O bond scission, which places these two surfaces on the two sides of the volcano plot.

  11. Core/shell face-centered tetragonal FePd/Pd nanoparticles as an efficient non-Pt catalyst for the oxygen reduction reaction

    DOE PAGES

    Zhu, Huiyuan; Jiang, Guangming; Zhang, Xu; Shen, Bo; Wu, Liheng; Zhang, Sen; Lu, Gang; Wu, Zhongbiao; Sun, Shouheng

    2015-10-04

    We report the synthesis of core/shell face-centered tetragonal (fct)-FePd/Pd nanoparticles (NPs) via reductive annealing of core/shell Pd/Fe3O4 NPs followed by temperature-controlled Fe etching in acetic acid. Among three different kinds of core/shell FePd/Pd NPs studied (FePd core at similar to 8 nm and Pd shell at 0.27, 0.65, or 0.81 nm), the fct-FePd/Pd-0.65 NPs are the most efficient catalyst for the oxygen reduction reaction (ORR) in 0.1 M HClO4 with Pt-like activity and durability. This enhanced ORR catalysis arises from the desired Pd lattice compression in the 0.65 nm Pd shell induced by the fct-FePd core. Lastly, our study offersmore » a general approach to enhance Pd catalysis in acid for ORB.« less

  12. Core/shell face-centered tetragonal FePd/Pd nanoparticles as an efficient non-Pt catalyst for the oxygen reduction reaction

    SciTech Connect

    Zhu, Huiyuan; Jiang, Guangming; Zhang, Xu; Shen, Bo; Wu, Liheng; Zhang, Sen; Lu, Gang; Wu, Zhongbiao; Sun, Shouheng

    2015-10-04

    We report the synthesis of core/shell face-centered tetragonal (fct)-FePd/Pd nanoparticles (NPs) via reductive annealing of core/shell Pd/Fe3O4 NPs followed by temperature-controlled Fe etching in acetic acid. Among three different kinds of core/shell FePd/Pd NPs studied (FePd core at similar to 8 nm and Pd shell at 0.27, 0.65, or 0.81 nm), the fct-FePd/Pd-0.65 NPs are the most efficient catalyst for the oxygen reduction reaction (ORR) in 0.1 M HClO4 with Pt-like activity and durability. This enhanced ORR catalysis arises from the desired Pd lattice compression in the 0.65 nm Pd shell induced by the fct-FePd core. Lastly, our study offers a general approach to enhance Pd catalysis in acid for ORB.

  13. Anisotropic thermal expansion of Ni, Pd and Pt germanides and silicides

    NASA Astrophysics Data System (ADS)

    Geenen, F. A.; Knaepen, W.; Moens, F.; Brondeel, L.; Leenaers, A.; Van den Berghe, S.; Detavernier, C.

    2016-07-01

    Silicon or germanium-based transistors are nowadays used in direct contact with silicide or germanide crystalline alloys for semiconductor device applications. Since these compounds are formed at elevated temperatures, accurate knowledge of the thermal expansion of both substrate and the contact is important to address temperature depending effects such as thermal stress. Here we report the linear coefficients of thermal expansion of Ni-, Pd- and Pt-based mono-germanides, mono-silicides and di-metal-silicides as determined by powder-based x-ray diffraction between 300 and 1225 K. The investigated mono-metallic compounds, all sharing the MnP crystal structure, as well as Pd2Si and Pt2Si exhibit anisotropic expansion. By consequence, this anisotropic behaviour should be taken into account for evaluating the crystal unit’s cell at elevated temperatures.

  14. Pt- and Pd-decorated MWCNTs for vapour and gas detection at room temperature

    PubMed Central

    Baccar, Hamdi; Clément, Pierrick; Abdelghani, Adnane

    2015-01-01

    Summary Here we report on the gas sensing properties of multiwalled carbon nanotubes decorated with sputtered Pt or Pd nanoparticles. Sputtering allows for an oxygen plasma treatment that removes amorphous carbon from the surface of the carbon nanotubes and creates oxygenated surface defects in which metal nanoparticles nucleate within a few minutes. The decoration with the 2 nm Pt or the 3 nm Pd nanoparticles is very homogeneous. This procedure is performed at the device level (i.e., for carbon nanotubes deposited onto sensor substrates) for many devices in one batch, which illustrates the scalability for the mass production of affordable nanosensors. The response to selected aromatic and non-aromatic volatile organic compounds, as well as pollutant gases has been studied. Pt- and Pd-decorated multiwalled carbon nanotubes show a fully reversible response to the non-aromatic volatile organic compounds tested when operated at room temperature. In contrast, these nanomaterials were not responsive to the aromatic compounds studied (measured at concentrations up to 50 ppm). Therefore, these sensors could be useful in a small, battery-operated alarm detector, for example, which is able to discriminate aromatic from non-aromatic volatile organic compounds in ambient. PMID:25977863

  15. Controlled Synthesis of Pd/Pt Core Shell Nanoparticles Using Area-selective Atomic Layer Deposition

    PubMed Central

    Cao, Kun; Zhu, Qianqian; Shan, Bin; Chen, Rong

    2015-01-01

    We report an atomic scale controllable synthesis of Pd/Pt core shell nanoparticles (NPs) via area-selective atomic layer deposition (ALD) on a modified surface. The method involves utilizing octadecyltrichlorosilane (ODTS) self-assembled monolayers (SAMs) to modify the surface. Take the usage of pinholes on SAMs as active sites for the initial core nucleation, and subsequent selective deposition of the second metal as the shell layer. Since new nucleation sites can be effectively blocked by surface ODTS SAMs in the second deposition stage, we demonstrate the successful growth of Pd/Pt and Pt/Pd NPs with uniform core shell structures and narrow size distribution. The size, shell thickness and composition of the NPs can be controlled precisely by varying the ALD cycles. Such core shell structures can be realized by using regular ALD recipes without special adjustment. This SAMs assisted area-selective ALD method of core shell structure fabrication greatly expands the applicability of ALD in fabricating novel structures and can be readily applied to the growth of NPs with other compositions. PMID:25683469

  16. Pt- and Pd-decorated MWCNTs for vapour and gas detection at room temperature.

    PubMed

    Baccar, Hamdi; Thamri, Atef; Clément, Pierrick; Llobet, Eduard; Abdelghani, Adnane

    2015-01-01

    Here we report on the gas sensing properties of multiwalled carbon nanotubes decorated with sputtered Pt or Pd nanoparticles. Sputtering allows for an oxygen plasma treatment that removes amorphous carbon from the surface of the carbon nanotubes and creates oxygenated surface defects in which metal nanoparticles nucleate within a few minutes. The decoration with the 2 nm Pt or the 3 nm Pd nanoparticles is very homogeneous. This procedure is performed at the device level (i.e., for carbon nanotubes deposited onto sensor substrates) for many devices in one batch, which illustrates the scalability for the mass production of affordable nanosensors. The response to selected aromatic and non-aromatic volatile organic compounds, as well as pollutant gases has been studied. Pt- and Pd-decorated multiwalled carbon nanotubes show a fully reversible response to the non-aromatic volatile organic compounds tested when operated at room temperature. In contrast, these nanomaterials were not responsive to the aromatic compounds studied (measured at concentrations up to 50 ppm). Therefore, these sensors could be useful in a small, battery-operated alarm detector, for example, which is able to discriminate aromatic from non-aromatic volatile organic compounds in ambient. PMID:25977863

  17. Role of Ag addition in L10 ordering of FePt-based nanocomposite magnets

    NASA Astrophysics Data System (ADS)

    Crisan, A. D.; Vasiliu, F.; Mercioniu, I.; Crisan, O.

    2014-01-01

    The FePt system has important perspectives as high-temperature corrosion-resistant magnets. In the form of rapidly solidified melt-spun ribbons, FePt-based magnets may exhibit in certain cases a two-phase hard-soft magnetic behaviour. The present paper deals with a microstructural and magnetic study of FePtAgB alloys with increasing Ag content. The aim is to identify and confirm the effect of Ag addition in decreasing the temperature of the FePt disorder-order structural phase transformation. A detailed high-resolution transmission electron microscopy study is employed, and the alternative disposal of hard and soft regions within the two-phase microstructure is observed and interpreted with respect to the X-ray diffraction results. In the as-cast Ag-containing samples, it is shown that there is an optimum of the Ag content for which best magnetic properties are obtained. Ag addition creates a nonlinear behaviour of the coercive field and the ordering parameter, similar to the RKKY interaction-induced interlayer exchange coupling (IEC) observed in magnetic layers separated by non-magnetic spacer layers. Direct formation of the L10 phase from the as-cast state in the FePtAgB alloys is reported with magnetic parameters compatible to other exchange spring permanent nanomagnets. These findings open novel perspectives into utilization of such alloys in applications requiring magnets operating in high-temperature industrial environments.

  18. Improving Electrocatalysts for O2 Reduction by Fine-Tuning the Pt-Support Interaction: Pt Monolayer on the Surfaces of a Pd3Fe(111) Single-Crystal Alloy

    SciTech Connect

    Zhou, Wei-Ping; Yang, Xiaofang; Vukmirovic, Miomir B.; Koel, Bruce E.; Jiao, Jiao; Peng, Guowen; Mavrikakis, Manos; Adzic, Radoslav R.

    2009-09-09

    We improved the effectiveness of Pt monolayer electrocatalysts for the oxygen-reduction reaction (ORR) using a novel approach to fine-tuning the Pt monolayer interaction with its support, exemplified by an annealed Pd3Fe(111) single-crystal alloy support having a segregated Pd layer. Low-energy ion scattering and low-energy electron diffraction studies revealed that a segregated Pd layer, with the same structure as Pd (111), is formed on the surface of high-temperature-annealed Pd3Fe(111). This Pd layer is considerably more active than Pd(111); its ORR kinetics is comparable to that of a Pt(111) surface. The enhanced catalytic activity of the segregated Pd layer compared to that of bulk Pd apparently reflects the modification of Pd surface’s electronic properties by underlying Fe. The Pd3Fe(111) suffers a large loss in ORR activity when the subsurface Fe is depleted by potential cycling (i.e., repeated excursions to high potentials in acid solutions). The Pd3Fe(111) surface is an excellent substrate for a Pt monolayer ORR catalyst, as verified by its enhanced ORR kinetics on PTML/Pd/Pd3Fe(111). Our density functional theory studies suggest that the observed enhancement of ORR activity originates mainly from the destabilization of OH binding and the decreased Pt-OH coverage on the Pt/Pd/Pd3Fe(111) surface. The activity of PtML/Pd(111) and Pt(111) is limited by OH removal, whereas the activity of PtML/Pd/Pd3Fe(111) is limited by the O-O bond scission, which places these two surfaces on the two sides of the volcano plot.

  19. Thermoelectric Scanning Study of Pt/Pd and Au/Pt Thermocouples up to 960 °C with a Pressure Controlled Sodium Heat-Pipe

    NASA Astrophysics Data System (ADS)

    Gotoh, Masahiko

    2003-09-01

    The performance of the Gold/Platinum (Au/Pt) thermocouple and the Platinum/Palladium (Pt/Pd) thermocouple has received considerable study and it is found that stability of these thermocouples approaches that of Standard Platinum Resistance Thermometers. However there is still some question on the uncertainties due to the different temperature profiles of the furnaces. In this paper results of the measurements on thermal emf variations by means of thermoelectric scanning are reported. Scanning is carried out in a pressure controlled heat pipe at 960 °C over 475 mm along the thermocouples. A Au/Pt thermocouple and three Pt/Pd thermocouples were tested. Pt/Pd thermocouples were subjected to 1000 hours exposure to 1200 °C in different furnaces. As the portion of thermocouple wire previously exposed to around 750 °C crossed the top of the heat-pipe, a 0.4 K apparent temperature drop was detected. It is found that with this thermoelectric scanning method, the effect of accumulated heat treatment on the Pt/Pd thermocouple can be detected at 960 °C. For Au/Pt no such irregularity is detected, but overall a 0.02 K deviation was observed.

  20. Enhanced electrocatalytic activity and stability of Pd3V/C nanoparticles with a trace amount of Pt decoration for the oxygen reduction reaction

    DOE PAGES

    Liu, Sufen; Han, Lili; Zhu, Jing; Xiao, Weiping; Wang, Jie; Liu, Hongfang; Xin, Huolin; Wang, Deli

    2015-09-14

    In this study, carbon supported Pd3V bimetallic alloy nanoparticles (Pd3V/C) have been successfully synthesized via a simple impregnation–reduction method, followed by high temperature treatment under a H2 atmosphere. Electrochemical tests reveal that the half-wave potential of Pd3V/C-500 shifts positively 40 mV compared with Pd/C. However, the catalytic activity of Pd3V/C-500 suffers from serious degradation after 1k cycles. By a spontaneous displacement reaction or co-reduction method, a trace amount of Pt was decorated on the surface or inside of the Pd3V/C nanoparticles. The catalytic activity and stability of the Pd3V@Pt/C and Pt-Pd3V/C catalysts for the oxygen reduction reaction (ORR) are enhancedmore » significantly, and are comparable to commercial Pt/C. In addition, the Pt mass activity of Pd3V@Pt/C and Pt-Pd3V/C improves by factors of 10.9 and 6.5 at 0.80 V relative to Pt/C. Moreover, Pt-decorated Pd3V/C nanoparticles show almost no obvious morphology change after durability tests, because the Pt-rich shell plays an important role in preventing degradation.« less

  1. Size-controllable synthesis of trimetallic RhPdPt island-shaped nanoalloys with enhanced electrocatalytic performance for ethanol oxidation in alkaline medium.

    PubMed

    Huang, Da-Bing; He, Pei-Lei; Yuan, Qiang; Wang, Xun

    2015-03-01

    Size-controllable, high-yield, island-shaped RhPdPt trimetallic nanocrystals with sub-2.0 nm islands have been successfully synthesized through a facile aqueous solution approach. The results of X-ray diffraction (XRD), energy-dispersive X-ray (EDX) line scanning and elemental mapping analysis showed the as-synthesized RhPdPt nanocrystals are alloy structures. These island-shaped RhPdPt trimetallic nanoalloys showed a composition-dependent electrocatalytic performance for ethanol oxidation in alkaline medium. Due to the special structure and intermetallic synergies, the Rh10Pd40Pt50 nanoalloys exhibited an enhanced catalytic activity and durability relative to island-shaped Pd50Pt50 bimetallic nanoalloys and commercial Pt black. The peak current density for Rh10Pd40Pt50 nanoalloys was 1.81 and 1.38 times that for commercial Pt black and Pd50Pt50 nanoalloys, respectively. In addition, the peak potential on Rh10Pd40Pt50 nanoalloys decreased 42 mV relative to commercial Pt black and Pd50Pt50 nanoalloys.

  2. Characterization and performance of Pt-Pd-Rh cordierite monolith catalyst for selectivity catalytic oxidation of ammonia.

    PubMed

    Hung, Chang-Mao

    2010-08-15

    This work considers the oxidation of ammonia (NH(3)) by selective catalytic oxidation (SCO) over a Pt-Pd-Rh cordierite monolith catalyst in a tubular fixed-bed flow quartz reactor (TFBR) at temperatures between 423 and 623K. A Pt-Pd-Rh cordierite monolith catalyst was prepared by incipient wetness impregnation with aqueous solutions of H(2)PtCl(6), Pd(NO(3))(3) and Rh(NO(3))(3) that were coated on cordierite substances. The catalysts were characterized using XRD, PSA and SEM. The experimental results show that around 99.0% NH(3) removal was achieved during catalytic oxidation over the Pt-Pd-Rh cordierite monolith catalyst at 623K with oxygen content of 4%. N(2) was the main product in the NH(3)-SCO process over the Pt-Pd-Rh cordierite monolith catalyst. These results also verify that the Pt-Pd-Rh metals on cordierite monolith surfaces, resulting in the formation of catalytically active sites at the metal-support interface in the reduction of NH(3) in the process. PMID:20451319

  3. Facile synthesis of hierarchical dendritic PtPd nanogarlands supported on reduced graphene oxide with enhanced electrocatalytic properties

    NASA Astrophysics Data System (ADS)

    Li, Shan-Shan; Zheng, Jie-Ning; Ma, Xiaohong; Hu, Yuan-Yuan; Wang, Ai-Jun; Chen, Jian-Rong; Feng, Jiu-Ju

    2014-05-01

    A simple and facile method is developed for one-pot preparation of hierarchical dendritic PtPd nanogarlands supported on reduced graphene oxide (PtPd/RGO) at room temperature, without using any seed, organic solvent, or complex apparatus. It is found that octylphenoxypolyethoxyethanol (NP-40) as a soft template and its amount are critical to the formation of PtPd garlands. The as-prepared nanocomposites are further applied to methanol and ethanol oxidation with significantly enhanced electrocatalytic activity and better stability in alkaline media.A simple and facile method is developed for one-pot preparation of hierarchical dendritic PtPd nanogarlands supported on reduced graphene oxide (PtPd/RGO) at room temperature, without using any seed, organic solvent, or complex apparatus. It is found that octylphenoxypolyethoxyethanol (NP-40) as a soft template and its amount are critical to the formation of PtPd garlands. The as-prepared nanocomposites are further applied to methanol and ethanol oxidation with significantly enhanced electrocatalytic activity and better stability in alkaline media. Electronic supplementary information (ESI) available: Experimental section, Fig. S1-S12 and Tables S1 and S2. See DOI: 10.1039/c3nr06808k

  4. Isolation and structural characterization of a silver-platinum nanocluster, Ag4Pt2(DMSA)4.

    PubMed

    Biltek, Scott R; Sen, Ayusman; Pedicini, Anthony F; Reber, Arthur C; Khanna, Shiv N

    2014-09-18

    We report the synthesis, isolation, and characterization of the ligand-protected bimetallic cluster, Ag4Pt2(DMSA)4 (DMSA = meso-2,3,-dimercaptosuccinic acid). The procedure is similar to the one employed for the synthesis of Ag4Ni2(DMSA)4. Theoretical studies suggest that the Pt and Ni atoms have square planar configurations. Because the crystal field splitting of 5d orbitals is typically larger than that for 3d orbitals, the Pt-based cluster has an optical spectrum that is significantly blue-shifted as compared to the Ni-based cluster.

  5. Deep oxidation of methane on particles derived from YSZ-supported Pd-Pt-(O) coatings synthesized by pulsed filtered cathodic arc

    SciTech Connect

    Horwat, D.; Endrino, J.L.; Boreave, A.; Karoum,R.; Pierson, J.F.; Weber, S.; Anders, A.; Vernoux, Ph.

    2008-12-12

    Methane conversion tests were performed on Pd, PdOy, Pd0.6Pt0.4Oy and Pd0.4Pt0.6Oy thin films deposited on yttria stabilized zirconia (YSZ) substrates. Pt containing films exhibited poor activity and high reducibility. As-deposited Pd and PdOy films showed good activity and transformed, during the cycling process, to particles dispersed on the YSZ substrates. The higher reaction rate of initially PdOy films was explained by a better dispersion of the catalyst. A drop of the reaction rate was observed when the temperature exceeded 735oC and 725oC for initially Pd and PdOy, respectively, which can be associated with the high-temperature reduction of PdO into Pd.

  6. Facile synthesis of PdAgTe nanowires with superior electrocatalytic activity

    NASA Astrophysics Data System (ADS)

    Hong, Wei; Wang, Jin; Wang, Erkang

    2014-12-01

    In this work, ultrathin Te nanowires (NWs) with high-aspect-ratio are prepared by a simple hydrothermal method. By using Te NWs as the sacrificial template, we demonstrate a facile and efficient method for the synthesis of PdAgTe NWs with high-quality through the partly galvanic replacement between Te NWs and the corresponding noble metal salts precursors in an aqueous solution. The compositions of PdAgTe NWs can be tuned by simply altering the concentration of the precursors. After cyclic voltammetry treatment, multi-component PdAgTe NW with a highly active and stable surface can be obtained. The structure and composition of the as-prepared nanomaterials are analyzed by transmission electron microscope, X-ray diffraction, energy dispersive X-ray spectroscopy, inductively coupled plasma-mass spectroscopy and X-ray photoelectron spectroscopy. Electrochemical catalytic measurement results prove that the as synthesized PdAgTe NWs present superior catalytic activity toward ethanol electrooxidation in alkaline solution than the commercial Pd/C catalyst, which making them can be used as effective catalysts for the direct ethanol fuel cells.

  7. Deformation-induced nanoscale mixing reactions in Cu/Ni and Ag/Pd multilayers

    SciTech Connect

    Wang, Z.; Perepezko, J. H.

    2013-11-04

    During the repeated cold rolling of Cu/Ni and Ag/Pd multilayers, a solid solution forms at the interfaces as nanoscale layer structure with a composition that replicates the overall multilayer composition. The interfacial mixing behavior was investigated by means of X-ray diffraction and scanning transmission electron microscopy. During deformation induced reaction, the intermixing behavior of the Cu/Ni and Ag/Pd multilayers is in contrast to thermally activated diffusion behavior. This distinct behavior can provide new kinetic pathways and offer opportunities for microstructure control that cannot be achieved by thermal processing.

  8. Melting phenomena: effect of composition for 55-atom Ag-Pd bimetallic clusters.

    PubMed

    Cheng, Daojian; Wang, Wenchuan; Huang, Shiping

    2008-05-14

    Understanding the composition effect on the melting processes of bimetallic clusters is important for their applications. Here, we report the relationship between the melting point and the metal composition for the 55-atom icosahedral Ag-Pd bimetallic clusters by canonical Monte Carlo simulations, using the second-moment approximation of the tight-binding potentials (TB-SMA) for the metal-metal interactions. Abnormal melting phenomena for the systems of interest are found. Our simulation results reveal that the dependence of the melting point on the composition is not a monotonic change, but experiences three different stages. The melting temperatures of the Ag-Pd bimetallic clusters increase monotonically with the concentration of the Ag atoms first. Then, they reach a plateau presenting almost a constant value. Finally, they decrease sharply at a specific composition. The main reason for this change can be explained in terms of the relative stability of the Ag-Pd bimetallic clusters at different compositions. The results suggest that the more stable the cluster, the higher the melting point for the 55-atom icosahedral Ag-Pd bimetallic clusters at different compositions.

  9. Investigation of Pd-Modified Ag-CuO Air Braze Filler Metals

    SciTech Connect

    Darsell, Jens T.; Hardy, John S.; Kim, Jin Yong; Weil, K. Scott

    2006-01-10

    Palladium was added as a ternary component to a series of silver - copper oxide alloys in an effort to increase the use temperature of these materials for potential ceramic air brazing applications. Large portions of the silver component of the Ag-CuO system were substituted by palladium forming the following alloys: (100-y)[(100-z)Pd - (z)Ag] - (y)CuOx where y = 0 - 34 mol% CuOx, z = 50 - 100 mol% silver, and x = 0, 0.5, and 1, denoting copper metal, Cu2O, or CuO. From differential scanning calorimetry, it was determined that the addition of palladium causes an increase in the solidus and liquidus temperatures of the resulting Pd-Ag-CuO brazes. In general, the liquidus was found to increase by approximately 220°C for the (100-y)(25Pd - 75Ag) - (z)CuOx filler metal compositions relative to comparable Ag-CuOx alloys. Likewise, the solidus was found to increase for these alloys, respectively by 185°C and 60°C, respectively for CuOx contents of y = 0 - 1mol% and 4 - 10 mol%. For the (100-y)(50Pd - 50Ag) - (y)CuOx alloys, the solidus increased between 280 - 390°C over a copper oxide compositional range of x = 0 to 8 mol%. It was determined from sessile drop experiments that palladium causes an increase in the wetting angle for all of the samples tested. Alloy compositions of (100-y)(25Pd - 75Ag) - (y)CuOx displayed increased wetting angles of 5-20° relative to comparable binary compositions. (100-y)(50Pd - 50Ag) - (y)CuOx alloys exhibited an increase in contact angle of 10-60° and compositions containing less than 10 mol% CuOx were not able to wet the substrate. Scanning electron microscopy indicates that the microstructure of the braze consists of Ag-Pd solid solution with CuOx precipitates. In general, a reaction layer consisting of CuAlO2 forms adjacent to the alumina substrate. However, the formation of this layer is apparently hindered by the addition of large amounts of palladium, causing poor wetting behavior, as denoted by substantial porosity found along

  10. Pd@Ag Nanosheets in Combination with Amphotericin B Exert a Potent Anti-Cryptococcal Fungicidal Effect.

    PubMed

    Zhang, Chao; Chen, Mei; Wang, Guizhen; Fang, Wei; Ye, Chen; Hu, Hanhua; Fa, Zhenzong; Yi, Jiu; Liao, Wan-Qing

    2016-01-01

    Silver nanoparticles have received considerable interest as new "nanoantibiotics" with the potential to kill drug-resistant microorganisms. Recently, a class of new core-shell nanostructures, Pd@Ag nanosheets (Pd@Ag NSs), were created using deposition techniques and demonstrated excellent inhibitory effects on various bacteria in vitro. In this study, we evaluated the antifungal activity of Pd@Ag NSs against common invasive fungal pathogens. Among these organisms, Cryptococcus neoformans complex species was most susceptible to Pd@Ag NSs, which exhibited potent antifungal activity against various molecular types or sources of cryptococcal strains including fluconazole-resistant isolates. The anticryptococcal activity of Pd@Ag NSs was significantly greater than fluconazole and similar to that of amphotericin B (AmB). At relatively high concentrations, Pd@Ag NSs exhibited fungicidal activity against Cryptococcus spp., which can likely be attributed to the disruption of cell integrity, intracellular protein synthesis, and energy metabolism. Intriguingly, Pd@Ag NSs also exhibited strong synergistic anti-cryptococcal fungicidal effects at low concentrations in combination with AmB but exhibited much better safety in erythrocytes than AmB, even at the minimal fungicidal concentration. Therefore, Pd@Ag NSs may be a promising adjunctive agent for treating cryptococcosis, and further investigation for clinical applications is required. PMID:27271376

  11. Pd@Ag Nanosheets in Combination with Amphotericin B Exert a Potent Anti-Cryptococcal Fungicidal Effect

    PubMed Central

    Wang, Guizhen; Fang, Wei; Ye, Chen; Hu, Hanhua; Fa, Zhenzong; Yi, Jiu; Liao, Wan-qing

    2016-01-01

    Silver nanoparticles have received considerable interest as new “nanoantibiotics” with the potential to kill drug-resistant microorganisms. Recently, a class of new core-shell nanostructures, Pd@Ag nanosheets (Pd@Ag NSs), were created using deposition techniques and demonstrated excellent inhibitory effects on various bacteria in vitro. In this study, we evaluated the antifungal activity of Pd@Ag NSs against common invasive fungal pathogens. Among these organisms, Cryptococcus neoformans complex species was most susceptible to Pd@Ag NSs, which exhibited potent antifungal activity against various molecular types or sources of cryptococcal strains including fluconazole-resistant isolates. The anticryptococcal activity of Pd@Ag NSs was significantly greater than fluconazole and similar to that of amphotericin B (AmB). At relatively high concentrations, Pd@Ag NSs exhibited fungicidal activity against Cryptococcus spp., which can likely be attributed to the disruption of cell integrity, intracellular protein synthesis, and energy metabolism. Intriguingly, Pd@Ag NSs also exhibited strong synergistic anti-cryptococcal fungicidal effects at low concentrations in combination with AmB but exhibited much better safety in erythrocytes than AmB, even at the minimal fungicidal concentration. Therefore, Pd@Ag NSs may be a promising adjunctive agent for treating cryptococcosis, and further investigation for clinical applications is required. PMID:27271376

  12. Selective Hydrogenation of Phenylacetylene on Bimetallic Cu-Pd and Cu-Pt Catalysts

    NASA Astrophysics Data System (ADS)

    Cladaras, George

    The development of selective catalysts has become a key concept in improving the efficiency of processes. Controlling the product distribution of a reaction can result in fewer by-products and reduce energy requirements for process equipment downstream. The selective hydrogenation of alkynes to alkenes is of major importance to industrial polymerization processes where alkyne/diene impurities can poison the polymerization catalyst and have an unwanted inhibiting effect on the growth of the polymer chain. In many circumstances, bimetallic catalysts have proved to have superior catalytic properties such as greater activity, selectivity or stability compared to their monometallic analogs. A study by the Sykes group (Chemistry, Tufts) in collaboration with our group has shown that in ultra-high vacuum (UHV), the addition of Pd minority species (0.01 ML) onto an otherwise inert Cu(111) single crystal surface can activate the Cu surface for selective hydrogenation reactions. This thesis work is an extension of the surface science study to the preparation of bimetallic catalysts at the nanoscale and their testing in hydrogenation reactions at ambient reaction conditions. The overall aim of this work was to develop single atom alloy Pd-Cu and Pt-Cu catalysts which are highly active and selective for the selective hydrogenation reaction of phenylacetylene to styrene. The bimetallic catalysts were prepared by a colloidal synthesis of Cu nanoparticles immobilized on gamma-alumina support and the precious metals as a minority species were deposited by galvanic replacement. The prepared materials and synthesis technique were characterized with electron microscopy (TEM), UV-Vis spectroscopy, X-Ray diffraction (XRD), temperature programmed reduction (TPR), BET surface area measurements, chemisorption experiments and X-ray photoelectron spectroscopy (XPS). The resulting catalysts can be described as gamma-Al2O3 supported Cu nanoparticles with a narrow size distribution. The Pt/Pd

  13. About contaminant element composition of roadside dust samples from Budapest and Seoul, including Pt and Pd

    NASA Astrophysics Data System (ADS)

    Sager, M.; Chon, H. T.; Marton, L.

    2012-04-01

    Roadside dust was sampled in Seoul megacity /Korea as well as in Budapest and some other places in Hungary, digested with reverse aqua regia in presence of bromine, and analyzed for 29 chemical elements with ICP-OES and ICP-MS methods. In addition to rather traditionally investigated elements, like Pb-Cd-Cr-Ni-As-Sb, newly emerging Pt and Pd from abrasion of automotive catalysts were included in the study. For the analysis of Pd, separation by precipitation with dithizone had to be applied. Principal component analysis was used as a tool to estimate the contribution of various sources. Geogenic element contents were used to estimate geogenic backgrounds und inputs from soils erosion. Seoul is an East Asian densely populated megacity, not far from the seaside, and surrounded by granite rocks. To the contrary, Budapest is a European continental city surrounded mainly by plains formed in the tertiary. Background concentrations were estimated from median concentrations in soils over alluvial deposits from the East of Austria, as well as from Poland. Background concentrations for Seoul were estimated from Shiheung farmland soil, a town close to the megacity. As a result, traffic related contaminations were highly effected by traffic related activities, like stop and go. Pt and Pb levels in roadside dusts from Budapest citiy were in the range of 2-133 μg/kg (av. 62,9 μg/kg), and 88 - 2838 mg/kg (av. 662 mg/kg) respectively. The highest Pt and Pb levels in roadside dust were found at major roads with high traffic volumes. Due to the geo-accumulation index, in all roadside soils sampled in Hungary, Cu-Pb-Zn were enriched, and Cd-Mo and occasionally Ba from Budapest in addition, but As-Co-Cr-Hg-Ni-Tl-V were not. In roadside dusts from Seoul, heavy contaminations of As-Cd-Cu-Mo-Pb-Zn were found, but no significant increase of Co-Cr-Ni-V. The pollution index, which refers to the permissible levels of As-Cd-Cu-Hg-Pb-Sb-Tl-V, indicates heavy pollution for roadside dusts from

  14. High-pressure/high-temperature synthesis and characterization of the first palladium or platinum containing lithium transition-metal sulfides Li2M3S4 (M=Pd, Pt)

    NASA Astrophysics Data System (ADS)

    Heymann, Gunter; Niehaus, Oliver; Krüger, Hannes; Selter, Philipp; Brunklaus, Gunther; Pöttgen, Rainer

    2016-10-01

    The new lithium transition-metal sulfides Li2M3S4 (M=Pd, Pt) were obtained via multianvil high-pressure/high-temperature syntheses at 8 GPa and 1150 °C starting from a stoichiometric mixture of lithium nitride, sulfur, and palladium or platinum. Single crystal structure analyses indicated the space group P21/c (no. 14) with the following lattice parameters and refinement results: a=492.9(1), b=1005.9(2), c=614.9(2) pm, β=110.9 (1)°, R1=0.0165, wR2=0.0308 (all data) for Li2Pd3S4 and a=498.2(1), b=1005.5(2), c=613.0(2) pm, β=110.8(1)°, R1=0.0215, wR2=0.0450 (all data) for Li2Pt3S4. The crystal structures are built up from two distinct Pd/Pt sites, one of which is a special position (0,0,0), two sulfur sites, and one lithium site. The atoms Pd2/Pt2 form isolated square planar PdS4/PtS4 units, whereas the Pd1/Pt1 atoms form pairs of square planar PdS4/PtS4 units, which are connected via a common edge. These two structural motives built up a three-dimensional network structure by linking through common corners. The lithium atoms are positioned inside of the so formed channels. Li2M3S4 (M=Pd, Pt) are isostructural to the minerals jaguéite, Cu2Pd3Se4 and chrisstanleyite, Ag2Pd3Se4, which are up to now the only representatives of this structure type. Both compounds were studied with respect to their magnetic properties and can be classified as Pauli paramagnetic or diamagnetic. Regarding the possibility of lithium mobility inside the channels, of the structure, solid state 7Li NMR and high-temperature single crystal investigations revealed localization of the lithium atoms on their crystallographic sites.

  15. From bio-mineralisation to fuel cells: biomanufacture of Pt and Pd nanocrystals for fuel cell electrode catalyst.

    PubMed

    Yong, P; Paterson-Beedle, M; Mikheenko, I P; Macaskie, L E

    2007-04-01

    Biosynthesis of nano-scale platinum and palladium was achieved via enzymatically-mediated deposition of metal ions from solution. The bio-accumulated Pt(0) and Pd(0) crystals were dried, applied onto carbon paper and tested as anodes in a polymer electrolyte membrane (PEM) fuel cell for power production. Up to 100% and 81% of the maximum power generation was achieved by the bio-Pt and bio-Pd catalysts, respectively, compared to commercial fuel cell grade Pt catalyst. Hence, biomineralisation could pave the way for economical production of fuel cell catalysts since previous studies have shown that precious metals can be biorecovered from wastes into catalytically active bionanomaterials.

  16. Ore mineralogy of the Serra Pelada Au-Pd-Pt deposit, Carajás, Brazil and implications for ore-forming processes

    NASA Astrophysics Data System (ADS)

    Berni, Gabriel V.; Heinrich, Christoph A.; Lobato, Lydia M.; Wall, Vic

    2016-08-01

    Serra Pelada is a world-class hydrothermal Au-Pd-Pt deposit located at the eastern border of the Amazon craton, northern Brazil. The rocks at Serra Pelada have experienced intense tropical weathering for about 70 Ma, but drill core samples preserve the primary mineralogy and hydrothermal alteration features, with extreme grades of Au, Pd and Pt individually reaching hundreds of parts per million (ppm) by weight. Mineralization at Serra Pelada occurs in hydrothermally altered metasiltstones and dolomitic metasandstones at the hinge zone of a recumbent syncline, comprising zones of hematite, chlorite-carbon, argillic, and siliceous alteration. The main hydrothermal gangue minerals are quartz, kaolinite, sericite, amesite, hematite, monazite, florencite and variable amounts of highly reflective carbonaceous matter. Hydrothermal carbon input is evident from precipitated carbon occurring along crenulation planes and veinlets associated with the precious metals. Ore and accessory minerals include a variety of sulphide, selenide, arsenide, sulphate and oxide minerals, including gold with variable metal contents, palladian gold, fischesserite, sudovikovite, sperrylite, selenian braggite, isomertieite, mertieite-II and secondary Au-Pt-Pd alloys. The composition of fischesserite varies from the ideal formula (Ag3AuSe2) towards a more Ag-rich composition, indicating a disordered solid solution form that is stable only above 260 °C, consistent with the high thermal maturity of associated carbonaceous matter approaching graphite. Primary ore and gangue minerals at Serra Pelada comprise a suite of elements that are best transported in oxidising conditions and precipitated upon reduction. This suggests that fluid mixing between a highly oxidised (metal carrier) and a reduced fluid was a key process for high-grade noble metal precipitation at Serra Pelada.

  17. Dissolution kinetics of Pd and Pt from automobile catalysts by naturally occurring complexing agents.

    PubMed

    Sebek, Ondřej; Mihaljevič, Martin; Strnad, Ladislav; Ettler, Vojtěch; Ježek, Josef; Stědrý, Robin; Drahota, Petr; Ackerman, Lukáš; Adamec, Vladimír

    2011-12-30

    Powder samples prepared from gasoline (Pt, Pd, Rh, new GN/old GO) and diesel (Pt, new DN/old DO) catalysts and recycled catalyst NIST 2556 were tested using kinetic leaching experiments following 1, 12, 24, 48, 168, 360, 720 and 1440-h interactions with solutions of 20mM citric acid (CA), 20 mM Na(2)P(4)O(7) (NaPyr), 1 g L(-1) NaCl (NaCl), a fulvic acid solution (FA-DOC 50 mg L(-1)) and 20 mM CA at pH 3, 4, 5, 6, 7, 8 and 9. The mobilisation of platinum group elements (PGEs) was fastest in solutions of CA and NaPyr. In the other interactions (NaCl, FA), the release of PGEs was probably followed by immobilisation processes, and the interactions were not found to correspond to the simple release of PGEs into solution. Because of their low concentrations, the individual complexing agents did not have any effect on the speciation of Pd and Pt in the extracts; both metals are present in solution as the complexes Me(OH)(2), Me(OH)(+). Immobilisation can take place through the adsorption of the positively charged hydroxyl complexes or flocculation of fulvic acid, complexing the PGEs on the surface of the extracted catalysts. The calculated normalised bulk released NRi values are similar to the reaction rate highest in the solutions of CA and NaPyr. PMID:22078491

  18. Growth of Pt/Cu(100): An Atomistic Modeling Comparison with the Pd/Cu(100) Surface Alloy

    NASA Technical Reports Server (NTRS)

    Demarco, Gustavo; Garces, Jorge E.; Bozzolo, Guillermo

    2002-01-01

    The Bozzolo, Ferrante, and Smith (BFS) method for alloys is applied to the study of Pt deposition on Cu(100). The formation of a Cu-Pt surface alloy is discussed within the framework of previous results for Pd/Cu(100). In spite of the fact that both Pd and Pt share the same basic behavior when deposited on Cu, it is seen that subtle differences become responsible for the differences in growth observed at higher cover-ages. In agreement with experiment, all the main features of Pt/Cu(100) and Pd/Cu(100) are obtained by means of a simple modeling scheme, and explained in terms of a few basic ingredients that emerge from the BFS analysis.

  19. Cluster Chemistry in Electron-Poor Ae-Pt-Cd Systems (Ae=Ca, Sr, Ba): (Sr,Ba)Pt2Cd4, Ca6Pt8Cd16, and Its Known Antitype Er6Pd16Sb8

    SciTech Connect

    Samal, Saroj L.; Gulo, Fakhili; Corbett, John D.

    2013-02-18

    Three new ternary polar intermetallic compounds, cubic Ca6Pt8Cd16, and tetragonal (Sr, Ba)Pt2Cd4 have been discovered during explorations of the Ae–Pt–Cd systems. Cubic Ca6Pt8Cd16 (Fm-3m, Z = 4, a = 13.513(1) Å) contains a 3D array of separate Cd8 tetrahedral stars (TS) that are both face capped along the axes and diagonally bridged by Pt atoms to generate the 3D anionic network Cd8[Pt(1)]6/2[Pt(2)]4/8. The complementary cationic surface of the cell consists of a face-centered cube of Pt(3)@Ca6 octahedra. This structure is an ordered ternary variant of Sc11Ir4 (Sc6Ir8Sc16), a stuffed version of the close relative Na6Au7Cd16, and a network inverse of the recent Er6Sb8Pd16 (compare Ca6Pt8Cd16). The three groups of elements each occur in only one structural version. The new AePt2Cd4, Ae = Sr, Ba, are tetragonal (P42/mnm,Z = 2, a ≈ 8.30 Å, c ≈ 4.47 Å) and contain chains of edge-sharing Cd4 tetrahedra along c that are bridged by four-bonded Ba/Sr. LMTO-ASA and ICOHP calculation results and comparisons show that the major bonding (Hamilton) populations in Ca6Pt8Cd16 and Er6Sb8Pd16 come from polar Pt–Cd and Pd–Sb interactions, that Pt exhibits larger relativistic contributions than Pd, that characteristic size and orbital differences are most evident for Sb 5s, Pt8, and Pd16, and that some terms remain incomparable, Ca–Cd versus Er–Pd.

  20. Tunable Catalysis of Water to Peroxide with Anionic, Cationic, and Neutral Atomic Au, Ag, Pd, Rh, and Os

    NASA Astrophysics Data System (ADS)

    Suggs, K.; Kiros, F.; Tesfamichael, A.; Felfli, Z.; Msezane, A. Z.

    2015-05-01

    Fundamental anionic, cationic, and neutral atomic metal predictions utilizing density functional theory calculations validate the recent discovery identifying the interplay between Regge resonances and Ramsauer-Townsend minima obtained through complex angular momentum analysis as the fundamental atomic mechanism underlying nanoscale catalysis. Here we investigate the optimization of the catalytic behavior of Au, Ag, Pd, Rh, and Os atomic systems via polarization effects and conclude that anionic atomic systems are optimal and therefore ideal for catalyzing the oxidation of water to peroxide, with anionic Os being the best candidate. The discovery that cationic systems increase the transition energy barrier in the synthesis of peroxide could be important as inhibitors in controlling and regulating catalysis. These findings usher in a fundamental and comprehensive atomic theoretical framework for the generation of tunable catalytic systems. The ultimate aim is to design giant atomic catalysts and sensors, in the context of the recently synthesized tri-metal Ag@Au@Pt and bimetal Ag@Au nanoparticles for greatly enhanced plasmonic properties and improved chemical stability for chemical and biological sensing. Research was supported by U.S. DOE Office of Basic Energy Sciences.

  1. Population genetic structure of Rhizoctonia solani AG 3-PT from potatoes in South Africa.

    PubMed

    Muzhinji, Norman; Woodhall, James W; Truter, Mariette; van der Waals, Jacquie E

    2016-05-01

    Rhizoctonia solani AG 3-PT is an important potato pathogen causing significant yield and quality losses in potato production. However, little is known about the levels of genetic diversity and structure of this pathogen in South Africa. A total of 114 R. solani AG 3-PT isolates collected from four geographic regions were analysed for genetic diversity and structure using eight microsatellite loci. Microsatellite analysis found high intra-population genetic diversity, population differentiation and evidence of recombination. A total of 78 multilocus genotypes were identified with few shared among populations. Low levels of clonality (13-39 %) and high levels of population differentiation were observed among populations. Most of the loci were in Hardy-Weinberg equilibrium and all four populations showed evidence of a mixed reproductive mode of both clonality and recombination. The PCoA clustering method revealed genetically distinct geographic populations of R. solani AG 3-PT in South Africa. This study showed that populations of R. solani AG 3-PT in South Africa are genetically differentiated and disease management strategies should be applied accordingly. This is the first study of the population genetics of R. solani AG 3-PT in South Africa and results may help to develop knowledge-based disease management strategies.

  2. DFT study of selective hydrogenation of acetylene to ethylene on Pd doping Ag nanoclusters

    NASA Astrophysics Data System (ADS)

    Liu, D.

    2016-11-01

    Recently, it has been reported that the reaction selectivity of catalytic hydrogenation of acetylene to ethylene can be significantly enhanced via the approach of Pd mono-atomic catalysis [Pei et al. ACS Catal. 5 (2015) 3717-3725]. To explain the catalytic mechanism of this binary alloy catalyst, C2H2 hydrogenation reactions on Pd doping Ag nanoclusters are studied using density functional theory simulations. The simulation results indicate that H2 and C2H2 can simultaneously bind with a single Pd doping atom no matter it is on vertex and edge sites of Ag clusters. The following H2 dissociation and C2H2 hydrogenation are not difficult since the corresponding reaction barrier values are no more than 0.58 eV. The generated C2H4 molecule can not be further hydrogenated since it locates on the top of Pd doping atom, which is the only adsorption site for H2. On two Pd doping atoms at contiguous sites of Ag clusters, C2H4 hydrogenation reactions can be carried out since there are enough sites for co-adsorption of H2 and C2H4.

  3. Synthesis of Pd9Ru@Pt nanoparticles for oxygen reduction reaction in acidic electrolytes

    SciTech Connect

    Sun, Yu; Hsieh, Yu -Chi; Chang, Li -Chung; Wu, Pu -Wei; Lee, Jyh -Fu

    2014-11-22

    Nanoparticles of PdRu, Pd₃Ru, and Pd₉Ru are synthesized and impregnated on carbon black via a wet chemical reflux process. X-ray diffraction patterns of the as-synthesized samples, PdxRu/C (x=1/3/9), suggest succesful formation of alloy without presence of individual Pd and Ru nanoparticles. Images from transmission electron microscope confirm irregularly-shaped nanoparticles with average size below 3 nm. Analysis from extended X-ray absorption fine structure on both Pd and Ru K-edge absorption profiles indicate the Ru atoms are enriched on the surface of PdxRu/C. Among these samples, the Pd₉Ru/C exhibits the strongest electrocatalytic activity for oxygen reduction reaction (ORR) in an oxygen-saturated 0.1 M aqueous HClO₄ solution. Subsequently, the Pd₉Ru/C undegoes Cu under potential deposition, followed by a galvanic displacement reaction to deposit a Pt monolayer on the Pd₉Ru surface (Pd₉Ru@Pt). The Pd₉Ru@Pt reveals better ORR performance than that of Pt, reaching a mass activity of 0.38 mA μg⁻¹ Pt, as compared to that of commercially available Pt nanoparticles (0.107 mA μg⁻¹ Pt). Thus, the mechanisms responsible for the ORR enhancement are attributed to the combined effects of lattice strain and ligand interaction. In addition, this core-shell Pd₉Ru@Pt electrocatalyst represents a substantial reduction in the amount of Pt consumption and raw material cost.

  4. Tunable magnetization dynamics in disordered FePdPt ternary alloys: Effects of spin orbit coupling

    SciTech Connect

    Ma, L.; Fan, W. J. Chen, F. L.; Zhou, S. M.; Li, S. F.; Lai, T. S.; He, P.; Xu, X. G.; Jiang, Y.

    2014-09-21

    The magnetization dynamics of disordered Fe₀.₅(Pd{sub 1–x}Pt{sub x})₀.₅ alloy films was studied by time-resolved magneto-optical Kerr effect and ferromagnetic resonance. The intrinsic Gilbert damping parameter α₀ and the resonance linewidth change linearly with the Pt atomic concentration. In particular, the induced in-plane uniaxial anisotropy constant K{sub U} also increases for x increasing from 0 to 1. All these results can be attributed to the tuning effect of the spin orbit coupling. For the disordered ternary alloys, an approach is proposed to control the induced in-plane uniaxial anisotropy, different from conventional thermal treat methods, which is helpful to design and fabrications of spintronic devices.

  5. In vitro cytotoxicity of Ag-Pd-Cu-based casting alloys.

    PubMed

    Niemi, L; Hensten-Pettersen, A

    1985-01-01

    The cytotoxicity and its correlation to alloy composition, structure, corrosion, as well as galvanic coupling was studied with 12 Ag-Pd-Cu-type alloys, one conventional type III gold alloy and pure Ag, Cu, and Pd. The agar overlay cell culture technique was used. Single phase binary CuPd alloys were only slightly cytotoxic below a Cu content of 30 wt%. The tested multiphase alloys were all toxic, but no correlation between toxicity and Cu content could be observed. Solid solution annealing increased the cytotoxicity of a multiphase alloy. Exposure of a single phase alloy to an artificial saliva for 1 week prior to the test decreased its cytotoxicity significantly. Galvanic coupling of the alloys through an outer copper wire decreased their cytotoxicity.

  6. Asymmetric AgPd-AuNR heterostructure with enhanced photothermal performance and SERS activity

    NASA Astrophysics Data System (ADS)

    Zhang, Han; Liu, Zeke; Kang, Xiaolin; Guo, Jun; Ma, Wanli; Cheng, Si

    2016-01-01

    Most as-reported nanostructures through galvanic replacement reactions are still symmetric hollow structures, until now. Asymmetric structures fabricated through a galvanic replacement reaction have been rarely reported. However, asymmetric heterostructures can generally lead to new intriguing properties through asymmetric synergistic coupling. Here, we report a simple synthesis of an asymmetric one-ended AgPd bimetal on Au nanorods (AuNR) by combining a galvanic replacement reaction with an Ostwald ripening process. The morphological evolution from a nanodumbbell to a dandelion structure is thoroughly investigated. The unique asymmetric AgPd-AuNR heterostructures possess the required plasmonic performance and avoid strong damping caused by the poor plasmonic metal Pd, resulting in a superior photothermal heating performance and enhanced SERS sensitivity for in situ monitoring of a catalytic reaction compared with the symmetric counterparts.Most as-reported nanostructures through galvanic replacement reactions are still symmetric hollow structures, until now. Asymmetric structures fabricated through a galvanic replacement reaction have been rarely reported. However, asymmetric heterostructures can generally lead to new intriguing properties through asymmetric synergistic coupling. Here, we report a simple synthesis of an asymmetric one-ended AgPd bimetal on Au nanorods (AuNR) by combining a galvanic replacement reaction with an Ostwald ripening process. The morphological evolution from a nanodumbbell to a dandelion structure is thoroughly investigated. The unique asymmetric AgPd-AuNR heterostructures possess the required plasmonic performance and avoid strong damping caused by the poor plasmonic metal Pd, resulting in a superior photothermal heating performance and enhanced SERS sensitivity for in situ monitoring of a catalytic reaction compared with the symmetric counterparts. Electronic supplementary information (ESI) available. See DOI: 10.1039/c5nr07333b

  7. Heterogenized Bimetallic Pd-Pt-Fe3O4 Nanoflakes as Extremely Robust, Magnetically Recyclable Catalysts for Chemoselective Nitroarene Reduction.

    PubMed

    Byun, Sangmoon; Song, Yeami; Kim, B Moon

    2016-06-15

    A very simple synthesis of bimetallic Pd-Pt-Fe3O4 nanoflake-shaped alloy nanoparticles (NPs) for cascade catalytic reactions such as dehydrogenation of ammonia-borane (AB) followed by the reduction of nitro compounds (R-NO2) to anilines or alkylamines (R-NH2) in methanol at ambient temperature is described. The Pd-Pt-Fe3O4 NPs were easily prepared via a solution phase hydrothermal method involving the simple one-pot coreduction of potassium tetrachloroplatinate (II) and palladium chloride (II) in polyvinylpyrrolidone with subsequent deposition on commercially available Fe3O4 NPs. The bimetallic Pd-Pt alloy NPs decorated on Fe3O4 NPs provide a unique synergistic effect for the catalysis of cascade dehydrogenation/reduction. Various nitroarene derivatives were reduced to anilines with very specific chemoselectivity in the presence of other reducible functional groups. The bimetallic Pd-Pt-Fe3O4 NPs provide a unique synergistic effect for the catalysis of cascade dehydrogenation/reduction. The nitro reduction proceeded in 5 min with nearly quantitative conversions and yields. Furthermore, the magnetically recyclable nanocatalysts were readily separated using an external magnet and reused up to 250 times without any loss of catalytic activity. A larger scale (10 mmol) reaction was also successfully performed with >99% yield. This efficient, recyclable Pd-Pt-Fe3O4 NPs system can therefore be repetitively utilized for the reduction of various nitro-containing compounds. PMID:27191706

  8. Reaction-driven restructuring of Pt and Pd catalysts: In operando X-ray absorption spectroscopy study

    NASA Astrophysics Data System (ADS)

    Elsen, Annika; Jung, Ulrich; Li, Yuanyuan; Frenkel, Anatoly; Nuzzo, Ralph

    2014-03-01

    The catalyzed hydrogenation of ethylene on supported metal catalysts has been intensively investigated, mainly because this reaction lies at the heart of many industrial processes. Most previous studies have been performed using surface science techniques in UHV. Therefor little is known about the nature of the active state of the catalyst at ambient pressure where the kinetics is very different. We employed operando X-ray absorption spectroscopy (XAS) to correlate the structural changes of SiO2-supported Pt and Pd catalysts with their activity for ethylene hydrogenation. The XAS experiments were performed at the beamlines X19A and X18B, NSLS, BNL. For both catalysts, strong and largely reversible transformations of the metal bonding were identified at about the maximum ethane conversion. The changes were different for Pt/SiO2 and Pd/SiO2 due to the ability of the latter to form bulk hydride, while the former can only adsorb hydrogen on the surface. As a result, Pt/SiO2 undergoes disordering of the surface, leading to a strong reduction of the Pt-Pt coordination number under H2-deficient conditions, while the main effect for Pd/SiO2 is the hydrogen uptake with concomitant increase in Pd-Pd bond length. The correlation between these different kinds of order transitions and differences in rates for these catalysts will be discussed.

  9. Anthropogenic platinum group element (Pt, Pd, Rh) concentrations in PM10 and PM2.5 from Kolkata, India.

    PubMed

    Diong, Huey Ting; Das, Reshmi; Khezri, Bahareh; Srivastava, Bijayen; Wang, Xianfeng; Sikdar, Pradip K; Webster, Richard D

    2016-01-01

    This study investigates platinum group elements (PGEs) in the breathable (PM10) and respirable (PM2.5) fractions of air particulates from a heavily polluted Indian metro city. The samples were collected from traffic junctions at the heart of the city and industrial sites in the suburbs during winter and monsoon seasons of 2013-2014. PGE concentrations were determined by inductively coupled plasma-mass spectrometry (ICP-MS). The PGE concentrations in the samples from traffic junctions are within the range of 2.7-111 ng/m(3) for Pd, 0.86-12.3 ng/m(3) for Pt and 0.09-3.13 ng/m(3) for Rh, and from industrial sites are within the range of 3.12-32.3 ng/m(3) for Pd, 0.73-7.39 ng/m(3) for Pt and 0.1-0.69 ng/m(3) for Rh. Pt concentrations were lower in the monsoon compared to winter while Pd concentrations increased during monsoon and Rh stayed relatively unaffected across seasons. For all seasons and locations, concentrations of Pd > Pt > Rh, indicating dominance of Pd-containing exhaust converters. Most of the PGEs were concentrated in the PM2.5 fraction. A strong correlation (R ≥ 0.62) between the PGEs from traffic junction indicates a common emission source viz. catalytic converters, whereas a moderate to weak correlation (R ≤ 0.5) from the industrial sites indicate mixing of different sources like coal, raw materials used in the factories and automobile. A wider range of Pt/Pd, Pt/Rh and Pd/Rh ratios measured in the traffic junction possibly hint towards varying proportions of PGEs used for catalyst productions in numerous rising and established car brands. PMID:27536525

  10. Anthropogenic platinum group element (Pt, Pd, Rh) concentrations in PM10 and PM2.5 from Kolkata, India.

    PubMed

    Diong, Huey Ting; Das, Reshmi; Khezri, Bahareh; Srivastava, Bijayen; Wang, Xianfeng; Sikdar, Pradip K; Webster, Richard D

    2016-01-01

    This study investigates platinum group elements (PGEs) in the breathable (PM10) and respirable (PM2.5) fractions of air particulates from a heavily polluted Indian metro city. The samples were collected from traffic junctions at the heart of the city and industrial sites in the suburbs during winter and monsoon seasons of 2013-2014. PGE concentrations were determined by inductively coupled plasma-mass spectrometry (ICP-MS). The PGE concentrations in the samples from traffic junctions are within the range of 2.7-111 ng/m(3) for Pd, 0.86-12.3 ng/m(3) for Pt and 0.09-3.13 ng/m(3) for Rh, and from industrial sites are within the range of 3.12-32.3 ng/m(3) for Pd, 0.73-7.39 ng/m(3) for Pt and 0.1-0.69 ng/m(3) for Rh. Pt concentrations were lower in the monsoon compared to winter while Pd concentrations increased during monsoon and Rh stayed relatively unaffected across seasons. For all seasons and locations, concentrations of Pd > Pt > Rh, indicating dominance of Pd-containing exhaust converters. Most of the PGEs were concentrated in the PM2.5 fraction. A strong correlation (R ≥ 0.62) between the PGEs from traffic junction indicates a common emission source viz. catalytic converters, whereas a moderate to weak correlation (R ≤ 0.5) from the industrial sites indicate mixing of different sources like coal, raw materials used in the factories and automobile. A wider range of Pt/Pd, Pt/Rh and Pd/Rh ratios measured in the traffic junction possibly hint towards varying proportions of PGEs used for catalyst productions in numerous rising and established car brands.

  11. Screening of electrocatalysts for direct ammonia fuel cell: Ammonia oxidation on PtMe (Me: Ir, Rh, Pd, Ru) and preferentially oriented Pt(1 0 0) nanoparticles

    NASA Astrophysics Data System (ADS)

    Vidal-Iglesias, F. J.; Solla-Gullón, J.; Montiel, V.; Feliu, J. M.; Aldaz, A.

    Ammonia has attracted attention as a possible fuel for direct fuel cells since it is easy to handle and to transport as liquid or as concentrated aqueous solution. However, on noble metal electrodes ammonia oxidation is a sluggish reaction and the electrocatalyst needs to be improved for developing efficient ammonia fuel cells. In this work, ammonia electrooxidation reaction on 3-4-nm bimetallic PtMe (Ir, Rh, Pd, Ru) and on preferentially oriented Pt(1 0 0) nanoparticles is reported. PtMe nanoparticles have been prepared by using water-in-oil microemulsions to obtain a narrow size distribution whereas preferentially oriented Pt nanoparticles have been prepared through colloidal routes. Among all the bimetallic samples tested, only Pt 75Ir 25 and Pt 75Rh 25 nanoparticles show, at the low potential range, an enhancement of the oxidation density current with respect to the behaviour found for pure platinum nanoparticles prepared by the same method. In addition, two Pt(1 0 0) preferentially oriented nanoparticles of different particle size (4 and 9 nm) have been also studied. These oriented nanoparticles show higher current densities than polycrystalline Pt nanoparticles due to the sensitivity of ammonia oxidation toward the presence of surface sites with square symmetry. The reactivity of the different 4-nm nanoparticles parallels well with that expected from bulk PtMe alloys and Pt single crystal electrodes.

  12. Selective hydrodechlorination of 1,2-dichloroethane to ethylene over Pd-Ag/Al2O3 catalysts prepared by surface reduction

    NASA Astrophysics Data System (ADS)

    Han, Yuxiang; Gu, Guangfeng; Sun, Jingya; Wang, Wenjuan; Wan, Haiqin; Xu, Zhaoyi; Zheng, Shourong

    2015-11-01

    Alumina supported Pd-Ag and (Cu) bimetallic catalysts (denoted as sr-Pd-Ag/Al2O3 or sr-Pd-Cu/Al2O3) with varied Pd/Ag (or Cu) ratios were prepared using the surface reduction method, and the gas-phase catalytic hydrodechlorination of 1,2-dichloroethane over the catalysts were investigated. For comparison, Pd-Ag bimetallic catalysts were prepared by the conventional co-impregnation method (denoted as im-Pd-Ag/Al2O3). The catalysts were characterized by N2 adsorption, X-ray diffraction, transmission electron microscopy, X-ray photoelectron spectroscopy, and CO chemisorption. Characterization results indicated that surface reduction led to selective deposition of metallic Ag on the surface of Pd particles, while Pd and Ag just disorderly mixed in the catalyst prepared by impregnation method. Therefore, sr-Pd-Ag/Al2O3 exhibited a higher ethylene selectivity than im-Pd-Ag/Al2O3 for hydrodechlorination of 1,2-dichloroethane at a similar Ag loading amount. Moreover, among sr-Pd-Ag/Al2O3, sr-Pd-Cu/Al2O3 and im-Pd-Ag/Al2O3 catalysts, the ethylene selectivity decreased over these catalysts following the order: sr-Pd-Ag/Al2O3 > sr-Pd-Cu/Al2O3 > im-Pd-Ag/Al2O3. The present results indicate that surface reduction can be used as a potential method to synthesize catalyst with enhanced ethylene selectivity in hydrodechlorination of 1,2-dichloroethane.

  13. Bidirectional threshold switching characteristics in Ag/ZrO2/Pt electrochemical metallization cells

    NASA Astrophysics Data System (ADS)

    Du, Gang; Wang, Chao; Li, Hongxia; Mao, Qinan; Ji, Zhenguo

    2016-08-01

    A bidirectional threshold switching (TS) characteristic was demonstrated in Ag/ZrO2/Pt electrochemical metallization cells by using the electrochemical active Ag electrode and appropriate programming operation strategies The volatile TS was stable and reproducible and the rectify ratio could be tuned to ˜107 by engineering the compliance current. We infer that the volatile behavior is essentially due to the moisture absorption in the electron beam evaporated films, which remarkably improved the anodic oxidation as well as the migration of Ag+ ions. The resultant electromotive force would act as a driving force for the metal filaments dissolution, leading to the spontaneous volatile characteristics. Moreover, conductance quantization behaviors were also achieved owing to formation and annihilation of atomic scale metal filaments in the film matrix. Our results illustrate that the Ag/ZrO2/Pt device with superior TS performances is a promising candidate for selector applications in passive crossbar arrays.

  14. Combinatorial PtSnM (M = Fe, Ni, Ru and Pd) nanoparticle catalyst library toward ethanol electrooxidation

    NASA Astrophysics Data System (ADS)

    Almeida, T. S.; Van Wassen, A. R.; VanDover, R. B.; de Andrade, A. R.; Abruña, H. D.

    2015-06-01

    Electrode arrays containing 91 combinations of Pt-Sn-M (M = Fe, Ni, Pd, and Ru) were prepared by borohydride reduction of aqueous metal salts on carbon paper, and screened by fluorescence assay for activity as ethanol electrooxidation catalysts. Catalysts that showed high activity for this reaction were identified as being Pt(80)Sn(10)Fe(10), Pt(80)Sn(10)Ni(10), Pt(70)Sn(20)Pd(10), and Pt(70)Sn(10)Ru(20) (numbers in parenthesis indicate atomic percent). These were significantly more active than Pt or PtSn catalysts, also present in the electrode arrays. These 4 compositions were synthesized as nanoparticles and characterized physically and electrochemically. X-ray diffraction showed a Pt face-centered cubic (fcc) structure with an average crystallite size of about 2.0 nm for all catalysts. The electrochemical tests for the oxidation of ethanol revealed excellent electrocatalytic activity and single cell (fuel cell) power density for all four catalyst formulations. Fe-containing catalysts exhibited the highest activity (13 A gPt-1) and single-cell performance (50 mW cm-2) followed by Ni- and Pd-containing materials with similar results; electrocatalytic activity around 10 A gPt-1 and power densities of 43 mW cm-2. The lowest performance was observed for the Ru-containing catalyst. However, its single-cell performance (30 mW cm-2) was still comparable to that of the commercial PtSn-Etek electrocatalyst.

  15. In situ spectroscopic ellipsometry during atomic layer deposition of Pt, Ru and Pd

    NASA Astrophysics Data System (ADS)

    Leick, N.; Weber, J. W.; Mackus, A. J. M.; Weber, M. J.; van de Sanden, M. C. M.; Kessels, W. M. M.

    2016-03-01

    The preparation of ultra-thin platinum-group metal films, such as Pt, Ru and Pd, by atomic layer deposition (ALD) was monitored in situ using spectroscopic ellipsometry in the photon energy range of 0.75-5 eV. The metals’ dielectric function was parametrized using a ‘flexible’ Kramers-Kronig consistent dielectric function because it was able to provide accurate curve shape control over the optical response of the metals. From this dielectric function, it was possible to extract the film thickness values during the ALD process. The important ALD process parameters, such as the nucleation period and growth per cycle of Pt, Ru and Pd could be determined from the thickness evolution. In addition to process parameters, the film resistivity in particular could be extracted from the modeled dielectric function. Spectroscopic ellipsometry thereby revealed itself as a feasible and valuable technique to be used in research and development applications, as well as for process monitoring during ALD.

  16. Multi-walled carbon nanotube supported Pd and Pt nanoparticles with high solution affinity for effective electrocatalysis

    NASA Astrophysics Data System (ADS)

    Ye, Weichun; Hu, Haiyuan; Zhang, Hong; Zhou, Feng; Liu, Weimin

    2010-09-01

    Multi-walled carbon nanotubes (MWCNTs) are easily wrapped with a functional biopolymer—polydopamine (Pdop) through self-polymerization of dopamine in a mild basic solution. The MWCNTs@Pdop exhibits long term dispersivity in water for at least one month. The Pdop has large capacity to coordinate [PdCl 4] 2- and [PtCl 6] 2- that upon reduction transform to corresponding metal nanoparticles. The nanoparticles strongly adhere to Pdop layer and can be used for the electrooxidation of haydrazine and methanol, respectively. Compared to Pd and Pt supported on unmodified MWCNTs, the Pd and Pt nanoparticle decorated on MWCNTs@Pdop exhibit much higher electrocatalytic activity and enhanced stability.

  17. Quantum valley Hall states and topological transitions in Pt(Ni, Pd)-decorated silicene: A first-principles study

    SciTech Connect

    Zhao, Bao; Zhang, Jiayong; Wang, Yicheng; Yang, Zhongqin

    2014-12-28

    The electronic states and topological behaviors of Pt(Ni, Pd)-decorated silicene are investigated by using an ab-initio method. All the three kinds of the adatoms prefer hollow sites of the silicene, guaranteeing the Dirac cones unbroken. The Pt(Ni, Pd)-decorated silicene systems all present quantum valley Hall (QVH) states with the gap opened exactly at the Fermi level. The gaps of the QVH states can be increased substantially by applying a positive electric field. Very fascinating phase transitions from QVH to quantum spin Hall (QSH) and then to QVH again are achieved in the Pt/Ni-decorated silicene when a negative electric field is applied. The QSH state in the Pd case with a negative electric field is, however, quenched because of relatively larger Rashba spin-orbit coupling (SOC) than the intrinsic SOC in the system. Our findings may be useful for the applications of silicene-based devices in valleytronics and spintronics.

  18. Quantum valley Hall states and topological transitions in Pt(Ni, Pd)-decorated silicene: a first-principles study.

    PubMed

    Zhao, Bao; Zhang, Jiayong; Wang, Yicheng; Yang, Zhongqin

    2014-12-28

    The electronic states and topological behaviors of Pt(Ni, Pd)-decorated silicene are investigated by using an ab-initio method. All the three kinds of the adatoms prefer hollow sites of the silicene, guaranteeing the Dirac cones unbroken. The Pt(Ni, Pd)-decorated silicene systems all present quantum valley Hall (QVH) states with the gap opened exactly at the Fermi level. The gaps of the QVH states can be increased substantially by applying a positive electric field. Very fascinating phase transitions from QVH to quantum spin Hall (QSH) and then to QVH again are achieved in the Pt/Ni-decorated silicene when a negative electric field is applied. The QSH state in the Pd case with a negative electric field is, however, quenched because of relatively larger Rashba spin-orbit coupling (SOC) than the intrinsic SOC in the system. Our findings may be useful for the applications of silicene-based devices in valleytronics and spintronics.

  19. Five-fold twinned Pd2NiAg nanocrystals with increased surface Ni site availability to improve oxygen reduction activity.

    PubMed

    Liu, Suli; Zhang, Qinghua; Li, Yafei; Han, Min; Gu, Lin; Nan, Cewen; Bao, Jianchun; Dai, Zhihui

    2015-03-01

    The synthesis of highly active oxygen reduction reaction (ORR) catalysts with good durability and low cost is highly desirable but still remains a significant challenge. In this work, we present the synthesis of five-fold twinned Pd2NiAg nanocrystals (NCs) with a Ni-terminal surface which exhibit excellent electrocatalytic performance for ORR in alkaline media, even better than the performance of the commercial Pt/C catalyst. Using high-angle annular-dark-field imaging together with density functional theory calculations, it is found that the surfaces of the five-fold twinned Pd2NiAg NCs exhibit an unusual valence electron density. The maximum catalytic activity originates from the increased availability of surface Ni sites in five-fold twinned Pd2NiAg NCs and the features of twinned structural defects. This study provides an explanation of the enhanced ORR from the special structure of this novel material, which opens up new avenues for the design of novel classes of electrocatalysts for fuel cells and metal-air batteries. PMID:25626352

  20. Pd-Ag chronology of volatile depletion, crystallization and shock in the Muonionalusta IVA iron meteorite and implications for its parent body

    NASA Astrophysics Data System (ADS)

    Horan, M. F.; Carlson, R. W.; Blichert-Toft, J.

    2012-10-01

    Muonionalusta, a Group IVA iron meteorite, was analyzed for its 107Pd-107Ag isotope systematics by multi-collector inductively coupled plasma mass spectrometry (MC-ICP-MS) in order to better constrain the initial Solar System abundance of 107Pd and to provide high resolution chronology of the evolution of its parent body. Six metal samples from Muonionalusta yield Ag abundances between 0.1012 and 1.461 ng/g, 107Ag/109Ag between 1.131 and 1.805, with 108Pd/109Ag ratios of 2201 to 52,300. The metal Pd/Ag and Ag isotopic data are correlated with a slope corresponding to a 107Pd/108Pd of (2.15±0.30)×10-5. If the Pd-Ag and Pb-Pb isotope systems closed at the same time in Muonionalusta, i.e., 2-3 Ma after CAI formation, then an initial Solar System ratio of 107Pd/108Pd=(2.8±0.5)×10-5 can be inferred. One troilite sample contains 8.478 ng/g Ag and has a 107Ag/109Ag ratio of 1.0833; its Pd concentration is 205.2 ng/g corresponding to a low 108Pd/109Ag of 13.56. The Pd-Ag results for this troilite plot near the extrapolation of the line passing through the metal points and define an initial 107Ag/109Ag that is substantially higher than chondritic, indicating that Muonionalusta formed from a precursor with high Pd/Ag. Pd and Ag concentrations in Muonionalusta metal suggest fractional crystallization from a source having Pd/Ag>4500, but the initial Ag isotopic composition for Muonionalusta troilite limits the duration of the high Pd/Ag to an interval of ≤0.6 Ma before cooling to closure of the Pd-Ag system. This result suggests that depletion of Ag and other volatile elements occurred shortly before accretion and cooling of the IVA parent body, and may have been associated with violent disruption of a progenitor to the IVA parent. Another troilite sample, its chromite inclusions and adjacent metal were isotopically homogenized locally after 107Pd had decayed, possibly by a later episode of shock >50 Ma after Solar System formation.

  1. Capability of defective graphene-supported Pd13 and Ag13 particles for mercury adsorption

    NASA Astrophysics Data System (ADS)

    Meeprasert, Jittima; Junkaew, Anchalee; Rungnim, Chompoonut; Kunaseth, Manaschai; Kungwan, Nawee; Promarak, Vinich; Namuangruk, Supawadee

    2016-02-01

    Reactivity of single-vacancy defective graphene (DG) and DG-supported Pdn and Agn (n = 1, 13) for mercury (Hg0) adsorption has been studied using density functional theory calculation. The results show that Pdn binds defective site of DG much stronger than the Agn, while metal nanocluster binds DG stronger than single metal atom. Metal clustering affects the adsorption ability of Pd composite while that of Ag is comparatively less. The binding strength of -8.49 eV was found for Pd13 binding on DG surface, indicating its high stability. Analyses of structure, energy, partial density of states, and d-band center (ɛd) revealed that the adsorbed metal atom or cluster enhances the reactivity of DG toward Hg adsorption. In addition, the Hg adsorption ability of Mn-DG composite is found to be related to the ɛd of the deposited Mn, in which the closer ɛd of Mn to the Fermi level correspond to the higher adsorption strength of Hg on Mn-DG composite. The order of Hg adsorption strength on Mn-DG composite are as follows: Pd13 (-1.68 eV) >> Ag13 (-0.67 eV) ∼ Ag1 (-0.69 eV) > Pd1 (-0.62 eV). Pd13-DG composite is therefore more efficient sorbent for Hg0 removal in terms of high stability and high adsorption reactivity compared to the Ag13. Further design of highly efficient carbon based sorbents should be focused on tailoring the ɛd of deposited metals.

  2. Experimental and theoretical investigations of the polar intermetallics SrPt3Al2 and Sr2Pd2Al

    NASA Astrophysics Data System (ADS)

    Stegemann, Frank; Benndorf, Christopher; Touzani, Rachid St.; Fokwa, Boniface P. T.; Janka, Oliver

    2016-10-01

    SrPt3Al2, a CaCu5 relative (P6/mmm; a = 566.29(3), c = 389.39(3) pm; wR2 = 0.0202, 121 F2 values, 9 parameters), and Sr2Pd2Al, isostructural to Ca2Pt2Ge (Fdd2; a = 1041.45(5), b = 1558.24(7), c = 604.37(3) pm; wR2 = 0.0291, 844 F2 values, 25 parameters) have been prepared from the elements. The crystal structures have been investigated by single crystal X-ray diffraction. Structural relaxation confirmed the electronic stability of SrPt3Al2, while orthorhombic Sr2Pd2Al might be a metastable polymorph as it is energetically competitive to its monoclinic variant. Both compounds are predicted to be metallic conductors as their density-of-states (DOS) are non-zero at the Fermi level. COHP bonding analysis coupled with Bader effective charge analysis suggest that the title compounds are polar intermetallic phases in which strong Pt-Al and Pd-Al covalent bonds are present, while a significant electron transfer from Sr atoms to the [Pt3Al2]δ- or [Pd2Al]δ- network is found.

  3. Synthesis and Catalytic Activity of Pt Monolayer on Pd Tetrahedral Nanocrystals with CO-adsorption-induced Removal of Surfactants

    SciTech Connect

    Gong K.; Vukmirovic M.B.; Ma C.; Zhu Y.; Adzic R.R.

    2011-11-01

    We synthesized the Pt monolayer shell-Pd tetrahedral core electrocatalysts that are notable for their high activity and stable performance. A small number of low-coordination sites and defects, and high content of the (1 1 1)-oriented facets on Pd tetrahedron makes them a suitable support for a Pt monolayer to obtain an active O{sub 2} reduction reaction (ORR) electrocatalyst. The surfactants, used to control size and shape of Pd tetrahedral nanoparticles, are difficult to remove and cause adverse effects on the ORR. We describe a simple and noninvasive method to synthesize high-purity tetrahedral Pd nanocrystals (TH Pd) by combining a hydrothermal route and CO adsorption-induced removal of surfactants. Poly(vinylpyrrolidone) (PVP), used as a protecting and reducing agent in hydrothermal reactions, is strongly bonded to the surface of the resulting nanocrystals. We demonstrate that PVP was displaced efficiently by adsorbed CO. A clean surface was achieved upon CO stripping at a high potential (1.0 V vs RHE). It played a decisive role in improving the activity of the Pt monolayer/TH Pd electrocatalyst for the ORR. Furthermore, the results demonstrate a versatile method for removal of surfactants from various nanoparticles that severely limited their applications.

  4. Enhanced electrocatalytic activity and stability of Pd3V/C nanoparticles with a trace amount of Pt decoration for the oxygen reduction reaction

    SciTech Connect

    Liu, Sufen; Han, Lili; Zhu, Jing; Xiao, Weiping; Wang, Jie; Liu, Hongfang; Xin, Huolin; Wang, Deli

    2015-09-14

    In this study, carbon supported Pd3V bimetallic alloy nanoparticles (Pd3V/C) have been successfully synthesized via a simple impregnation–reduction method, followed by high temperature treatment under a H2 atmosphere. Electrochemical tests reveal that the half-wave potential of Pd3V/C-500 shifts positively 40 mV compared with Pd/C. However, the catalytic activity of Pd3V/C-500 suffers from serious degradation after 1k cycles. By a spontaneous displacement reaction or co-reduction method, a trace amount of Pt was decorated on the surface or inside of the Pd3V/C nanoparticles. The catalytic activity and stability of the Pd3V@Pt/C and Pt-Pd3V/C catalysts for the oxygen reduction reaction (ORR) are enhanced significantly, and are comparable to commercial Pt/C. In addition, the Pt mass activity of Pd3V@Pt/C and Pt-Pd3V/C improves by factors of 10.9 and 6.5 at 0.80 V relative to Pt/C. Moreover, Pt-decorated Pd3V/C nanoparticles show almost no obvious morphology change after durability tests, because the Pt-rich shell plays an important role in preventing degradation.

  5. Clean method for the synthesis of reduced graphene oxide-supported PtPd alloys with high electrocatalytic activity for ethanol oxidation in alkaline medium.

    PubMed

    Ren, Fangfang; Wang, Huiwen; Zhai, Chunyang; Zhu, Mingshan; Yue, Ruirui; Du, Yukou; Yang, Ping; Xu, Jingkun; Lu, Wensheng

    2014-03-12

    In this article, a clean method for the synthesis of PtPd/reduced graphene oxide (RGO) catalysts with different Pt/Pd ratios is reported in which no additional components such as external energy (e.g., high temperature or high pressure), surfactants, or stabilizing agents are required. The obtained catalysts were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), induced coupled plasma atomic emission spectroscopy (ICP-AES), and electrochemical measurements. The HRTEM measurements showed that all of the metallic nanoparticles (NPs) exhibited well-defined crystalline structures. The composition of these Pt-Pd/RGO catalysts can be easily controlled by adjusting the molar ratio of the Pt and Pd precursors. Both cyclic voltammetry (CV) and chronoamperometry (CA) results demonstrate that bimetallic PtPd catalysts have superior catalytic activity for the ethanol oxidation reaction compared to the monometallic Pt or Pd catalyst, with the best performance found with the PtPd (1:3)/RGO catalyst. The present study may open a new approach for the synthesis of PtPd alloy catalysts, which is expected to have promising applications in fuel cells.

  6. Solvent-free Hydrodeoxygenation of Bio-oil Model Compounds Cyclopentanone and Acetophenone over Flame-made Bimetallic Pt-Pd/ZrO2 Catalysts

    PubMed Central

    Jiang, Yijiao; Büchel, Robert; Huang, Jun; Krumeich, Frank; Pratsinis, Sotiris E.; Baiker, Alfons

    2013-01-01

    Bimetallic Pt-Pd/ZrO2 catalysts with different Pt/Pd atomic ratio and homogeneous dispersion of the metal nanoparticles were prepared in a single step by flame-spray pyrolysis. The catalysts show high activity and tuneable product selectivity for the solvent-free hydrodeoxygenation of the bio-oil model compounds cyclopentanone and acetophenone. PMID:22674738

  7. Effects of Alloyed Metal on the Catalysis Activity of Pt for Ethanol Partial Oxidation: Adsorption and Dehydrogenation on Pt3M (M=Pt, Ru, Sn, Re, Rh, and Pd)

    PubMed Central

    Xu, Zhen-Feng; Wang, Yixuan

    2011-01-01

    The adsorption and dehydrogenation reactions of ethanol over bimetallic clusters, Pt3M (M = Pt, Ru, Sn, Re, Rh, and Pd), have been extensively investigated with density functional theory. Both the α-hydrogen and hydroxyl adsorptions on Pt as well as on the alloyed transition metal M sites of PtM were considered as initial reaction steps. The adsorptions of ethanol on Pt and M sites of some PtM via the α-hydrogen were well established. Although the α-hydrogen adsorption on Pt site is weaker than the hydroxyl, the potential energy profiles show that the dehydrogenation via the α-hydrogen path has much lower energy barrier than that via the hydroxyl path. Generally for the α-hydrogen path the adsorption is a rate-determining-step because of rather low dehydrogenation barrier for the α-hydrogen adsorption complex (thermodynamic control), while the hydroxyl path is determined by its dehydrogenation step (kinetic control). The effects of alloyed metal on the catalysis activity of Pt for ethanol partial oxidation, including adsorption energy, energy barrier, electronic structure, and eventually rate constant were discussed. Among all of the alloyed metals only Sn enhances the rate constant of the dehydrogenation via the α-hydrogen path on the Pt site of Pt3Sn as compared with Pt alone, which interprets why the PtSn is the most active to the oxidation of ethanol. PMID:22102920

  8. Effects of Alloyed Metal on the Catalysis Activity of Pt for Ethanol Partial Oxidation: Adsorption and Dehydrogenation on Pt(3)M (M=Pt, Ru, Sn, Re, Rh, and Pd).

    PubMed

    Xu, Zhen-Feng; Wang, Yixuan

    2011-10-27

    The adsorption and dehydrogenation reactions of ethanol over bimetallic clusters, Pt(3)M (M = Pt, Ru, Sn, Re, Rh, and Pd), have been extensively investigated with density functional theory. Both the α-hydrogen and hydroxyl adsorptions on Pt as well as on the alloyed transition metal M sites of PtM were considered as initial reaction steps. The adsorptions of ethanol on Pt and M sites of some PtM via the α-hydrogen were well established. Although the α-hydrogen adsorption on Pt site is weaker than the hydroxyl, the potential energy profiles show that the dehydrogenation via the α-hydrogen path has much lower energy barrier than that via the hydroxyl path. Generally for the α-hydrogen path the adsorption is a rate-determining-step because of rather low dehydrogenation barrier for the α-hydrogen adsorption complex (thermodynamic control), while the hydroxyl path is determined by its dehydrogenation step (kinetic control). The effects of alloyed metal on the catalysis activity of Pt for ethanol partial oxidation, including adsorption energy, energy barrier, electronic structure, and eventually rate constant were discussed. Among all of the alloyed metals only Sn enhances the rate constant of the dehydrogenation via the α-hydrogen path on the Pt site of Pt(3)Sn as compared with Pt alone, which interprets why the PtSn is the most active to the oxidation of ethanol. PMID:22102920

  9. Supersaturation-controlled surface structure evolution of Pd@Pt core-shell nanocrystals: enhancement of the ORR activity at a sub-10 nm scale

    NASA Astrophysics Data System (ADS)

    Qi, Kun; Zheng, Weitao; Cui, Xiaoqiang

    2016-01-01

    Here, we designed and implemented a facile strategy for controlling the surface evolution of Pd@Pt core-shell nanostructures by simply adjusting the volume of OH- to control the reducing ability of ascorbic acid and finally manipulating the supersaturation in the reaction system. The surface structure of the obtained Pd@Pt bimetallic nanocrystals transformed from a Pt {111} facet-exposed island shell to a conformal Pt {100} facet-exposed shell by increasing the pH value. The as-prepared well aligned Pd@Pt core-island shell nanocubes present both significantly enhanced electrocatalytic activity and favorable long-term stability toward the oxygen reduction reaction in alkaline media.Here, we designed and implemented a facile strategy for controlling the surface evolution of Pd@Pt core-shell nanostructures by simply adjusting the volume of OH- to control the reducing ability of ascorbic acid and finally manipulating the supersaturation in the reaction system. The surface structure of the obtained Pd@Pt bimetallic nanocrystals transformed from a Pt {111} facet-exposed island shell to a conformal Pt {100} facet-exposed shell by increasing the pH value. The as-prepared well aligned Pd@Pt core-island shell nanocubes present both significantly enhanced electrocatalytic activity and favorable long-term stability toward the oxygen reduction reaction in alkaline media. Electronic supplementary information (ESI) available. See DOI: 10.1039/c5nr07940c

  10. Ultrasonic-assisted synthesis of Pd-Pt/carbon nanotubes nanocomposites for enhanced electro-oxidation of ethanol and methanol in alkaline medium.

    PubMed

    Yang, Guohai; Zhou, Yazhou; Pan, Horng-Bin; Zhu, Chengzhou; Fu, Shaofang; Wai, Chien M; Du, Dan; Zhu, Jun-Jie; Lin, Yuehe

    2016-01-01

    Herein, a facile ultrasonic-assisted strategy was proposed to fabricate the Pd-Pt alloy/multi-walled carbon nanotubes (Pd-Pt/CNTs) nanocomposites. A good number of Pd-Pt alloy nanoparticles with an average of 3.4 ± 0.5 nm were supported on sidewalls of CNTs with uniform distribution. The composition of the Pd-Pt/CNTs nanocomposites could also be easily controlled, which provided a possible approach for the preparation of other architectures with anticipated properties. The Pd-Pt/CNTs nanocomposites were extensively studied by electron microscopy, induced coupled plasma atomic emission spectroscopy, X-ray diffraction, and X-ray photoelectron spectroscopy, and applied for the ethanol and methanol electro-oxidation reaction in alkaline medium. The electrochemical results indicated that the nanocomposites had better electrocatalytic activities and stabilities, showing promising applications for fuel cells.

  11. Rapid, general synthesis of PdPt bimetallic alloy nanosponges and their enhanced catalytic performance for ethanol/methanol electrooxidation in an alkaline medium.

    PubMed

    Zhu, Chengzhou; Guo, Shaojun; Dong, Shaojun

    2013-01-14

    We have demonstrated a rapid and general strategy to synthesize novel three-dimensional PdPt bimetallic alloy nanosponges in the absence of a capping agent. Significantly, the as-prepared PdPt bimetallic alloy nanosponges exhibited greatly enhanced activity and stability towards ethanol/methanol electrooxidation in an alkaline medium, which demonstrates the potential of applying these PdPt bimetallic alloy nanosponges as effective electrocatalysts for direct alcohol fuel cells. In addition, this simple method has also been applied for the synthesis of AuPt, AuPd bimetallic, and AuPtPd trimetallic alloy nanosponges. The as-synthesized three-dimensional bimetallic/trimetallic alloy nanosponges, because of their convenient preparation, well-defined sponge-like network, large-scale production, and high electrocatalytic performance for ethanol/methanol electrooxidation, may find promising potential applications in various fields, such as formic acid oxidation or oxygen reduction reactions, electrochemical sensors, and hydrogen-gas sensors.

  12. Newly-designed complex ternary Pt/PdCu nanoboxes anchored on three-dimensional graphene framework for highly efficient ethanol oxidation.

    PubMed

    Hu, Chuangang; Cheng, Huhu; Zhao, Yang; Hu, Yue; Liu, Yong; Dai, Liming; Qu, Liangti

    2012-10-23

    Newly-designed ternary Pt/PdCu nanoboxes on three-dimensional graphene framework (Pt/PdCu/3DGF) have been fabricated via a dual solvothermal strategy. This structurally well-defined Pt/PdCu/3DGF system possesses an approximately 4-fold improvement in catalytic activity for ethanol oxidation in alkaline media over the commercial 20% Pt/C catalyst as normalized by the total mass of active metals, showing the great potential for direct fuel cell applications. PMID:22886893

  13. Distribution of Pd clusters on ultrathin, epitaxial TiOx films on Pt3Ti(111)

    PubMed Central

    Breinlich, Christian; Buchholz, Maria; Pertram, Tobias; Becker, Conrad; Wandelt, Klaus

    2015-01-01

    Summary Scanning tunnelling microscopy (STM) was used to investigate the nucleation and growth of palladium clusters on two different, ultrathin, epitaxial, titania films grown on a Pt3Ti(111) surface. The first oxide phase, z'-TiOx, is anisotropic and consists of parallel stripes separated by trenches. Defects (i.e., oxygen vacancies) in this structure are confined to these trenches and act as nucleation sites. Therefore, the Pd clusters are mostly arranged in unidirectional rows along the trenches, creating a template effect. The second phase, w'-TiOx, exhibits a hexagonal, long range, (7 × 7)R21.8°, Moiré-type superstructure with fewer and shallower defects, making the template effect less discernible. PMID:26665071

  14. Hemichelation, a way to stabilize electron-unsaturated complexes: the case of T-shaped Pd and Pt metallacycles.

    PubMed

    Werlé, Christophe; Bailly, Corinne; Karmazin-Brelot, Lydia; Le Goff, Xavier-Frédéric; Ricard, Louis; Djukic, Jean-Pierre

    2013-11-27

    A rational method of synthesis of stable neutral T-shaped 14 electron Pd and Pt complexes is proposed. It takes advantage of the ambiphilic character of the tricarbonyl(η(6)-indenyl)chromium anion, of which the main property is to behave as a hemichelating ligand, that is a nonconventional heteroditopic ligand capable of chelating a metal center by way of covalent and noncovalent bonding, thus preserving its unsaturated valence shell. The reaction of the in situ formed tricarbonyl(η(6)-2-methylindenyl)chromium anion with a series of Pd and Pt metallacycles afforded new air-stable and persistent synfacial heterobimetallic complexes in which the metallacycle binds the indenyl fragment via its metal in an η(1) fashion, leaving the fourth coordination site at the chelated metal virtually vacant. The structures of eight of these novel complexes are disclosed, and their bonding features are investigated by an array of theoretical methods based on the density functional theory (NBO, EDA, ETS-NOCV, AIM, NCI region analysis). Theory shows that the formation of these unusual structures of bimetallic synfacial η(1)-indenyl-Pd/Pt complexes is driven thermodynamically by attractive Coulombic occlusion of the fourth vacant coordination site at Pd/Pt centers by the Cr(CO)3 moiety. PMID:24182317

  15. Atomic Layer-by-Layer Deposition of Pt on Pd Nanocubes for Catalysts with Enhanced Activity and Durability toward Oxygen Reduction

    SciTech Connect

    Xie, Shuifen; Choi, Sang; Lu, Ning; Roling, Luke T.; Herron, Jeffrey A.; Zhang, Lei; Park, Jinho; Wang, Jinguo; Kim, Moon J.; Xie, Zhaoxiong; Mavrikakis, Manos; Xia, Younan

    2014-06-11

    An effective strategy for reducing the Pt content while retaining the activity of a Pt-based catalyst is to deposit the Pt atoms as ultrathin skins of only a few atomic layers thick on nanoscale substrates made of another metal. During deposition, however, the Pt atoms often take an island growth mode because of a strong bonding between Pt atoms. Here we report a versatile route to the conformal deposition of Pt as uniform, ultrathin shells on Pd nanocubes in a solution phase. The introduction of the Pt precursor at a relatively slow rate and high temperature allowed the deposited Pt atoms to spread across the entire surface of a Pd nanocube to generate a uniform shell. The thickness of the Pt shell could be controlled from one to six atomic layers by varying the amount of Pt precursor added into the system. Compared to a commercial Pt/C catalyst, the Pd@PnL (n = 1-6) core-shell nanocubes showed enhancements in specific activity and durability toward the oxygen reduction reaction (ORR). Density functional theory (DFT) calculations on model (100) surfaces suggest that the enhancement in specific activity can be attributed to the weakening of OH binding through ligand and strain effects, which, in turn, increases the rate of OH hydrogenation. A volcano-type relationship between the ORR specific activity and the number of Pt atomic layers was derived, in good agreement with the experimental results. Both theoretical and experimental studies indicate that the ORR specific activity was maximized for the catalysts based on Pd@Pt2-3L nanocubes. Because of the reduction in Pt content used and the enhancement in specific activity, the Pd@Pt1L nanocubes showed a Pt mass activity with almost three-fold enhancement relative to the Pt/C catalyst.

  16. Pt, Au, Pd and Ru Partitioning Between Mineral and Silicate Melts: The Role of Metal Nanonuggets

    NASA Technical Reports Server (NTRS)

    Malavergne, V.; Charon, E.; Jones, J.; Agranier, A.; Campbell, A.

    2012-01-01

    The partition coefficients of Pt and other Pt Group Elements (PGE) between metal and silicate D(sub Metal-Silicate) and also between silicate minerals and silicate melts D(sub Metal-Silicate) are among the most challenging coefficients to obtain precisely. The PGE are highly siderophile elements (HSE) with D(sub Metal-Silicate) >10(exp 3) due to the fact that their concentrations in silicates are very low (ppb to ppt range). Therefore, the analytical difficulty is increased by the possible presence of HSE-rich-nuggets in reduced silicate melts during experiments). These tiny HSE nuggets complicate the interpretation of measured HSE concentrations. If the HSE micro-nuggets are just sample artifacts, then their contributions should be removed before calculations of the final concentration. On the other hand, if they are produced during the quench, then they should be included in the analysis. We still don't understand the mechanism of nugget formation well. Are they formed during the quench by precipitation from precursor species dissolved homogeneously in the melts, or are they precipitated in situ at high temperature due to oversaturation? As these elements are important tracers of early planetary processes such as core formation, it is important to take up this analytical and experimental challenge. In the case of the Earth for example, chondritic relative abundances of the HSE in some mantle xenoliths have led to the concept of the "late veneer" as a source of volatiles (such as water) and siderophiles in the silicate Earth. Silicate crystal/liquid fractionation is responsible for most, if not all, the HSE variation in the martian meteorite suites (SNC) and Pt is the element least affected by these fractionations. Therefore, in terms of reconstructing mantle HSE abundances for Mars, Pt becomes a very important player. In the present study, we have performed high temperature experiments under various redox conditions in order to determine the abundances of Pt, Au

  17. Spin-orbit interaction tuning of perpendicular magnetic anisotropy in L1{sub 0} FePdPt films

    SciTech Connect

    Ma, X.; Lüpke, G. E-mail: hbzhao@fudan.edu.cn; He, P.; Ma, L.; Zhou, S. M.; Guo, G. Y. E-mail: hbzhao@fudan.edu.cn; Zhao, H. B. E-mail: hbzhao@fudan.edu.cn

    2014-05-12

    The dependence of perpendicular magnetic anisotropy K{sub u} on spin-orbit coupling strength ξ is investigated in L1{sub 0} ordered FePd{sub 1−x}Pt{sub x} films by time-resolved magneto-optical Kerr effect measurements and ab initio density functional calculations. Continuous tuning of K{sub u} over a wide range of magnitude is realized by changing the Pt/Pd concentration ratio, which strongly modifies ξ but keeps other leading parameters affecting K{sub u} nearly unchanged. Ab initio calculations predict a nearly quadratic dependence of K{sub u} on ξ, consistent with experimental data. K{sub u} increases with increasing chemical order and decreasing thermal spin fluctuations, which becomes more significant for samples with higher Pt concentration. The results demonstrate an effective method to tune K{sub u} utilizing its sensitivity on ξ, which will help fabricate magnetic systems with desirable magnetic anisotropy.

  18. Modeling closure of the Pd-Ag system in iron meteorites

    NASA Astrophysics Data System (ADS)

    Van Orman, J.; Matthes, M.; Fischer-Gödde, M.; Krawczynski, M. J.; Kleine, T.

    2015-12-01

    J.A. Van Orman1, M. Matthes2, M. Fischer-Godde2, M.J. Krawczynski3, T. Kleine21 Case Western Reserve University, Cleveland, OH 44106 (james.vanorman@case.edu) 2 Westfalische Wilhelms-Universitat Muenster, 48149 Muenster, Germany 3 Washington University, St. Louis, MO 63130 The short-lived Pd-107/Ag-107 system can provide constraints on the timing of assembly and cooling of iron meteorite parent bodies, but to interpret the dates derived from this system it is necessary to understand the closure conditions. Palladium is strongly enriched in the metal phases, and sulphide (troilite) is the primary sink for radiogenic silver. Closure of the system hence depends primarily on the transfer of Ag-107 from metal to troilite. Because cation diffusion in troilite is extremely rapid, Ag-107 transfer is likely to be controlled by diffusion through the metal. Sugiura and Hoshino (2003) estimated a closure temperature of ~1100 K for the Pd/Ag system in iron meteorites under the assumption that the diffusion rate of Ag in the metal is similar to that of Ni diffusion in taenite. Here we consider the problem in more detail, utilizing constraints on Ag diffusion in taenite and kamacite from the metallurgical literature to numerically model diffusive exchange between metal and troilite with simultaneous radiogenic ingrowth. The process is complicated by exsolution of the metal into bcc kamacite and fcc taenite phases during cooling. We will discuss approaches to the treatment of this issue and their influence on the derived closure temperatures. Sugiura N., Hoshino H. (2003) Meteorit. Planet. Sci. 38, 117-143.

  19. Ag-Pd-Cu alloy inserted transparent indium tin oxide electrodes for organic solar cells

    SciTech Connect

    Kim, Hyo-Joong; Seo, Ki-Won; Kim, Han-Ki; Noh, Yong-Jin; Na, Seok-In

    2014-09-01

    The authors report on the characteristics of Ag-Pd-Cu (APC) alloy-inserted indium tin oxide (ITO) films sputtered on a glass substrate at room temperature for application as transparent anodes in organic solar cells (OSCs). The effect of the APC interlayer thickness on the electrical, optical, structural, and morphological properties of the ITO/APC/ITO multilayer were investigated and compared to those of ITO/Ag/ITO multilayer electrodes. At the optimized APC thickness of 8 nm, the ITO/APC/ITO multilayer exhibited a resistivity of 8.55 × 10{sup −5} Ω cm, an optical transmittance of 82.63%, and a figure-of-merit value of 13.54 × 10{sup −3} Ω{sup −1}, comparable to those of the ITO/Ag/ITO multilayer. Unlike the ITO/Ag/ITO multilayer, agglomeration of the metal interlayer was effectively relieved with APC interlayer due to existence of Pd and Cu elements in the thin region of the APC interlayer. The OSCs fabricated on the ITO/APC/ITO multilayer showed higher power conversion efficiency than that of OSCs prepared on the ITO/Ag/ITO multilayer below 10 nm due to the flatness of the APC layer. The improved performance of the OSCs with ITO/APC/ITO multilayer electrodes indicates that the APC alloy interlayer prevents the agglomeration of the Ag-based metal interlayer and can decrease the thickness of the metal interlayer in the oxide-metal-oxide multilayer of high-performance OSCs.

  20. Phase Structure and Site Preference Behavior of Ternary Alloying Additions to PdTi and PtTi Shape-Memory Alloys

    NASA Technical Reports Server (NTRS)

    Bozzolo, Guillermo; Mosca, Hugo O.; Noebe, Ronald D.

    2006-01-01

    The phasc structure and concentration dependence of the lattice parameter and energy of formation of ternary Pd-'I-X and Pt-Ti-X alloys for a large number of ternary alloying additions X (X = Na, Mg, Al, Si, Sc. V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Y, Zr, Nb, Mo, Tc, Ru, Rh, Ag, Cd, Hf, Ta, W, Re, Os, Ir) are investigated with an atomistic modeling approach. In addition, a detailed description of the site preference behavior of such additions showing that the elements can be grouped according to their absolute preference for a specific site, regardless of concentration, or preference for available sites in the deficient sublattice is provided.

  1. Catalytic Properties of AgPt Nanoshells as a Function of Size: Larger Outer Diameters Lead to Improved Performances.

    PubMed

    Rodrigues, Thenner S; da Silva, Anderson G M; Gonçalves, Mariana C; Fajardo, Humberto V; Balzer, Rosana; Probst, Luiz F D; da Silva, Alisson H M; Assaf, Jose M; Camargo, Pedro H C

    2016-09-13

    We report herein a systematic investigation on the effect of the size of silver (Ag) nanoparticles employed as starting materials over the morphological features and catalytic performances of AgPt nanoshells produced by a combination of galvanic replacement between Ag and PtCl6(2-) and PtCl6(2-) reduction by hydroquinone. More specifically, we focused on Ag nanoparticles of four different sizes as starting materials, and found that the outer diameter, shell thickness, and the number of Pt surface atoms of the produced nanoshells increased with the size of the starting Ag nanoparticles. The produced AgPt nanoshells were supported into SiO2, and the catalytic performances of the AgPt/SiO2 nanocatalysts toward the gas-phase oxidation of benzene, toluene, and o-xylene (BTX oxidation) followed the order: AgPt 163 nm/SiO2 > AgPt 133 nm/SiO2 > AgPt 105 nm/SiO2 > AgPt 95 nm/SiO2. Interestingly, bigger AgPt nanoshell sizes lead to better catalytic performances in contrast to the intuitive prediction that particles having larger outer diameters tend to present poorer catalytic activities due to their lower surface to volume ratios as compared to smaller particles. This is in agreement with the H2 chemisorption results, and can be assigned to the increase in the Pt surface area with size due to the presence of smaller NPs islands at the surface of the nanoshells having larger outer diameters. This result indicates that, in addition to the overall diameters, the optimization of the surface morphology may play an important role over the optimization of catalytic activities in metal-based nanocatalysts, which can be even more pronounced that the size effect. Our data demonstrate that the control over surface morphology play a very important role relative to the effect of size to the optimization of catalytic performances in catalysts based on noble-metal nanostructures. PMID:27556904

  2. Multiple Condensation Reactions Involving Pt(II) /Pd(II) -OH2 , Pt-NH3 , and Cytosine-NH2 Groups: New Twists in Cisplatin-Nucleobase Chemistry.

    PubMed

    Yin-Bandur, Lu; Sanz Miguel, Pablo J; Rodríguez-Santiago, Luis; Sodupe, Mariona; Berghaus, Melanie; Lippert, Bernhard

    2016-09-12

    The coordination chemistry of the antitumor agent cisplatin and related complexes with DNA and its constituents, that is, the nucleobases, appears to be dominated by 1:1 and 1:2 adducts of the types cis-[Pta2 (nucleobase)X] and cis-[Pta2 (nucleobase)2 ] (a=NH3 or amine; a2 =diamine or diimine; X=Cl, OH or OH2 ). Here, we have studied the interactions of the putative 1:1 adducts cis-[Pta2 (1-MeC-N3)(OH2 )](2+) (with a=NH3 , a2 =2,2'-bpy (2,2'-bipyridine), 1-MeC=model nucleobase 1-methylcytosine) with additional cis-[Pt(NH3 )2 (OH2 )2 ](2+) or its kinetically superior analogues [Pd(en)(OH2 )2 ](2+) (en=ethylenediamine) and [Pd(2,2'-bpy)(OH2 )2 ](2+) . Depending upon the conditions applied different compounds of different nuclearity are formed. Without exception they represent condensation products of the components, containing μ-1-MeC-H , μ-OH(-) , as well as μ-NH2 (-) bridges. In the presence of Ag(+) ions, the isolated products in several cases display additionally Pt→Ag dative bonds. On the basis of the cytosine-containing structures established by X-ray crystallography, it is proposed that any of the feasible initial 1:1 nucleobase adducts of cisplatin could form dinuclear Pt complexes upon reaction with additional hydrolyzed cisplatin, thereby generating nucleobase adducts other than the presently established ones. Two findings appear to be of particular significance: First, hydrolyzed cisplatin can have a moderately accelerating effect on the formation of a secondary nucleobase product. Second, NH3 ligands of the cisplatin moiety can be converted into bridging amido ligands following condensation with the diaqua species of cisplatin.

  3. CO Sensing Performance of a Micro Thermoelectric Gas Sensor with AuPtPd/SnO₂ Catalyst and Effects of a Double Catalyst Structure with Pt/α-Al₂O₃.

    PubMed

    Goto, Tomoyo; Itoh, Toshio; Akamatsu, Takafumi; Shin, Woosuck

    2015-12-15

    The CO sensing properties of a micro thermoelectric gas sensor (micro-TGS) with a double AuPtPd/SnO₂ and Pt/α-Al₂O₃ catalyst were investigated. While several nanometer sized Pt and Pd particles were uniformly dispersed on SnO₂, the Au particles were aggregated as particles measuring >10 nm in diameter. In situ diffuse reflectance Fourier transform Infrared spectroscopy (DRIFT) analysis of the catalyst showed a CO adsorption peak on Pt and Pd, but no clear peak corresponding to the interaction between CO and Au was detected. Up to 200 °C, CO combustion was more temperature dependent than that of H₂, while H₂ combustion was activated by repeated exposure to H₂ gas during the periodic gas test. Selective CO sensing of the micro-TGS against H₂ was attempted using a double catalyst structure with 0.3-30 wt% Pt/α-Al₂O₃ as a counterpart combustion catalyst. The sensor output of the micro-TGS decreased with increasing Pt content in the Pt/α-Al₂O₃ catalyst, by cancelling out the combustion heat from the AuPtPd/SnO₂ catalyst. In addition, the AuPtPd/SnO₂ and 0.3 wt% Pt/α-Al₂O₃ double catalyst sensor showed good and selective CO detection. We therefore demonstrated that our micro-TGS with double catalyst structure is useful for controlling the gas selectivity of CO against H₂.

  4. Pt and Pd as catalyst deposited by hydrogen reduction of metal salts on WO3 films for gasochromic application

    NASA Astrophysics Data System (ADS)

    Tahmasebi Garavand, N.; Mahdavi, S. M.; Iraji zad, A.

    2013-05-01

    In this study, tungsten oxide films were deposited by pulsed-laser deposition (PLD) technique. The as-deposited films were annealed at 250 °C in air for 1 h. The surface morphology, microstructure, crystalline phase, and chemical composition of the films were characterized by SEM, XRD and XPS techniques. Pt nanoparticles were deposited onto the tungsten oxide films through a two-step process. First of all, a layer of PtCl2 was coated on the WO3 surface by drop-drying the PtCl2 solution onto the WO3 surface at 60 °C. Consequently, the reduction of the PtCl2 into the metallic Pt nanoparticles was performed at 200 °C. In this study, the effect of the temperature during hydrogen reduction of PtCl2 as well as the influence of operating temperature on the gasochromic performance of Pt-WO3 samples were investigated. Results revealed that the gasochromic responses of the Pt-WO3 samples have attained approximately a constant value at temperatures above 90 °C. On the other hand, their responses are insignificant at temperatures below 90 °C. Additionally, for the sake of comparison, some results of the gasochromic performance of Pd-WO3 films were presented.

  5. Homogeneity and elemental distribution in self-assembled bimetallic Pd-Pt aerogels prepared by a spontaneous one-step gelation process.

    PubMed

    Oezaslan, M; Liu, W; Nachtegaal, M; Frenkel, A I; Rutkowski, B; Werheid, M; Herrmann, A-K; Laugier-Bonnaud, C; Yilmaz, H-C; Gaponik, N; Czyrska-Filemonowicz, A; Eychmüller, A; Schmidt, T J

    2016-07-27

    Multi-metallic aerogels have recently emerged as a novel and promising class of unsupported electrocatalyst materials due to their high catalytic activity and improved durability for various electrochemical reactions. Aerogels can be prepared by a spontaneous one-step gelation process, where the chemical co-reduction of metal precursors and the prompt formation of nanochain-containing hydrogels, as a preliminary stage for the preparation of aerogels, take place. However, detailed knowledge about the homogeneity and chemical distribution of these three-dimensional Pd-Pt aerogels at the nano-scale as well as at the macro-scale is still unclear. Therefore, we used a combination of spectroscopic and microscopic techniques to obtain a better insight into the structure and elemental distribution of the various Pd-rich Pd-Pt aerogels prepared by the spontaneous one-step gelation process. Synchrotron-based extended X-ray absorption fine structure (EXAFS) spectroscopy and high-angle annular dark-field (HAADF) scanning transmission electron microscopy (STEM) in combination with energy-dispersive X-ray spectroscopy (EDX) were employed in this work to uncover the structural architecture and chemical composition of the various Pd-rich Pd-Pt aerogels over a broad length range. The Pd80Pt20, Pd60Pt40 and Pd50Pt50 aerogels showed heterogeneity in the chemical distribution of the Pt and Pd atoms inside the macroscopic nanochain-network. The features of mono-metallic clusters were not detected by EXAFS or STEM-EDX, indicating alloyed nanoparticles. However, the local chemical composition of the Pd-Pt alloys strongly varied along the nanochains and thus within a single aerogel. To determine the electrochemically active surface area (ECSA) of the Pd-Pt aerogels for application in electrocatalysis, we used the electrochemical CO stripping method. Due to their high porosity and extended network structure, the resulting values of the ECSA for the Pd-Pt aerogels were higher than that for

  6. Facile self-assembly synthesis of PdPt bimetallic nanotubes with good performance for ethanol oxidation in an alkaline medium.

    PubMed

    Huang, Zhongyuan; Zhou, Haihui; Sun, Feifei; Fu, Chaopeng; Zeng, Fanyan; Li, Tianqi; Kuang, Yafei

    2013-10-01

    PdPt bimetallic nanotubes were prepared by the self-assembly of Pt and Pd on Te nanowires at room temperature. The morphologies of the as-prepared PdPt nanotubes were investigated by scanning electron microscopy and transmission electron microscopy, and the results display a large amount of PdPt bimetallic nanotubes with a diameter of 10-20 nm and a length of several micrometers. The composition and structure of the nanotubes were characterized by X-ray diffraction, high-resolution transmission electron microscopy, scanning transmission electron microscopy, and energy spectrum analysis, and the results display uniform compositional distributions of both elements (Pd and Pt). The mechanism of the formation of the nanotube structure was supposed. The electrocatalytic performance of PdPt nanotubes were studied by cyclic voltammetry and chronoamperometry. Electrochemical results show that the as-prepared PdPt nanotube catalysts have not only high activity but also good stability for ethanol oxidation in alkaline medium.

  7. Colorimetric detection of the flux of hydrogen peroxide released from living cells based on the high peroxidase-like catalytic performance of porous PtPd nanorods.

    PubMed

    Ge, Shenguang; Liu, Weiyan; Liu, Haiyun; Liu, Fang; Yu, Jinghua; Yan, Mei; Huang, Jiadong

    2015-09-15

    One-dimensional PtPd porous nanorods (PtPd PNRs) were successfully synthesized through a bromide-induced galvanic replacement reaction between Pd nanowires and K2PtCl6. The PtPd PNRs were porous and alloy-structured with Pt/Pd atomic ratio up to 1:1 which were demonstrated by spectroscopic methods. We had also proved that the nanorods could function as peroxidase mimetic for the detection of H2O2, with the detection limit of 8.6 nM and the linear range from 20 nM to 50 mM. The result demonstrated that PtPd PNRs exhibited much higher affinity to H2O2 over other peroxidase mimetics due to synergistically integrating highly catalytic activity of two metals. On the basis of the peroxidase-like activity, the PtPd PNRs were used as a signal transducer to develop a novel and simple colorimetric method for the study of the flux of H2O2 released from living cell. By using 3,3,5,5-tetramethylbenzidine as substrate, the H2O2 concentration could be distinguished by naked-eye observation without any instrumentation or complicated design. The method developed a new platform for a reliable collection of information on cellular reactive oxygen species release. And the nanomaterial could be used as a power tool for a wide range of potential applications in biotechnology and medicine.

  8. PdAgAu alloy with high resistance to corrosion by H2S

    SciTech Connect

    Braun, Fernando; Miller, James B.; Gellman, Andrew J.; Tarditi, Ana M.; Fleutot, Benoit; Kondratyuk, Petro; Cornaglia, Laura M.

    2012-12-01

    PdAgAu alloy films were prepared on porous stainless steel supports by sequential electroless deposition. Two specific compositions, Pd83Ag2Au15 and Pd74Ag14Au12, were studied for their sulfur tolerance. The alloys and a reference Pd foil were exposed to 1000 H2S /H2 at 623 K for periods of 3 and 30 hours. The microstructure, morphology and bulk composition of both nonexposed and H2S-exposed samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS). XRD and SEM analysis revealed time-dependent growth of a bulk Pd{sub 4}S phase on the Pd foil during H2S exposure. In contrast, the PdAgAu ternary alloys displayed the same FCC structure before and after H2S exposure. In agreement with the XRD and SEM results, sulfur was not detected in the bulk of either ternary alloy samples by EDS, even after 30 hours of H2S exposure. X-ray photoelectron spectroscopy (XPS) depth profiles were acquired for both PdAgAu alloys after 3 and 30 hours of exposure to characterize sulfur contamination near their surfaces. Very low S 2p and S 2s XPS signals were observed at the top-surfaces of the PdAgAu alloys, and those signals disappeared before the etch depth reached ~ 10 nm, even for samples exposed to H2S for 30 hours. The depth profile analyses also revealed silver and gold segregation to the surface of the alloys; preferential location of Au on the alloys surface may be related to their resistance to bulk sulfide formation. In preliminary tests, a PdAgAu alloy membrane displayed higher initial H{sub 2} permeability than a similarly prepared pure Pd sample and, consistent with resistance to bulk sulfide formation, lower permeability loss in H2S than pure Pd.

  9. Fabrication of catalytically active Au/Pt/Pd trimetallic nanoparticles by rapid injection of NaBH{sub 4}

    SciTech Connect

    Zhang, Haijun; Lu, Lilin; Cao, Yingnan; Du, Shuang; Cheng, Zhong; Zhang, Shaowei

    2014-01-01

    Graphical abstract: The synthesis and characterization of 2.0 nm-diameter Au/Pt/Pd nanoparticles are reported. The catalytic activity for glucose oxidation of the nanoparticles is several times higher than that of Au nanoparticles with nearly same size. - Highlights: • PVP-protected Au/Pt/Pd trimetallic nanoparticles (TNPs) of 2.0 nm in diameter were prepared. • The catalytic activity of TNPs is several times higher than that of Au nanoparticles. • Negatively charged Au atoms in the TNPs were confirmed by DFT calculation. - Abstract: Au/Pt/Pd trimetallic nanoparticles (TNPs) with an alloyed structure and an average diameter of about 2.0 nm were prepared via reducing the corresponding ions with rapidly injected NaBH{sub 4}, and characterized by UV–vis, TEM and HR-TEM. The catalytic activity of as-prepared TNPs for the aerobic glucose oxidation is several times higher than that of Au monometallic nanoparticles with about the same average size, which could be attributed to the catalytically active sites provided by the negatively charged Au atoms as a result of the electron donation from the neighboring Pd atoms. This was well supported by the electron density calculations based on the density functional theory.

  10. Transparent ITO/Ag-Pd-Cu/ITO multilayer cathode use in inverted organic solar cells

    SciTech Connect

    Kim, Hyo-Joong; Kim, Han-Ki; Lee, Hyun Hwi; Kal, Jinha; Hahn, Jungseok

    2015-10-15

    The characteristics of transparent ITO/Ag-Pd-Cu (APC)/ITO multilayer cathodes were investigated for use in inverted organic solar cells (IOSCs). The insertion of an APC interlayer into the ITO film effectively led to crystallization of the top ITO layer, unlike that in the Ag interlayer, and resulted in a low sheet resistance of 6.55 Ohm/square and a high optical transmittance of 84.14% without post annealing. In addition, the alloying of the Pd and Cu elements into Ag prevented agglomeration and oxidization of the metal interlayer and led to more stable ITO/APC/ITO films under ambient conditions. The microstructure and interfacial structure of the transparent ITO/APC/ITO cathode in the IOSCs were examined in detail by synchrotron X-ray scattering and high resolution transmission electron microscopy. Furthermore, we suggested a possible mechanism to explain the lower PCE of the IOSCs with an ITO/APC/ITO cathode than that of a reference IOSC with a crystalline ITO cathode using the external quantum efficiency of the IOSCs.

  11. Nanosized (mu12-Pt)Pd164-xPtx(CO)72(PPh3)20 (x approximately 7) containing Pt-centered four-shell 165-atom Pd-Pt core with unprecedented intershell bridging carbonyl ligands: comparative analysis of icosahedral shell-growth patterns with geometrically related Pd145(CO)x(PEt3)30 (x approximately 60) containing capped three-shell Pd145 core.

    PubMed

    Mednikov, Evgueni G; Jewell, Matthew C; Dahl, Lawrence F

    2007-09-19

    Presented herein are the preparation and crystallographic/microanalytical/magnetic/spectroscopic characterization of the Pt-centered four-shell 165-atom Pd-Pt cluster, (mu(12)-Pt)Pd(164-x)Pt(x)(CO)(72)(PPh(3))(20) (x approximately 7), 1, that replaces the geometrically related capped three-shell icosahedral Pd(145) cluster, Pd(145)(CO)(x)(PEt(3))(30) (x approximately 60), 2, as the largest crystallographically determined discrete transition metal cluster with direct metal-metal bonding. A detailed comparison of their shell-growth patterns gives rise to important stereochemical implications concerning completely unexpected structural dissimilarities as well as similarities and provides new insight concerning possible synthetic approaches for generation of multi-shell metal clusters. 1 was reproducibly prepared in small yields (<10%) from the reaction of Pd(10)(CO)(12)(PPh(3))(6) with Pt(CO)(2)(PPh(3))(2). Its 165-atom metal-core geometry and 20 PPh(3) and 72 CO ligands were established from a low-temperature (100 K) CCD X-ray diffraction study. The well-determined crystal structure is attributed largely to 1 possessing cubic T(h) (2/m3) site symmetry, which is the highest crystallographic subgroup of the noncrystallographic pseudo-icosahedral I(h) (2/m35) symmetry. The "full" four-shell Pd-Pt anatomy of 1 consists of: (a) shell 1 with the centered (mu(12)-Pt) atom encapsulated by the 12-atom icosahedral Pt(x)Pd(12-x) cage, x = 1.2(3); (b) shell 2 with the 42-atom nu(2) icosahedral Pt(x)Pd(42-x) cage, x = 3.5(5); (c) shell 3 with the anti-Mackay 60-atom semi-regular rhombicosidodecahedral Pt(x)Pd(60-x) cage, x = 2.2(6); (d) shell 4 with the 50-atom nu(2) pentagonal dodecahedral Pd(50) cage. The total number of crystallographically estimated Pt atoms, 8 +/- 3, which was obtained from least-squares (Pt(x)/Pd(1-x))-occupancy analysis of the X-ray data that conclusively revealed the central atom to be pure Pt (occupancy factor, x = 1.00(3)), is fortuitously in agreement

  12. Concentration and distribution of platinum group elements (Pt, Pd, Rh) in airborne particulate matter in Frankfurt am Main, Germany.

    PubMed

    Zereini, Fathi; Alt, Friedrich; Messerschmidt, Jürge; von Bohlen, Alex; Liebl, Karlheinz; Püttmann, Wilhelm

    2004-03-15

    The concentrations and distribution of platinum group elements (Pt, Pd, Rh) in airborne particulate matter were studied in a period of one year from August 2001 to July 2002 in urban and in nonurban areas. Airborne dust samples were collected as a total amount (particles with an aerodynamic diameter <22 microm) and classified using an eight-stage Andersen impactor (<10 microm) at three locations with different traffic density roads in the Frankfurt am Main and nonurban areas. Sampling at the three locations was performed simultaneously for total airborne dust and fractionated airborne dust. Pd was determined by total reflection X-ray fluorescence after Hg coprecipitation. Pt and Rh were analyzed by adsorptive striping voltammetry after HPA digestion. The results show that the PGE concentrations in airborne samples depend on the traffic density. The highest PGE concentrations in air were found in the vicinity of major roads with heavy traffic, and the lowest ones were found in the nonurban area. The presence of PGE at the sampling station relatively free of traffic in a nonurban area hints to a transport of some of the emitted PGE from the city to this station by wind. At all three sampling locations, a heterogeneous distribution of the Pd, Pt, and Rh concentrations during the sampling year can be observed. The sum of PGE concentrations in total airborne dust is comparable with the sum of impactor samples. However, the concentration of Pt and Rh in total airborne dust (<22 microm) is on average higher than in impactor samples (<10 microm). On the contrary, Pd concentration is higher in impactor samples in most cases. The airborne PGE distribution is dominated by Pt, followed by Pd and Rh. The impactor samples are dominated by Pd, followed by Pt and Rh. This fact indicates that palladium occurs mainly in relatively fine airborne particles. The main fraction of PGE is found on average in particle sizes between 1.1 and 4.7 microm. Knowledge of the size distribution of

  13. Pd@Pt core-shell concave decahedra: A class of catalysts for the oxygen reduction reaction with enhanced activity and durability

    SciTech Connect

    Wang, Xue; Vera, Madeline; Chi, Miaofang; Xia, Younan; Luo, Ming; Huang, Hongwen; Ruditskiy, Aleksey; Park, Jinho; Bao, Shixiong; Liu, Jingyue; Howe, Jane; Xie, Zhaoxiong

    2015-11-13

    Here, we report a facile synthesis of multiply twinned Pd@Pt core shell concave decahedra by controlling the deposition of Pt on preformed Pd decahedral seeds. The Pt atoms are initially deposited on the vertices of a decahedral seed, followed by surface diffusion to other regions along the edges/ridges and then across the faces. Different from the coating of a Pd icosahedral seed, the Pt atoms prefer to stay at the vertices and edges/ridges of a decahedral seed even when the deposition is conducted at 200 degrees C, naturally generating a core shell structure covered by concave facets. The nonuniformity in the Pt coating can be attributed to the presence of twin boundaries at the vertices, as well as the {100} facets and twin defects along the edges/ridges of a decahedron, effectively trapping the Pt adatoms at these high-energy sites. As compared to a commercial Pt/C catalyst, the Pd@Pt concave decahedra show substantial enhancement in both catalytic activity and durability toward the oxygen reduction reaction (ORR). For the concave decahedra with 29.6% Pt by weight, their specific (1.66 mA/cm2pt) and mass (1.60 A/mg/2pt) ORR activities are enhanced by 4.4 and 6.6 times relative to those of the Pt/C catalyst (0.36 mA/cm2pt and 0.32 A/mgpt, respectively). After 10 000 cycles of accelerated durability test, the concave decahedra still exhibit a mass activity of 0.69 A/mgpt, more than twice that of the pristine Pt/C catalyst.

  14. The population genetic structure of Rhizoctonia solani AG-3PT from potato in the Colombian Andes.

    PubMed

    Ferrucho, Rosa L; Ceresini, Paulo C; Ramirez-Escobar, Ursula M; McDonald, Bruce A; Cubeta, Marc A; García-Domínguez, Celsa

    2013-08-01

    The soilborne fungus Rhizoctonia solani anastomosis group 3 (AG-3PT) is a globally important potato pathogen. However, little is known about the population genetic processes affecting field populations of R. solani AG-3PT, especially in the South American Colombian Andes, which is near the center of diversity of the two most common groups of cultivated potato, Solanum tuberosum and S. phureja. We analyzed the genetic structure of 15 populations of R. solani AG-3PT infecting potato in Colombia using 11 simple-sequence repeat (SSR) markers. In total, 288 different multilocus genotypes were identified among 349 fungal isolates. Clonal fractions within field populations were 7 to 33%. RST statistics indicated a very low level of population differentiation overall, consistent with high contemporary gene flow, though moderate differentiation was found for the most distant southern populations. Genotype flow was also detected, with the most common genotype found widely distributed among field populations. All populations showed evidence of a mixed reproductive mode, including both asexual and sexual reproduction, but two populations displayed evidence of inbreeding.

  15. Nitriding-induced texture, ordering and coercivity enhancement in FePtAgB nanocomposite magnets

    NASA Astrophysics Data System (ADS)

    Crisan, O.; Vasiliu, F.; Palade, P.; Mercioniu, I.

    2016-03-01

    FePt system attracts currently a great deal of interest for applications as future RE free permanent magnets. Among the key issues to be solved one may count the decreasing of the ordering temperature and improvement of magnetic behavior. For that purpose we have studied the effect of a nitriding post-synthesis procedure on the FePtAgB melt spun ribbons, aimed at refining the microstructure and enhancing the magnetic performances. Deep structural characterization by transmission electron microscopy, electron diffraction, energy dispersive X-ray spectroscopy and X-ray diffraction allowed us to observe the morphology and to correctly assign and identify the nature of the main granular phases observed. Nitriding procedure is shown to strongly enhance the (001) texturing and the degree of ordering of the L10 FePt phase, as well as largely increase of coercivity, compared to the as-cast state. These changes are interpreted in terms of Ag segregation towards intergranular region associated to N diffusion and creation of vacancies that favor consistently the process of ordering the FePt grains into the L10 tetragonal phase.

  16. In situ XAS studies of Pt{sub x}Pd{sub 1-x} nanoparticles under thermal annealing

    SciTech Connect

    Bernardi, F.; Morais, J.; Alves, M. C. M.

    2009-01-29

    In this work, we have studied Pt{sub x}Pd{sub 1-x}(x = 1, 0.7 or 0.5) nanoparticles subjected to H{sub 2} reduction and sulfidation under H{sub 2}S atmosphere, both at 300 deg. C. The system was studied by in-situ x-ray absorption spectroscopy (in-situ XAS). We observed that the efficiency of sulfidation is directly proportional to the quantity of Pd atoms in the nanoparticle, provided the reduction process has been achieved.

  17. A comparative study on the bond strength of porcelain to the millingable Pd-Ag alloy

    PubMed Central

    Hong, Jun-Tae

    2014-01-01

    PURPOSE The porcelain fused to gold has been widely used as a restoration both with the natural esthetics of the porcelain and durability and marginal fit of metal casting. However, recently, due to the continuous rise in the price of gold, an interest towards materials to replace gold alloy is getting higher. This study compared the bond strength of porcelain to millingable palladium-silver (Pd-Ag) alloy, with that of 3 conventionally used metal-ceramic alloys. MATERIALS AND METHODS Four types of metal-ceramic alloys, castable nonprecious nickel-chrome alloy, castable precious metal alloys containing 83% and 32% of gold, and millingable Pd-Ag alloy were used to make metal specimens (n=40). And porcelain was applied on the center area of metal specimen. Three-point bending test was performed with universal testing machine. The bond strength data were analyzed with a one-way ANOVA and post hoc Scheffe's tests (α=.05). RESULTS The 3-point bending test showed the strongest (40.42 ± 5.72 MPa) metal-ceramic bond in the nonprecious Ni-Cr alloy, followed by millingable Pd-Ag alloy (37.71 ± 2.46 MPa), precious metal alloy containing 83% of gold (35.89 ± 1.93 MPa), and precious metal alloy containing 32% of gold (34.59 ± 2.63 MPa). Nonprecious Ni-Cr alloy and precious metal alloy containing 32% of gold showed significant difference (P<.05). CONCLUSION The type of metal-ceramic alloys affects the bond strength of porcelain. Every metal-ceramic alloy used in this study showed clinically applicable bond strength with porcelain (25 MPa). PMID:25352959

  18. Structural and magnetic phase transitions in CeCu6 -xTx (T =Ag ,Pd )

    NASA Astrophysics Data System (ADS)

    Poudel, L.; de la Cruz, C.; Payzant, E. A.; May, A. F.; Koehler, M.; Garlea, V. O.; Taylor, A. E.; Parker, D. S.; Cao, H. B.; McGuire, M. A.; Tian, W.; Matsuda, M.; Jeen, H.; Lee, H. N.; Hong, T.; Calder, S.; Zhou, H. D.; Lumsden, M. D.; Keppens, V.; Mandrus, D.; Christianson, A. D.

    2015-12-01

    The structural and the magnetic properties of CeCu6 -xAgx (0 ≤x ≤0.85 ) and CeCu6 -xPdx (0 ≤x ≤0.4 ) have been studied using neutron diffraction, resonant ultrasound spectroscopy (RUS), x-ray diffraction measurements, and first principles calculations. The structural and magnetic phase diagrams of CeCu6 -xAgx and CeCu6 -xPdx as a function of Ag/Pd composition are reported. The end member, CeCu6, undergoes a structural phase transition from an orthorhombic (P n m a ) to a monoclinic (P 21/c ) phase at 240 K. In CeCu6 -xAgx , the structural phase transition temperature (Ts) decreases linearly with Ag concentration and extrapolates to zero at xS ≈0.1 . The structural transition in CeCu6 -xPdx remains unperturbed with Pd substitution within the range of our study. The lattice constant b slightly decreases with Ag/Pd doping, whereas a and c increase with an overall increase in the unit cell volume. Both systems, CeCu6 -xAgx and CeCu6 -xPdx , exhibit a magnetic quantum critical point (QCP), at x ≈0.2 and x ≈0.05 , respectively. Near the QCP, long range antiferromagnetic ordering takes place at an incommensurate wave vector (δ10 δ2), where δ1˜0.62 ,δ2˜0.25 ,x =0.125 for CeCu6 -xPdx and δ1˜0.64 ,δ2˜0.3 ,x =0.3 for CeCu6 -xAgx . The magnetic structure consists of an amplitude modulation of the Ce moments which are aligned along the c axis of the orthorhombic unit cell.

  19. Mesoporous TiN as a noncarbon support of Ag-rich PtAg nanoalloy catalysts for oxygen reduction reaction in alkaline media.

    PubMed

    Cui, Zhiming; Yang, Minghui; Chen, Hao; Zhao, Mengtian; DiSalvo, Francis J

    2014-12-01

    There has been growing interest in noncarbon supports for fuel cell reactions, especially for the oxygen reduction reaction (ORR) in alkaline media. Herein, we report a robust mesoporous titanium nitride (TiN) which is not only kinetically stable in alkaline media, but also electrochemically stable in the potential range of fuel cell operation. This binary nitride exhibits an order of magnitude higher electronic conductivity than carbon black. Bimetallic Ag-rich PtAg nanoalloy is selected as the catalyst for the ORR in alkaline media due to their superior activity and relatively low cost. TiN-supported Pt1 Ag9 nanoalloy catalysts are synthesized by a new and efficient approach with KEt3 BH as reducing agent and THF as solvent. Pt1 Ag9 /TiN exhibits much higher mass activity and durability for the ORR in alkaline media than Pt1 Ag9 /C, Pt/C and Ag/C catalysts, suggesting that mesoporous TiN is a very promising support in alkaline media. PMID:25320003

  20. Interfacial nanodroplets guided construction of hierarchical Au, Au-Pt, and Au-Pd particles as excellent catalysts

    PubMed Central

    Ma, Aijing; Xu, Jie; Zhang, Xuehua; Zhang, Bin; Wang, Dayang; Xu, Haolan

    2014-01-01

    Interfacial nanodroplets were grafted to the surfaces of self-sacrificed template particles in a galvanic reaction system to assist the construction of 3D Au porous structures. The interfacial nanodroplets were formed via direct adsorption of surfactant-free emulsions onto the particle surfaces. The interfacial nanodroplets discretely distributed at the template particle surfaces and served as soft templates to guide the formation of porous Au structures. The self-variation of footprint sizes of interfacial nanodroplets during Au growth gave rise to a hierarchical pore size distribution of the obtained Au porous particles. This strategy could be easily extended to synthesize bimetal porous particles such as Au-Pt and Au-Pd. The obtained porous Au, Au-Pt, and Au-Pd particles showed excellent catalytic activity in catalytic reduction of 4-nitrophenol. PMID:24797697

  1. Anticancer Potencies of Pt(II) - and Pd(II)-linked M2L4 Coordination Capsules with Improved Selectivity.

    PubMed

    Ahmedova, Anife; Momekova, Denitsa; Yamashina, Masahiro; Shestakova, Pavletta; Momekov, Georgi; Akita, Munetaka; Yoshizawa, Michito

    2016-02-18

    Pt(II) - and Pd(II)-linked M2 L4 coordination capsules, providing a confined cavity encircled by polyaromatic frameworks, exhibit anticancer activities superior to cisplatin against two types of leukemic cells (HL-60 and SKW-3) and pronounced toxicity against cisplatin-resistant cells (HL-60/CDDP). Notably, the cytotoxic selectivities of the Pt(II) and Pd(II) capsules toward cancerous cells are up to 5.3-fold higher than that of cisplatin, as estimated through the non-malignant/malignant-cells toxicity ratio employing normal kidney cells (HEK-293). In addition, the anticancer activity of the coordination capsules can be easily altered upon encapsulation of organic guest molecules.

  2. Effect of copper content on Pt-Pd-CuO/{gamma}-alumina catalysts for motorcycle soot conversion

    SciTech Connect

    Chien, C.C.; Huang, T.J.

    1995-06-01

    Catalytic combustion of motorcycle soot particulates over {gamma}-alumina-supported CuO, Pt, Pd, Pt-CuO, and Pd-CuO catalysts was studied. The catalyst coated with motorcycle soots was placed in a flow reactor to perform temperature-programmed oxidation. Results indicated that the CuO catalyst was quite effective for the catalytic combustion. The high activity of the CuO catalyst could be illustrated by a redox mechanism and an induced particle-motion mechanism. A higher copper content enhanced the reducibility of the copper oxide and induced a higher activity for catalytic combustion until the copper oxide content reached 5 wt%. A redispersion phenomenon of the CuO species was observed and was consistent with the induced particle-motion mechanism. Additionally, the effect of the noble metal additive was to promote the activity of the CuO species by a mechanism including dissociative adsorption and spillover of oxygen.

  3. Allylic amination reactivity of Ni, Pd, and Pt heterobimetallic and monometallic complexes.

    PubMed

    Carlsen, Ryan W; Ess, Daniel H

    2016-06-14

    Transition metal heterobimetallic complexes with dative metal-metal interactions have the potential for novel fast reactivity. There are few studies that both compare the reactivity of different metal centers in heterobimetallic complexes and compare bimetallic reactivity to monometallic reactivity. Here we report density-functional calculations that show the reactivity of [Cl2Ti(N(t)BuPPh2)2M(II)(η(3)-methallyl)] heterobimetallic complexes for allylic amination follows M = Ni > Pd > Pt. This reactivity trend was not anticipated since the amine addition transition state involves M(II) to M(0) reduction and this could disadvantage Ni. Comparison of heterobimetallic complexes to the corresponding monometallic (CH2)2(N(t)BuPPh2)2M(II)(η(3)-methallyl) complexes reveals that this reactivity trend is due to the bimetallic interaction and that the bimetallic interaction significantly lowers the barrier height for amine addition by >10 kcal mol(-1). The impact of the early transition metal center on the amination addition barrier height depends on the late transition metal center. The lowest barrier heights for this reaction occur when late and early transition metal centers are from the same periodic table row. PMID:26893287

  4. Lattice thermal conductivity of disordered NiPd and NiPt alloys

    NASA Astrophysics Data System (ADS)

    Alam, Aftab; Mookerjee, Abhijit

    2006-05-01

    Numerical calculations of lattice thermal conductivity are reported for the binary alloys NiPd and NiPt. The present work is a continuation of an earlier paper by us (Alam and Mookerjee 2005 Phys. Rev. B 72 214207), which developed a theoretical framework for the calculation of configuration-averaged lattice thermal conductivity and thermal diffusivity in disordered alloys. The formulation was based on the augmented space theorem (Mookerjee 1973 J. Phys. C: Solid State Phys. 6 L205) combined with a scattering diagram technique. In this paper we shall show the dependence of the lattice thermal conductivity on a series of variables like phonon frequency, temperature and alloy composition. The temperature dependence of κ(T) and its relation to the measured thermal conductivity is discussed. The concentration dependence of κ appears to justify the notion of a minimum thermal conductivity as discussed by Kittel, Slack and others (Kittel 1948 Phys. Rev. 75 972, Brich and Clark 1940 Am. J. Sci. 238 613; Slack 1979 Solid State Physics vol 34, ed H Ehrenreich, F Seitz and D Turnbull (New York: Academic) p 1). We also study the frequency and composition dependence of the thermal diffusivity averaged over modes. A numerical estimate of this quantity gives an idea about the location of the mobility edge and the fraction of states in the frequency spectrum which is delocalized.

  5. The role of water in the adsorption of oxygenated aromatics on Pt and Pd.

    PubMed

    Yang, Jin; Dauenhauer, Paul J; Ramasubramaniam, Ashwin

    2013-01-01

    Catalytic processing of biomass-derived oxygenates to valuable chemical products will contribute to a sustainable future. To provide insight into the conversion of processed sugars and lignin monomers, we present density functional theory studies of adsorption of phloroglucinol, a potentially valuable biomass derivative, on Pt(111) and Pd(111) surfaces. A comprehensive study of adsorption geometries and associated energies indicates that the bridge site is the most preferred adsorption site for phloroglucinol, with binding energies in the range of 2-3 eV in the vapor phase. Adsorption of phloroglucinol on these metal surfaces occurs via hybridization between the carbon p(z) orbitals and the metal d(z(2)) and d(yz) orbitals. With explicit solvent, hydrogen bonds are formed between phloroglucinol and water molecules thereby decreasing binding of phloroglucinol to the metal surfaces relative to the vapor phase by 20-25%. Based on these results, we conclude that solvent effects can significantly impact adsorption of oxygenated aromatic compounds derived from biomass and influence catalytic hydrogenation and hydrodeoxygenation reactions as well. PMID:22941861

  6. Thermomechanical behavior of NiTiPdPt high temperature shape memory alloy springs

    NASA Astrophysics Data System (ADS)

    Nicholson, D. E.; Padula, S. A., II; Noebe, R. D.; Benafan, O.; Vaidyanathan, R.

    2014-12-01

    Transformation strains in high temperature shape memory alloys (HTSMAs) are generally smaller than for conventional NiTi alloys and can be purposefully limited in cases where stability and repeatability at elevated temperatures are desired. Yet such alloys can still be used in actuator applications that require large strokes when used in the form of springs. Thus there is a need to understand the thermomechanical behavior of shape memory alloy spring actuators, particularly those consisting of alternative alloys. In this work, a modular test setup was assembled with the objective of acquiring stroke, stress, temperature, and moment data in real time during joule heating and forced convective cooling of Ni19.5Ti50.5Pd25Pt5 HTSMA springs. The spring actuators were subjected to both monotonic axial loading and thermomechanical cycling. The role of rotational constraints (i.e., by restricting rotation or allowing for free rotation at the ends of the springs) on stroke performance was also assessed. Finally, recognizing that evolution in the material microstructure can result in changes in HTSMA spring geometry, the effect of material microstructural evolution on spring performance was examined. This was done by taking into consideration the changes in geometry that occurred during thermomechanical cycling. This work thus provides insight into designing with HTSMA springs and predicting their thermomechanical performance.

  7. Pt and Pd catalyzed oxidation of Li2O2 and DMSO during Li–O2 battery charging

    DOE PAGES

    Gittleson, Forrest S.; Ryu, Won-Hee; Schwab, Mark; Tong, Xiao; Taylor, André D.

    2016-01-01

    Rechargeable Li-O2 and Li-air batteries require electrode and electrolyte materials that synergistcally promote long-term cell operation. We investigate the role of noble metals Pt and Pd as catalysts for the Li-O2 oxidation process and their compatibility with a dimethyl sulfoxide (DMSO) based electrolyte. Lastly, we identify a basis for low potential Li2O2 evolution followed by oxidative decomposition of the electrolyte to form carbonate side products.

  8. Pt and Pd catalyzed oxidation of Li2O2 and DMSO during Li-O2 battery charging.

    PubMed

    Gittleson, Forrest S; Ryu, Won-Hee; Schwab, Mark; Tong, Xiao; Taylor, André D

    2016-05-01

    Rechargeable Li-O2 and Li-air batteries require electrode and electrolyte materials that synergistically promote long-term cell operation. In this study, we investigate the role of noble metals Pt and Pd as catalysts in the Li-O2 oxidation process and their compatibility with dimethyl sulfoxide (DMSO) based electrolytes. We identify a basis for low potential Li2O2 evolution followed by oxidative decomposition of the electrolyte to form carbonate side products. PMID:27111589

  9. A novel reverse rectifying effects and negative differential resistance in asymmetric X-biphenyl-X (X=Pt, Pd, Pb) molecular junctions

    NASA Astrophysics Data System (ADS)

    Parashar, Sweta; Srivastava, Pankaj

    2016-04-01

    We investigate the electronic transport properties of asymmetric biphenyl systems for X-electrodes (X=Pt, Pd, Pb) using non-equilibrium Green's function approach combined with density functional theory. The asymmetry in such systems is constructed by coupling biphenyl molecule to Pt, Pd, Pb electrode materials through dithiocarboxylate anchoring group on the left side and thiol group on the right side. Interestingly, novel reverse rectifying behaviors are observed for Pt and Pd electrode case. This is due to stronger d-orbital characteristics of Pt and Pd electrodes which produces intense transmission peak near the Fermi level. However, negative differential resistance is realized in case of Pb electrode. These observed distinct features for different electrodes are important for next generation nanoscale devices.

  10. Water-Free Proton Conduction in Discotic Pyridylpyrazolate-based Pt(II) and Pd(II) Metallomesogens.

    PubMed

    Cuerva, Cristián; Campo, José A; Cano, Mercedes; Sanz, Jesús; Sobrados, Isabel; Diez-Gómez, Virginia; Rivera-Calzada, Alberto; Schmidt, Rainer

    2016-07-18

    In this work we report on water-free proton conductivity in liquid-crystal pyridylpyrazolate-based Pt(II) and Pd(II) complexes [M(pz(R(n,n)py))2] (pz(R(n,n)py) = 3-(3,5-dialkyloxyphenyl)-5-(pyridin-2-yl)pyrazolate, R(n,n) = C6H3(OCnH2n+1)2; n = 4, 12, 16, M = Pd; n = 12, M = Pt) with potential application as electrolyte materials in proton exchange membrane fuel cells. The columnar ordering of the complexes in the liquid-crystalline phase opens nanochannels, which are used for fast proton exchange as detected by impedance spectroscopy and NMR. The NMR spectra indicate that the proton conduction mechanism is associated with a novel C-H···N proton transfer, which persists above the clearing point of the material. The highest conductivity of ∼0.5 μS cm(-1) at 180 °C with an activation energy of 1.2 eV is found for the Pt(II) compound in the mesophase. The Pd(II) complexes with different chain length (n = 4, 12, and 16) show lower conductivity but smaller activation energies, in the range of 0.74-0.93 eV. PMID:27362555

  11. East Scandinavian and Noril'sk plume mafic large igneous provinces of Pd-Pt ores: Geological and metallogenic comparison

    NASA Astrophysics Data System (ADS)

    Mitrofanov, F. P.; Bayanova, T. B.; Korchagin, A. U.; Groshev, N. Yu.; Malitch, K. N.; Zhirov, D. V.; Mitrofanov, A. F.

    2013-09-01

    This paper compares the geological, geophysical, and isotopic geochemical data on the Paleoproterozoic East Scandinavian Pd-Pt province in the Baltic Shield and the Late Paleozoic Noril'sk Pd-Pt province in the Siberian Craton. Both provinces contain large magmatic PGE deposits: low-sulfide in the Baltic Shield and high-sulfide in the Siberian Craton. Multidisciplinary evidence shows that the East Scandinavian mafic large igneous province, which has a plume nature, is intracratonic and was not subjected to the crucial effect of subduction-related and other contamination processes, whereas the Noril'sk province is pericratonic with substantial crustal contamination of the intrusive processes. Low-sulfide Pd-Pt deposits dominate in the East Scandinavian province, while high-sulfide Ni-Cu-PGE deposits play the leading role in the Noril'sk province. The U-Pb, Sm-Nd, and Rb-Sr isotopic data indicate multistage and long-term (tens of millions of years) geological history of mafic large igneous provinces. The plume magmatism with specific geochemistry and metallogeny is probably related to lower mantle sources.

  12. Water-Free Proton Conduction in Discotic Pyridylpyrazolate-based Pt(II) and Pd(II) Metallomesogens.

    PubMed

    Cuerva, Cristián; Campo, José A; Cano, Mercedes; Sanz, Jesús; Sobrados, Isabel; Diez-Gómez, Virginia; Rivera-Calzada, Alberto; Schmidt, Rainer

    2016-07-18

    In this work we report on water-free proton conductivity in liquid-crystal pyridylpyrazolate-based Pt(II) and Pd(II) complexes [M(pz(R(n,n)py))2] (pz(R(n,n)py) = 3-(3,5-dialkyloxyphenyl)-5-(pyridin-2-yl)pyrazolate, R(n,n) = C6H3(OCnH2n+1)2; n = 4, 12, 16, M = Pd; n = 12, M = Pt) with potential application as electrolyte materials in proton exchange membrane fuel cells. The columnar ordering of the complexes in the liquid-crystalline phase opens nanochannels, which are used for fast proton exchange as detected by impedance spectroscopy and NMR. The NMR spectra indicate that the proton conduction mechanism is associated with a novel C-H···N proton transfer, which persists above the clearing point of the material. The highest conductivity of ∼0.5 μS cm(-1) at 180 °C with an activation energy of 1.2 eV is found for the Pt(II) compound in the mesophase. The Pd(II) complexes with different chain length (n = 4, 12, and 16) show lower conductivity but smaller activation energies, in the range of 0.74-0.93 eV.

  13. Pd@Pt core-shell concave decahedra: A class of catalysts for the oxygen reduction reaction with enhanced activity and durability

    DOE PAGES

    Wang, Xue; Vera, Madeline; Chi, Miaofang; Xia, Younan; Luo, Ming; Huang, Hongwen; Ruditskiy, Aleksey; Park, Jinho; Bao, Shixiong; Liu, Jingyue; et al

    2015-11-13

    Here, we report a facile synthesis of multiply twinned Pd@Pt core shell concave decahedra by controlling the deposition of Pt on preformed Pd decahedral seeds. The Pt atoms are initially deposited on the vertices of a decahedral seed, followed by surface diffusion to other regions along the edges/ridges and then across the faces. Different from the coating of a Pd icosahedral seed, the Pt atoms prefer to stay at the vertices and edges/ridges of a decahedral seed even when the deposition is conducted at 200 degrees C, naturally generating a core shell structure covered by concave facets. The nonuniformity inmore » the Pt coating can be attributed to the presence of twin boundaries at the vertices, as well as the {100} facets and twin defects along the edges/ridges of a decahedron, effectively trapping the Pt adatoms at these high-energy sites. As compared to a commercial Pt/C catalyst, the Pd@Pt concave decahedra show substantial enhancement in both catalytic activity and durability toward the oxygen reduction reaction (ORR). For the concave decahedra with 29.6% Pt by weight, their specific (1.66 mA/cm2pt) and mass (1.60 A/mg/2pt) ORR activities are enhanced by 4.4 and 6.6 times relative to those of the Pt/C catalyst (0.36 mA/cm2pt and 0.32 A/mgpt, respectively). After 10 000 cycles of accelerated durability test, the concave decahedra still exhibit a mass activity of 0.69 A/mgpt, more than twice that of the pristine Pt/C catalyst.« less

  14. Catalytic Properties Dominated by Electronic Structures in PdZn, NiZn, and PtZn Intermetallic Compounds

    NASA Astrophysics Data System (ADS)

    Nozawa, Kazuki; Endo, Naruki; Kameoka, Satoshi; Tsai, An Pang; Ishii, Yasushi

    2011-06-01

    The catalytic functions of Pd are completely modified by alloying with Zn, and PdZn exhibits comparable catalytic selectivity to Cu in the steam reforming of methanol (SRM). We perform theoretical and experimental studies to confirm our previous argument that the position of the d-band is a significant factor determining catalytic properties. First-principles slab calculations for M--Zn (M = Pd, Ni, Pt) reveal that the bond breaking on the surface leads to some reduction in the d-bandwidth, but that the position of the d-band for stable surfaces remains essentially unchanged from that of the bulk. The origin of the dramatic change in the electronic structure caused by alloying is theoretically demonstrated. Our previous argument is experimentally examined not only in SRM, but also in elemental reactions such as CO and H2 adsorptions. Magnetic measurements also indicate the importance of the d-band position in SRM.

  15. Magnetic properties of ZnS doped with noble metals (X = Ru, Rh, Pd, and Ag)

    NASA Astrophysics Data System (ADS)

    Tan, Zhiyun; Xiao, Wenzhi; Wang, Lingling; Yang, Youchang

    2012-12-01

    Density functional theory calculations are carried out to study the electronic structures and magnetic properties in zinc-blende structure ZnS doped with nonmagnetic noble metals (X = Ru, Rh, Pd, and Ag). Results show robust magnetic ground states for X-doped ZnS. The total magnetic moments are about 2.0, 3.0, and 2.0 μB per supercell for the Ru-, Rh-, and Pd-doped ZnS, respectively. As the atomic number of X element increases, the local magnetic moment tends toward delocalize and the hybridization between X-4d and S-3p states become stronger. This trend is strongly related to the difference in electronegativity between the substitutional X and the cation in the ZnS host. For Ag-doped ZnS, both non-spin- and spin-polarized calculations yield nearly equal total energy. The substitution of Zn in ZnS parent material by the nonmagnetic 4d transition-metals may lead to half-metallic ferromagnetism which stems from the hybridization between X-4d and S-3p states and could be attributed to a double-exchange mechanism. Curie temperature values are estimated using mean-field approximation.

  16. EFFECT OF IMPURITIES ON THE PERFORMANCE OF A Pd-Ag DIFFUSER

    SciTech Connect

    Morgan, G.

    2010-12-16

    A commercially fabricated diffuser purchased from Johnson-Matthey, Inc. was evaluated for performance characterization testing at the Savannah River National Laboratory (SRNL). Different impurities are often present in the feed streams of the process diffusers, but the effect of these impurities on the diffuser performance is currently unknown. Various impurities were introduced into the feed stream of the diffuser at various levels ranging from 0.5% to 10% of the total flow in order to determine the effect that these impurities have on the permeation of hydrogen through the palladium-silver membrane. The introduction of various impurities into the feed stream of the diffuser had a minimal effect on the overall permeation of hydrogen through the Pd-Ag membrane. Of the four impurities introduced into the feed stream, carbon monoxide (CO) was the only impurity that showed any evidence of causing a reduction in the amount of hydrogen permeating through the Pd-Ag membrane. The hydrogen permeation returned to its baseline level after the CO was removed from the feed stream. There were no lasting effects of the CO exposure on the ability of the membrane to effectively separate hydrogen from the non-hydrogen species in the gas stream under the conditions tested.

  17. Pd/Ag coated fiber Bragg grating sensor for hydrogen monitoring in power transformers

    NASA Astrophysics Data System (ADS)

    Ma, G. M.; Jiang, J.; Li, C. R.; Song, H. T.; Luo, Y. T.; Wang, H. B.

    2015-04-01

    Compared with conventional DGA (dissolved gas analysis) method for on-line monitoring of power transformers, FBG (fiber Bragg grating) hydrogen sensor represents marked advantages over immunity to electromagnetic field, time-saving, and convenience to defect location. Thus, a novel FBG hydrogen sensor based on Pd/Ag (Palladium/Silver) along with polyimide composite film to measure dissolved hydrogen concentration in large power transformers is proposed in this article. With the help of Pd/Ag composite coating, the enhanced performance on mechanical strength and sensitivity is demonstrated, moreover, the response time and sensitivity influenced by oil temperature are solved by correction lines. Sensitivity measurement and temperature calibration of the specific hydrogen sensor have been done respectively in the lab. And experiment results show a high sensitivity of 0.055 pm/(μl/l) with instant response time about 0.4 h under the typical operating temperature of power transformers, which proves a potential utilization inside power transformers to monitor the health status by detecting the dissolved hydrogen concentration.

  18. Pd/Ag coated fiber Bragg grating sensor for hydrogen monitoring in power transformers.

    PubMed

    Ma, G M; Jiang, J; Li, C R; Song, H T; Luo, Y T; Wang, H B

    2015-04-01

    Compared with conventional DGA (dissolved gas analysis) method for on-line monitoring of power transformers, FBG (fiber Bragg grating) hydrogen sensor represents marked advantages over immunity to electromagnetic field, time-saving, and convenience to defect location. Thus, a novel FBG hydrogen sensor based on Pd/Ag (Palladium/Silver) along with polyimide composite film to measure dissolved hydrogen concentration in large power transformers is proposed in this article. With the help of Pd/Ag composite coating, the enhanced performance on mechanical strength and sensitivity is demonstrated, moreover, the response time and sensitivity influenced by oil temperature are solved by correction lines. Sensitivity measurement and temperature calibration of the specific hydrogen sensor have been done respectively in the lab. And experiment results show a high sensitivity of 0.055 pm/(μl/l) with instant response time about 0.4 h under the typical operating temperature of power transformers, which proves a potential utilization inside power transformers to monitor the health status by detecting the dissolved hydrogen concentration.

  19. Synthesis, Characterization, and Antibacterial Studies of Pd(II) and Pt(II) Complexes of Some Diaminopyrimidine Derivatives

    PubMed Central

    Ajibade, Peter A.; Idemudia, Omoruyi G.

    2013-01-01

    Pd(II) and Pt(II) complexes of trimethoprim and pyrimethamine were synthesized and characterized by elemental analysis, UV-Vis, FTIR, and NMR spectroscopy. The complexes are formulated as four coordinate square planar species containing two molecules of the drugs and two chloride or thiocyanate ions. The coordination of the metal ions to the pyrimidine nitrogen atom of the drugs was confirmed by spectroscopic analyses. The complexes were screened for their antibacterial activities against eight bacterial isolates. They showed varied activities with the active metal complexes showing more enhanced inhibition than either trimethoprim or pyrimethamine. The Pd(II) complexes of pyrimethamine showed unique inhibitory activities against P. aeruginosa and B. pumilus, and none of the other complexes or the drugs showed any activity against these bacteria isolates. The MIC and MBC determinations revealed that these Pd(II) complexes are the most active. Structure activity relationship showed that Pt(II) complexes containing chloride ions are more active, while for Pd(II) complexes containing thiocyanate ions showed more enhanced activity than those containing chloride ions. PMID:23573071

  20. Deviations from one-electron behavior in the Ag and Pd M4,5-VV Auger spectra of AgcPd1-c alloys

    NASA Astrophysics Data System (ADS)

    Mariot, J.-M.; Hague, C. F.; Dufour, G.

    1981-04-01

    A systematic investigation of the Ag and Pd M4,5-VV Auger spectra in the pure metals and in the AgcPd1-c(0.1<=c<=0.9) alloys is presented. The shape of the Auger spectra is discussed in relation to the values of the effective Coulomb interaction Ueff between the two holes present in the final state of the Auger transition and of the width W of the one-electron local densities of states as obtained from Lβ2,15 soft-x-ray emission bands. The Auger spectra of Ag in the metal and the alloys have a pronounced quasiatomic character, as can be expected from the Ueff2W ratio which is found to be close to unity. The Auger spectrum of pure Pd (Ueff2W~0.4) can be explained in terms of an atomic model in which strong band effects are present. For alloys with low-Pd content where Pd forms an impurity state, it is shown that final states other than the localized [4d2] two-hole state have to be invoked to explain the line shape.

  1. A new electrochemical sensor of nitro aromatic compound based on three-dimensional porous Pt-Pd nanoparticles supported by graphene-multiwalled carbon nanotube composite.

    PubMed

    Yuan, Cai-Xia; Fan, Yan-Ru; Tao-Zhang; Guo, Hui-Xia; Zhang, Jing-Xuan; Wang, Yong-Lan; Shan, Duo-Liang; Lu, Xiao-Quan

    2014-08-15

    In this study, an electrochemical sensor of nitro aromatic compound based on three-dimensional porous Pt-Pd nanoparticles (Pt-Pd NPs) supported by reduced graphene oxide (rGO) nanosheets-multiwalled carbon nanotube (CNTs) nanocomposite (marked as Pt-Pd NPs/CNTs-rGO) was investigated for the first time. This hybrid nanocomposite has been prepared via a facile and versatile hydrothermal synthetic strategy while its structure and property are evaluated by X-ray diffraction (XRD), transmission electron microscopy (TEM) and electrochemical impedance spectroscopy (EIS). The result shows that 3D porous Pt-Pd NPs/CNTs-rGO nanocomposite has a large specific surface area of 326.6m(2)g(-1) and exhibited ultrahigh rate capability and good cycling properties at high rates. Electrochemical studies have been performed for the nitro aromatic compounds detection by using different pulse voltammetry (DPV) techniques. The proposed nanocomposite exhibited much enhanced elctrocatalytic activity and high sensitivity toward the detection of nitro aromatic compounds which compared with Pt-Pd NPs dispersed on functionalized rGO, Pt-Pd NPs dispersed on functionalized CNTs, rGO-CNTs and bare glass carbon electrode (GCE). On the basis of the above synergetic electrochemical sensing and synthesis procedure, the hybrid material can be recommended as a robust material for sensor-related applications. Moreover, the proposed sensor exhibits high reproducibility, long-time storage stability and satisfactory anti-interference ability.

  2. One-Electron Oxidation of [M(P(t) Bu3 )2 ] (M=Pd, Pt): Isolation of Monomeric [Pd(P(t) Bu3 )2 ](+) and Redox-Promoted C-H Bond Cyclometalation.

    PubMed

    Troadec, Thibault; Tan, Sze-Yin; Wedge, Christopher J; Rourke, Jonathan P; Unwin, Patrick R; Chaplin, Adrian B

    2016-03-01

    Oxidation of zero-valent phosphine complexes [M(P(t) Bu3 )2 ] (M=Pd, Pt) has been investigated in 1,2-difluorobenzene solution using cyclic voltammetry and subsequently using the ferrocenium cation as a chemical redox agent. In the case of palladium, a mononuclear paramagnetic Pd(I) derivative was readily isolated from solution and fully characterized (EPR, X-ray crystallography). While in situ electrochemical measurements are consistent with initial one-electron oxidation, the heavier congener undergoes C-H bond cyclometalation and ultimately affords the 14 valence-electron Pt(II) complex [Pt(κ(2) PC -P(t) Bu2 CMe2 CH2 )(P(t) Bu3 )](+) with concomitant formation of [Pt(P(t) Bu3 )2 H](+) .

  3. Tuning magnetotransport in PdPt/Y{sub 3}Fe{sub 5}O{sub 12}: Effects of magnetic proximity and spin-orbit coupling

    SciTech Connect

    Zhou, X.; Ma, L.; Shi, Z.; Zhou, S. M.; Guo, G. Y.; Hu, J.; Wu, R. Q.

    2014-07-07

    We report that anisotropic magnetoresistance (AMR) and anomalous Hall conductivity (AHC) in the Pd{sub 1−x}Pt{sub x}/Y{sub 3}Fe{sub 5}O{sub 12} (YIG) bilayers could be tuned by varying the Pt concentration (x) and also temperature (T). In particular, the AHC at low T changes its sign when x increases from 0 to 1, agreeing with the negative and positive AHC predicted by our ab initio calculations for the magnetic proximity (MP)-induced ferromagnetic Pd and Pt, respectively. The AMR ratio is enhanced by ten times when x increases from 0 to 1. Furthermore, the AMR of PdPt/YIG bilayers shows similar T-dependence as the magnetic susceptibility of the corresponding bulk Pd/Pt, also indicating the MP effect as the origin of the AMR. The present work demonstrates that the alloying of Pt and Pd not only offers tunable spin-orbit coupling but also is useful to reveal the nature of the AMR and AHC in Pt/YIG bilayers, which are useful for spintronics applications.

  4. Ag(I)-Catalyzed C-H Activation: The Role of the Ag(I) Salt in Pd/Ag-Mediated C-H Arylation of Electron-Deficient Arenes.

    PubMed

    Whitaker, Daniel; Burés, Jordi; Larrosa, Igor

    2016-07-13

    The use of stoichiometric Ag(I)-salts as additives in Pd-catalyzed C-H functionalization reactions is widespread. It is commonly proposed that this additive acts as an oxidant or as a halide scavenger promoting Pd-catalyst turnover. We demonstrate that, contrary to current proposals, phosphine ligated Ag(I)-carboxylates can efficiently carry out C-H activation on electron-deficient arenes. We show through a combination of stoichiometric and kinetic studies that a (PPh3)Ag-carboxylate is responsible for the C-H activation step in the Pd-catalyzed arylation of Cr(CO)3-complexed fluorobenzene. Furthermore, the reaction rate is controlled by the rate of Ag(I)-C-H activation, leading to an order zero on the Pd-catalyst. H/D scrambling studies indicate that this Ag(I) complex can carry out C-H activation on a variety of aromatic compounds traditionally used in Pd/Ag-mediated C-H functionalization methodologies. PMID:27303956

  5. Nano-assemblies consisting of Pd/Pt nanodendrites and poly (diallyldimethylammonium chloride)-coated reduced graphene oxide on glassy carbon electrode for hydrogen peroxide sensors.

    PubMed

    Zhang, Yanyan; Zhang, Cong; Zhang, Di; Ma, Min; Wang, Weizhen; Chen, Qiang

    2016-01-01

    Non-enzymatic hydrogen peroxide (H2O2) sensors were fabricated on the basis of glassy carbon (GC) electrode modified with palladium (Pd) core-platinum (Pt) nanodendrites (Pt-NDs) and poly (diallyldimethylammonium chloride) (PDDA)-coated reduced graphene oxide (rGO). A facile wet-chemical method was developed for preparing Pd core-Pt nanodendrites. In this approach, the growth of Pt NDs was directed by Pd nanocrystal which could be regarded as seed. The PDDA-coated rGO could form uniform film on the surface of GC electrode, which provided a support for Pd core- Pt NDs adsorption by self-assembly. The morphologies of the nanocomposites were characterized by transmission electron microscopy, energy-dispersive X-ray spectroscopy and X-ray diffraction (spectrum). Electrocatalytic ability of the nanocomposites was evaluated by cyclic voltammetry and chronoamperometric methods. The sensor fabricated by Pd core-Pt NDs/PDDA-rGO/GCE exhibited high sensitivity (672.753 μA mM(-1) cm(-2)), low detection limit (0.027 μM), wider linear range (0.005-0.5mM) and rapid response time (within 5s). Besides, it also exhibited superior reproducibility, excellent anti-interference performance and long-term stability. The present work could afford a viable method and efficient platform for fabricating all kinds of amperometric sensors and biosensors. PMID:26478428

  6. Nano-assemblies consisting of Pd/Pt nanodendrites and poly (diallyldimethylammonium chloride)-coated reduced graphene oxide on glassy carbon electrode for hydrogen peroxide sensors.

    PubMed

    Zhang, Yanyan; Zhang, Cong; Zhang, Di; Ma, Min; Wang, Weizhen; Chen, Qiang

    2016-01-01

    Non-enzymatic hydrogen peroxide (H2O2) sensors were fabricated on the basis of glassy carbon (GC) electrode modified with palladium (Pd) core-platinum (Pt) nanodendrites (Pt-NDs) and poly (diallyldimethylammonium chloride) (PDDA)-coated reduced graphene oxide (rGO). A facile wet-chemical method was developed for preparing Pd core-Pt nanodendrites. In this approach, the growth of Pt NDs was directed by Pd nanocrystal which could be regarded as seed. The PDDA-coated rGO could form uniform film on the surface of GC electrode, which provided a support for Pd core- Pt NDs adsorption by self-assembly. The morphologies of the nanocomposites were characterized by transmission electron microscopy, energy-dispersive X-ray spectroscopy and X-ray diffraction (spectrum). Electrocatalytic ability of the nanocomposites was evaluated by cyclic voltammetry and chronoamperometric methods. The sensor fabricated by Pd core-Pt NDs/PDDA-rGO/GCE exhibited high sensitivity (672.753 μA mM(-1) cm(-2)), low detection limit (0.027 μM), wider linear range (0.005-0.5mM) and rapid response time (within 5s). Besides, it also exhibited superior reproducibility, excellent anti-interference performance and long-term stability. The present work could afford a viable method and efficient platform for fabricating all kinds of amperometric sensors and biosensors.

  7. Pumice-supported Pd-Pt bimetallic catalysts: Synthesis, structural characterization, and liquid-phase hydrogenation of 1,3-cyclooctadiene

    SciTech Connect

    Deganello, G.; Duca, D.; Liotta, L.F.; Martorana, A.; Venezia, M.; Benedetti, A.; Fagherazz, G.

    1995-01-01

    A series of pumice-supported palladium-platinum bimetallic catalysts were prepared and investigated by X-ray scattering (WAXS and SAXS) and XPS techniques. An alloy Pd-Pt was formed. The less abundant metal was found to segregate to the surface. The catalysts were tested in the liquid-phase hydrogenation of 1,3-cyclooctadiene to cyclooctene, and compared with similarly prepared pumice-supported palladium and platinum catalysts and other supported Pd-Pt catalysts reported in the literature. The addition of platinum reduces the activity and the selectivity of the palladium catalysts. Differences between the activity of these pumice-supported catalysts and the activity of previously described Pd and Pd-Pt catalysts on other supports, are attributed to the presence, in the latter, of diffusional processes. 50 refs., 4 figs. 2 tabs.

  8. A green approach to ethyl acetate: quantitative conversion of ethanol through direct dehydrogenation in a Pd-Ag membrane reactor.

    PubMed

    Zeng, Gaofeng; Chen, Tao; He, Lipeng; Pinnau, Ingo; Lai, Zhiping; Huang, Kuo-Wei

    2012-12-01

    Pincers do the trick: The conversion of ethanol to ethyl acetate and hydrogen was achieved using a pincer-Ru catalyst in a Pd-Ag membrane reactor. Near quantitative conversions and yields could be achieved without the need for acid or base promoters or hydrogen acceptors (see scheme). PMID:23136053

  9. Electrospun polyacrylonitrile nanofibers supported Ag/Pd nanoparticles for hydrogen generation from the hydrolysis of ammonia borane

    NASA Astrophysics Data System (ADS)

    Tong, Yan; Lu, Xiaofeng; Sun, Weining; Nie, Guangdi; Yang, Liu; Wang, Ce

    2014-09-01

    A high-performance hydrogen generation system based on the electrospun polyacrylonitrile (PAN)/Ag/Pd composite nanofibers, which were prepared by microwave reducing the electrospun PAN/AgNO3 nanofibers and followed by a replacement reaction has been demonstrated. The morphology of the as-prepared PAN/Ag/Pd composite nanofibers and the metal nanoparticles on the fibers were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), high resolution TEM (HRTEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) measurements. It has been demonstrated that the obtained PAN/Ag/Pd composite nanofibers possess fine morphology and high catalytic activities for H2 generation from aqueous solution of ammonia borane (NH3BH3, AB). The H2 generation test exhibited that the catalyst had excellent catalytic activity (with turnover frequency (TOF) of 377.2 mol H2 h-1 (mol Pd)-1), good recycle stability and easy-separation from the reaction system. This new kind of nanofibers possesses great potential application for the new clean energy development.

  10. Green Synthesis of Ag and Pd Nanospheres, Nanowires, and Nanorods Using Vitamin B2: Catalytic Polymerisation of Aniline and Pyrrole

    EPA Science Inventory

    For the first time, we report green chemistry approach using vitamin B2 in the synthesis of silver (Ag) and palladium (Pd), nanospheres, nanowires and nanorods at room temperature without using any harmful reducing agents, such as sodium borohydride (NaBH4) or hydroxylamine hydro...

  11. Thermodynamic guidelines for the design of bimetallic catalysts for oxygen electroreduction and rapid screening by scanning electrochemical microscopy. M-co (M: Pd, Ag, Au).

    PubMed

    Fernández, José L; Walsh, Darren A; Bard, Allen J

    2005-01-12

    We propose guidelines for the design of improved bimetallic (and related) electrocatalysts for the oxygen reduction reaction (ORR) in acidic media. This guide is based on simple thermodynamic principles assuming a simple mechanism where one metal breaks the oxygen-oxygen bond of molecular O(2) and the other metal acts to reduce the resulting adsorbed atomic oxygen. Analysis of the Gibbs free energies of these two reactions guides the selection of combinations of metals that can produce alloy surfaces with enhanced activity for the ORR when compared to the constituent metals. Selected systems have been tested by fabricating arrays of metallic catalysts consisting of various binary and ternary combinations of Pd, Au, Ag, and Co deposited on glassy carbon (GC) substrates. The electrocatalytic activity of these materials for the ORR in acidic medium was examined using scanning electrochemical microscopy (SECM) in a new rapid-imaging mode. This was used to rapidly screen arrays covering a wide range of catalyst compositions for their activity for the ORR in 0.5 M H(2)SO(4). Using the SECM technique, we have identified combinations of metals with enhanced electrocatalytic activities when compared with the constituent, pure metals. Addition of Co to Pd, Au, and Ag clearly decreases the ORR overpotential, in agreement with the proposed model. Catalyst spots that exhibited enhanced electrocatalytic activity in the SECM screening technique were then examined using classical rotating disk electrode (RDE) experiments. The activity of carbon black supported catalyst mixtures on a GC RDE and the electrocatalytic activity determined using the SECM screening technique showed excellent agreement. C/Pd-Co electrodes (10-30% Co) exhibited remarkable activity for ORR catalysis, close to that of carbon-supported Pt.

  12. Joint contributions of Ag ions and oxygen vacancies to conducting filament evolution of Ag/TaO{sub x}/Pt memory device

    SciTech Connect

    Chung, Yu-Lung; Cheng, Wen-Hui; Chen, Wei-Chih; Jhan, Sheng-An; Chen, Jen-Sue; Jeng, Jiann-Shing

    2014-10-28

    The electroforming and resistive switching behaviors in the Ag/TaO{sub x}/Pt trilayer structure are investigated under a continual change of temperatures between 300 K and 100 K to distinguish the contributions of Ag ions and oxygen vacancies in developing of conducting filaments. For either electroforming or resistive switching, a significantly higher forming/set voltages is needed as the device is operated at 100 K, as compared to that observed when operating at 300 K. The disparity in forming/set voltages of Ag/TaO{sub x}/Pt operating at 300 K and 100 K is attributed to the contribution of oxygen vacancies, in addition to Ag atoms, in formation of conducting filament at 100 K since the mobilities of oxygen vacancies and Ag ions become comparable at low temperature. The presence of oxygen vacancy segment in the conducting filament also modifies the reset current from a gradually descending behavior (at 300 K) to a sharp drop (at 100 K). Furthermore, the characteristic set voltage and reset current are irreversible as the operation temperature is brought from 100 K back to 300 K, indicating the critical role of filament constituents on the switching behaviors of Ag/oxide/Pt system.

  13. Crystalline monolayer surface of liquid Au-Cu-Si-Ag-Pd: Metallic glass former

    SciTech Connect

    Mechler, S; Yahel, E; Pershan, P S; Meron, M; Lin, B

    2012-02-06

    It is demonstrated by means of x-ray synchrotron reflectivity and diffraction that the surface of the liquid phase of the bulk metallic glass forming alloy Au49Cu26.9Si16.3Ag5.5Pd2.3 consists of a two-dimensional crystalline monolayer phase for temperatures of up to about 50 K above the eutectic temperature. The present alloy as well as glass forming Au82Si18 and Au-Si-Ge alloys containing small amounts of Ge are the only metallic liquids to exhibit surface freezing well above the melting temperature. This suggests that the phenomena of surface freezing in metallic liquids and glass forming ability are related and probably governed by similar physical properties.

  14. Ti/Pd/Ag Contacts to n-Type GaAs for High Current Density Devices

    NASA Astrophysics Data System (ADS)

    Huo, Pengyun; Rey-Stolle, Ignacio

    2016-06-01

    The metallization stack Ti/Pd/Ag on n-type Si has been readily used in solar cells due to its low metal/semiconductor specific contact resistance, very high sheet conductance, bondability, long-term durability, and cost-effectiveness. In this study, the use of Ti/Pd/Ag metallization on n-type GaAs is examined, targeting electronic devices that need to handle high current densities and with grid-like contacts with limited surface coverage (i.e., solar cells, lasers, or light emitting diodes). Ti/Pd/Ag (50 nm/50 nm/1000 nm) metal layers were deposited on n-type GaAs by electron beam evaporation and the contact quality was assessed for different doping levels (from 1.3 × 1018 cm-3 to 1.6 × 1019 cm-3) and annealing temperatures (from 300°C to 750°C). The metal/semiconductor specific contact resistance, metal resistivity, and the morphology of the contacts were studied. The results show that samples doped in the range of 1018 cm-3 had Schottky-like I- V characteristics and only samples doped 1.6 × 1019 cm-3 exhibited ohmic behavior even before annealing. For the ohmic contacts, increasing annealing temperature causes a decrease in the specific contact resistance ( ρ c,Ti/Pd/Ag ~ 5 × 10-4 Ω cm2). In regard to the metal resistivity, Ti/Pd/Ag metallization presents a very good metal conductivity for samples treated below 500°C ( ρ M,Ti/Pd/Ag ~ 2.3 × 10-6 Ω cm); however, for samples treated at 750°C, metal resistivity is strongly degraded due to morphological degradation and contamination in the silver overlayer. As compared to the classic AuGe/Ni/Au metal system, the Ti/Pd/Ag system shows higher metal/semiconductor specific contact resistance and one order of magnitude lower metal resistivity.

  15. Facile Synthesis of Pt-/Pd-MODIFIED NiTi Electrode with Superior Electro-Catalytic Activities Toward Methanol, Ethanol and Ethylene Glycol Oxidation

    NASA Astrophysics Data System (ADS)

    He, Yongwei; Wang, Mei; Ma, Zizai; Li, Ruixue; Kundu, Manab; Ma, Guanshui; Lin, Naiming; Tang, Bin; Wang, Xiaoguang

    2016-11-01

    Surface functional modification of NiTi electrode with noble Pt and Pd metal has been successfully carried out by simple and cost effective electro-spark deposition technique (ESD). Thin-film X-ray diffraction (TF-XRD), scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDX) and cyclic voltammetry (CV) have been carried out in order to investigate the structure, morphology, chemical composition and electrochemical behavior of the modified electrode surface. The modified Pt/NiTi and Pd/NiTi electrode surface exhibit a circular splash pattern with a tiny amount of Pt (˜5.30 at.% Pt) and Pd (˜5.71 at.% Pd) existence. The electrochemical results demonstrate that the Pt/NiTi and Pd/NiTi electrode possess an improved electro-catalytic activities toward methanol (MeOH), ethanol (EtOH) and ethylene glycol (EG) oxidation in alkaline media in comparison with the bare NiTi electrode. In acidic environments, the Pt/NiTi electrode exhibits even much better catalytic activities than the pure Pt sheet electrode due to the bi-functional mechanism. In the same way, the electro-catalytic activity of the modified Pd/NiTi electrode is also slightly larger than that of the pure Pd sheet electrode in alkaline environment. The electro-spark surface modification approach is rapid and environmentally-benign, being attractive to widen the application of traditional surface modification technique in the field of material surface/interface design and functionalization.

  16. Experimental Study on a Compact Methanol Steam Reformer with Pd/Ag Membrane

    NASA Astrophysics Data System (ADS)

    Faizal, Hasan Mohd; Kuwabara, Masato; Kizu, Ryo; Yokomori, Takeshi; Ueda, Toshihisa

    The performance of high purity hydrogen production from methanol for a compact steam reformer with a hydrogen purification membrane was investigated experimentally. A 77 wt.% Pd/23 wt.% Ag membrane with 25µm thickness and CuO/ZnO/ Al2O3 catalyst were used. Heating was performed by a Bunsen type burner using City Gas 13A. The methanol reforming and purification of H2 were investigated at different reference catalyst zone temperatures (589-689K), pressures at the retentate side (0.2-0.5MPa), steam to methanol(S/C) ratios (0.8-1.6) and reactant flow rates (1.7 ×10-4 to 4.4×10-4 mol/s). The results show that at high reference temperature, high pressure and certain points of the reactant flow rate, the maximum hydrogen permeation rate is obtained when the S/C ratio is around 1. The modified Sieverts’ equation which considers the decrease in H2 concentration at the membrane surface, was proposed. The experimental result was lower than the permeation rate estimated by the modified Sieverts’ equation, which is probably caused by the adsorption of non-H2 species during permeation. It is further demonstrated that the modified Sieverts’ equation is able to estimate a more reasonable hydrogen permeation rate in comparison to the estimation by the ordinary Sieverts’ equation. In addition, it is shown that the compact methanol steam reformer with a Pd/Ag membrane is able to produce high purity hydrogen with very low CO concentration, which fulfills the Polymer Electrolyte Fuel Cell (PEFC) requirement (<10ppm).

  17. Different structural preference of Ag(I) and Au(I) in neutral and cationic luminescent heteropolynuclear platinum(II) complexes: Z (U)-shaped Pt2M2 type vs. trinuclear PtM2 type.

    PubMed

    Nishihara, Kazuki; Ueda, Misa; Higashitani, Ami; Nakao, Yoshihide; Arikawa, Yasuhiro; Horiuchi, Shinnosuke; Sakuda, Eri; Umakoshi, Keisuke

    2016-03-28

    The reactions of monocationic Pt(II) complexes bearing N^C chelate ligands and Me2pzH, [Pt(N^C)(Me2pzH)2]PF6 (N^C = 2-phenylpyridinate (ppy(-)), 2-(2,4-difluorophenyl)pyridinate (dfppy(-)), benzo[h]quinolinate (bzq(-)); Me2pzH = 3,5-dimethylpyrazole), with Ag(I) ions gave Z (or U)-shaped neutral tetranuclear Pt2Ag2 complexes [Pt2Ag2(N^C)2(Me2pz)4], while those with Au(I) ions gave neutral trinuclear PtAu2 complexes [PtAu2(N^C)(Me2pz)3]. On the contrary, the reactions of the dicationic Pt(II) complex bearing a N^N chelate ligand and Me2pzH, [Pt(bpy)(Me2pzH)2](PF6)2 (bpy = 2,2'-bipyridine), with Ag(I) and Au(I) ions both gave Z (or U)-shaped dicationic tetranuclear Pt2M2 complexes, [Pt2M2(bpy)2(Me2pz)4](PF6)2 (M = Ag, Au). The structures of heteropolynuclear Pt(II) complexes were dominated by the nature of incorporated group 11 metal ions and the charge of complexes.

  18. Microsegregation in and Phase Stability of As-Cast Ti-Zr-Hf-Ni-Pd-Pt High-Entropy Alloys

    NASA Astrophysics Data System (ADS)

    Yokoyama, Yoshihiko; Itoh, Shun; Murakami, Yoshihiro; Narita, Issei; Wang, Gongyao; Liaw, Peter K.

    2015-04-01

    Microsegregation in as-cast Ti-Zr-Hf-Ni-Pd-Pt high-entropy alloys (HEAs) was examined by scanning electron microscopy and transmission electron microscopy. The structure of the microsegregated HEAs was composed of dendrite grains and grain boundaries. Since Hf, Zr, and Pt show both high melting temperatures and large negative mixing enthalpy, microsegregation on a micrometer scale occurred easily, similar to the spontaneous inoculation during solidification of copper-mold casts. In contrast, the grain boundaries were identified as being Ti- and Ni-enriched regions. Macroscopic X-ray data showed the combination of a distinct body-centered-cubic structure and broad halo peaks (amorphous structure). Microstructure analysis revealed that heteroamorphous and nanocrystalline regions are observed when the Ti group:Ni group molar ratio was 50/50. This unique microsegregated structure resulted in an ultimate compression strength of more than 2 GPa.

  19. Behavior of alloys of the PtPd intermetallic compound with Hf and Zr in the electrosynthesis of peroxo salts

    SciTech Connect

    Toroptseva, N.T.; Vaseva, A.Yu.

    1988-08-10

    The objective of this study was to investigate the behavior of anodes made of alloys of the PtPd intermetallic compound with Hf and Zr in the synthesis of potassium peroxodicarbonates and peroxoborates. The investigations were based on polarization measurements in different regimes on stationary and rotating electrodes, the determination of the current yield of active oxygen in galvano- and potentiostatic syntheses, and the study of the kinetics of catalytic decomposition of peroxide solutions in the presence of the electrode in the range 289-308 K.

  20. Site preference of ternary alloying additions to NiTi: Fe, Pt, Pd, Au, Al, Cu, Zr and Hf

    NASA Technical Reports Server (NTRS)

    Bozzolo, Guillermo; Noebe, Ronald D.; Mosca, Hugo O.

    2004-01-01

    Atomistic modeling of the site substitution behavior of Pd in NiTi (J. Alloys and Comp. (2004), in press) has been extended to examine the behavior of several other alloying additions, namely, Fe, Pt, Au, Al, Cu, Zr and Hf in this important shape memory alloy. It was found that all elements, to a varying degree, displayed absolute preference for available sites in the deficient sublattice. How- ever, the energetics of the different substitutional schemes, coupled with large scale simulations indicate that the general trend in all cases is for the ternary addition to want to form stronger ordered structures with Ti.

  1. Green Synthesis of Ag and Pd Nanospheres, Nanowires, and Nanorods Using Vitamin B 2 : Catalytic Polymerisation of Aniline and Pyrrole

    DOE PAGES

    Nadagouda, Mallikarjuna N.; Varma, Rajender S.

    2008-01-01

    Formore » the first time, we report green chemistry approach using vitamin B 2 in the synthesis of silver (Ag) and palladium (Pd), nanospheres, nanowires, and nanorods at room temperature without using any harmful reducing agents, such as sodium borohydride ( NaBH 4 ) or hydroxylamine hydrochloride and any special capping or dispersing agent. Vitamin B 2 was used as reducing agent as well as capping agent due to its high-water solubility, biodegradability, and low-toxicity compared with other reducing agents. The average particle size of nanoprticle was found to be Ag (average size 6.1 ± 0.1 nm) and Pd (average size 4.1 ± 0.1 nm) nanoparticles in ethylene glycol and Ag (average size 5.9 ± 0.1 nm, and average size 6.1 ± 0.1) nanoparticles in acetic acid and NMP, respectively. The formation of noble multiple shape nanostructures and their self assembly were dependent on the solvent employed for the preparation. When water was used as solvent media, Ag and Pd nanoparticles started to self-assemble into rod-like structures and in isopropanol Ag and Pd nanoparticles yielded wire-like structures with a thickness in the range of 10 to 20 nm and several hundred microns in length. In acetone and acetonitrile medium, the Ag and Pd nanoparticles are self-assembled into a regular pattern making nanorod structures with thicknesses ranging from 100 to 200 nm and lengths of a few microns. The so-synthesized nanostructures were characterized using scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive X-ray (EDX) analysis, and UV spectroscopy. The ensuing Ag and Pd nanoparticles catalyzed the reactions of aniline and pyrrole to generate polyaniline and polypyrrole nanofibers and may find various technological and biological applications. This single-step greener approach is general and can be extended to other noble metals and transition metal oxides.« less

  2. Roadside Accumulation of Pt, Pd, Rh and Other Trace Elements From Automobiles: Catalytic Converter Attrition and Platinum-Group Element Mobility in the Roadside Environment.

    NASA Astrophysics Data System (ADS)

    Ely, J. C.; Dahlheimer, S. R.; Neal, C. R.

    2003-12-01

    Elemental abundances of Pt, Pd and Rh have been documented across the industrialized world in roadside environments due to attrition of automotive catalytic converters (Zereini and Alt, 2000, Anthropogenic PGE Emissions, Springer, 308pp; Ely et al., 2001, EnvSci&Tech, 35:3816-3822; Whiteley and Murray, 2003, SciTotEnv, in press). In our ongoing study, the highest reported roadside Pt abundance 1.8 ppm has been found immediately adjacent to the road at a field site in South Bend, IN, USA. Furthermore, initial studies show positive correlations of Pt, Pd and Rh with some trace elements (Ni, Cu, Zn and Pb), which has been confirmed by further analysis for these and other elements (Ce, Cr). It has been demonstrated that elements such as Ce are present in catalytic converters at concentrations of 100's ppm to 3-wt.%. These elements are also being attrited with Pt, Pd and Rh and aerially transported and deposited. Our field site was established next to US-933 adjacent to the Notre Dame campus. Areas were cleared of the top 2-4 cm of soil (removing surficial Pt, Pd and Rh) at 1, 5, 10 and 50 meters from the roadside. Within 3 months the 1-meter site contained 67% of the initial Rh and Pt concentrations and 100% of the initial Pd concentration. The sites at 5, 10 and 50 meters showed similar results, in some cases exceeding the initial concentrations. After 6 months the concentrations of Pt, Pd and Rh were all within error of the initial concentrations, indicating steady state abundances had probably been reached. Grass samples from each site showed that washed vs. unwashed samples were within error of each other, and there may be a slight enrichment (approx. 1 ppb) in the grasses of Pd and Pt, but this enrichment was independent of distance from the road. The steady-state situation suggests that the PGEs are being removed from the immediate roadside environment, which requires that the metals are being oxidized and/or complexed in such a way to facilitate transport. The

  3. Electrochemical immunosensor for detecting typical bladder cancer biomarker based on reduced graphene oxide-tetraethylene pentamine and trimetallic AuPdPt nanoparticles.

    PubMed

    Ma, Hongmin; Zhang, Xiaoyue; Li, Xiaojian; Li, Rongxia; Du, Bin; Wei, Qin

    2015-10-01

    A highly sensitive electrochemical immunosensor for detection of typical bladder cancer biomarker-nuclear matrix protein 22 (NMP22) was developed by using reduced graphene oxide-tetraethylene pentamine (rGO-TEPA) and trimetallic AuPdPt nanoparticles (NPs). rGO-TEPA was used as the ideal material for signal amplification and AuPdPt NPs immobilization due to its excellent conductivity and large surface area. An effective platform was constructed for antibodies anchoring by using AuPdPt NPs, which kept the antibodies' high stability and bioactivity. Moreover, AuPdPt NPs could accelerate the electron transfer and enhance the signal response, which assisted by the synergistic effect of the three different metals (Au, Pd and Pt). The proposed immunosensor showed satisfied performance such as simple fabrication, low detection limits (0.01 U/mL), wide linear range (from 0.040 to 20 U/mL), short analysis time (2 min), high stability and selectivity in the detection of NMP22. Furthermore, the proposed immunosensor was employed to test real urine samples with satisfactory results.

  4. Multi-functional ultrathin PdxCu1-x and Pt~PdxCu1-x one-dimensional nanowire motifs for various small molecule oxidation reactions

    SciTech Connect

    Liu, Haiqing; Wong, Stanislaus S.; Adzic, Radoslav R.

    2015-11-18

    Developing novel electrocatalysts for small molecule oxidation processes, including formic acid oxidation (FAOR), methanol oxidation reaction (MOR), and ethanol oxidation reaction (EOR), denoting the key anodic reactions for their respective fuel cell configurations, is a significant and relevant theme of recent efforts in the field. Herein, in this report, we demonstrated a concerted effort to couple and combine the benefits of small size, anisotropic morphology, and tunable chemical composition in order to devise a novel “family” of functional architectures. In particular, we have fabricated not only ultrathin 1-D Pd1–xCux alloys but also Pt-coated Pd1–xCux (i.e., Pt~Pd1–xCux; herein the ~ indicates an intimate association, but not necessarily actual bond formation, between the inner bimetallic core and the Pt outer shell) core–shell hierarchical nanostructures with readily tunable chemical compositions by utilizing a facile, surfactant-based, wet chemical synthesis coupled with a Cu underpotential deposition technique. Our main finding is that our series of as-prepared nanowires are functionally flexible. More precisely, we demonstrate that various examples within this “family” of structural motifs can be tailored for exceptional activity with all 3 of these important electrocatalytic reactions. In particular, we note that our series of Pd1–xCux nanowires all exhibit enhanced FAOR activities as compared with not only analogous Pd ultrathin nanowires but also commercial Pt and Pd standards, with Pd9Cu representing the “optimal” composition. Moreover, our group of Pt~Pd1–xCux nanowires consistently outperformed not only commercial Pt NPs but also ultrathin Pt nanowires by several fold orders of magnitude for both the MOR and EOR reactions in alkaline media. As a result, the variation of the MOR and EOR performance with

  5. Ab initio investigation of the oxygen reduction reaction activity on noble metal (Pt, Au, Pd), Pt3M (M = Fe, Co, Ni, Cu) and Pd3M (M = Fe, Co, Ni, Cu) alloy surfaces, for Lisbnd O2 cells

    NASA Astrophysics Data System (ADS)

    Sankarasubramanian, Shrihari; Singh, Nikhilendra; Mizuno, Fuminori; Prakash, Jai

    2016-07-01

    First principles, density functional theory (DFT) modelling of the oxygen reduction reaction (ORR) on noble metal (Pt, Au, Pd), Pt3M (M = Fe, Co, Ni, Cu) and Pd3M (M = Fe, Co, Ni, Cu) alloy surfaces, was carried out. Periodic models of close-packed (111) surfaces were constructed, their geometry was optimized and the most stable geometric surface configuration was identified. The correlation between the intermediate species binding energy and the favored reaction pathway from amongst 1e-, 2e-, and 4e- mechanisms were studied by calculating the binding energies of a 1/4 monolayer of O, O2, LiO, LiO2, Li2O2, and Li2O on various sites and orientations. The reaction free energies (ΔGrxn) were calculated and used to compute the catalytic activity of the surfaces using molecular kinetics theory. Plots of the catalytic activity vs. Oxygen binding energy (EBinding (O)) showed a typical "volcano" profile. The insights gained from this study can be used to guide the choice of cathode catalysts in Lisbnd O2 cells.

  6. Structural analysis of polymer-protected Pd/Pt bimetallic clusters as dispersed catalysts by using extended x-ray absorption fine structure spectroscopy

    SciTech Connect

    Toshima, Naoki; Harada, Masafumi; Yonezawa, Tetsu; Kushihashi, Kakuta; Asakura, Kiyotaka )

    1991-09-19

    Extended X-ray absorption fine structure (EXAFS) was applied to the determination of the structure of colloidal dispersions of the poly (N-vinyl-2-pyrrolidone)-protected palladium/platinum bimetallic clusters, which work as the catalysts for selective partial hydrogenation of 1,3-cyclooctadiene to cyclooctene. The catalytic activity was found to depend on the structure of the bimetallic clusters. The EXAFS data on the Pd/Pt (4/1) bimetallic clusters, which are the most active catalysts, indicate a Pt core structure, in which the 42 Pd atoms are on the surface of the cluster particle and 13 Pt atoms are at the center of the particle, forming a core. In contrast, the Pd/Pt (1/1) bimetallic clusters are suggested to have a modified Pt core structure, in which 28 Pt atoms connect directly with each other, being located both in the core and on the surface, and 27 Pd atoms form three islands on the surface of the cluster particle. These bimetallic clusters work as active catalysts for selective hydrogenation of olefins, selective partial hydrogenation of diene to monoene, and visible light-induced hydrogen generation from water.

  7. A sandwich-type immunosensor using Pd-Pt nanocrystals as labels for sensitive detection of human tissue polypeptide antigen

    NASA Astrophysics Data System (ADS)

    Wang, Yaoguang; Wei, Qin; Zhang, Yong; Wu, Dan; Ma, Hongmin; Guo, Aiping; Du, Bin

    2014-02-01

    A sandwich-type immunosensor was developed for the detection of human tissue polypeptide antigen (hTPA). In this work, a graphene sheet (GS) was synthesized to modify the surface of a glassy carbon electrode (GCE), and Pd-Pt bimetallic nanocrystals were used as secondary-antibody (Ab2) labels for the fabrication of the immunosensor. The amperometric response of the immunosensor for catalyzing hydrogen peroxide (H2O2) was recorded. And electrochemical impedance spectroscopy was used to characterize the fabrication process of the immunosensor. The anti-human tissue polypeptide antigen primary antibody (Ab1) was immobilized onto the GS modified GCE via cross-linking with 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide hydrochloride and N-hydroxysuccinimide (EDC/NHS). With Ab1 immobilized onto the GS modified GCE and Ab2 linked on Pd-Pt bimetallic nanocrystals, the immunosensor demonstrated a wide linear range (0.0050-15 ng ml-1), a low detection limit (1.2 pg ml-1), good reproducibility, good selectivity and acceptable stability. This design strategy may provide many potential applications in the detection of other cancer biomarkers.

  8. Exploring the spin states of 90Zr populated by (p,p'), (p,d), and (p,t) reactions

    NASA Astrophysics Data System (ADS)

    Ota, S.; Burke, J. T.; Casperson, R. J.; Escher, J. E.; Hughes, R. O.; Ressler, J. J.; Scielzo, N. D.; Thompson, I. J.; Austin, R. A. E.; Abromeit, B.; Foley, N. J.; McCleskey, E.; McCleskey, M.; Park, H. I.; Saastamoinen, A.; Ross, T. J.

    2016-06-01

    The 90Zr nucleus was produced by three different reactions: 90Zr(p,p'), 91Zr(p,d), and 92Zr(p,t), and the spin-parity (Jπ) population of the 90Zr states produced by these reactions was studied to investigate the surrogate reaction approach, which aims at indirectly determining cross sections for compound-nuclear reactions involving unstable targets such as 89Zr(n,γ). Discrete γ-rays, associated with the de-excitation of 90Zr and 89Zr, were measured in coincidence with light ions at 90Zr excitation energies extending above the neutron separation energy. Low-lying states populated by (p,d) and (p,t) reactions agreed well with the previous measurements. The measured γ transition systematics were used to gain insights into the Jπ distribution of 90Zr around the neutron separation energy and it was found that the (p,p') reaction preferentially produces lower J states than (p,d) and (p,t) reactions in the studied energy region.

  9. Prediction of Reliable Metal-PH₃ Bond Energies for Ni, Pd, and Pt in the 0 and +2 Oxidation States

    SciTech Connect

    Craciun, Raluca; Vincent, Andrew J.; Shaughnessy, Kevin H.; Dixon, David A.

    2010-06-21

    Phosphine-based catalysts play an important role in many metal-catalyzed carbon-carbon bond formation reactions yet reliable values of their bond energies are not available. We have been studying homogeneous catalysts consisting of a phosphine bonded to a Pt, Pd, or Ni. High level electronic structure calculations at the CCSD(T)/complete basis set level were used to predict the M-PH₃ bond energy (BE) for the 0 and +2 oxidation states for M=Ni, Pd, and Pt. The calculated bond energies can then be used, for example, in the design of new catalyst systems. A wide range of exchange-correlation functionals were also evaluated to assess the performance of density functional theory (DFT) for these important bond energies. None of the DFT functionals were able to predict all of the M-PH3 bond energies to within 5 kcal/mol, and the best functionals were generalized gradient approximation functionals in contrast to the usual hybrid functionals often employed for main group thermochemistry.

  10. Final Technical Report: First Principles Investigations for the Ensemble Effects of PdAu and PtAu Bimetallic Nanocatalysts

    SciTech Connect

    Ruqian Wu

    2012-05-18

    Bimetallic surfaces with tunable chemical properties have attracted broad attention in recent years due to their ample potential for heterogeneous catalysis applications. The local chemical properties of constituents are strongly altered from their parent metals by 'ligand effect', a term encompassing the influences of charge transfer, orbital rehybridization and lattice strain. In comparison to the aforementioned, the 'ensemble effect' associated with particular arrangements of the active constituents have received much less attention, despite their notable importance towards the determination of reactivity and selectivity of bimetallic catalysts. We performed theoretical studies for understanding the ensemble effects on bimetallic catalysis: (i) simulations for the formation of different ensembles on PdAu and PtAu nanoclusters; (ii) studies of the size, shape, and substrate dependence of their electronic properties; and (iii) simulations for model reactions such as CO oxidation, methanol, ethylene and water dehydrogenation on PdAu and PtAu nanoclusters. In close collaboration with leading experimental groups, our theoretical research elucidated the fundamentals of Au based bimetallic nanocatalysts.

  11. The effect of nanoparticles size on photocatalytic and antimicrobial properties of Ag-Pt/TiO2 photocatalysts

    NASA Astrophysics Data System (ADS)

    Zielińska-Jurek, Anna; Wei, Zhishun; Wysocka, Izabela; Szweda, Piotr; Kowalska, Ewa

    2015-10-01

    Ag-Pt-modified TiO2 nanocomposites were synthesized using the sol-gel method. Bimetallic modified TiO2 nanoparticles exhibited improved photocatalytic activity under visible-light irradiation, better than monometallic Ag/TiO2 and Pt/TiO2 nanoparticles (NPs). All modified powders showed localized surface plasmon resonance (LSPR) in visible region. The photocatalysts' characteristics by X-ray diffractometry (XRD), scanning transmission electron microscopy (STEM), diffuse reflectance spectroscopy (DRS), X-ray photoelectron spectroscopy (XPS), nitrogen adsorption (BET method for specific surface area) showed that sample with the highest photocatalytic activity had anatase structure, about 93 m2/g specific surface area, maximum plasmon absorption at ca. 420 nm and contained small NPs of silver of 6 nm and very fine platinum NPs of 3 nm. The photocatalytic activity was estimated by measuring the decomposition rate of phenol in 0.2 mM aqueous solution under Vis and UV/vis light irradiation. It was found that size of platinum was decisive for the photocatalytic activity under visible light irradiation, i.e., the smaller Pt NPs were, the higher was photocatalytic activity. While, antimicrobial activities, estimated for bacteria Escherichia coli and Staphylococcus aureus, and pathogenic fungi belonging to Candida family, were only observed for photocatalysts containing silver, i.e., Ag/TiO2 and Ag-Pt/TiO2 nanocomposites.

  12. Hardening behavior after high-temperature solution treatment of Ag-20Pd-12Au-xCu alloys with different Cu contents for dental prosthetic restorations.

    PubMed

    Kim, Yonghwan; Niinomi, Mitsuo; Hieda, Junko; Nakai, Masaaki; Cho, Ken; Fukui, Hisao

    2014-07-01

    Ag-Pd-Au-Cu alloys have been used widely for dental prosthetic applications. Significant enhancement of the mechanical properties of the Ag-20Pd-12Au-14.5Cu alloy as a result of the precipitation of the β' phase through high-temperature solution treatment (ST), which is different from conventional aging treatment in these alloys, has been reported. The relationship between the unique hardening behavior and precipitation of the β' phase in Ag-20Pd-12Au-xCu alloys (x=6.5, 13, 14.5, 17, and 20mass%) subjected to the high-temperature ST at 1123K for 3.6ks was investigated in this study. Unique hardening behavior after the high-temperature ST also occurs in Ag-20Pd-12Au-xCu alloys (x=13, 17, and 20) with precipitation of the β' phase. However, hardening is not observed and the β' phase does not precipitate in the Ag-20Pd-12Au-6.5Cu alloy after the same ST. The tensile strength and 0.2% proof stress also increase in Ag-20Pd-12Au-xCu alloys (x=13, 14.5, 17, and 20) after the high-temperature ST. In addition, these values after the high-temperature ST increase with increasing Cu content in Ag-20Pd-12Au-xCu alloys (x=14.5, 17, and 20). The formation process of the β' phase can be explained in terms of diffusion of Ag and Cu atoms and precipitation of the β' phase. Clarification of the relationship between hardening and precipitation of the β' phase via high-temperature ST is expected to help the development of more effective heat treatments for hardening in Ag-20Pd-12Au-xCu alloys.

  13. Novel PdAgCu ternary alloy as promising materials for hydrogen separation membranes: Synthesis and characterization

    NASA Astrophysics Data System (ADS)

    Tarditi, Ana M.; Cornaglia, Laura M.

    2011-01-01

    The use of the sequential electroless plating method allowed us to obtain the PdAgCu ternary alloy on top of dense stainless steel (SS) 316 L disks. The XRD analysis indicated that initially the nucleation of the two phases of the alloy (FCC and BCC) takes place, but the FCC/BCC ratio increases with the annealing time at 500 °C in H 2 stream. After 162 h, the film contained only the FCC phase, which presents promising properties to be applied in the synthesis of hydrogen selective membranes. SEM cross-section results showed that a dense, continuous, defect-free film was deposited on top of the SS support, and the EDS data indicated that no significant gradient was present on the thickness of the film. XPS and LEIS allowed us to determine that Cu and Ag surface segregation takes place after annealing up to 500 °C/5 days. In the top-most surface layer, Ag enrichment takes place as determined by ARXPS experiments which can be the result of the lower surface tension of Ag compared to that of Cu and Pd. Increasing the annealing temperature results in an increase of the Ag surface segregation while the Cu concentration in the top-most surface layer decreases.

  14. Leaching of Au, Ag, and Pd from waste printed circuit boards of mobile phone by iodide lixiviant after supercritical water pre-treatment

    SciTech Connect

    Xiu, Fu-Rong; Qi, Yingying; Zhang, Fu-Shen

    2015-07-15

    Highlights: • We report a novel process for recovering Au, Ag, and Pd from waste PCBs. • The effect of SCWO on the leaching of Au, Ag, and Pd in waste PCBs was studied. • SCWO was highly efficient for enhancing the leaching of Au, Ag, and Pd. • The optimum leaching parameters for Au, Ag, and Pd in iodine–iodide were studied. - Abstract: Precious metals are the most attractive resources in waste printed circuit boards (PCBs) of mobile phones. In this work, an alternative process for recovering Au, Ag, and Pd from waste PCBs of mobile phones by supercritical water oxidation (SCWO) pre-treatment combined with iodine–iodide leaching process was developed. In the process, the waste PCBs of mobile phones were pre-treated in supercritical water, then a diluted hydrochloric acid leaching (HL) process was used to recovery the Cu, whose leaching efficiency was approximately 100%, finally the resulting residue was subjected to the iodine–iodide leaching process for recovering the Au, Ag, and Pd. Experimental results indicated that SCWO pre-treatment temperature, time, and pressure had significant influence on the Au, Ag, and Pd leaching from (SCWO + HL)-treated waste PCBs. The optimal SCWO pre-treatment conditions were 420 °C and 60 min for Au and Pd, and 410 °C and 30 min for Ag. The optimum dissolution parameters for Au, Pd, and Ag in (SCWO + HL)-treated PCBs with iodine–iodide system were leaching time of 120 min (90 min for Ag), iodine/iodide mole ratio of 1:5 (1:6 for Ag), solid-to-liquid ratio (S/L) of 1:10 g/mL (1:8 g/mL for Ag), and pH of 9, respectively. It is believed that the process developed in this study is environment friendly for the recovery of Au, Ag, and Pd from waste PCBs of mobile phones by SCWO pre-treatment combined with iodine–iodide leaching process.

  15. Metal nanostructures with complex surface morphology: The case of supported lumpy Pd and Pt nanoparticles produced by laser processing of metal films

    NASA Astrophysics Data System (ADS)

    Ruffino, F.; Maugeri, P.; Cacciato, G.; Zimbone, M.; Grimaldi, M. G.

    2016-09-01

    In this work we report on the formation of lumpy Pd and Pt nanoparticles on fluorine-doped tin oxide/glass (FTO/glass) substrate by a laser-based approach. In general, complex-surface morphology metal nanoparticles can be used in several technological applications exploiting the peculiarities of their physical properties as modulated by nanoscale morphology. For example plasmonic metal nanoparticles presenting a lumpy morphology (i.e. larger particles coated on the surface by smaller particles) can be used in plasmonic solar cell devices providing broadband scattering enhancement over the smooth nanoparticles leading, so, to the increase of the device efficiency. However, the use of plasmonic lumpy nanoparticles remains largely unexplored due to the lack of simply, versatile, low-cost and high-throughput methods for the controllable production of such nanostructures. Starting from these considerations, we report on the observation that nanoscale-thick Pd and Pt films (17.6 and 27.9 nm, 12.1 and 19.5 nm, respectively) deposited on FTO/glass surface irradiated by nanosecond pulsed laser at fluences E in the 0.5-1.5 J/cm2 range, produce Pd and Pt lumpy nanoparticles on the FTO surface. In addition, using scanning electron microscopy analyses, we report on the observation that starting from each metal film of fixed thickness h, the fraction F of lumpy nanoparticles increases with the laser fluence E and saturates at the higher fluences. For each fixed fluence, F was found higher starting from the Pt films (at each starting film thickness h) with respect to the Pd films. For each fixed metal and fluence, F was found to be higher decreasing the starting thickness of the deposited film. To explain the formation of the lumpy Pd and Pt nanoparticles and the behavior of F as a function of E and h both for Pd and Pt, the thermodynamic behavior of the Pd and Pt films and nanoparticles due to the interaction with the nanosecond laser is discussed. In particular, the

  16. Amperometric biosensor of SnO2 thin film modified by Pd, In and Ag nanostructure synthesized by CSP method

    NASA Astrophysics Data System (ADS)

    Hassan, Marwa Abdul Muhsien; Hateef, Areej Adnan; Majeed, Aseel Mustafa Abdul; Al-Jabiry, Ali Jasim Mohammed; Jameel, Sabah; Hussian, Haidar Abdul Razaq Abdul

    2013-10-01

    Palladium, Indium and Silver-doped SnO2 thin film was deposited by chemical spray pyrolysis on ITO and porous silicon substrates to be a fast MgSO4·7H2O amperometric biosensor. The prepared SnO2 films were doped by dipping in palladium chloride PdCl2, indium chloride, InCl3 and silver nitrides AgNO3 dissolved in ethanol C2H5OH. The structural and optical properties of the prepared films were studied. The sensitivity behaviors of SnO2, SnO2: Pd, SnO2: In and SnO2: Ag based on the amperometric biosensor to MgSO4·7H2O salts were investigated at room temperature with different doping.

  17. Magnetic properties of self-organized L1 0 FePtAg nanoparticle arrays

    NASA Astrophysics Data System (ADS)

    Wang, S.; Kang, S. S.; Nikles, D. E.; Harrell, J. W.; Wu, X. W.

    2003-10-01

    The magnetic properties of chemically synthesized high anisotropy L1 0 [Fe 49Pt 51] 88Ag 12 nanoparticle arrays have been studied as a function of annealing temperature. Particles were prepared by the simultaneous polyol reduction of platinum acetylacetonate and silver acetate and the thermal decomposition of iron carbonyl, yielding monodispersed particles of diameter ˜3.5 nm. Addition of Ag lowers the ordering temperature of self-assembled arrays by ˜150°C. After annealing at Ta=500°C for 30 min in an Ar/H 2 atmosphere, the coercivity was 13,800 Oe. TEM and delta- M measurements indicate weak particle aggregation up to Ta=400°C, with evidence of sintering at higher temperatures. Large ratios of remanent to hysteresis coercivity indicate a large distribution in anisotropy energies. Anomalously large thermal stability constants, KV/ kBT, and switching volumes were measured, even in samples with very little evidence of sintering. Zero field viscosity versus remanence curves show evidence of exchange interactions.

  18. Study of the interaction of DNA with cisplatin and other Pd(II) and Pt(II) complexes by atomic force microscopy.

    PubMed Central

    Onoa, G B; Cervantes, G; Moreno, V; Prieto, M J

    1998-01-01

    Modifications in the structure of a 260 bp DNA (hlyM) fragment from Escherichia coli caused by interaction with Pd(II) and Pt(II) complexes were studied. Cisplatin and transplatin [cis- and trans-PtCl2(NH3)2 respectively], Pt2Cl2(Spym)4 (Spym = 2-mercaptopyrimidine anion), Pd-famotidine and Pt-famotidine were incubated with DNA for 24 h at 37 degrees C and then observed with an atomic force microscope. Atomic force microscopy (AFM) provides the opportunity for nanometer resolution in research on the interaction between nucleic acids and metal complexes. The complexes induced noticeable changes in DNA topography according to their different characteristics and structure. In the case of cisplatin a shortening in DNA strands was observed. Transplatin and Pt2Cl2(Spym)4 caused shortening and compaction, whilst an aggregation of two strands was observed for the Pt-famotidine compound but not for the Pd-famotidine compound or the metal-free famotidine. PMID:9490794

  19. Effect of thione primers on adhesive bonding between an indirect composite material and Ag-Pd-Cu-Au alloy.

    PubMed

    Imai, Hideyuki; Koizumi, Hiroyasu; Shimoe, Saiji; Hirata, Isao; Matsumura, Hideo; Nikawa, Hiroki

    2014-01-01

    The current study evaluated the effect of primers on the shear bond strength of an indirect composite material joined to a silverpalladium-copper-gold (Ag-Pd-Cu-Au) alloy (Castwell). Disk specimens were cast from the alloy and were air-abraded with alumina. Eight metal primers were applied to the alloy surface. A light-polymerized indirect composite material (Solidex) was bonded to the alloy. Shear bond strength was determined both before and after the application of thermocycling. Two groups primed with Metaltite (thione) and M. L. Primer (sulfide) showed the greatest post-thermocycling bond strength (8.8 and 6.5 MPa). The results of the X-ray photoelectron spectroscopic (XPS) analysis suggested that the thione monomer (MTU-6) in the Metaltite primer was strongly adsorbed onto the Ag-Pd-Cu-Au alloy surface even after repeated cleaning with acetone. The application of either the thione (MTU-6) or sulfide primer is effective for enhancing the bonding between a composite material and Ag-Pd-Cu-Au alloy.

  20. Study on deposition technique and properties of Pd/Ag alloy film sensor supported on ceramic substrate

    NASA Astrophysics Data System (ADS)

    Geng, Z. T.; He, Q.; Jin, C. G.

    2016-07-01

    Developing high-quality hydrogen sensitive material is the core part of hydrogen sensor, whose performance is determined by the sensitive response, reproducibility and recovery of hydrogen material etc. In order to overcome the defects of hydrogen embrittlement in previous hydrogen sensor which were based on the pure palladium, sliver as the second component added to the palladium was studied. Using photochemical etching technology to produce a bent metal mask, the mask is put on the ceramic substrate. Firstly, the thin film of Ta2O5 as a transition layer grew on the ceramic substrate. Then, a series of Pd/Ag alloy film sensors were prepared, and each performance characterization of Pd/Ag alloy film was studied. Testing results indicated that the thin film had a good linear output performance at 0∼⃒30% hydrogen concentration range, and demonstrates a high responsiveness and good repeatability. With temperature increasing, the strength of the responsive signal of the Pd/Ag alloy film decreases and its responsive time was also shortened.

  1. Gyroscope-like molecules consisting of PdX₂/PtX₂ rotators within three-spoke dibridgehead diphosphine stators: syntheses, substitution reactions, structures, and dynamic properties.

    PubMed

    Nawara-Hultzsch, Agnieszka J; Stollenz, Michael; Barbasiewicz, Michał; Szafert, Sławomir; Lis, Tadeusz; Hampel, Frank; Bhuvanesh, Nattamai; Gladysz, John A

    2014-04-14

    Threefold intramolecular ring-closing metatheses of trans-[MCl2(P{(CH2)(m)CH=CH2}3)2] are effected with Grubbs' catalyst. Following hydrogenation catalyzed by [RhCl(PPh3)3], the title complexes trans-[MCl2(P((CH2)n)3P)] (n=2m+2; M/n=Pt/14, 4 c; Pt/16, 4 d; Pt/18, 4 e; Pd/14, 5 c; Pd/18, 5 e) and sometimes isomers partly derived from intraligand metathesis, trans-[MCl2{P(CH2)n(CH2)n}P(CH2)n)] (4'c-e, 5'e), are isolated. These react with LiBr, NaI, and KCN to give the corresponding MBr2, MI2, and M(CN)2 species (58-99%). (13)C NMR data show that the MX2 moieties rapidly rotate within the diphosphine cage on the NMR timescale, even at -120 °C. The reaction of 4 c and KSCN gives separable Pt(NCS)2 and Pt(NCS)(SCN) adducts (13 c, 28%; 14 c, 20%), and those of 4 c,e and Ph2Zn give PtPh2 species (15 c, 61%; 15 e, 90%). (13)C NMR spectra of 13 c-15 c show two sets of CH2 signals (ca. 2:1 intensity ratios), indicating that MX2 rotation is no longer rapid. Reactions of 4 c or 4'c and excess NaC≡CH afford the free diphosphines P{(CH2)14}3P (91%) and (CH2)14P(CH2)14P(CH2)14 (90%). The latter has been crystallographically characterized as a bis(BH3) adduct. The crystal structures of eight complexes with P(CH2)14P linkages (PtCl2, PtBr2, PtI2, Pt(NCS)2, PtPh2, PdCl2, PdBr2, PdI2) and 15 e have been determined, and intramolecular distances analyzed with respect to MX2 rotation. The conformations of the (CH2)14 moieties and features of the crystal lattices are also discussed.

  2. Competitive C{double_bond}C and C{double_bond}O adsorption of {alpha}-{beta} unsaturated aldehydes on Pt and Pd surfaces in relation with the selectivity of hydrogenation reactions: A theoretical approach

    SciTech Connect

    Delbecq, F.; Sautet, P.

    1995-04-01

    The adsorption geometries of acrolein, crotonaldehyde, methylcrotonaldehyde (prenal), and cinnamaldehyde on Pt and Pd surfaces have been studied by means of semiempirical extended Hueckel calculations: Pt(111), Pt(100), Pt(110), and Pd(111) surfaces, and steps on Pt(111) have been compared. Depending on the face and the substituents of the organic molecule, the adsorption geometries are totally different: a di-{sigma} form is preferred on Pt(111), a planar {eta}{sub 4} one on Pd(111) and Pt(100), and a {pi}{sub cc} one on Pt(110) and on the step. These preferred adsorption modes allow one to explain the selectivity observed during the hydrogenation of prenal on these well-defined surfaces. The results obtained in this work also allow one to understand the behavior of different metal catalysts towards the hydrogenation of the {alpha}-{beta} unsaturated aldehydes. 32 refs., 8 figs., 8 tabs.

  3. The Disposition of Pt, Pd, Ir, Os, and Ru in Marine Sediments and the K/T Boundary

    NASA Technical Reports Server (NTRS)

    Lee, Cin-Ty; Wasserburg, Gerald; Kyte, Frank

    2003-01-01

    The marine record of platinum group elements (PGEs) and Os isotopic compositions provides information on different inputs of PGEs into the oceans. Some studies based on a smaller subset of the PGEs suggest that the PGEs may suffer post-depositional mobility during diagenesis. In some K/T boundary clays, Kyte and others showed that the relative abundances of Pt, Pd, Ir, and Os can differ significantly from chondritic, which is the signature expected from fallout of the meteorite impact. In some K/T boundary sections, elevated Ir concentrations are observed as far as 1 meter from the cm-thick boundary clay containing the meteoritic ejecta. The purpose of this study was to characterize Pt, Pd, Ir, Os, and Ru abundances in zones including the K/T boundary. We determined PGE abundances of boundary clays at two hemipelagic sites (Stevns Klint, Denmark and Caravaca, Spain) in which previous studies by Kyte and others showed that the Ir anomaly is confined to within a few cm. We also analyzed two pelagic Pacific sites: a boundary clay from the north Pacific (Hole 465A) characterized by a 0.5 m thick Ir anomaly and a transect across the K/T boundary from the south Pacific (Hole 596) where the Ir anomaly spans 2 m. The Stevns Klint, Caravaca, and north Pacific sites are characterized by abundant marls and limestones in the section, whereas the south Pacific site is dominated by clays. Samples were spiked with isotopic tracers, mixed with a flux, S and Ni, and equilibrated by fusion. PGEs were extracted from the Ni and analyzed on a Finnigan Element ICP-MS. We find that the narrow Caravaca and Stevns Klint boundary clays have relative PGE abundance patterns indistinguishable from chondritic values. The two Pacific sites were found to have nearly identical PGE patterns but have ratios at the peak, which differ from chondritic values as found earlier by Evans et al. The Pacific sites were found to have nearly identical PGE patterns but are extremely depleted in OS (Os/Ir = 0

  4. Enhanced Selectivity to H2 Formation in Decomposition of HCOOH on the Ag19@Pd60 Core-Shell Nanocluster from First-Principles.

    PubMed

    Cho, Jinwon; Lee, Sangheon; Han, Jonghee; Yoon, Sung Pil; Nam, Suk Woo; Choi, Sun Hee; Hong, Seong-Ahn; Lee, Kwan-Young; Ham, Hyung Chul

    2015-10-01

    In this study, using spin-polarized density functional theory calculation we examined the origin of enhanced catalytic activity toward H2 production from HCOOH in Ag19@Pd60 core-shell nanoclusters (a 79-atom truncated octahedral cluster models). First, we find that the Pd monolayer shell on the Ag core can greatly enhance the selectivity to H2 formation via HCOOH decomposition compared to the pure Pd79 cluster by substantially reducing the binding energy of key intermediate HCOO and in turn the barrier for dehydrogenation. This activity enhancement is related to the modification of d states in the Pd monolayer shell by the strong ligand effect between Ag core and Pd shell, rather than the tensile strain effect by Ag core. In particular, the absence of dz2-r2 density of states near the Fermi level in the Pd monolayer shell (which originated from the substantial charge transfer from Ag to Pd) is the main reason for the increased H2 production from HCOOH decomposition. PMID:26726494

  5. Enhanced Selectivity to H2 Formation in Decomposition of HCOOH on the Ag19@Pd60 Core-Shell Nanocluster from First-Principles.

    PubMed

    Cho, Jinwon; Lee, Sangheon; Han, Jonghee; Yoon, Sung Pil; Nam, Suk Woo; Choi, Sun Hee; Hong, Seong-Ahn; Lee, Kwan-Young; Ham, Hyung Chul

    2015-10-01

    In this study, using spin-polarized density functional theory calculation we examined the origin of enhanced catalytic activity toward H2 production from HCOOH in Ag19@Pd60 core-shell nanoclusters (a 79-atom truncated octahedral cluster models). First, we find that the Pd monolayer shell on the Ag core can greatly enhance the selectivity to H2 formation via HCOOH decomposition compared to the pure Pd79 cluster by substantially reducing the binding energy of key intermediate HCOO and in turn the barrier for dehydrogenation. This activity enhancement is related to the modification of d states in the Pd monolayer shell by the strong ligand effect between Ag core and Pd shell, rather than the tensile strain effect by Ag core. In particular, the absence of dz2-r2 density of states near the Fermi level in the Pd monolayer shell (which originated from the substantial charge transfer from Ag to Pd) is the main reason for the increased H2 production from HCOOH decomposition.

  6. Chemical bonding and charge redistribution - Valence band and core level correlations for the Ni/Si, Pd/Si, and Pt/Si systems

    NASA Technical Reports Server (NTRS)

    Grunthaner, P. J.; Grunthaner, F. J.; Madhukar, A.

    1982-01-01

    Via a systematic study of the correlation between the core and valence level X-ray photoemission spectra, the nature of the chemical bonding and charge redistribution for bulk transition metal silicides has been examined. Particular emphasis is placed on Pt2Si and PtSi. It is observed that the strength of the metal (d)-silicon (p) interaction increases in the order Ni2Si, Pd2Si, Pt2Si. It is also observed that both the metal and silicon core lines shift to higher binding energy as the silicides are formed. The notion of charge redistribution for metallic bonds is invoked to explain these data.

  7. Oxygen chemisorption effects on the spatial atomic distribution of CuNi, CuPd and NiPt nanostructures

    NASA Astrophysics Data System (ADS)

    Montejano-Carrizales, J. M.; Morán-López, J. L.

    1993-05-01

    The spatial atomic distribution in cubo-octahedral CuNi, CuPd and NiPt clusters with a total number of atoms, N = 147, in the presence of chemisorbed oxygen, is studied. The equilibrium atomic configuration is obtained by calculating the free energy within the regular solution model and by assuming that the surface of the cluster is covered by oxygen atoms. Depending on the interaction between oxygen and the cluster components, the atomic distribution in the cluster can be completely modified as compared to the case of clusters with a clean surface. We present result for the temperature dependence of the concentration at the different shells around the central atom.

  8. A study of the dispersity of iron oxide and iron oxide-noble metal (Me = Pd, Pt) supported systems

    NASA Astrophysics Data System (ADS)

    Cherkezova-Zheleva, Z. P.; Shopska, M. G.; Krstić, J. B.; Jovanović, D. M.; Mitov, I. G.; Kadinov, G. B.

    2007-09-01

    Samples of one-(Fe) and two-component (Fe-Pd and Fe-Pt) catalysts were prepared by incipient wetness impregnation of four different supports: TiO2 (anatase), γ-Al2O3, activated carbon, and diatomite. The chosen synthesis conditions resulted in the formation of nanosized supported phases—iron oxide (in the one-component samples), or iron oxide-noble metal (in the two-component ones). Different agglomeration degrees of these phases were obtained as a result of thermal treatment. Ultradisperse size of the supported phase was maintained in some samples, while a process of partial agglomeration occurred in others, giving rise to nearly bidisperse (ultra-and highdisperse) supported particles. The different texture of the used supports and their chemical composition are the reasons for the different stability of the nanosized supported phases. The samples were tested as heterogeneous catalysts in total benzene oxidation reaction.

  9. Porous alumina-metallic Pt/Pd, Cr or Al layered nanocoatings with fully controlled variable interference colors.

    PubMed

    Pashchanka, Mikhail; Yadav, Sandeep; Cottre, Thorsten; Schneider, Jörg J

    2014-11-01

    Metallic Cr, Al, and Pt/Pd alloy have been deposited by magnetron sputtering or thermal evaporation (resistance heating or electron beam heating) onto nanoporous anodic alumina and have allowed to facilitate a cost-effective technique for manufacturing of pigment-free colored coatings on aluminum. Bright and saturated colors were achieved using the interference effect, and tuned by variation of the uniform oxide film thickness. Morphology and properties of these coatings were investigated by scanning electron microscopy (SEM) and reflectance measurements (UV/Vis/NIR spectrometry). Some optical properties of anodic alumina membranes are rather variable and strongly depend on oxidation parameters, non-stoichiometric composition, and porosity. However, the established correspondence between the film thickness, metallic coating type, and observed interference colors, allows facile, scalable, and inexpensive deposition of colored decorative and wear-resistant coatings onto aluminum and alloys surfaces.

  10. H2 production by the photocatalytic reforming of cellulose and raw biomass using Ni, Pd, Pt and Au on titania

    PubMed Central

    Jones, W.; Hardacre, C.; Bowker, M.

    2016-01-01

    Here, we report a method for sustainable hydrogen production using sunlight and biomass. It is shown that cellulose can be photoreformed to produce hydrogen, even in solid form, by use of metal-loaded titania photocatalysts. The experiments performed verified that the process is enabled by initial hydrolysis via glucose, which itself is shown to be efficiently converted to produce hydrogen by photocatalysis. Importantly, it is shown that not only precious metals such as Pt, Pd and Au can be used as the metal component, but also much more economic and less environmentally damaging Ni is effective. Even more importantly, we show for the first time, to the best our knowledge, that fescue grass as raw biomass can be effective for hydrogen production without significant pre-treatment. This provides additional benefits for the efficiency of biomass hydrogen production, because fewer processing steps for the raw material are required than in the production of purer forms of cellulose, for example. PMID:27493561

  11. Thermodynamic temperature determinations of Co C, Pd C, Pt C and Ru C eutectic fixed-point cells

    NASA Astrophysics Data System (ADS)

    Anhalt, K.; Hartmann, J.; Lowe, D.; Machin, G.; Sadli, M.; Yamada, Y.

    2006-04-01

    Thermodynamic temperatures during the melt and the freeze of Co-C, Pd-C, Pt-C and Ru-C metal-carbon fixed-point cells manufactured by LNE-INM/CNAM, NMIJ and NPL were determined by absolutely calibrated filter radiometers traceable to the PTB cryogenic radiometer and a radiance comparison method using an IKE LP3 radiation thermometer. The measurement uncertainties were below 400 mK at temperatures up to 2250 K. The results are in agreement within the combined uncertainties with a study on relative temperature differences of the same set of fixed-point cells. For the fixed-point cells manufactured by NPL the results are compared with a previous thermodynamic temperature measurement.

  12. Determination of the compositions of the DIGM zone in nanocrystalline Ag/Au and Ag/Pd thin films by secondary neutral mass spectrometry

    PubMed Central

    Molnár, Gábor Y; Shenouda, Shenouda S; Katona, Gábor L; Langer, Gábor A

    2016-01-01

    Summary Alloying by grain boundary diffusion-induced grain boundary migration is investigated by secondary neutral mass spectrometry depth profiling in Ag/Au and Ag/Pd nanocrystalline thin film systems. It is shown that the compositions in zones left behind the moving boundaries can be determined by this technique if the process takes place at low temperatures where solely the grain boundary transport is the contributing mechanism and the gain size is less than the half of the grain boundary migration distance. The results in Ag/Au system are in good accordance with the predictions given by the step mechanism of grain boundary migration, i.e., the saturation compositions are higher in the slower component (i.e., in Au or Pd). It is shown that the homogenization process stops after reaching the saturation values and further intermixing can take place only if fresh samples with initial compositions, according to the saturation values, are produced and heat treated at the same temperature. The reversal of the film sequence resulted in the reversal of the inequality of the compositions in the alloyed zones, which is in contrast to the above theoretical model, and explained by possible effects of the stress gradients developed by the diffusion processes itself. PMID:27335738

  13. Determination of the compositions of the DIGM zone in nanocrystalline Ag/Au and Ag/Pd thin films by secondary neutral mass spectrometry.

    PubMed

    Molnár, Gábor Y; Shenouda, Shenouda S; Katona, Gábor L; Langer, Gábor A; Beke, Dezső L

    2016-01-01

    Alloying by grain boundary diffusion-induced grain boundary migration is investigated by secondary neutral mass spectrometry depth profiling in Ag/Au and Ag/Pd nanocrystalline thin film systems. It is shown that the compositions in zones left behind the moving boundaries can be determined by this technique if the process takes place at low temperatures where solely the grain boundary transport is the contributing mechanism and the gain size is less than the half of the grain boundary migration distance. The results in Ag/Au system are in good accordance with the predictions given by the step mechanism of grain boundary migration, i.e., the saturation compositions are higher in the slower component (i.e., in Au or Pd). It is shown that the homogenization process stops after reaching the saturation values and further intermixing can take place only if fresh samples with initial compositions, according to the saturation values, are produced and heat treated at the same temperature. The reversal of the film sequence resulted in the reversal of the inequality of the compositions in the alloyed zones, which is in contrast to the above theoretical model, and explained by possible effects of the stress gradients developed by the diffusion processes itself. PMID:27335738

  14. A close look of Au/Pt/Ag nanocomposites using SERS assisted with optical, electrochemical, spectral and theoretical methods

    NASA Astrophysics Data System (ADS)

    Karthikeyan, B.; Loganathan, B.

    2013-03-01

    In the hope of gaining a close look or better characterization of trimetallic nanoparticles that are expected to possess higher surface-enhanced Raman scattering (SERS) activity, we have analysed Au/Pt/Ag trimetallic nanocomposites prepared by the microwave irradiation method. The plasmon absorption of the trimetallic nanocomposites shows a linear shift with the addition of 7-azaindole. The addition of 7-azaindole on trimetallic nanocomposites and the obtained spectral, optical and electrochemical studies give a close look of trimetallic nanocomposite's structure and its properties. In addition to that, core-shell preferences and Pt adsorbed surface complex of 7-azaindole are theoretically explained.

  15. Isothermal nucleation and growth kinetics of Pd/Ag alloy phase via in-situ time-resolved high-temperature x-ray diffraction (HTXRD) analysis

    SciTech Connect

    Ayturk, Mahmut Engin; Payzant, E Andrew; Speakman, Scott A; Ma, Yi Hua

    2008-01-01

    Among several different approaches to form Pd/Ag alloys for hydrogen separation applications, ex-situ studies carried by conventional X-ray point scanning detectors might fail to reveal the key aspects of the phase transformation between Pd and Ag metals. In this respect, in-situ time-resolved high temperature X-ray diffraction (HTXRD) was employed to study the Pd/Ag alloy phase nucleation and growth kinetics. By the use of linear position sensitive detectors, advanced optics and profile fitting with the use of JADE-6.5 software, isothermal phase evolution of the Pd/Ag alloy at 500 C, 550 C and 600 C under hydrogen atmosphere were quantified to elucidate the mechanistic details of the Pd/Ag alloy phase nucleation and growth pattern. Analysis of the HTXRD data by the Avrami model indicated that the nucleation of the Pd/Ag alloy phase was instantaneous where the growth mechanism was through diffusion-controlled one-dimensional thickening of the Pd/Ag alloy layer. The value of the Avrami exponent, n, was found to increase with temperature with the values of 0.34, 0.39 and 0.67 at 500oC, 550oC and 600oC, respectively. In addition, parabolic rate law analysis suggested that the nucleation of the Pd/Ag alloy phase was through a heterogeneous nucleation mode, in which the nucleation sites were defined as the non-equilibrium defects. The cross-sectional SEI micrographs indicated that the Pd/Ag alloy phase growth was strongly dependent upon the deposition morphology of the as-synthesized Pd and Ag layers formed by the electroless plating. Based on the Avrami model and the parabolic rate law, the estimated activation energies for the phase transformation were 236.5 and 185.6 kJ/mol and in excellent agreement with the literature values (183-239.5 kJ/mol).

  16. Leaching of Au, Ag, and Pd from waste printed circuit boards of mobile phone by iodide lixiviant after supercritical water pre-treatment.

    PubMed

    Xiu, Fu-Rong; Qi, Yingying; Zhang, Fu-Shen

    2015-07-01

    Precious metals are the most attractive resources in waste printed circuit boards (PCBs) of mobile phones. In this work, an alternative process for recovering Au, Ag, and Pd from waste PCBs of mobile phones by supercritical water oxidation (SCWO) pre-treatment combined with iodine-iodide leaching process was developed. In the process, the waste PCBs of mobile phones were pre-treated in supercritical water, then a diluted hydrochloric acid leaching (HL) process was used to recovery the Cu, whose leaching efficiency was approximately 100%, finally the resulting residue was subjected to the iodine-iodide leaching process for recovering the Au, Ag, and Pd. Experimental results indicated that SCWO pre-treatment temperature, time, and pressure had significant influence on the Au, Ag, and Pd leaching from (SCWO+HL)-treated waste PCBs. The optimal SCWO pre-treatment conditions were 420°C and 60min for Au and Pd, and 410°C and 30min for Ag. The optimum dissolution parameters for Au, Pd, and Ag in (SCWO+HL)-treated PCBs with iodine-iodide system were leaching time of 120min (90min for Ag), iodine/iodide mole ratio of 1:5 (1:6 for Ag), solid-to-liquid ratio (S/L) of 1:10g/mL (1:8g/mL for Ag), and pH of 9, respectively. It is believed that the process developed in this study is environment friendly for the recovery of Au, Ag, and Pd from waste PCBs of mobile phones by SCWO pre-treatment combined with iodine-iodide leaching process.

  17. Effects of single atom doping on the ultrafast electron dynamics of M1Au24(SR)18 (M = Pd, Pt) nanoclusters

    NASA Astrophysics Data System (ADS)

    Zhou, Meng; Qian, Huifeng; Sfeir, Matthew Y.; Nobusada, Katsuyuki; Jin, Rongchao

    2016-03-01

    Atomically precise, doped metal clusters are receiving wide research interest due to their synergistic properties dependent on the metal composition. To understand the electronic properties of doped clusters, it is highly desirable to probe the excited state behavior. Here, we report the ultrafast relaxation dynamics of doped M1@Au24(SR)18 (M = Pd, Pt; R = CH2CH2Ph) clusters using femtosecond visible and near infrared transient absorption spectroscopy. Three relaxation components are identified for both mono-doped clusters: (1) sub-picosecond relaxation within the M1Au12 core states; (2) core to shell relaxation in a few picoseconds; and (3) relaxation back to the ground state in more than one nanosecond. Despite similar relaxation pathways for the two doped nanoclusters, the coupling between the metal core and surface ligands is accelerated by over 30% in the case of the Pt dopant compared with the Pd dopant. Compared to Pd doping, the case of Pt doping leads to much more drastic changes in the steady state and transient absorption of the clusters, which indicates that the 5d orbitals of the Pt atom are more strongly mixed with Au 5d and 6s orbitals than the 4d orbitals of the Pd dopant. These results demonstrate that a single foreign atom can lead to entirely different excited state spectral features of the whole cluster compared to the parent Au25(SR)18 cluster. The detailed excited state dynamics of atomically precise Pd/Pt doped gold clusters help further understand their properties and benefit the development of energy-related applications.Atomically precise, doped metal clusters are receiving wide research interest due to their synergistic properties dependent on the metal composition. To understand the electronic properties of doped clusters, it is highly desirable to probe the excited state behavior. Here, we report the ultrafast relaxation dynamics of doped M1@Au24(SR)18 (M = Pd, Pt; R = CH2CH2Ph) clusters using femtosecond visible and near infrared

  18. Preparation of Pt Ag alloy nanoisland/graphene hybrid composites and its high stability and catalytic activity in methanol electro-oxidation

    PubMed Central

    2011-01-01

    In this article, PtAg alloy nanoislands/graphene hybrid composites were prepared based on the self-organization of Au@PtAg nanorods on graphene sheets. Graphite oxides (GO) were prepared and separated to individual sheets using Hummer's method. Graphene nano-sheets were prepared by chemical reduction with hydrazine. The prepared PtAg alloy nanomaterial and the hybrid composites with graphene were characterized by SEM, TEM, and zeta potential measurements. It is confirmed that the prepared Au@PtAg alloy nanorods/graphene hybrid composites own good catalytic function for methanol electro-oxidation by cyclic voltammograms measurements, and exhibited higher catalytic activity and more stability than pure Au@Pt nanorods and Au@AgPt alloy nanorods. In conclusion, the prepared PtAg alloy nanoislands/graphene hybrid composites own high stability and catalytic activity in methanol electro-oxidation, so that it is one kind of high-performance catalyst, and has great potential in applications such as methanol fuel cells in near future. PMID:21982417

  19. Preparation of Pt Ag alloy nanoisland/graphene hybrid composites and its high stability and catalytic activity in methanol electro-oxidation.

    PubMed

    Feng, Lili; Gao, Guo; Huang, Peng; Wang, Xiansong; Zhang, Chunlei; Zhang, Jiali; Guo, Shouwu; Cui, Daxiang

    2011-01-01

    In this article, PtAg alloy nanoislands/graphene hybrid composites were prepared based on the self-organization of Au@PtAg nanorods on graphene sheets. Graphite oxides (GO) were prepared and separated to individual sheets using Hummer's method. Graphene nano-sheets were prepared by chemical reduction with hydrazine. The prepared PtAg alloy nanomaterial and the hybrid composites with graphene were characterized by SEM, TEM, and zeta potential measurements. It is confirmed that the prepared Au@PtAg alloy nanorods/graphene hybrid composites own good catalytic function for methanol electro-oxidation by cyclic voltammograms measurements, and exhibited higher catalytic activity and more stability than pure Au@Pt nanorods and Au@AgPt alloy nanorods. In conclusion, the prepared PtAg alloy nanoislands/graphene hybrid composites own high stability and catalytic activity in methanol electro-oxidation, so that it is one kind of high-performance catalyst, and has great potential in applications such as methanol fuel cells in near future. PMID:21982417

  20. Preparation of Pt Ag alloy nanoisland/graphene hybrid composites and its high stability and catalytic activity in methanol electro-oxidation

    NASA Astrophysics Data System (ADS)

    Feng, Lili; Gao, Guo; Huang, Peng; Wang, Xiansong; Zhang, Chunlei; Zhang, Jiali; Guo, Shouwu; Cui, Daxiang

    2011-10-01

    In this article, PtAg alloy nanoislands/graphene hybrid composites were prepared based on the self-organization of Au@PtAg nanorods on graphene sheets. Graphite oxides (GO) were prepared and separated to individual sheets using Hummer's method. Graphene nano-sheets were prepared by chemical reduction with hydrazine. The prepared PtAg alloy nanomaterial and the hybrid composites with graphene were characterized by SEM, TEM, and zeta potential measurements. It is confirmed that the prepared Au@PtAg alloy nanorods/graphene hybrid composites own good catalytic function for methanol electro-oxidation by cyclic voltammograms measurements, and exhibited higher catalytic activity and more stability than pure Au@Pt nanorods and Au@AgPt alloy nanorods. In conclusion, the prepared PtAg alloy nanoislands/graphene hybrid composites own high stability and catalytic activity in methanol electro-oxidation, so that it is one kind of high-performance catalyst, and has great potential in applications such as methanol fuel cells in near future.

  1. Effects of single atom doping on the ultrafast electron dynamics of M1Au24(SR)18 (M = Pd, Pt) nanoclusters.

    PubMed

    Zhou, Meng; Qian, Huifeng; Sfeir, Matthew Y; Nobusada, Katsuyuki; Jin, Rongchao

    2016-04-01

    Atomically precise, doped metal clusters are receiving wide research interest due to their synergistic properties dependent on the metal composition. To understand the electronic properties of doped clusters, it is highly desirable to probe the excited state behavior. Here, we report the ultrafast relaxation dynamics of doped M1@Au24(SR)18 (M = Pd, Pt; R = CH2CH2Ph) clusters using femtosecond visible and near infrared transient absorption spectroscopy. Three relaxation components are identified for both mono-doped clusters: (1) sub-picosecond relaxation within the M1Au12 core states; (2) core to shell relaxation in a few picoseconds; and (3) relaxation back to the ground state in more than one nanosecond. Despite similar relaxation pathways for the two doped nanoclusters, the coupling between the metal core and surface ligands is accelerated by over 30% in the case of the Pt dopant compared with the Pd dopant. Compared to Pd doping, the case of Pt doping leads to much more drastic changes in the steady state and transient absorption of the clusters, which indicates that the 5d orbitals of the Pt atom are more strongly mixed with Au 5d and 6s orbitals than the 4d orbitals of the Pd dopant. These results demonstrate that a single foreign atom can lead to entirely different excited state spectral features of the whole cluster compared to the parent Au25(SR)18 cluster. The detailed excited state dynamics of atomically precise Pd/Pt doped gold clusters help further understand their properties and benefit the development of energy-related applications.

  2. Effects of single atom doping on the ultrafast electron dynamics of M1Au24(SR)18 (M = Pd, Pt) nanoclusters

    DOE PAGES

    Zhou, Meng; Qian, Huifeng; Sfeir, Matthew Y.; Nobusada, Katsuyuki; Jin, Rongchao

    2016-02-29

    Atomically precise, doped metal clusters are receiving wide research interest due to their synergistic properties dependent on the metal composition. To understand the electronic properties of doped clusters, it is highly desirable to probe the excited state behavior. Here, we report the ultrafast relaxation dynamics of doped M1@Au24(SR)18 (M = Pd, Pt; R = CH2CH2Ph) clusters using femtosecond visible and near infrared transient absorption spectroscopy. Three relaxation components are identified for both mono-doped clusters: (1) sub-picosecond relaxation within the M1Au12 core states; (2) core to shell relaxation in a few picoseconds; and (3) relaxation back to the ground state inmore » more than one nanosecond. Despite similar relaxation pathways for the two doped nanoclusters, the coupling between the metal core and surface ligands is accelerated by over 30% in the case of the Pt dopant compared with the Pd dopant. Compared to Pd doping, the case of Pt doping leads to much more drastic changes in the steady state and transient absorption of the clusters, which indicates that the 5d orbitals of the Pt atom are more strongly mixed with Au 5d and 6s orbitals than the 4d orbitals of the Pd dopant. These results demonstrate that a single foreign atom can lead to entirely different excited state spectral features of the whole cluster compared to the parent Au25(SR)18 cluster. As a result, the detailed excited state dynamics of atomically precise Pd/Pt doped gold clusters help further understand their properties and benefit the development of energy-related applications.« less

  3. Noble metal (Pd, Ru, Rh, Pt, Au, Ag) doped graphene hybrids for electrocatalysis

    NASA Astrophysics Data System (ADS)

    Giovanni, Marcella; Poh, Hwee Ling; Ambrosi, Adriano; Zhao, Guanjia; Sofer, Zdeněk; Šaněk, Filip; Khezri, Bahareh; Webster, Richard D.; Pumera, Martin

    2012-07-01

    Metal decorated graphene materials are highly important for catalysis. In this work, noble metal doped-graphene hybrids were prepared by a simple and scalable method. The thermal reductions of metal doped-graphite oxide precursors were carried out in nitrogen and hydrogen atmospheres and the effects of these atmospheres as well as the metal components on the characteristics and catalytic capabilities of the hybrid materials were studied. The hybrids exfoliated in nitrogen atmosphere contained a higher amount of oxygen-containing groups and lower density of defects on their surfaces than hybrids exfoliated in hydrogen atmosphere. The metals significantly affected the electrochemical behavior and catalysis of compounds that are important in energy production and storage and in electrochemical sensing. Research in the field of energy storage and production, electrochemical sensing and biosensing as well as biomedical devices can take advantage of the properties and catalytic capabilities of the metal doped graphene hybrids.

  4. Band bending at Al, In, Ag, and Pt interfaces with CdTe and ZnTe (110)

    SciTech Connect

    Wahi, A.K.; Miyano, K.; Carey, G.P.; Chiang, T.T.; Lindau, I.; Spicer, W.E. )

    1990-05-01

    Band bending behavior and interfacial chemistry for Al, In, Ag, and Pt overlayers on vacuum-cleaved {ital p}-CdTe and {ital p}-ZnTe (110) have been studied using ultraviolet photoelectron spectroscopy (UPS) and x-ray photoelectron spectroscopy (XPS). These metals provide a range of metal--substrate reactivities: Al reacts strongly with Te, Ag moderately, and In minimally, with no evidence seen for In reaction on ZnTe. Pt exhibits strong alloying behavior with both Cd and Zn. All four metals are found to yield Schottky barriers on CdTe and ZnTe, with a narrow range of final Fermi level positions, {ital E}{sub {ital fi}}={ital E}{sub {ital f}}{minus}{ital E}{sub VBM}, observed on CdTe, from 0.9 to 1.05{plus minus}0.1 eV, and on ZnTe from 0.65 to 1.0{plus minus}0.1 eV. The prediction of the MIGS model that a difference in barrier height exists for two semiconductors dependent upon their band lineup (valence band offset) is examined and found to agree with experiment for Ag, Pt, and Al, but not for In. For the highly reactive Al, no evidence for the overlayer metallicity required for metal-induced gap states (MIGS) to operate is seen on CdTe or ZnTe until after band bending has stabilized. Reaction and intermixing for Al, Ag, and Pt overlayers on CdTe and ZnTe indicate these interfaces are not ideal. The possible role of defects at these four metal/CdTe and metal/ZnTe interfaces is considered, and provides a consistent explanation for the final Fermi level positions observed.

  5. Facile Synthesis of Ag Nanorods with No Plasmon Resonance Peak in the Visible Region by Using Pd Decahedra of 16 nm in Size as Seeds.

    PubMed

    Luo, Ming; Huang, Hongwen; Choi, Sang-Il; Zhang, Chao; da Silva, Robson Rosa; Peng, Hsin-Chieh; Li, Zhi-Yuan; Liu, Jingyue; He, Zhike; Xia, Younan

    2015-10-27

    This article describes a seed-mediated approach to the synthesis of Ag nanorods with thin diameters and tunable aspect ratios. The success of this method is built upon our recent progress in the synthesis of Pd decahedra as uniform samples, together with controllable sizes. When used as a seed, the Pd decahedron could direct the deposition of Ag atoms along the 5-fold axis to generate a nanorod, with its diameter being determined by the lateral dimension of the seed. We were able to generate Ag nanorods with uniform diameters down to 20 nm. Under the conditions we used for growth, symmetry breaking occurred as the Ag atoms were only deposited along one side of the Pd decahedral seed to generate a Ag nanorod with the Pd seed being positioned at one of its two ends. We also systematically investigated the localized surface plasmon resonance (LSPR) properties of the Ag nanorods. With the transverse mode kept below 400 nm, the longitudinal mode could be readily tuned from the visible to the near-infrared region by varying the aspect ratio. As an important demonstration, we obtained Ag nanorods with no LSPR peak in the visible spectrum (400-800 nm), which are attractive for applications related to the fabrication of touchscreen displays, solar films, and energy-saving smart windows. PMID:26372854

  6. Localized Pd Overgrowth on Cubic Pt Nanocrystals for Enhanced Electrocatalytic Oxidation of Formic Acid

    SciTech Connect

    Lee, Hyunjoo; Habas, Susan; Somorjai, Gabor; Yang, Peidong

    2007-12-14

    Single crystalline surface such as (100), (111), (110) has been studied as an idealized platform for electrocatalytic reactions since the atomic arrangement affects a catalytic property. The secondary metal deposition on these surfaces also alters the catalytic property often showing improvement such as poisoning decrease. On the other hand, electrocatalysts used for practical purpose usually have a size on the order of nanometers. Therefore, linking the knowledge from single crystalline studies to nanoparticle catalysts is of enormous importance. Recently, the Pt nanoparticles which surface structure was preferentially oriented was synthesized and used as electrocatalysts. Here, we demonstrate a rational design of a binary metallic nanocatalyst based on the single crystalline study.

  7. Temperature, pressure, and size dependence of Pd-H interaction in size selected Pd-Ag and Pd-Cu alloy nanoparticles: In-situ X-ray diffraction studies

    SciTech Connect

    Sengar, Saurabh K.; Mehta, B. R.; Kulriya, P. K.

    2014-03-21

    In this study, in-situ X-ray diffraction has been carried out to investigate the effect of temperature and pressure on hydrogen induced lattice parameter variation in size selected Pd-Ag and Pd-Cu alloy nanoparticles. The nanoparticles of three different mobility equivalent diameters (20, 40, and 60 nm) having a narrow size distribution were prepared by gas phase synthesis method. In the present range of temperature (350 K to 250 K) and pressure (10{sup −4} to 100 millibars), no α (H/Pd ≤ 0.03) ↔ β (H/Pd ≥ 0.54) phase transition is observed. At temperature higher than 300 °C or pressure lower than 25 millibars, there is a large difference in the rate at which lattice constant varies as a function of pressure and temperature. Further, the lattice variation with temperature and pressure is also observed to depend upon the nanoparticle size. At lower temperature or higher pressure, size of the nanoparticle seems to be relatively less important. These results are explained on the basis of the relative dominance of physical absorption and diffusion of H in Pd alloy nanoparticles at different temperature and pressure. In the present study, absence of α ↔ β phase transition points towards the advantage of using Pd-alloy nanoparticles in applications requiring long term and repeated hydrogen cycling.

  8. A facile approach to prepare silicon-based Pt-Ag tubular dendritic nano-forests (tDNFs) for solar-light-enhanced methanol oxidation reaction.

    PubMed

    Lin, Chun-Ting; Shiao, Ming-Hua; Chang, Mao-Nan; Chu, Nancy; Chen, Yu-Wei; Peng, Yu-Hsuan; Liao, Bo-Huei; Huang, Hung Ji; Hsiao, Chien-Nan; Tseng, Fan-Gang

    2015-01-01

    In this paper, a facile two-step Galvanic replacement reaction (GRR) is proposed to prepare Pt-Ag tubular dendritic nano-forests (tDNFs) in ambient condition for enhancing methanol oxidation reaction (MOR) under solar illumination. In the first GRR, a homogeneous layer of silver dendritic nano-forests (DNFs) with 10 μm in thickness was grown on Si wafer in 5 min in silver nitride (AgNO3) and buffer oxide etchant (BOE) solution. In the second GRR, we utilized chloroplatinic acid (H2PtCl6) as the precursor for platinum (Pt) deposition to further transform the prepared Ag DNFs into Pt-Ag tDNFs. The catalytic performance and solar response of the Pt-Ag tDNFs toward methanol electro-oxidation are also studied by cyclic voltammetry (CV) and chronoamperometry (CA). The methanol oxidation current was boosted by 6.4% under solar illumination on the Pt-Ag tDNFs due to the induced localized surface plasmon resonance (LSPR) on the dendritic structure. Current results provide a cost-effective and facile approach to prepare solar-driven metallic electrodes potentially applicable to photo-electro-chemical fuel cells.

  9. A facile approach to prepare silicon-based Pt-Ag tubular dendritic nano-forests (tDNFs) for solar-light-enhanced methanol oxidation reaction

    NASA Astrophysics Data System (ADS)

    Lin, Chun-Ting; Shiao, Ming-Hua; Chang, Mao-Nan; Chu, Nancy; Chen, Yu-Wei; Peng, Yu-Hsuan; Liao, Bo-Huei; Huang, Hung Ji; Hsiao, Chien-Nan; Tseng, Fan-Gang

    2015-02-01

    In this paper, a facile two-step Galvanic replacement reaction (GRR) is proposed to prepare Pt-Ag tubular dendritic nano-forests (tDNFs) in ambient condition for enhancing methanol oxidation reaction (MOR) under solar illumination. In the first GRR, a homogeneous layer of silver dendritic nano-forests (DNFs) with 10 μm in thickness was grown on Si wafer in 5 min in silver nitride (AgNO3) and buffer oxide etchant (BOE) solution. In the second GRR, we utilized chloroplatinic acid (H2PtCl6) as the precursor for platinum (Pt) deposition to further transform the prepared Ag DNFs into Pt-Ag tDNFs. The catalytic performance and solar response of the Pt-Ag tDNFs toward methanol electro-oxidation are also studied by cyclic voltammetry (CV) and chronoamperometry (CA). The methanol oxidation current was boosted by 6.4% under solar illumination on the Pt-Ag tDNFs due to the induced localized surface plasmon resonance (LSPR) on the dendritic structure. Current results provide a cost-effective and facile approach to prepare solar-driven metallic electrodes potentially applicable to photo-electro-chemical fuel cells.

  10. Ultrasonic-electrodeposition of PtPd alloy nanoparticles on ionic liquid-functionalized graphene paper: towards a flexible and versatile nanohybrid electrode

    NASA Astrophysics Data System (ADS)

    Sun, Yimin; Zheng, Huaming; Wang, Chenxu; Yang, Mengmeng; Zhou, Aijun; Duan, Hongwei

    2016-01-01

    Here we fabricate a new type of flexible and versatile nanohybrid paper electrode by ultrasonic-electrodeposition of PtPd alloy nanoparticles on freestanding ionic liquid (IL)-functionalized graphene paper, and explore its multifunctional applications in electrochemical catalysis and sensing systems. The graphene-based paper materials demonstrate intrinsic flexibility, exceptional mechanical strength and high electrical conductivity, and therefore can serve as an ideal freestanding flexible electrode for electrochemical devices. Furthermore, the functionalization of graphene with IL (i.e., 1-butyl-3-methylimidazolium tetrafluoroborate) not only increases the electroactive surface area of a graphene-based nanohybrid paper electrode, but also improves the adhesion and dispersion of metal nanoparticles on the paper surface. These unique attributes, combined with the merits of an ultrasonic-electrodeposition method, lead to the formation of PtPd alloy nanoparticles on IL-graphene paper with high loading, uniform distribution, controlled morphology and favourable size. Consequently, the resultant nanohybrid paper electrode exhibits remarkable catalytic activity as well as excellent cycle stability and improved anti-poisoning ability towards electrooxidation of fuel molecules such as methanol and ethanol. Furthermore, for nonenzymatic electrochemical sensing of some specific biomarkers such as glucose and reactive oxygen species, the nanohybrid paper electrode shows high selectivity, sensitivity and biocompatibility in these bio-catalytic processes, and can be used for real-time tracking hydrogen peroxide secretion by living human cells. All these features demonstrate its promising application as a versatile nanohybrid electrode material in flexible and lightweight electrochemical energy conversion and biosensing systems such as bendable on-chip power sources, wearable/implantable detectors and in vivo micro-biosensors.Here we fabricate a new type of flexible and

  11. Solid-solution precursor to melting in onion-ring Pd-Pt nanoclusters: a case of second-order-like phase change?

    PubMed

    Calvo, Florent

    2008-01-01

    The thermodynamical behaviour of icosahedral, multilayer Pd-Pt clusters is addressed using a combination of simulation tools, mainly parallel tempering Monte Carlo. A preferential swapping trial move is introduced to increase the chance of successfully exchanging Pd and Pt atoms in the cluster. The 2-, 3- and 4-shell, Pd-rich clusters have been studied. We generally find that the clusters melt at a temperature significantly below the bulk melting point at the same corresponding composition. More interestingly, for the smaller clusters melting is initiated by a solid-solution intermediate phase in which the overall icosahedral frame remains, but the Pd and Pt atoms can swap sites. The transition to this solid-solution phase is seen to have a continuous, second-order like character, which is interpreted from the similarity between the present system with the ferromagnetic Ising model on the 3D cubic lattice. As the cluster grows, the onion-ring structure becomes thermodynamically unstable. The 4-layer cluster already exhibits a solid-solution in its core at temperatures as low as 100 K. The bulk behaviour is thus recovered at very small scales. PMID:18447010

  12. Structural and magnetic phase transitions in CeCu6-xTx (T = Ag,Pd)

    DOE PAGES

    Poudel, Lekhanath N.; De la cruz, Clarina; Payzant, E. Andrew; Koehler, Michael R.; May, Andrew F.; Garlea, Vasile O.; Taylor, Alice E.; Parker, David S.; Cao, Huibo B.; McGuire, Michael A.; et al

    2015-12-15

    The structural and the magnetic properties of CeCu6-xAgx (0 ≤ x ≤ 0.85) and CeCu6-xPdx (0 ≤ x ≤ 0.4) have been studied using neutron diffraction, resonant ultrasound spectroscopy (RUS), x-ray diffraction measurements, and first principles calculations. The structural and magnetic phase diagrams of CeCu6-xAgx and CeCu6-xPdx as a function of Ag/Pd composition are reported. The end member, CeCu6, undergoes a structural phase transition from an orthorhombic (Pnma) to a monoclinic (P21/c) phase at 240 K. In CeCu6-xAgx, the structural phase transition temperature (Ts) decreases linearly with Ag concentration and extrapolates to zero at xS ≈ 0.1. The structural transitionmore » in CeCu6-xPdx remains unperturbed with Pd substitution within the range of our study. The lattice constant b slightly decreases with Ag/Pd doping, whereas a and c increase with an overall increase in the unit cell volume. Both systems, CeCu6-xAgx and CeCu6-xPdx, exhibit a magnetic quantum critical point (QCP), at x ≈ 0.2 and x ≈ 0.05, respectively. Near the QCP, long range antiferromagnetic ordering takes place at an incommensurate wave vector (δ1 0 δ2), where δ1 ~ 0.62, δ2 ~ 0.25, x = 0.125 for CeCu6-xPdx and δ1 ~ 0.64, δ2 ~ 0.3, x = 0.3 for CeCu6-xAgx. As a result, the magnetic structure consists of an amplitude modulation of the Ce moments which are aligned along the c axis of the orthorhombic unit cell.« less

  13. Multilevel unipolar resistive switching with negative differential resistance effect in Ag/SiO2/Pt device

    NASA Astrophysics Data System (ADS)

    Sun, Haitao; Liu, Qi; Long, Shibing; Lv, Hangbing; Banerjee, Writam; Liu, Ming

    2014-10-01

    In this paper, we report a multilevel unipolar resistive switching (RS) phenomenon with negative differential resistance (NDR) effect in Ag/SiO2/Pt sandwich structure. After positive electroforming process with low compliance current (ICC, 10 nA), a conductive filament consisting of isolated Ag nanocrystals is formed inside SiO2 layer. Then, an abnormal unipolar resistive switching (RESET voltage is larger than SET voltage) with NDR effect is obtained under negative voltage sweep without ICC. Based on I-V fitting and temperature dependence of the resistance results, we suggest that the abnormal unipolar RS is dominated by the charging/discharging of carriers in Ag nanocrystals. In addition, we demonstrate that the unipolar RS exhibits good performances, including large Roff/Ron ratio, high uniformity, long retention time, and multilevel storage potential.

  14. Growth of L10-ordered crystal in FePt and FePd thin films on MgO(001) substrate

    NASA Astrophysics Data System (ADS)

    Futamoto, Masaaki; Nakamura, Masahiro; Ohtake, Mitsuru; Inaba, Nobuyuki; Shimotsu, Teruho

    2016-08-01

    Formation of L10-oredered structure from disordered A1 phase has been investigated for FePt and FePd films on MgO(001) substrates employing a two-step method consisting of low temperature deposition at 200 °C followed by high-temperature annealing at 600 °C. L10-(001) variant crystal with the c-axis perpendicular to the substrate grows preferentially in FePd films whereas L10-(100), (010) variants tend to be mixed with the L10-(001) variant in FePt films. The structure analysis by X-ray diffraction indicates that a difference in A1 lattice strain is the influential factor that determines the resulting L10-variant structure in ordered thin films. Misfit dislocations and anti-phase boundaries are observed in high-resolution transmission electron micrographs of 10 nm-thick Fe(Pt, Pd) film consisting of L10-(001) variants which are formed through atomic diffusion at 600 °C in a laterally strained FePt/PeFd epitaxial thin film. Based on the experimental results, a nucleation and growth model for explaining L10-variant formation is proposed, which suggests a possibility in tailoring the L10 variant structure in ordered magnetic thin films by controlling the alloy composition, the layer structure, and the substrate material.

  15. Investigation of nanostructured Pd-Ag/n-ZnO thin film based Schottky junction for methane sensing

    NASA Astrophysics Data System (ADS)

    Roy, S.; Das, S.; Sarkar, C. K.

    2016-07-01

    Undoped nanocrystalline n-type ZnO thin film was deposited by chemical deposition technique on a thermally oxidized p-Si (~5 Ω cm resistivity and <100> orientation) substrate. Formation of stable zinc oxide thin film was confirmed by two-dimensional X-Ray Diffraction (XRD) and EDX analysis. The average crystallite size of the ZnO sample was evaluated as ~50 nm. The surface was characterized by Field Emission Scanning Electron Microscopy (FESEM) and Atomic Force Microscopy (AFM) that confirm the formation of nanocrystalline (grain size ~50 nm) ZnO thin film with surface roughness of ~100 nm. Good conversion of precursor into ZnO thin film in the chemical deposition method was evident by Fourier Transform Infrared Spectroscopy (FTIR). A small peak at 479 cm-1was observed in the FTIR spectrum confirming the formation of quartzite structure of the ZnO. The band gap (~3.44 eV) of the material was calculated from the optical absorption spectroscopy. To prepare Pd-Ag/n-ZnO Schottky junction, Pd-Ag contacts were taken by electron beam evaporation method. I-V characteristics of the junction were studied at different temperatures in inert and reducing ambient (N2 and N2 + CH4) with turn on voltage of around 0.2 V. The parameters like ideality factor ( η), saturation current ( I 0), series resistance ( Rs), and barrier height ( Φ BO) of the junction were calculated in the temperature range 50-200 °C in N2 as well as in 1 % CH4 + N2 ambient. It was observed that the ideality factor decreases in the temperature range 50-200 °C ( η = 12.34 at 50 °C and η = 1.52 at 200 °C) in N2 ambient and η = 1.18 in N2 +CH4 ambient at 200 °C. Schottky Barrier Height ( Φ BO) of the Pd-Ag/n-ZnO junction was found to increase with temperature. A close observation of Pd-Ag/n-ZnO junction in the presence of methane was performed to appreciate its application as methane sensor. The sensing mechanism was illustrated by a simplified energy band diagram.

  16. Indole-7-carbaldehyde thiosemicarbazone as a flexidentate ligand toward ZnII, CdII, PdII and PtII ions: cytotoxic and apoptosis-inducing properties of the PtII complex.

    PubMed

    Ibrahim, Abeer A; Khaledi, Hamid; Hassandarvish, Pouya; Mohd Ali, Hapipah; Karimian, Hamed

    2014-03-14

    A new thiosemicarbazone (LH2) derived from indole-7-carbaldehyde was synthesized and reacted with Zn(II), Cd(II), Pd(II) and Pt(II) salts. The reactions with zinc and cadmium salts in 2 : 1 (ligand-metal) molar ratio afforded complexes of the type MX2(LH2)2, (X = Cl, Br or OAc), in which the thiosemicarbazone acts as a neutral S-monodentate ligand. In the presence of potassium hydroxide, the reaction of LH2 with ZnBr2 resulted in deprotonation of the thiosemicarbazone at the hydrazine and indole nitrogens to form Zn(L)(CH3OH). The reaction of LH2 with K2PdCl4 in the presence of triethylamine, afforded Pd(L)(LH2) which contains two thiosemicarbazone ligands: one being dianionic N,N,S-tridentate while the other one is neutral S-monodentate. When PdCl2(PPh3)2 was used as the Pd(II) ion source, Pd(L)(PPh3) was obtained. In a similar manner, the analogous platinum complex, Pt(L)(PPh3), was synthesized. The thiosemicarbazone in the latter two complexes behaves in a dianionic N,N,S-tridentate fashion. The platinum complex was found to have significant cytotoxicity toward four cancer cells lines, namely MDA-MB-231, MCF-7, HT-29, and HCT-116 but not toward the normal liver WRL-68 cell line. The apoptosis-inducing properties of the Pt complex was explored through fluorescence microscopy visualization, DNA fragmentation analysis and propidium iodide flow cytometry.

  17. Low-energy vibrations of the group 10 metal monocarbonyl MCO (M = Ni, Pd, and Pt): rotational spectroscopy and force field analysis.

    PubMed

    Okabayashi, Toshiaki; Yamamoto, Takuya; Okabayashi, Emi Y; Tanimoto, Mitsutoshi

    2011-03-17

    The rotational spectra of NiCO and PdCO in the ground and ν(2) excited vibrational states were observed by employing a source-modulated microwave spectrometer. The NiCO and PdCO molecules were generated in a free space cell by the sputtering reaction of nickel and palladium sheets, respectively, lining the inner surface of a stainless steel cathode with a dc glow plasma of CO and Ar. The molecular constants of NiCO and PdCO were determined by least-squares analysis. By force field analysis for the molecular constants of not only NiCO and PdCO but also of PtCO as previously reported, the harmonic force constants were determined for these three group 10 metal monocarbonyls. The vibrational wavenumbers derived for the lower M-C stretching vibrations were in good agreement with those obtained from the IR spectra in noble gas matrices and those predicted by several quantum chemical calculations published in the past. The bending vibrational wavenumbers derived by the force field analysis were also consistent with most quantum chemical calculations previously reported, but showed systematic discrepancies from the matrix IR values by about 40 cm(-1), even after reassignment (ν(2) band → 2ν(2) band) of the matrix IR spectra of PdCO and PtCO. PMID:21332227

  18. Highly Unsaturated Platinum and Palladium Carbenes PtC3 and PdC3 Isolated and Characterized in the Gas Phase

    PubMed Central

    Bittner, Dror M.; Zaleski, Daniel P.; Tew, David P.

    2016-01-01

    Abstract Carbenes of platinum and palladium, PtC3 and PdC3, were generated in the gas phase through laser vaporization of a metal target in the presence of a low concentration of a hydrocarbon precursor undergoing supersonic expansion. Rotational spectroscopy and ab initio calculations confirm that both molecules are linear. The geometry of PtC3 was accurately determined by fitting to the experimental moments of inertia of twenty‐six isotopologues. The results are consistent with the proposal of an autogenic isolobal relationship between O, Au+, and Pt atoms. PMID:27478275

  19. Highly Unsaturated Platinum and Palladium Carbenes PtC3 and PdC3 Isolated and Characterized in the Gas Phase

    PubMed Central

    Bittner, Dror M.; Zaleski, Daniel P.; Tew, David P.

    2016-01-01

    Abstract Carbenes of platinum and palladium, PtC3 and PdC3, were generated in the gas phase through laser vaporization of a metal target in the presence of a low concentration of a hydrocarbon precursor undergoing supersonic expansion. Rotational spectroscopy and ab initio calculations confirm that both molecules are linear. The geometry of PtC3 was accurately determined by fitting to the experimental moments of inertia of twenty‐six isotopologues. The results are consistent with the proposal of an autogenic isolobal relationship between O, Au+, and Pt atoms. PMID:26879473

  20. Highly Unsaturated Platinum and Palladium Carbenes PtC3 and PdC3 Isolated and Characterized in the Gas Phase

    DOE PAGES

    Bittner, Dror M.; Zaleski, Daniel P.; Tew, David P.; Walker, Nicholas R.; Legon, Anthony C.

    2016-02-16

    Carbenes of platinum and palladium, PtC3 and PdC3 , were generated in the gas phase through laser vaporization of a metal target in the presence of a low concentration of a hydrocarbon precursor undergoing supersonic expansion. Rotational spectroscopy and abinitio calculations confirm that both molecules are linear. The geometry of PtC3 was accurately determined by fitting to the experimental moments of inertia of twenty-six isotopologues. In conclusion, the results are consistent with the proposal of an autogenic isolobal relationship between O, Au+ , and Ptatoms.

  1. New sterically-hindered o-quinones annelated with metal-dithiolates: regiospecificity in oxidative addition reactions of a bifacial ligand to the Pd and Pt complexes.

    PubMed

    Martyanov, K A; Cherkasov, V K; Abakumov, G A; Samsonov, M A; Khrizanforova, V V; Budnikova, Y H; Kuropatov, V A

    2016-04-25

    An unusual reactivity of sterically hindered o-quinones with an annelated dithiete ring towards coordination at a dithiolene site has been discovered. New Pd and Pt dithiolate complexes have been synthesized. The reaction proceeds regioselectively, and the quinone site of the parent ligand is not affected even while using an excess of the metal complex. Both Pt and Pd complexes display a square planar surrounding for the metal ion and have very similar NMR, IR and UV/Vis spectra. Surprisingly, being coordinated at the dithiolene site to the metal, the ligand exhibits activity like an o-quinone, it could be reduced with different metals resulting in the corresponding o-semiquinonates which were confirmed by EPR spectroscopy. It was shown that an unpaired electron exhibits HFC with the phosphorus nuclei of phosphine ligands coordinated to the metal ions at the dithiolene site of the molecule.

  2. Quadratic scaling of intrinsic Gilbert damping with spin-orbital coupling in L10 FePdPt films: experiments and Ab initio calculations.

    PubMed

    He, P; Ma, X; Zhang, J W; Zhao, H B; Lüpke, G; Shi, Z; Zhou, S M

    2013-02-15

    The dependence of the intrinsic Gilbert damping parameter α(0) on the spin-orbital coupling strength ξ is investigated in L1(0) ordered FePd(1-x) Pt(x) films by time-resolved magneto-optical Kerr effect measurements and spin-dependent ab initio calculations. Continuous tuning of α(0) over more than one order of magnitude is realized by changing the Pt/Pd concentration ratio showing that α(0) is proportional to ξ(2) as changes of other leading parameters are found to be negligible. The perpendicular magnetic anisotropy is shown to have a similar variation trend with x. The present results may facilitate the design and fabrication of new magnetic alloys with large perpendicular magnetic anisotropy and tailored damping properties. PMID:25166400

  3. Quadratic scaling of intrinsic Gilbert damping with spin-orbital coupling in L10 FePdPt films: experiments and Ab initio calculations.

    PubMed

    He, P; Ma, X; Zhang, J W; Zhao, H B; Lüpke, G; Shi, Z; Zhou, S M

    2013-02-15

    The dependence of the intrinsic Gilbert damping parameter α(0) on the spin-orbital coupling strength ξ is investigated in L1(0) ordered FePd(1-x) Pt(x) films by time-resolved magneto-optical Kerr effect measurements and spin-dependent ab initio calculations. Continuous tuning of α(0) over more than one order of magnitude is realized by changing the Pt/Pd concentration ratio showing that α(0) is proportional to ξ(2) as changes of other leading parameters are found to be negligible. The perpendicular magnetic anisotropy is shown to have a similar variation trend with x. The present results may facilitate the design and fabrication of new magnetic alloys with large perpendicular magnetic anisotropy and tailored damping properties.

  4. Magneto-optical Kerr effect in L1{sub 0} FePdPt ternary alloys: Experiments and first-principles calculations

    SciTech Connect

    Ma, L.; Shi, Z.; Zhou, S. M. E-mail: shiming@tongji.edu.cn; Hu, J.; Costa, M.; Wu, R. Q. E-mail: shiming@tongji.edu.cn; Li, J.; Xu, X. G.; Jiang, Y.; Guo, G. Y.

    2014-05-14

    We have studied the magneto-optical Kerr effect (MOKE) of L1{sub 0} Fe{sub 0.5}(Pd{sub 1−x}Pt{sub x}){sub 0.5} alloy films with both experiments and first-principles calculations. In the visible region, negative Kerr rotation and ellipticity peaks are, respectively, observed in the regions of 1.5–2.0 eV and 1.7–2.6 eV. These peaks are shifted towards higher energies, and their magnitudes are enhanced for larger x. The MOKE evolution is mainly ascribed to the anomalous Hall conductivity contributed by the spin-down d{sub ↓,x{sup 2}−y{sup 2}} bands from Pd and Pt. We established a close correlation among the MOKE spectra, the spin orbit coupling strength, and the band feature for this prototypical system.

  5. Schottky Barrier Height and S-Parameter of Ti, Cu, Pd, and Pt Contacts on p-Type GaN

    NASA Astrophysics Data System (ADS)

    Park, Youngjun; Ahn, Kwang-Soon; Kim, Hyunsoo

    2012-09-01

    The Schottky barrier height (SBH) of Ti, Cu, Pd, and Pt contacts on p-GaN and their work-function dependence, the S-parameter, were investigated. According to thermionic emission model, the SBH was obtained to be 0.85, 0.70, 0.61, and 0.59 eV for Ti, Cu, Pd, and Pt, respectively, yielding an S-parameter of 0.19. However, the ideality factor was as large as ˜4 and anomalous temperature dependences of the SBH and ideality factors were observed, indicating that the pure thermionic emission is not appropriate to explain carrier transport. Based on the barrier inhomogeneity and thermionic field emission models, S-parameters of 0.27 and 0.38 could be reasonably obtained.

  6. Adsorption of thiophene on Pt, Pd, Au, and Rh(100) surfaces with the role of the van der Waals' interaction

    NASA Astrophysics Data System (ADS)

    Malone, Walter; Matos, Jeronimo; Kara, Abdelkader

    We explore the adsorption of thiophene (C4H4S) on Pt(100), Au(100), Pd(100), and Rh(100) surfaces using density functional theory with and without self-consistent van der Waals interactions (vdWs). The six functionals we use are PBE, optB86b-vdW, optB88-vdW, optPBE-vdW, revPBE-vdW, and rPW86-vdW2. We examine a variety of adsorption sites with the molecule's plane both parallel and perpendicular to the surface. In the case of parallel adsorption the highest binding energy occurs when the molecule is centered over a hollow site with the sulfur atom near an atop site. The highest adsorption energy for perpendicular configurations is achieved when the sulfur atom lies over a bridge site and the carbon atoms near hollow sites. We find that for thiophene on the coinage metals the vdW functionals predict higher adsorption energies than those predicted by the PBE functional. On the other hand, for thiophene on the reactive transition metal substrates only optB86b-vdW, optB88-vdW, and optPBE-vdW result in an enhancement in the adsorption energy over the PBE value. We also explore some of the electronic properties of the system including charge transfer and change in the work function. Our results indicate that adsorption characteristics depends heavily on the functional used and geometry.

  7. Lithography-Free Fabrication of Large Area Subwavelength Antireflection Structures Using Thermally Dewetted Pt/Pd Alloy Etch Mask

    PubMed Central

    2009-01-01

    We have demonstrated lithography-free, simple, and large area fabrication method for subwavelength antireflection structures (SAS) to achieve low reflectance of silicon (Si) surface. Thin film of Pt/Pd alloy on a Si substrate is melted and agglomerated into hemispheric nanodots by thermal dewetting process, and the array of the nanodots is used as etch mask for reactive ion etching (RIE) to form SAS on the Si surface. Two critical parameters, the temperature of thermal dewetting processes and the duration of RIE, have been experimentally studied to achieve very low reflectance from SAS. All the SAS have well-tapered shapes that the refractive index may be changed continuously and monotonously in the direction of incident light. In the wavelength range from 350 to 1800 nm, the measured reflectance of the fabricated SAS averages out to 5%. Especially in the wavelength range from 550 to 650 nm, which falls within visible light, the measured reflectance is under 0.01%. PMID:20596495

  8. Size-dependent effects in supported highly dispersed Fe2O3 catalysts, doped with Pt and Pd

    NASA Astrophysics Data System (ADS)

    Cherkezova-Zheleva, Zara; Shopska, Maya; Mitov, Ivan; Kadinov, Georgi

    2010-06-01

    Series of Fe and Fe-Me (Me = Pt or Pd) catalyst supported on γ-Al2O3, TiO2 (anatase) or diatomite were prepared by the incipient wetness impregnation method. The metal loading was 8 wt.% Fe and 0.7 wt.% noble metal. The preparation and pretreatment conditions of all studied samples were kept to be the same. X-ray diffraction, Moessbauer spectroscopy, X-ray photoelectron spectroscopy and temperature-programmed reduction are used for characterization of the supports and the samples at different steps during their treatment and catalytic tests. The catalytic activity of the samples was tested in the reaction of total benzene oxidation. The physicochemical and catalytic properties of the obtained materials are compared with respect of the different chemical composition, dispersion of used carriers and of the supported phases. Samples with the same composition prepared by mechanical mixing are studied as catalysts for comparison and for clearing up the presence of size-dependent effect, also.

  9. Development of Pd-Ag Compostie Membrane for Separation of Hydrogen at Elevated Temperature

    SciTech Connect

    Shamsuddin Ilias

    2009-02-28

    Pd-based membrane reactor offers the possibility of combining reaction and separation in a single operation at high temperatures to overcome the equilibrium limitations experienced in conventional reactor configurations. In this project to develop a defect-free and hermally-stable Pd-film on microporous stainless steel (MPSS) support for H2-separation and membrane reactor applications, the electroless plating process was revisited with an aim to improve the membrane morphology. Specifically, this study includes; (a) an improvement f activation step using Pulse Laser Deposition (PLD), (b) development of a novel surfactant induced electroless plating (SIEP) for depositing robust Pd-film on microporous support, and (c) application of Pd-membrane as membrane reactor in steam methanol reforming (SMR) reactions.

  10. Structural and magnetic phase transitions in CeCu6-xTx (T = Ag,Pd)

    SciTech Connect

    Poudel, Lekhanath N.; De la cruz, Clarina; Payzant, E. Andrew; Koehler, Michael R.; May, Andrew F.; Garlea, Vasile O.; Taylor, Alice E.; Parker, David S.; Cao, Huibo B.; McGuire, Michael A.; Tian, Wei; Matsuda, Masaaki; Jeen, Hyoung Jeen; Lee, Ho Nyung; Hong, Tao; Calder, Stuart A.; Lumsden, Mark D.; Zhou, Haidong; Keppens, Veerle; Mandrus, D.; Christianson, Andrew D.

    2015-12-15

    The structural and the magnetic properties of CeCu6-xAgx (0 ≤ x ≤ 0.85) and CeCu6-xPdx (0 ≤ x ≤ 0.4) have been studied using neutron diffraction, resonant ultrasound spectroscopy (RUS), x-ray diffraction measurements, and first principles calculations. The structural and magnetic phase diagrams of CeCu6-xAgx and CeCu6-xPdx as a function of Ag/Pd composition are reported. The end member, CeCu6, undergoes a structural phase transition from an orthorhombic (Pnma) to a monoclinic (P21/c) phase at 240 K. In CeCu6-xAgx, the structural phase transition temperature (Ts) decreases linearly with Ag concentration and extrapolates to zero at xS ≈ 0.1. The structural transition in CeCu6-xPdx remains unperturbed with Pd substitution within the range of our study. The lattice constant b slightly decreases with Ag/Pd doping, whereas a and c increase with an overall increase in the unit cell volume. Both systems, CeCu6-xAgx and CeCu6-xPdx, exhibit a magnetic quantum critical point (QCP), at x ≈ 0.2 and x ≈ 0.05, respectively. Near the QCP, long range antiferromagnetic ordering takes place at an incommensurate wave vector (δ1 0 δ2), where δ1 ~ 0.62, δ2 ~ 0.25, x = 0.125 for CeCu6-xPdx and δ1 ~ 0.64, δ2 ~ 0.3, x = 0.3 for CeCu6-xAgx. As a result, the magnetic structure consists of an amplitude modulation of the Ce moments which are aligned along the c axis of the orthorhombic unit cell.

  11. Modification of energy band alignment and electric properties of Pt/Ba0.6Sr0.4TiO3/Pt thin-film ferroelectric varactors by Ag impurities at interfaces

    NASA Astrophysics Data System (ADS)

    Hirsch, S.; Komissinskiy, P.; Flege, S.; Li, S.; Rachut, K.; Klein, A.; Alff, L.

    2014-06-01

    We report on the effects of Ag impurities at interfaces of parallel-plate Pt/Ba0.6Sr0.4TiO3/Pt thin film ferroelectric varactors. Ag impurities occur at the interfaces due to diffusion of Ag from colloidal silver paint used to attach the varactor samples with their back side to the plate heated at 600-750 °C during deposition of Ba0.6Sr0.4TiO3. X-ray photoelectron spectroscopy and secondary ion mass spectrometry suggest that amount and distribution of Ag adsorbed at the interfaces depend strongly on the adsorbent surface layer. In particular, Ag preferentially accumulates on top of the Pt bottom electrode. The presence of Ag significantly reduces the barrier height between Pt and Ba0.6Sr0.4TiO3 leading to an increased leakage current density and, thus, to a severe degradation of the varactor performance.

  12. Modification of energy band alignment and electric properties of Pt/Ba{sub 0.6}Sr{sub 0.4}TiO{sub 3}/Pt thin-film ferroelectric varactors by Ag impurities at interfaces

    SciTech Connect

    Hirsch, S.; Komissinskiy, P. Flege, S.; Li, S.; Rachut, K.; Klein, A.; Alff, L.

    2014-06-28

    We report on the effects of Ag impurities at interfaces of parallel-plate Pt/Ba{sub 0.6}Sr{sub 0.4}TiO{sub 3}/Pt thin film ferroelectric varactors. Ag impurities occur at the interfaces due to diffusion of Ag from colloidal silver paint used to attach the varactor samples with their back side to the plate heated at 600–750 °C during deposition of Ba{sub 0.6}Sr{sub 0.4}TiO{sub 3}. X-ray photoelectron spectroscopy and secondary ion mass spectrometry suggest that amount and distribution of Ag adsorbed at the interfaces depend strongly on the adsorbent surface layer. In particular, Ag preferentially accumulates on top of the Pt bottom electrode. The presence of Ag significantly reduces the barrier height between Pt and Ba{sub 0.6}Sr{sub 0.4}TiO{sub 3} leading to an increased leakage current density and, thus, to a severe degradation of the varactor performance.

  13. Synthesis and structural characterisation of Pd(II) and Pt(II) complexes with a flexible, ferrocene-based P,S-donor amidophosphine ligand.

    PubMed

    Tauchman, Jiří; Císařová, Ivana; Stěpnička, Petr

    2014-01-28

    1'-Diphenylphosphino-1-{[(2-(methylthio)ethyl)amino]carbonyl}ferrocene (1), accessible via amidation of 1'-(diphenylphosphino)ferrocene-1-carboxylic acid (Hdpf) with 2-(methylthio)ethylamine, reacts with [PdCl2(cod)] (cod = cycloocta-1,5-diene) at a 1 : 1 metal-to-ligand ratio to give trans-[PdCl2(1-κ(2)P,S)] (trans-2) as the sole product. A similar reaction with [PtCl2(cod)] affords a mixture of cis- and trans-[PtCl2(1-κ(2)P,S)] (cis- and trans-3), which can be separated by fractional crystallisation. Complexation reactions performed with 2 equiv. of the ligand are less selective, yielding mixtures of the expected bis-phosphine complexes (i.e., trans-[PdCl2(1-κP)2], or a mixture of cis- and trans-[PtCl2(-κP)2]) with the respective monophosphine complexes. The structures of 1, trans-2, cis-3 and trans-3 determined by X-ray diffraction demonstrate the ability of the title ligand to act as a flexible cis- or trans-P,S-chelate donor (the ligand bite angles are 174.03(2)/173.05(2)° for trans-2/3 and 92.86(2)° for cis-3).

  14. Interfacial properties of Ce0.75Zr0.25O2 supported noble metals (Pd, Pt) from first principles

    NASA Astrophysics Data System (ADS)

    Lu, Z.; Yang, Z.

    2008-06-01

    First-principles electronic structure calculations of noble metals (NM=Pd, Pt)/Ce0.75Zr0.25O2 systems are presented. It is found that: the NM adatoms do not prefer to stay at the atop or the bridge sites of the cations (Ce and Zr), but prefer to be adsorbed at or around the anion sites. The most preferable adsorption sites for both the Pd and Pt adatoms are the O-bridge sites neighboring the Zr dopant. The Pt adatom show much stronger interaction with the Ce0.75Zr0.25O2(111) surface than does the Pd adatom. The interactions of the NM/Ce0.75Zr0.25O2(111) interfaces are stronger than those of the corresponding NM/ceria(111) interfaces. There are some metal induced gap states (MIGS) appeared in the gaps of the NM/Ce0.75Zr0.25O2(111) interfaces, which are important to catalytic properties of the NM/Ce0.75Zr0.25O2(111) catalysts.

  15. A pseudo triple-enzyme electrochemical aptasensor based on the amplification of Pt-Pd nanowires and hemin/G-quadruplex.

    PubMed

    Zheng, Yingning; Chai, Yaqin; Yuan, Yali; Yuan, Ruo

    2014-06-27

    Our present work aimed at developing a pseudo triple-enzyme cascade electrocatalytic electrochemical aptasensor for determination of thrombin with the amplification of alcohol dehydrogenase (ADH)-Pt-Pd nanowires bionanocomposite and hemin/G-quadruplex structure that simultaneously acted as NADH oxidase and HRP-mimicking DNAzyme. With the addition of ethanol to the electrolyte, the ADH immobilized on the Pt-Pd nanowires catalyzed ethanol to acetaldehyde accompanied by NAD(+) being converted to NADH. Then the hemin/G-quadruplex firstly served as NADH oxidase, converting the produced NADH to NAD(+) with the concomitant local formation of high concentration of H2O2. Subsequently, the hemin/G-quadruplex acted as HRP-mimicking DNAzyme, bioelectrocatalyzing the produced H2O2. At the same time, the Pt-Pd nanowires employed in our strategy not only provided a large surface area for immobilizing thrombin binding aptamer (TBA) and ADH, but also served as HRP-mimicking DNAzyme which rapidly bioelectrocatalyzed the reduction of the produced H2O2. Thus, such a pseudo triple-enzyme cascade electrochemical aptasensor could greatly promote the electron transfer of hemin and resulted in the dramatic enhancement of electrochemical signal. As a result, a wide dynamic concentration linear range from 0.2 pM to 20 nM with a low detection limit of 0.067 pM for thrombin (TB) determination was obtained. The excellent performance indicated that our strategy was a promising way for ultrasensitive assays in electrochemical aptasensors.

  16. Electron Microprobe and Raman Spectroscopy Investigation of an Oxygen-Bearing Pt-Fe-Pd-Ni-Cu Compound from Nurali Chromitite (Southern Urals, Russia).

    PubMed

    Zaccarini, Federica; Garuti, Giorgio; Bakker, Ronald J; Pushkarev, Evgeny

    2015-10-01

    One grain, about 100×80 μm in size, occurring in chromitite associated with the layered sequence of the Nurali mafic-ultramafic complex (Southern Urals, Russia) was investigated by electron-microprobe analyses and Raman spectroscopy. The grain is characterized by a spotty, rugged appearance and chemical zoning from which two compositions were calculated: (Pt(0.35)Pd(0.26)Fe(0.22)Cu(0.01)Ni(0.05))(0.98)O(1.02) and (Fe(0.90)Pt(0.58)Ni(0.28)Pd(0.13)Cu(0.08)Rh(0.01))(1.98)O(1.02). In the lack of X-ray data, Raman spectroscopy established the presence of a diffuse 500-700 band and a sharp peak at 657 cm⁻¹ of relative wavenumber that strongly resemble the Raman spectra of synthetic PtO and PdO (palladinite). It is concluded that the Nurali grain probably represents a platinum group element (PGE) oxide, and does not consist of a mixture of PGE alloys with Fe oxide or hydroxide as reported for other natural PGE-O compounds.

  17. Ultrasensitive strategy based on PtPd nanodendrite/nano-flower-like@GO signal amplification for the detection of long non-coding RNA.

    PubMed

    Liu, Fei; Xiang, Guiming; Jiang, Dongneng; Zhang, Liqun; Chen, Xuemei; Liu, Linlin; Luo, Fukang; Li, Yi; Liu, Chang; Pu, Xiaoyun

    2015-12-15

    Highly up-regulated in liver cancer (HULC) is a novel promising noninvasive biomarker for hepatocellular carcinoma (HCC), which is a kind of long non-coding RNAs (lncRNAs). But traditional methods limited HULC clinical detection for ownself drawbacks. Development a new HULC detection approach is urgent and necessary. Electrochemical nucleic acid sensor based on different signal amplification strategies with high sensitivity, fast, simple, and convenient, may solve this problem. Herein, we propose a novel strategy based on Pt-Pd bimetallic nanodendrites/nanoflower-like clusters on graphene oxide/Au/horseradish peroxidase (PtPd BND/BNF@GO/Au/HRP) to enhance the catalytic efficiency and sensitivity. And Au particles were simultaneously and separately capped with thionine or detection probe, which increase the binding amount of detection probe and decrease the electronic background. The results indicated that the catalytic effect was noticeably elevated and that the biosensor provides ultrasensitive detection for the lncRNA HULC. The linear calibration of the biosensor ranged from 1.00×10(-3) to 1.00×10(3) pM/mL, and the limit of detection was 0.247 fM/mL. The lncRNA biosensor based on the PtPd BND/BNF@GO/Au/HRP/Au/thionine exhibited acceptable reproducibility and clear selectivity. This strategy may provide a new alternative for clinical HCC diagnosis through the detection of HULC.

  18. Particle swarm optimization of the stable structure of tetrahexahedral Pt-based bimetallic nanoparticles

    NASA Astrophysics Data System (ADS)

    Liu, Tun-Dong; Fan, Tian-E.; Shao, Gui-Fang; Zheng, Ji-Wen; Wen, Yu-Hua

    2014-08-01

    Bimetallic nanoparticles, enclosed by high-index facets, have great catalytic activity and selectivity owing to the synergy effects of high-index facets and the electronic structures of alloy. In this paper, a discrete particle swarm optimization algorithm was employed to systematically investigate the structural stability and features of tetrahexahedral Pt-based bimetallic nanoparticles with high-index facets. Different Pt/Ag, Pt/Cu, Pt/Pd atom ratios and particle sizes were considered in this work. The simulation results reveal that these alloy nanoparticles exhibit considerably different structural characteristics. Pt-Ag nanoparticles tend to form Pt-Ag core-shell structure. Pt-Cu nanoparticles are preferred to take multi-shell structure with Cu on the outer surface while Pt-Pd nanoparticles present a mixing structure in the interior and Pd-dominated surface. Atomic distribution and bonding characteristics were applied to further characterize the structural features of Pt-based nanoparticles. This study provides an important insight into the structural stability and features of Pt-based nanoparticles with different alloys.

  19. Synthesis, crystal structure, and electronic properties of high-pressure PdF2-type oxides MO2 (M = Ru, Rh, Os, Ir, Pt).

    PubMed

    Shirako, Yuichi; Wang, Xia; Tsujimoto, Yoshihiro; Tanaka, Kie; Guo, Yanfeng; Matsushita, Yoshitaka; Nemoto, Yoshihiro; Katsuya, Yoshio; Shi, Youguo; Mori, Daisuke; Kojitani, Hiroshi; Yamaura, Kazunari; Inaguma, Yoshiyuki; Akaogi, Masaki

    2014-11-01

    The polycrystalline MO2's (HP-PdF2-type MO2, M = Rh, Os, Pt) with high-pressure PdF2 compounds were successfully synthesized under high-pressure conditions for the first time, to the best of our knowledge. The crystal structures and electromagnetic properties were studied. Previously unreported electronic properties of the polycrystalline HP-PdF2-type RuO2 and IrO2 were also studied. The refined structures clearly indicated that all compounds crystallized into the HP-PdF2-type structure, M(4+)O(2-)2, rather than the pyrite-type structure, M(n+)(O2)(n-) (n < 4). The MO2 compounds (M = Ru, Rh, Os, Ir) exhibited metallic conduction, while PtO2 was highly insulating, probably because of the fully occupied t2g band. Neither superconductivity nor a magnetic transition was detected down to a temperature of 2 K, unlike the case of 3d transition metal chalcogenide pyrites. PMID:25337807

  20. Synthesis, crystal structure, and electronic properties of high-pressure PdF2-type oxides MO2 (M = Ru, Rh, Os, Ir, Pt).

    PubMed

    Shirako, Yuichi; Wang, Xia; Tsujimoto, Yoshihiro; Tanaka, Kie; Guo, Yanfeng; Matsushita, Yoshitaka; Nemoto, Yoshihiro; Katsuya, Yoshio; Shi, Youguo; Mori, Daisuke; Kojitani, Hiroshi; Yamaura, Kazunari; Inaguma, Yoshiyuki; Akaogi, Masaki

    2014-11-01

    The polycrystalline MO2's (HP-PdF2-type MO2, M = Rh, Os, Pt) with high-pressure PdF2 compounds were successfully synthesized under high-pressure conditions for the first time, to the best of our knowledge. The crystal structures and electromagnetic properties were studied. Previously unreported electronic properties of the polycrystalline HP-PdF2-type RuO2 and IrO2 were also studied. The refined structures clearly indicated that all compounds crystallized into the HP-PdF2-type structure, M(4+)O(2-)2, rather than the pyrite-type structure, M(n+)(O2)(n-) (n < 4). The MO2 compounds (M = Ru, Rh, Os, Ir) exhibited metallic conduction, while PtO2 was highly insulating, probably because of the fully occupied t2g band. Neither superconductivity nor a magnetic transition was detected down to a temperature of 2 K, unlike the case of 3d transition metal chalcogenide pyrites.

  1. Spectroscopic, thermal characterization and cytotoxic activity of bi-, tri- and tetra-nuclear Pd(II) and Pt(II) complexes with diSchiff base ligands

    NASA Astrophysics Data System (ADS)

    Hegazy, Wael Hussein

    2014-10-01

    In this paper; new di-, tri-, and tetra-nuclear Pd(II) and Pt(II) complexes of N,N‧-bis(3,4-dihydroxybenzylidene)ethan-1,2-diamine (EDH4), N,N‧-bis(3,4-dihydroxy-benzylidene)-benzene-1,2-diamine (PDH4) and N,N‧-bis-(3,4-dihydroxybenzylidene)-4,5-dimethyl-1,2-diamine (MPDH4) ligands were synthesized by two different methods. The first method involve the synthesis of the three ligands from condensation reaction of 3,4-dihydroxybenzaldehyde (L‧H2) with ethylenediamine (en), o-phenylenediamine (o-PD), or 4,5-dimethyl-1,2-phenylendiamine (DMPD) in a mole ratio of 2:1 followed by the reaction of the resulting Schiff bases ligands with Pd(II) or Pt(II) ions in the presence of 2,2‧-dipyridyl (L) to form the di- and tri-nuclear metal complexes. The second method involve the condensation of the Pd complex LPd(II)L‧, (L = 2,2‧-dipyridyl, L‧ = 4-formylbenzene-1,2-bis(olate)) with en, o-PD, or DMPD in a mole ratio of 2:1, respectively, followed by reaction with PdCl2 to form di-, tri-, and tetra-nuclear palladium(II) complexes, respectively. Structures of ligands and metal complexes are characterized by physical properties, FT-IR spectra and nuclear magnetic resonance. The geometries of metal complexes are suggested according to elemental analysis, electronic absorption spectra, thermal analysis, atomic absorption, magnetic susceptibility and molar conductance. Cytotoxic activity against lung large cell carcinoma (H460), prostate carcinoma (DU145), breast adenocarcinoma (MCF-7), amelanotic melanoma (M-14), colon adenocarcinoma (HT-29), and chronic myelogenous leukemia (K562) is also reported.

  2. Associations of Pd, U and Ag in the SiC layer of neutron-irradiated TRISO fuel

    NASA Astrophysics Data System (ADS)

    Lillo, T. M.; van Rooyen, I. J.

    2015-05-01

    Knowledge of the associations and composition of fission products in the neutron irradiated SiC layer of high-temperature gas reactor TRISO fuel is important to the understanding of various aspects of fuel performance that presently are not well understood. Recently, advanced characterization techniques have been used to examine fuel particles from the Idaho National Laboratory's AGR-1 experiment. Nano-sized Ag and Pd precipitates were previously identified in grain boundaries and triple points in the SiC layer of irradiated TRISO nuclear fuel. Continuation of this initial research is reported in this paper and consists of the characterization of a relatively large number of nano-sized precipitates in three areas of the SiC layer of a single irradiated TRISO nuclear fuel particle using standardless EDS analysis on focused ion beam-prepared transmission electron microscopy samples. Composition and distribution analyses of these precipitates, which were located on grain boundaries, triple junctions and intragranular precipitates, revealed low levels, generally <10 atomic %, of palladium, silver and/or uranium with palladium being the most common element found. Palladium by itself, or associated with either silver or uranium, was found throughout the SiC layer. A small number of precipitates on grain boundaries and triple junctions were found to contain only silver or silver in association with palladium while uranium was always associated with palladium but never found by itself or in association with silver. Intergranular precipitates containing uranium were found to have migrated ∼23 μm along a radial direction through the 35 μm thick SiC coating during the AGR-1 experiment while silver-containing intergranular precipitates were found at depths up to ∼24 μm in the SiC layer. Also, Pd-rich, nano-precipitates (∼10 nm in diameter), without evidence for the presence of either Ag or U, were revealed in intragranular regions throughout the SiC layer. Because not

  3. Associations of Pd, U and Ag in the SiC layer of neutron-irradiated TRISO fuel

    SciTech Connect

    Lillo, Thomas; Rooyen, Isabella Van

    2015-05-01

    Knowledge of the associations and composition of fission products in the neutron irradiated SiC layer of high-temperature gas reactor TRISO fuel is important to the understanding of various aspects of fuel performance that presently are not well understood. Recently, advanced characterization techniques have been used to examine fuel particles from the Idaho National Laboratory’s AGR-1 experiment. Nano-sized Ag and Pd precipitates were previously identified in grain boundaries and triple points in the SiC layer of irradiated TRISO nuclear fuel. Continuation of this initial research is reported in this paper and consists of the characterization of a relatively large number of nano-sized precipitates in three areas of the SiC layer of a single irradiated TRISO nuclear fuel particle using standardless EDS analysis on focused ion beam-prepared transmission electron microscopy samples. Composition and distribution analyses of these precipitates, which were located on grain boundaries, triple junctions and intragranular precipitates, revealed low levels, generally <10 atomic %, of palladium, silver and/or uranium with palladium being the most common element found. Palladium by itself, or associated with either silver or uranium, was found throughout the SiC layer. A small number of precipitates on grain boundaries and triple junctions were found to contain only silver or silver in association with palladium while uranium was always associated with palladium but never found by itself or in association with silver. Intergranular precipitates containing uranium were found to have migrated ~23 μm along a radial direction through the 35 μm thick SiC coating during the AGR-1 experiment while silver-containing intergranular precipitates were found at depths up to ~24 μm in the SiC layer. Also, Pd-rich, nano-precipitates (~10 nm in diameter), without evidence for the presence of either Ag or U, were revealed in intragranular regions throughout the SiC layer. Because not all

  4. Ultrasonic-electrodeposition of PtPd alloy nanoparticles on ionic liquid-functionalized graphene paper: towards a flexible and versatile nanohybrid electrode

    NASA Astrophysics Data System (ADS)

    Sun, Yimin; Zheng, Huaming; Wang, Chenxu; Yang, Mengmeng; Zhou, Aijun; Duan, Hongwei

    2016-01-01

    Here we fabricate a new type of flexible and versatile nanohybrid paper electrode by ultrasonic-electrodeposition of PtPd alloy nanoparticles on freestanding ionic liquid (IL)-functionalized graphene paper, and explore its multifunctional applications in electrochemical catalysis and sensing systems. The graphene-based paper materials demonstrate intrinsic flexibility, exceptional mechanical strength and high electrical conductivity, and therefore can serve as an ideal freestanding flexible electrode for electrochemical devices. Furthermore, the functionalization of graphene with IL (i.e., 1-butyl-3-methylimidazolium tetrafluoroborate) not only increases the electroactive surface area of a graphene-based nanohybrid paper electrode, but also improves the adhesion and dispersion of metal nanoparticles on the paper surface. These unique attributes, combined with the merits of an ultrasonic-electrodeposition method, lead to the formation of PtPd alloy nanoparticles on IL-graphene paper with high loading, uniform distribution, controlled morphology and favourable size. Consequently, the resultant nanohybrid paper electrode exhibits remarkable catalytic activity as well as excellent cycle stability and improved anti-poisoning ability towards electrooxidation of fuel molecules such as methanol and ethanol. Furthermore, for nonenzymatic electrochemical sensing of some specific biomarkers such as glucose and reactive oxygen species, the nanohybrid paper electrode shows high selectivity, sensitivity and biocompatibility in these bio-catalytic processes, and can be used for real-time tracking hydrogen peroxide secretion by living human cells. All these features demonstrate its promising application as a versatile nanohybrid electrode material in flexible and lightweight electrochemical energy conversion and biosensing systems such as bendable on-chip power sources, wearable/implantable detectors and in vivo micro-biosensors.Here we fabricate a new type of flexible and

  5. A general approach to fabricate diverse noble-metal (Au, Pt, Ag, Pt/Au)/Fe2O3 hybrid nanomaterials.

    PubMed

    Zhang, Jun; Liu, Xianghong; Guo, Xianzhi; Wu, Shihua; Wang, Shurong

    2010-07-19

    A novel, facile, and general one-pot strategy is explored for the synthesis of diverse noble-metal (Au, Pt, Ag, or Pt/Au)/Fe(2)O(3) hybrid nanoparticles with the assistance of lysine (which is a nontoxic, user friendly amino acid that is compatible with organisms) and without using any other functionalization reagents. Control experiments show that lysine, which contains both amino and carboxylic groups, plays dual and crucial roles as both linker and capping agents in attaching noble metals with a small size and uniform distribution onto an Fe(2)O(3) support. Considering the perfect compatibility of lysine with organism, this approach may find potentials in biochemistry and biological applications. Furthermore, this novel route is also an attractive alternative and supplement to the current methods using a silane coupling agent or polyelectrolyte for preparing hybrid nanomaterials. To demonstrate the usage of such hybrid nanomaterials, a chemical gas sensor has been fabricated from the as-synthesized Au/Fe(2)O(3) nanoparticles and investigated for ethanol detection. Results show that the hybrid sensor exhibits significantly improved sensor performances in terms of high sensitivity, low detection limit, better selectivity, and good reproducibility in comparison with pristine Fe(2)O(3). Most importantly, this general approach can be further employed to fabricate other hybrid nanomaterials based on different support materials.

  6. Isolation and Structural Characterization of a Mackay 55-Metal-Atom Two-Shell Icosahedron of Pseudo-Ih Symmetry, Pd55L12(μ3-CO)20 (L = PR3, R = Isopropyl): Comparative Analysis with Interior Two-Shell Icosahedral Geometries in Capped Three-Shell Pd145, Pt-Centered Four-Shell Pd-Pt M165, and Four-Shell Au133 Nanoclusters.

    PubMed

    Erickson, Jeremiah D; Mednikov, Evgueni G; Ivanov, Sergei A; Dahl, Lawrence F

    2016-02-10

    We present the first successful isolation and crystallographic characterization of a Mackay 55-metal-atom two-shell icosahedron, Pd55L12(μ3-CO)20 (L = PPr(i)3) (1). Its two-shell icosahedron of pseudo-Ih symmetry (without isopropyl substituents) enables a structural/bonding comparison with interior 55-metal-atom two-shell icosahedral geometries observed within the multi-shell capped 145-metal-atom three-shell Pd145(CO)72(PEt3)30 and 165-metal-atom four-shell Pt-centered (μ12-Pt)Pd164-xPtx(CO)72(PPh3)20 (x ≈ 7) nanoclusters, and within the recently reported four-shell Au133(SC6H4-p-Bu(t))52 nanocluster. DFT calculations carried out on a Pd55(CO)20(PH3)12 model analogue, with triisopropyl phosphine substituents replaced by H atoms, revealed a positive +0.84 e charge for the entire Pd55 core, with a highly positive second-shell Pd42 surface of +1.93 e.

  7. Schottky or Ohmic metal-semiconductor contact: influence on photocatalytic efficiency of Ag/ZnO and Pt/ZnO model systems.

    PubMed

    Yan, Fengpo; Wang, Yonghao; Zhang, Jiye; Lin, Zhang; Zheng, Jinsheng; Huang, Feng

    2014-01-01

    The relationship between the contact type in metal-semiconductor junctions and their photocatalytic efficiencies is investigated. Two metal-semiconductor junctions, silver on zinc oxide (Ag/ZnO) and platinum on zinc oxide (Pt/ZnO) serve as model system for Ohmic and Schottky metal-semiconductor contact, respectively. Ag/ZnO, with Ohmic contact, exhibits a higher photocatalytic efficiency than Pt/ZnO, with Schottky contact. The direction of electric fields within the semiconductor is found to play a crucial role in the separation of photogenerated charges, and thus strongly influences the photocatalytic efficiency.

  8. Perpendicular magnetic tunnel junctions with a synthetic storage or reference layer: A new route towards Pt- and Pd-free junctions

    PubMed Central

    Cuchet, Léa; Rodmacq, Bernard; Auffret, Stéphane; Sousa, Ricardo C.; Prejbeanu, Ioan L.; Dieny, Bernard

    2016-01-01

    We report here the development of Pt and Pd-free perpendicular magnetic tunnel junctions (p-MTJ) for STT-MRAM applications. We start by studying a p-MTJ consisting of a bottom synthetic Co/Pt reference layer and a synthetic FeCoB/Ru/FeCoB storage layer covered with an MgO layer. We first investigate the evolution of RKKY coupling with Ru spacer thickness in such a storage layer. The coupling becomes antiferromagnetic above 0.5 nm and its strength decreases monotonously with increasing Ru thickness. This contrasts with the behavior of Co-based systems for which a maximum in interlayer coupling is generally observed around 0.8 nm. A thin Ta insertion below the Ru spacer considerably decreases the coupling energy, without basically changing its variation with Ru thickness. After optimization of the non-magnetic and magnetic layer thicknesses, it appears that such a FeCoB/Ru/FeCoB synthetic storage layer sandwiched between MgO barriers can be made stable enough to actually be used as hard reference layer in single or double magnetic tunnel junctions, the storage layer being now a single soft FeCoB layer. Finally, we realize Pt- or Pd-free robust perpendicular magnetic tunnel junctions, still keeping the advantage of a synthetic reference layer in terms of reduction of stray fields at small pillar sizes. PMID:26883933

  9. Aerosol-assisted chemical vapor deposition (AACVD) of binary alloy (Ag{sub x}Pd{sub 1-x}, Cu{sub x}Pd{sub 1-x}, Ag{sub x}Cu{sub 1-x}) films and studies of their compositional variation

    SciTech Connect

    Xu, C.; Hampden-Smith, M.J.; Kodas, T.T.

    1995-08-01

    Atmospheric pressure chemical vapor deposition (CVD) of Ag-Pd,Cu-Pd, and Ag-Cu alloys using aerosol precursor delivery over a range of preheating temperatures, 70-80{degrees}C and substrate temperatures, 250-300{degrees}C is described. The precursors were (hfac)Ag(SEt{sub 2}), (hfac)Cu{sup I}(1,5-COD), Cu(hfac){sub 2}, Pd(hfac){sub 2}, and Pd(hfac){sub 2}(SE5{sub 2}) dissolved in toluene with 10% H{sub 2} in Ar as carrier gas. The films were characterized by scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS), and X-ray diffraction. The X-ray diffraction results showed the Ag PD films consisted of AgNO{sub 3} and volatile (hfac)Ag(SEt{sub 2}) as precursors to Ag films were consistent with a chemical vapor deposition (CVD) process. Reactivity studies between precursors and H{sub 2} suggested Pd(hfac){sub 2} is likely to undergo a small amount (<2%) of decomposition during the aerosol-assisted CVD experiments, and Pd(hfac){sub 2}(SEt{sub 2})/Pd(hfac){sub 2{minus}}(SEt{sub 2}) in different ratios in toluene solution. The films were characterized by X-ray diffraction and the results showed the composition of the films was dependent upon the solution stoichiometry. The possible rate-limiting steps are discussed, and it is proposed that the deposition rate is limited by the feed rate of the precursors to the reactor. These predictions were consistent with a study of deposition rate as a function of substrate temperature at constant feed rate in the (hfac)Ag(SEt{sub 2})/Pd(hfac){sub 2}(SEt{sub 2}) system, which showed no variation in the deposition rate over a 75{degrees}C temperature range. It was concluded that conditions of feed-rate or diffusion-rate limited deposition are useful approaches to control film composition. 42 refs., 12 figs., 1 tab.

  10. Spatial variation of contaminant elements of roadside dust samples from Budapest (Hungary) and Seoul (Republic of Korea), including Pt, Pd and Ir.

    PubMed

    Sager, Manfred; Chon, Hyo-Taek; Marton, Laszlo

    2015-02-01

    Roadside dusts were studied to explain the spatial variation and present levels of contaminant elements including Pt, Pd and Ir in urban environment and around Budapest (Hungary) and Seoul (Republic of Korea). The samples were collected from six sites of high traffic volumes in Seoul metropolitan city and from two control sites within the suburbs of Seoul, for comparison. Similarly, road dust samples were obtained two times from traffic focal points in Budapest, from the large bridges across the River Danube, from Margitsziget (an island in the Danube in the northern part of Budapest, used for recreation) as well as from main roads (no highways) outside Budapest. The samples were analysed for contaminant elements by ICP-AES and for Pt, Pd and Ir by ICP-MS. The highest Pt, Pd and Ir levels in road dusts were found from major roads with high traffic volume, but correlations with other contaminant elements were low, however. This reflects automobile catalytic converter to be an important source. To interpret the obtained multi-element results in short, pollution index, contamination index and geo-accumulation index were calculated. Finally, the obtained data were compared with total concentrations encountered in dust samples from Madrid, Oslo, Tokyo and Muscat (Oman). Dust samples from Seoul reached top level concentrations for Cd-Zn-As-Co-Cr-Cu-Mo-Ni-Sn. Just Pb was rather low because unleaded gasoline was introduced as compulsory in 1993. Concentrations in Budapest dust samples were lower than from Seoul, except for Pb and Mg. Compared with Madrid as another continental site, Budapest was higher in Co-V-Zn. Dust from Oslo, which is not so large, contained more Mn-Na-Sr than dust from other towns, but less other metals.

  11. Final report of APMP.T-S7: APMP regional comparison of Co-C eutectic melting point using Pt/Pd thermocouples

    NASA Astrophysics Data System (ADS)

    Kim, Y.-G.; Wei, Z.; Ogura, H.; Jahan, F.; Singh, Y. P.

    2016-01-01

    A regional supplementary comparison on the Co-C eutectic point (1324 °C in ITS-90) was carried out in APMP involving five NMIs: KRISS (Korea), NIM (China), NMIJ (Japan), NMIA (Australia) and NPLI (India). The comparison was done through a round robin style with two Pt/Pd thermocouples having greatly different thermoelectric inhomogeneity (± 0.0196 % and ± 0.132 % at 1324 °C), which were made by the pilot laboratory (KRISS). Both were calibrated twice, before and after the circulation by the pilot laboratory. As a reference value, the weighted mean was adopted since the Birge ration criterion was safely satisfied. The participants were asked to supply the temperature profile of the furnace used to realize the Co-C point in order to estimate the uncertainty due to thermoelectric inhomogeneity. Results from all laboratories were consistent with the reference value within the calculated uncertainties. Birge number of 0.2 to 0.3 and En number less than 0.5 were obtained, meaning that the comparison successfully demonstrated the use of Pt/Pd thermocouple to compare the calibration capabilities of participating laboratories at the melting temperature of Co-C eutectic point regardless of the amount of thermoelectric inhomogeneity. It was verified that the calibration uncertainty level of {(0.2 °C ~ 0.3 °C) + ucell} (k = 2) can be obtained at the Co-C eutectic melting point by means of Pt/Pd thermocouple having a small inhomogeneity of about 0.02 %. Main text To reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database kcdb.bipm.org/. The final report has been peer-reviewed and approved for publication by the CCT, according to the provisions of the CIPM Mutual Recognition Arrangement (CIPM MRA).

  12. Solvent extraction of palladium(II) with a Schiff base and separation of palladium from Pd(II)-Pt(VI) mixture

    SciTech Connect

    Ouyang, J.M.

    1999-09-01

    A new Schiff base extractant, N,N{prime}-bis[1-phenyl-3-methyl-5-hydroxy-pyrazole-4-benzylidenyl]-1,3-propylene diamine (H{sub 2}A) was synthesized and characterized. The extraction mechanism of palladium(II) from HNO{sub 3} or HCIO{sub 2} medium with H{sub 2}A in chloroform or toluene was investigated. The influences of the Schiff base concentration in the organic phase, the concentration of palladium, the pH and anions (Cl{sup {minus}}, SO{sub 4}{sup =}, NO{sub 3}{sup {minus}}, ClO{sub 4}{sup {minus}}) in the aqueous phase and the temperature on the distribution ration for palladium (II) have been examined. The extracted complex has been confirmed by chemical analysis, thermoanalyses and IR spectroscopy. It was found that palladium is extracted according to the following extraction reaction: Pd(H{sub 2}O){sub 2}Cl{sub 2(a)} + H{sub 2}A{sub (o)} == Pd(HA)Cl{sub (o)}+H{sup +}{sub (a)} + Cl{sup {minus}}{sub (a)} + 2H{sub 2}O. The extraction equilibrium constants of palladium(II) were 8.4 and 21.3 in chloroform and toluene diluents, respectively. The values for the enthalpy and standard free energy of extraction were also obtained. The separation of Pd(II) from the mixed solution of Pd(II)-Pt(IV) was achieved by adjusting the pH.

  13. Pt and Pd catalyzed oxidation of Li2O2 and DMSO during Li–O2 battery charging

    SciTech Connect

    Gittleson, Forrest S.; Ryu, Won-Hee; Schwab, Mark; Tong, Xiao; Taylor, André D.

    2016-01-01

    Rechargeable Li-O2 and Li-air batteries require electrode and electrolyte materials that synergistcally promote long-term cell operation. We investigate the role of noble metals Pt and Pd as catalysts for the Li-O2 oxidation process and their compatibility with a dimethyl sulfoxide (DMSO) based electrolyte. Lastly, we identify a basis for low potential Li2O2 evolution followed by oxidative decomposition of the electrolyte to form carbonate side products.

  14. DFT study of the formate formation on Ni(111) surface doped by transition metals [Ni(111)-M; M=Cu, Pd, Pt, Rh

    NASA Astrophysics Data System (ADS)

    Nugraha; Saputro, A. G.; Agusta, M. K.; Rusydi, F.; Maezono, R.; Dipojono, H. K.

    2016-08-01

    We report on a theoretical study of the formation of formate (HCOO) from the reaction of CO2 gas and a pre- adsorbed H atom (CO2 (g) + *H → *HCOO) on Ni(111) surface doped by transition-metals [Ni(111)-M; M= Cu, Pd, Pt, Rh] by means of density functional theory (DFT) calculations. This *HCOO formation reaction is one of the most important rate- limiting steps in the methanol synthesis process. We find that the presence of transition metal doping on the first-layer of Ni(111) surface could reduce the activation barrier of this reaction [up to ~38.4%, compared to clean Ni(111) surface].

  15. Enhancement of order degree and perpendicular magnetic anisotropy of L10 ordered Fe(Pt,Pd) alloy film by introducing a thin MgO cap-layer

    NASA Astrophysics Data System (ADS)

    Noguchi, Youhei; Ohtake, Mitsuru; Futamoto, Masaaki; Kirino, Fumiyoshi; Inaba, Nobuyuki

    2016-07-01

    Fe50PtxPd50-x (at%, x=0-50) alloy films of 10 nm thickness with and without 2-nm-thick MgO cap-layers are prepared on MgO(001) single-crystal substrates by employing a two-step method consisting of low-temperature deposition at 200 °C followed by high-temperature annealing at 600 °C. The influences of MgO cap-layer on the structure and the magnetic properties are investigated. Fe50PtxPd50-x films epitaxially grow on the substrates at 200 °C. The Fe50Pd50 and the Fe50Pt12.5Pd37.5 films are respectively composed of (001) single-crystals with disordered fcc-based (A1) and bcc-based (A2) structures. The films with x>25 consist of mixtures of A1 and A2 crystals. The volume ratio of A2 to A1 crystal decreases with increasing the x value from 25 to 50. The in-plane and out-of-plane lattices are respectively expanded and shrunk due to accommodation of lattice mismatch between film and substrate. When the films are annealed at 600 °C, phase transformation to L10 ordered phase takes place. L10 phase transformation of Fe50PtxPd50-x film is promoted for a sample with MgO cap-layer and the order degree is higher than that without cap-layer. Furthermore, L10 ordering with the c-axis perpendicular to the substrate surface is enhanced for the film with cap-layer. The cap-layer is considered to be giving a tension stress to the magnetic film in lateral direction which promotes L10 ordering with the c-axis perpendicular to the substrate. Deposition of cap-layer is shown effective in achieving higher order degree and in enhancing perpendicular magnetic anisotropy with Fe(Pt,Pd) films.

  16. Facile fabrication of Pt-Ag bimetallic nanoparticles decorated reduced graphene oxide for highly sensitive non-enzymatic hydrogen peroxide sensing.

    PubMed

    Zhang, Cong; Zhang, Yanyan; Du, Xin; Chen, Yuan; Dong, Wenhao; Han, Bingkai; Chen, Qiang

    2016-10-01

    A new electrocatalyst, Pt-Ag bimetallic nanoparticles decorated reduced graphene oxide nanocomposite, was successfully synthesized by a facile, eco-friendly and controllable route. The morphological characterization of RGO/Pt-Ag NPs nanocomposite was examined by transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDX) analyzer, X-ray diffraction (XRD) spectrum, and Fourier transform infrared spectrum (FT-IR), respectively. And then, the RGO/Pt-Ag NPs nanocomposite was immobilized on the surface of glassy carbon (GC) electrode to fabricate a novel and highly sensitive non-enzymatic hydrogen peroxide sensor. The electrochemical behaviors of the prepared sensor were investigated by cyclic voltammetry and chronoamperometry. The sensor showed excellent performance toward H2O2 with sensitivity as high as 699.6 μA mM(-1)cm(-2) and 402.7 μA mM(-1)cm(-2), wide linear range of 0.005-1.5mM and 1.5-7mM, and low detection limit of 0.04μM (S/N=3). Moreover, the prepared hydrogen peroxide sensor was applied to in real samples with satisfactory results. These excellent results indicate that the prepared RGO/Pt-Ag NPs nanocomposite has broad application prospect in the field of sensors. PMID:27474309

  17. Facile fabrication of Pt-Ag bimetallic nanoparticles decorated reduced graphene oxide for highly sensitive non-enzymatic hydrogen peroxide sensing.

    PubMed

    Zhang, Cong; Zhang, Yanyan; Du, Xin; Chen, Yuan; Dong, Wenhao; Han, Bingkai; Chen, Qiang

    2016-10-01

    A new electrocatalyst, Pt-Ag bimetallic nanoparticles decorated reduced graphene oxide nanocomposite, was successfully synthesized by a facile, eco-friendly and controllable route. The morphological characterization of RGO/Pt-Ag NPs nanocomposite was examined by transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDX) analyzer, X-ray diffraction (XRD) spectrum, and Fourier transform infrared spectrum (FT-IR), respectively. And then, the RGO/Pt-Ag NPs nanocomposite was immobilized on the surface of glassy carbon (GC) electrode to fabricate a novel and highly sensitive non-enzymatic hydrogen peroxide sensor. The electrochemical behaviors of the prepared sensor were investigated by cyclic voltammetry and chronoamperometry. The sensor showed excellent performance toward H2O2 with sensitivity as high as 699.6 μA mM(-1)cm(-2) and 402.7 μA mM(-1)cm(-2), wide linear range of 0.005-1.5mM and 1.5-7mM, and low detection limit of 0.04μM (S/N=3). Moreover, the prepared hydrogen peroxide sensor was applied to in real samples with satisfactory results. These excellent results indicate that the prepared RGO/Pt-Ag NPs nanocomposite has broad application prospect in the field of sensors.

  18. Photocatalytic Properties of TiO2 Thin Films Modified with Ag and Pt Nanoparticles Deposited by Gas Flow Sputtering.

    PubMed

    Maicu, M; Glöss, D; Frach, Peter; Hecker, D; Gerlach, G; Córdoba, José M

    2015-09-01

    In this work, a gas flow sputtering (GFS) process which allows the production and deposition of metal nanoparticles (NPs) in a vacuum environment is described. Aim of the study is to prove the potential of this technology for the fabrication of new TiO2 films with enhanced photocatalytic properties. For this purpose, Ag and Pt NPs have been produced and deposited on photocatalytic float glass coated with TiO2 thin films by magnetron sputtering. The influence of the process parameters and of the metal amount on the final properties of the particles (quantity, size, size distribution, oxidation state etc.,) was widely investigated. Moreover, the effect of the NPs on the photocatalytic activity of the resulting materials was evaluated for the case of the decomposition of stearic acid (SA) during UV-A irradiation. The reduction of the water contact angle (WCA) during the irradiation period was measured in order to test the photo-induced super-hydrophilicity (PSH).

  19. Photodeposition of Ag or Pt onto TiO2 nanoparticles decorated on step edges of HOPG.

    PubMed

    Taing, James; Cheng, Ming H; Hemminger, John C

    2011-08-23

    Ordered linear arrays of titanium dioxide nanoparticles were fabricated on highly oriented pyrolytic graphite utilizing a step edge decoration method. Ag- or Pt-based nanoparticles were then photodeposited onto the titanium dioxide nanoparticles (∼18 nm) to simultaneously verify photocatalytic activity and to demonstrate a viable route to load the titanium dioxide nanoparticles with metals. Scanning electron microscopy and atomic force microscopy determined the morphology, size, and distribution of the particles. X-ray photoelectron spectroscopy confirmed the identity of the titanium dioxide nanoparticles, and transmission electron microscopy showed that some of the particles were rutile single crystals. Energy-dispersive X-ray spectroscopy and X-ray photoelectron spectroscopy determined the chemical composition of the metal-based nanoparticles selectively loaded on the linear arrays of titanium dioxide nanoparticles.

  20. Investigation of electrode processes on th Pt/. cap alpha. -AgI boundary with the aid of estance measurements

    SciTech Connect

    Tarasov, A.Y.; Filyaev, A.T.; Karpachev, S.V.; Prusov, V.A.

    1985-10-01

    It was established that elemental silver is deposited on Pt after the latter is brought into contact with AgI and the temperature is held constant. The dependence of the estance on the electrode potential is shown; the potential was varied by causing anodic polarization relative to a silver reference electrode. The profile of the oscillogram presented is described. The decrease of estance may be explained on the basis of the theories on the influence of adsorption process on the estance, if it is assumed that the occurrence of the electrode reaction which results in the appearance of adsorbed iodine on the interface, becomes appreciable at potentials more positive than +130 mV.

  1. Ag/GeSx/Pt-based complementary resistive switches for hybrid CMOS/Nanoelectronic logic and memory architectures

    NASA Astrophysics Data System (ADS)

    van den Hurk, Jan; Havel, Viktor; Linn, Eike; Waser, Rainer; Valov, Ilia

    2013-10-01

    Complementary resistive switches based on two anti-serially connected Ag/GeSx/Pt devices were studied. The main focus was placed on the pulse mode properties as typically required in memory and logic applications. A self-designed measurement setup was applied to access each CRS part-cell individually. Our findings reveal the existence of two distinct read voltage regimes enabling both spike read as well as level read approaches. Furthermore, we experimentally verified the theoretically predicted kinetic properties in terms of pulse height vs. switching time relationship. The results obtained by this alternative approach allow a significant improvement of the basic understanding of the interplay between the two part-cells in a complementary resistive switch configuration. Furthermore, from these observations we can deduce a simplified write voltage scheme which is applicable for the considered type of memory cell.

  2. Fabrication of nanoporous Cu-Pt(Pd) core/shell structure by galvanic replacement and its application in electrocatalysis.

    PubMed

    Xu, Caixia; Liu, Yunqing; Wang, Jinping; Geng, Haoran; Qiu, Huajun

    2011-12-01

    We describe a general strategy to fabricate a new type of nanoporous core/shell structured bimetallic nanocomposites with controllable metal components. Nanoporous copper (NPC) obtained by dealloying Cu/Al alloy is used as both reducing agent and three-dimensional substrate. Electron microscope and X-ray diffraction characterizations demonstrated that a simply galvanic-replacement reaction with H(2)PtCl(6) aqueous solution can easily generate nanoporous core/shell structure with a thin Pt/Cu alloy shell and Cu (or Pt/Cu alloy) core. The morphology and crystal structure evolution of the nanocomposites are studied and discussed in detail. The as-prepared bimetallic PtCu nanocomposites show greatly enhanced catalytic activity and stability toward methanol electro-oxidation as compared with commercial Pt/C catalyst. This facile in situ preparation strategy is also suitable for large-scale production of this novel and inexpensive catalyst. PMID:22034948

  3. Pt(II), Pd(II) and UO2(II) complexes of N,N‧-bis(2-pyridyl)thiourea; structural, thermal and biological studies

    NASA Astrophysics Data System (ADS)

    El-Ayaan, Usama

    2011-07-01

    Novel complexes of Pt 2+, Pd 2+ and UO 22+ with N,N'-bis(2-pyridyl)thiourea (H 2BPT) 1 were synthesized. These complexes namely [Pt(HBPT) 2] 2, [Pd(HBPT) 2] 3 and [UO 2(HBPT)(OAc)(H 2O)] 4 , were characterized by elemental analysis and spectral measurements. Suggested structures (square-planar for both 2 and 3 complexes and pentagonal-bipyramidal geometry for 4) were confirmed by applying geometry optimization and conformational analysis. Thermal properties and decomposition kinetics of all compounds are investigated. The interpretation, mathematical analysis and evaluation of kinetic parameters ( E, A, ΔH, ΔS and ΔG) of all thermal decomposition stages have been evaluated using Coats-Redfern, Horowitz-Metzger and MKN methods. The biochemical studies showed that, complex 2 has powerful and complete degradation effect on DNA. The antibacterial screening demonstrated that, complex 2 has the maximum and broad range activities against Gram-positive and Gram-negative bacterial strains.

  4. Pt-Pd bimetallic nanoparticles dispersed in an ionic liquid and peroxidase immobilized on nanoclay applied in the development of a biosensor.

    PubMed

    Pusch, Jessica M E; Brondani, Daniela; Luza, Leandro; Dupont, Jairton; Vieira, Iolanda C

    2013-09-01

    Pt-Pd bimetallic alloy nanoparticles (NPs) dispersed in the ionic liquid 1-butyl-3-methylimidazolium hexafluorophosphate (Pt-Pd-BMI·PF6) were employed together with a peroxidase (PO) enzyme from cauliflower immobilized on nanoclay for the development of a new biosensor for polyphenol determination by square-wave voltammetry (SWV). The biosensor demonstrated good repeatability and reproducibility, low limit of detection (LOD = 3.7 × 10(-7) mol L(-1) for caffeic acid (CA)), and adequate lifetime and stability (maintaining over 80% of the response over 80 days of evaluation, and allowing over 600 measurements by SWV for each electrode). Under optimized conditions, the proposed biosensor was applied in the determination of the bioelectrochemical polyphenolic index (BPI) for samples of commercial white wine, using CA as the phenolic compound standard. The recovery of CA from wine samples ranged from 95.5 to 108.3%. The values for the polyphenolic content obtained using the proposed biosensor showed a good correlation (r = 0.990) with those obtained with the reference spectrophotometric method (Folin-Ciocalteu method). Therefore, the proposed biosensor represents a useful tool for the rapid and accurate monitoring of polyphenolic content in wine samples and may also be applicable to other beverage samples, such as juices and teas.

  5. Study of Nd3+, Pd2+, Pt4+, and Fe3+ dopant effect on photoreactivity of TiO2 nanoparticles

    PubMed Central

    Shah, S. I.; Li, W.; Huang, C.-P.; Jung, O.; Ni, C.

    2002-01-01

    The metallorganic chemical vapor deposition method was successfully used to synthesize pure TiO2 and Nd3+-, Pd2+-, Pt4+-, and Fe3+-doped TiO2 nanoparticles. Polycrystalline TiO2 structure was verified with x-ray diffraction, which showed typical characteristic anatase reflections without any separate dopant-related peaks. Transmission electron microscopy observations confirmed the existence of homogeneously distributed 22 ± 3 nm TiO2 nanoparticles. The particle size remained the same for the doped samples. The doping level of transition metals was kept at ≈1 atomic percent, which was determined by x-ray photoelectron spectra and energy dispersive x-ray spectroscopy. The effects of different types of dopants on the photocatalytic activity were revealed by the degradation of 2-chlorophenols with an UV light source. The photocatalytic efficiency was remarkably enhanced by the introduction of Pd2+ and Nd3+. Nd3+-doped TiO2 showed the largest enhancement. However, Pt4+ changed the 2-chlorophenol degradation rate only slightly, and Fe3+ was detrimental to this process. These effects were related to the position of the dopants in the nanoparticles and the difference in their ionic radii with respect to that of Ti4+. PMID:11880607

  6. Preparation and characterization of platinum (Pt) and palladium (Pd) nanoparticle decorated graphene sheets and their utilization for the elimination of basic fuchsin and indigo carmine dyes

    NASA Astrophysics Data System (ADS)

    Kurt, Belma Zengin; Durmus, Zehra; Durmus, Ali

    2016-01-01

    In this study, graphene nano sheets, prepared with chemical oxidation and reduction routes via modified-Hummer method, were successfully decorated with platinum (Pt) and palladium (Pd) nanoparticles. Structural and morphological features of resulted graphene-metal nanocomposites were characterized with FT-IR, XRD, SEM and TEM methods. Anti-oxidant activity (AOA) values of nanocomposites were determined. The IC50 values of Pt-graphene and Pd-graphene nanocomposites were found to be 46.1 and 90.2 μg/mL, respectively based on the ABTS method and 80.2 and 143.7 μg/mL according to the DPPH method. It was found that the graphene-metal nanocomposites exhibited superior free radical scavenging activity compared to several types of noble metal nano particles although the nanocomposites consist of much lower amount of active metal sites than the nano-crystalline metal powders. It was consequently reported that the graphene-metal nanocomposites could be successfully used for the photocatalytic elimination of fuchsin and indigo carmine dyes under light irradiation.

  7. Pt-Pd reefs in magnetitites of the Stella layered intrusion, South Africa: A world of new exploration opportunities for platinum group elements

    NASA Astrophysics Data System (ADS)

    Maier, W. D.; Barnes, S.-J.; Gartz, V.; Andrews, G.

    2003-10-01

    The 3033 Ma Stella layered intrusion of South Africa consists largely of magnetite gabbros and gabbros that are hosted by greenstones of the Kraaipan belt. The intrusion contains a 100-m-thick, platinum group element (PGE) enriched interval that includes a number of laterally continuous PGE reefs constituting the oldest mineralization of this type known on Earth. The richest of the reefs is hosted by magnetitite and contains 10 15 ppm Pt + Pd over 1 m, representing by far the highest PGE grades known up to this time in magnetitite-hosted Pt-Pd reefs. The PGEs are interpreted to have been concentrated by sulfide melt, after S saturation had been reached in the advanced stages of magmatic differentiation, in response to magnetite crystallization. Reaction between sulfide melt and oxides led to late magmatic S loss, causing a paucity of sulfides in most of the PGE mineralized interval. As a result, the reefs cannot be distinguished macroscopically from their unmineralized host rocks, and we suggest that similar mineralization may have been overlooked in the upper parts of other tholeiitic intrusions elsewhere.

  8. Single Atom (Pd/Pt) Supported on Graphitic Carbon Nitride as an Efficient Photocatalyst for Visible-Light Reduction of Carbon Dioxide.

    PubMed

    Gao, Guoping; Jiao, Yan; Waclawik, Eric R; Du, Aijun

    2016-05-18

    Reducing carbon dioxide to hydrocarbon fuel with solar energy is significant for high-density solar energy storage and carbon balance. In this work, single atoms of palladium and platinum supported on graphitic carbon nitride (g-C3N4), i.e., Pd/g-C3N4 and Pt/g-C3N4, respectively, acting as photocatalysts for CO2 reduction were investigated by density functional theory calculations for the first time. During CO2 reduction, the individual metal atoms function as the active sites, while g-C3N4 provides the source of hydrogen (H*) from the hydrogen evolution reaction. The complete, as-designed photocatalysts exhibit excellent activity in CO2 reduction. HCOOH is the preferred product of CO2 reduction on the Pd/g-C3N4 catalyst with a rate-determining barrier of 0.66 eV, while the Pt/g-C3N4 catalyst prefers to reduce CO2 to CH4 with a rate-determining barrier of 1.16 eV. In addition, deposition of atom catalysts on g-C3N4 significantly enhances the visible-light absorption, rendering them ideal for visible-light reduction of CO2. Our findings open a new avenue of CO2 reduction for renewable energy supply. PMID:27116595

  9. Single Atom (Pd/Pt) Supported on Graphitic Carbon Nitride as an Efficient Photocatalyst for Visible-Light Reduction of Carbon Dioxide.

    PubMed

    Gao, Guoping; Jiao, Yan; Waclawik, Eric R; Du, Aijun

    2016-05-18

    Reducing carbon dioxide to hydrocarbon fuel with solar energy is significant for high-density solar energy storage and carbon balance. In this work, single atoms of palladium and platinum supported on graphitic carbon nitride (g-C3N4), i.e., Pd/g-C3N4 and Pt/g-C3N4, respectively, acting as photocatalysts for CO2 reduction were investigated by density functional theory calculations for the first time. During CO2 reduction, the individual metal atoms function as the active sites, while g-C3N4 provides the source of hydrogen (H*) from the hydrogen evolution reaction. The complete, as-designed photocatalysts exhibit excellent activity in CO2 reduction. HCOOH is the preferred product of CO2 reduction on the Pd/g-C3N4 catalyst with a rate-determining barrier of 0.66 eV, while the Pt/g-C3N4 catalyst prefers to reduce CO2 to CH4 with a rate-determining barrier of 1.16 eV. In addition, deposition of atom catalysts on g-C3N4 significantly enhances the visible-light absorption, rendering them ideal for visible-light reduction of CO2. Our findings open a new avenue of CO2 reduction for renewable energy supply.

  10. In situ {sup 13}C MAS NMR study of n-hexane conversion on Pt and Pd supported on basic materials. II. On the mechanism of isomerization and hydrocracking

    SciTech Connect

    Ivanova, I.I.; Seirvert, M.; Pasau-Claerbout, A.; Derouane, E.G.; Blom, N.

    1996-12-01

    {sup 13}C MAS NMR spectroscopy was performed in situ to investigate the mechanisms of n-hexane isomerization and hydrocracking on Pt and Pd supported on Al-stabilized magnesia (Pt/Mg(Al)O and Pd/Mg(Al)O), and Pt on KL zeolite (Pt/KL). All the catalysts had high metal dispersion, the metal particle sizes being 13, 11, and 18 {Angstrom}, respectively. n-Hexane 1-{sup 13}C was used for in situ label tracer experiments. {sup 13}C MAS NMR spectra were obtained during the time course of the reaction at 573 and 653 K. The NMR results were then quantified, and the reaction kinetics were studied. Identification of the primary and secondary labeled reaction products led to the conclusion that both cyclic and bond-shift isomerization mechanisms operate on the three catalysts. In the case of Pt/Mg(Al)O, the cyclic mechanism accounts for 80% of the isomerization products. In the case of Pt/KL and Pd/Mg(Al)O, the contribution of bond-shift reactions increases due to restricted formation of the methylcyclopentane intermediate on the former and to suppressed hydrogenolysis of methylcyclopentane on the latter. A nonselective cyclic isomerization mechanism operates on magnesia catalysts, while on Pt/KL selective bisecondary bond rupturing occurs. Mechanistic pathways of bond-shift and hydrocracking reactions involve both 1,3- and 2,4-metallocyclobutane intermediates in the case of magnesia-supported catalysts, while in the case of the Pt/KL catalyst a 1,3-metallocyclobutane intermediate is preferentially formed. Only terminal scission occurs on Pt/KL. The Pd catalyst demonstrates enhanced activity in demethylation. The observed differences in the mechanistic pathways are explained on the basis of the specific properties of the metal and support. 64 refs., 14 figs., 6 tabs.

  11. Effect of long-range order on elastic properties of Pd{sub 0.5}Ag{sub 0.5} alloy from first principles

    SciTech Connect

    Delczeg-Czirjak, E. K.; Nurmi, E.; Kokko, K.; Vitos, L.

    2011-09-01

    The effect of long-range order on single-crystal elastic constants of Pd{sub 0.5}Ag{sub 0.5} alloy has been investigated using first-principles electronic structure calculations. The lowest energy among the considered ordered, partially ordered, and disordered structures is found to be the L1{sub 1} layered structure, which is formed by alternate (111) Pd and Ag layers. The ordering effect is found to follow a clear trend: in contrast to the disordered phase, for which the K{sub a} and K{sub c} compressibilities are equal, the L1{sub 1} structure becomes less compressible along the c axis than along the a axis.

  12. {sup 45}Sc Solid State NMR studies of the silicides ScTSi (T=Co, Ni, Cu, Ru, Rh, Pd, Ir, Pt)

    SciTech Connect

    Harmening, Thomas; Eckert, Hellmut; Fehse, Constanze M.; Sebastian, C. Peter; Poettgen, Rainer

    2011-12-15

    The silicides ScTSi (T=Fe, Co, Ni, Cu, Ru, Rh, Pd, Ir, Pt) were synthesized by arc-melting and characterized by X-ray powder diffraction. The structures of ScCoSi, ScRuSi, ScPdSi, and ScIrSi were refined from single crystal diffractometer data. These silicides crystallize with the TiNiSi type, space group Pnma. No systematic influences of the {sup 45}Sc isotropic magnetic shift and nuclear electric quadrupolar coupling parameters on various structural distortion parameters calculated from the crystal structure data can be detected. {sup 45}Sc MAS-NMR data suggest systematic trends in the local electronic structure probed by the scandium atoms: both the electric field gradients and the isotropic magnetic shifts relative to a 0.2 M aqueous Sc(NO{sub 3}){sub 3} solution decrease with increasing valence electron concentration and within each T group the isotropic magnetic shift decreases monotonically with increasing atomic number. The {sup 45}Sc nuclear electric quadrupolar coupling constants are generally well reproduced by quantum mechanical electric field gradient calculations using the WIEN2k code. Highlights: Black-Right-Pointing-Pointer Arc-melting synthesis of silicides ScTSi. Black-Right-Pointing-Pointer Single crystal X-ray data of ScCoSi, ScRuSi, ScPdSi, and ScIrSi. Black-Right-Pointing-Pointer {sup 45}Sc solid state NMR of silicides ScTSi.

  13. A general and high-yield galvanic displacement approach to Au-M (M = Au, Pd, and Pt) core-shell nanostructures with porous shells and enhanced electrocatalytic performances.

    PubMed

    Kuai, Long; Geng, Baoyou; Wang, Shaozhen; Sang, Yan

    2012-07-23

    In this work, we utilize the galvanic displacement synthesis and make it a general and efficient method for the preparation of Au-M (M = Au, Pd, and Pt) core-shell nanostructures with porous shells, which consist of multilayer nanoparticles. The method is generally applicable to the preparation of Au-Au, Au-Pd, and Au-Pt core-shell nanostructures with typical porous shells. Moreover, the Au-Au isomeric core-shell nanostructure is reported for the first time. The lower oxidation states of Au(I), Pd(II), and Pt(II) are supposed to contribute to the formation of porous core-shell nanostructures instead of yolk-shell nanostructures. The electrocatalytic ethanol oxidation and oxygen reduction reaction (ORR) performance of porous Au-Pd core-shell nanostructures are assessed as a typical example for the investigation of the advantages of the obtained core-shell nanostructures. As expected, the Au-Pd core-shell nanostructure indeed exhibits a significantly reduced overpotential (the peak potential is shifted in the positive direction by 44 mV and 32 mV), a much improved CO tolerance (I(f)/I(b) is 3.6 and 1.63 times higher), and an enhanced catalytic stability in comparison with Pd nanoparticles and Pt/C catalysts. Thus, porous Au-M (M = Au, Pd, and Pt) core-shell nanostructures may provide many opportunities in the fields of organic catalysis, direct alcohol fuel cells, surface-enhanced Raman scattering, and so forth.

  14. Spin polarization and additional magneto-optical activity of nonmagnetic layers in Fe/Ag CMF

    NASA Astrophysics Data System (ADS)

    Xu, Y. B.; Zhai, H. R.; Lu, M.; Jin, Q. Y.; Miao, Y. Z.

    1992-08-01

    The experimental magneto-optical Kerr rotation spectra of Fe/Ag compositionally modulated films reported by Katayama et al. are studied theoretically. It is found that the free electrons of Ag are spin polarized. The magnitude of the polarization is about 1% with a direction opposite to that of Fe. The polarized Ag also gives rise to an additional magneto-optical activity as in Pt and Pd.

  15. Novel Galvanic Nanostructures of Ag and Pd for Efficient Laser Desorption/Ionization of Low Molecular Weight Compounds

    NASA Astrophysics Data System (ADS)

    Silina, Yuliya E.; Meier, Florian; Nebolsin, Valeriy A.; Koch, Marcus; Volmer, Dietrich A.

    2014-05-01

    A simple approach for synthesis of palladium and silver nanostructures with readily adjustable morphologies was developed using galvanic electrochemical deposition, for application to surface-assisted laser desorption/ionization (SALDI) of small biological molecules. A range of fatty acids, triglycerides, carbohydrates, and antibiotics were investigated to assess the performance of the new materials. Intense analyte cations were generated from the galvanic surfaces upon UV laser irradiation such as potassium adducts for a film thickness <100 nm (originating from impurities of the electrolyte solution) and Pd and Ag cluster ions for films with a thickness >120 nm. Possible laser desorption/ionization mechanisms of these galvanic structures are discussed. The films exhibited self-organizing abilities and adjustable morphologies by changing electrochemical parameters. They did not require any stabilizing agents and were inexpensive and very easy to produce. SALDI analysis showed that the materials were stable under ambient conditions and analytical results with excellent measurement reproducibility and detection sensitivity similar to MALDI were obtained. Finally, we applied the galvanic surfaces to fast screening of natural oils with minimum sample preparation.

  16. Hardening by cooling rate control and post-firing heat treatment in Pd-Ag-Sn alloy for bonding porcelain.

    PubMed

    Yu, Young-Jun; Seol, Hyo-Joung; Cho, Mi-Hyang; Kim, Hyung-Il; Kwon, Yong Hoon

    2016-01-01

    The aim of this study was to determine the hardening effect by controlling the cooling rate during the porcelain firing process and performing an additional post-firing heat treatment in a Pd-Ag-Sn alloy. The most effective cooling rate for alloy hardening was determined by cooling the specimens at various cooling rates after oxidation treatment. A subsequent porcelain firing simulation followed by cooling at the selected cooling rate was performed. A post-firing heat treatment was then done at 600°C in a porcelain furnace. The hardening mechanism was characterized by a hardness test, X-ray diffraction, field emission scanning electron microscopy and energy dispersive X-ray spectroscopy. Alloy softening occurred during the porcelain firing process followed by cooling at a controlled cooling rate. A post-firing heat treatment allowed apparent precipitation hardening. It is advisable to perform a postfiring heat treatment at 600°C in a porcelain furnace by annealing metal substructure after porcelain fusing.

  17. Hardening by cooling rate control and post-firing heat treatment in Pd-Ag-Sn alloy for bonding porcelain.

    PubMed

    Yu, Young-Jun; Seol, Hyo-Joung; Cho, Mi-Hyang; Kim, Hyung-Il; Kwon, Yong Hoon

    2016-01-01

    The aim of this study was to determine the hardening effect by controlling the cooling rate during the porcelain firing process and performing an additional post-firing heat treatment in a Pd-Ag-Sn alloy. The most effective cooling rate for alloy hardening was determined by cooling the specimens at various cooling rates after oxidation treatment. A subsequent porcelain firing simulation followed by cooling at the selected cooling rate was performed. A post-firing heat treatment was then done at 600°C in a porcelain furnace. The hardening mechanism was characterized by a hardness test, X-ray diffraction, field emission scanning electron microscopy and energy dispersive X-ray spectroscopy. Alloy softening occurred during the porcelain firing process followed by cooling at a controlled cooling rate. A post-firing heat treatment allowed apparent precipitation hardening. It is advisable to perform a postfiring heat treatment at 600°C in a porcelain furnace by annealing metal substructure after porcelain fusing. PMID:27041022

  18. [Thermal expansion of Au-Pd-Ag system alloys. Casting stress and deformation of addition of Sn and In].

    PubMed

    Ohkuma, K

    1989-03-01

    To study the dimensional changes due to the release of casting stress in metal-ceramic alloys, a wheel-like pattern in which casting stress is liable to occur and rod- and barrel-like wax patterns in which the likelihood of such stress is low, were investigated with a phosphate-bonded investment compound. Furthermore, simultaneous casting was done using Au-Pd-Ag system alloys, 21 types of mother alloys and alloys with tin or indium or both, and accurate determinations of the thermal expansion rate with increased or decreased temperature were carried out. The results obtained were as follows. The mean thermal expansion rates of the mother alloys and the alloys with tin and indium upon increase and decrease of temperature were lowest for the large wheel-like pattern, followed by the small wheel-like pattern, rod-like pattern and barrel-like pattern, in that order. The mean thermal expansion rates of the mother alloys and the alloys with tin or indium or both were decreased when the palladium content was increased, but tended to increase when the silver content was higher. Gold had no influence on the thermal expansion rate. When the temperature decreased, the complex addition of tin and indium provided alloys showing only a slight deformation. PMID:2690394

  19. Quantitative description of short-range order and its influence on the electronic structure in Ag-Pd alloys

    NASA Astrophysics Data System (ADS)

    Hoffmann, M.; Marmodoro, A.; Ernst, A.; Hergert, W.; Dahl, J.; Lång, J.; Laukkanen, P.; Punkkinen, M. P. J.; Kokko, K.

    2016-08-01

    We investigate the effect of short-range order (SRO) on the electronic structure in alloys from the theoretical point of view using density of states (DOS) data. In particular, the interaction between the atoms at different lattice sites is affected by chemical disorder, which in turn is reflected in the fine structure of the DOS and, hence, in the outcome of spectroscopic measurements. We aim at quantifying the degree of potential SRO with a proper parameter. The theoretical modeling is done with the Korringa–Kohn–Rostoker Green’s function method. Therein, the extended multi-sublattice non-local coherent potential approximation is used to include SRO. As a model system, we use the binary solid solution Ag c Pd1‑c at three representative concentrations c  =  0.25, 0.5 and 0.75. The degree of SRO is varied from local ordering to local segregation through an intermediate completely uncorrelated state. We observe some pronounced features, which change over the whole energy range of the valence bands as a function of SRO in the alloy. These spectral variations should be traceable in modern photoemission experiments.

  20. Quantitative description of short-range order and its influence on the electronic structure in Ag-Pd alloys

    NASA Astrophysics Data System (ADS)

    Hoffmann, M.; Marmodoro, A.; Ernst, A.; Hergert, W.; Dahl, J.; Lång, J.; Laukkanen, P.; Punkkinen, M. P. J.; Kokko, K.

    2016-08-01

    We investigate the effect of short-range order (SRO) on the electronic structure in alloys from the theoretical point of view using density of states (DOS) data. In particular, the interaction between the atoms at different lattice sites is affected by chemical disorder, which in turn is reflected in the fine structure of the DOS and, hence, in the outcome of spectroscopic measurements. We aim at quantifying the degree of potential SRO with a proper parameter. The theoretical modeling is done with the Korringa-Kohn-Rostoker Green’s function method. Therein, the extended multi-sublattice non-local coherent potential approximation is used to include SRO. As a model system, we use the binary solid solution Ag c Pd1-c at three representative concentrations c  =  0.25, 0.5 and 0.75. The degree of SRO is varied from local ordering to local segregation through an intermediate completely uncorrelated state. We observe some pronounced features, which change over the whole energy range of the valence bands as a function of SRO in the alloy. These spectral variations should be traceable in modern photoemission experiments.

  1. Contribution of β' and β precipitates to hardening in as-solutionized Ag-20Pd-12Au-14.5Cu alloys for dental prosthesis applications.

    PubMed

    Kim, Yonghwan; Niinomi, Mitsuo; Hieda, Junko; Nakai, Masaaki; Cho, Ken; Fukui, Hisao

    2014-04-01

    Dental Ag-20Pd-12Au-14.5Cu alloys exhibit a unique hardening behavior, which the mechanical strengths enhance significantly which enhances the mechanical strength significantly after high-temperature (1123K) solution treatment without aging treatment. The mechanism of the unique hardening is not clear. The contribution of two precipitates (β' and β phases) to the unique hardening behavior in the as-solutionized Ag-20Pd-12Au-14.5Cu alloys was investigated. In addition, the chemical composition of the β' phase was investigated. The fine β' phase densely precipitates in a matrix. The β' phase (semi-coherent precipitate), which causes lattice strain, contributes greatly to the unique hardening behavior. On the other hand, the coarse β phase sparsely precipitates in the matrix. The contribution of the β phase (incoherent precipitate), which does not cause lattice strain, is small. The chemical composition of the β' phase was determined. This study reveals that the fine β' phase precipitated by high-temperature solution treatment leads to the unique hardening behavior in dental Ag-20Pd-12Au-14.5Cu alloys in the viewpoints of the lattice strain contrast and interface coherency. It is expected to make the heat treatment process more practical for hardening. The determined chemical composition of β' phase would be helpful to study an unknown formation process of β' phase.

  2. 1H, 13C, 195Pt and 15N NMR structural correlations in Pd(II) and Pt(II) chloride complexes with various alkyl and aryl derivatives of 2,2'-bipyridine and 1,10-phenanthroline.

    PubMed

    Pawlak, Tomasz; Pazderski, Leszek; Sitkowski, Jerzy; Kozerski, Lech; Szłyk, Edward

    2011-02-01

    (1)H, (13)C, (195)Pt and (15)N NMR studies of platinide(II) (M = Pd, Pt) chloride complexes with such alkyl and aryl derivatives of 2,2'-bipyridine and 1,10-phenanthroline as LL = 6,6'-dimethyl-bpy, 5,5'-dimethyl-bpy, 4,4'-di-tert-butyl-bpy, 2,9-dimethyl-phen, 2,9-dimethyl-4,7-diphenyl-phen, 3,4,7,8-tetramethyl-phen, having the general [M(LL)Cl(2)] formula were performed and the respective chemical shifts (δ(1H), δ(13C), δ(195Pt), δ(15N)) reported. (1)H high-frequency coordination shifts (Δ(coord)(1H) = δ(complex)(1H)-δ(ligand)(1H)) mostly pronounced for nitrogen-adjacent protons and methyl groups in the nearest adjacency of nitrogen, as well as (15)N low-frequency coordination shifts (Δ(coord)(15H) = δ(complex)(15H)-δ(ligand)(15H)) were discussed in relation to the molecular structures.

  3. New N^C^N-coordinated Pd(ii) and Pt(ii) complexes of a tridentate N-heterocyclic carbene ligand featuring a 6-membered central ring: synthesis, structures and luminescence.

    PubMed

    Moussa, Jamal; Haddouche, Kamel; Chamoreau, Lise-Marie; Amouri, Hani; Gareth Williams, J A

    2016-08-01

    We describe Pd(ii) and Pt(ii) complexes of an N^C^N-coordinating pincer-like ligand featuring two lateral pyridine rings and a 6-membered carbene core. Their crystal structures display 1-dimensional chains with short π-π and M(ii)M(ii) interactions. Such interactions also impact on the photophysical properties, with the Pt(ii) complex being luminescent in the solid state at room temperature. PMID:27465432

  4. The Development of a PdCr Integral Weldable Strain Measurement System Based on NASA Lewis PdCr/Pt Strain Sensor for User-Friendly Elevated Temperature Strain Measurements

    NASA Technical Reports Server (NTRS)

    Wnuk, S. P., Jr.; Wnuk, V. P.

    1997-01-01

    This report describes the development of a user friendly weldable strain gage employing the NASA Lewis PdCr/Pt wire strain sensor. The NASA sensors are pre-attached to Hastelloy X or Titanium alloy shims using name spray techniques developed under previous NASA programs. The weldable sensors are then pre-stabilized for 50 hours at 780 C in air. A weldable terminal and high temperature cable is then connected to the sensor and the assembly is pre-calibrated over the full test temperature range. Calibrated resistors are inserted into a bridge completion module at the cool end of the cable to condition the sensor in half or full bridge configuration. The sensor is attached to the structure using a common capacitive discharge spot welder. No additional high temperature stabilization or calibration is required. The resultant device is a pre-calibrated strain transducer which can be plugged into any common variety strain instrumentation.

  5. Site-specific growth of AgPd nanodendrites on highly purified Au bipyramids with remarkable catalytic performance

    NASA Astrophysics Data System (ADS)

    Zhou, Lin; Liu, Zeke; Zhang, Han; Cheng, Si; Fan, Li-Juan; Ma, Wanli

    2014-10-01

    Au nanorods have been extensively explored in various applications as the template for heterogeneous metallic nanostructures. However, Au bipyramids (AuBPs) have been paid much less attention although they possess an intriguing crystalline structure and extremely superior plasmonic properties which are absent in AuNRs. The state-of-the-art synthesis cannot produce pure AuBPs, which has become a major barrier to their various applications like catalysis since purity is often critical for achieving the desired performance. Herein, we have shown a facile approach to obtain large-scale high-purity AuBPs. The purity of AuBPs can be improved from 30 to 50% for the as-synthesized AuBP solution to over 95% for the purified solution. Site-specific growth of AgPd nanodendrites on multiply twinned AuBPs from core-shell to tipped nanostructures was achieved for the first time by coupling a galvanic replacement with a co-reduction process, which show remarkable catalytic activity in the reduction reaction of 4-nitrophenol (4-NP) by NaBH4. The use of ascorbic acid (AA) as a reductant in the co-reduction process and the intriguing crystalline structure of AuBPs play a critical role in forming these unique structures. We believe that this work would provide a general strategy to prepare high-purity AuBP based trimetallic nanostructures, which offers the opportunity for AuBPs to be widely used in catalysis or other plasmonic-effect related applications in the near future.Au nanorods have been extensively explored in various applications as the template for heterogeneous metallic nanostructures. However, Au bipyramids (AuBPs) have been paid much less attention although they possess an intriguing crystalline structure and extremely superior plasmonic properties which are absent in AuNRs. The state-of-the-art synthesis cannot produce pure AuBPs, which has become a major barrier to their various applications like catalysis since purity is often critical for achieving the desired

  6. 5f delocalization-induced suppression of quadrupolar order in U(Pd1-xPtx)₃

    SciTech Connect

    Walker, H. C.; Le, M. D.; McEwen, K. A.; Bleckmann, M.; Süllow, S.; Mazzoli, C.; Wilkins, S. B.; Fort, D.

    2011-12-27

    We present bulk magnetic and transport measurements and x-ray resonant scattering measurements on U(Pd1-xPtx)₃ for x=0.005 and 0.01, which demonstrate the high sensitivity of the quadrupolar order in the canonical antiferroquadrupolar ordered system UPd₃ to doping with platinum. Bulk measurements for x=0.005 reveal behavior similar to that seen in UPd₃, albeit at a lower temperature, and x-ray resonant scattering provides evidence of quadrupolar order described by the Qxy order parameter. In contrast, bulk measurements reveal only an indistinct transition in x=0.01, consistent with the observation of short-range quadrupolar order in our x-ray resonant scattering results.

  7. A theoretical investigation on hydrolysis mechanism of biologically relevant Pt(II)/Pd(II) complexes with σ-donor and π-acceptor carrier ligand

    NASA Astrophysics Data System (ADS)

    Reddy B., Venkata P.; Mitra, Ishani; Mukherjee, Subhajit; Sengupta, P. S.; Dodda, Subba Reddy; Moi, Sankar Ch.

    2016-07-01

    The hydrolysis mechanism of cytotoxic agents complex 1 cis-[Pt(pic)Cl2] and complex 2 cis-[Pd(pic)Cl2] (where pic = 2-aminomethylpyridine) have been studied in solvent phase using DFT. The stationary states on potential energy surfaces were fully optimized and characterized. The rate constants and activation parameters of both the substitution processes has been calculated in CPCM model and the values were found to be k1 = 3.29 × 10-4 s-1, k2 = 8.88 × 10-9 s-1 for complex 1 and k1 = 0.13 × 10-1 s-1, k2 = 2.0 × 10-10 s-1 for complex 2 respectively. The second step is the rate-limiting process having higher activation energy compared to that of the first step for both the complexes.

  8. Large exchange bias enhancement in (Pt(or Pd)/Co)/IrMn/Co trilayers with ultrathin IrMn thanks to interfacial Cu dusting

    SciTech Connect

    Vinai, G.; Moritz, J.; Bandiera, S.; Prejbeanu, I. L.; Dieny, B.

    2014-04-21

    The magnitude of exchange bias (H{sub ex}) at room temperature can be significantly enhanced in IrMn/Co and (Pt(or Pd)/Co)/IrMn/Co structures thanks to the insertion of an ultrathin Cu dusting layer at the IrMn/Co interface. The combination of trilayer structure and interfacial Cu dusting leads to a three-fold increase in H{sub ex} as compared to the conventional IrMn/Co bilayer structure, with an increased blocking temperature (T{sub B}) and a concave curvature of the temperature dependence H{sub ex}(T), ideal for improved Thermally Assisted-Magnetic Random Access Memory storage layer. This exchange bias enhancement is ascribed to a reduction of the spin frustration at the IrMn/Co interface thanks to interfacial Cu addition.

  9. Electro-catalytic activity of multiwall carbon nanotube-metal (Pt or Pd) nanohybrid materials synthesized using microwave-induced reactions and their possible use in fuel cells

    PubMed Central

    V, Lakshman Kumar; Ntim, Susana Addo; Sae-Khow, Ornthida; Janardhana, Chelli; Lakshminarayanan, V.; Mitra, Somenath

    2012-01-01

    Microwave induced reactions for immobilizing platinum and palladium nanoparticles on multiwall carbon nanotubes are presented. The resulting hybrid materials were used as catalysts for direct methanol, ethanol and formic acid oxidation in acidic as well as alkaline media. The electrodes are formed by simply mixing the hybrids with graphite paste, thus using a relatively small quantity of the precious metal. We report Tafel slopes and apparent activation energies at different potentials and temperatures. Ethanol electro-oxidation with the palladium hybrid showed an activation energy of 7.64 kJmol−1 which is lower than those observed for other systems. This system is economically attractive because Pd is significantly less expensive than Pt and ethanol is fast evolving as a commercial biofuel. PMID:23118490

  10. Electro-catalytic activity of multiwall carbon nanotube-metal (Pt or Pd) nanohybrid materials synthesized using microwave-induced reactions and their possible use in fuel cells.

    PubMed

    V, Lakshman Kumar; Ntim, Susana Addo; Sae-Khow, Ornthida; Janardhana, Chelli; Lakshminarayanan, V; Mitra, Somenath

    2012-11-30

    Microwave induced reactions for immobilizing platinum and palladium nanoparticles on multiwall carbon nanotubes are presented. The resulting hybrid materials were used as catalysts for direct methanol, ethanol and formic acid oxidation in acidic as well as alkaline media. The electrodes are formed by simply mixing the hybrids with graphite paste, thus using a relatively small quantity of the precious metal. We report Tafel slopes and apparent activation energies at different potentials and temperatures. Ethanol electro-oxidation with the palladium hybrid showed an activation energy of 7.64 kJmol(-1) which is lower than those observed for other systems. This system is economically attractive because Pd is significantly less expensive than Pt and ethanol is fast evolving as a commercial biofuel.

  11. Characterization of Ni19.5Ti50.5Pd25Pt5 High-Temperature Shape Memory Alloy Springs and their Potential Application in Aeronautics

    NASA Technical Reports Server (NTRS)

    Stebner, Aaron; Padula, Santo A.; Noebe, Ronald D.

    2008-01-01

    Shape memory alloys (SMAs) have been used as actuators in many different industries since the discovery of the shape memory effect, but the use of SMAs as actuation devices in aeronautics has been limited due to the temperature constraints of commercially available materials. Consequently, work is being done at NASA's Glenn Research Center to develop new SMAs capable of being used in high temperature environments. One of the more promising high-temperature shape memory alloys (HTSMAs) is Ni19.5Ti50.5Pd25Pt5. Recent work has shown that this material is capable of being used in operating environments of up to 250 C. This material has been shown to have very useful actuation capabilities, demonstrating repeatable strain recoveries up to 2.5% in the presence of an externally applied load. Based on these findings, further work has been initiated to explore potential applications and alternative forms of this alloy, such as springs. Thus, characterization of Ni19.5Ti50.5Pd25Pt5 springs, including their mechanical response and how variations in this response correlate to changes in geometric parameters, are discussed. The effects of loading history, or training, on spring behavior were also investigated. A comparison of the springs with wire actuators is made and the benefits of using one actuator form as opposed to the other discussed. These findings are used to discuss design considerations for a surge-control mechanism that could be used in the centrifugal compressor of a T-700 helicopter engine.

  12. Ultrasonic-electrodeposition of PtPd alloy nanoparticles on ionic liquid-functionalized graphene paper: towards a flexible and versatile nanohybrid electrode.

    PubMed

    Sun, Yimin; Zheng, Huaming; Wang, Chenxu; Yang, Mengmeng; Zhou, Aijun; Duan, Hongwei

    2016-01-21

    Here we fabricate a new type of flexible and versatile nanohybrid paper electrode by ultrasonic-electrodeposition of PtPd alloy nanoparticles on freestanding ionic liquid (IL)-functionalized graphene paper, and explore its multifunctional applications in electrochemical catalysis and sensing systems. The graphene-based paper materials demonstrate intrinsic flexibility, exceptional mechanical strength and high electrical conductivity, and therefore can serve as an ideal freestanding flexible electrode for electrochemical devices. Furthermore, the functionalization of graphene with IL (i.e., 1-butyl-3-methylimidazolium tetrafluoroborate) not only increases the electroactive surface area of a graphene-based nanohybrid paper electrode, but also improves the adhesion and dispersion of metal nanoparticles on the paper surface. These unique attributes, combined with the merits of an ultrasonic-electrodeposition method, lead to the formation of PtPd alloy nanoparticles on IL-graphene paper with high loading, uniform distribution, controlled morphology and favourable size. Consequently, the resultant nanohybrid paper electrode exhibits remarkable catalytic activity as well as excellent cycle stability and improved anti-poisoning ability towards electrooxidation of fuel molecules such as methanol and ethanol. Furthermore, for nonenzymatic electrochemical sensing of some specific biomarkers such as glucose and reactive oxygen species, the nanohybrid paper electrode shows high selectivity, sensitivity and biocompatibility in these bio-catalytic processes, and can be used for real-time tracking hydrogen peroxide secretion by living human cells. All these features demonstrate its promising application as a versatile nanohybrid electrode material in flexible and lightweight electrochemical energy conversion and biosensing systems such as bendable on-chip power sources, wearable/implantable detectors and in vivo micro-biosensors. PMID:26681401

  13. Characterization of Ni 19.5Ti 50.5Pd 25Pt 5 high-temperature shape memory alloy springs and their potential applications in aeronautics

    NASA Astrophysics Data System (ADS)

    Stebner, Aaron; Padula, Santo A., II; Noebe, Ronald D.; Quinn, D. Dane

    2008-03-01

    Shape memory alloys (SMAs) have been used as actuators in many different industries since the discovery of the shape memory effect, but the use of SMAs as actuation devices in aeronautics has been limited due to the temperature constraints of commercially available materials. Consequently, work is being done at NASA's Glenn Research Center to develop new SMAs capable of being used in high temperature environments. One of the more promising high-temperature shape memory alloys (HTSMAs) is Ni 19.5Ti 50.5Pd 25Pt 5. Recent work has shown that this material is capable of being used in operating environments of up to 250°C. This material has been shown to have very useful actuation capabilities, demonstrating repeatable strain recoveries up to 2.5% in the presence of an externally applied load. Based on these findings, further work has been initiated to explore potential applications and alternative forms of this alloy, such as springs. Thus, characterization of Ni 19.5Ti 50.5Pd 25Pt 5 springs, including their mechanical response and how variations in this response correlate to changes in geometric parameters, are discussed. The effects of loading history, or training, on spring behavior were also investigated. A comparison of the springs with wire actuators is made and the benefits of using one actuator form as opposed to the other discussed. These findings are used to discuss design considerations for a surge-control mechanism that could be used in the centrifugal compressor of a T-700 helicopter engine.

  14. Electrochemical promotion of propane oxidation on Pt deposited on a dense β″-Al2O3 ceramic Ag+ conductor

    PubMed Central

    Tsampas, Mihalis N.; Kambolis, Anastasios; Obeid, Emil; Lizarraga, Leonardo; Sapountzi, Foteini M.; Vernoux, Philippe

    2013-01-01

    A new kind of electrochemical catalyst based on a Pt porous catalyst film deposited on a β″-Al2O3 ceramic Ag+ conductor was developed and evaluated during propane oxidation. It was observed that, upon anodic polarization, the rate of propane combustion was significantly electropromoted up to 400%. Moreover, for the first time, exponential increase of the catalytic rate was evidenced during galvanostatic transient experiment in excellent agreement with EPOC equation. PMID:24790942

  15. Precipitation of β' phase and hardening in dental-casting Ag-20Pd-12Au-14.5Cu alloys subjected to aging treatments.

    PubMed

    Kim, Yonghwan; Niinomi, Mitsuo; Hieda, Junko; Nakai, Masaaki; Cho, Ken; Fukui, Hisao

    2014-03-01

    The age-hardening behavior of the dental-casting Ag-20Pd-12Au-14.5Cu alloy subjected to aging treatment at around 673K is well known, and this hardening has been widely employed in various applications. To date, the age-hardening of this alloy has been explained to attribute to the precipitation of a β phase, which is a B2-type ordered CuPd phase or PdCuxZn1-x phase. In this study, results obtained from microstructural observations using a transmission electron microscopy and a scanning transmission electron microscopy revealed that a fine L10-type ordered β' phase precipitated in the matrix and a coarse-structure region (consisting of Ag- and Cu-rich regions) appeared after aging treatment at 673K and contributed to increase in hardness. The microstructure of the coarse β phase, which existed before aging treatment, did not change by aging treatment. Thus, it is concluded that the fine β' phase precipitated by aging treatment contributed more to increase in hardness than the coarse-structure region and coarse β phase.

  16. Interfacial Engineering of Bimetallic Ag/Pt Nanoparticles on Reduced Graphene Oxide Matrix for Enhanced Antimicrobial Activity.

    PubMed

    Zhang, Mei; Zhao, Yanhua; Yan, Li; Peltier, Raoul; Hui, Wenli; Yao, Xi; Cui, Yali; Chen, Xianfeng; Sun, Hongyan; Wang, Zuankai

    2016-04-01

    Environmental biofouling caused by the formation of biofilm has been one of the most urgent global concerns. Silver nanoparticles (NPs), owing to their wide-spectrum antimicrobial property, have been widely explored to combat biofilm, but their extensive use has raised growing concern because they persist in the environment. Here we report a novel hybrid nanocomposite that imparts enhanced antimicrobial activity and low cytotoxicity yet with the advantage of reduced silver loading. The nanocomposite consists of Pt/Ag bimetallic NPs (BNPs) decorated on the porous reduced graphene oxide (rGO) nanosheets. We demonstrate that the enhanced antimicrobial property against Escherichia coli is ascribed to the intricate control of the interfaces between metal compositions, rGO matrix, and bacteria, where the BNPs lead to a rapid release of silver ions, and the trapping of bacteria by the porous rGO matrix further provides high concentration silver ion sites for efficient bacteria-bactericide interaction. We envision that our facile approach significantly expands the design space for the creation of silver-based antimicrobial materials to achieve a wide spectrum of functionalities. PMID:27007980

  17. Photocatalytic Properties of TiO2 Thin Films Modified with Ag and Pt Nanoparticles Deposited by Gas Flow Sputtering.

    PubMed

    Maicu, M; Glöss, D; Frach, Peter; Hecker, D; Gerlach, G; Córdoba, José M

    2015-09-01

    In this work, a gas flow sputtering (GFS) process which allows the production and deposition of metal nanoparticles (NPs) in a vacuum environment is described. Aim of the study is to prove the potential of this technology for the fabrication of new TiO2 films with enhanced photocatalytic properties. For this purpose, Ag and Pt NPs have been produced and deposited on photocatalytic float glass coated with TiO2 thin films by magnetron sputtering. The influence of the process parameters and of the metal amount on the final properties of the particles (quantity, size, size distribution, oxidation state etc.,) was widely investigated. Moreover, the effect of the NPs on the photocatalytic activity of the resulting materials was evaluated for the case of the decomposition of stearic acid (SA) during UV-A irradiation. The reduction of the water contact angle (WCA) during the irradiation period was measured in order to test the photo-induced super-hydrophilicity (PSH). PMID:26716202

  18. 45Sc Solid State NMR studies of the silicides Sc TSi ( T=Co, Ni, Cu, Ru, Rh, Pd, Ir, Pt)

    NASA Astrophysics Data System (ADS)

    Harmening, Thomas; Eckert, Hellmut; Fehse, Constanze M.; Sebastian, C. Peter; Pöttgen, Rainer

    2011-12-01

    The silicides Sc TSi ( T=Fe, Co, Ni, Cu, Ru, Rh, Pd, Ir, Pt) were synthesized by arc-melting and characterized by X-ray powder diffraction. The structures of ScCoSi, ScRuSi, ScPdSi, and ScIrSi were refined from single crystal diffractometer data. These silicides crystallize with the TiNiSi type, space group Pnma. No systematic influences of the 45Sc isotropic magnetic shift and nuclear electric quadrupolar coupling parameters on various structural distortion parameters calculated from the crystal structure data can be detected. 45Sc MAS-NMR data suggest systematic trends in the local electronic structure probed by the scandium atoms: both the electric field gradients and the isotropic magnetic shifts relative to a 0.2 M aqueous Sc(NO 3) 3 solution decrease with increasing valence electron concentration and within each T group the isotropic magnetic shift decreases monotonically with increasing atomic number. The 45Sc nuclear electric quadrupolar coupling constants are generally well reproduced by quantum mechanical electric field gradient calculations using the WIEN2k code.

  19. Simplified method for the determination of Ru, Pd, Re, Os, Ir and Pt in chromitites and other geological materials by isotope dilution ICP-MS and acid digestion.

    PubMed

    Meisel, T; Moser, J; Fellner, N; Wegscheider, W; Schoenberg, R

    2001-03-01

    A method for the determination of low Ru, Pd, Re, Os, Ir and Pt abundances in geological reference materials by isotope dilution inductively coupled plasma mass spectrometry (ICP-MS) after acid digestion in a high pressure asher (HPA-S) is presented. The digestion technique is similar to that using Carius tubes but easier to handle and reaches higher temperatures. Osmium can be determined as OsO4 with ICP-MS directly after digestion through a sparging technique. The remaining elements are preconcentrated by means of anion column chromatography. The resin is digested directly without elution leading to high yields but this causes problems if Zr is present at higher levels in the silicate rich materials. The analytical results for international platinum group element (PGE) reference materials, chromitite CHR-Bkg, basalt TDB-1 and gabbro WGB-1, are presented and compared with literature data, demonstrating the validity of the described method. Although higher in concentration, PGEs determined for reference material WGB-1 were worse than for TDB-1 indicating a more inhomogeneous distribution of the platinum group mineral phases. The low PGE abundance chromitite standard, CHR-Bkg, is likely to be homogeneous for Ru, Re, Os and Ir and is recommended as a reference material for the study of chromitites. Detection limits (3s x total procedure blank) range from 0.012 ng (Re and Os) to 0.77 ng (Pt), which could be further improved by applying higher quality acids.

  20. Simplified method for the determination of Ru, Pd, Re, Os, Ir and Pt in chromitites and other geological materials by isotope dilution ICP-MS and acid digestion.

    PubMed

    Meisel, T; Moser, J; Fellner, N; Wegscheider, W; Schoenberg, R

    2001-03-01

    A method for the determination of low Ru, Pd, Re, Os, Ir and Pt abundances in geological reference materials by isotope dilution inductively coupled plasma mass spectrometry (ICP-MS) after acid digestion in a high pressure asher (HPA-S) is presented. The digestion technique is similar to that using Carius tubes but easier to handle and reaches higher temperatures. Osmium can be determined as OsO4 with ICP-MS directly after digestion through a sparging technique. The remaining elements are preconcentrated by means of anion column chromatography. The resin is digested directly without elution leading to high yields but this causes problems if Zr is present at higher levels in the silicate rich materials. The analytical results for international platinum group element (PGE) reference materials, chromitite CHR-Bkg, basalt TDB-1 and gabbro WGB-1, are presented and compared with literature data, demonstrating the validity of the described method. Although higher in concentration, PGEs determined for reference material WGB-1 were worse than for TDB-1 indicating a more inhomogeneous distribution of the platinum group mineral phases. The low PGE abundance chromitite standard, CHR-Bkg, is likely to be homogeneous for Ru, Re, Os and Ir and is recommended as a reference material for the study of chromitites. Detection limits (3s x total procedure blank) range from 0.012 ng (Re and Os) to 0.77 ng (Pt), which could be further improved by applying higher quality acids. PMID:11284333

  1. CO 2 Adsorption on Anatase TiO 2 (101) Surfaces in the Presence of Subnanometer Ag/Pt Clusters: Implications for CO 2 Photoreduction

    DOE PAGES

    Yang, Chi-Ta; Wood, Brandon C.; Bhethanabotla, Venkat R.; Joseph, Babu

    2014-10-20

    We show how CO2 adsorption on perfect and reduced anatase TiO2 (101) surfaces can be substantially modified by the presence of surface Ag and Pt octamer clusters, using density functional theory calculations. Furthermore, we found that adsorption was affected even at sites where the adsorbate was not in direct contact with the octamer, which we attributed to charge donation to CO2 from the Ag/Pt-modified surface, as well as an electrostatic competition between attractive (Ti–O) and repulsive (Ti–C) interactions. Additionally, TiO2-supported Pt octamers offer key advantages that could be leveraged for CO2 photoreduction, including providing additional stable adsorption sites for bentmore » CO2 species and facilitating charge transfer to aid in CO2– anion formation. Electronic structure analysis suggests these factors arise primarily from the hybridization of the bonding molecular orbitals of CO2 with d orbitals of the Pt atoms. Our results show that, for adsorption on TiO2-supported Pt octamers, the O–C–O bending and C–O asymmetric stretching frequencies can be used as reliable indicators of the presence of the CO2– anion intermediate as well as to distinguish unique adsorption geometries or sites. Finally, we suggest a possible pathway for subsequent CO2 dissociation to CO at the surface of a reduced anatase TiO2 (101)-supported Pt octamer, which has a computed energy barrier of 1.01 eV.« less

  2. Titanocene-phosphine derivatives as precursors to cytotoxic heterometallic TiAu2 and TiM (M = Pd, Pt) compounds. Studies of their interactions with DNA.

    PubMed

    González-Pantoja, Jose F; Stern, Michael; Jarzecki, Andrzej A; Royo, Eva; Robles-Escajeda, Elisa; Varela-Ramírez, Armando; Aguilera, Renato J; Contel, María

    2011-11-01

    A series of tri- and bimetallic titanium-gold, titanium-palladium, and titanium-platinum derivatives of the general formulas [Ti{η(5)-C(5)H(4)(CH(2))(n)PPh(2)(AuCl)}(2)]·2THF [n = 0 (1); n = 2 (2); n = 3 (3)] and [TiCl(2){η(5)-C(5)H(4)κ-(CH(2))(n)PPh(2)}(2)(MCl(2))]·2THF [M = Pd, n = 0 (4); n = 2 (5); n = 3 (6) ; M = Pt, n = 0 (7); n = 2 (8); n = 3 (9)] have been synthesized and characterized by different spectroscopic techniques and mass spectrometry. The molecular structures of compounds 1-9 have been investigated by means of density functional theory calculations. The calculated IR spectra of the optimized structures fit well with the experimental IR data obtained for 1-9. The stability of the heterometallic compounds in deuterated solvents [CDCl(3), dimethyl sulfoxide (DMSO)-d(6), and mixtures 50:50 DMSO-d(6)/D(2)O and 1:99 DMSO-d(6)/D(2)O at acidic and neutral pH] has been evaluated by (31)P and (1)H NMR spectroscopy showing a higher stability for these compounds than for Cp(2)TiCl(2) or precursors [Ti{η(5)-C(5)H(4)(CH(2))(n)PPh(2)}(2)]. The new compounds display a lower acidity (1-2 units) than Cp(2)TiCl(2). The decomposition products have been identified over time. Complexes 1-9 have been tested as potential anticancer agents, and their cytotoxicity properties were evaluated in vitro against HeLa human cervical carcinoma and DU-145 human prostate cancer cells. TiAu(2) and TiPd compounds were highly cytotoxic for these two cell lines. The interactions of the compounds with calf thymus DNA have been evaluated by thermal denaturation (1-9) and by circular dichroism (1, 3, 4, and 7) spectroscopic methods. All of these complexes show a stronger interaction with DNA than that displayed by Cp(2)TiCl(2) at neutral pH. The data are consistent with electrostatic interactions with DNA for TiAu(2) compounds and for a covalent binding mode for TiM (M = Pd, Pt) complexes.

  3. One-pot facile synthesis of reusable tremella-like M1@M2@M1(OH)2 (M1 = Co, Ni, M2 = Pt/Pd, Pt, Pd and Au) three layers core-shell nanostructures as highly efficient catalysts.

    PubMed

    Liu, Yadong; Fang, Zhen; Kuai, Long; Geng, Baoyou

    2014-08-21

    In this work, a general, facile, successive and eco-friendly method for multilayer nanostructures has been established for the first time. We take full advantage of the structural and compositional character of M1@M2 (M1 = Co, Ni, M2 = Pt/Pd, Pt, Pd and Au) core-shell nanostructures to prepare a series of reusable tremella-like M1@M2@M1(OH)2 three layer core-shell or yolk-shell nanocomposites with a magnetic core, a porous noble metal shell, and an ultrathin cobalt or nickel hydroxide shell. We evaluated their catalytic performance using a model reaction based on the reduction of 4-nitrophenol. These novel M1@M2@M1(OH)2 nanomaterials with a unique internal micro environment promoted the efficiency of the catalytic reaction, prolonged the service life of the catalyst and enhanced the overall activity of the catalyst in the catalytic process. The novel three layer core-shell nanocomposites can be extended to other applications such as biomedical detection, energy conversion and storage systems. PMID:25008373

  4. Low temperature processing of single domain YBa 2Cu 3O y thick films from Y 2O 3 fabrics on Ag-Pd alloy substrates

    NASA Astrophysics Data System (ADS)

    Reddy, E. S.; Goodilin, E. A.; Tarka, M.; Zeisberger, M.; Schmitz, G. J.

    2002-08-01

    Single domain YBa 2Cu 3O y (Y123) thick films (∼100 μm) were fabricated on untextured Ag12 wt.%Pd alloy substrates from Y 2O 3 cloths by an infiltration and growth process. The process involves the infiltration of Y 2O 3 cloths placed on metallic substrates by barium cuprates and copper oxide liquids at 970 °C. The infiltrated Y 2O 3 cloth is subsequently transformed into single domain Y123 during a slow cooling schedule in the presence of a c-axis oriented Nd123 seed crystal placed at the top center of the fabric. The solidification window for single domain growth is lowered to 970-950 °C using liquid phases containing up 10 wt.% Ag and small amounts of BaF 2.

  5. Experimental partitioning studies near the Fe-FeS eutectic, with an emphasis on elements important to iron meteorite chronologies (Pb, Ag, Pd, and Tl)

    NASA Technical Reports Server (NTRS)

    Jones, J. H.; Hart, S. R.; Benjamin, T. M.

    1993-01-01

    Partitioning coefficients for metal/sulfide liquid, troilite/sulfide liquid, and schreibersite/sulfide liquid were determined for Ag, Au, Mo, Ni, Pd, and Tl (using EMPA and proton-induced X-ray microprobe and ion microprobe analyses) in order to understand the chronometer systems of iron meteorites. In general, the obtained schreibersite/metal and troilite/metal partition coefficients for 'compatible' elements were quite similar to those inferred from natural assemblages, reinforcing an earlier made conclusion that there is a class of elements for which experimental troilite/metal and schreibersite/metal partition coefficients approximate those inferred from natural samples. The consistency between experimental and natural assemblages, however, was not observed for Ag, Pb, and Tl, indicating that the abundances of these elements determined in 'metal' and 'troilite' separates from iron meteorites are influenced by trace minerals that concentrate incompatible elements.

  6. A GREENER SYNTHESIS OF CORE (FE, CU)-SHELL (AU, PT, PD AND AG) NANOCRYSTALS USING AQUEOUS VITAMIN C

    EPA Science Inventory

    A greener method to fabricate the novel core (Fe and Cu)-shell (noble metals) metal nanocrystals using aqueous ascorbic acid (vitamin C) is described. Transition metal salts such as Cu and Fe were reduced using ascorbic acid, a benign naturally available antioxidant, and then add...

  7. Investigation of the interactions between Pt(II) and Pd(II) derivatives of 5,10,15,20-tetrakis (N-methyl-4-pyridyl) porphyrin and G-quadruplex DNA.

    PubMed

    Sabharwal, Navin C; Mendoza, Oscar; Nicoludis, John M; Ruan, Thomas; Mergny, Jean-Louis; Yatsunyk, Liliya A

    2016-04-01

    G-quadruplexes are non-canonical DNA structures formed by guanine-rich DNA sequences that are implicated in cancer and aging. Understanding how small molecule ligands interact with quadruplexes is essential both to the development of novel anticancer therapeutics and to the design of new quadruplex-selective probes needed for elucidation of quadruplex biological functions. In this work, UV-visible, fluorescence, and circular dichroism spectroscopies, fluorescence resonance energy transfer (FRET) melting assays, and resonance light scattering were used to investigate how the Pt(II) and Pd(II) derivatives of the well-studied 5,10,15,20-tetrakis(N-methyl-4-pyridyl)porphyrin (TMPyP4) interact with quadruplexes formed by the human telomeric DNA, Tel22, and by the G-rich sequences from oncogene promoters. Our results suggest that Pt- and PdTMPyP4 interact with Tel22 via efficient π-π stacking with a binding affinity of 10(6)-10(7) M(-1). Under porphyrin excess, PtTMPyP4 aggregates using Tel22 as a template; the aggregates reach maximum size at [PtTMPyP4]/[Tel22] ~8 and dissolve at [PtTMPyP4]/[Tel22] ≤ 2. FRET assays reveal that both porphyrins are excellent stabilizers of human telomeric DNA, with stabilization temperature of 30.7 ± 0.6 °C for PtTMPyP4 and 30.9 ± 0.4 °C for PdTMPyP4 at [PtTMPyP4]/[Tel22] = 2 in K(+) buffer, values significantly higher as compared to those for TMPyP4. The porphyrins display modest selectivity for quadruplex vs. duplex DNA, with selectivity ratios of 150 and 330 for Pt- and PdTMPyP4, respectively. This selectivity was confirmed by observed 'light switch' effect: fluorescence of PtTMPyP4 increases significantly in the presence of a variety of DNA secondary structures, yet the strongest effect is produced by quadruplex DNA. PMID:26748794

  8. Promotion effect of Pd on TiO2 for visible light photocatalytic degradation of gaseous formaldehyde.

    PubMed

    Wu, Ren-Jang; Liu, Yung-Shiuan; Lai, Hsiao-Fang; Wang, Jhe-Hao; Chavali, Murthy

    2014-09-01

    TiO2 and Pd doped TiO2 (Pd/TiO2) nanoparticles were prepared by sol gel method. Pd/TiO2 material was characterized by XRD, TEM, TPR, XPS and BET. From XRD data, the crystalline type of TiO2 is known to as Anatase type. TiO2 and Pd/TiO2 were in the order of 9-10 nm and 10-13 nm respectively. The photocatalytic activities of the TiO2 and Pd/TiO2 nanomaterials were evaluated and compared for the photodegradation of formaldehyde (HCHO). HCHO degradation on Pd/TiO2 catalyst, at 60 min, the degradation rate of gaseous HCHO is 95%. Using Pd/TiO2, the rate was faster than TiO2 or doped with other metals (Au/TiO2; Ag/TiO2; Pt/TiO2).

  9. Pt74Ag26 nanoparticle-decorated ultrathin MoS2 nanosheets as novel peroxidase mimics for highly selective colorimetric detection of H2O2 and glucose

    NASA Astrophysics Data System (ADS)

    Cai, Shuangfei; Han, Qiusen; Qi, Cui; Lian, Zheng; Jia, Xinghang; Yang, Rong; Wang, Chen

    2016-02-01

    To extend the functionalities of two-dimensional graphene-like layered compounds as versatile materials, the modification of transition metal dichalcogenide nanosheets such as MoS2 with metal nanoparticles is of great and widespread interest. However, few studies are available on the preparation of bimetallic nanoparticles supported on MoS2. Herein, a facile and efficient method to synthesize MoS2-PtAg nanohybrids by decorating ultrathin MoS2 nanosheets with octahedral Pt74Ag26 alloy nanoparticles has been reported. The as-prepared MoS2-Pt74Ag26 nanohybrids were investigated as novel peroxidase mimics to catalyze the oxidation of classical peroxidase substrate 3,3',5,5'-tetramethylbenzidine (TMB) in the presence of H2O2, producing a blue colored reaction and exhibiting typical Michaelis-Menten kinetics. MoS2-Pt74Ag26 has a higher affinity for H2O2 than horseradish peroxidase (HRP) and a higher vmax value with TMB as the substrate than MoS2. The improved catalytic activity of hybrids for colorimetric reactions could be attributed to the synergistic effects of octahedral Pt74Ag26 nanoparticles and ultrathin MoS2 nanosheets as supports. Meanwhile, the generation of active oxygen species (&z.rad;OH) by H2O2 decomposition with MoS2-Pt74Ag26 was responsible for the oxidation of TMB. On the basis of these findings, a colorimetric method based on MoS2-Pt74Ag26 nanohybrids that is highly sensitive and selective was developed for glucose detection. Lower values of the limit of detection (LOD) were obtained, which is more sensitive than MoS2 nanosheets.To extend the functionalities of two-dimensional graphene-like layered compounds as versatile materials, the modification of transition metal dichalcogenide nanosheets such as MoS2 with metal nanoparticles is of great and widespread interest. However, few studies are available on the preparation of bimetallic nanoparticles supported on MoS2. Herein, a facile and efficient method to synthesize MoS2-PtAg nanohybrids by decorating

  10. Near-infrared-emitting phthalocyanines. A combined experimental and density functional theory study of the structural, optical, and photophysical properties of Pd(II) and Pt(II) α-butoxyphthalocyanines.

    PubMed

    Soldatova, Alexandra V; Kim, Junhwan; Rizzoli, Corrado; Kenney, Malcolm E; Rodgers, Michael A J; Rosa, Angela; Ricciardi, Giampaolo

    2011-02-01

    The structural, optical, and photophysical properties of 1,4,8,11,15,18,22,25-octabutoxyphthalocyaninato-palladium(II), PdPc(OBu)(8), and the newly synthesized platinum analogue PtPc(OBu)(8) are investigated combining X-ray crystallography, static and transient absorption spectroscopy, and relativistic zeroth-order regular approximation (ZORA) Density Functional Theory (DFT)/Time Dependent DFT (TDDFT) calculations where spin-orbit coupling (SOC) effects are explicitly considered. The results are compared to those previously reported for NiPc(OBu)(8) (J. Phys. Chem. A 2005, 109, 2078) in an effort to highlight the effect of the central metal on the structural and photophysical properties of the group 10 transition metal octabutoxyphthalocyanines. Different from the nickel analogue, PdPc(OBu)(8) and PtPc(OBu)(8) show a modest and irregular saddling distortion of the macrocycle, but share with the first member of the group similar UV-vis spectra, with the deep red and intense Q-band absorption experiencing a blue shift down the group, as observed in virtually all tetrapyrrolic complexes of this triad. The blue shift of the Q-band along the MPc(OBu)(8) (M = Ni, Pd, Pt) series is interpreted on the basis of the metal-induced electronic structure changes. Besides the intense deep red absorption, the title complexes exhibit a distinct near-infrared (NIR) absorption due to a transition to the double-group 1E (π,π*) state, which is dominated by the lowest single-group (3)E (π,π*) state. Unlike NiPc(OBu)(8), which is nonluminescent, PdPc(OBu)(8) and PtPc(OBu)(8) show both deep red fluorescence emission and NIR phosphorescence emission. Transient absorption experiments and relativistic spin-orbit TDDFT calculations consistently indicate that fluorescence and phosphorescence emissions occur from the S(1)(π,π*) and T(1)(π,π*) states, respectively, the latter being directly populated from the former, and the triplet state decays directly to the S(0) surface (the triplet

  11. Structural and in vitro cytotoxicity studies on 1H-benzimidazol-2-ylmethyl-N-phenyl amine and its Pd(II) and Pt(II) complexes

    NASA Astrophysics Data System (ADS)

    Abdel Ghani, Nour T.; Mansour, Ahmed M.

    2011-10-01

    [MLCl 2]· zH 2O (L = (1H-benzimidazol-2-ylmethyl)-N-phenyl amine; M = Pd, z = 0; M = Pt, z = 1) and [PdL(OH 2) 2]·2X·zH 2O (X = Br, I, NO 3, z = 0; X = SCN, z = 1) complexes were synthesized as potential anticancer compounds and characterized by elemental analysis, spectral and thermal methods. FT-IR and 1H NMR studies revealed that the benzimidazole L is coordinated to the metal ions via the pyridine-type nitrogen (N py) of the benzimidazole ring and secondary amino group (NH sec). Quantum mechanical calculations of energies, geometries, vibrational wavenumbers, and 1H NMR of the benzimidazole L and its complexes were carried out by density functional theory using B3LYP functional combined with 6-31G(d) and LANL2DZ basis sets. Natural bond orbitals (NBOs) and frontier molecular orbitals were performed at B3LYP/LANL2DZ level of theory. The synthesized ligand, in comparison to its metal complexes was screened for its antibacterial activity. The benzimidazole L is more toxic against the bacterium Staphylococcus aureus (MIC = 58 μg/mL) than the standard tetracycline (MIC = 82 μg/mL). The complexes showed cytotoxicity against breast cancer, Colon Carcinoma, and human heptacellular Carcinoma cells. The platinum complex ( 6) displays cytotoxicity (IC 50 = 12.4 μM) against breast cancer compared with that reported for cis-platin 9.91 μM.

  12. Characterization studies and cytotoxicity assays of Pt(II) and Pd(II) dithiocarbamate complexes by means of FT-IR, NMR spectroscopy and mass spectrometry.

    PubMed

    Alverdi, V; Giovagnini, L; Marzano, C; Seraglia, R; Bettio, F; Sitran, S; Graziani, R; Fregona, D

    2004-06-01

    The precursors [M(ESDTM)Cl(2)] (M=Pt(II), Pd(II); ESDTM=EtO(2)CCH(2)(CH(3))NCS(2)Me, S-methyl(ethylsarcosinedithiocarbamate)) were synthesized as previously reported [J. Inorg. Biochem. 83 (2001) 31] and used to obtain [M(ESDT)Cl](n) (ESDT=ethylsarcosinedithiocarbamate anion) species. The complexes formed through reaction between [M(ESDT)Cl](n) and the two chiral amino-alcohols synephryne (Syn) and norphenylephrine (Nor) have been synthesized, with the ultimate goal of preparing mixed dithiocarbamate/amino metal complexes of the type [M(ESDT)(Am)Cl] (Am=Syn, Nor). These compounds have been isolated, purified and characterized by means of FT-IR, mono- and bidimensional NMR spectroscopy and mass spectrometry ESI/MS (electronspray mass spectra). The experimental data suggest that in all cases coordination of the dithiocarbamate ligand (ESDT) takes a place through the two sulfur atoms, the -NCSS moiety acting as a symmetrical bidentate chelating group, in a square-planar geometry around the M(II) ion, while the other two coordination positions are occupied by the chlorine atom and the amino-alcohol ligand, respectively. In particular, synephrine and norphenylephrine appear to be bound to the metal atom through the amino nitrogen atom by means of a dative bond. Finally, the biological activity of the new complexes has been studied by MTT (tetrazolio salt reduction) test and by detecting the inhibition of DNA synthesis and of clonal growth in various cancer cell lines. All Pd(II) derivatives showed a noticeable activity very close to that of cisplatin, used as reference drug. Moreover, they showed significantly reduced cross-resistance to cisplatin in a pair of cell lines (2008/C13*) with known acquired cisplatin resistance mechanisms. PMID:15149823

  13. Cross-sections for populating excited states in 150-153Sm via the (p,d) and (p,t) reactions

    NASA Astrophysics Data System (ADS)

    Humby, P.; Simon, A.; Beausang, C. W.; Gell, K.; Tarlow, T.; Vyas, G.; Ross, T. J.; Hughes, R. O.; Burke, J. T.; Casperson, R. J.; Koglin, J.; Ota, S.; Allmond, J. M.; McCleskey, M.; McCleskey, E.; Saastamoinen, A.; Chyzh, R.; Dag, M.

    2014-09-01

    Light ion transfer reactions were used to populate low/medium spin states in 150-154Sm via the (p,p' γ), (p,d γ) and (p,t γ) reactions. The 25 MeV proton beam, with an average current of 1 nA, was provided by the K-150 Cyclotron at the Cyclotron Institute of Texas A&M University. The outgoing charged particles and coincident gamma-rays were detected using the STARLiTeR arrays. STARs (Silicon Telescope Array for Reaction studies), a highly segmented ΔE-E silicon telescope, provides particle identification as well as the energies, times and angular distributions of the protons, deuterons and tritons in the exit channels. LiTeR (Livermore Texas Richmond array), an array of six BGO shielded HPGe clover detectors, records the energy, time and angular distribution of the coincident gamma rays, providing excellent selectivity of the states of interest. Preliminary results for the cross-sections for direct population of states in 150-153Sm will be presented. Light ion transfer reactions were used to populate low/medium spin states in 150-154Sm via the (p,p' γ), (p,d γ) and (p,t γ) reactions. The 25 MeV proton beam, with an average current of 1 nA, was provided by the K-150 Cyclotron at the Cyclotron Institute of Texas A&M University. The outgoing charged particles and coincident gamma-rays were detected using the STARLiTeR arrays. STARs (Silicon Telescope Array for Reaction studies), a highly segmented ΔE-E silicon telescope, provides particle identification as well as the energies, times and angular distributions of the protons, deuterons and tritons in the exit channels. LiTeR (Livermore Texas Richmond array), an array of six BGO shielded HPGe clover detectors, records the energy, time and angular distribution of the coincident gamma rays, providing excellent selectivity of the states of interest. Preliminary results for the cross-sections for direct population of states in 150-153Sm will be presented. This work was partly supported by the US Department of Energy

  14. Pt74Ag26 nanoparticle-decorated ultrathin MoS2 nanosheets as novel peroxidase mimics for highly selective colorimetric detection of H2O2 and glucose.

    PubMed

    Cai, Shuangfei; Han, Qiusen; Qi, Cui; Lian, Zheng; Jia, Xinghang; Yang, Rong; Wang, Chen

    2016-02-14

    To extend the functionalities of two-dimensional graphene-like layered compounds as versatile materials, the modification of transition metal dichalcogenide nanosheets such as MoS2 with metal nanoparticles is of great and widespread interest. However, few studies are available on the preparation of bimetallic nanoparticles supported on MoS2. Herein, a facile and efficient method to synthesize MoS2-PtAg nanohybrids by decorating ultrathin MoS2 nanosheets with octahedral Pt74Ag26 alloy nanoparticles has been reported. The as-prepared MoS2-Pt74Ag26 nanohybrids were investigated as novel peroxidase mimics to catalyze the oxidation of classical peroxidase substrate 3,3',5,5'-tetramethylbenzidine (TMB) in the presence of H2O2, producing a blue colored reaction and exhibiting typical Michaelis-Menten kinetics. MoS2-Pt74Ag26 has a higher affinity for H2O2 than horseradish peroxidase (HRP) and a higher vmax value with TMB as the substrate than MoS2. The improved catalytic activity of hybrids for colorimetric reactions could be attributed to the synergistic effects of octahedral Pt74Ag26 nanoparticles and ultrathin MoS2 nanosheets as supports. Meanwhile, the generation of active oxygen species (˙OH) by H2O2 decomposition with MoS2-Pt74Ag26 was responsible for the oxidation of TMB. On the basis of these findings, a colorimetric method based on MoS2-Pt74Ag26 nanohybrids that is highly sensitive and selective was developed for glucose detection. Lower values of the limit of detection (LOD) were obtained, which is more sensitive than MoS2 nanosheets.

  15. Phase stabilities of pyrite-related MTCh compounds (M=Ni, Pd, Pt; T=Si, Ge, Sn, Pb; Ch=S, Se, Te): A systematic DFT study

    SciTech Connect

    Bachhuber, Frederik; Krach, Alexander; Furtner, Andrea; Söhnel, Tilo; Peter, Philipp; Rothballer, Jan; Weihrich, Richard

    2015-03-15

    Pyrite-type and related systems appear for a wide range of binary and ternary combinations of transition metals and main group elements that form Zintl type dumbbell anion units. Those representatives with 20 valence electrons exhibit an extraordinary structural flexibility and interesting properties as low-gap semiconductors or thermoelectric and electrode materials. This work is devoted to the systematic exploration of novel compounds within the class of MTCh compounds (M=Ni, Pd, Pt; T=Si, Ge, Sn, Pb; Ch=S, Se, Te) by means of density functional calculations. Their preferred structures are predicted from an extended scheme of colored pyrites and marcasites. To determine their stabilities, competing binary MT{sub 2} and MCh{sub 2} boundary phases are taken into account as well as ternary M{sub 3}T{sub 2}Ch{sub 2} and M{sub 2}T{sub 3}Ch{sub 3} systems. Recently established stability diagrams are presented to account for MTCh ordering phenomena with a focus on a not-yet-reported ordering variant of the NiAs{sub 2} type. Due to the good agreement with experimental data available for several PtTCh systems, the predictions for the residual systems are considered sufficiently accurate. - Graphical abstract: Compositional and structural stability of MTCh compounds is investigated from first principle calculations. A conceptional approach is presented to study and predict novel stable and metastable compounds and structures of low gap semiconductors with TCh dumbbell units that are isoelectronic and structurally related to pyrite (FeS{sub 2}). - Highlights: • Study of compositional stability of MTCh vs. M{sub 3}T{sub 2}Ch{sub 2} and M{sub 2}T{sub 3}Ch{sub 3} compounds. • Study of structural stability of known and novel MTCh compounds. • Prediction of novel stable and metastable structures and compounds isoelectronic to pyrite, FeS{sub 2}.

  16. Competition between ferromagnetism and frustrated antiferromagnetism in quasi 2D Ce2.15(Pd1-x Ag x )1.95In0.9 alloys.

    PubMed

    Sereni, J G; Giovannini, M; Gómez Berisso, M; Gastaldo, F

    2016-11-30

    Low temperature thermal and magnetic measurements performed on ferro-magneticl (FM) alloys of composition Ce2.15(Pd1-x Ag x )1.95In0.9 are presented. Pd substitution by Ag depresses [Formula: see text] from 4.1 K down to 1.1 K for x  =  0.5, which is related to the increase of band electrons, with a critical concentration extrapolated to [Formula: see text]. The [Formula: see text] decrease is accompanied by a weakening of the magnetization of the FM phase. At high temperature (T  >  30 K) the inverse magnetic susceptibility reveals the presence of robust magnetic moments ([Formula: see text] [Formula: see text]), whereas the low value of the Curie-Weiss temperature [Formula: see text] K excludes any relevant effect from Kondo screening. The specific heat jump at [Formula: see text] decreases accordingly, while an anomaly emerges at a fixed temperature [Formula: see text] K. This unexpected anomaly does not show any associated sign of magnetism checked by AC-susceptibility measurements. Since the total magnetic entropy (evaluated around [Formula: see text]) practically does not change with Ag concentration, the transference of degrees of freedom from the FM component to the non-magnetic T (*) anomaly is deduced. The origin of this anomaly is attributed to an arising magnetic frustration of the ground state and the consequent entropy bottleneck produced by the divergent increasing of density of excitations at low temperature. PMID:27633336

  17. Competition between ferromagnetism and frustrated antiferromagnetism in quasi 2D Ce2.15(Pd1-x Ag x )1.95In0.9 alloys

    NASA Astrophysics Data System (ADS)

    Sereni, J. G.; Giovannini, M.; Gómez Berisso, M.; Gastaldo, F.

    2016-11-01

    Low temperature thermal and magnetic measurements performed on ferro-magneticl (FM) alloys of composition Ce2.15(Pd1-x Ag x )1.95In0.9 are presented. Pd substitution by Ag depresses {{T}\\text{C}}(x) from 4.1 K down to 1.1 K for x  =  0.5, which is related to the increase of band electrons, with a critical concentration extrapolated to {{x}\\text{cr}}≈ 0.6 . The {{T}\\text{C}}(x) decrease is accompanied by a weakening of the magnetization of the FM phase. At high temperature (T  >  30 K) the inverse magnetic susceptibility reveals the presence of robust magnetic moments (2.56≥slant ~{μ\\text{eff}}≥slant 2.4 {μ\\text{B}} ), whereas the low value of the Curie-Weiss temperature {θP}≈ -10 K excludes any relevant effect from Kondo screening. The specific heat jump at {{T}\\text{C}}(x) decreases accordingly, while an anomaly emerges at a fixed temperature {{T}\\ast}≈ 1 K. This unexpected anomaly does not show any associated sign of magnetism checked by AC-susceptibility measurements. Since the total magnetic entropy (evaluated around T={{T}\\text{C}}(x=0) ) practically does not change with Ag concentration, the transference of degrees of freedom from the FM component to the non-magnetic T * anomaly is deduced. The origin of this anomaly is attributed to an arising magnetic frustration of the ground state and the consequent entropy bottleneck produced by the divergent increasing of density of excitations at low temperature.

  18. Competition between ferromagnetism and frustrated antiferromagnetism in quasi 2D Ce2.15(Pd1-x Ag x )1.95In0.9 alloys.

    PubMed

    Sereni, J G; Giovannini, M; Gómez Berisso, M; Gastaldo, F

    2016-11-30

    Low temperature thermal and magnetic measurements performed on ferro-magneticl (FM) alloys of composition Ce2.15(Pd1-x Ag x )1.95In0.9 are presented. Pd substitution by Ag depresses [Formula: see text] from 4.1 K down to 1.1 K for x  =  0.5, which is related to the increase of band electrons, with a critical concentration extrapolated to [Formula: see text]. The [Formula: see text] decrease is accompanied by a weakening of the magnetization of the FM phase. At high temperature (T  >  30 K) the inverse magnetic susceptibility reveals the presence of robust magnetic moments ([Formula: see text] [Formula: see text]), whereas the low value of the Curie-Weiss temperature [Formula: see text] K excludes any relevant effect from Kondo screening. The specific heat jump at [Formula: see text] decreases accordingly, while an anomaly emerges at a fixed temperature [Formula: see text] K. This unexpected anomaly does not show any associated sign of magnetism checked by AC-susceptibility measurements. Since the total magnetic entropy (evaluated around [Formula: see text]) practically does not change with Ag concentration, the transference of degrees of freedom from the FM component to the non-magnetic T (*) anomaly is deduced. The origin of this anomaly is attributed to an arising magnetic frustration of the ground state and the consequent entropy bottleneck produced by the divergent increasing of density of excitations at low temperature.

  19. Rich spectroscopic and molecular dynamic studies on the interaction of cytotoxic Pt(II) and Pd(II) complexes of glycine derivatives with calf thymus DNA.

    PubMed

    Eslami Moghadam, Mahboube; Saidifar, Maryam; Divsalar, Adeleh; Mansouri-Torshizi, Hassan; Saboury, Ali Akbar; Farhangian, Hossein; Ghadamgahi, Maryam

    2016-01-01

    Some amino acid derivatives, such as R-glycine, have been synthesized together with their full spectroscopic characterization. The sodium salts of these bidentate amino acid ligands have been interacted with [M(bpy)(H2O)2](NO3)2 giving the corresponding some new complexes with formula [M(bpy)(R-gly)]NO3 (where M is Pt(II) or Pd(II), bpy is 2,2'-bipyridine and R-gly is butyl-, hexyl- and octyl-glycine). Due to less solubility of octyl derivatives, the biological activities of butyl and hexyl derivatives have been tested against chronic myelogenous leukemia cell line, K562. The interaction of these complexes with highly polymerized calf thymus DNA has been extensively studied by means of electronic absorption, fluorescence and other measurements. The experimental results suggest that these complexes positive cooperatively bind to DNA presumably via groove binding. Molecular dynamic results show that the DNA structure is largely maintained its native structure in hexylglycine derivative-water mixtures and at lower temperatures. The simulation data indicates that the more destabilizing effect of butylglycine is induced by preferential accumulation of these molecules around the DNA and due to their more negative free energy of binding via groove binding.

  20. The role of vdW interactions in coverage dependent adsorption energies of atomic adsorbates on Pt(111) and Pd(111)

    NASA Astrophysics Data System (ADS)

    Thirumalai, Hari; Kitchin, John R.

    2016-08-01

    Adsorption, a fundamental process in heterogeneous catalysis is known to be dependent on the adsorbate-adsorbate and surface-adsorbate bonds. van der Waals (vdW) interactions are one of the types of interactions that have not been examined thoroughly as a function of adsorbate coverage. In this work we quantify the vdW interactions for atomic adsorbates on late transition metal surfaces, and determine how these long range forces affect the coverage dependent adsorption energies. We calculate the adsorption energies of carbon, nitrogen, oxygen, sulfur, fluorine, bromine and chlorine species on Pt(111) and Pd(111) at coverages ranging from 1/4 to 1 ML using the BEEF-vdW functional. We observe that adsorption energies remain coverage dependent, and this coverage dependence is shown to be statistically significant. vdW interactions are found to be coverage dependent, but more significantly, they are found to be dependent on molecular properties such as adsorbate size, and consequently, correlate with the adsorbate effective nuclear charge. We observe that these interactions account for a reduction in the binding energy of the system, due to the destabilizing attractive interactions between the adsorbates which weaken its bond with the surface.

  1. Materials discovery by crystal growth: Lanthanide metal containing oxides of the platinum group metals (Ru, Os, Ir, Rh, Pd, Pt) from molten alkali metal hydroxides

    SciTech Connect

    Mugavero, Samuel J.; Gemmill, William R.; Roof, Irina P.; Loye, Hans-Conrad zur

    2009-07-15

    This review addresses the process of materials discovery via crystal growth, specifically of lanthanide metal containing oxides of the platinum group metals (Ru, Os, Ir, Rh, Pd, Pt). It provides a detailed overview of the use of hydroxide fluxes for crystal growth. The melt chemistry of hydroxide fluxes, specifically, the extensive acid base chemistry, the metal cation solubility, and the ability of hydroxide melts to oxidize metals are described. Furthermore, a general methodology for the successful crystal growth of oxides is provided, including a discussion of experimental considerations, suitable reaction vessels, reaction profiles and temperature ranges. Finally, a compilation of complex platinum group metal oxides recently synthesized using hydroxide melts, focusing on their crystal growth and crystal structures, is included. - Graphical abstract: A review that addresses the process of materials discovery via crystal growth using hydroxide fluxes. It provides a detailed overview of the use of hydroxide fluxes for crystal growth and describes the melt chemistry of hydroxide fluxes, specifically, the extensive acid base chemistry, the metal cation solubility, and the ability of hydroxide melts to oxidize metals. In addition, a compilation of complex platinum group metal oxides recently synthesized using hydroxide melts is included.

  2. Effect of MgO(100) support on structure and properties of Pd and Pt nanoparticles with 49-155 atoms

    NASA Astrophysics Data System (ADS)

    Kozlov, Sergey M.; Aleksandrov, Hristiyan A.; Goniakowski, Jacek; Neyman, Konstantin M.

    2013-08-01

    Presently, density functional computational studies of nanostructures in heterogeneous catalysts consider either sufficiently big ("scalable with size") unsupported metal nanoparticles (NPs) or small supported metal clusters. Both models may not be sufficiently representative of a few nm in size supported transition metal NPs dealt with in experiment. As a first step in closing the gap between theoretical models and prepared systems, we investigate the effect of a rather chemically inert oxide support, MgO(100), on relative energies and various properties of Pd and Pt NPs that consist of 49-155 atoms (1.2-1.6 nm in size) and exhibit bulk-like fcc structural arrangements. Shapes and interface configurations of metal NPs on MgO were obtained as a result of thorough optimization within the fcc motif using interatomic potentials. Then the stability and properties of the NPs were studied with a density functional method. We comprehensively characterize interaction between the NPs and MgO(100) support, their interface and effect of the support on NP properties. While the effect of MgO on relative stabilities of NPs with different shapes is found to be significant, other properties of the NPs such as electronic structure and interatomic distances within NP do not notably change upon deposition. This work paves the way to large-scale first-principles computational studies of more realistic models of oxide-supported metal catalysts.

  3. Investigation of low/medium spin excited states in 150-154Sm via the (p,d) and (p,t) reactions

    NASA Astrophysics Data System (ADS)

    Humby, P.; Simon, A.; Beausang, C.; Gell, K.; Tarlow, T.; Vyas, G.; Ross, T. J.; Hughes, R. O.; Burke, J. T.; Casperson, R. J.; Koglin, J.; Ota, S.; Allmond, J. M.; McCleskey, M.; McCleskey, E.; Saastamoinen, A.; Chyzh, R.; Dag, M.

    2014-03-01

    Low/medium spin excited states of 151,153Sm and 150,152Sm were studied via the (p,d) and (p,t) reactions, respectively, utilizing the STARLITER arrays at the Cyclotron Institute of Texas A&M University. In the experiment 152Sm and 154Sm targets were bombarded with 25 MeV protons and the outgoing light charged particles (p, d and t) in the exit channels were detected using the STARS ΔE - E silicon telescope, thus allowing particle identification and a measurement of the nuclear excitation energy. Six BGO shielded HPGe detectors were used to observe the emitted gamma rays in coincidence with the particles. A post-run measurement of gamma rays emitted from the activated target allowed an improved measurement of the half life of the 96 minute Jπ =8- isomer of 152Eu. Preliminary results are presented. This work was partly supported by the US Department of Energy under Grants No. DE-FG52-06NA26206 and No. DE-FG02-05ER41379.

  4. The adsorption of CO and NO on the MoS2 monolayer doped with Au, Pt, Pd, or Ni: A first-principles study

    NASA Astrophysics Data System (ADS)

    Ma, Dongwei; Ju, Weiwei; Li, Tingxian; Zhang, Xiwei; He, Chaozheng; Ma, Benyuan; Lu, Zhansheng; Yang, Zongxian

    2016-10-01

    By performing the first-principles calculation, the adsorption of CO and NO molecules on the Au, Pt, Pd, or Ni doped MoS2 monolayer has been studied. The interaction between CO or NO with the doped MoS2 monolayer is strong and belongs to the chemisorption, as evidenced by the large adsorption energy and the short distance between the adsorbed molecules and the dopants. The charge transfer and the electronic property induced by the molecule adsorption are discussed. It is found that for both CO and NO adsorption, for all the cases charge transfer between the substrates and the adsorbed molecules has been observed. For NO, the adsorption obviously induces new impurity states in the band gap or the redistribution of the original impurity states. These can lead to the change of the transport properties of the doped MoS2 monolayer, by which the adsorbed CO or NO can be detected. The present work shows that introducing appropriate dopants may be a feasible method to improve the performance of MoS2-based gas sensors.

  5. Ni(II), Pd(II) and Pt(II) complexes of (1H-1,2,4-triazole-3-ylimino)methyl]naphthalene-2-ol. Structural, spectroscopic, biological, cytotoxicity, antioxidant and DNA binding

    NASA Astrophysics Data System (ADS)

    Gaber, M.; El-Ghamry, H. A.; Fathalla, S. K.

    2015-03-01

    Metal complexes of the general formula [ML(H2O)Cl]nH2O; n = 1 for M = Ni and Pt and n = 2 for M = Pd, L = Schiff base (HL) derived from the condensation of 3-amino-1,2,4-triazole and 2-hydroxy-1-naphthaldehyde, were prepared. The synthesized ligand and its metal complexes were characterized on the basis of elemental analyses, spectral and magnetic studies as well as thermal analysis. The IR spectra revealed that the ligand is coordinated to the metal ions in bidentate manner via the N-atom of the azomethine group and the phenolic OH group. Square planar geometry was proposed for Pd(II) and Pt(II) complexes and tetrahedral for Ni(II) complex. The ligand and its metal complexes were screened against the sensitive organisms Escherichia coli as Gram-negative bacteria, Staphylococcus aureus as Gram-positive bacteria, Aspergillus flavus and Candida albicans as fungi. Moreover, the anticancer activity of the ligand and its metal complexes was evaluated in liver carcinoma (HEPG2) cell line. The results obtained indicated that the Schiff base ligand is more effective than its metal complexes towards the tested cell line. Ni(II), Pd(II) and Pt(II) complexes as well as the free Schiff base ligand were tested for their antioxidant activities. The DNA-binding properties of the studied complexes have been investigated by electronic absorption and viscosity measurements.

  6. Ni(II), Pd(II) and Pt(II) complexes of (1H-1,2,4-triazole-3-ylimino)methyl]naphthalene-2-ol. Structural, spectroscopic, biological, cytotoxicity, antioxidant and DNA binding.

    PubMed

    Gaber, M; El-Ghamry, H A; Fathalla, S K

    2015-03-15

    Metal complexes of the general formula [ML(H2O)Cl]nH2O; n=1 for M=Ni and Pt and n=2 for M=Pd, L=Schiff base (HL) derived from the condensation of 3-amino-1,2,4-triazole and 2-hydroxy-1-naphthaldehyde, were prepared. The synthesized ligand and its metal complexes were characterized on the basis of elemental analyses, spectral and magnetic studies as well as thermal analysis. The IR spectra revealed that the ligand is coordinated to the metal ions in bidentate manner via the N-atom of the azomethine group and the phenolic OH group. Square planar geometry was proposed for Pd(II) and Pt(II) complexes and tetrahedral for Ni(II) complex. The ligand and its metal complexes were screened against the sensitive organisms Escherichia coli as Gram-negative bacteria, Staphylococcus aureus as Gram-positive bacteria, Aspergillus flavus and Candida albicans as fungi. Moreover, the anticancer activity of the ligand and its metal complexes was evaluated in liver carcinoma (HEPG2) cell line. The results obtained indicated that the Schiff base ligand is more effective than its metal complexes towards the tested cell line. Ni(II), Pd(II) and Pt(II) complexes as well as the free Schiff base ligand were tested for their antioxidant activities. The DNA-binding properties of the studied complexes have been investigated by electronic absorption and viscosity measurements. PMID:25576936

  7. Effect of filler metal composition on the strength of yttria stabilized zirconia joints brazed with Pd-Ag-CuOx

    SciTech Connect

    Darsell, Jens T.; Weil, K. Scott

    2008-09-08

    The Ag-CuOx system is of interest to be used to be used as an air braze filler metal for joining high temperature electrochemical devices. Previous work has shown that the melting temperatures can be increased by adding palladium to Ag-CuOx and it is expected that this may aid high temperature stability. This work compares the room temperature bend strength of joints made between yttria-stabilized zirconia (YSZ) air brazed using Ag-CuOx without palladium and with 5 and 15mol% palladium additions. It has been found that in general palladium decreases joint strength, especially in low copper oxide compositions filler metals. At high copper oxide contents, brittle fracture through both copper oxide rich phases and the YSZ limits joint strength.

  8. New Au (III), Pt (II) and Pd (II) complexes with pentapeptide glycyl-glycyl-(L)-methyonyl-glycyl-glycine and their interaction with calf thymus DNA.

    PubMed

    Chapkanov, A; Miteva, Y; Kolev, T; Spiteller, M; Koleva, B

    2010-02-01

    The three new Au (III), Pt (II) and Pd (II) complexes with pentapeptide glycyl-glycyl-(L)-methyonyl-glycyl-glycine have been synthesized, isolated, and spectroscopically and structurally elucidated in solution and in the solid-state. Solid-state linear-dichroic infrared (IR-LD) spectroscopy of oriented colloids in a nematic liquid crystal host, (1)H- and (13)C-NMR, TGA and DSC, UV-VIS spectroscopy, EPR, ESI- and FAB- mass spectrometry and HPLC tandem mass spectrometry (HPLC-MS/MS) have been used. Quantum chemical calculations and molecular modelling were carried out in order to determine the structures and spectroscopic properties of the ligand, the newly synthesised metal complexes and their interactions with calf thymus DNA. The pentapeptide coordinates in a tetradentate manner with the metal ions via an S-atom on the methyonyl-side chain, two N-amide nitrogens, (after a deprotonation of gly(1) and gly(2) residues) and the primary NH(2) nitrogen of N(termini). The MN(3)S chromophores are distorted to near square planar geometry. Their interaction with calf thymus DNA shows the competitive N7 (G) coordination position, where the pentapeptide residues is coordinated with the metal centers in a tridentate manner through the S-atom and both N-amide centers. This interaction leads to a transfer from a distorted square planar geometry (D(4h) symmetry) to a pseudo tetrahedral (T(d) symmetry) of the metal ions with the obtained dihedral angle values of the MN(3)N7(G) chromophors within 114.67 degrees to 110.92 degrees . The isolated Au (III) complex is stable for about 1.5 months, while the stability of the Au (III) complex/DNA adduct is decreased to 33 days. PMID:19508228

  9. Effect of Thick Film Firing Conditions on the Solderability and Structure of Au-Pt-Pd Conductor for Low-Temperature, Co-Fired Ceramic Substrates

    SciTech Connect

    Hernandez, C.L; Vianco, P.T.

    1999-03-16

    Low-temperature, co-fired ceramics (LTCC) are the substrate material-of-choice for a growing number of multi-chip module (MCM) applications. Unlike the longer-standing hybrid microcircuit technology based upon alumina substrates, the manufacturability and reliability of thick film solder joints on LTCC substrates have not been widely studied. An investigation was undertaken to fully characterize such solder joints. A surface mount test vehicle with Daisy chain electrical connections was designed and built with Dupont{trademark} 951 tape. The Dupont{trademark} 4569 thick film ink (Au76-Pt21 -Pd3 wt.%) was used to establish the surface conductor pattern. The conductor pattern was fired onto the LTCC substrate in a matrix of process conditions that included: (1) double versus triple prints, (2) dielectric frame versus no frame, and (3) three firing temperatures (800 C, 875 C and 950 C). Pads were examined from the test vehicles. The porosity of the thick film layers was measured using quantitative image analysis in both the transverse and short transverse directions. A significant dependence on firing temperature was recorded for porosity. Solder paste comprised of Sn63-Pb37 powder with an RMA flux was screen printed onto the circuit boards. The appropriate components, which included chip capacitors of sizes 0805 up to 2225 and 50 mil pitch, leadless ceramic chip carriers having sizes of 16 I/O to 68 I/O, were then placed on the circuit boards. The test vehicles were oven reflowed under a N{sub 2} atmosphere. The solderability of the thick film pads was also observed to be sensitive to the firing conditions. Solderability appeared to degrade by the added processing steps needed for the triple print and dielectric window depositions. However, the primary factor in solderability was the firing temperature. Solderability was poorer when the firing temperature was higher.

  10. Steady-State Spectroscopic Analysis of Proton-Dependent Electron Transfer on Pyrazine-Appended Metal Dithiolenes [Ni(pdt)2], [Pd(pdt)2], and [Pt(pdt)2] (pdt = 2,3-Pyrazinedithiol).

    PubMed

    Kennedy, Steven R; Kozar, Morgan N; Yennawar, Hemant P; Lear, Benjamin J

    2016-09-01

    We report the structural, electronic, and acid/base properties of a series of ML2 metal dithiolene complexes, where M = Ni, Pd, Pt and L = 2,3-pyrazinedithiol. These complexes are non-innocent and possess strong electronic coupling between ligands across the metal center. The electronic coupling can be readily quantified in the monoanionic mixed valence state using Marcus-Hush theory. Analysis of the intervalence charge transfer (IVCT) band reveals that that electronic coupling in the mixed valence state is 5800, 4500, and 5700 cm(-1) for the Ni, Pd, and Pt complexes, respectively. We then focus on their response to acid titration in the mixed valence state, which generates the asymmetrically protonated mixed valence mixed protonated state. For all three complexes, protonation results in severe attenuation of the electronic coupling, as measured by the IVCT band. We find nearly 5-fold decreases in electronic coupling for both Ni and Pt, while, for the Pd complex, the electronic coupling is reduced to the point that the IVCT band is no longer observable. We ascribe the reduction in electronic coupling to charge pinning induced by asymmetric protonation. The more severe reduction in coupling for the Pd complex is a result of greater energetic mismatch between ligand and metal orbitals, reflected in the smaller electronic coupling for the pure mixed valence state. This work demonstrates that the bridging metal center can be used to tune the electronic coupling in both the mixed valence and mixed valence mixed protonated states, as well as the magnitude of change of the electronic coupling that accompanies changes in protonation state. PMID:27500686

  11. Flexible conductive-bridging random-access-memory cell vertically stacked with top Ag electrode, PEO, PVK, and bottom Pt electrode.

    PubMed

    Seung, Hyun-Min; Kwon, Kyoung-Cheol; Lee, Gon-Sub; Park, Jea-Gun

    2014-10-31

    Flexible conductive-bridging random-access-memory (RAM) cells were fabricated with a cross-bar memory cell stacked with a top Ag electrode, conductive polymer (poly(n-vinylcarbazole): PVK), electrolyte (polyethylene oxide: PEO), bottom Pt electrode, and flexible substrate (polyethersulfone: PES), exhibiting the bipolar switching behavior of resistive random access memory (ReRAM). The cell also exhibited bending-fatigue-free nonvolatile memory characteristics: i.e., a set voltage of 1.0 V, a reset voltage of -1.6 V, retention time of >1 × 10(5) s with a memory margin of 9.2 × 10(5), program/erase endurance cycles of >10(2) with a memory margin of 8.4 × 10(5), and bending-fatigue-free cycles of ∼1 × 10(3) with a memory margin (I(on)/I(off)) of 3.3 × 10(5). PMID:25297517

  12. Flexible conductive-bridging random-access-memory cell vertically stacked with top Ag electrode, PEO, PVK, and bottom Pt electrode

    NASA Astrophysics Data System (ADS)

    Seung, Hyun-Min; Kwon, Kyoung-Cheol; Lee, Gon-Sub; Park, Jea-Gun

    2014-10-01

    Flexible conductive-bridging random-access-memory (RAM) cells were fabricated with a cross-bar memory cell stacked with a top Ag electrode, conductive polymer (poly(n-vinylcarbazole): PVK), electrolyte (polyethylene oxide: PEO), bottom Pt electrode, and flexible substrate (polyethersulfone: PES), exhibiting the bipolar switching behavior of resistive random access memory (ReRAM). The cell also exhibited bending-fatigue-free nonvolatile memory characteristics: i.e., a set voltage of 1.0 V, a reset voltage of -1.6 V, retention time of >1 × 105 s with a memory margin of 9.2 × 105, program/erase endurance cycles of >102 with a memory margin of 8.4 × 105, and bending-fatigue-free cycles of ˜1 × 103 with a memory margin (Ion/Ioff) of 3.3 × 105.

  13. Search for strangelets and other rare objects in Au + Pt collisions at the AGS using a fixed-angle focusing spectrometer

    SciTech Connect

    Rusek, A.; Bassalleck, B.; Fischer, H.; Berdoz, A.; Franklin, G.B.; Buerger, T.; Burger, M.; Chrien, R.E.; Diebold, G.E.; En`yo, H.

    1995-12-31

    During the 1993 AGS heavy ion run, experiment E886 conducted a strangelet search in Au + Pt reactions, with beam momentum of 10.8 GeV/c per nucleon. Presented here are the upper limit for strangelet production, invariant cross sections for p, t, d, {sup 3}He, {sup 4}He, {sup 6}He, {sup 8}He, {sup 6}Li, {sup 7}Li, {sup 8}Li and {sup 7}Be, along with a demonstration of their agreement with a coalescence model fit to data collected by E886 during the 1992 engineering run, and upper limits for production cross sections for other rare objects, such as (H dibaryon)-nucleus systems. All results reported are preliminary.

  14. SnO₂(β-Bi₂O₃)/Bi₂Sn₂O₇ nanohybrids doped with Pt and Pd nanoparticles: applications in visible light photocatalysis, electrical conductivity and dye-sensitized solar cells.

    PubMed

    Khairy, M; Mohamed, Mohamed Mokhtar

    2015-09-01

    Bi2O3-SnO2 nanocomposites formed at a nominal molar ratio of 3 : 1 and loaded with Pd/Pt nanoparticles synthesized by a sol gel-hydrothermal method with the aid of a template were thoroughly characterized by X-ray diffraction, TEM-EDX, N2 sorptiometry, diffuse reflectance UV-Vis, FTIR, photoluminescence and electrical conductivity. It has been shown that Pd and Pt stimulate the existence of β-Bi2O3 and SnO2, respectively together with the key component Bi2Sn2O7. The photocatalytic results indicate that Pd/β-Bi2O3-Bi2Sn2O7 revealed a remarkable performance for the degradation of methylene blue (MB) dye as compared to the Pt/SnO2-Bi2Sn2O7 and Bi2O3-SnO2 samples in both the UV and visible regions. The enhanced photocatalytic activity of the Pd/β-Bi2O3-Bi2Sn2O7 nanocomposite is primarily attributed to the broad contact between the β-Bi2O3 and Bi2Sn2O7 phases, which indicates high mesoporosity and heterojunction structures resulting in separation efficacy between photo-induced electron-hole pairs. Specifically, the photosensitive β-Bi2O3 is easily excited and released electrons to be accepted by Bi2Sn2O7 and Pd that might be deposited in the interlayer between β-Bi2O3 and Bi2Sn2O7. The degradation mechanism of MB over Pd/β-Bi2O3-Bi2Sn2O7 in the visible region showed that the dye degradation proceeds through evolution of ˙O2(-) and ˙OH radicals as evaluated using photoluminescence and free radical trapping experiments. An insight into the electrical properties including the dielectric constant and impedance of the materials indicates that Pd/β-Bi2O3-Bi2Sn2O7 has the highest conductivity based on increasing the ionic transport and defects at the β-Bi2O3/Bi2Sn2O7 heterojunction. This material displayed an improved photocurrent response of a higher power conversion efficiency, exceeding that of Pt/SnO2-Bi2Sn2O7 and SnBi3 by 50% and 250%, respectively, in dye-sensitized solar cells. Picosecond-resolved photoluminescence (PL) and polarization gated PL

  15. Cationic Pd(II)/Pt(II) 5,5-diethylbarbiturate complexes with bis(2-pyridylmethyl)amine and terpyridine: Synthesis, structures,DNA/BSA interactions, intracellular distribution, cytotoxic activity and induction of apoptosis.

    PubMed

    Icsel, Ceyda; Yilmaz, Veysel T; Kaya, Yunus; Durmus, Selvi; Sarimahmut, Mehmet; Buyukgungor, Orhan; Ulukaya, Engin

    2015-11-01

    Four new cationic Pd(II) and Pt(II) 5,5-diethylbarbiturate (barb) complexes, [M(barb)(bpma)]X·H2O [M = Pd(II), X = Cl (1); M = Pt(II), X = NO3(-) (2)] and [M(barb)(terpy)]NO3·0.5H2O [M = Pd(II) (3); M = Pt(II) (4)], where bpma = bis(2-pyridylmethyl)amine and terpy = terpyridine, were synthesized and characterized by elemental analysis, IR, UV–vis, NMR, ESI-MS and X-ray crystallography. The DNA binding properties of the cationic complexes were investigated by spectroscopic titrations, displacement experiments, viscosity, DNA melting and electrophoresis measurements. The results revealed that the complexes effectively bind to FS-DNA (fish sperm DNA) via intercalative/minor groove binding modes with intrinsic binding constants (Kb) in the range of 0.50 × 10(4)–1.67 × 10(5) M(-1). Absorption, emission and synchronous fluorescence measurements showed strong association of the complexes with protein (BSA) through a static mechanism. The mode of interaction of complexes towards DNA and protein was also supported by molecular docking. Complexes 1 and 3 showed significant nuclear uptake in HT-29 cells. In addition, 1 and 3 showed higher inhibition than cisplatin on the growth of MCF-7 and HT-29 cells and induced apoptosis on these cells much more effectively than the rest of the complexes as evidenced by pyknotic nuclear morphology. The levels of caspase-cleaved cytokeratin 18 (M30 antigen) in HT-29 cells treated with 1 and 3 increased in a dose-dependent manner, suggesting apoptosis. Moreover, qRT-PCR experiments showed that 1 and 3 caused significant increases in the expression of TNFRSF10B in HT-29 cells, indicating the initiation of apoptosis via cell surface death receptors.

  16. Dopant dependent band gap tailoring of hydrothermally prepared cubic SrTi{sub x}M{sub 1-x}O{sub 3} (M=Ru,Rh,Ir,Pt,Pd) nanoparticles as visible light photocatalysts

    SciTech Connect

    Bae, Sang Won; Borse, Pramod H.; Lee, Jae Sung

    2008-03-10

    Nanostructured cubic SrTiO{sub 3} particles were hydrothermally synthesized and studied experimentally/theoretically for photoreduction of water. The particles were doped with metal atoms (M=Ru,Rh,Ir,Pt,Pd), which acquired high cyrstallinity after thermal treatment. SrTiO{sub 3}:Rh showed the highest rate of H{sub 2} evolution under {lambda}>420 nm photons. The density functional theory calculations of SrTi{sub x}M{sub 1-x}O{sub 3} (M=Ru,Rh,Ir,Pt) implied that the photocatalytic activity of SrTi{sub x}Rh{sub 1-x}O{sub 3} was due to its suitable band energetics, and the induced hybridized Ti/Rh orbitals in the bandgap of SrTiO{sub 3}.

  17. The Synthesis and Characterization of a Group of Transition Metal Octabutoxynaphthalocyanines and the Absorption and Emission Properties of the Co, Rh, Ir, Ni, Pd and Pt Members of This Group.

    PubMed

    Kim, Junhwan; Soldatova, Alexandra V; Rodgers, Michael A J; Kenney, Malcolm E

    2013-07-01

    The synthesis and photophysical properties of new metallo-octabutoxynaphthalocyanines with Rh(III), Ir(III), and Pt(II) are reported. Various metals were inserted into the metal-free octabutoxynaphthalocyanine and the resultant metal complexes were fully characterized by NMR, UV-vis spectroscopy, and mass spectrometry. The absorption and emission properties of these new complexes were also examined and compared to those of Co(II), Ni(II), and Pd(II) octabutoxynaphthalocyanines. The results provide useful information to understand the effect of these transition metals on the properties of this macrocyclic ring. PMID:23745014

  18. The Synthesis and Characterization of a Group of Transition Metal Octabutoxynaphthalocyanines and the Absorption and Emission Properties of the Co, Rh, Ir, Ni, Pd and Pt Members of This Group

    PubMed Central

    Kim, Junhwan; Soldatova, Alexandra V.; Rodgers, Michael A. J.; Kenney, Malcolm E.

    2013-01-01

    The synthesis and photophysical properties of new metallo-octabutoxynaphthalocyanines with Rh(III), Ir(III), and Pt(II) are reported. Various metals were inserted into the metal-free octabutoxynaphthalocyanine and the resultant metal complexes were fully characterized by NMR, UV-vis spectroscopy, and mass spectrometry. The absorption and emission properties of these new complexes were also examined and compared to those of Co(II), Ni(II), and Pd(II) octabutoxynaphthalocyanines. The results provide useful information to understand the effect of these transition metals on the properties of this macrocyclic ring. PMID:23745014

  19. Element-specific structure of materials with intrinsic disorder by high-energy resonant x-ray diffraction and differential atomic pair-distribution functions: A study of PtPd nanosized catalysts

    NASA Astrophysics Data System (ADS)

    Petkov, V.; Shastri, S. D.

    2010-04-01

    We demonstrate how high-energy resonant x-ray diffraction (XRD) and differential atomic-pair-distribution function (PDF) analysis can be used to characterize the atomic ordering in materials of limited structural coherence with both excellent spatial resolution and element specificity. First we prove that this experimental approach is feasible by probing the K -absorption edge of Au(˜81keV) atoms in chemically ordered and disordered bulk Cu3Au alloys. The resulting Au-differential PDFs show very clearly the different ways Au atoms are known to occupy the sites of otherwise identical cubic lattices of those materials. Next we apply it to a more complex material: PtPd alloy and core-shell nanosized (˜2-4nm) particles by probing the K -absorption edge of Pt(˜78keV) . The resulting Pt-differential atomic PDFs reveal how exactly the atomic ordering of catalytically active Pt atoms is affected by the nanoparticles’ design, thus providing a firm structural basis for understanding their properties. The work is a step forward in expanding the limits of applicability of nontraditional XRD to the rapidly growing field of materials of unusual structural complexity.

  20. Stabilization of Pt monolayer catalysts under harsh conditions of fuel cells.

    PubMed

    Zhang, Xiaoming; Yu, Shansheng; Qiao, Liang; Zheng, Weitao; Liu, Ping

    2015-05-21

    We employed density functional theory to explore the stability of core (M = Cu, Ru, Rh, Pd, Ag, Os, Ir, Au)-shell (Pt) catalysts under harsh conditions, including solutions and reaction intermediates involved in the oxygen reduction reaction (ORR) in fuel cells. A pseudomorphic surface alloy (PSA) with a Pt monolayer (Pt(1ML)) supported on an M surface, Pt(1ML)/M(111) or (001), was considered as a model system. Different sets of candidate M cores were identified to achieve a stable Pt(1ML) shell depending on the conditions. In vacuum conditions, the Pt1ML shell can be stabilized on the most of M cores except Cu, Ag, and Au. The situation varies under various electrochemical conditions. Depending on the solutions and the operating reaction pathways of the ORR, different M should be considered. Pd and Ir are the only core metals studied, being able to keep the Pt(ML) shell intact in perchloric acid, sulfuric acid, phosphoric acid, and alkaline solutions as well as under the ORR conditions via different pathways. Ru and Os cores should also be paid attention, which only fall during the ORR via the *OOH intermediate. Rh core works well as long as the ORR does not undergo the pathway via *O intermediate. Our results show that PSAs can behave differently from the near surface alloy, Pt(1ML)/M(1ML)/Pt(111), highlighting the importance of considering both chemical environments and the atomic structures in rational design of highly stable core-shell nanocatalysts. Finally, the roles that d-band center of a core M played in determining the stability of supported Pt(1ML) shell were also discussed.

  1. Stabilization of Pt monolayer catalysts under harsh conditions of fuel cells

    SciTech Connect

    Zhang, Xiaoming; Liu, Ping; Yu, Shansheng; Qiao, Liang; Zheng, Weitao

    2015-05-21

    We employed density functional theory (DFT) to explore the stability of core (M = Cu, Ru, Rh, Pd, Ag, Os, Ir, Au)-shell (Pt) catalysts under harsh conditions, including solutions and reaction intermediates involved in the oxygen reduction reaction (ORR) in fuel cells. A pseudomorphic surface alloy (PSA) with a Pt monolayer (Pt1ML) supported on an M surface, Pt1ML/M(111) or (001), was considered as a model system. Different sets of candidate M cores were identified to achieve a stable Pt1ML shell depending on the conditions. In vacuum conditions, the Pt1ML shell can be stabilized on the most of M cores except Cu, Ag, and Au. The situation varies under various electrochemical conditions. Depending on the solutions and the operating reaction pathways of the ORR, different M should be considered. Pd and Ir are the only core metals studied, being able to keep the PtML shell intact in perchloric acid, sulfuric acid, phosphoric acid, and alkaline solutions as well as under the ORR conditions via different pathways. Ru and Os cores should also be paid attention, which only fall during the ORR via the *OOH intermediate. Rh core works well as long as the ORR does not undergo the pathway via *O intermediate. Our results show that PSAs can behave differently from the near surface alloy, Pt1ML/M1ML/Pt(111), highlighting the importance of considering both chemical environments and the atomic structures in rational design of highly stable core-shell nanocatalysts. Finally, the roles that d-band center of a core M played in determining the stability of supported Pt1ML shell were also discussed.

  2. Stabilization of Pt monolayer catalysts under harsh conditions of fuel cells

    SciTech Connect

    Zhang, Xiaoming; Yu, Shansheng; Zheng, Weitao E-mail: pingliu3@bnl.gov; Qiao, Liang; Liu, Ping E-mail: pingliu3@bnl.gov

    2015-05-21

    We employed density functional theory to explore the stability of core (M = Cu, Ru, Rh, Pd, Ag, Os, Ir, Au)-shell (Pt) catalysts under harsh conditions, including solutions and reaction intermediates involved in the oxygen reduction reaction (ORR) in fuel cells. A pseudomorphic surface alloy (PSA) with a Pt monolayer (Pt{sub 1ML}) supported on an M surface, Pt{sub 1ML}/M(111) or (001), was considered as a model system. Different sets of candidate M cores were identified to achieve a stable Pt{sub 1ML} shell depending on the conditions. In vacuum conditions, the Pt{sub 1ML} shell can be stabilized on the most of M cores except Cu, Ag, and Au. The situation varies under various electrochemical conditions. Depending on the solutions and the operating reaction pathways of the ORR, different M should be considered. Pd and Ir are the only core metals studied, being able to keep the Pt{sub ML} shell intact in perchloric acid, sulfuric acid, phosphoric acid, and alkaline solutions as well as under the ORR conditions via different pathways. Ru and Os cores should also be paid attention, which only fall during the ORR via the *OOH intermediate. Rh core works well as long as the ORR does not undergo the pathway via *O intermediate. Our results show that PSAs can behave differently from the near surface alloy, Pt{sub 1ML}/M{sub 1ML}/Pt(111), highlighting the importance of considering both chemical environments and the atomic structures in rational design of highly stable core-shell nanocatalysts. Finally, the roles that d-band center of a core M played in determining the stability of supported Pt{sub 1ML} shell were also discussed.

  3. Stabilization of Pt monolayer catalysts under harsh conditions of fuel cells

    DOE PAGES

    Zhang, Xiaoming; Liu, Ping; Yu, Shansheng; Qiao, Liang; Zheng, Weitao

    2015-05-21

    We employed density functional theory (DFT) to explore the stability of core (M = Cu, Ru, Rh, Pd, Ag, Os, Ir, Au)-shell (Pt) catalysts under harsh conditions, including solutions and reaction intermediates involved in the oxygen reduction reaction (ORR) in fuel cells. A pseudomorphic surface alloy (PSA) with a Pt monolayer (Pt1ML) supported on an M surface, Pt1ML/M(111) or (001), was considered as a model system. Different sets of candidate M cores were identified to achieve a stable Pt1ML shell depending on the conditions. In vacuum conditions, the Pt1ML shell can be stabilized on the most of M cores exceptmore » Cu, Ag, and Au. The situation varies under various electrochemical conditions. Depending on the solutions and the operating reaction pathways of the ORR, different M should be considered. Pd and Ir are the only core metals studied, being able to keep the PtML shell intact in perchloric acid, sulfuric acid, phosphoric acid, and alkaline solutions as well as under the ORR conditions via different pathways. Ru and Os cores should also be paid attention, which only fall during the ORR via the *OOH intermediate. Rh core works well as long as the ORR does not undergo the pathway via *O intermediate. Our results show that PSAs can behave differently from the near surface alloy, Pt1ML/M1ML/Pt(111), highlighting the importance of considering both chemical environments and the atomic structures in rational design of highly stable core-shell nanocatalysts. Finally, the roles that d-band center of a core M played in determining the stability of supported Pt1ML shell were also discussed.« less

  4. Stabilization of Pt monolayer catalysts under harsh conditions of fuel cells

    NASA Astrophysics Data System (ADS)

    Zhang, Xiaoming; Yu, Shansheng; Qiao, Liang; Zheng, Weitao; Liu, Ping

    2015-05-01

    We employed density functional theory to explore the stability of core (M = Cu, Ru, Rh, Pd, Ag, Os, Ir, Au)-shell (Pt) catalysts under harsh conditions, including solutions and reaction intermediates involved in the oxygen reduction reaction (ORR) in fuel cells. A pseudomorphic surface alloy (PSA) with a Pt monolayer (Pt1ML) supported on an M surface, Pt1ML/M(111) or (001), was considered as a model system. Different sets of candidate M cores were identified to achieve a stable Pt1ML shell depending on the conditions. In vacuum conditions, the Pt1ML shell can be stabilized on the most of M cores except Cu, Ag, and Au. The situation varies under various electrochemical conditions. Depending on the solutions and the operating reaction pathways of the ORR, different M should be considered. Pd and Ir are the only core metals studied, being able to keep the PtML shell intact in perchloric acid, sulfuric acid, phosphoric acid, and alkaline solutions as well as under the ORR conditions via different pathways. Ru and Os cores should also be paid attention, which only fall during the ORR via the *OOH intermediate. Rh core works well as long as the ORR does not undergo the pathway via *O intermediate. Our results show that PSAs can behave differently from the near surface alloy, Pt1ML/M1ML/Pt(111), highlighting the importance of considering both chemical environments and the atomic structures in rational design of highly stable core-shell nanocatalysts. Finally, the roles that d-band center of a core M played in determining the stability of supported Pt1ML shell were also discussed.

  5. Theoretical study of the structure, bonding and electronic behaviour of sandwich complexes [M3(C7H7)2X3]- (M = Ni, Pd, Pt; X = F, Cl)

    NASA Astrophysics Data System (ADS)

    Zhou, Ke; Min, Suotian; Xue, Ganglin; Huang, Wendeng

    2014-08-01

    The correlations between the structural and electronic properties of the clusters [M3X3]3- and sandwich complexes [M3(C7H7)2X3]- (where M = Ni, Pd, Pt; X = F, Cl) were studied with density functional theory (B3PW91). All of the sandwich complexes are donating and back-donating metal-ligand bonding structures. The influence of the ligand, significant variations in the Msbnd C, Msbnd X, Msbnd M, Csbnd C bond lengths and binding energies were examined to obtain qualitative and quantitative pictures of the intramolecular C7R7+-M3X33- interactions. Our theoretical investigations show that the binding energies of the sandwich complexes gradually reduce from Ni to Pt, as well as from F to Cl. Meanwhile, the geometric and electronic structures and the relative stabilities have a strong relation to each other. Pt (13% s orbital of each Pt, 19% dz2 orbital of each Pt), and there is almost no contribution from Cl (Table S1). 7-B-(H-10) is a delocalised σ orbital, which has contributions from Pt (15% s orbital of each Pt, 8% d orbital of each Pt), and there is little contribution from Cl (Table S2). 7-C-(H-11) is a delocalised π orbital, which mainly involves contribution from Pt (25% dxz and dyz of each Pt) and Cl (8.5% pz of each Cl) (Table S3). 7-D-(H-14) is a delocalised σ orbital, which is mostly composed of d orbitals (14% for each Pt) and p orbitals (16% for each Cl) (Table S4). Pt s (10%) and d (10%) orbitals mainly participate in the formations of 7-E-(H-23), and there is a 13% p orbital contribution from each Cl (Table S5). For structure 13, the LUMO is mainly s orbitals of C, and there is some contribution from the s and d orbitals of Pt (Table S6), whereas the HOMO is mainly s orbitals of C

  6. DEVELOPMENT OF A HIGH-TEMPERATURE CERAMIC BRAZE: ANALYSIS OF PHASE EQUILIBRIA IN THE Pd-Ag-CuOx SYSTEM

    SciTech Connect

    Weil, K. Scott; Darsell, Jens T.

    2006-01-18

    This paper describes the effects of small palladium additions on the phase equilibria in the Ag-CuOx system. Below a concentration of 5 mol%, palladium was found to increase the temperature of the eutectic reaction present in the pseudobinary system, but have little effect on a higher temperature monotectic reaction. However once enough palladium was added to increase the pseudoternary solidus temperature to that of the lower boundary for this three-phase field (~970°C), the lower boundary begins to increase in temperature as well. The addition of palladium also causes the original eutectic point to move to lower silver concentrations, which also causes a convergence of the two new three-phase fields, CuOx + L1 + L2 and CuOx + α + L1. This suggests that with higher palladium concentrations, a peritectic reaction, α + L1 + L2 → CuOx, may eventually be observed in the system.

  7. Electron Affinities, Fluoride Affinities, and Heats of Formation of the Second Row Transition Metal Hexafluorides: MF6 (M = Mo, Tc, Ru, Rh, Pd, Ag)

    SciTech Connect

    Craciun, Raluca; Long, Rebecca T.; Dixon, David A.; Christe, Karl O.

    2010-07-22

    High-level electronic structure calculations were used to evaluate reliable, self-consistent thermochemical data sets for the second row transition metal hexafluorides. The electron affinities, heats of formation, first (MF{sub 6} {yields} MF{sub 5} + F) and average M-F bond dissociation energies, and fluoride affinities of MF{sub 6} (MF{sub 6} + F{sup -} {yields} MF{sub 7}{sup -}) and MF{sub 5} (MF{sub 5} + F{sup -} {yields} MF{sub 6}{sup -}) were calculated. The electron affinities are higher than those of the corresponding third row hexafluorides, making them stronger one-electron oxidizers. The calculated electron affinities, in good agreement with the available experimental values, are 4.23 eV for MoF{sub 6}, 5.89 eV for TcF{sub 6}, 7.01 eV for RuF{sub 6}, 6.80 eV for RhF{sub 6}, 7.95 eV for PdF{sub 6}, and 8.89 eV for AgF{sub 6}. The corresponding pentafluorides are also very strong Lewis acids, although their acidities on the pF{sup -} scale are about one unit lower than those of the third row pentafluorides. The performance of a wide range of DFT exchange-correlation functionals was benchmarked by comparing them to our more accurate CCSD(T) results.

  8. Synthesis, spectral and theoretical studies of Ni(II), Pd(II) and Pt(II) complexes of 5-mercapto-1,2,4-triazole-3-imine-2'-hydroxynaphthaline.

    PubMed

    Gaber, Mohamed; El-Ghamry, Hoda; Atlam, Faten; Fathalla, Shaimaa

    2015-02-25

    Ni(II), Pd(II) and Pt(II) complexes of 5-mercapto-1,2,4-triazole-3-imine-2'-hydroxynaphthaline have been isolated and characterized by elemental analysis, IR, (1)H NMR, EI-mass, UV-vis, molar conductance, magnetic moment measurements and thermogravimetric analysis. The molar conductance values indicated that the complexes are non-electrolytes. The magnetic moment values of the complexes displayed diamagnetic behavior for Pd(II) and Pt(II) complexes and tetrahedral geometrical structure for Ni(II) complex. From the bioinorganic applications point of view, the interaction of the ligand and its metal complexes with CT-DNA was investigated using absorption and viscosity titration techniques. The Schiff-base ligand and its metal complexes have also been screened for their antimicrobial and antitumor activities. Also, theoretical investigation of molecular and electronic structures of the studied ligand and its metal complexes has been carried out. Molecular orbital calculations were performed using DFT (density functional theory) at B3LYP level with standard 6-31G(d,p) and LANL2DZ basis sets to access reliable results to the experimental values. The calculations were performed to obtain the optimized molecular geometry, charge density distribution, extent of distortion from regular geometry, the highest occupied molecular orbital (HOMO), the lowest unoccupied molecular orbital (LUMO), Mulliken atomic charges, reactivity index (ΔE), dipole moment (D), global hardness (η), softness (σ), electrophilicity index (ω), chemical potential and Mulliken electronegativity (χ). PMID:25282021

  9. Vibrational study of new Pt(II) and Pd(II) complexes with functionalized nitrogen-containing tertiary phosphine oxides. Ab initio study of ortho-, meta- and para-dimethylphosphinylmethyleneoxyaniline.

    PubMed

    Trendafilova, N; Bauer, G; Georgieva, I; Tosheva, T; Varbanov, S

    2003-01-01

    Vibrational study of new Pt(II) and Pd(II) complexes of functionalized nitrogen-containing tertiary phosphine oxides, namely ortho-, meta- and para-dimethylphosphinylmethyleneoxyaniline (o-, m- and p-dpmoa), (CH3)2P(O)CH2OC6H4NH2, have been presented. Geometry optimization of the ligands was performed at HF/6-31G* and B3LYP/6-31G* levels of the theory. Harmonic frequencies were calculated at HF/6-31G* optimized geometries. Relative gas-phase and solution-phase (H2O and CH3CN) basicities of o-, m- and p-dpmoa ligands have been determined by ab initio calculations at STO-3G level with the Onsager reaction field model. On the basis of the vibrational study, physical and analytical data it was suggested that the ligands in the complexes studied coordinate through the amino group and form square-planar platinum and palladium complexes of the general formula ML2Cl2 (M = Pt, Pd, L = o-, m- and p-dpmoa).

  10. Synthesis, spectral and theoretical studies of Ni(II), Pd(II) and Pt(II) complexes of 5-mercapto-1,2,4-triazole-3-imine-2‧-hydroxynaphyhaline

    NASA Astrophysics Data System (ADS)

    Gaber, Mohamed; El-Ghamry, Hoda; Atlam, Faten; Fathalla, Shaimaa

    2015-02-01

    Ni(II), Pd(II) and Pt(II) complexes of 5-mercapto-1,2,4-triazole-3-imine-2‧-hydroxynaphthaline have been isolated and characterized by elemental analysis, IR, 1H NMR, EI-mass, UV-vis, molar conductance, magnetic moment measurements and thermogravimetric analysis. The molar conductance values indicated that the complexes are non-electrolytes. The magnetic moment values of the complexes displayed diamagnetic behavior for Pd(II) and Pt(II) complexes and tetrahedral geometrical structure for Ni(II) complex. From the bioinorganic applications point of view, the interaction of the ligand and its metal complexes with CT-DNA was investigated using absorption and viscosity titration techniques. The Schiff-base ligand and its metal complexes have also been screened for their antimicrobial and antitumor activities. Also, theoretical investigation of molecular and electronic structures of the studied ligand and its metal complexes has been carried out. Molecular orbital calculations were performed using DFT (density functional theory) at B3LYP level with standard 6-31G(d,p) and LANL2DZ basis sets to access reliable results to the experimental values. The calculations were performed to obtain the optimized molecular geometry, charge density distribution, extent of distortion from regular geometry, the highest occupied molecular orbital (HOMO), the lowest unoccupied molecular orbital (LUMO), Mulliken atomic charges, reactivity index (ΔE), dipole moment (D), global hardness (η), softness (σ), electrophilicity index (ω), chemical potential and Mulliken electronegativity (χ).

  11. Reducing Pt use in the catalysts for formic acid electrooxidation via nanoengineered surface structure

    NASA Astrophysics Data System (ADS)

    Liao, Mengyin; Wang, Yulu; Chen, Guoqin; Zhou, Hua; Li, Yunhua; Zhong, Chuan-Jian; Chen, Bing H.

    2014-07-01

    The design of active and durable catalysts for formic acid (FA) electrooxidation requires controlling the amount of three neighboring platinum atoms in the surface of Pt-based catalysts. Such requirement is studied by preparing Pt decorated Pd/C (donated as Pt-Pd/C) with various Pt:Pd molar ratios via galvanic displacement making the amount of three neighboring Pt atoms in the surface of Pt-Pd/C tunable. The decorated nanostructures are confirmed by XPS, HS-LEIS, cyclic voltammetry and chronoamperometric measurements, demonstrating that Pt-Pd/C (the optimal molar ratio, Pt:Pd = 1:250) exhibits superior activity and durability than Pd/C and commercial Pt/C (J-M, 20%) catalysts for FA electrooxidation. The mass activity of Pt-Pd/C (Pt:Pd = 1:250) (3.91 A mg-1) is about 98 and 6 times higher than that of commercial Pt/C (0.04 A mg-1) and Pd/C (0.63 A mg-1) at a given potential of 0.1 V vs SCE, respectively. The controlled synthesis of Pt-Pd/C lead to the formation of largely discontinuous Pd and Pt sites and inhibition of CO formation, exhibiting unprecedented electrocatalytic performance toward FA electrooxidation while the cost of the catalyst almost the same as Pd/C. These findings have profound implications to the design and nanoengineering of decorated surfaces of catalysts for FA electrooxidation.

  12. Using degrees of rate control to improve selective n-butane oxidation over model MOF-encapsulated catalysts: sterically-constrained Ag3Pd(111).

    PubMed

    Dix, Sean T; Scott, Joseph K; Getman, Rachel B; Campbell, Charles T

    2016-07-01

    Metal nanoparticles encapsulated within metal organic frameworks (MOFs) offer steric restrictions near the catalytic metal that can improve selectivity, much like in enzymes. A microkinetic model is developed for the regio-selective oxidation of n-butane to 1-butanol with O2 over a model for MOF-encapsulated bimetallic nanoparticles. The model consists of a Ag3Pd(111) surface decorated with a 2-atom-thick ring of (immobile) helium atoms which creates an artificial pore of similar size to that in common MOFs, which sterically constrains the adsorbed reaction intermediates. The kinetic parameters are based on energies calculated using density functional theory (DFT). The microkinetic model was analysed at 423 K to determine the dominant pathways and which species (adsorbed intermediates and transition states in the reaction mechanism) have energies that most sensitively affect the reaction rates to the different products, using degree-of-rate-control (DRC) analysis. This analysis revealed that activation of the C-H bond is assisted by adsorbed oxygen atoms, O*. Unfortunately, O* also abstracts H from adsorbed 1-butanol and butoxy as well, leading to butanal as the only significant product. This suggested to (1) add water to produce more OH*, thus inhibiting these undesired steps which produce OH*, and (2) eliminate most of the O2 pressure to reduce the O* coverage, thus also inhibiting these steps. Combined with increasing butane pressure, this dramatically improved the 1-butanol selectivity (from 0 to 95%) and the rate (to 2 molecules per site per s). Moreover, 40% less O2 was consumed per oxygen atom in the products. Under these conditions, a terminal H in butane is directly eliminated to the Pd site, and the resulting adsorbed butyl combines with OH* to give the desired 1-butanol. These results demonstrate that DRC analysis provides a powerful approach for optimizing catalytic process conditions, and that highly selectivity oxidation can sometimes be achieved by

  13. Phonon spectra and temperature variation of bulk properties of Cu, Ag, Au and Pt using Sutton-Chen and modified Sutton-Chen potentials

    NASA Astrophysics Data System (ADS)

    Januszko