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Description: Platinum and platinum/nickel alloy electrocatalysts supported on graphitized (gCNT) or nitrogen doped carbon nanotubes (nCNT) are prepared and characterized. Pt deposition onto carbon nanotubes results in Pt 'needle' formations that are 3.5 nm in diameter and {approx}100 nm in length. Subsequent Ni deposition and heat treatment results in PtNi 'needles' with an increased diameter. All Pt and Pt/Ni materials were tested as electrocatalysts for the oxygen reduction reaction (ORR). The Pt and Pt/Ni catalysts showed excellent performance for the ORR, with the heat treated PtNi/gCNT (1.06 mA/cm{sup 2}) and PtNi/nCNT (0.664 mA/cm{sup 2}) showing the highest activity.
Date: November 10, 2011
Creator: Colon-Mercado, H.
Partner: UNT Libraries Government Documents Department

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

Description: 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.
Date: December 12, 2008
Creator: Horwat, D.; Endrino, J.L.; Boreave, A.; Karoum,R.; Pierson, J.F.; Weber, S. et al.
Partner: UNT Libraries Government Documents Department

Precious Metal Recovery from Fuel Cell MEA's

Description: In 2003, Engelhard Corporation received a DOE award to develop a cost-effective, environmentally friendly approach to recover Pt from fuel cell membrane electrode assemblies (MEA’s). The most important precious metal used in fuel cells is platinum, but ruthenium is also added to the anode electrocatalyst if CO is present in the hydrogen stream. As part of the project, a large number of measurements of Pt and Ru need to be made. A low-cost approach to measuring Pt is using the industry standard spectrophotometric measurement of Pt complexed with stannous chloride. The interference of Ru can be eliminated by reading the Pt absorbance at 450 nm. Spectrophotometric methods for measuring Ru, while reported in the literature, are not as robust. This paper will discuss the options for measuring Pt and Ru using the method of UV-VIS spectrophotometry
Date: April 25, 2004
Creator: Shore, Lawrence
Partner: UNT Libraries Government Documents Department

LDRD final report on synthesis of shape-and size-controlled platinum and platinum alloy nanostructures on carbon with improved durability.

Description: This project is aimed to gain added durability by supporting ripening-resistant dendritic platinum and/or platinum-based alloy nanostructures on carbon. We have developed a new synthetic approach suitable for directly supporting dendritic nanostructures on VXC-72 carbon black (CB), single-walled carbon nanotubes (SWCNTs), and multi-walled carbon nanotubes (MWCNTs). The key of the synthesis is to creating a unique supporting/confining reaction environment by incorporating carbon within lipid bilayer relying on a hydrophobic-hydrophobic interaction. In order to realize size uniformity control over the supported dendritic nanostructures, a fast photocatalytic seeding method based on tin(IV) porphyrins (SnP) developed at Sandia was applied to the synthesis by using SnP-containing liposomes under tungsten light irradiation. For concept approval, one created dendritic platinum nanostructure supported on CB was fabricated into membrane electrode assemblies (MEAs) for durability examination via potential cycling. It appears that carbon supporting is essentially beneficial to an enhanced durability according to our preliminary results.
Date: October 1, 2008
Creator: Shelnutt, John Allen; Garcia, Robert M.; Song, Yujiang; Moreno, Andres M. & Stanis, Ronald J.
Partner: UNT Libraries Government Documents Department

Direct Determination of the Ionization Energies of PtC, PtO, and PtO2 with VUVRadiation

Description: Photoionization efficiency curves were measured for gas-phase PtC, PtO, and PtO2 using tunable vacuum ultraviolet (VUV) radiation at the Advanced Light Source. The molecules were prepared by laser ablation of a platinum tube, followed by reaction with CH4 or N2O and supersonic expansion. These measurements providethe first directly measured ionization energy for PtC, IE(PtC) = 9.45 +- 0.05 eV. The direct measurement also gives greatly improved ionization energies for the platinum oxides, IE(PtO) = 10.0 +- 0.1 eV and IE(PtO2) = 11.35 +- 0.05 eV. The ionization energy connects the dissociation energies of the neutral and cation, leading to greatly improved 0 K bond dissociation energies for the neutrals: D0(Pt-C) = 5.95 +- 0.07 eV, D0(Pt-O)= 4.30 +- 0.12 eV, and D0(OPt-O) = 4.41 +- 0.13 eV, as well as enthalpies of formation for the gas-phase molecules Delta H0 f,0(PtC(g)) = 701 +- 7 kJ/mol, Delta H0f,0(PtO(g)) = 396 +- 12 kJ/mol, and Delta H0f,0(PtO2(g)) = 218 +- 11 kJ/mol. Much of the error in previous Knudsen cell measurements of platinum oxide bond dissociation energies is due to the use of thermodynamic second law extrapolations. Third law values calculated using statistical mechanical thermodynamic functions are in much better agreement with values obtained from ionization energies and ion energetics. These experiments demonstrate that laser ablation production with direct VUV ionization measurements is a versatile tool to measure ionization energies and bond dissociation energies for catalytically interesting species such as metal oxides and carbides.
Date: July 21, 2008
Creator: Citir, Murat; Metz, Ricardo B.; Belau, Leonid & Ahmed, Musahid
Partner: UNT Libraries Government Documents Department

Controlled-potential-coulometric determination of uranium at a platinum electrode

Description: A controlled-potential-coulometric method has been developed for determining uranium at a solid electrode which features high specificity and a precision of 0.1% relative standard deviation at the 5 mg uranium level. Uranium and added iron, necessary for the electrolytic oxidation of uranium, are reduced to U(IV) and Fe(II) with excess Cr(II). At a sequence of controlled potentials, the excess Cr(II) is oxidized to Cr(III), Fe(II) and U(IV) are oxidized to Fe(III) and U(VI), then the Fe(III) is reduced to Fe(II). The difference in the measured number of coulombs for the oxidation of Fe(II) and U(IV) and for the reduction of Fe(III) to Fe(II) is proportional to the quantity of uranium.
Date: January 1, 1983
Creator: Saponara, N.M. & Jackson, D.D.
Partner: UNT Libraries Government Documents Department

Effect of H2S on performance of Pd4Pt alloy membranes

Description: The effect of H2S on the performance of a hydrogen separation membrane with the composition Pd4Pt was evaluated at 350, 400 and 450°C. Exposure to hydrogen containing 1000 ppm H2S and 10%He resulted in two performance trends. At 350°C, a continuous decline in flux was observed which was attributed to the growth of sulphide corrosion on the membrane surface linked to surface contamination by stainless steel derived particles. At 400 and 450°C, the H2 flux decreased sharply followed by a slow recovery. This trend was attributed to Pt enrichment of the surface resulting from extraction of Pd through the formation of Pd4Pt. Also at 400 and 450°C, stainless steel based particle contamination was found to modify and/or enhance the corrosive effects of the H2S containing test gas. The implications of the metallic and/or metal sulphide surface contaminant effects are significant in that these contaminants could result in severe performance degradation and ultimately even mechanical failure.
Date: January 1, 2008
Creator: Howard, B.H. & Morreale, B.D.
Partner: UNT Libraries Government Documents Department

Platinum Catalyzed Decomposition of Activated Carbon: 1. Initial Studies

Description: Carbon is an important support for heterogeneous catalysts, such as platinum supported on activated carbon (AC). An important property of these catalysts is that they decompose upon heating in air. Consequently, Pt/AC catalysts can be used in applications requiring rapid decomposition of a material, leaving little residue. This report describes the catalytic effects of platinum on carbon decomposition in an attempt to maximize decomposition rates. Catalysts were prepared by impregnating the AC with two different Pt precursors, Pt(NH{sub 3}){sub 4}(NO{sub 3}){sub 2} and H{sub 2}PtCl{sub 6}. Some catalysts were treated in flowing N{sub 2} or H{sub 2} at elevated temperatures to decompose the Pt precursor. The catalysts were analyzed for weight loss in air at temperatures ranging from 375 to 450 C, using thermogravimetric analysis (TGA). The following results were obtained: (1) Pt/AC decomposes much faster than pure carbon; (2) treatment of the as-prepared 1% Pt/AC samples in N{sub 2} or H{sub 2} enhances decomposition; (3) autocatalytic behavior is observed for 1% Pt/AC samples at temperatures {ge} 425 C; (4) oxygen is needed for decomposition to occur. Overall, the Pt/AC catalyst with the highest activity was impregnated with H{sub 2}PtCl{sub 6} dissolved in acetone, and then treated in H{sub 2}. However, further research and development should produce a more active Pt/AC material.
Date: December 1, 2001
Partner: UNT Libraries Government Documents Department

Preconversion catalytic deoxygenation of phenolic functional groups. Quarterly technical progress report, July 1, 1995--September 30, 1995

Description: Compared to alkoxy complexes, the chemistry of late transition metal aryloxy complexes is expected to reflect somewhat weaker M-O bonds since aryloxides are weaker nucleophiles than alkoxides. To understand the chemistry of the phenoxides, several thiophenoxide derivatives were synthesized. Pt(II) thiolate complexes are obtained either by reaction of Pt(II) chlorides with RSH in presence of base or the reaction of Pt(0) with dialkyl disulfides. NMR was used to study the structure.
Date: December 31, 1995
Creator: Kubiak, C.P.
Partner: UNT Libraries Government Documents Department

The Kernel Polynomial Method for non-orthogonal electronic structure calculations

Description: The Kernel Polynomial Method (KPM) has been successfully applied to tight-binding electronic structure calculations as an O(N) method. Here we extend this method to nonorthogonal basis sets with a sparse overlap matrix S and a sparse Hamiltonian H. Since the KPM method utilizes matrix vector multiplications it is necessary to apply S{sup -1} H onto a vector. The multiplication of S{sup -1} is performed using a preconditioned conjugate gradient method and does not involve the explicit inversion of S. Hence the method scales the same way as the original KPM method, i.e. O(N), although there is an overhead due to the additional conjugate gradient part. We show an application of this method to defects in a titanate/platinum interface and to a large scale electronic structure calculation of amorphous diamond.
Date: October 1, 1996
Creator: Roeder, H.; Silver, R.N.; Kress, J.D. & Landrum, G.A.
Partner: UNT Libraries Government Documents Department

LWRHU EB weld development

Description: Electron beam weld development studies were performed for both the platinum frit vent-to-vent cap weld and also the vent cap-to-body weld for the LWRHU Project using a Hamilton Standard EBW-6 Electron Beam Welder. A total of six (6) development welds each was performed to establish welding parameters and procedures which would produce satisfactory and acceptable welds. The relatively small size of the platinum frit vent dictated that the frit-to-vent cap weld would have to be limited as to depth of penetration and also to minimize the reduction of the porous frit areas.
Date: January 22, 1980
Creator: Greene, L.A.
Partner: UNT Libraries Government Documents Department

Fundamental studies of hydrogen chemisorption on supported monometallic and bimetallic catalysts using microcalorimetry

Description: Highly dispersed transition metal catalysts are used in numerous commercial processes such as hydrocarbon conversions. For example, the use of Pt supported on acidic alumina or silica-alumina for reforming of naphtha in the production of gasoline is well known. Another use of supported catalysts is in automobile emission control where supported Pt-Rh bimetallic catalysts are used. Supported Ru can be used in Fischer-Tropsch synthesis for the production of higher hydrocarbons from synthesis gas. While many of these catalyst systems have been in commercial operation for several decades there is still a lack of consensus regarding the exact role of the catalyst on a molecular level. In particular, little is known about the mechanisms operating on the catalyst surface at the high pressure and high temperature conditions typically used in commercial operations. This report contains the general introduction and conclusions and an appendix containing the operating instructions for a microcalorimeter. Three chapters have been processed separately. They are: the effect of K on the kinetics and thermodynamics of hydrogen adsorption on Ru/SiO{sub 2}; hydrogen adsorption states on silica supported Ru-Ag and Ru-Cu bimetallic catalysts investigated via microcalorimetry; a comparative study of hydrogen chemisorption on silica supported Ru, Rh, and Pt.
Date: June 24, 1997
Creator: Narayan, R.L.
Partner: UNT Libraries Government Documents Department

Probing the {sup 196}Pt(n,xn{gamma}) reactions using GEANIE at LANSCE/WNR

Description: In this paper we will present the results from an experiment studying the {sup 196}Pt(n,xn) reactions for n < 14 at moderate to high angular momentum using the combination of the LANSCE/WNR spallation neutron source and the multi-Ge detector spectrometer, GEANIE.
Date: June 20, 1997
Creator: Bernstein, L.A.; Archer, D.E.; Becker, J.A.; Drake, D.; Garrett, P.E.; Johns, G.D. et al.
Partner: UNT Libraries Government Documents Department

Superlattices of platinum and palladium nanoparticles

Description: The authors have used a nonionic inverse micelle synthesis technique to form nanoclusters of platinum and palladium. These nanoclusters can be rendered hydrophobic or hydrophilic by the appropriate choice of capping ligand. Unlike Au nanoclusters, Pt nanoclusters show great stability with thiol ligands in aqueous media. Alkane thiols, with alkane chains ranging from C{sub 6} to C{sub 18} were used as hydrophobic ligands, and with some of these they were able to form 2-D and/or 3-D superlattices of Pt nanoclusters as small as 2.7 nm in diameter. Image processing techniques were developed to reliably extract from transmission electron micrographs (TEMs) the particle size distribution, and information about the superlattice domains and their boundaries. The latter permits one to compute the intradomain vector pair correlation function of the particle centers, from which they can accurately determine the lattice spacing and the coherent domain size. From these data the gap between the particles in the coherent domains can be determined as a function of the thiol chain length. It is found that as the thiol chain length increases, the gaps between particles within superlattice domains increases, but more slowly than one might expect, possibly indicating thiol chain interdigitation.
Date: April 6, 2000
Partner: UNT Libraries Government Documents Department

Diimine(dithiolate)platinum(ii) Chromophores: Synthesis, Spectroscopy, and Material Applications

Description: A series of 28 square-planar dithiol(diimine)platinum(II) chromophoric complexes have been synthesized, characterized, and evaluated for potential efficacy in sensitization of solid state photovoltaic devices to the near-infrared regions of the electromagnetic spectrum. The effect of molecular stacking in the solid state and self-association in solution are shown to influence spectral, electronic, and magnetic properties of the chromophores. Such properties are investigated in the pure form and as partners in donor-acceptor charge transfer adducts. Finally, selected chromophores have been incorporated into single layer schottky diodes as neat films and as dopants in multi-layer organic photovoltaic devices. Evaluation of the devices internal quantum efficiency and voltage-current was measured as proof of concept.
Date: August 2014
Creator: Browning, Charles
Partner: UNT Libraries

A method of producing very high resistivity surface conduction on ceramic accelerator components using metal ion implantation

Description: An important technique used for the suppression of surface flashover on high voltage DC ceramic insulators as well as for RF windows is that of providing some surface conduction to bleed off accumulated surface charge. The authors have used metal ion implantation to modify the surface of high voltage ceramic vacuum insulators to provide a uniform surface resistivity of approximately 5 x 10{sup 10} Q{sup 2}. A vacuum arc ion source based implanter was used to implant Pt at an energy of about 135 MeV to doses of up to more than 5 x 10{sup 16} ions cm{sup 2} into small ceramic test coupons and also into the inside surface of several ceramic accelerator columns 25 cm I. D. by 28 cm long. Here they describe the experimental set-up used to do the ion implantation and summarize the results of their exploratory work on implantation into test coupons as well as the implantations of the actual ceramic columns.
Date: May 1, 1997
Creator: Liu, F.; Brown, I.; Phillips, L.; Biallas, G. & Siggins, T.
Partner: UNT Libraries Government Documents Department

The CO/Pt(111) Puzzle

Description: Notwithstanding half a dozen theoretical publications, well-converged density-functional calculations, whether based on a local or generalized-gradient exchange-correlation potential, whether all-electron or employing pseudopotentials underestimate CO's preference for low-coordination binding sites on Pt(111) and vicinals to it. For example, they imply that CO should prefer hollow- to atop-site adsorption on Pt(111), in apparent contradiction to a host of low temperature experimental studies.
Date: July 12, 2000
Partner: UNT Libraries Government Documents Department

Magnetism in single-crystalline CePtSn.

Description: CePtSn exhibits two antiferromagnetic transitions at low temperatures. We report on magnetoresistance and in magnetization studies of single-crystalline CePtSn in magnetic fields up to 18 T. The data were taken to establish the magnetic phase diagrams for CePtSn in fields applied along the principal directions.
Date: August 4, 1999
Creator: Bordallo, H. N.; Chang, S.; Lacerda, A. H.; Nakotte, H.; Takabatake, T. & Torikachvili, M. S.
Partner: UNT Libraries Government Documents Department

Photoelectron holography applied to surface structural determination

Description: Photoemitted electron waves are used as coherent source waves for angstrom-scale holographic imaging of local atomic geometry at surfaces. Electron angular distribution patterns are collected above a sample surface and serve as a record of the interference between source wave and waves scattered from surrounding ion cores. Using a mathematical imaging integral transformation, the three-dimensional structural information is obtained directly from these collected patterns. Patterns measured with different electron kinetic energies are phase-summed for image improvement. Pt (111) surface is used as a model system. A pattern 9.6{angstrom}{sup {minus}1} (351 eV) is used to generate a full 3-D image of atom locations around an emitter with nearest neighbors within 0.l{angstrom} of the expected bulk positions. Atoms several layers beyond the nearest neighbors are also apparent. Twin-image reduction and artifact suppression is obtained by phase-summing eight patterns measured from 8.8 to 10.2{angstrom}{sup {minus}1} (295 to 396 eV). 32 were measured in 0.2{angstrom}{sup {minus}1} steps from 6.0 to 12.2{angstrom}{sup {minus}1} (137 to 567 eV) are presented here. Simple models of two-slit interference are compared with electron scattering to illuminate understanding of holographic recording of the structural information. This also shows why it sometimes fails due to destructive interferences. Simple theoretical models of electron scattering are compared to experiment to show the origin of the structural information and the differences that result from atomic scattering and from the source wave. Experimental parameters and their relation to imaging is discussed. Comparison is made to the Pt pattern measured at 351 eV using the simple theoretical model. The remaining data set is also modeled, and the eight appropriate theoretical patterns are used to regenerate the multiple-wavenumber experimental result. A clean Cu (001) surface is also measured and imaged.
Date: May 1, 1995
Creator: Petersen, B.L.
Partner: UNT Libraries Government Documents Department

An atomic view of cluster diffusion on metal surfaces

Description: Field ion microscopy show a strong correlation between mobility and shape of small clusters on fcc(100) metal surfaces. For self-diffusion on Rh(100) this correlation lead to an oscillatory behavior in the activation energy of surface diffusion as a function of cluster size. Comparison of measured activation energies to theory indicate that the mechanism of cluster diffusion involves individual displacements of edge atoms (ie, perimeter diffusion). Rate-determining step in migration of clusters is partial detachment of one of the perimeter atoms. Relative ease of adatom motion along straight edges of stationary clusters also permits measurements of diffusion barriers at steps, which can be useful in interpretation of fractal vs compact island growth on fcc metal surfaces.
Date: June 1, 1996
Creator: Kellogg, G.L.
Partner: UNT Libraries Government Documents Department

Photoelectron holography of platinum (111)

Description: Platinum atoms near a (111) single-crystal face have been imaged using photoelectron holography. Electron angular intensity patterns were collected at equally spaced wavenumbers from 6 to 12{Angstrom}{sup {minus}1}. Images of atoms near expected atomic positions are obtained from single-wavenumber analyses over the range of the data set. Positions are detected further from the emitter than we have seen previously, and symmetry assumptions are not required. We have also adopted a three dimensional means of representing the data in order to help understand the results. Twin image suppression and artifact reduction in the holographically reconstructed data are set are obtained when images at different wavenumbers are correctly phase-summed. We are assessing the capability of the technique for rendering true three-dimensional structural information for unknown systems.
Date: April 1, 1993
Creator: Petersen, B.L.; Terminello, L.J.; Barton, J.J. & Shirley, D.A.
Partner: UNT Libraries Government Documents Department