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Sample records for active pt surface

  1. Oxygen reduction reaction activity on Pt{111} surface alloys.

    PubMed

    Attard, Gary A; Brew, Ashley; Ye, Jin-Yu; Morgan, David; Sun, Shi-Gang

    2014-07-21

    PtM overlayers (where M=Fe, Co or Ni) supported on Pt{111} are prepared via thermal annealing in either a nitrogen/water or hydrogen ambient of dilute aqueous droplets containing M(Z+) cations directly attached to the electrode. Two different PtM phases are detected depending on the nature of the post-annealing cooling environment. The first of these consists of small (<20 nm), closely packed microcrystals comprised of a central metallic core and a shell (several monolayers thick) of mixed metal oxides/hydroxides. The second type of PtM phase is prepared by cooling in a stream of hydrogen gas. Although this second phase also consists of numerous microcrystals covering the Pt{111} electrode surface, these are both flatter than before and moreover are entirely metallic in character. A positive shift in the onset of PtM oxide formation correlates with increased activity towards the oxygen reduction reaction (ORR), which we ascribe to the greater availability of platinum metallic sites under ORR conditions. PMID:24986646

  2. Experimental and theoretical studies of ammonia decomposition activity on Fe-Pt, Co-Pt, and Cu-Pt bimetallic surfaces

    NASA Astrophysics Data System (ADS)

    Hansgen, Danielle A.; Thomanek, Lisa M.; Chen, Jingguang G.; Vlachos, Dionisios G.

    2011-05-01

    We investigate the decomposition of ammonia on bimetallic surfaces prepared by the deposition of a monolayer of Fe, Co, or Cu on a Pt(111) surface computationally and experimentally. We explore the correlation between predicted activities based on the nitrogen binding energies with experimental decomposition activity on these bimetallic and corresponding monometallic surfaces. Through density functional theory calculations and microkinetic modeling, it is predicted that the Fe-Pt-Pt(111) and Co-Pt-Pt(111) surfaces, with a monolayer of Fe or Co on top of Pt(111), are active toward decomposing ammonia. In contrast, the corresponding subsurface configurations, Pt-Fe-Pt(111) and Pt-Co-Pt(111) are inactive. These predictions were confirmed experimentally through temperature programmed desorption experiments. Decomposition was seen at temperatures below 350 K for the Fe-Pt-Pt(111) and Co-Pt-Pt(111) surfaces. For the Cu/Pt(111) system, the surface, subsurface and parent metals were each predicted to be inactive, consistent with experiments, further validating the model predictions. The stability of these bimetallic surfaces in the presence of adsorbed nitrogen is also discussed.

  3. Improved oxygen reduction activity on Pt3Ni(111) via increased surface site availability.

    PubMed

    Stamenkovic, Vojislav R; Fowler, Ben; Mun, Bongjin Simon; Wang, Guofeng; Ross, Philip N; Lucas, Christopher A; Marković, Nenad M

    2007-01-26

    The slow rate of the oxygen reduction reaction (ORR) in the polymer electrolyte membrane fuel cell (PEMFC) is the main limitation for automotive applications. We demonstrated that the Pt3Ni(111) surface is 10-fold more active for the ORR than the corresponding Pt(111) surface and 90-fold more active than the current state-of-the-art Pt/C catalysts for PEMFC. The Pt3Ni(111) surface has an unusual electronic structure (d-band center position) and arrangement of surface atoms in the near-surface region. Under operating conditions relevant to fuel cells, its near-surface layer exhibits a highly structured compositional oscillation in the outermost and third layers, which are Pt-rich, and in the second atomic layer, which is Ni-rich. The weak interaction between the Pt surface atoms and nonreactive oxygenated species increases the number of active sites for O2 adsorption. PMID:17218494

  4. Correlation of Water Activation, Surface Properties, and Oxygen Reduction Reactivity of Supported PtM/C Bimetallic Electrocatalysts Using XAS

    SciTech Connect

    Teliska,M.; Murthi, V.; Mukerjee, S.; Ramaker, D.

    2005-01-01

    An analysis of X-ray absorption spectroscopy (XAS) data [X-ray absorption near-edge structure (XANES) and extended X-ray absorption fine structure (EXAFS)] at the Pt L{sub 3} edge for Pt-M bimetallic materials (M=Co, Cr, Ni, Fe) and at the Co K edge for Pt-Co is reported for Pt-M/C electrodes in HClO{sub 4} at different potentials. The XANES data are analyzed using the {Delta}{mu} method, which utilizes the spectrum at some potential V minus that at 0.54 V reversible hydrogen electrode (RHE) representing a reference spectrum. These {Delta}{mu} data provide direct spectroscopic evidence for the inhibition of OH chemisorption on the cluster surface in the Pt-M. This OH chemisorption, decreasing in the direction Pt>Pt-Ni>Pt-Co>Pt-Fe>Pt-Cr, is directly correlated with the previously reported fuel cell performance (electrocatalytic activities) of these bimetallics, confirming the role of OH poisoning of Pt sites in fuel cells. EXAFS analysis shows that the prepared clusters studied have different morphologies, the Pt-Ni and Pt-Co clusters were more homogeneous with M atoms at the surface, while the Pt-Fe and Pt-Cr clusters had a 'Pt skin.' The cluster morphology determines which previously proposed OH inhibition mechanism dominates, the electronic mechanism in the presence of the Pt skin, or lateral interactions when M-OH groups exist on the surface.

  5. Surface Activation of Pt Nanoparticles Synthesised by “Hot Injection” in the Presence of Oleylamine

    PubMed Central

    Humphrey, Jo J L; Sadasivan, Sajanikumari; Plana, Daniela; Celorrio, Verónica; Tooze, Robert A; Fermín, David J

    2015-01-01

    Oleylamine (OA) based “hot injection” colloidal synthesis offers a versatile approach to the synthesis of highly monodisperse metallic and multi-metallic alloyed nanostructures in the absence of potentially toxic and unstable phosphine compounds. For application in heterogeneous catalysis and electrocatalysis, the adsorbed OA species at the metal surfaces should be effectively removed without compromising the structure and composition of the nanostructures. Herein, we investigate the removal of OA from colloidal Pt nanoparticles through 1) “chemical methods” such as washing in acetic acid or ethanol, and ligand exchange with pyridine; and 2) thermal pre-treatment between 185 and 400 °C in air, H2 or Ar atmospheres. The electrochemical reactivity of Pt nanoparticles is acutely affected by the presence of surface organic impurities, making this material ideal for monitoring the effectiveness of OA removal. The results showed that thermal treatment in Ar at temperatures above 400 °C provides highly active particles, with reactivity comparable to the benchmark commercial catalyst, Pt/ETEK. The mechanism involved in thermal desorption of OA was also investigated by thermogravimetric analysis coupled to mass spectrometry (TGA-MS). Oxidation of HCOOH and adsorbed CO in acidic solution were used as test reactions to assess the Pt electrocatalytic activity. PMID:26201954

  6. 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

  7. Aniline hydrogenolysis on the Pt(111) single crystal surface: Mechanisms for C-N bond activation

    SciTech Connect

    Huang, S.X.; Gland, J.L.; Fischer, D.A. |

    1993-12-31

    Hydrogenolysis of C-N bond on transition metals is a crucial step in hydrodenitrogenation (HDN) reactions. Despite the overall complexity of HDN processes, the details of important surface reactions can be characterized using model reactions of organonitrogen compounds on single crystal model catalysts. The structure and reactivity of well characterized aniline monolayers on the Pt(111) surface both in vacuum and in the presence of hydrogen is discussed here. Adsorption and reactions of aniline were studied by Gland and Somorjai on the Pt(111) and Pt(100) surfaces, and more recently by Benziger`s group on the Ni(111) and Ni(100) surfaces. On both Pt and Ni surfaces, aniline {pi} bonds through the aromatic ring with its ring parallel to the substrate surface.

  8. Hydrogen induced C-C, C-N, and C-S bond activation on Pt and Ni surfaces

    SciTech Connect

    Gland, J.L.

    1992-01-01

    The work has focussed on hydrogen induced bond activation in adsorbed organic molecules and intermediates containin C-S and C-N and C-C bonds on Ni(100), Ni(111), and Pt(111) surfaces. Fluorescence Yield Near Edge Spectroscopy (FYNES) above the carbon K edge was used for adsorbed organic reactants and in-situ kinetic studies of bond activation. Results indicate that the activation is enhanced on Ni relative to Pt. Methylthiolate and methylamine adsorbed on Pt(111) were studied.

  9. Hydrogen induced C-C, C-N, and C-S bond activation on Pt and Ni surfaces

    SciTech Connect

    Gland, J.L.

    1992-12-01

    The work has focussed on hydrogen induced bond activation in adsorbed organic molecules and intermediates containin C-S and C-N and C-C bonds on Ni(100), Ni(111), and Pt(111) surfaces. Fluorescence Yield Near Edge Spectroscopy (FYNES) above the carbon K edge was used for adsorbed organic reactants and in-situ kinetic studies of bond activation. Results indicate that the activation is enhanced on Ni relative to Pt. Methylthiolate and methylamine adsorbed on Pt(111) were studied.

  10. Effect of gold subsurface layer on the surface activity and segregation in Pt/Au/Pt3M (where M = 3d transition metals) alloy catalyst from first-principles

    NASA Astrophysics Data System (ADS)

    Kim, Chang-Eun; Lim, Dong-Hee; Jang, Jong Hyun; Kim, Hyoung Juhn; Yoon, Sung Pil; Han, Jonghee; Nam, Suk Woo; Hong, Seong-Ahn; Soon, Aloysius; Ham, Hyung Chul

    2015-01-01

    The effect of a subsurface hetero layer (thin gold) on the activity and stability of Pt skin surface in Pt3M system (M = 3d transition metals) is investigated using the spin-polarized density functional theory calculation. First, we find that the heterometallic interaction between the Pt skin surface and the gold subsurface in Pt/Au/Pt3M system can significantly modify the electronic structure of the Pt skin surface. In particular, the local density of states projected onto the d states of Pt skin surface near the Fermi level is drastically decreased compared to the Pt/Pt/Pt3M case, leading to the reduction of the oxygen binding strength of the Pt skin surface. This modification is related to the increase of surface charge polarization of outmost Pt skin atoms by the electron transfer from the gold subsurface atoms. Furthermore, a subsurface gold layer is found to cast the energetic barrier to the segregation loss of metal atoms from the bulk (inside) region, which can enhance the durability of Pt3M based catalytic system in oxygen reduction condition at fuel cell devices. This study highlights that a gold subsurface hetero layer can provide an additional mean to tune the surface activity toward oxygen species and in turn the oxygen reduction reaction, where the utilization of geometric strain already reaches its practical limit.

  11. Effect of gold subsurface layer on the surface activity and segregation in Pt/Au/Pt3M (where M = 3d transition metals) alloy catalyst from first-principles.

    PubMed

    Kim, Chang-Eun; Lim, Dong-Hee; Jang, Jong Hyun; Kim, Hyoung Juhn; Yoon, Sung Pil; Han, Jonghee; Nam, Suk Woo; Hong, Seong-Ahn; Soon, Aloysius; Ham, Hyung Chul

    2015-01-21

    The effect of a subsurface hetero layer (thin gold) on the activity and stability of Pt skin surface in Pt3M system (M = 3d transition metals) is investigated using the spin-polarized density functional theory calculation. First, we find that the heterometallic interaction between the Pt skin surface and the gold subsurface in Pt/Au/Pt3M system can significantly modify the electronic structure of the Pt skin surface. In particular, the local density of states projected onto the d states of Pt skin surface near the Fermi level is drastically decreased compared to the Pt/Pt/Pt3M case, leading to the reduction of the oxygen binding strength of the Pt skin surface. This modification is related to the increase of surface charge polarization of outmost Pt skin atoms by the electron transfer from the gold subsurface atoms. Furthermore, a subsurface gold layer is found to cast the energetic barrier to the segregation loss of metal atoms from the bulk (inside) region, which can enhance the durability of Pt3M based catalytic system in oxygen reduction condition at fuel cell devices. This study highlights that a gold subsurface hetero layer can provide an additional mean to tune the surface activity toward oxygen species and in turn the oxygen reduction reaction, where the utilization of geometric strain already reaches its practical limit. PMID:25612725

  12. Effect of gold subsurface layer on the surface activity and segregation in Pt/Au/Pt{sub 3}M (where M = 3d transition metals) alloy catalyst from first-principles

    SciTech Connect

    Kim, Chang-Eun; Lim, Dong-Hee; Jang, Jong Hyun; Kim, Hyoung Juhn; Yoon, Sung Pil; Han, Jonghee; Nam, Suk Woo; Hong, Seong-Ahn; Soon, Aloysius E-mail: hchahm@kist.re.kr; Ham, Hyung Chul E-mail: hchahm@kist.re.kr

    2015-01-21

    The effect of a subsurface hetero layer (thin gold) on the activity and stability of Pt skin surface in Pt{sub 3}M system (M = 3d transition metals) is investigated using the spin-polarized density functional theory calculation. First, we find that the heterometallic interaction between the Pt skin surface and the gold subsurface in Pt/Au/Pt{sub 3}M system can significantly modify the electronic structure of the Pt skin surface. In particular, the local density of states projected onto the d states of Pt skin surface near the Fermi level is drastically decreased compared to the Pt/Pt/Pt{sub 3}M case, leading to the reduction of the oxygen binding strength of the Pt skin surface. This modification is related to the increase of surface charge polarization of outmost Pt skin atoms by the electron transfer from the gold subsurface atoms. Furthermore, a subsurface gold layer is found to cast the energetic barrier to the segregation loss of metal atoms from the bulk (inside) region, which can enhance the durability of Pt{sub 3}M based catalytic system in oxygen reduction condition at fuel cell devices. This study highlights that a gold subsurface hetero layer can provide an additional mean to tune the surface activity toward oxygen species and in turn the oxygen reduction reaction, where the utilization of geometric strain already reaches its practical limit.

  13. The Role of OOH Binding Site and Pt Surface Structure on ORR Activities

    PubMed Central

    Jia, Qingying; Caldwell, Keegan; Ziegelbauer, Joseph M.; Kongkanand, Anusorn; Wagner, Frederick T.; Mukerjee, Sanjeev; Ramaker, David E.

    2015-01-01

    We present experimentally observed molecular adsorbate coverages (e.g., O(H), OOH and HOOH) on real operating dealloyed bimetallic PtMx (M = Ni or Co) catalysts under oxygen reduction reaction (ORR) conditions obtained using X-ray absorption near edge spectroscopy (XANES). The results reveal a complex Sabatier catalysis behavior and indicate the active ORR mechanism changes with Pt–O bond weakening from the O2 dissociative mechanism, to the peroxyl mechanism, and finally to the hydrogen peroxide mechanism. An important rearrangement of the OOH binding site, an intermediate in the ORR, enables facile H addition to OOH and faster O–O bond breaking on 111 faces at optimal Pt–O bonding strength, such as that occurring in dealloyed PtM core-shell nanoparticles. This rearrangement is identified by previous DFT calculations and confirmed from in situ measured OOH adsorption coverages during the ORR. The importance of surface structural effects and 111 ordered faces is confirmed by the higher specific ORR rates on solid core vs porous multi-core nanoparticles. PMID:26190857

  14. On the design of Pt based catalysts. Combining porous architecture with surface modification by Sn for electrocatalytic activity enhancement

    NASA Astrophysics Data System (ADS)

    Flórez-Montaño, Jonathan; García, Gonzalo; Rodríguez, José L.; Pastor, Elena; Cappellari, Paula; Planes, Gabriel A.

    2015-05-01

    Metallic mesoporous (MP) catalysts with large surface area can be obtained in-situ, in a single step, by electrochemical reduction. In this work, the electrochemical behavior of MPPt and Sn modified mesoporous Pt (MPPt/Sn) was studied and compared with commercial carbon supported PtSn alloy (3:1). The electrochemical activity toward carbon monoxide and methanol oxidation reactions were evaluated by cyclic voltammetry and chronoamperometry, whereas X-ray photoelectron spectroscopy was used to determine the surface composition and oxidation state of the atoms in the top layers of the catalysts. The analysis of methanol conversion to CO2 was performed with aid of differential electrochemical mass spectrometry (DEMS). Results reveal a better performance of the MPPt/Sn, which shows higher current density and energy conversion efficiency of fuel to CO2 than conventional carbon supported PtSn alloy (3:1).

  15. Availability of surface boron species in improved oxygen reduction activity of Pt catalysts: A first-principles study

    NASA Astrophysics Data System (ADS)

    Zhang, Libo; Zhou, Gang

    2016-04-01

    The oxidation process of boron (B) species on the Pt(111) surface and the beneficial effects of boron oxides on the oxygen reduction activity are investigated by first-principles calculations. The single-atom B anchored on the Pt surface has a great attraction for the oxygen species in the immediate environment. With the dissociation of molecular oxygen, a series of boron oxides is formed in succession, both indicating exothermic oxidation reactions. After BO2 is formed, the subsequent O atom immediately participates in the oxygen reduction reaction. The calculated O adsorption energy is appreciably decreased as compared to Pt catalysts, and more approximate to the optimal value of the volcano plot, from which is clear that O hydrogenation kinetics is improved. The modulation mechanism is mainly based on the electron-deficient nature of stable boron oxides, which normally reduces available electronic states of surface Pt atoms that bind the O by facilitating more electron transfer. This modification strategy from the exterior opens the new way, different from the alloying, to efficient electrocatalyst design for PEMFCs.

  16. Availability of surface boron species in improved oxygen reduction activity of Pt catalysts: A first-principles study.

    PubMed

    Zhang, Libo; Zhou, Gang

    2016-04-14

    The oxidation process of boron (B) species on the Pt(111) surface and the beneficial effects of boron oxides on the oxygen reduction activity are investigated by first-principles calculations. The single-atom B anchored on the Pt surface has a great attraction for the oxygen species in the immediate environment. With the dissociation of molecular oxygen, a series of boron oxides is formed in succession, both indicating exothermic oxidation reactions. After BO2 is formed, the subsequent O atom immediately participates in the oxygen reduction reaction. The calculated O adsorption energy is appreciably decreased as compared to Pt catalysts, and more approximate to the optimal value of the volcano plot, from which is clear that O hydrogenation kinetics is improved. The modulation mechanism is mainly based on the electron-deficient nature of stable boron oxides, which normally reduces available electronic states of surface Pt atoms that bind the O by facilitating more electron transfer. This modification strategy from the exterior opens the new way, different from the alloying, to efficient electrocatalyst design for PEMFCs. PMID:27083744

  17. Ultrafine sputter-deposited Pt nanoparticles for triiodide reduction in dye-sensitized solar cells: impact of nanoparticle size, crystallinity and surface coverage on catalytic activity.

    PubMed

    Mukherjee, Somik; Ramalingam, Balavinayagam; Griggs, Lauren; Hamm, Steven; Baker, Gary A; Fraundorf, Phil; Sengupta, Shramik; Gangopadhyay, Shubhra

    2012-12-01

    This paper presents a detailed electrochemical impedance spectroscopy and cyclic voltammetry (CV) investigation into the electrocatalytic activity of ultrafine (i.e., smaller than 2 nm) platinum (Pt) nanoparticles generated on a fluorine-doped tin oxide (FTO) surface via room temperature tilted target sputter deposition. In particular, the Pt-decorated FTO electrode surfaces were tested as counter electrode candidates for triiodide (I3(-)) reduction in dye-sensitized solar cells (DSSCs). We observed a direct correlation between size-dependent Pt nanoparticle crystallinity and the I3(-) reduction activity underlying DSSC performance. CV analysis confirmed the higher electrocatalytic activities of sputter-deposited crystalline Pt nanoparticles (1-2 nm) compared with either sub-nanometre Pt clusters or a continuous Pt thin film. While the low catalytic activity and DSSC performance of Pt clusters smaller in size than 1 nm is believed to arise from their non-crystalline nature and charge-trapping attributes, we attribute the high catalytic performance of larger Pt nanoparticles in the 1-2 nm regime to their well-defined crystallinity and fast electron transfer kinetics. For DSSC applications, the optimized Pt loading was calculated to be ~2.54 × 10(-7) g cm(-2), which corresponds to surface coverage by ~1.6 nm sized Pt nanoparticles. PMID:23138541

  18. Effect of surface roughening on the catalytic activity of Pt-Cr electrocatalysts for the oxygen reduction in phosphoric acid fuel cell

    SciTech Connect

    Kim, K.T.; Kim, Y.G.; Chung, J.S.

    1995-05-01

    A Pt-Cr bimetallic catalyst with an atomic ratio of 3 to 1 was prepared by the impregnation method using a Pt/C catalyst (Pt loading: 10 weight percent). The catalyst was subjected to heat-treatment from 400 to 1,200 C. Its physical properties were characterized by H{sub 2}-O{sub 2} chemisorption, X-ray diffraction, transmission electron microscopy, and energy dispersive spectroscopy. Changes in the catalytic activity for oxygen reduction in PAFC were also examined. In particular, surface roughening caused by acid pretreatment and/or potential excursion was investigated to see its effect on the activity. Acid treatment (in 1M H{sub 2}SO{sub 4} for 1 day) and/or potential excursion at a mild condition (with a limited upper potential of 0.9 V vs. RHE) effectively created surface roughening without showing particle growth via sintering. The surface roughening increased the Pt surface area and consequently mass activity (catalytic activity based on mass of Pt) of the catalysts due to the selective leaching of surface-enriched chromium species. Concerning the specific activity (catalytic activity based on the Pt surface area), Pt-Cr having a smaller lattice parameter than Pt-Fe or Pt showed better performance, and this rule could be extended for other alloy systems. The mass activity, which is more important for practical applications, could be enhanced substantially when the surface roughening was brought on the catalyst surface while keeping the metal particle size small. The largest enhancement in the mass activity was observed when a partially alloyed or disordered alloy of Pt-Cr catalyst was subjected to the acid treatment or to the potential excursion.

  19. 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

  20. Modeling surface segregation phenomena in the (111) surface of ordered Pt3Ti crystal

    NASA Astrophysics Data System (ADS)

    Duan, Zhiyao; Zhong, Jun; Wang, Guofeng

    2010-09-01

    We investigated the surface segregation phenomena in the (111) surface of ordered Pt3Ti crystal using density functional theory (DFT) calculation (with no configuration sampling) and Monte Carlo (MC) simulation method (employing modified embedded atom method potentials and with extensive configuration sampling). Our DFT study suggested that the off-stoichiometric effect (specifically, a Pt concentration higher than 75 at. %) accounted for the experimentally observed Pt segregation to the outermost layer of the Pt3Ti (111). Our MC simulations predicted that in a Pt3Ti (111) sample with a Pt concentration slightly above 75 at. %, Pt atoms would segregate to the surface to form a pure Pt outermost layer, while the ordered Pt3Ti crystal structure would be maintained in the second layer and below. Moreover, our DFT calculations revealed that the d-band center of the Pt-segregated Pt3Ti (111) surface would downshift by 0.21 eV as compared to that of a pure Pt (111) surface. As a result, O adsorption energy on the Pt-segregated Pt3Ti (111) surface was found to be at least 0.16 eV weaker than that on the pure Pt (111) surface. Thus, we theoretically modeled the geometric and electronic structures of the Pt-segregated Pt3Ti (111) surface and further suggested that the Pt surface segregation could lead to enhanced catalytic activity for oxygen reduction reactions on Pt3Ti alloy catalysts.

  1. Identical Location Transmission Electron Microscopy Imaging of Site-Selective Pt Nanocatalysts: Electrochemical Activation and Surface Disordering.

    PubMed

    Arán-Ais, Rosa M; Yu, Yingchao; Hovden, Robert; Solla-Gullón, Jose; Herrero, Enrique; Feliu, Juan M; Abruña, Héctor D

    2015-12-01

    We have employed identical location transmission electron microscopy (IL-TEM) to study changes in the shape and morphology of faceted Pt nanoparticles as a result of electrochemical cycling; a procedure typically employed for activating platinum surfaces. We find that the shape and morphology of the as-prepared hexagonal nanoparticles are rapidly degraded as a result of potential cycling up to +1.3 V. As few as 25 potential cycles are sufficient to cause significant degradation, and after about 500-1000 cycles the particles are dramatically degraded. We also see clear evidence of particle migration during potential cycling. These finding suggest that great care must be exercised in the use and study of shaped Pt nanoparticles (and related systems) as electrocatlysts, especially for the oxygen reduction reaction where high positive potentials are typically employed. PMID:26524187

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

    PubMed

    Qi, Kun; Zheng, Weitao; Cui, Xiaoqiang

    2016-01-21

    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. PMID:26693587

  3. Surface segregation effects in electrocatalysis: Kinetics ofoxygen reduction reaction on polycrystalline Pt3Ni alloy surfaces

    SciTech Connect

    Stamenkovic, V.; Schmidt, T.J.; Ross, P.N.; Markovic, N.M.

    2002-11-01

    Effects of surface segregation on the oxygen reduction reaction (ORR) have been studied on a polycrystalline Pt3Ni alloy in acid electrolyte using ultra high vacuum (UHV) surface sensitive probes and the rotating ring disk electrode (RRDE) method. Preparation, modification and characterization of alloy surfaces were done in ultra high vacuum (UHV). Depending on the preparation method, two different surface compositions of the Pt3Ni alloy are produced: a sputtered surface with 75 % Pt and an annealed surface (950 K ) with 100 % Pt. The latter surface is designated as the 'Pt-skin' structure, and is a consequence of surface segregation, i.e., replacement of Ni with Pt atoms in the first few atomic layers. Definitive surface compositions were established by low energy ion scattering spectroscopy (LEISS). The cyclic voltammetry of the 'Pt-skin' surface as well as the pseudocapacitance in the hydrogen adsorption/desorption potential region is similar to a polycrystalline Pt electrode. Activities of ORR on Pt3Ni alloy surfaces were compared to polycrystalline Pt in 0.1M HClO4 electrolyte for the observed temperature range of 293 < T < 333 K. The order of activities at 333 K was: 'Pt-skin' > Pt3Ni (75% Pt) > Pt with the maximum catalytic enhancement obtained for the 'Pt-skin' being 4 times that for pure Pt. Catalytic improvement of the ORR on Pt3Ni and 'Pt-skin' surfaces was assigned to the inhibition of Pt-OHad formation (on Pt sites) versus polycrystalline Pt. Production of H2O2 on both surfaces were similar compared to the pure Pt. Kinetic analyses of RRDE data confirmed that kinetic parameters for the ORR on the Pt3Ni and 'Pt-skin' surfaces are the same as on pure Pt: reaction order, m=1, two identical Tafel slopes, activation energy, {approx} 21-25 kJ/mol. Therefore the reaction mechanism on both Pt3Ni and 'Pt-skin' surfaces is the same as one proposed for pure Pt i.e. 4e{sup -} reduction pathway.

  4. Surface structure and chemistry of Pt/Cu/Pt(1 1 1) near surface alloy model catalyst in CO

    NASA Astrophysics Data System (ADS)

    Zeng, Shibi; Nguyen, Luan; Cheng, Fang; Liu, Lacheng; Yu, Ying; Tao, Franklin (Feng)

    2014-11-01

    Near surface alloy (NSA) model catalyst Pt/Cu/Pt(1 1 1) was prepared on Pt(1 1 1) through a controlled vapor deposition of Cu atoms. Different coordination environments of Pt atoms of the topmost Pt layer with the underneath Cu atoms in the subsurface result in different local electronic structures of surface Pt atoms. Surface structure and chemistry of the NAS model catalyst in Torr pressure of CO were studied with high pressure scanning tunneling microscopy (HP-STM) and ambient pressure X-ray photoelectron spectroscopy (AP-XPS). In Torr pressure of CO, the topmost Pt layer of Pt/Cu/Pt(1 1 1) is restructured to thin nanoclusters with size of about 1 nm. Photoemission feature of O 1s of CO on Pt/Cu/Pt(1 1 1) suggests CO adsorbed on both edge and surface of these formed nanoclusters. This surface is active for CO oxidation. Atomic layers of carbon are formed on Pt/Cu/Pt(1 1 1) at 573 K in 2 Torr of CO.

  5. Intrinsic activity and poisoning rate for HCOOH oxidation at Pt(100) and vicinal surfaces containing monoatomic (111) steps.

    PubMed

    Grozovski, Vitali; Climent, Víctor; Herrero, Enrique; Feliu, Juan M

    2009-08-01

    Pulsed voltammetry is used to study formic acid oxidation on Pt(2n-1,1,1) surfaces and determine the effects of the size of the (100) terrace and the (111) step density on the reaction mechanism. The intrinsic activity of the electrode through the active intermediate reaction path (j(theta=) (0)), as well as the rate constant for the CO formation (k(ads)), are calculated from the current transients obtained at different potentials. For surfaces with wide terraces, j(theta=) (0) and k(ads) are almost insensitive to the step density, which suggests that step and terrace sites have a similar activity for this reaction. For narrow terraces (n<6), the intrinsic activity diminishes. The dependence of the reaction rates on the electrode potential is also elucidated. The CO formation only takes place in a narrow potential window, very close to the potential of zero total charge, while the direct oxidation takes place even when the surface is covered by anions. The different behavior for both reactions suggests that the adsorption mode of formic acid is different for each path. PMID:19569091

  6. Surface-layered ordered alloy (Pt/Pt3Mn) on Pt(111)

    NASA Astrophysics Data System (ADS)

    Gallego, S.; Ocal, C.; Muñoz, M. C.; Soria, F.

    1997-11-01

    A Mn-Pt layered intermetallic compound formed by alternated planes of Pt(111) and Pt3Mn(111) composition has been stabilized in a controlled way by two different mechanisms, which confirm the great stability of the final system. The surface exhibits a 2×2 superstructure due to chemical order underneath a Pt topmost layer. The structural analysis by low-energy electron diffraction gives a Pendry reliability factor (R-factor) of RP=0.17. The hybridization of the Pt and Mn atomic levels leads to atomic magnetic moments of 3.17μB and ~0.10μB at the Mn and Pt sites of the topmost layers, respectively.

  7. Dehydrogenation of benzene on Pt(111) surface

    NASA Astrophysics Data System (ADS)

    Gao, W.; Zheng, W. T.; Jiang, Q.

    2008-10-01

    The dehydrogenation of benzene on Pt(111) surface is studied by ab initio density functional theory. The minimum energy pathways for benzene dehydrogenation are found with the nudge elastic band method including several factors of the associated barriers, reactive energies, intermediates, and transient states. The results show that there are two possible parallel minimum energy pathways on the Pt(111) surface. Moreover, the tilting angle of the H atom in benzene can be taken as an index for the actual barrier of dehydrogenation. In addition, the properties of dehydrogenation radicals on the Pt(111) surface are explored through their adsorption energy, adsorption geometry, and electronic structure on the surface. The vibrational frequencies of the dehydrogenation radicals derived from the calculations are in agreement with literature data.

  8. Coating Pt-Ni Octahedra with Ultrathin Pt Shells to Enhance the Durability without Compromising the Activity toward Oxygen Reduction.

    PubMed

    Park, Jinho; Liu, Jingyue; Peng, Hsin-Chieh; Figueroa-Cosme, Legna; Miao, Shu; Choi, Sang-Il; Bao, Shixiong; Yang, Xuan; Xia, Younan

    2016-08-23

    We describe a new strategy to enhance the catalytic durability of Pt-Ni octahedral nanocrystals in the oxygen reduction reaction (ORR) by conformally depositing an ultrathin Pt shell on the surface. The Pt-Ni octahedra were synthesized according to a protocol reported previously and then employed directly as seeds for the conformal deposition of ultrathin Pt shells by introducing a Pt precursor dropwise at 200 °C. The amount of Pt precursor was adjusted relative to the number of Pt-Ni octahedra involved to obtain Pt-Ni@Pt1.5L octahedra of 12 nm in edge length for the systematic evaluation of their chemical stability and catalytic durability compared to Pt-Ni octahedra. Specifically, we compared the elemental compositions of the octahedra before and after treatment with acetic and sulfuric acids. We also examined their electrocatalytic stability toward the ORR through an accelerated durability test by using a rotating disk electrode method. Even after treatment with sulfuric acid for 24 h, the Pt-Ni@Pt1.5L octahedra maintained their original Ni content, whereas 11 % of the Ni was lost from the Pt-Ni octahedra. After 10 000 cycles of ORR, the mass activity of the Pt-Ni octahedra decreased by 75 %, whereas the Pt-Ni@Pt1.5L octahedra only showed a 25 % reduction. PMID:27460459

  9. 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.

  10. Temperature dependence of oxygen reduction activity at Nafion-coated bulk Pt and Pt/carbon black catalysts.

    PubMed

    Yano, Hiroshi; Higuchi, Eiji; Uchida, Hiroyuki; Watanabe, Masahiro

    2006-08-24

    Oxygen reduction reaction (ORR) activity and H(2)O(2) formation at Nafion-coated film electrodes of bulk-Pt and Pt nanoparticles dispersed on carbon black (Pt/CB) were investigated in 0.1 M HClO(4) solution at 30 to 110 degrees C by using a channel flow double electrode method. We have found that the apparent rate constants k(app) (per real Pt active surface area) for the ORR at bulk-Pt (with and without Nafion-coating) and Nafion-coated Pt/CB (19.3 and 46.7 wt % Pt, d(Pt) = 2.6 to 2.7 nm) thin-film electrodes were in beautiful agreement with each other in the operation conditions of polymer electrolyte fuel cells (PEFCs), i.e., 30-110 degrees C and ca. 0.7 to 0.8 V vs RHE. The H(2)O(2) yield was 0.6-1.0% at 0.7-0.8 V on all Nafion-coated Pt/CB and bulk-Pt and irrespective of Pt-loading level and temperature. Nafion coating was pointed out to be a major factor for the H(2)O(2) formation on Pt catalysts modifying the surface property, because H(2)O(2) production was not detected at the bulk-Pt electrode without Nafion coating. PMID:16913788

  11. CO adsorption on (111) and (100) surfaces of the Pt sub 3 Ti alloy. Evidence for parallel binding and strong activation of CO

    NASA Technical Reports Server (NTRS)

    Mehandru, S. P.; Anderson, A. B.; Ross, P. N.

    1985-01-01

    The CO adsorption on a 40 atom cluster model of the (111) surface and a 36 atom cluster model of the (100) surface of the Pt3Ti alloy was studied. Parallel binding to high coordinate sites associated with Ti and low CO bond scission barriers are predicted for both surfaces. The binding of CO to Pt sites occurs in an upright orientation. These orientations are a consequence of the nature of the CO pi donation interactions with the surface. On the Ti sites the orbitals donate to the nearly empty Ti 3d band and the antibonding counterpart orbitals are empty. On the Pt sites, however, they are in the filled Pt 5d region of the alloy band, which causes CO to bond in a vertical orientation by 5 delta donation from the carbon end.

  12. Surface diffusion of xenon on Pt(111)

    NASA Astrophysics Data System (ADS)

    Meixner, D. Laurence; George, Steven M.

    1993-06-01

    The surface diffusion of xenon on the Pt(111) surface was investigated using laser induced thermal desorption (LITD) and temperature programmed desorption (TPD) techniques. The surface diffusion coefficient at 80 K decreased dramatically from D=8×10-7 cm2/s at θ=0.05θs to approximately D=2×10-8 cm2/s at θ=θs, where θs denotes the saturation coverage at 85 K, corresponding to a commensurate monolayer coverage of 5.0×1014 xenon atoms/cm2. This coverage dependence was consistent with attractive interactions between the adsorbed xenon atoms and the existence of two-dimensional condensed phases of xenon on Pt(111). The kinetic parameters for surface diffusion at θ=θs were Edif=1.3±0.1 kcal/mol and D0=1.1×10-4±0.2 cm2/s. The magnitude of Edif at θ=θs represented the combined effect of the intrinsic corrugation of the adsorbate-surface potential and attractive interactions between the adsorbed xenon atoms. LITD experiments at θ=0.25 θs revealed diffusion kinetic parameters of Edif=1.2±0.2 kcal/mol and D0=3.4×10-4±0.5 cm2/s. The constant Edif at low and high coverage was attributed to the ``breakaway'' of xenon atoms from the edges of condensed phase xenon islands. The coverage dependence of the surface diffusion coefficient for Xe/Pt(111) was explained by a multiple site diffusion mechanism, where collisions with xenon islands limit diffusional motion. Thermal desorption kinetics for xenon on Pt(111) were determined using TPD experiments. Using the variation of heating rates method, the desorption parameters were Edes=6.6±0.2 kcal/mol and νdes=1.3×1013±0.4 s-1, in good agreement with previous studies. The xenon TPD peak shifted to higher temperature versus initial coverage at a fixed heating rate, providing further evidence for attractive interactions between the adsorbed xenon atoms.

  13. CO adsorption on (111) and (100) surfaces of the Pt/sub 3/Ti alloy: evidence for parallel binding and strong activation of CO

    SciTech Connect

    Mehandru, S.P.; Anderson, A.B.; Ross, P.N.

    1986-07-01

    An atom superposition and electron delocalization molecular orbital (ASED-MO) study has been made of CO adsorption on a 40-atom cluster model of the (111) surface and a 36-atom cluster model of the (100) surface of the Pt/sub 3/Ti alloy. Parallel binding to high-coordinate sites associated with Ti and low CO bond scission barriers are predicted for both surfaces. The preference for parallel adsorption is a consequence of the nature of the CO ..pi..=to-surface donation interactions. On Ti sites the ..pi.. orbitals donate to the early empty Ti 3d band and the antibonding counterpart orbitals are empty. Thus the ..pi.. donation makes substantial contributions to the adsorption bond order that are in addition to the contributions from 5 sigma donation and metal backbonding to the ..pi../sup */ orbitals. Altogether these bonding interactions favor the lying down orientation. On Pt sites, on the other hand, the ..pi.. donation antibonding counterpart orbitals are occupied so that the net interaction with Pt is a closed-shell repulsion. CO bonds upright in order to minimize the ..pi.. interaction, and concomitantly, the closed-shell repulsion, while maintaining 5sigma donation and ..pi../sup */ backbonding stabilizations. Comparisons are made with the results for a 40-atom cluster model of the unalloyed Pt(111) surface. It is shown that the extended Hueckel parameterization is inappropriate for studying CO and adsorption to Pt with ASED-MO theory because it incorrectly favors adsorption bonding through the oxygen end.

  14. A new experimental setup for high-pressure catalytic activity measurements on surface deposited mass-selected Pt clusters

    SciTech Connect

    Watanabe, Yoshihide; Isomura, Noritake

    2009-09-15

    A new experimental setup to study catalytic and electronic properties of size-selected clusters on metal oxide substrates from the viewpoint of cluster-support interaction and to formulate a method for the development of heterogeneous catalysts such as automotive exhaust catalysts has been developed. The apparatus consists of a size-selected cluster source, a photoemission spectrometer, a scanning tunneling microscope (STM), and a high-pressure reaction cell. The high-pressure reaction cell measurements provided information on catalytic properties in conditions close to practical use. The authors investigated size-selected platinum clusters deposited on a TiO{sub 2}(110) surface using a reaction cell and STM. Catalytic activity measurements showed that the catalytic activities have a cluster-size dependency.

  15. Pt{sub 3}Au and PtAu clusters: Electronic states and potential energy surfaces

    SciTech Connect

    Dai, D.; Balasubramanian, K.

    1994-03-15

    We carried out complete active space multiconfiguration self-consistent-field calculations followed by multireference singles+doubles configuration interaction with the Davidson correction which included up to 3.55 million configurations employing relativistic effective core potentials on Pt{sub 3}+Au and PtAu clusters. Four low-lying electronic states were identified for Pt{sub 3}+Au. The {sup 2}{ital A}{sub 2} electronic state ({ital C}{sub 3{ital v}}) was found to be the ground state of Pt{sub 3}Au. Spin--orbit effects were found to be significant. We also computed six low-lying electronic states of PtAu and four low-lying electronic states of PtAu{sup +}. The 5/2 ({sup 2}{Delta}) and 0{sup +}({sup 1}{Sigma}{sup +}) states were found to be the ground states of PtAu and PtAu{sup +}, respectively.

  16. Beneficial compressive strain for oxygen reduction reaction on Pt (111) surface

    SciTech Connect

    Kattel, Shyam; Wang, Guofeng

    2014-09-28

    We investigated the influence of compressive surface strain on the progression of oxygen reduction reaction (ORR) on Pt(111) surface using the density functional theory (DFT) calculation method. Specifically, we calculated the binding energies of all the chemical species possibly involved in ORR and the reaction energies (heat of reaction and activation energy) of all the possible ORR elementary reactions on the Pt(111) surfaces with −2% and −3% strain. Our DFT results indicate that all the ORR species bind more weakly on the compressively strained surfaces than on an unstrained surface owing to strain-induced d-electron band broadening. Our DFT calculations further predict that both OOH dissociation and HOOH dissociation pathways could be active for ORR on the Pt(111) surface with compressive strain between −2% and −3%. Moreover, the activation energies of the ORR rate-determining steps on the compressively strained Pt(111) surfaces were found to be lower than that on the unstrained Pt(111) surface. It was thus inferred that a −2% to −3% surface strain could lead to enhanced ORR activity on the Pt(111) catalysts. Consequently, our study suggests that tuning surface strain is an effective way to improve the performance of Pt-based electrocatalysts for ORR.

  17. Distinguishing molecular environments in supported Pt catalysts and their influences on activity and selectivity

    NASA Astrophysics Data System (ADS)

    Jones, Louis Chin

    This thesis entails the synthesis, automated catalytic testing, and in situ molecular characterization of supported Pt and Pt-alloy nanoparticle (NP) catalysts, with emphasis on how to assess the molecular distributions of Pt environments that are affecting overall catalytic activity and selectivity. We have taken the approach of (a) manipulating nucleation and growth of NPs using oxide supports, surfactants, and inorganic complexes to create Pt NPs with uniform size, shape, and composition, (b) automating batch and continuous flow catalytic reaction tests, and (c) characterizing the molecular environments of Pt surfaces using in situ infrared (IR) spectroscopy and solid-state 195Pt NMR. The following will highlight the synthesis and characterization of Ag-doped Pt NPs and their influence on C 2H2 hydrogenation selectivity, and the implementation of advanced solid-state 195Pt NMR techniques to distinguish how distributions of molecular Pt environments vary with nanoparticle size, support, and surface composition.

  18. Adsorption and coupling of 4-aminophenol on Pt(111) surfaces

    NASA Astrophysics Data System (ADS)

    Otero-Irurueta, G.; Martínez, J. I.; Bueno, R. A.; Palomares, F. J.; Salavagione, H. J.; Singh, M. K.; Méndez, J.; Ellis, G. J.; López, M. F.; Martín-Gago, J. A.

    2016-04-01

    We have deposited 4-aminophenol on Pt(111) surfaces in ultra-high vacuum and studied the strength of its adsorption through a combination of STM, LEED, XPS and ab initio calculations. Although an ordered (2√3 × 2√3)R30° phase appears, we have observed that molecule-substrate interaction dominates the adsorption geometry and properties of the system. At RT the high catalytic activity of Pt induces aminophenol to lose the H atom from the hydroxyl group, and a proportion of the molecules lose the complete hydroxyl group. After annealing above 420 K, all deposited aminophenol molecules have lost the OH moiety and some hydrogen atoms from the amino groups. At this temperature, short single-molecule oligomer chains can be observed. These chains are the product of a new reaction that proceeds via the coupling of radical species that is favored by surface diffusion.

  19. Adsorption and Coupling of 4-aminophenol on Pt(111) surfaces

    PubMed Central

    Otero-Irurueta, G.; Martínez, J. I.; Bueno, R.A.; Palomares, F. J.; Salavagione, H. J.; Singh, M. K.; Méndez, J.; Ellis, G. J.; López, M. F.; Martín-Gago, J. A.

    2016-01-01

    We have deposited 4-aminophenol on Pt(111) surfaces in ultra-high vacuum and studied the strength of its adsorption through a combination of STM, LEED, XPS and ab initio calculations. Although an ordered (2√3×2√3)R30° phase appears, we have observed that molecule-substrate interaction dominates the adsorption geometry and properties of the system. At RT the high catalytic activity of Pt induces aminophenol to lose the H atom from the hydroxyl group, and a proportion of the molecules lose the complete hydroxyl group. After annealing above 420K, all deposited aminophenol molecules have lost the OH moiety and some hydrogen atoms from the amino groups. At this temperature, short single-molecule oligomer chains can be observed. These chains are the product of a new reaction that proceeds via the coupling of radical species that is favoured by surface diffusion. PMID:27279673

  20. Reforming of oxygenates for H2 production: correlating reactivity of ethylene glycol and ethanol on Pt(111) and Ni/Pt(111) with surface d-band center.

    PubMed

    Skoplyak, Orest; Barteau, Mark A; Chen, Jingguang G

    2006-02-01

    The dehydrogenation and decarbonylation of ethylene glycol and ethanol were studied using temperature programmed desorption (TPD) on Pt(111) and Ni/Pt(111) bimetallic surfaces, as probe reactions for the reforming of oxygenates for the production of H2 for fuel cells. Ethylene glycol reacted via dehydrogenation to form CO and H2, corresponding to the desired reforming reaction, and via total decomposition to produce C(ad), O(ad), and H2. Ethanol reacted by three reaction pathways, dehydrogenation, decarbonylation, and total decomposition, producing CO, H2, CH4, C(ad), and O(ad). Surfaces prepared by deposition of a monolayer of Ni on Pt(111) at 300 K, designated Ni-Pt-Pt(111), displayed increased reforming activity compared to Pt(111), subsurface monolayer Pt-Ni-Pt(111), and thick Ni/Pt(111). Reforming activity was correlated with the d-band center of the surfaces and displayed a linear trend for both ethylene glycol and ethanol, with activity increasing as the surface d-band center moved closer to the Fermi level. This trend was opposite to that previously observed for hydrogenation reactions, where increased activity occurred on subsurface monolayers as the d-band center shifted away from the Fermi level. Extrapolation of the correlation between activity and the surface d-band center of bimetallic systems may provide useful predictions for the selection and rational design of bimetallic catalysts for the reforming of oxygenates. PMID:16471734

  1. RhPt/graphite catalysts for CO electrooxidation: Performance of mixed metal and alloyed surfaces

    NASA Astrophysics Data System (ADS)

    Fang, L.; Vidal-Iglesias, F. J.; Huxter, S. E.; Attard, G. A.; Wells, P. B.

    2015-01-01

    Cyclic voltammetry (CV) and X-ray photoelectron spectroscopy (XPS) have been used to characterise novel PtRh mixed metal and surface alloyed active phases supported on 5% Pt/graphite catalysts (5% Pt/G). The active phases could be prepared using forced deposition or a combination of forced deposition and thermal annealing in a flowing 5% hydrogen in argon gas mixture at 700 K. The protocols employed originate directly from previous single crystal studies of Rh on Pt{100} whereby Rh overlayers (either singly adsorbed or as a 'sandwich structure' of alternate Pt/Rh/Pt layers) could be transformed into surface PtRh alloys by careful thermal annealing. We demonstrate that this method is also successful for the preparation of active supported catalysts for CO electrooxidation whereby a peak potential as low as 0.60 V (Pd/H) for the CO oxidation is reported (0.12 V lower than that on 5% Pt/G). Moreover, the onset potential for CO stripping is lowered to 0.33 V (Pd/H). The presence of alloyed PtRh phases gives rise to a small but reproducible 0.1-0.2 eV shift to higher binding energy of the Pt 4f7/2 XPS peak together with strongly modified Pt and Rh electrosorption features in the CV which correlate with changes in surface composition. Unusual kinetic behaviour in the CO stripping peaks from the PtRh catalyst as a function of CO coverage is ascribed to competition between electrochemical oxide on Rh and CO-induced blocking of electrochemical oxide formation sites at the highest CO coverage. For PtRh alloys, the onset of electrochemical oxide formation shifts to more positive potentials relative to Rh overlayers and so a different behaviour towards CO electrooxidation is observed.

  2. Activity of dealloyed PtCo 3 and PtCu 3 nanoparticle electrocatalyst for oxygen reduction reaction in polymer electrolyte membrane fuel cell

    NASA Astrophysics Data System (ADS)

    Oezaslan, Mehtap; Strasser, Peter

    We report a comparative study of the alloy formation and electrochemical activity of dealloyed PtCo 3 and PtCu 3 nanoparticle electrocatalysts for the oxygen reduction reaction (ORR). For the Pt-Co system the maximum annealing temperatures were 650 °C, 800 °C and 900 °C for 7 h to drive the Pt-Co alloy formation and the particle growth. EDS and XRD were employed for the characterization of catalyst powders. The RDE and RRDE experiments were conducted in 0.1 M HClO 4 at room temperature. We demonstrate that the mass and surface area specific ORR activities of Pt-Co and Pt-Cu alloys after voltammetric activation exhibit a considerable improvement compared to those of pure Pt/C. The dealloyed PtCo 3 (800 °C/7 h) electrocatalyst performs 3 times higher in terms of Pt-based mass activity and 4-5 times higher in terms of ECSA-based specific activity than a 28.2 wt.% Pt/C. Dealloyed Pt-Co catalysts (800 °C/7 h) show the most favorable balance between mass and specific ORR activity with a particle size of 2.2 ± 0.1 nm. We hypothesize that geometric strain effects of the dealloyed Pt-Co nanoparticles, similar to those found in dealloyed PtCu 3 nanoparticles, are responsible for the improvement in ORR activity [1].

  3. PT AND PT/NI "NEEDLE" ELETROCATALYSTS ON CARBON NANOTUBES WITH HIGH ACTIVITY FOR THE ORR

    SciTech Connect

    Colon-Mercado, H.

    2011-11-10

    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.

  4. Surface carbonaceous deposits as activity and selectivity influencing species in ring-opening reactions of propylcyclobutane catalyzed by Pt/SiO[sub 2

    SciTech Connect

    Toeroek, B.; Molnar, A.; Palinko, I.; Bartok, M. )

    1994-02-01

    Active site formation in the hydrogenative ring opening of propylcyclobutane over Pt/SiO[sub 2] was investigated in a static reactor, mainly at 373 K. Changes in the ring-opening rates and selectivities on variously treated catalyst are described. Three types of treatment were applied: repeated runs with (i) only evacuation or (ii) inter-run reduction (H[sub 2], 473 K, 0.5 h), or (iii) prepoisoning of the catalyst with propylcyclobutane at 373 K or 673 K. The observed (in some cases dramatic) increase in selectivity towards the formation of heptane (1,2 C-C bond scission) is interpreted in terms of the formation of a metal-carbonaceous deposit interface where the deposit provides an anchoring site for the adsorption of the propyl side-chain and the ring opens on the clean Pt atoms. Changes in activity due to the various treatments are also discussed. 19 refs., 2 figs., 2 tabs.

  5. Tuning the surface electronic structure of a Pt3Ti(111) electro catalyst.

    PubMed

    Paßens, M; Caciuc, V; Atodiresei, N; Moors, M; Blügel, S; Waser, R; Karthäuser, S

    2016-07-21

    Increasing the efficiency and stability of bimetallic electro catalysts is particularly important for future clean energy technologies. However, the relationship between the surface termination of these alloys and their catalytic activity is poorly understood. Therefore, we report on fundamental UHV-SPM, LEED, and DFT calculations of the Pt3Ti(111) single crystal surface. Using voltage dependent imaging the surface termination of Pt3Ti(111) was studied with atomic resolution. Combining these images with simulated STM maps based on ab initio DFT calculations allowed us to identify the three upper layers of the Pt3Ti(111) single crystal and their influence upon the surface electronic structure. Our results show that small changes in the composition of the second and third atomic layer are of significant influence upon the surface electronic structure of the Pt3Ti electro catalyst. Furthermore, we provide relevant insights into the dependence of the surface termination on the preparation conditions. PMID:26865393

  6. High temperature growth of Pt on the Rh(111) surface

    NASA Astrophysics Data System (ADS)

    Duisberg, M.; Dräger, M.; Wandelt, K.; Gruber, E. L. D.; Schmid, M.; Varga, P.

    1999-08-01

    The epitaxial growth of Pt on the Rh(111) surface at 700 K was studied with AES, UPS, ISS and STM. From AES and ISS measurements a 2D growth mode is concluded at this substrate temperature. The morphology of the surface is studied by photoemission spectra of adsorbed Xe (PAX) and STM. A disperse distribution of the Pt atoms is suggested by PAX and is consistent with an incorporation of these atoms into the first substrate layer. Atomically and chemically resolved STM measurements confirm these conclusions. The interaction of CO with the surface alloy is investigated by UPS. The CO-induced features in UP spectra show significant differences in the peak positions and shape between the clean substrate and the surface precovered with different amounts of Pt. The CO induced emissions are, thus, used for a quantitative titration of Pt on the Rh surface.

  7. Tuning the surface electronic structure of a Pt3Ti(111) electro catalyst

    NASA Astrophysics Data System (ADS)

    Paßens, M.; Caciuc, V.; Atodiresei, N.; Moors, M.; Blügel, S.; Waser, R.; Karthäuser, S.

    2016-07-01

    Increasing the efficiency and stability of bimetallic electro catalysts is particularly important for future clean energy technologies. However, the relationship between the surface termination of these alloys and their catalytic activity is poorly understood. Therefore, we report on fundamental UHV-SPM, LEED, and DFT calculations of the Pt3Ti(111) single crystal surface. Using voltage dependent imaging the surface termination of Pt3Ti(111) was studied with atomic resolution. Combining these images with simulated STM maps based on ab initio DFT calculations allowed us to identify the three upper layers of the Pt3Ti(111) single crystal and their influence upon the surface electronic structure. Our results show that small changes in the composition of the second and third atomic layer are of significant influence upon the surface electronic structure of the Pt3Ti electro catalyst. Furthermore, we provide relevant insights into the dependence of the surface termination on the preparation conditions.Increasing the efficiency and stability of bimetallic electro catalysts is particularly important for future clean energy technologies. However, the relationship between the surface termination of these alloys and their catalytic activity is poorly understood. Therefore, we report on fundamental UHV-SPM, LEED, and DFT calculations of the Pt3Ti(111) single crystal surface. Using voltage dependent imaging the surface termination of Pt3Ti(111) was studied with atomic resolution. Combining these images with simulated STM maps based on ab initio DFT calculations allowed us to identify the three upper layers of the Pt3Ti(111) single crystal and their influence upon the surface electronic structure. Our results show that small changes in the composition of the second and third atomic layer are of significant influence upon the surface electronic structure of the Pt3Ti electro catalyst. Furthermore, we provide relevant insights into the dependence of the surface termination on the

  8. SISGR: Theoretically relating the surface composition of Pt alloys to their performance as the electrocatalysts of low-temperature fuel cells

    SciTech Connect

    Wang, Guofeng

    2010-12-31

    The main goal of this project is to gain fundamental knowledge about the relation between surface composition and catalytic performance of Pt alloy catalysts for oxygen reduction reaction (ORR). Specific objectives are: to develop and improve a first-principles based multiscale computation approach to simulating surface segregation phenomena in Pt alloy surfaces; to evaluate the surface electronic structure and catalytic activity of Pt alloy catalysts and; to relate the surface composition to the catalytic performance of Pt alloy catalysts.

  9. 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

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

    NASA Astrophysics Data System (ADS)

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

    2014-02-01

    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.

  11. 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

  12. Insight into the adsorption and dissociation of CH4 on Pt(h k l) surfaces: A theoretical study

    NASA Astrophysics Data System (ADS)

    Zhang, Riguang; Song, Luzhi; Wang, Yuhan

    2012-07-01

    A density functional theory slab calculations of CH4 dissociation on Pt(h k l) surfaces have been systematically presented. On the basis of the energetic analysis, the favorable adsorption sites and stable configurations of CHx(x = 0-4) and H species on Pt(1 1 1), Pt(1 1 0) and Pt(1 0 0) surfaces are first obtained, respectively. Afterwards, the most stable configurations of coadsorbed CHx/H(x = 0-3) are located. Further, the kinetic and thermodynamical results of CH4 dissociation on Pt(h k l) surface suggest that CH is the most abundant CHx species. Our results mean that Pt catalyst can resist the carbon deposition in the CH4 dissociation, which can give a microscopic reason that why Pt catalyst can lead to lower carbon deposition and show a high activity in the reaction related to CH4.

  13. A Cu/Pt Near-Surface Alloy for Water-Gas Shift Catalysis.

    SciTech Connect

    Knudsen, Jan; Nilekar, Anand U.; Vang, Ronnie T.; Schnadt, Joachim; Kunkes, Edward L.; Dumesic, James A.; Mavrikakis, Manos; Besenbacher, Fleming

    2007-05-01

    The research described in this product was performed in part in the Environmental Molecular Sciences Laboratory, a national scientific user facility sponsored by the Department of Energy's Office of Biological and Environmental Research and located at Pacific Northwest National Laboratory. The primary route to hydrogen production from fossil fuels involves the water-gas shift (WGS) reaction, and an improvement in the efficiency of WGS catalysts could therefore lead to a major leap forward in the realization of hydrogen economy. On the basis of a combination of high-resolution scanning tunneling microscopy, X-ray photoelectron spectroscopy, and density functional theory (DFT) calculations, we suggest the existence of a new thermodynamically stable Cu/Pt near-surface alloy (NSA). Temperature-programmed desorption and DFT reveal that this Cu/Pt NSA binds CO significantly more weakly than does Pt alone, thereby implying a considerable reduction in the potential for CO poisoning of the Cu/Pt NSA surface as compared to that of pure Pt. In addition, DFT calculations show that this Cu/Pt NSA is able to activate H2O easily, which is the rate-determining step for the WGS on several metal surfaces, and, at the same time, to bind the products of that reaction and formate intermediates rather weakly, thus avoiding possible poisoning of the catalyst surface. The Cu/Pt NSA is thus a promising candidate for an improved WGS catalyst.

  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. 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.

  16. Observation of Single Pt Nanoparticle Collisions: Enhanced Electrocatalytic Activity on a Pd Ultramicroelectrode.

    PubMed

    Shin, Changhwan; Park, Tae Eun; Park, Changki; Kwon, Seong Jung

    2016-06-01

    Single Pt nanoparticle (NP) collisions on an electrode surface were detected by using an electrocatalytic amplification method with a Pd ultramicroelectrode (UME). Pd is not a preferred material for UMEs for the detection of single Pt NP collisions, because Pd shows similar electrocatalytic activity compared with Pt for hydrazine oxidation, thus resulting in a high background current level. However, a Pt NP colliding on the Pd UME shows greatly enhanced activity compared with a Pt NP on an inert UME, such as a Au UME, which is usually used for the detection of single Pt NP collisions. The use of an electroactive UME material instead of an inert one facilitated the study of single-NP activity on the various solid supports, which is important in many NP applications. PMID:26955784

  17. In situ surface X-ray scattering of stepped surface of platinum: Pt(311).

    PubMed

    Nakahara, Akira; Nakamura, Masashi; Sumitani, Kazushi; Sakata, Osami; Hoshi, Nagahiro

    2007-10-23

    Surface structure of a stepped surface of Pt, Pt(311) (=2(100)-(111)), has been determined under potential control in 0.1 M HClO4 with the use of in situ surface X-ray scattering (SXS). The crystal truncation rods (CTRs) are reproduced well with the (1x2) missing-row model. Relaxation of surface layers, which is observed on the low-index planes of Pt, is not found on Pt(311) in the "adsorbed hydrogen region". CTRs at 0.10 (RHE) have the same feature as those at 0.50 V, showing that the surface layers of Pt(311) have no potential dependence. Scanning tunneling microscopy (STM) also supports the (1x2) structure of Pt(311) in 0.1 M HClO4. PMID:17902717

  18. Mechanistic insight into size-dependent activity and durability in Pt/CNT catalyzed hydrolytic dehydrogenation of ammonia borane.

    PubMed

    Chen, Wenyao; Ji, Jian; Feng, Xiang; Duan, Xuezhi; Qian, Gang; Li, Ping; Zhou, Xinggui; Chen, De; Yuan, Weikang

    2014-12-01

    We report a size-dependent activity in Pt/CNT catalyzed hydrolytic dehydrogenation of ammonia borane. Kinetic study and model calculations revealed that Pt(111) facet is the dominating catalytically active surface. There is an optimized Pt particle size of ca. 1.8 nm. Meanwhile, the catalyst durability was found to be highly sensitive to the Pt particle size. The smaller Pt particles appear to have lower durability, which could be related to more significant adsorption of B-containing species on Pt surfaces as well as easier changes in Pt particle size and shape. The insights reported here may pave the way for the rational design of highly active and durable Pt catalysts for hydrogen generation. PMID:25405630

  19. Ultrathin Icosahedral Pt-Enriched Nanocage with Excellent Oxygen Reduction Reaction Activity.

    PubMed

    He, Dong Sheng; He, Daping; Wang, Jing; Lin, Yue; Yin, Peiqun; Hong, Xun; Wu, Yuen; Li, Yadong

    2016-02-10

    Cost-efficient utilization of Pt in the oxygen reduction reaction (ORR) is of great importance for the potential industrial scale demand of proton-exchange membrane fuel cells. Designing a hollow structure of a Pt catalyst offers a great opportunity to enhance the electrocatalytic performance and maximize the use of precious Pt. Herein we report a routine to synthesize ultrathin icosahedral Pt-enriched nanocages. In detail, the Pt atoms were conformally deposited on the surface of Pd icosahedral seeds, followed by selective removal of the Pd core by a concentrated HNO3 solution. The icosahedral Pt-enriched nanocage that is a few atomic layers thick includes the merits of abundant twin defects, an ultrahigh surface/volume ratio, and an ORR-favored Pt{111} facet, all of which have been demonstrated to be promoting factors for ORR. With a 10 times higher specific activity and 7 times higher mass activity, this catalyst shows more extraordinary ORR activity than the commercial Pt/C. The ORR activity of icosahedral Pt-enriched nanocages outperforms the cubic and octahedral nanocages reported in the literature, demonstrating the superiority of the icosahedral nanocage structure. PMID:26808073

  20. Highly Active Pt(3)Pb and Core-Shell Pt(3)Pb-Pt Electrocatalysts for Formic Acid Oxidation

    SciTech Connect

    Kang Y.; Stach E.; Qi L.; Li M.; Diaz R.E.; Su D.; Adzic R.R.; Li J.; Murray C.B.

    2012-03-27

    Formic acid is a promising chemical fuel for fuel cell applications. However, due to the dominance of the indirect reaction pathway and strong poisoning effects, the development of direct formic acid fuel cells has been impeded by the low activity of existing electrocatalysts at desirable operating voltage. We report the first synthesis of Pt{sub 3}Pb nanocrystals through solution phase synthesis and show they are highly efficient formic acid oxidation electrocatalysts. The activity can be further improved by manipulating the Pt{sub 3}Pb-Pt core-shell structure. Combined experimental and theoretical studies suggest that the high activity from Pt{sub 3}Pb and the Pt-Pb core-shell nanocrystals results from the elimination of CO poisoning and decreased barriers for the dehydrogenation steps. Therefore, the Pt{sub 3}Pb and Pt-Pb core-shell nanocrystals can improve the performance of direct formic acid fuel cells at desired operating voltage to enable their practical application.

  1. Integrated X-ray photoelectron spectroscopy and DFT characterization of benzene adsorption on Pt(111), Pt(355) and Pt(322) surfaces.

    PubMed

    Zhang, Renqin; Hensley, Alyssa J; McEwen, Jean-Sabin; Wickert, Sandra; Darlatt, Erik; Fischer, Kristina; Schöppke, Matthias; Denecke, Reinhard; Streber, Regine; Lorenz, Michael; Papp, Christian; Steinrück, Hans-Peter

    2013-12-21

    We systematically investigate the adsorption of benzene on Pt(111), Pt(355) and Pt(322) surfaces by high-resolution X-ray photoelectron spectroscopy (XPS) and first-principle calculations based on density functional theory (DFT), including van der Waals corrections. By comparing the adsorption energies at 1/9, 1/16 and 1/25 ML on Pt(111), we find significant lateral interactions exist between the benzene molecules at 1/9 ML. The adsorption behavior on Pt(355) and Pt(322) is very different. While on Pt(355) a step species is clearly identified in the C 1s spectra at low coverages followed by occupation of a terrace species at high coverages, no evidence for a step species is found on Pt(322). These different adsorption sites are confirmed by extensive DFT calculations, where the most favorable adsorption configurations on Pt(355) and Pt(322) are also found to vary: a highly distorted across the step molecule is found on Pt(355) while a less distorted configuration adjacent to the step molecule is deduced for Pt(322). The theoretically proposed C 1s core level binding energy shifts between these most favorable configurations and the terrace species are found to correlate well with experiment: for Pt(355), two adsorbate states are found, separated by ~0.4 eV in XPS and 0.3 eV in the calculations, in contrast to only one state on Pt(322). PMID:24189500

  2. Bulk ordering and surface segregation in Ni50Pt50

    NASA Astrophysics Data System (ADS)

    Pourovskii, L. V.; Ruban, A. V.; Abrikosov, I. A.; Vekilov, Y. Kh.; Johansson, B.

    2001-07-01

    Interatomic interactions obtained from the effective screened generalized-perturbation method have been applied in Monte Carlo simulations to derive the bulk and surface-alloy configurations for Ni50Pt50. The calculated order-disorder transition temperature and short-range order parameters in the bulk compare well with experimental data. The surface-alloy compositions for the (111) and (110) facets above the ordering transition temperature are also found to be in a good agreement with experiments. It is demonstrated that the segregation profile at the (110) surface of NiPt is mainly caused by the unusually strong segregation of Pt into the second layer and the interlayer ordering due to large chemical nearest-neighbor interactions.

  3. Mesoporous graphene-like nanobowls as Pt electrocatalyst support for highly active and stable methanol oxidation

    NASA Astrophysics Data System (ADS)

    Yan, Zaoxue; He, Guoqiang; Jiang, Zhifeng; Wei, Wei; Gao, Lina; Xie, Jimin

    2015-06-01

    Mesoporous graphene-like nanobowls (GLBs) with high surface area of 1091 m2 g-1, high pore volume of 2.7 cm3 g-1 and average pore diameter of 9.8 nm are synthesized through template method. The GLBs with inherent excellent electrical conductivity and chemical inertia show the properties of well mass transfer, poison resistance and stable loading of smaller Pt particles. Therefore, the Pt/GLB catalyst shows much higher activity and stability than that of commercial Pt/C (TKK) for methanol oxidation reaction (MOR). Therein, the peak current density on Pt/GLB (2075 mA mgPt-1) for MOR is 2.87 times that of commercial Pt/C (723 mA mgPt-1); and the onset potential for the MOR on the former is negatively shifted about 160 mV compared with that on the latter. The catalytic performances of the Pt/GLB are also better than those of the Pt loading on mesoporous amorphous carbon nanobowls (Pt/BLC), indicating promotion effect of graphite on Pt catalytic performance.

  4. Adsorption of aromatics on the (111) surface of PtM and PtM3 (M = Fe, Ni) alloys

    SciTech Connect

    Hensley, Alyssa; Schneider, Sebastian; Wang, Yong; McEwen, Jean-Sabin

    2015-09-18

    The adsorption of benzene and phenol was studied on PtM and PtM3 (111) surfaces, with M being either Ni or Fe. Under vacuum, the most favorable near surface structures showed an enrichment in Pt over the M species. An analysis of the electronic structure of the metal species in the clean surfaces with different near surface structures was done with the d-band model and showed that the Pt's d-states are significantly shifted away from the Fermi level due to the Pt-M interactions while the M species' d-states were less affected, with Ni's d-band shifting closer to the Fermi level and Fe's d-band shifting away from the Fermi level. The adsorption of aromatics, benzene and phenol, on several near surface structures for the PtM and PtM3 (111) surfaces showed that higher surface M concentrations resulted in a stronger adsorption due to the larger amount of charge transferred between the adsorbate and surface. However, compared to the adsorption of benzene and phenol on monometallic surfaces, the adsorption of these species on the PtM and PtM3 (111) surfaces was significantly weakened. Overall, our results show that the observed behavior of these Pt/Fe and Pt/Ni alloys is similar to that seen for the previously studied Pd/Fe surfaces. Furthermore, balancing the weakly adsorbing Pt surface species with the more strongly interacting Fe or Ni species can lead to the tailored adsorption of aromatics with applications in both hydrodeoxygenation and hydrogenation reactions by increasing the desorption rate of wanted aromatic products.

  5. Highly branched PtCu bimetallic alloy nanodendrites with superior electrocatalytic activities for oxygen reduction reactions

    NASA Astrophysics Data System (ADS)

    Fu, Shaofang; Zhu, Chengzhou; Shi, Qiurong; Xia, Haibing; Du, Dan; Lin, Yuehe

    2016-02-01

    Morphology control is a promising strategy to improve the catalytic performance of Pt-based catalysts. In this work, we reported a facile synthesis of PtCu bimetallic alloy nanodendrites using Brij 58 as a template. The highly branched structures and porous features offer relatively large surface areas, which is beneficial to the enhancement of the catalytic activity for oxygen reduction reactions in fuel cells. In addition, the elimination of carbon supports showed an important effect on the stability of the catalysts. By tuning the ratio of Pt and Cu precursors, PtCu nanodendrites were almost four times more active on the basis of an equivalent Pt mass for oxygen reduction reactions than the commercial Pt/C catalyst.Morphology control is a promising strategy to improve the catalytic performance of Pt-based catalysts. In this work, we reported a facile synthesis of PtCu bimetallic alloy nanodendrites using Brij 58 as a template. The highly branched structures and porous features offer relatively large surface areas, which is beneficial to the enhancement of the catalytic activity for oxygen reduction reactions in fuel cells. In addition, the elimination of carbon supports showed an important effect on the stability of the catalysts. By tuning the ratio of Pt and Cu precursors, PtCu nanodendrites were almost four times more active on the basis of an equivalent Pt mass for oxygen reduction reactions than the commercial Pt/C catalyst. Electronic supplementary information (ESI) available. See DOI: 10.1039/c5nr07682j

  6. Adsorption of ethene on Pt(1 1 1) and ordered Pt xSn/Pt(1 1 1) surface alloys: A comparative HREELS and DFT investigation

    NASA Astrophysics Data System (ADS)

    Essen, J. M.; Haubrich, J.; Becker, C.; Wandelt, K.

    2007-08-01

    The adsorption of ethene (C 2H 4) on Pt(1 1 1) and the Pt 3Sn/Pt(1 1 1) and Pt 2Sn/Pt(1 1 1) surface alloys has been investigated experimentally by high-resolution electron energy loss spectroscopy and temperature programmed desorption. The experimental results have been compared with density functional theory (DFT) calculations allowing us to perform a complete assignment of all vibration modes and loss features to the species present on the surfaces. On Pt(1 1 1) as well as on the Pt-Sn surface alloys an η2 di-σ-bonded conformation of ethene has been found to be the most stable adsorbed form. In addition to this majority species a minor amount of π-bonded ethene has been identified, which is more abundant on the Pt 2Sn surface alloy than on the other surfaces. Additionally the HREELS spectra of ethene on Pt(1 1 1) and the Pt-Sn surface alloys differ only slightly in terms of the energetic positions of the loss peaks.

  7. Insight into the active phase of CO oxidation on Ni/Pt and NiO1 - x/Pt model catalysts from a first principles investigation

    NASA Astrophysics Data System (ADS)

    Wang, Chen; Lv, Yong-kang; Wang, Gui-Chang

    2013-08-01

    CO oxidation on bimetallic and metal oxide has drawn much attention in the past years due to its importance both technologically and theoretically, but the active phase as well as the detailed reaction mechanism on the bimetallic surface oxide (i.e., a sandwich-like surface structure) are still unclear. In this work, the CO oxidation on the various Pt-Ni model catalysts [including Pt(111), Pt/Ni/Pt(111), Ni/Pt(111), NiO1 - x/Pt(111) and NiO1 - x/Pt/Ni/Pt(111)] was studied by performing the density functional theory calculations. It was found that the CO oxidation reaction would process with a higher reaction barrier on metals at lower oxygen coverage via the Langmuir-Hinshelwood (L-H) mechanism, whereas CO oxidation reaction would take place with a lower barrier at higher oxygen coverage on metals or in the presence of molecular oxygen/CO (on NiO1 - x-like systems) via the Eley-Rideal mechanism. The calculation results show that the activation energy of CO oxidation follows the order: Pt(111) (0.75 eV) > Pt/Ni/Pt(111) (0.69 eV) > Ni/Pt(111) (0.47 eV at 1 ML oxygen), which is in general agreement with the experimental observations. On the surface oxide NiO1 - x/Pt(111) and NiO1 - x/Pt/Ni/Pt(111) systems, it was found that the molecular CO can subtract the surface lattice oxygen to form CO2 spontaneously through the Eley-Rideal mechanism on NiO1 - x/Pt/Ni/Pt(111), whereas such kinetic behavior cannot occur on the NiO1 - x/Pt(111) system, suggesting the high reactivity of CO oxidation on NiO1 - x/Pt/Ni/Pt(111). The possible reason was analyzed by the magnitude of surface oxygen vacancy formation energy, namely NiO1 - x/Pt/M/Pt(111) with relatively low vacancy formation energy as compared to that of NiO1 - x/Pt(111) (3.46 vs 4.51 eV). Moreover, we extend the above study to a more general case in which the subsurface metals in NiO1 - x/Pt/M/Pt(111) system including VIII group metals like Fe/Co/Ni and the IB group metals like Cu, and it was found that the molecular CO

  8. Elucidation of adsorption processes at the surface of Pt(331) model electrocatalysts in acidic aqueous media.

    PubMed

    Pohl, Marcus D; Colic, Viktor; Scieszka, Daniel; Bandarenka, Aliaksandr S

    2016-04-20

    The Pt(331) surface has long been known to be the most active pure metal electrocatalyst for the oxygen reduction reaction (ORR) in acidic media. Its activity is often higher than those known for the Pt-based alloys towards ORR, being comparable with the most active Pt3Ni(111), Pt3Y or Pt5Gd, and being more active than e.g. polycrystalline Pt3Ni. Multiple active sites at this surface offer adsorption energies which are close to the optimal binding energy with respect to the main ORR intermediates; nevertheless, the exact location of these sites is still not clear. Taking into account the unique surface geometry of Pt(331), some adsorbates (including some oxygenated ORR-intermediates) should also contribute to the electronic structure of the neighbouring catalytic centres. However, the experimental elucidation of the specific adsorption of oxygenated species at this surface appears to be a non-trivial task. Such information holds the keys to the understanding of the high activity of this material and would enable the rational design of nanostructured ORR catalysts even without alloying. In this work, the electrified Pt(331)/electrolyte interface has been characterised using cyclic voltammetry (CV) combined with potentiodynamic electrochemical impedance spectroscopy (PDEIS) in 0.1 M HClO4 solutions. The systems were studied in the potential region between 0.05 V and 1.0 V vs. RHE, where the adsorption of *H, *OH and *O species is possible in both O2-free and O2-saturated electrolytes. Our CV and PDEIS results support the hypothesis that in contrast to Pt(111), many Pt(331) surface sites are likely blocked by *O species at the polymer electrolyte membrane fuel cell benchmark potential of 0.9 V (RHE). We propose a model illustrated by simplified adsorbate structures at different electrode potentials, which is, however, able to explain the voltammetric and impedance data, and which is in good agreement with previously reported electrocatalytic measurements. PMID

  9. Hydrogen adsorption-mediated synthesis of concave Pt nanocubes and their enhanced electrocatalytic activity

    NASA Astrophysics Data System (ADS)

    Lu, Bang-An; Du, Jia-Huan; Sheng, Tian; Tian, Na; Xiao, Jing; Liu, Li; Xu, Bin-Bin; Zhou, Zhi-You; Sun, Shi-Gang

    2016-06-01

    Concave nanocubes are enclosed by high-index facets and have negative curvature; they are expected to have enhanced reactivity, as compared to nanocubes with flat surfaces. Herein, we propose and demonstrate a new strategy for the synthesis of concave Pt nanocubes with {hk0} high-index facets, by using a hydrogen adsorption-mediated electrochemical square-wave potential method. It was found that Pt atoms prefer to deposit on edge sites rather than terrace sites on Pt surfaces with intensive hydrogen adsorption, resulting in the formation of concave structures. The as-prepared concave Pt nanocubes exhibit enhanced catalytic activity and stability towards oxidation of ethanol and formic acid in acidic solutions, compared to commercial Pt/C catalysts.Concave nanocubes are enclosed by high-index facets and have negative curvature; they are expected to have enhanced reactivity, as compared to nanocubes with flat surfaces. Herein, we propose and demonstrate a new strategy for the synthesis of concave Pt nanocubes with {hk0} high-index facets, by using a hydrogen adsorption-mediated electrochemical square-wave potential method. It was found that Pt atoms prefer to deposit on edge sites rather than terrace sites on Pt surfaces with intensive hydrogen adsorption, resulting in the formation of concave structures. The as-prepared concave Pt nanocubes exhibit enhanced catalytic activity and stability towards oxidation of ethanol and formic acid in acidic solutions, compared to commercial Pt/C catalysts. Electronic supplementary information (ESI) available: Details of DFT calculation, SEM images of concave Pt nanocubes, mass activity and stability characterization of the catalysts. See DOI: 10.1039/c6nr02349e

  10. Surface enrichment of Pt in Ga2O3 films grown on liquid Pt/Ga alloys

    NASA Astrophysics Data System (ADS)

    Grabau, Mathias; Krick Calderón, Sandra; Rietzler, Florian; Niedermaier, Inga; Taccardi, Nicola; Wasserscheid, Peter; Maier, Florian; Steinrück, Hans-Peter; Papp, Christian

    2016-09-01

    The formation of surface Ga2O3 films on liquid samples of Ga, and Pt-Ga alloys with 0.7 and 1.8 at.% Pt was examined using near-ambient pressure (NAP) X-ray photoelectron spectroscopy (XPS). Thickness, composition and growth of the oxide films were deduced as a function of temperature and Pt content of the alloys, in ultra-high vacuum and at oxygen pressures of 3 × 10- 7, 3 × 10- 3 and 1 mbar. We examined oxide layers up to a thickness of 37 Å. Different growth modes were found for oxidation at low and high pressures. The formed Ga2O3 oxide films showed an increased Pt content, while the pristine GaPt alloy showed a surface depletion of Pt at the examined temperatures. Upon growth of Ga2O3 on Pt/Ga alloys a linear increase of Pt content was observed, due to the incorporation of 3.6 at.% Pt in the Ga2O3. The Pt content in Ga2O3, at the examined temperatures and bulk Pt concentrations is found to be independent of pressure, temperature and the nominal Pt content of the metallic alloy.

  11. First-principles study of oxygen and hydrogen adsorption on Pt(111) and PtML/Pd(111) surfaces

    NASA Astrophysics Data System (ADS)

    Nie, J. L.; Ao, L.; Zu, X. T.

    2015-11-01

    In this paper, first-principles calculations based on density functional theory (DFT) have been performed to investigate the adsorption of oxygen and hydrogen on Pt(111) and Pd(111) surfaces covered by monolayer (ML) of Pt(PtML/Pd(111)). The results have shown that the oxygen molecule tends to adsorb on fcc site on both surfaces at the coverage of 0.25 ML, which becomes degeneration with hcp site when the coverage increases to 1 ML. For both oxygen and hydrogen, the adsorption on PtML/Pd(111) surface are stronger than those on Pt(111) surface. The adsorption energy difference for oxygen on the two surfaces is ˜0.2 eV at the coverage of 1 ML, which increases to ˜0.6 eV with the coverage decreasing to 0.25 ML. The similar energy difference was also found for hydrogen adsorption. The density of states analysis have demonstrated the chemical interaction of adsorbed oxygen with both pure Pt(111) and PtML/Pd(111) surfaces with certain shift of O2p states to lower level compared to isolated oxygen. For hydrogen adsorption, the hybridization of H1s with Pt5d states were observed for both surfaces, indicating the covalent bonding component of H-Pt bond.

  12. Surface science of Cs, CsO and CsI ionic layers on Pt(111)

    NASA Astrophysics Data System (ADS)

    Drnec, Jakub

    Cesium adsorption on Pt(111) and its coadsorption with iodine and oxygen is studied in this dissertation. The work function during Cs dosing first decreases and at Deltaφ ≈ 3 eV (thetaCs = 0.15) the surface undergoes surface transition between a disordered anomalous state (Pt(111)(anom)-Cs) and islands of a Pt(111)(2x2)-Cs causing a change in the slope of the work function curve. The work function curve reaches minimum at --5.5 eV where the surface is fully covered with the Pt(111)(2 x 2)-Cs structure( thetaCs = 0.25). Further Cs dosing results in a work function increase and the surface undergoes a phase transition to Pt(111)(√3 x√3)-Cs. The Cs saturated structure (Pt(111)(ihcp)-Cs) has an hexagonal symmetry with the unit cell vector aligned with the (1, 0) direction of the substrate. Cs in the anomalous state desorbs from the surface in a high-temperature TDS peak (> 1000 K). When the lock-in TDS detection technique is used, this peak appears to be phase shifted by 180° when compared to the desorption peak of normally adsorbed Cs (thetaCs> 0.15) . This phase shift is a consequence of a positive charge of desorbing Cs. The TDS and work function behavior were explained by a Monte Carlo desorption model incorporating di¤erent desorption behavior for all four observed adsorption phases. When O2 is dosed on a Pt(111)-Cs surface, the maximum coverage of oxygen bonded to the surface is signi.cantly increased in comparison to Pt(111). Anomalously adsorbed Cs activates the O2 bond but does not interact strongly with coadsorbed O. However, when O2 is dosed on Pt(111)(ihcp)-Cs, the oxygen first adsorbs to a sub-layer adsorption site and strongly interacts with Cs. The oxygen in this state is responsible for thermal stabilization of coadsorbed Cs. When iodine is coadsorbed on a Pt(111)-Cs surface, it also strongly interacts with and thermally stabilizes Cs. During the desorption of Cs,I layers, some Cs and I desorb together in the form of a CsxIy cluster. The

  13. Shape-dependent photocatalytic hydrogen evolution activity over a Pt nanoparticle coupled g-C3N4 photocatalyst.

    PubMed

    Cao, Shaowen; Jiang, Jing; Zhu, Bicheng; Yu, Jiaguo

    2016-07-28

    Cubic, octahedral and spherical platinum (Pt) nanoparticles (NPs) ex situ supported on a graphitic carbon nitride (g-C3N4) substrate are synthesized using a colloidal adsorption-deposition method for photocatalytic hydrogen evolution reactions. These Pt NPs of different shapes have similar sizes of around 10 nm but have different facets exposed. It is found that the visible-light-driven photocatalytic activities for the Pt/g-C3N4 hybrid photocatalysts follow the order as: cubic Pt/g-C3N4 < octahedral Pt/g-C3N4 < spherical Pt/g-C3N4, revealing the significant cocatalyst shape-sensitive photocatalytic activity in the Pt/g-C3N4 hybrids. This is mainly due to the different surface atomic structures of different exposed facets of Pt NPs, which lead to the disparity of active sites and adsorption energies in photocatalytic reactions. PMID:27409401

  14. 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.

  15. Surface X-ray scattering of stepped surfaces of platinum in an electrochemical environment: Pt(331) = 3(111)-(111) and Pt(511) = 3(100)-(111).

    PubMed

    Hoshi, Nagahiro; Nakamura, Masashi; Sakata, Osami; Nakahara, Akira; Naito, Keita; Ogata, Hiroyuki

    2011-04-01

    Real surface structures of the high-index planes of Pt with three atomic rows of terraces (Pt(331) = 3(111)-(111) and Pt(511) = 3(100)-(111)) have been determined in 0.1 M HClO(4) at 0.1 and 0.5 V(RHE) with the use of surface X-ray scattering (SXS). The surfaces with two atomic rows of terraces, Pt(110) = 2(111)-(111) and Pt(311) = 2(100)-(111) = 2(111)-(100), are reconstructed to a (1 × 2) structure according to previous studies. However, the surfaces with three atomic rows of terraces have pseudo-(1 × 1) structures. The interlayer spacing between the first and the second layers, d(12), is expanded 13% on Pt(331) compared to that of the bulk, whereas it is contracted 37% on Pt(511). The surface structures do not depend on the applied potential on either surface. PMID:21381779

  16. Interfacial Structure and Proton Conductivity of Nafion at the Pt-Deposited Surface.

    PubMed

    Ono, Yutaro; Nagao, Yuki

    2016-01-12

    Understanding the Nafion-Pt interface structure is important because fuel cell reactions occur at the three-phase boundary. Infrared (IR) p-polarized multiple-angle incidence resolution spectrometry (p-MAIRS) technique was used to investigate the in-plane (IP) and out-of-plane (OP) spectra in the identical substrate. Our previous study revealed that the proton conductivity of the Nafion thin films decreased at the MgO and SiO2 surfaces. We proposed that the origin for the lower proton conductivity can be derived from the highly oriented structure at the interface. However, the interface structure of the Nafion-Pt interface remains unclear. In this study, Nafion thin films were prepared by spin-coating on a Pt-deposited MgO substrates. The IP spectrum exhibited a well-known spectrum, but the OP spectrum was quite differed considerably from the IP spectrum. Furthermore, thickness dependence of the degree of orientation for this OP band was observed at the Nafion-Pt interface. This OP band can be assigned as the vibration mode of the mixture of the CF2 and sulfonic acid groups. At the low-RH region, proton conductivity of the Nafion thin film on the Pt-deposited surface was 1 order of magnitude higher than that on the SiO2 surface. Furthermore, the activation energy was 0.4-0.5 eV, which is lower than that of the SiO2 surface. These results, which suggest that the Pt surface influenced the proton transport property of Nafion thin film, can contribute to understand the relationship between the proton transport property and thin film structure on the Pt-deposited surface at the three-phase boundary for fuel cells. PMID:26653839

  17. Hydrogen adsorption-mediated synthesis of concave Pt nanocubes and their enhanced electrocatalytic activity.

    PubMed

    Lu, Bang-An; Du, Jia-Huan; Sheng, Tian; Tian, Na; Xiao, Jing; Liu, Li; Xu, Bin-Bin; Zhou, Zhi-You; Sun, Shi-Gang

    2016-06-01

    Concave nanocubes are enclosed by high-index facets and have negative curvature; they are expected to have enhanced reactivity, as compared to nanocubes with flat surfaces. Herein, we propose and demonstrate a new strategy for the synthesis of concave Pt nanocubes with {hk0} high-index facets, by using a hydrogen adsorption-mediated electrochemical square-wave potential method. It was found that Pt atoms prefer to deposit on edge sites rather than terrace sites on Pt surfaces with intensive hydrogen adsorption, resulting in the formation of concave structures. The as-prepared concave Pt nanocubes exhibit enhanced catalytic activity and stability towards oxidation of ethanol and formic acid in acidic solutions, compared to commercial Pt/C catalysts. PMID:27211517

  18. Methane dissociation on Pt(1 1 1), Ir(1 1 1) and PtIr(1 1 1) surface: A density functional theory study

    NASA Astrophysics Data System (ADS)

    Qi, Qiuhong; Wang, Xiujun; Chen, Li; Li, Baitao

    2013-11-01

    A periodic density functional theory (DFT) was utilized to calculate the dissociation process of methane (CH4) on Pt(1 1 1), Ir(1 1 1) and PtIr(1 1 1) surfaces. As compared to the adsorption energy, the most stable configurations of methane, methane dissociation species and co-adsorption of CHx (x = 0-3) with H were obtained. The kinetic results of the CH4 dissociation indicated that the dissociating of CH4 into CH3 and H is the rate-limiting step on the PtIr(1 1 1) and Ir(1 1 1) surfaces. CH was the most abundant species that was difficult to dehydrogenate into C and H. Particularly, the activation barrier for CH3 → CH2 + H and CH2 → CH + H on the Pt(1 1 1) surface is 3.5 and 1.4 times, respectively, higher than that on the PtIr(1 1 1) surface. According to the thermodynamics principles, the successive dehydrogenation of CH4 preferred to take place on the PtIr surface.

  19. Surface electrochemistry of CO on Pt(111): Anion Effects

    SciTech Connect

    Markovic, N.M.; Lucas, C.A.; Rodes, A.; Stamenkovic, V.; Ross, P.N.

    2001-07-30

    In-situ studies of CO adsorption by surface x-ray scattering (SXS) and Fourier transform infrared (FTIR) spectroscopy techniques are used to create the link between the macroscopic kinetic rates of CO oxidation and the microscopic level of understanding the structure/site occupancy of CO on Pt(111). A remarkable difference in activity was observed between alkaline and acid solutions. In alkaline solution the oxidation of CO proceeds at low overpotential (<0.2 V) by the surface reaction between the adsorbed CO and OH, the latter forming selectively in the hydrogen underpotential potential region at defect sites. In acid solution these sites are blocked by specific adsorption of anions, and consequently in a solution containing Br{sup -} the ignition potential is shifted positively by 0.6 V. Anions of supporting electrolytes also have dramatic effects on both the potential range of stability and the domain size of the p(2x2)-3CO structure which is formed at 0.05 V. The stability/domain size of this structure increases from KOH (ca. 30 {angstrom} between 0.05 < E < 0.3V), to HClO{sub 4} (ca. 140 {angstrom} between 0.05 < E < 0.6V) to HClO{sub 4} + Br{sup -} (ca 350 {angstrom} between 0.05 < E < 0.8V). The larger the ordered domains of the p(2x2)-CO{sub ad} structure are, the less active the surface is towards CO oxidation.

  20. Surface relaxation of Pt(1 1 1) and Cu/Pt(1 1 1) revealed by DEPES

    NASA Astrophysics Data System (ADS)

    Miszczuk, A.; Morawski, I.; Kucharczyk, R.; Nowicki, M.

    2016-06-01

    In this paper, we report the results of surface relaxation investigations for a clean Pt(1 1 1) as well as Pt(1 1 1) covered with a pseudomorphic monolayer of Cu. The pseudomorphic (1 × 1) Cu overlayer on Pt(1 1 1) was formed upon continuous copper adsorption at the substrate temperature equal to 450 K. Considerations include both the experimental and theoretical studies employing directional elastic peak electron spectroscopy (DEPES), multiple scattering (MS) formalism, and density functional theory (DFT). A quantitative analysis of two-dimensional DEPES intensity distributions is presented and the contribution of consecutive subsurface Pt atomic layers to the measured signal is identified. The experimental DEPES distributions are compared with theoretical maps MS-simulated for a variable separation between the outermost atomic planes. For the clean Pt(1 1 1), the best fit is obtained assuming the outward relaxation of the surface layer by +0.7% with respect to the interplanar distance in the bulk, confirming the slight expansion of the Pt(1 1 1) surface. Similar analysis performed for the Cu/Pt(1 1 1) adsorption system indicates the inward shift of the pseudomorphic Cu overlayer by -6.9% with respect to the substrate lattice continuation sites. Such DEPES-determined surface relaxations of Pt(1 1 1) and Cu/Pt(1 1 1) agree with the values predicted by the corresponding DFT computations.

  1. Suppression of oxygen reduction reaction activity on Pt-based electrocatalysts from ionomer incorporation

    NASA Astrophysics Data System (ADS)

    Shinozaki, Kazuma; Morimoto, Yu; Pivovar, Bryan S.; Kocha, Shyam S.

    2016-09-01

    The impact of Nafion on the oxygen reduction reaction (ORR) activity is studied for Pt/C and Pt-alloy/C catalysts using thin-film rotating disk electrode (TF-RDE) methods in 0.1 M HClO4. Ultrathin uniform catalyst layers and standardized activity measurement protocols are employed to obtain accurate and reproducible ORR activity. Nafion lowers the ORR activity which plateaus with increasing loading on Pt catalysts. Pt particle size is found not to have significant influence on the extent of the SA decrease upon Nafion incorporation. Catalysts using high surface area carbon (HSC) support exhibit attenuated activity loss resulting from lower ionomer coverage on catalyst particles located within the deep pores. The impact of metallic composition on the activity loss due to Nafion incorporation is also discussed.

  2. Exceptional methanol electro-oxidation activity by bimetallic concave and dendritic Pt-Cu nanocrystals catalysts

    NASA Astrophysics Data System (ADS)

    Wang, Ying-Xia; Zhou, Hui-Jing; Sun, Ping-Chuan; Chen, Tie-Hong

    2014-01-01

    PtCux (x = 1, 2 and 3) bimetallic nanocrystals with concave surface and dendritic morphology were prepared and used as electrocatalysts in methanol oxidation reaction (MOR) for polymer electrolyte membrane fuel cells. The bimetallic nanocrystals were synthesized via one-pot co-reduction of H2PtCl6 and Cu(acac)2 by oleylamine and polyvinyl pyrrolidone (PVP) in an autoclave at 180 °C. The concave dendritic bimetallic nanostructure consisted of a core rich in Cu and nanodendrites rich in Pt, which was formed via galvanic replacement of Cu by Pt. It was found that PVP played an important role in initiating, facilitating, and directing the replacement reaction. The electrochemical properties of the PtCux were characterized by cyclic voltammetry (CV) and chronoamperometry (CA). The concave dendritic PtCu2/C nanocrystals exhibited exceptionally high activity and strong poisoning resistance in MOR. At 0.75 V (vs. reversible hydrogen electrode, RHE) the mass activity and specific activity of PtCu2/C were 3.3 and 4.1 times higher than those of the commercial Pt/C catalysts, respectively. The enhanced catalytic activity could be attributed to the unique concave dendritic morphology of the bimetallic nanocrystals.

  3. Comparison of iridium- and ruthenium-based, Pt-surface-enriched, nanosize catalysts for the oxygen-reduction reaction

    NASA Astrophysics Data System (ADS)

    Kaplan, D.; Goor, M.; Alon, M.; Tsizin, S.; Burstein, L.; Rosenberg, Y.; Popov, I.; Peled, E.

    2016-02-01

    Pt-surface-enriched nanosize catalysts (Pt-SENS catalysts) with ruthenium and iridium cores, supported on XC72, were synthesized and characterized. The structure and composition of the catalysts are determined by Energy-Dispersive X-ray Spectroscopy (EDS), X-ray Photoelectron Spectroscopy (XPS), Scanning Transmission Electron Microscopy (STEM) and X-Ray Diffraction (XRD). Electrochemical characterization tests, including oxygen-reduction-catalysis activity and durability studies of catalysts are performed with the use of cyclic-voltammetry and rotating-disk-electrode (RDE) techniques at room temperature. The ORR activity of the homemade catalysts is also compared to ORR activity of commercial 50%Pt/C catalyst. It is determined that the Ir-based catalyst (Pt/Ir/XC72) shows higher ORR activity in terms of A g-1 of Pt (at 0.85 V vs. RHE) than the Ru-based catalyst (Pt/Ru/XC72) and the commercial 50%Pt/C. The Ru-based catalyst shows similar ORR activity in terms of A g-1 of Pt, to that of the commercial 50%Pt/C, but with much lower durability.

  4. Elucidating the activity of stepped Pt single crystals for oxygen reduction.

    PubMed

    Bandarenka, Aliaksandr S; Hansen, Heine A; Rossmeisl, Jan; Stephens, Ifan E L

    2014-07-21

    The unexpectedly high measured activity of Pt[n(111) × (111)] and Pt[n(111) × (100)] stepped single crystal surfaces towards the oxygen reduction reaction (ORR) is explained utilizing the hydroxyl binding energy as the activity descriptor. Using this descriptor (estimated using experimental data obtained by different groups), a well-defined Sabatier-type volcano is observed for the activities measured for the Pt[n(111) × (111)] and Pt[n(111) × (100)] stepped single crystals, in remarkable agreement with earlier theoretical studies. We propose that the observed destabilisation of *OH species at these surfaces is due to the decreased solvation of the adsorbed hydroxyl intermediates on adjacent terrace sites. PMID:24643715

  5. Determination of the crotonaldehyde structures on Pt and PtSn surface alloys from a combined experimental and theoretical study

    NASA Astrophysics Data System (ADS)

    Haubrich, Jan; Loffreda, David; Delbecq, Françoise; Jugnet, Yvette; Sautet, Philippe; Krupski, Aleksander; Becker, Conrad; Wandelt, Klaus

    2006-12-01

    A complementary experimental and theoretical study of the alloying effects of Sn on the molecule-surface bonding of crotonaldehyde on Pt(1 1 1) is presented. By comparing high-resolution electron energy loss spectroscopy (HREELS) data and density-functional theory (DFT) calculations of vibrational spectra from a complete set of possible adsorption configurations of crotonaldehyde on the Pt(1 1 1) and Pt 2Sn(1 1 1) surfaces, we are able to identify the adsorption structures present on the surface. An interpretation of the HREELS spectra for these highly complex systems is proposed and the effect of alloying with Sn on the molecule-surface interactions is addressed.

  6. Tuning the Catalytic Activity of Ru@Pt Core-Shell Nanoparticles for the Oxygen Reduction Reaction by Varying the Shell Thickness

    SciTech Connect

    Yang, Lijun; Vukmirovic, Miomir B.; Su, Dong; Sasaki, Kotaro; Herron, Jeffrey A.; Mavrikakis, Manos; Liao, Shijun; Adzic, Radoslav R.

    2013-01-31

    The kinetics of the oxygen reduction reaction (ORR) was investigated in acid solutions on Pt monolayers that were deposited on carbon-supported Ru nanoparticles using the rotating disk electrode technique. The Pt mass and specific ORR activities greatly depend on the number of Pt monolayers, and the optimum activity occurs with two Pt monolayers. Density functional theory calculations showed that Pt overlayers destabilize O* and OH* with respect to pure Pt, leading to more favorable hydrogenation kinetics. However, with only a single Pt overlayer, the destabilization is too much, and O–O bond breaking becomes rate limiting. Two to three Pt monolayers supported on the Ru core of our nanoparticles lead to increased activity. This work demonstrates that one can modulate the ORR activity of Pt monolayers supported on other metals by eliminating a part of the ligand effect by increasing the thickness of the Pt shell on top of the supporting metal surface.

  7. Hemoglobin–Albumin Cluster Incorporating a Pt Nanoparticle: Artificial O2 Carrier with Antioxidant Activities

    PubMed Central

    Hosaka, Hitomi; Haruki, Risa; Yamada, Kana; Böttcher, Christoph; Komatsu, Teruyuki

    2014-01-01

    A covalent core–shell structured protein cluster composed of hemoglobin (Hb) at the center and human serum albumins (HSA) at the periphery, Hb-HSAm, is an artificial O2 carrier that can function as a red blood cell substitute. Here we described the preparation of a novel Hb-HSA3 cluster with antioxidant activities and its O2 complex stable in aqueous H2O2 solution. We used an approach of incorporating a Pt nanoparticle (PtNP) into the exterior HSA unit of the cluster. A citrate reduced PtNP (1.8 nm diameter) was bound tightly within the cleft of free HSA with a binding constant (K) of 1.1×107 M−1, generating a stable HSA-PtNP complex. This platinated protein showed high catalytic activities for dismutations of superoxide radical anions (O2•–) and hydrogen peroxide (H2O2), i.e., superoxide dismutase and catalase activities. Also, Hb-HSA3 captured PtNP into the external albumin unit (K = 1.1×107 M−1), yielding an Hb-HSA3(PtNP) cluster. The association of PtNP caused no alteration of the protein surface net charge and O2 binding affinity. The peripheral HSA-PtNP shell prevents oxidation of the core Hb, which enables the formation of an extremely stable O2 complex, even in H2O2 solution. PMID:25310133

  8. Enhanced Catalytic Activities of NiPt Truncated Octahedral Nanoparticles toward Ethylene Glycol Oxidation and Oxygen Reduction in Alkaline Electrolyte.

    PubMed

    Xia, Tianyu; Liu, Jialong; Wang, Shouguo; Wang, Chao; Sun, Young; Gu, Lin; Wang, Rongming

    2016-05-01

    The high cost and poor durability of Pt nanoparticles (NPs) are great limits for the proton exchange membrane fuel cells (PEMFCs) from being scaled-up for commercial applications. Pt-based bimetallic NPs together with a uniform distribution can effectively reduce the usage of expensive Pt while increasing poison resistance of intermediates. In this work, a simple one-pot method was used to successfully synthesize ultrafine (about 7.5 nm) uniform NiPt truncated octahedral nanoparticles (TONPs) in dimethylformamid (DMF) without any seeds or templates. The as-prepared NiPt TONPs with Pt-rich surfaces exhibit greatly improved catalytic activities together with good tolerance and better stability for ethylene glycol oxidation reaction (EGOR) and oxygen reduction reaction (ORR) in comparison with NiPt NPs and commercial Pt/C catalysts in alkaline electrolyte. For example, the value of mass and specific activities for EGOR are 23.2 and 17.6 times higher comparing with those of commercial Pt/C, respectively. Our results demonstrate that the dramatic enhancement is mainly attributed to Pt-rich surface, larger specific surface area, together with coupling between Ni and Pt atoms. This developed method provides a promising pathway for simple preparation of highly efficient electrocatalysts for PEMFCs in the near future. PMID:27093304

  9. Effects of a TiC substrate on the catalytic activity of Pt for NO reduction.

    PubMed

    Chu, Xingli; Fu, Zhaoming; Li, Shasha; Zhang, Xilin; Yang, Zongxian

    2016-05-11

    Density functional theory calculations are used to elucidate the catalytic properties of a Pt monolayer supported on a TiC(001) substrate (Pt/TiC) toward NO reduction. It is found that the compound system of Pt/TiC has a good stability due to the strong Pt-TiC interaction. The diverse dissociation paths (namely the direct dissociation mechanism and the dimeric mechanism) are investigated. The transition state searching calculations suggest that NO has strong diffusion ability and small activation energy for dissociation on the Pt/TiC. For NO reduction on the Pt/TiC surface, we have found that the direct dissociation mechanisms (NO + N + O → NO2 + N and NO + N + O → N2 + O + O) are easier with a smaller dissociation barrier than those on the Pt(111) surface; and the dimeric process (NO + NO → (NO)2 → N2O + O → N2 + O + O) is considered to be dominant or significant with even a lower energy barrier than that of the direct dissociation. The results show that Pt/TiC can serve as an efficient catalyst for NO reduction. PMID:27117987

  10. Theoretical studies of the adsorption of hydroxymethylidyne (COH) on Pt-alloy surfaces using density functional theory

    NASA Astrophysics Data System (ADS)

    Cahyanto, Wahyu Tri; Widanarto, Wahyu; Shukri, Ganes; Kasai, Hideaki

    2016-02-01

    We present density functional calculations for the adsorption of hydroxymethylidyne (COH) on Pt, PtRu, and PtRuMo (111) surfaces. Here we clarify the adsorption mechanism by using a charge transfer analysis related to the adsorption energy. We observe that the preferred binding sites for COH are the hcp hollow Pt-Pt-Pt, hcp hollow Pt-Ru-Pt, and hcp hollow Pt-Ru-Pt adsorption sites for Pt, PtRu, and PtRuMo, respectively. Addition of Ru to form a PtRu surface increases the adsorption energy, while addition of Mo to form a PtRuMo surface decreases it. Our analyses show that the adsorption energy is determined by electron transfer between the molecular COH and the metal surfaces associated with bonding.

  11. Tuning the activity of Pt(111) for oxygen electroreduction by subsurface alloying.

    PubMed

    Stephens, Ifan E L; Bondarenko, Alexander S; Perez-Alonso, Francisco J; Calle-Vallejo, Federico; Bech, Lone; Johansson, Tobias P; Jepsen, Anders K; Frydendal, Rasmus; Knudsen, Brian P; Rossmeisl, Jan; Chorkendorff, Ib

    2011-04-13

    To enable the development of low temperature fuel cells, significant improvements are required to the efficiency of the Pt electrocatalysts at the cathode, where oxygen reduction takes place. Herein, we study the effect of subsurface solute metals on the reactivity of Pt, using a Cu/Pt(111) near-surface alloy. Our investigations incorporate electrochemical measurements, ultrahigh vacuum experiments, and density functional theory. Changes to the OH binding energy, ΔE(OH), were monitored in situ and adjusted continuously through the subsurface Cu coverage. The incorporation of submonolayer quantities of Cu into Pt(111) resulted in an 8-fold improvement in oxygen reduction activity. The most optimal catalyst for oxygen reduction has an ΔE(OH) ≈ 0.1 eV weaker than that of pure Pt, validating earlier theoretical predictions. PMID:21417329

  12. One pot aqueous synthesis of nanoporous Au85Pt15 material with surface bound Pt islands: an efficient methanol tolerant ORR catalyst.

    PubMed

    Anandha Ganesh, P; Jeyakumar, D

    2014-11-01

    For the first time, we are reporting the synthesis of Au100-xPtx nanoporous materials in the size range of 7-10 nm through the galvanic replacement of Ag by Pt from Au100-xAg2x spherical nano-alloys (x = 20, 15, 10 and 5) in an aqueous medium. The galvanic replacement reaction follows the 'Volmer-Weber' growth mode, resulting in the formation of surface bound platinum islands on a nanoporous gold surface. The high angle annular dark field image and low angle X-ray diffraction studies confirm the presence of nanoporous Au100-xPtx NPs. The electrochemical studies using the Au85Pt15/C catalyst show excellent methanol tolerance behaviour and better performance towards oxygen reduction reaction (ORR) in terms of high mass activity, mass-specific activity and figure of merit (FOM) when compared to HiSPEC Pt/C commercial catalyst. Preliminary studies on a full cell using nanoporous Au85Pt15/C (loading 1.0 mg cm(-2)) as the cathode material and Pt-Ru/C (loading: 0.5 mg cm(-2)) as the anode material performed better (38 mW cm(-2)) than the HiSPEC Pt/C cathode material (16 mW cm(-2)). PMID:25241856

  13. Surface Structures of Cubo-octahedral Pt-Mo Catalyst Nanoparticles from Monte Carlo Simulations

    SciTech Connect

    Wang, Guofeng; Van Hove, M.A.; Ross, P.N.; Baskes, M.I.

    2005-03-31

    The surface structures of cubo-octahedral Pt-Mo nanoparticles have been investigated using the Monte Carlo method and modified embedded atom method potentials that we developed for Pt-Mo alloys. The cubo-octahedral Pt-Mo nanoparticles are constructed with disordered fcc configurations, with sizes from 2.5 to 5.0 nm, and with Pt concentrations from 60 to 90 at. percent. The equilibrium Pt-Mo nanoparticle configurations were generated through Monte Carlo simulations allowing both atomic displacements and element exchanges at 600 K. We predict that the Pt atoms weakly segregate to the surfaces of such nanoparticles. The Pt concentrations in the surface are calculated to be 5 to 14 at. percent higher than the Pt concentrations of the nanoparticles. Moreover, the Pt atoms preferentially segregate to the facet sites of the surface, while the Pt and Mo atoms tend to alternate along the edges and vertices of these nanoparticles. We found that decreasing the size or increasing the Pt concentration leads to higher Pt concentrations but fewer Pt-Mo pairs in the Pt-Mo nanoparticle surfaces.

  14. Kinetic limitations in surface alloy formation: PtCu/Ru(0001)

    NASA Astrophysics Data System (ADS)

    Engstfeld, A. K.; Jung, C. K.; Behm, R. J.

    2016-01-01

    We have systematically investigated the structure and structure formation of two-dimensional PtCu monolayer surface alloys on Ru(0001) as model systems for bimetallic PtCu catalysts and surfaces by scanning tunneling microscopy (STM). The surface alloys were prepared by deposition of Pt and Cu on Ru(0001) and thermal intermixing; different procedures were developed and tested to produce bimetallic surfaces with homogeneous structure, including also a homogeneous distribution of the different surface species, while at the same time intermixing with the Ru(0001) substrate should be inhibited. STM imaging revealed that for Pt concentrations below 65% surface alloys with homogeneous distribution could be formed, while at higher concentrations in the mixed phase, up to 82%, pure Pt or Pt-rich surface areas were formed as well. At Pt contents of 0.20 < xPt < 0.65, the PtxCu1 -x/Ru(0001) surface alloys were pseudomorphic, while lower Pt contents resulted in triangular dislocation line patterns. Also at xPt > 0.65 line structures were observed, but of different nature. The distribution of surface atoms in the mixed phase was evaluated from STM images with chemical contrast, the related short-range order parameters were determined. The resulting structures and their energetics, the influence of different deposition and annealing procedures and the suitability of these surfaces as model systems for studies of the surface chemistry of bimetallic PtCu surfaces are discussed.

  15. First-principles computation of surface segregation in L10 CoPt magnetic nanoparticles

    NASA Astrophysics Data System (ADS)

    Liu, Zhenyu; Lei, Yinkai; Wang, Guofeng

    2016-07-01

    In this study, we have employed the first-principles density functional theory (DFT) computational method to predict the influence of surface segregation on the magnetic properties of small L10 CoPt nanoparticles. For both the modelled cuboidal (with a chemical formula of Co26Pt12) and cuboctahedral (with a chemical formula of Co18Pt20) CoPt nanoparticles, the DFT calculations predict that Pt surface segregation should occur thermodynamically. Associated with this Pt surface segregation, the surface-segregated CoPt magnetic nanoparticles are predicted to have significantly reduced magnetic moments and magnetic anisotropy energies than those of the corresponding bulk-terminated (i.e. non-segregated) nanoparticles. Hence, our study suggests that surface segregation could deteriorate the magnetic properties of CoPt nanoparticles.

  16. First-principles computation of surface segregation in L10 CoPt magnetic nanoparticles.

    PubMed

    Liu, Zhenyu; Lei, Yinkai; Wang, Guofeng

    2016-07-01

    In this study, we have employed the first-principles density functional theory (DFT) computational method to predict the influence of surface segregation on the magnetic properties of small L10 CoPt nanoparticles. For both the modelled cuboidal (with a chemical formula of Co26Pt12) and cuboctahedral (with a chemical formula of Co18Pt20) CoPt nanoparticles, the DFT calculations predict that Pt surface segregation should occur thermodynamically. Associated with this Pt surface segregation, the surface-segregated CoPt magnetic nanoparticles are predicted to have significantly reduced magnetic moments and magnetic anisotropy energies than those of the corresponding bulk-terminated (i.e. non-segregated) nanoparticles. Hence, our study suggests that surface segregation could deteriorate the magnetic properties of CoPt nanoparticles. PMID:27194486

  17. Fabrication of Pt-loaded NiCo nanochains with superior catalytic dehydrogenation activity.

    PubMed

    Wen, Ming; Wu, Qingnan; Peng, Jin; Wu, Qingsheng; Wang, Chenxiang

    2014-02-15

    A new magnetic Pt-loaded NiCo nanochain, with the diameter from 80 nm to 120 nm, has been prepared through microwave-induced assembly process followed by the galvanic displacement performance. Pt nanoparticles are distributed on the surface of NiCo nanochains. The products are investigated as hydrolytic dehydrogenation catalyst for potential hydrogen energy applications. Compared with NiCo nanochains, the Pt-loaded NiCo nanochains present exceedingly high catalytic activity toward the hydrolytic dehydrogenation of ammonia borane aqueous under ambient atmosphere at room temperature, where the Ni16Co80/Pt4 nanochains exhibit high catalytic activity with a lower activation energy of 45.72 kJ mol(-1) and a superior dehydrogenation rate of 1.17 × 10(4) mL min(-1) g(-1), suggesting the potential application in hydrogen fuel and chemical industry. PMID:24370425

  18. Low-energy Alkali Ion Scattering and X-ray Photoelectron Diffraction Studies of the Structure of Pt-Zn/Pt(111) Bimetallic Surfaces

    NASA Astrophysics Data System (ADS)

    Koel, Bruce; Roszell, John; Martono, Eddie; Vohs, John

    2013-03-01

    Pt-Zn alloys have applications in heterogeneous catalysis, and studies on surfaces of well-defined, ordered Pt-Zn alloys, or intermetallic compounds, clarify the origins of changes that occur in catalysis by the alloy. Many stable intermetallic compounds of Pt and Zn occur in bulk materials, but no long-range ordered surface alloys were formed by depositing Zn on a Pt(111) single-crystal substrate in a search over a considerable range of conditions. These results can be contrasted to those from Pt-Sn, where ordered surface alloys were formed. Zn alloys with Pt upon heating, and XPD and ALISS were used to characterize the Pt-Zn alloy created by annealing one monolayer of Zn on Pt(111) to 650 K. This Pt-Zn/Pt(111) surface alloy had a diffuse (1x1) LEED pattern due to formation of a random, substitutional alloy between Pt and Zn with 0.05-monolayer Zn in the topmost layer. Zn atoms are substitutionally incorporated into Pt lattice positions and alloyed Zn atoms in the surface layer are located coplanar with the surface Pt atoms, without any buckling. TPD shows that both CO and NO chemisorb more weakly on the Pt-Zn alloy than on the clean Pt(111) surface, with NO more strongly affected. This material is based upon work supported by the National Science Foundation under Grant No. CHE-1129417.

  19. Surface composition of magnetron sputtered Pt-Co thin film catalyst for proton exchange membrane fuel cells

    NASA Astrophysics Data System (ADS)

    Vorokhta, Mykhailo; Khalakhan, Ivan; Václavů, Michal; Kovács, Gábor; Kozlov, Sergey M.; Kúš, Peter; Skála, Tomáš; Tsud, Natalia; Lavková, Jaroslava; Potin, Valerie; Matolínová, Iva; Neyman, Konstantin M.; Matolín, Vladimír

    2016-03-01

    Recently we have tested a magnetron sputtered Pt-Co catalyst in a hydrogen-fed proton exchange membrane fuel cell and showed its high catalytic activity for the oxygen reduction reaction. Here we present further investigation of the magnetron sputtered Pt-Co thin film catalyst by both experimental and theoretical methods. Scanning electron microscopy and transmission electron microscopy experiments confirmed the nanostructured character of the catalyst. The surface composition of as-deposited and annealed at 773 K Pt-Co films was investigated by surface analysis techniques, such as synchrotron radiation photoelectron spectroscopy and X-ray photoelectron spectroscopy. Modeling based on density functional theory showed that the surface of 6 nm large 1:1 Pt-Co nanoparticles is almost exclusively composed of Pt atoms (>90%) at typical operation conditions and the Co content does not exceed 20% at 773 K, in agreement with the experimental characterization of such films annealed in vacuum. According to experiment, the density of valence states of surface atoms in Pt-Co nanostructures is shifted by 0.3 eV to higher energies, which can be associated with their higher activity in the oxygen reduction reaction. The changes in electronic structure caused by alloying are also reflected in the measured Pt 4f, Co 3p and Co 2p photoelectron peak binding energies.

  20. Pt3Co concave nanocubes: synthesis, formation understanding, and enhanced catalytic activity toward hydrogenation of styrene.

    PubMed

    Wang, Chenyu; Lin, Cuikun; Zhang, Lihua; Quan, Zewei; Sun, Kai; Zhao, Bo; Wang, Feng; Porter, Nathan; Wang, Yuxuan; Fang, Jiye

    2014-02-01

    We report a facile synthesis route to prepare high-quality Pt3Co nanocubes with a concave structure, and further demonstrate that these concave Pt3Co nanocubes are terminated with high-index crystal facets. The success of this preparation is highly dependent on an appropriate nucleation process with a successively anisotropic overgrowth and a preservation of the resultant high-index planes by control binding of oleyl-amine/oleic acid with a fine-tuned composition. Using a hydrogenation of styrene as a model reaction, these Pt3Co concave nanocubes as a new class of nanocatalysts with more open structure and active atomic sites located on their high-index crystallographic planes exhibit an enhanced catalytic activity in comparison with low-indexed surface terminated Pt3Co nanocubes in similar size. PMID:24382713

  1. Adsorption Structure of Nitric Oxide on the Pt(111) Surface

    NASA Astrophysics Data System (ADS)

    Matsumoto, Masuaki

    The adsorption structure of Pt(111) surface was studied by thermal desorption spectroscopy (TDS), infra-red absorption spectroscopy (IRAS), scanning tunneling microscopy (STM) and low-energy electron diffraction (LEED). LEED dynamical analysis, with the aid of other techniques, concluded that NO occupies the fcc hollow site at a low coverage, the fcc hollow and ontop sites at a medium coverage and the fcc hollow, ontop and hcp hollow sites at a high coverage, which is consistent with the other experimental and theoretical results. The desorption temperatures of NO on the fcc hollow (α species), ontop (β species) and hcp hollow sites (γ species) are 390, 300 and 200 K, respectively. The N-O stretching vibrations of each species are 1430-1490 cm-1, 1710 cm-1 and 1508 cm-1, respectively. Annealing to 250 K causes the desorption of the γ species, which results in the highly ordered two site occupied (α and β) surface. The high energy (>1 eV) electron injection from the STM tip causes the desorption of the β species, which enables us to get the surface of highly ordered α species. The mechanism of the desorption of the β species is the electron injection to the 2πa orbital, which has an anti-bonding character for the Pt-N bonding of the β species.

  2. Relating the composition of Pt(x)Ru(100-x)/C nanoparticles to their structural aspects and electrocatalytic activities in the methanol oxidation reaction.

    PubMed

    Taufany, Fadlilatul; Pan, Chun-Jern; Lai, Feng-Ju; Chou, Hung-Lung; Sarma, Loka Subramanyam; Rick, John; Lin, Jhih-Min; Lee, Jyh-Fu; Tang, Mau-Tsu; Hwang, Bing-Joe

    2013-01-14

    A controlled composition-based method--that is, the microwave-assisted ethylene glycol (MEG) method--was successfully developed to prepare bimetallic Pt(x)Ru(100-x)/C nanoparticles (NPs) with different alloy compositions. This study highlights the impact of the variation in alloy composition of Pt(x)Ru(100-x)/C NPs on their alloying extent (structure) and subsequently their catalytic activity towards the methanol oxidation reaction (MOR). The alloying extent of these Pt(x)Ru(100-x)/C NPs has a strong influence on their Pt d-band vacancy and Pt electroactive surface area (Pt ECSA); this relationship was systematically evaluated by using X-ray absorption (XAS), scanning electron microscopy (SEM) coupled with energy dispersive X-ray spectroscopy (EDX), transmission electron microscopy (TEM), density functional theory (DFT) calculations, and electrochemical analyses. The MOR activity depends on two effects that act in cooperation, namely, the number of active Pt sites and their activity. Here the number of active Pt sites is associated with the Pt ECSA value, whereas the Pt-site activity is associated with the alloying extent and Pt d-band vacancy (electronic) effects. Among the Pt(x)Ru(100-x)/C NPs with various Pt:Ru atomic ratios (x = 25, 50, and 75), the Pt(75)Ru(25)/C NPs were shown to be superior in MOR activity on account of their favorable alloying extent, Pt d-band vacancy, and Pt ECSA. This short study brings new insight into probing the synergistic effect on the surface reactivity of the Pt(x)Ru(100-x)/C NPs, and possibly other bimetallic Pt-based alloy NPs. PMID:23197430

  3. PdPt bimetallic nanoparticles enabled by shape control with halide ions and their enhanced catalytic activities

    NASA Astrophysics Data System (ADS)

    Zhang, Jinfeng; Wan, Lei; Liu, Lei; Deng, Yida; Zhong, Cheng; Hu, Wenbin

    2016-02-01

    In this study, a new and convenient one step approach is described for synthesizing shape controlled PdPt bimetallic nanoparticles. It is found that the resultant morphologies of these PdPt nanoparticles can be well controlled by simply altering the participation of different halide ions that serve as shape controlling agents in the reaction solution. The dendritic core-shell PdPt bimetallic nanoparticles generated with Pt atoms adopt usual island growth pattern in the presence of Cl- ions, whereas the introduction of Br- ions with a relatively strong adsorption effect facilitate the formation of a layered core-shell structure due to the layered growth mode of Pt atoms on the exterior surface of the central Pd core. Moreover, the stronger adsorption function of I- ions and the resulting fast atomic diffusion promoted the generation of mesoporous core-shell PdPt bimetallic nanoparticles with many pore channels. In addition, the size of these synthesized PdPt nanoparticles exhibited a significant dependence on the concentration of the halide ions involved. Due to their specific structural features and synergistic effects, these PdPt catalysts exhibited shape-dependent catalytic performance and drastically enhanced electrocatalytic activities relative to that of commercial Pt black and Pt/C toward methanol oxidation.In this study, a new and convenient one step approach is described for synthesizing shape controlled PdPt bimetallic nanoparticles. It is found that the resultant morphologies of these PdPt nanoparticles can be well controlled by simply altering the participation of different halide ions that serve as shape controlling agents in the reaction solution. The dendritic core-shell PdPt bimetallic nanoparticles generated with Pt atoms adopt usual island growth pattern in the presence of Cl- ions, whereas the introduction of Br- ions with a relatively strong adsorption effect facilitate the formation of a layered core-shell structure due to the layered growth

  4. 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.

  5. Electron Induced Surface Reactions of cis-Pt(CO)2Cl2: A Route to Focused Electron Beam Induced Deposition of Pure Pt Nanostructures.

    PubMed

    Spencer, Julie A; Wu, Yung-Chien; McElwee-White, Lisa; Fairbrother, D Howard

    2016-07-27

    Using mechanistic data from surface science studies on electron-induced reactions of organometallic precursors, cis-Pt(CO)2Cl2 (1) was designed specifically for use in focused electron beam induced deposition (FEBID) of Pt nanostructures. Electron induced decomposition of adsorbed 1 under ultrahigh vacuum (UHV) conditions proceeds through initial CO loss as determined by in situ X-ray photoelectron spectroscopy and mass spectrometry. Although the Pt-Cl bonds remain intact during the initial decomposition step, larger electron doses induce removal of the residual chloride through an electron-stimulated desorption process. FEBID structures created from cis-Pt(CO)2Cl2 under steady state deposition conditions in an Auger spectrometer were determined to be PtCl2, free of carbon and oxygen. Coupled with the electron stimulated removal of chlorine demonstrated in the UHV experiments, the Auger deposition data establish a route to FEBID of pure Pt. Results from this study demonstrate that structure-activity relationships can be used to design new precursors specifically for FEBID. PMID:27346707

  6. Quantitative Prediction of Surface Segregation in Bimetallic Pt-MAlloy Nanoparticles (M=Ni, Re, Mo)

    SciTech Connect

    Wang, Guofeng; Van Hove, Michel A.; Ross, Phil N.; Baskes,Michael I.

    2005-06-20

    This review addresses the issue of surface segregation inbimetallic alloy nanoparticles, which are relevant to heterogeneouscatalysis, in particular for electro-catalysts of fuel cells. We describeand discuss a theoretical approach to predicting surface segregation insuch nanoparticles by using the Modified Embedded Atom Method and MonteCarlo simulations. In this manner it is possible to systematicallyexplore the behavior of such nanoparticles as a function of componentmetals, composition, and particle size, among other variables. We choseto compare Pt75Ni25, Pt75Re25, and Pt80Mo20 alloys as example systems forthis discussion, due to the importance of Pt in catalytic processes andits high-cost. It is assumed that the equilibrium nanoparticles of thesealloys have a cubo-octahedral shape, the face-centered cubic lattice, andsizes ranging from 2.5 nm to 5.0 nm. By investigating the segregation ofPt atoms to the surfaces of the nanoparticles, we draw the followingconclusions from our simulations at T= 600 K. (1) Pt75Ni25 nanoparticlesform a surface-sandwich structure in which the Pt atoms are stronglyenriched in the outermost and third layers while the Ni atoms areenriched in the second layer. In particular, a nearly pure Pt outermostsurface layer can be achieved in those nanoparticles. (2) EquilibriumPt75Re25 nanoparticles adopt a core-shell structure: a nearly pure Ptshell surrounding a more uniform Pt-Re core. (3) In Pt80Mo20nanoparticles, the facets are fully occupied by Pt atoms, the Mo atomsonly appear at the edges and vertices, and the Pt and Mo atoms arrangethemselves in an alternating sequence along the edges and vertices. Oursimulations quantitatively agree with previous experimental andtheoretical results for the extended surfaces of Pt-Ni, Pt-Re, and Pt-Moalloys. We further discuss the reasons for the different types of surfacesegregation found in the different alloys, and some of theirimplications.

  7. Peroxidase-like activity of mesoporous silica encapsulated Pt nanoparticle and its application in colorimetric immunoassay.

    PubMed

    Wang, Zhifei; Yang, Xia; Yang, Jingjing; Jiang, Yanyun; He, Nongyue

    2015-03-01

    Nanomaterial-based artificial enzymes have received great attention in recent year due to their potential application in immunoassay techniques. However, such potential is usually limited by poor dispersion stability or low catalytic activity induced by the capping agent essentially required in the synthesis. In an attempt to address these challenges, here, we studied the novel Pt nanoparticles (NPs) based peroxidase-like mimic by encapsulating Pt NP in mesoporous silica (Pt@mSiO2 NPs). Compared with other nanomaterial-based artificial enzymes, the obtained Pt@mSiO2 NPs not only exhibit high peroxidase-like activity but also have good dispersion stability in buffer saline solution when grafted with spacer PEG. Results show that when the thickness of silica shell is about 9 nm the resulting Pt@mSiO2 NPs exhibit the catalytic activity similar to that of Pt NPs, which is approximately 26 times higher than that of Fe3O4 NPs (in terms of Kcat for H2O2). Due to the protection of silica shell, the subsequent surface modification with antibody has little effect on their catalytic activity. The analytical performance of this system in detecting hCG shows that after 5 min incubation the limit of detection can reach 10 ng mL(-1) and dynamic linear working range is 5-200 ng mL(-1). Our findings pave the way for design and development of novel artificial enzyme labeling. PMID:25682428

  8. Dual role of CO in the stability of subnano Pt clusters at the Fe3O4(001) surface

    PubMed Central

    Bliem, Roland; van der Hoeven, Jessi E. S.; Hulva, Jan; Pavelec, Jiri; Gamba, Oscar; de Jongh, Petra E.; Schmid, Michael; Blaha, Peter; Diebold, Ulrike; Parkinson, Gareth S.

    2016-01-01

    Interactions between catalytically active metal particles and reactant gases depend strongly on the particle size, particularly in the subnanometer regime where the addition of just one atom can induce substantial changes in stability, morphology, and reactivity. Here, time-lapse scanning tunneling microscopy (STM) and density functional theory (DFT)-based calculations are used to study how CO exposure affects the stability of Pt adatoms and subnano clusters at the Fe3O4(001) surface, a model CO oxidation catalyst. The results reveal that CO plays a dual role: first, it induces mobility among otherwise stable Pt adatoms through the formation of Pt carbonyls (Pt1–CO), leading to agglomeration into subnano clusters. Second, the presence of the CO stabilizes the smallest clusters against decay at room temperature, significantly modifying the growth kinetics. At elevated temperatures, CO desorption results in a partial redispersion and recovery of the Pt adatom phase. PMID:27457953

  9. Dual role of CO in the stability of subnano Pt clusters at the Fe3O4(001) surface.

    PubMed

    Bliem, Roland; van der Hoeven, Jessi E S; Hulva, Jan; Pavelec, Jiri; Gamba, Oscar; de Jongh, Petra E; Schmid, Michael; Blaha, Peter; Diebold, Ulrike; Parkinson, Gareth S

    2016-08-01

    Interactions between catalytically active metal particles and reactant gases depend strongly on the particle size, particularly in the subnanometer regime where the addition of just one atom can induce substantial changes in stability, morphology, and reactivity. Here, time-lapse scanning tunneling microscopy (STM) and density functional theory (DFT)-based calculations are used to study how CO exposure affects the stability of Pt adatoms and subnano clusters at the Fe3O4(001) surface, a model CO oxidation catalyst. The results reveal that CO plays a dual role: first, it induces mobility among otherwise stable Pt adatoms through the formation of Pt carbonyls (Pt1-CO), leading to agglomeration into subnano clusters. Second, the presence of the CO stabilizes the smallest clusters against decay at room temperature, significantly modifying the growth kinetics. At elevated temperatures, CO desorption results in a partial redispersion and recovery of the Pt adatom phase. PMID:27457953

  10. Oxygen reduction reaction activity and structural stability of Pt-Au nanoparticles prepared by arc-plasma deposition.

    PubMed

    Takahashi, Shuntaro; Chiba, Hiroshi; Kato, Takashi; Endo, Shota; Hayashi, Takehiro; Todoroki, Naoto; Wadayama, Toshimasa

    2015-07-28

    The oxygen reduction reaction (ORR) activity and durability of various Au(x)/Pt100 nanoparticles (where x is the atomic ratio of Au against Pt) are evaluated herein. The samples were fabricated on a highly-oriented pyrolytic graphite substrate at 773 K through sequential arc-plasma depositions of Pt and Au. The electrochemical hydrogen adsorption charges (electrochemical surface area), particularly the characteristic currents caused by the corner and edge sites of the Pt nanoparticles, decrease with increasing Au atomic ratio (x). In contrast, the specific ORR activities of the Au(x)/Pt100 samples were dependent on the atomic ratios of Pt and Au: the Au28/Pt100 sample showed the highest specific activity among all the investigated samples (x = 0-42). As for ORR durability evaluated by applying potential cycles between 0.6 and 1.0 V in oxygen-saturated 0.1 M HClO4, Au28/Pt100 was the most durable sample against the electrochemical potential cycles. The results clearly showed that the Au atoms located at coordinatively-unsaturated sites, e.g. at the corners or edges of the Pt nanoparticles, can improve the ORR durability by suppressing unsaturated-site-induced degradation of the Pt nanoparticles. PMID:26118789

  11. Pt monolayer coating on complex network substrate with high catalytic activity for the hydrogen evolution reaction

    PubMed Central

    Li, Man; Ma, Qiang; Zi, Wei; Liu, Xiaojing; Zhu, Xuejie; Liu, Shengzhong (Frank)

    2015-01-01

    A deposition process has been developed to fabricate a complete-monolayer Pt coating on a large-surface-area three-dimensional (3D) Ni foam substrate using a buffer layer (Ag or Au) strategy. The quartz crystal microbalance, current density analysis, cyclic voltammetry integration, and X-ray photoelectron spectroscopy results show that the monolayer deposition process accomplishes full coverage on the substrate and the deposition can be controlled to a single atomic layer thickness. To our knowledge, this is the first report on a complete-monolayer Pt coating on a 3D bulk substrate with complex fine structures; all prior literature reported on submonolayer or incomplete-monolayer coating. A thin underlayer of Ag or Au is found to be necessary to cover a very reactive Ni substrate to ensure complete-monolayer Pt coverage; otherwise, only an incomplete monolayer is formed. Moreover, the Pt monolayer is found to work as well as a thick Pt film for catalytic reactions. This development may pave a way to fabricating a high-activity Pt catalyst with minimal Pt usage. PMID:26601247

  12. Recent Advances in Platinum Monolayer Electrocatalysts for Oxygen Reduction Reaction: Scale-up Synthesis Structure and Activity of Pt Shells on Pd Cores

    SciTech Connect

    Sasaki K.; Wang J.X.; Naohara H.; Marinkovic N.; More K.; Inada H.; Adzic R.R.

    2010-03-01

    We have established a scale-up synthesis method to produce gram-quantities of Pt monolayer electrocatalysts. The core-shell structure of the Pt/Pd/C electrocatalyst has been verified using the HAADF-STEM Z-contrast images, STEM/EELS, and STEM/EDS line profile analysis. The atomic structure of this electrocatalyst and formation of a Pt monolayer on Pd nanoparticle surfaces were examined using in situ EXAFS. The Pt mass activity of the Pt/Pd/C electrocatalyst for ORR is considerably higher than that of commercial Pt/C electrocatalysts. The results with Pt monolayer electrocatalysts may significantly impact science of electrocatalysis and fuel-cell technology, as they have demonstrated an exceptionally effective way of using Pt that can resolve problems of other approaches, including electrocatalysts inadequate activity and high Pt content.

  13. Surface and bulk reconstruction of Pt(111) 1 × 1

    NASA Astrophysics Data System (ADS)

    Gallego, S.; Ocal, C.; Soria, F.

    1997-04-01

    A new structural analysis of the Pt(111) 1 × 1 surface by low energy electron diffraction gives an unexpected lattice parameter compression of a o=3.904 Å with respect to the crystallographic value of 3.924 Å, yielding a Pendry R-factor of 0.078. This implies a 0.5% contraction for both the in-plane lattice parameter, a p=2.761 Å, and bulk vertical interplanar distances, d b=2.25 Å, as compared to the crystallographic values of 2.775 and 2.265 Å, respectively. The topmost surface layer exhibits an expansion of 0.9%, 2.285 Å, and the second a contraction of 0.9%, 2.245 Å. Deeper layers are bulk layers.

  14. 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.

  15. Surface composition determination of Pt--Sn alloys by chemical titration with carbon monoxide

    SciTech Connect

    Haner, A.H.; Ross, P.N. ); Bardi, U.; Atrei, A. )

    1992-07-01

    The use of chemical titration with carbon monoxide to determine the surface composition of Pt--Sn alloys was studied using Pt{sub 3}Sn single crystals of known surface composition. The surface composition of the (111) and (100) faces were determined independently by the combination of low-energy electron diffraction (LEED) crystallography and low-energy ion scattering (LEIS). CO was adsorbed on these surfaces to saturation at 250 K and thermally desorbed into a mass spectrometer. The area under the thermal desorption spectroscopy curve for the alloy surface was compared to the area under the curve for the pure Pt surface of the same orientation. The ratios were 0.5{plus minus}0.05 for Pt{sub 3}Sn(100) and 0.7{plus minus}0.05 for Pt{sub 3}Sn(111), in excellent agreement with the 50% Pt and 75% Pt surface compositions derived from LEED and LEIS. The success of the titration method in this case appears to be due to (a) selective adsorption of CO on Pt atoms and (b) the relatively weak effect of the Pt--Sn intermetallic bond on the Pt--CO bonding.

  16. A first principles study of oxygen reduction reaction on a Pt(111) surface modified by a subsurface transition metal M (M = Ni, Co, or Fe).

    PubMed

    Duan, Zhiyao; Wang, Guofeng

    2011-12-01

    We have performed first-principle density functional theory calculations to investigate how a subsurface transition metal M (M = Ni, Co, or Fe) affects the energetics and mechanisms of oxygen reduction reaction (ORR) on the outermost Pt mono-surface layer of Pt/M(111) surfaces. In this work, we found that the subsurface Ni, Co, and Fe could down-shift the d-band center of the Pt surface layer and thus weaken the binding of chemical species to the Pt/M(111) surface. Moreover, the subsurface Ni, Co, and Fe could modify the heat of reaction and activation energy of various elementary reactions of ORR on these Pt/M(111) surfaces. Our DFT results revealed that, due to the influence of the subsurface Ni, Co, and Fe, ORR would adopt a hydrogen peroxide dissociation mechanism with an activation energy of 0.15 eV on Pt/Ni(111), 0.17 eV on Pt/Co(111), and 0.16 eV on Pt/Fe(111) surface, respectively, for their rate-determining O2 protonation reaction. In contrast, ORR would follow a peroxyl dissociation mechanism on a pure Pt(111) surface with an activation energy of 0.79 eV for its rate-determining O protonation reaction. Thus, our theoretical study explained why the subsurface Ni, Co, and Fe could lead to multi-fold enhancement in catalytic activity for ORR on the Pt mono-surface layer of Pt/M(111) surfaces. PMID:22187733

  17. Immobilizing highly catalytically active Pt nanoparticles inside the pores of metal-organic framework: a double solvents approach.

    PubMed

    Aijaz, Arshad; Karkamkar, Abhi; Choi, Young Joon; Tsumori, Nobuko; Rönnebro, Ewa; Autrey, Tom; Shioyama, Hiroshi; Xu, Qiang

    2012-08-29

    Ultrafine Pt nanoparticles were successfully immobilized inside the pores of a metal-organic framework, MIL-101, without aggregation of Pt nanoparticles on the external surfaces of framework by using a "double solvents" method. TEM and electron tomographic measurements clearly demonstrated the uniform three-dimensional distribution of the ultrafine Pt NPs throughout the interior cavities of MIL-101. The resulting Pt@MIL-101 composites represent the first highly active MOF-immobilized metal nanocatalysts for catalytic reactions in all three phases: liquid-phase ammonia borane hydrolysis, solid-phase ammonia borane thermal dehydrogenation, and gas-phase CO oxidation. PMID:22888976

  18. Surface Plasmon Enhanced Photocatalysis of Au/Pt-decorated TiO2 Nanopillar Arrays

    PubMed Central

    Shuang, Shuang; Lv, Ruitao; Xie, Zheng; Zhang, Zhengjun

    2016-01-01

    The low quantum yields and lack of visible light utilization hinder the practical application of TiO2 in high-performance photocatalysis. Herein, we present a design of TiO2 nanopillar arrays (NPAs) decorated with both Au and Pt nanoparticles (NPs) directly synthesized through successive ion layer adsorption and reaction (SILAR) at room temperature. Au/Pt NPs with sizes of ~4 nm are well-dispersed on the TiO2 NPAs as evidenced by electron microscopic analyses. The present design of Au/Pt co-decoration on the TiO2 NPAs shows much higher visible and ultraviolet (UV) light absorption response, which leads to remarkably enhanced photocatalytic activities on both the dye degradation and photoelectrochemical (PEC) performance. Its photocatalytic reaction efficiency is 21 and 13 times higher than that of pure TiO2 sample under UV-vis and visible light, respectively. This great enhancement can be attributed to the synergy of electron-sink function of Pt and surface plasmon resonance (SPR) of Au NPs, which significantly improves charge separation of photoexcited TiO2. Our studies demonstrate that through rational design of composite nanostructures one can harvest visible light through the SPR effect to enhance the photocatalytic activities initiated by UV-light, and thus realize more effectively utilization of the whole solar spectrum for energy conversion. PMID:27215703

  19. Surface Plasmon Enhanced Photocatalysis of Au/Pt-decorated TiO2 Nanopillar Arrays.

    PubMed

    Shuang, Shuang; Lv, Ruitao; Xie, Zheng; Zhang, Zhengjun

    2016-01-01

    The low quantum yields and lack of visible light utilization hinder the practical application of TiO2 in high-performance photocatalysis. Herein, we present a design of TiO2 nanopillar arrays (NPAs) decorated with both Au and Pt nanoparticles (NPs) directly synthesized through successive ion layer adsorption and reaction (SILAR) at room temperature. Au/Pt NPs with sizes of ~4 nm are well-dispersed on the TiO2 NPAs as evidenced by electron microscopic analyses. The present design of Au/Pt co-decoration on the TiO2 NPAs shows much higher visible and ultraviolet (UV) light absorption response, which leads to remarkably enhanced photocatalytic activities on both the dye degradation and photoelectrochemical (PEC) performance. Its photocatalytic reaction efficiency is 21 and 13 times higher than that of pure TiO2 sample under UV-vis and visible light, respectively. This great enhancement can be attributed to the synergy of electron-sink function of Pt and surface plasmon resonance (SPR) of Au NPs, which significantly improves charge separation of photoexcited TiO2. Our studies demonstrate that through rational design of composite nanostructures one can harvest visible light through the SPR effect to enhance the photocatalytic activities initiated by UV-light, and thus realize more effectively utilization of the whole solar spectrum for energy conversion. PMID:27215703

  20. Surface Plasmon Enhanced Photocatalysis of Au/Pt-decorated TiO2 Nanopillar Arrays

    NASA Astrophysics Data System (ADS)

    Shuang, Shuang; Lv, Ruitao; Xie, Zheng; Zhang, Zhengjun

    2016-05-01

    The low quantum yields and lack of visible light utilization hinder the practical application of TiO2 in high-performance photocatalysis. Herein, we present a design of TiO2 nanopillar arrays (NPAs) decorated with both Au and Pt nanoparticles (NPs) directly synthesized through successive ion layer adsorption and reaction (SILAR) at room temperature. Au/Pt NPs with sizes of ~4 nm are well-dispersed on the TiO2 NPAs as evidenced by electron microscopic analyses. The present design of Au/Pt co-decoration on the TiO2 NPAs shows much higher visible and ultraviolet (UV) light absorption response, which leads to remarkably enhanced photocatalytic activities on both the dye degradation and photoelectrochemical (PEC) performance. Its photocatalytic reaction efficiency is 21 and 13 times higher than that of pure TiO2 sample under UV-vis and visible light, respectively. This great enhancement can be attributed to the synergy of electron-sink function of Pt and surface plasmon resonance (SPR) of Au NPs, which significantly improves charge separation of photoexcited TiO2. Our studies demonstrate that through rational design of composite nanostructures one can harvest visible light through the SPR effect to enhance the photocatalytic activities initiated by UV-light, and thus realize more effectively utilization of the whole solar spectrum for energy conversion.

  1. Construction of modified embedded atom method potentials for Cu, Pt and Cu-Pt and modelling surface segregation in Cu 3Pt alloys

    NASA Astrophysics Data System (ADS)

    Luyten, Jan; Schurmans, Maarten; Creemers, Claude; Bunnik, Bouke S.; Kramer, Gert Jan

    2007-07-01

    In this work, surface segregation to Cu 3Pt surfaces is studied with the modified embedded atom method (MEAM). This work is triggered by the catalytic importance of Cu-Pt alloys, together with the contradictory experimental results for the surface segregation in Cu 3Pt(1 1 1) alloys based on low energy ion scattering (LEIS) [Y.G. Shen, D.J. O'Connor, K. Wandelt, R.J. MacDonald, Surf. Sci. 328 (1995) 21] and low energy electron diffraction (LEED) [Y. Gauthier, A. Senhaji, B. Legrand, G. Tréglia, C. Becker, K. Wandelt, Surf. Sci. 527 (2003) 71]. In order to accurately describe the segregation behaviour in the Cu 3Pt system, a reliable potential, that is also applicable to surface phenomena, is indispensable. Therefore, first, new MEAM parameters are derived, consistently based on ab initio density functional theory (DFT) calculations, according to a method that is a modification of previous work [P. van Beurden, G.J. Kramer, Phys. Rev. B 63 (2001) 165106]. Upon testing, these parameters prove to reproduce very well various surface properties of this system. Next, Monte Carlo (MC) simulations combined with the newly derived MEAM potentials are set up to investigate surface segregation to low index single crystal surfaces. For the Cu 3Pt(1 1 1) surface, our MC/MEAM simulations agree completely with the available LEIS evidence and contradict the unusual depth profile based on LEED. However, the slight Pt enrichment observed in the LEED experiments can be reproduced by assuming a slight Pt excess in the bulk of the sample. The simulated composition depth profile, on the other hand, does not agree with the LEED evidence. Also, for the Cu 3Pt(1 0 0) surface, the MC/MEAM results agree completely with LEIS experiments. For the Cu 3Pt(1 1 0) surface, finally, the MC/MEAM simulations show a somewhat deviating behaviour with respect to the experimental LEIS evidence. The possibility of a missing-row reconstruction is evaluated, but cannot explain the discrepancy for the Cu 3Pt

  2. Surface-Regulated Nano-SnO2/Pt3Co/C Cathode Catalysts for Polymer Electrolyte Fuel Cells Fabricated by a Selective Electrochemical Sn Deposition Method.

    PubMed

    Nagasawa, Kensaku; Takao, Shinobu; Nagamatsu, Shin-ichi; Samjeské, Gabor; Sekizawa, Oki; Kaneko, Takuma; Higashi, Kotaro; Yamamoto, Takashi; Uruga, Tomoya; Iwasawa, Yasuhiro

    2015-10-14

    We have achieved significant improvements for the oxygen reduction reaction activity and durability with new SnO2-nanoislands/Pt3Co/C catalysts in 0.1 M HClO4, which were regulated by a strategic fabrication using a new selective electrochemical Sn deposition method. The nano-SnO2/Pt3Co/C catalysts with Pt/Sn = 4/1, 9/1, 11/1, and 15/1 were characterized by STEM-EDS, XRD, XRF, XPS, in situ XAFS, and electrochemical measurements to have a Pt3Co core/Pt skeleton-skin structure decorated with SnO2 nanoislands at the compressive Pt surface with the defects and dislocations. The high performances of nano-SnO2/Pt3Co/C originate from efficient electronic modification of the Pt skin surface (site 1) by both the Co of the Pt3Co core and surface nano-SnO2 and more from the unique property of the periphery sites of the SnO2 nanoislands at the compressive Pt skeleton-skin surface (more active site 2), which were much more active than expected from the d-band center values. The white line peak intensity of the nano-SnO2/Pt3Co/C revealed no hysteresis in the potential up-down operations between 0.4 and 1.0 V versus RHE, unlike the cases of Pt/C and Pt3Co/C, resulting in the high ORR performance. Here we report development of a new class of cathode catalysts with two different active sites for next-generation polymer electrolyte fuel cells. PMID:26412503

  3. Highly efficient Ni@Ni-Pt/La2O3 catalyst for hydrogen generation from hydrous hydrazine decomposition: Effect of Ni-Pt surface alloying

    NASA Astrophysics Data System (ADS)

    Zhong, Yu-Jie; Dai, Hong-Bin; Jiang, Yuan-Yuan; Chen, De-Min; Zhu, Min; Sun, Li-Xian; Wang, Ping

    2015-12-01

    Hydrous hydrazine has received increasing attention as a promising hydrogen carrier owing to its many favorable attributes, such as high hydrogen content, low material cost, stable liquid state at ambient conditions, and free of solid decomposition byproduct. Herein, we report the synthesis of a supported core-shell structured Ni@Ni-Pt/La2O3 catalyst by a combination of co-precipitation and galvanic replacement methods. The catalyst exhibits high catalytic activity and 100% selectivity towards hydrogen generation from hydrous hydrazine at mild conditions, which outperforms most reported hydrous hydrazine decomposition catalysts. The favorable catalytic performance of the Ni@Ni-Pt/La2O3 catalyst is correlated with the Pt-induced electronic and geometric modifications on the catalyst surface.

  4. One pot aqueous synthesis of nanoporous Au85Pt15 material with surface bound Pt islands: an efficient methanol tolerant ORR catalyst

    NASA Astrophysics Data System (ADS)

    Anandha Ganesh, P.; Jeyakumar, D.

    2014-10-01

    For the first time, we are reporting the synthesis of Au100-xPtx nanoporous materials in the size range of 7-10 nm through the galvanic replacement of Ag by Pt from Au100-xAg2x spherical nano-alloys (x = 20, 15, 10 and 5) in an aqueous medium. The galvanic replacement reaction follows the `Volmer-Weber' growth mode, resulting in the formation of surface bound platinum islands on a nanoporous gold surface. The high angle annular dark field image and low angle X-ray diffraction studies confirm the presence of nanoporous Au100-xPtx NPs. The electrochemical studies using the Au85Pt15/C catalyst show excellent methanol tolerance behaviour and better performance towards oxygen reduction reaction (ORR) in terms of high mass activity, mass-specific activity and figure of merit (FOM) when compared to HiSPEC Pt/C commercial catalyst. Preliminary studies on a full cell using nanoporous Au85Pt15/C (loading 1.0 mg cm-2) as the cathode material and Pt-Ru/C (loading: 0.5 mg cm-2) as the anode material performed better (38 mW cm-2) than the HiSPEC Pt/C cathode material (16 mW cm-2).For the first time, we are reporting the synthesis of Au100-xPtx nanoporous materials in the size range of 7-10 nm through the galvanic replacement of Ag by Pt from Au100-xAg2x spherical nano-alloys (x = 20, 15, 10 and 5) in an aqueous medium. The galvanic replacement reaction follows the `Volmer-Weber' growth mode, resulting in the formation of surface bound platinum islands on a nanoporous gold surface. The high angle annular dark field image and low angle X-ray diffraction studies confirm the presence of nanoporous Au100-xPtx NPs. The electrochemical studies using the Au85Pt15/C catalyst show excellent methanol tolerance behaviour and better performance towards oxygen reduction reaction (ORR) in terms of high mass activity, mass-specific activity and figure of merit (FOM) when compared to HiSPEC Pt/C commercial catalyst. Preliminary studies on a full cell using nanoporous Au85Pt15/C (loading 1.0 mg

  5. Novel TiO₂-Pt@SiO₂ nanocomposites with high photocatalytic activity.

    PubMed

    Wu, Hao-Shuai; Sun, Ling-Dong; Zhou, Huan-Ping; Yan, Chun-Huan

    2012-05-21

    This article reports a facile and controllable two-step method to construct TiO(2)-Pt@SiO(2) nanocomposites. TiO(2) nanoparticles (NPs), with small size and high surface energy, were synthesized by a solvothermal reaction process. The TiO(2)-Pt@SiO(2) nanocomposites were fabricated by a reverse micro-emulsion method. SiO(2) shell coated NPs were adopted for further photocatalytic reaction. Because of their small size and high surface energy, TiO(2)@SiO(2) and TiO(2)-Pt@SiO(2) nanocomposites show higher photocatalytic activity than commercial Degussa P25. Compared with TiO(2)@SiO(2), TiO(2)-Pt@SiO(2)nanocomposites have improved photocatalytic activity due to the Pt induced spatial separation of electrons and holes. The silica shells not only maintain the structure of the nanocomposites but also prevent their aggregation during the photocatalytic reactions, which is highly important for the good durability of the photocatalyst. This strategy is simple, albeit efficient, and can be extended to the synthesis of other composites of noble metals. It has opened a new window for the construction of hetero-nanocomposites with high activity and durability, which would serve as excellent models in catalytic systems of both theoretical and practical interest. PMID:22495690

  6. Enhanced electrocatalytic activity of the Au-electrodeposited Pt nanoparticles-coated conducting oxide for the quantum dot-sensitized solar cells

    NASA Astrophysics Data System (ADS)

    Yoon, Yeung-Pil; Kim, Jae-Hong; Kang, Soon-Hyung; Kim, Hyunsoo; Choi, Chel-Jong; Kim, Kyong-Kook; Ahn, Kwang-Soon

    2014-08-01

    Au was electrodeposited potentiostatically at 0.3 V for 5 min on nanoporous Pt nanoparticle-coated F-doped SnO2 (FTO/Pt) substrates. For comparison, Au-electrodeposited FTO (FTO/Au) and Au-uncoated FTO/Pt were prepared. FTO/Au showed large-sized Au clusters dispersed sparsely over FTO, which resulted in lower electrocatalytic activity than FTO/Pt. In contrast, FTO/Pt exhibited poor stability unlike FTO/Au due to poisoning by the adsorption of sulfur species. The Au-electrodeposited FTO/Pt (FTO/Pt/Au) consisted of small Au clusters deposited over the entire area of Pt due to the effective Au nucleation provided by nanoporous metallic Pt. FTO/Pt/Au exhibited enhanced electrocatalytic activity and excellent stability because the small Au particles well-dispersed over the nanoporous metallic Pt network provided numerous electrochemical reaction sites, and the Pt surface was not exposed to the electrolyte. When FTO/Pt/Au was used as the counter electrode (CE) of a quantum dot-sensitized solar cell, the significantly enhanced electrocatalytic activity of the FTO/Pt/Au CE facilitated the reduction reaction of Sn2- + 2e- (CE) → Sn-12- + S2- at the CE/electrolyte interface, resulting in a significantly hindered recombination reaction, Sn2- + 2e- (TiO2 in the photoanode) → Sn-12- + S2-, and significantly improved overall energy conversion efficiency.

  7. Antisite-defect induced surface segregation in ordered NiPt

    NASA Astrophysics Data System (ADS)

    Pourovskii, Leonid V.; Ruban, Andrei V.; Abrikosov, Igor A.; Johansson, Borje

    2003-03-01

    By means of bulk and surface Monte Carlo simulations using effective interatomic interactions obtained from first principles Green's function calculations, we demonstrate that tiny deviations from stoichiometry in the bulk composition of the NiPt-L10 ordered alloy have a great impact on the segregation behavior and atomic configuration of the (111) surface. We predict that at T = 600 K the (111) surface of the Ni_51Pt_49 and Ni_50Pt_50 alloys has the usual 2 × 1 structure which corresponds to the (111) truncation of the bulk L10 ordered structure. However, the (111) surface of the nickel deficient Ni_49Pt_51 alloy is strongly enriched by Pt and should exhibit the pattern of the 2 × 2 structure. Such a drastic change in the segregation behavior is due to the presence of different antisite defects in the Ni- and Pt-rich alloys, and is a manifestation of the so-called offstoichiometric effect.

  8. Theoretical investigation of surface states and energetics of PtSi surfaces

    NASA Astrophysics Data System (ADS)

    Niranjan, Manish K.

    2016-07-01

    Platinum silicide (PtSi) is highly promising material for applications in microelectronic devices. In this article, the surface electronic structure, surface energetics and work functions of stoichiometric and non-stoichiometric PtSi(010) surfaces are explored within the framework of first-principle density functional theory. The surface rumpling is found to be significant only for the top surface layer. The computed values of the rumpling parameter for the top three layers are ~ 11.0%, ~ 0.9% and ~ 1.9%. Further, the interlayer relaxation is found to be largest for the top layer and decreases rapidly for inner layers. Localized surface states are obtained in the valence band at ~ 9.0 eV below the Fermi level. Under rich Pt and Si growth conditions, nonstoichiometric (010) terminations are found to have the lowest surface energies, whereas stoichiometric termination has the lowest surface energy (~ 1.74 J/m2) under mixed conditions. The work function of stoichiometric (010) termination is computed to be 5.15 eV and differ as much as by ± 0.5 eV for nonstoichiometric terminations.

  9. Surface electrochemistry of CO and H{sub 2}/CO mixtures at Pt(100) interface: Electrode kinetics and interfacial structures

    SciTech Connect

    Markovic, N.M.; Lucas, C.A.; Grgur, B.N.; Ross, P.N.

    1999-11-04

    The Pt(100)-CO interaction in aqueous electrolytes was examined by using rotating disk methods in combination with in-situ surface X-ray scattering (SXS) measurements. The analysis of the SXS results indicates that the topmost platinum atoms expand away from the second layer by ca. 4% when H{sub upd} was completely displaced from Pt(100) by CO to form a saturated layer of CO. Assuming that gas-phase heats of adsorption for CO apply as well to the liquid-solid interface, the authors estimate that the Gibbs energy change for the displacement of H{sub upd} by CO on Pt(100) is close to {minus}90 kJ/mol. A Pt(100)-CO surface normal interlayer spacing of 1.4 {+-} 0.4 {angstrom} was extracted from SXS measurements, suggesting that CO is adsorbed primarily at the 2-fold bridge-bonded sites, or possibly a mixture of bridge and atop sites. In contrast to the Pt(111)-CO system, no structures of CO{sub ad} with long-range order were formed on Pt(100). Two different forms of CO{sub ad} are formed at the Pt(100)-electrolyte interface: the weakly adsorbed state which is oxidized in the pre-ignition potential region, and the strongly adsorbed state which is oxidized in the ignition potential region. Although the nature of CO{sub ad} is different before and after the ignition potential, the authors proposed that the mechanism for CO oxidation on Pt(100) is the same in both the pre-ignition and ignition potential regions, e.g., adsorbed CO reacts with hydroxyl species (OH{sub ad}) through a Langmuir-Hinshelwood type reaction. The kinetics of CO oxidation on Pt(hkl) surfaces is found to vary with crystal face. The difference in activity is attributed to the structure-sensitive adsorption of CO, OH{sub ad}, and anions from the supporting electrolytes.

  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, 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.

  11. Controlled FCC/on-top binding of H/Pt(111) using surface stress

    NASA Astrophysics Data System (ADS)

    Shuttleworth, I. G.

    2016-08-01

    The preferred binding site of H/Pt(111) has been shown to be change from the on-top to FCC as the Pt(111) surface goes approximately from a state of compressive to tensile strain. A chemical analysis of the system has shown that for both FCC and on-top bound cases the H ssbnd Pt s and H ssbnd Pt d interactions have a similar importance in determining the preferred binding position. It has been seen that FCC-bound H forms a distinct state below the Pt d-band, whereas the on-top bound H does not.

  12. PdPt bimetallic nanoparticles enabled by shape control with halide ions and their enhanced catalytic activities.

    PubMed

    Zhang, Jinfeng; Wan, Lei; Liu, Lei; Deng, Yida; Zhong, Cheng; Hu, Wenbin

    2016-02-21

    In this study, a new and convenient one step approach is described for synthesizing shape controlled PdPt bimetallic nanoparticles. It is found that the resultant morphologies of these PdPt nanoparticles can be well controlled by simply altering the participation of different halide ions that serve as shape controlling agents in the reaction solution. The dendritic core-shell PdPt bimetallic nanoparticles generated with Pt atoms adopt usual island growth pattern in the presence of Cl(-) ions, whereas the introduction of Br(-) ions with a relatively strong adsorption effect facilitate the formation of a layered core-shell structure due to the layered growth mode of Pt atoms on the exterior surface of the central Pd core. Moreover, the stronger adsorption function of I(-) ions and the resulting fast atomic diffusion promoted the generation of mesoporous core-shell PdPt bimetallic nanoparticles with many pore channels. In addition, the size of these synthesized PdPt nanoparticles exhibited a significant dependence on the concentration of the halide ions involved. Due to their specific structural features and synergistic effects, these PdPt catalysts exhibited shape-dependent catalytic performance and drastically enhanced electrocatalytic activities relative to that of commercial Pt black and Pt/C toward methanol oxidation. PMID:26511671

  13. Morphological and compositional evolution of Pt-Si intermetallic thin films prepared by the activated adsorption of SiH{sub 4} on Pt(111)

    SciTech Connect

    Bondos, J.C.; Gewirth, A.A.; Nuzzo, R.G.

    1999-04-22

    The authors have investigated using scanning tunneling microscopy (STM) and Auger electron spectroscopy (AES) the growth and structural evolution of Pt-Si intermetallic phases formed via a chemical vapor deposition (CVD) mediated process. The Pt silicide thin films were prepared though the exposure of a Pt(111) crystal to silane (SiH{sub 4}) followed by various annealing treatments. The deposition of Si via the decomposition of silane at room temperature preferentially forms clusters at step edges that avoid the centers of Pt terraces. The sizes and coverages of the clusters increases with silane exposure. The clusters are of intermetallic character (composed of both Si and Pt) and coarsen to give cluster heights much larger than a Pt(111) step height. These observations implicitly establish that Si interdiffusion in the near-surface region is weakly activated. Studies performed as a function of the silane exposure and annealing temperature reveal a complicated phase behavior that incorporates seven separate atomically ordered phases in addition to large-scale surface features such as three-dimensional islands. Growth and degradation mechanisms have been constructed, and the phenomena observed are contrasted with standard kinetic models based on sequential phase growth.

  14. 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 2

    NASA Astrophysics Data System (ADS)

    Pech-Pech, I. E.; Gervasio, Dominic F.; Pérez-Robles, J. F.

    2015-02-01

    In the first part of this work, the feasibility of developing a catalyst with high activity for the oxygen electroreduction reaction (ORR) in acid media and with low Pt loading was demonstrated by over coating a silver (Ag) nanoparticle with a shell of platinum (Pt) and palladium (Pd) [7]. The results show that best activity is not directly related to a higher PtPd loading on the surface of the Ag. The best catalyst in a series of this type of catalyst is found with Ag@Pt0.3Pd0.3/C which gives a specific activity for oxygen reduction, jk (in units of mA cm-2 of real area), of 0.07 mA cm-2 at 0.85 V vs. NHE, as compared to 0.04 mA cm-2 when with a commercial Pt on carbon catalyst (Pt20/C) is used in an identical electrode except for the catalyst. The mass activity, jm (in units of mA μg-1 of Pt), for Ag@Pt0.3Pd0.3/C is 0.04 mA μg-1 of Pt at 0.85 V vs. NHE, whereas that for the Pt20/C gives 0.02 mA μg-1 of Pt, showing Ag@Pt0.3Pd0.3/C is a lower-cost catalyst, because using a Ag core and Pd with Pt in the shell gives the highest catalytic activity using less Pt.

  15. Promotion of oxygen reduction reaction durability of carbon-supported PtAu catalysts by surface segregation and TiO₂ addition.

    PubMed

    Liu, Chen-Wei; Chen, Hong-Shuo; Lai, Chien-Ming; Lin, Jiunn-Nan; Tsai, Li-Duan; Wang, Kuan-Wen

    2014-02-12

    Highly effective carbon supported-Pt75Au25 catalysts for oxygen reduction reaction (ORR) are prepared though titanium dioxide modification and post heat treatment. After accelerated durability test (ADT) of 1700 cycles, the ORR activity of PtAu/C catalysts modified by TiO2 and air heat treatment is 3 times higher than that of the commercial Pt/C. The enhancement of ORR activity is attributed to surface and structural alteration by air-induced Pt surface segregation and lower unfilled d states. On the contrary, for TiO2 modified and H2 treated PtAu/C catalysts, the deterioration of the ORR activity may be due to the loss of electrochemical surface area after ADT and the increase of d-band vacancy. PMID:24447040

  16. Antisite-Defect-Induced Surface Segregation in Ordered NiPt Alloy

    NASA Astrophysics Data System (ADS)

    Pourovskii, L. V.; Ruban, A. V.; Johansson, B.; Abrikosov, I. A.

    2003-01-01

    By means of first principles simulations we demonstrate that tiny deviations from stoichiometry in the bulk composition of the NiPt-L10 ordered alloy have a great impact on the atomic configuration of the (111) surface. We predict that at T=600 K the (111) surface of the Ni51Pt49 and Ni50Pt50 alloys corresponds to the (111) truncation of the bulk L10 ordered structure. However, the (111) surface of the nickel deficient Ni49Pt51 alloy is strongly enriched by Pt and should exhibit the pattern of the 2×2 structure. Such a drastic change in the segregation behavior is due to the presence of different antisite defects in the Ni- and Pt-rich alloys and is a manifestation of the so-called off-stoichiometric effect.

  17. Correlation between the surface configurations and hydrogenolysis: Aniline on the Pt(111) surface

    SciTech Connect

    Huang, S.X. ); Fischer, D.A. ); Gland, J.L. )

    1994-07-01

    A correlation has been developed between the structure of adsorbed reaction intermediates and their hydrogenolysis reactivity for aniline in hydrogen pressures up to 0.001 Torr on the Pt(111) surface. The composition and orientation of the species involved in aniline hydrogenolysis were characterized using temperature programmed reaction (TPR) and near edge x-ray absorption fine structure (NEXAFS) measurements. The benzene and ammonia formed by aniline hydrogenolysis during TPR on the Pt(111) surface increase substantially in the presence of hydrogen atmospheres. At reaction temperatures, the aromatic ring in aniline remains parallel to the surface in the presence of coadsorbed hydrogen, while in the absence of hydrogen the aromatic ring is tilted relative to the surface. This correlation between orientation and reactivity suggests that a parallel configuration may facilitate hydrogenolysis of the C--N bond in aniline. These [ital in] [ital situ] studies provide new insight into the structure of surface intermediates which may play a critical role in the mechanisms of aniline hydrogenolysis on the Pt(111) surface in 0.001 Torr of hydrogen.

  18. Adsorption and desorption of NO and CO on a Pt(111)Ge surface alloy

    NASA Astrophysics Data System (ADS)

    Fukutani, K.; Magkoev, T. T.; Murata, Y.; Terakura, K.

    1996-08-01

    Adsorption of NO and CO on Pt(111) alloyed with a few per cent of Ge is investigated by reflection—absorption infrared spectroscopy and thermal desorption spectroscopy. Both molecules exclusively occupy the on-top site in contrast to bridge and on-top adsorption on clean Pt(111). The adsorption energy of NO is dramatically reduced compared with that on clean Pt(111). Photodesorption of CO observed on the clean Pt(111) is noticeably suppressed on the Pt(111)Ge surface alloy, while NO desorption is induced by photon irradiation. The rotational and translational temperatures of photodesorbed No are similar to those on clean Pt(111). The change in chemical properties of Pt(111) for molecular adsorption is discussed in terms of d-band filling of the substrate.

  19. Interaction of methanol and its dehydrogenation species with Pt-alloy surfaces

    NASA Astrophysics Data System (ADS)

    Cahyanto, Wahyu Tri; Widanarto, Wahyu; Effendi, Mukhtar; Hamdi, Muhammad Raihan; Kasai, Hideaki

    2016-02-01

    Adsorption of sequential single methanol dehydrogenation intermediate species on Pt-, PtRu-, and PtRuMo-surfaces is investigated by using density functional theory (DFT). This work is a part of our efforts in understanding the methanol oxidation reaction (MOR) on Pt-alloy surfaces for further possible prediction of decomposition processes. Particularly, effects of Ru and Mo impurity to the pure Pt surface to form PtRu and PtRuMo surfaces as possible candidates for promising catalysts of direct methanol fuel cells (DMFCs) are given. However, the study is limited to the scientific point of view, i.e., fundamental interactions between adsorbates and surfaces, in correspondence with adsorption mechanism using charge transfer analysis. The trend in the increase of adsorption energy and charge transfer by alloying Ru and Mo to the Pt surface is observed. Moreover, the increase of the d-orbital vacancy caused by alloying Ru and Mo possessing lesser filled d-orbital is suggested to responsible for the increase of surface-adsorbate interaction strength.

  20. Impurity and Support Effects on Surface Composition and CO+NO Reactions Over Pt-Rh/CeO2 Nanoparticles:

    NASA Astrophysics Data System (ADS)

    Khanra, Badal C.; de Sarkar, Abir

    A Monte Carlo simulation technique has been used to investigate the effect of sulphur impurity and ceria support on the surface composition and catalytic activity of Pt-Rh/ceria nanocatalysts. For temperatures in the range of 400-1300 K the surface Pt concentration decreases with increase in sulphur coverage. The Pt concentration at the base of the nanocatalyst in contact with the support increases with metal-support interaction. However, for weak metal-support interaction (Vms<-0.01 eV) the surface Pt concentration slightly increases with metal-support interaction. Overall, sulphur is found to influence the surface composition much more strongly than the metal-support interaction. The MC-simulated surface composition results have been used to study the energetics of the CO+NO reactions over Pt-Rh/CeO2 catalysts. It is found that the CO2 formation rate decreases with increase in sulphur coverage and marginally increases with metal-support interaction up to Vms=-0.01 eV. All the results qualitatively agree with the experimental results.

  1. Novel strategy for preparation of graphene-Pd, Pt composite, and its enhanced electrocatalytic activity for alcohol oxidation.

    PubMed

    Gao, Lina; Yue, Wenbo; Tao, Shanshan; Fan, Louzhen

    2013-01-22

    As advanced electrodes for direct alcohol fuel cells, graphene-Pd and graphene-Pt composites with a trace of SnO(2) have been successfully synthesized by a modified electroless plating technique. The surface of graphene oxide is first sensitized by Sn(2+) ions, and subsequently, Pd or Pt nanoparticles are deposited on the surface of graphene oxide. Finally, graphene oxide was reduced to graphene by further adding NaBH(4). Compared to other carbon-(e.g., Vulcan XC-72R) supported Pd and Pt, the resultant graphene-Pd and Pt composites exhibit better electrocatalytic activity and long-term stability toward alcohol electrooxidation. Additionally, a trace amount of SnO(2) formed around active catalysts may also be beneficial to the enhancement of electrochemical activity. PMID:23259819

  2. Shape-control and electrocatalytic activity-enhancement of Pt-based bimetallic nanocrystals.

    PubMed

    Porter, Nathan S; Wu, Hong; Quan, Zewei; Fang, Jiye

    2013-08-20

    Due to the increasing worldwide energy demand and environ-mental concerns, the need for alternative energy sources is growing stronger, and platinum catalysts in fuel cells may help make the technologies a reality. However, the pursuit of highly active Pt-based electrocatalysts continues to be a challenge. Scientists developing electrocatalysts continue to focus on characterizing and directing the construction of nanocrystals and advancing their electrochemical applications. Although chemists have worked on Pt-based bimetallic (Pt-M) preparations in the past, more recent research shows that both shape-controlled Pt-M nanocrystals and the assembly of these nanocrystals into supercrystals are promising new directions. A solution-based synthesis approach is an effective technique for preparing crystallographic facet-directed nanocatalysts. This is aided by careful selection of the metal precursor, capping ligand, reducing agent, and solvent. Incorporating a secondary metal M into the Pt lattice and manipulating the crystal facets on the surface cooperatively alter the electrocatalytic behavior of these Pt-M bimetallic nanocrystals. Specifically, chemists have extensively studied the {111}- and {100}-terminated crystal facets because they show unique atomic arrangement on surfaces, exhibit different catalytic performance, and possess specific resistance to toxic adsorbed carbon monoxide (COads). For catalysts to have maximum efficiency, they need to have resistance to COads and other poisonous carbon-containing intermediates when the catalysts operate under harsh conditions. A necessary design to any synthesis is to clearly understand and utilize the role of each component in order to successfully induce shape-controlled growth. Since chemists began to understand Pt nanocrystal shape-dependent electrocatalytic activity, the main obstacles blocking proton exchange membrane fuel cells are anode poisoning, sluggish kinetics at the cathode, and low activity. In this

  3. The surface chemistry of vinyl iodide on Pt(111)

    SciTech Connect

    Liu, Z.M.; Zhou, X.L.; Buchanan, D.A.

    1992-03-11

    Regardless of exposure, only submonolayer amounts of vinyl iodide (CH{sub 2}CHI) decompose, either during adsorption on Pt(111) at 100 K or during subsequent heating to 165 K. The remainder desorbs molecularly. The dissociation products are vinyl (CH{sub 2}CH) fragments, an important C{sub 2} intermediate in hydrocarbon catalysis, and atomic iodine. Using the tools of surface science the authors have explored the formation and subsequent reactions of vinyl species in the presence of unavoidable coadsorbed atomic iodine. While some vinyl exists up to 450 K, there are two important and competitive lower temperature reaction channels which lead to ethylidyne (CCH{sub 3}) and ethylene (CH{sub 2}CH{sub 2}). From these results, the authors conclude that the rate of ethylidyne formation from adsorbed ethylene is controlled by the rate at which the first C-H bond in ethylene breaks, and in agreement with Zaera, the authors find that vinyl is a facile intermediate in the process. 28 refs., 12 figs., 3 tabs.

  4. Enhancing the photovoltaic performance and stability of QDSSCs using surface reinforced Pt nanostructures with controllable morphology and superior electrocatalysis via cost-effective chemical bath deposition.

    PubMed

    Rao, S Srinivasa; Durga, Ikkurthi Kanaka; Kang, Tae-Su; Kim, Soo-Kyoung; Punnoose, Dinah; Gopi, Chandu V V M; Eswar Reddy, Araveeti; Krishna, T N V; Kim, Hee-Je

    2016-02-28

    To make quantum-dot sensitized solar cells (QDSSCs) competitive, photovoltaic parameters such as the power conversion efficiency (PCE) and fill factor (FF) must become comparable to those of other emerging solar cell technologies. In the present study, a novel strategy has been successfully developed for a highly efficient surface-modified platinum (Pt) counter electrode (CE) with high catalytic activity and long-term stability in a polysulfide redox electrolyte. The reinforcement of the Pt surface was performed using a thin passivating layer of CuS, NiS, or CoS by simple chemical bath deposition techniques. This method was a more efficient method for reducing the electron recombination in QDSSCs. The optimized Pt/CuS CE shows a very low charge transfer resistance of 37.01 Ω, which is an order of magnitude lower than those of bare Pt (86.32 Ω), Pt/NiS (53.83 Ω), and Pt/CoS (73.51 Ω) CEs. Therefore, the Pt/CuS CEs show much greater catalytic activity in the polysulfide redox electrolyte than Pt, Pt/NiS and Pt/CoS CEs. As a result, under one-sun illumination (AM 1.5G, 100 mW cm(-2)), the Pt/CuS CE exhibits a PCE of 4.32%, which is higher than the values of 1.77%, 2.95%, and 3.25% obtained with bare Pt, Pt/CoS, and Pt/NiS CEs, respectively. The performance of the Pt/CuS CE was enhanced by the improved current density, Cu vacancies with increased S composition, and surface morphology, which enable rapid electron transport and lower the electron recombination rate for the polysulfide electrolyte redox couple. Electrochemical impedance spectroscopy and Tafel polarization revealed that the hybrid CEs reduce interfacial recombination and exhibit better electrochemical and photovoltaic performance compared with a bare Pt CE. The Pt/CuS CE also shows superior stability in the polysulfide electrolyte in a working state for over 10 h, resulting in a long-term electrode stability than Pt CE. PMID:26796086

  5. Facile synthesis of PtAu alloy nanoparticles with high activity for formic acid oxidation

    SciTech Connect

    Zhang, Sheng; Shao, Yuyan; Yin, Geping; Lin, Yuehe

    2010-02-15

    We report the facile synthesis of carbon supported PtAu alloy nanoparticles with high electrocatalytic activity as the anode catalyst for direct formic acid fuel cells (DFAFCs). PtAu alloy nanopaticles are synthesized by co-reducing HAuCl4 and H2PtCl6 with NaBH4 in the presence of sodium citrate and then the nanoparticles are deposited on Vulcan XC-72R carbon support (PtAu/C). The obtained catalysts are characterized with X-ray diffraction (XRD) and transmission electron microscope (TEM), which reveal PtAu alloy formation with an average diameter of 4.6 nm. PtAu/C exhibits 8 times higher catalytic activity toward formic acid oxidation than Pt/C. The enhanced activity of PtAu/C catalyst is attributed to noncontinuous Pt sites formed in the presence of the neighbored Au sites, which promotes direct oxidation of formic acid by avoiding poison CO.

  6. Effects of Reduction Temperature and Metal-support Interactions on the Catalytic Activity of Pt/γ-Al2O3 and Pt/TiO2 for the Oxidation of CO in the Presence and Absence of H2

    SciTech Connect

    Alexeev, Oleg S.; Chin, Soo Yin; Engelhard, Mark H.; Ortiz-Soto, Lorna; Amiridis, Michael D.

    2005-12-15

    TiO2- and ?-Al2O3-supported Pt catalysts were characterized by HRTEM, XPS, EXAFS, and in-situ FTIR after activation at various conditions and their catalytic properties were examined for the oxidation of CO in the absence and presence of H2 (PROX). When ?-Al2O3 was used as the support, the catalytic, electronic, and structural properties of the Pt particles formed were not affected substantially by the pretreatment conditions. In contrast, the surface properties and catalytic activity of Pt/TiO2 were strongly influenced by the pretreatment conditions. In this case, an increase in the reduction temperature led to higher electron density on Pt, altering its chemisorptive properties, weakening the Pt-CO bonds, and increasing its activity for the oxidation of CO. The in-situ FTIR data suggest that both the terminal and bridging CO species adsorbed on fully reduced Pt are active for this reaction. The high activity of Pt/TiO2 for the oxidation of CO can also be attributed to the ability of TiO2 to provide or stabilize highly reactive oxygen species at the metal-support interface. However, such species appear to be more reactive towards H2 than CO. Consequently, Pt/TiO2 shows substantially lower selectivities towards CO oxidation under PROX conditions than Pt/?-Al2O3.

  7. Effects of Reduction Temperature and Metal-Support Interactions on the Catalytic Activity of Pt/g-Al2O3 and Pt/TiO2 for the Oxidation of CO in the Presence and Absence of H2.

    SciTech Connect

    Alexeev,O.; Chin, S.; Engelhard, M.; Ortiz-Soto, L.; Amiridis, M.

    2005-01-01

    TiO2- and -Al2O3-supported Pt catalysts were characterized by HRTEM, XPS, EXAFS, and in situ FTIR spectroscopy after activation at various conditions, and their catalytic properties were examined for the oxidation of CO in the absence and presence of H2 (PROX). When {gamma}-Al{sub 2}O{sub 3} was used as the support, the catalytic, electronic, and structural properties of the Pt particles formed were not affected substantially by the pretreatment conditions. In contrast, the surface properties and catalytic activity of Pt/TiO2 were strongly influenced by the pretreatment conditions. In this case, an increase in the reduction temperature led to higher electron density on Pt, altering its chemisorptive properties, weakening the Pt-CO bonds, and increasing its activity for the oxidation of CO. The in situ FTIR data suggest that both the terminal and bridging CO species adsorbed on fully reduced Pt are active for this reaction. The high activity of Pt/TiO2 for the oxidation of CO can also be attributed to the ability of TiO2 to provide or stabilize highly reactive oxygen species at the metal-support interface. However, such species appear to be more reactive toward H{sub 2} than CO. Consequently, Pt/TiO{sub 2} shows substantially lower selectivities toward CO oxidation under PROX conditions than Pt/{gamma}-Al{sub 2}O{sub 3}.

  8. Effects of reduction temperature and metal-support interactions on the catalytic activity of Pt/gamma-Al2O3 and Pt/TiO2 for the oxidation of CO in the presence and absence of H2.

    PubMed

    Alexeev, Oleg S; Chin, Soo Yin; Engelhard, Mark H; Ortiz-Soto, Lorna; Amiridis, Michael D

    2005-12-15

    TiO2- and gamma-Al2O3-supported Pt catalysts were characterized by HRTEM, XPS, EXAFS, and in situ FTIR spectroscopy after activation at various conditions, and their catalytic properties were examined for the oxidation of CO in the absence and presence of H2 (PROX). When gamma-Al2O3 was used as the support, the catalytic, electronic, and structural properties of the Pt particles formed were not affected substantially by the pretreatment conditions. In contrast, the surface properties and catalytic activity of Pt/TiO2 were strongly influenced by the pretreatment conditions. In this case, an increase in the reduction temperature led to higher electron density on Pt, altering its chemisorptive properties, weakening the Pt-CO bonds, and increasing its activity for the oxidation of CO. The in situ FTIR data suggest that both the terminal and bridging CO species adsorbed on fully reduced Pt are active for this reaction. The high activity of Pt/TiO2 for the oxidation of CO can also be attributed to the ability of TiO2 to provide or stabilize highly reactive oxygen species at the metal-support interface. However, such species appear to be more reactive toward H2 than CO. Consequently, Pt/TiO2 shows substantially lower selectivities toward CO oxidation under PROX conditions than Pt/gamma-Al2O3. PMID:16375316

  9. Ethanol oxidation on Pt single-crystal electrodes: surface-structure effects in alkaline medium.

    PubMed

    Busó-Rogero, Carlos; Herrero, Enrique; Feliu, Juan M

    2014-07-21

    Ethanol oxidation in 0.1 M NaOH on single-crystal electrodes has been studied using electrochemical and FTIR techniques. The results show that the activity order is the opposite of that found in acidic solutions. The Pt(111) electrode displays the highest currents and also the highest onset potential of all the electrodes. The onset potential for the oxidation of ethanol is linked to the adsorption of OH on the electrode surface. However, small (or even negligible) amounts of CO(ads) and carbonate are detected by FTIR, which implies that cleavage of the C-C bond is not favored in this medium. The activity of the electrodes diminishes quickly upon cycling. The diminution of the activity is proportional to the measured currents and is linked to the formation and polymerization of acetaldehyde, which adsorbs onto the electrode surface and prevents further oxidation. PMID:24782218

  10. The deposition of Au-Pt core-shell nanoparticles on reduced graphene oxide and their catalytic activity

    NASA Astrophysics Data System (ADS)

    Cui, Xiu; Wu, Shengnan; Jungwirth, Scott; Chen, Zhibing; Wang, Zhenghua; Wang, Lun; Li, Yongxin

    2013-07-01

    Au-Pt core-shell nanoparticles have been synthesized on a reduced graphene oxide (RGO) surface by an under-potential deposition (UPD) redox replacement technique, which involves redox replacement of a copper UPD monolayer by {{PtCl}}_{4}^{2-} that could be reduced and deposited simultaneously. Scanning electron microscopy (SEM) and electrochemical methods have been used to characterize the graphene decorated with Au-Pt core-shell nanoparticles. The electrochemical experiments show that the materials exhibit excellent catalytic activity towards the oxygen reduction reaction and the methanol oxidation reaction. It is believed that the high-performance of this new catalyst is due to the ultrathin Pt shell on the Au nanoparticles surface and the oxygen-containing functional groups on the RGO surface.

  11. Formation of a Pt-Decorated Au Nanoparticle Monolayer Floating on an Ionic Liquid by the Ionic Liquid/Metal Sputtering Method and Tunable Electrocatalytic Activities of the Resulting Monolayer.

    PubMed

    Sugioka, Daisuke; Kameyama, Tatsuya; Kuwabata, Susumu; Yamamoto, Takahisa; Torimoto, Tsukasa

    2016-05-01

    A novel strategy to prepare a bimetallic Au-Pt particle film was developed through sequential sputter deposition of Au and Pt on a room temperature ionic liquid (RTIL). Au sputter deposition onto an RTIL containing hydroxyl-functionalized cations produced a monolayer of Au particles 4.2 nm in size on the liquid surface. Subsequent Pt sputtering onto the original Au particle monolayer floating on the RTIL enabled decoration of individual Au particles with Pt metals, resulting in the formation of a bimetallic Au-Pt particle monolayer with a Pt-enriched particle surface. The particle size slightly increased to 4.8 nm with Pt deposition for 120 min. The shell layer of a bimetallic particle was composed of Au-Pt alloy, the composition of which was tunable by controlling the Pt sputter deposition time. The electrochemical surface area (ECSA) was determined by cyclic voltammetry of bimetallic Au-Pt particle monolayers transferred onto HOPG electrodes by a horizontal liftoff method. The Pt surface coverage, determined by ECSAs of Au and Pt, increased from 0 to 56 mol % with elapse of the Pt sputter deposition time up to 120 min. Thus-obtained Au-Pt particle films exhibited electrocatalytic activity for methanol oxidation reaction (MOR) superior to the activities of pure Au or Pt particles. Volcano-type dependence was observed between the MOR activity and Pt surface coverage on the particles. Maximum activity was obtained for Au-Pt particles with a Pt coverage of 49 mol %, being ca. 120 times higher than that of pure Pt particles. This method enables direct decoration of metal particles with different noble metal atoms, providing a novel strategy to develop highly efficient multinary particle catalysts. PMID:27074631

  12. Glycine-mediated syntheses of Pt concave nanocubes with high-index {hk0} facets and their enhanced electrocatalytic activities.

    PubMed

    Zhang, Zhi-cheng; Hui, Jun-feng; Liu, Zhi-Chang; Zhang, Xin; Zhuang, Jing; Wang, Xun

    2012-10-23

    Metal nanocrystals with high-index facets (HIFs) have drawn significant attention for their superior catalysis activity compared to that of low-index faces. However, because of the high surface energy of HIFs, it is still challenging to preserve HIFs during the growth of nanocrystals. In this study, highly selective Pt concave nanocubes (CNCs) with high-index {hk0} facets have been successfully prepared in a simple aqueous solution. The vital role of glycine as the surface controller in the formation of CNCs was demonstrated. These Pt CNCs exhibited enhanced specific activities toward the electro-oxidation of methanol and formic acid in comparison to commercial Pt black and Pt/C catalysts. PMID:23046108

  13. High electrocatalytic activity of Pt-Pd binary spherocrystals chemically assembled in vertically aligned TiO2 nanotubes.

    PubMed

    Lei, Yanzhu; Zhao, Guohua; Tong, Xili; Liu, Meichuan; Li, Dongming; Geng, Rong

    2010-01-18

    To obtain noble metal catalysts with high efficiency, long-term stability, and poison resistance, Pt and Pd are assembled in highly ordered and vertically aligned TiO(2) nanotubes (NTs) by means of the pulsed-current deposition (PCD) method with assistance of ultrasonication (UC). Here, Pd serves as a dispersant which prevents agglomeration of Pt. Thus Pt-Pd binary catalysts are embed into TiO(2) NTs array under UC in sunken patterns of composite spherocrystals (Sps). Owing to this synthesis method and restriction by the NTs, the these catalysts show improved dispersion, more catalytically active sites, and higher surface area. This nanotubular metallic support material with good physical and chemical stability prevents catalyst loss and poisoning. Compared with monometallic Pt and Pd, the sunken-structured Pt-Pd spherocrystal catalyst exhibits better catalytic activity and poison resistance in electrocatalytic methanol oxidation because of its excellent dispersion. The catalytic current density is enhanced by about 15 and 310 times relative to monometallic Pt and Pd, respectively. The poison resistance of the Pt-Pd catalyst was 1.5 times higher than that of Pt and Pd, and they show high electrochemical stability with a stable current enduring for more than 2100 s. Thus, the TiO(2) NTs on a Ti substrate serve as an excellent support material for the loading and dispersion of noble metal catalysts. PMID:19924757

  14. Promotion effect of manganese oxide on the electrocatalytic activity of Pt/C for methanol oxidation in acid medium

    NASA Astrophysics Data System (ADS)

    Abdel Hameed, R. M.; Fetohi, Amani E.; Amin, R. S.; El-Khatib, K. M.

    2015-12-01

    The modification of Pt/C by incorporating metal oxides for electrocatalytic oxidation of methanol has gained major attention because of the efficiency loss during the course of long-time operation. This work describes the preparation of Pt-MnO2/C electrocatalysts through a chemical route using ethylene glycol or a mixture of ethylene glycol and sodium borohydride as a reducing agent. The crystallite structure and particle size of synthesized electrocatalysts are determined using X-ray diffraction (XRD) and transmission electron microscopy (TEM). The addition of MnO2 improves the dispersion of Pt nanoparticles. The electrocatalytic activity of Pt-MnO2/C towards methanol oxidation in H2SO4 solution is investigated using cyclic voltammetry and electrochemical impedance spectroscopy. The onset potential value of methanol oxidation peak is negatively shifted by 169 mV when MnO2 is introduced to Pt/C. Moreover, the charge transfer resistance value at Pt-MnO2/C is about 10 times as low as that at Pt/C. Chronoamperometry and chronopotentiometry show that CO tolerance is greatly improved at Pt-MnO2/C. The increased electrocatalytic activity and enhanced ability to clean platinum surface elect manganese oxide as a suitable promoter for the anode performance in direct methanol fuel cells (DMFCs).

  15. Synthesis and structure of ordered stoichiometric Pt 3Mn-based surface alloys

    NASA Astrophysics Data System (ADS)

    Gallego, S.; Ocal, C.; Méndez, J.; Torrelles, X.; Soria, F.

    2001-06-01

    By annealing at 500°C thick deposits of Mn on Pt(1 1 1), a chemically ordered 2×2 surface compound is formed. From a dynamical low energy electron diffraction (LEED) analysis, it consists of a Pt 3Mn(1 1 1) bulk-like structure covered by a Pt layer. A different layered structure of alternated Pt and Pt 3Mn ordered planes is obtained by the same procedure using annealing temperatures of 650°C. The distinction between the two phases is based in measurements by LEED, STM and XRD. One phase evolves to the other via a progressive enrichment of Pt, while keeping the structure and composition of the two outermost layers as the temperature increases.

  16. Kinetic study of Pt nanocrystal deposition on Ag nanowires with clean surfaces via galvanic replacement

    PubMed Central

    2012-01-01

    Without using any templates or surfactants, this study develops a high-yield process to prepare vertical Ag-Pt core-shell nanowires (NWs) by thermally assisted photoreduction of Ag NWs and successive galvanic replacement between Ag and Pt ions. The clean surface of Ag nanowires allows Pt ions to reduce and deposit on it and forms a compact sheath comprising Pt nanocrystals. The core-shell structural feature of the NWs thus produced has been demonstrated via transmission electron microscopy observation and Auger electron spectroscopy elemental analysis. Kinetic analysis suggests that the deposition of Pt is an interface-controlled reaction and is dominated by the oxidative dissolution of Ag atoms. The boundaries in between Pt nanocrystals may act as microchannels for the transport of Ag ions during galvanic replacement reactions. PMID:22559242

  17. Disorder and surface effects on work function of Ni-Pt metal gates

    NASA Astrophysics Data System (ADS)

    Xu, Guigui; Wu, Qingyun; Chen, Zhigao; Huang, Zhigao; Wu, Rongqin; Feng, Yuan Ping

    2008-09-01

    Work functions of NiPt alloys with different compositions are investigated using first-principles methods based on density-functional theory. Results of our calculations reveal that surface alloy composition has a significant effect on the work function of the NiPt alloy. However, for a given surface composition, the work function is insensitive to the distributions of Ni/Pt atoms in the alloy and it is only slightly affected by alloy disorder. Our work suggests surface atomic modification as a promising way of tuning the work function of alloy metal gate.

  18. Utilization of Active Ni to Fabricate Pt-Ni Nanoframe/NiAl Layered Double Hydroxide Multifunctional Catalyst through In Situ Precipitation.

    PubMed

    Ren, Fumin; Wang, Zheng; Luo, Liangfeng; Lu, Haiyuan; Zhou, Gang; Huang, Weixin; Hong, Xun; Wu, Yuen; Li, Yadong

    2015-09-14

    Integration of different active sites into metallic catalysts, which may impart new properties and functionalities, is desirable yet challenging. Herein, a novel dealloying strategy is demonstrated to decorate nickel-aluminum layered double hydroxide (NiAl-LDH) onto a Pt-Ni alloy surface. The incorporation of chemical etching of Pt-Ni alloy and in situ precipitation of LDH are studied by joint experimental and theoretical efforts. The initial Ni-rich Pt-Ni octahedra transform by interior erosion into Pt3 Ni nanoframes with enlarged surface areas. Furthermore, owing to the basic active sites of the decorated LDH together with the metallic sites of Pt3 Ni, the resulting Pt-Ni nanoframe/NiAl-LDH composites exhibit excellent catalytic activity and selectivity in the dehydrogenation of benzylamine and hydrogenation of furfural. PMID:26241390

  19. 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.

  20. Catalytic Activity and Thermal Stability of Arc Plasma Deposited Pt Nano-Particles on CeO2-Al2O3.

    PubMed

    Jeong, Young Eun; Kumar, Pullur Anil; Choi, Hee Lack; Lee, Kwan-Young; Ha, Heon Phil

    2015-11-01

    In this study, catalytic activity and thermal stability of the arc plasma deposited (APD) Pt nano-particles on A12O3 and CeO2-Al2O3 were compared with that of the conventionally prepared Pt/Al2O3. All the catalysts were characterized by BET-surface area, transmission electron microscopy, X-ray photoelectron spectroscopy, CO-pulse chemisorption, H2-temperarture programmed reduction and X-ray absorption near edge spectroscopy. Through the quantum chemical calculations of different metal oxide support, CeO2 was identified as a suitable anchoring material with high energy level between the Pt species (Pt(0) and PtO(x)) on ceria. Subsequently, the results of XPS and XANES revealed the presence of abundant Pt(0) metal species in APD catalysts. The addition of ceria to Al2O3 support enhanced the dispersion of Pt nano-particles. The H2-TPR of Pt/CeO2-Al2O3 (APD) catalyst showed high-temperature reduction peaks corresponding to the interaction of Pt with ceria on alumina by Pt-O-Ce. Consequently, the Pt nano-particles deposited on CeO2-Al2O3 by APD attained strong thermal resistance at high temperatures. In addition, superior catalytic activities for CO and C3H6 oxidation and NO(x) reduction were obtained for the Pt/CeO2- Al2O3 (APD) catalyst. PMID:26726541

  1. Novel TiO2-Pt@SiO2 nanocomposites with high photocatalytic activity

    NASA Astrophysics Data System (ADS)

    Wu, Hao-Shuai; Sun, Ling-Dong; Zhou, Huan-Ping; Yan, Chun-Huan

    2012-05-01

    This article reports a facile and controllable two-step method to construct TiO2-Pt@SiO2 nanocomposites. TiO2 nanoparticles (NPs), with small size and high surface energy, were synthesized by a solvothermal reaction process. The TiO2-Pt@SiO2 nanocomposites were fabricated by a reverse micro-emulsion method. SiO2 shell coated NPs were adopted for further photocatalytic reaction. Because of their small size and high surface energy, TiO2@SiO2 and TiO2-Pt@SiO2 nanocomposites show higher photocatalytic activity than commercial Degussa P25. Compared with TiO2@SiO2, TiO2-Pt@SiO2nanocomposites have improved photocatalytic activity due to the Pt induced spatial separation of electrons and holes. The silica shells not only maintain the structure of the nanocomposites but also prevent their aggregation during the photocatalytic reactions, which is highly important for the good durability of the photocatalyst. This strategy is simple, albeit efficient, and can be extended to the synthesis of other composites of noble metals. It has opened a new window for the construction of hetero-nanocomposites with high activity and durability, which would serve as excellent models in catalytic systems of both theoretical and practical interest.This article reports a facile and controllable two-step method to construct TiO2-Pt@SiO2 nanocomposites. TiO2 nanoparticles (NPs), with small size and high surface energy, were synthesized by a solvothermal reaction process. The TiO2-Pt@SiO2 nanocomposites were fabricated by a reverse micro-emulsion method. SiO2 shell coated NPs were adopted for further photocatalytic reaction. Because of their small size and high surface energy, TiO2@SiO2 and TiO2-Pt@SiO2 nanocomposites show higher photocatalytic activity than commercial Degussa P25. Compared with TiO2@SiO2, TiO2-Pt@SiO2nanocomposites have improved photocatalytic activity due to the Pt induced spatial separation of electrons and holes. The silica shells not only maintain the structure of the

  2. Support Effects on the Catalytic Activity of Graphene-Supported Pt13 Nanoclusters for CO Oxidation

    NASA Astrophysics Data System (ADS)

    Fampiou, Ioanna; Ramasubramaniam, Ashwin

    2015-03-01

    Sub-nanometer Pt nanoparticles supported on graphene are shown to exhibit increased stability, uniform dispersion and increased tolerance to CO poisoning, making them attractive candidates as electrocatalysts for fuel-cell electrodes. A fundamental understanding of support effects on the catalytic activity of the nanoparticles is important for effective catalyst design. In this study, we use density functional theory to investigate support effects on the catalytic activity for CO oxidation on Pt13 nanoclusters supported at point defects (vacancies, divacancies) in graphene in the high CO-coverage regime. Our results suggest that support defects are crucial in stabilizing the clusters on the support at high CO cluster coverage, preventing sintering and catalyst loss. By sampling the CO oxidation reaction at various surface sites on graphene-supported and free Pt13 nanoclusters, we show that strong cluster-support interactions can substantially reduce the barrier for CO oxidation on supported versus free nanoclusters, by more than 0.5 eV. Our results suggest that defect engineering of graphene supports could serve to enhance the catalytic activity of sub-nanometer Pt nanoclusters, allowing for tuning of catalytic properties through cluster-support interactions. We acknowledge support by U.S. DOE under Award Number DE-SC0010610 and computational resources by NERSC, supported by the Office of Science, U.S DOE under Contract No. DE-AC02-05CH11231.

  3. A first principles study of O2 dissociation on Pt modified ZrC(100) surface

    NASA Astrophysics Data System (ADS)

    Zhang, Xilin; Lu, Zhansheng; Yang, Zongxian

    2016-04-01

    The growth process of Pt monolayer on ZrC(100) were investigated using density functional theory calculations. The strong interaction of Pt atoms with ZrC(100) was beneficial to improving the stability and activity of Pt catalyst. The adsorption and dissociation of O2 on the bare and Pt modified ZrC(100) were comparably investigated, and found that the supported Pt on ZrC(100) have a positive impact on promoting the scission of the Osbnd O bond and weakening the adsorption of produced O, which shed meaningful light on the important role of ZrC(100) as support to improve the efficiency of Pt for oxygen reduction.

  4. Improved oxygen reduction activity on the Ih Cu@Pt core-shell nanoparticles

    NASA Astrophysics Data System (ADS)

    Yang, Zongxian; Geng, Zhixia; Zhang, Yanxing; Wang, Jinlong; Ma, Shuhong

    2011-09-01

    The minimum energy path (MEP) for the dissociation of O 2 on the Ih Cu@Pt12 core-shell nanoparticle. Ih Cu@Pt12 is the most stable among the symmetric Cu@Pt12 core-shell isomers. O 2 prefers to be adsorbed on the Ih Cu@Pt12 with the t-b-t configuration. The Ih Cu@Pt12 has enhanced activity for O 2 dissociation and O diffusion. Ih Cu@Pt12 nanoparticle is a good candidate for being the ORR catalyst.

  5. 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.

  6. Growth of epitaxial Pt1-xPbx alloys by surface limited redox replacement and study of their adsorption properties.

    PubMed

    Mercer, M P; Plana, D; Fermίn, D J; Morgan, D; Vasiljevic, N

    2015-10-01

    The surface limited redox replacement (SLRR) method has been used to design two-dimensional Pt-Pb nanoalloys with controlled thickness, composition, and structure. The electrochemical behavior of these alloys has been systematically studied as a function of alloy composition. A single-cell, two-step SLRR protocol based on the galvanic replacement of underpotentially deposited monolayers of Pb with Pt was used to grow epitaxial Pt1-xPbx (x < 0.1) alloys of up to 10 ML thickness on Au substrates. It is shown that by varying the terminating potential of the galvanic replacement step, the Pb atomic content can be controlled in the films. Electrochemical analysis of the alloys showed that the adsorption of both H and CO exhibits similar, and systematic, decreases with small increases in the Pb content. These measurements, commonly used in electrocatalysis for the determination of active surface areas of Pt, suggested area values much lower than those expected based on the net Pt composition in the alloy as measured by XPS. These results show that Pb has a strong screening effect on the adsorption of both H and CO. Moreover, changes in alloy composition result in a negative shift in the potential of the peaks of CO oxidation that scales with the increase of Pb content. The results suggest electronic and bifunctional effects of incorporated Pb on the electrochemical behavior of Pt. The study illustrates the potential of the SLRR methodology, which could be employed in the design of 2-dimensional bimetallic Pt nanoalloys for fundamental studies of electrocatalytic behavior in fuel cell reactions dependent on the nature of alloying metal and its composition. PMID:26372676

  7. Sum-frequency generation of acetate adsorption on Au and Pt surfaces: Molecular structure effects

    NASA Astrophysics Data System (ADS)

    Braunschweig, Björn; Mukherjee, Prabuddha; Kutz, Robert B.; Wieckowski, Andrzej; Dlott, Dana D.

    2010-12-01

    The reversible adsorption of acetate on polycrystalline Au and Pt surfaces was investigated with broadband sum-frequency generation (SFG) and cyclic voltammetry. Specifically adsorbed acetate as well as coadsorbed sulfuric acid anions are observed for the first time with SFG and give rise to dramatically different SFG intensities on Au and Pt surfaces. While similar coverages of acetate adlayers on Au and Pt surfaces are well established by previous studies, an identification of the interfacial molecular structure has been elusive. However, we have applied the high sensitivity of SFG for interfacial polar ordering to identify different acetate structures at Au and Pt surfaces in contact with HClO4 and H2SO4 electrolytes. Acetate competes with the formation of surface oxides and shifts the oxidation threshold of both Au and Pt electrodes anodically. Effects of the supporting electrolyte on the formation of acetate adlayers are revealed by comparing SFG spectra in HClO4 and H2SO4 solutions: Sulfuric acid anions modify the potential-dependent acetate adsorption, compete with adsorbed acetate on Au and coadsorb with acetate on Pt surfaces.

  8. Electrocatalytic oxidation of formic acid at an ordered intermetallic PtBi surface.

    PubMed

    Casado-Rivera, Emerilis; Gál, Zoltán; Angelo, A C D; Lind, Cora; DiSalvo, Francis J; Abruña, Héctor D

    2003-02-17

    The electrocatalytic oxidation of formic acid at a PtBi ordered intermetallic electrode surface has been investigated using cyclic voltammetry, rotating disk electrode (RDE) voltammetry and differential electrochemical mass spectrometry (DEMS). The results are compared to those at a polycrystalline platinum electrode surface. The PtBi electrode exhibits superior properties when compared to polycrystalline platinum in terms of oxidation onset potential, current density, and a much diminished poisoning effect by CO. Using the RDE technique, a value of 1.4 x 10(-4) cm s-1 was obtained for the heterogeneous charge transfer rate constant. The PtBi surface did not appear to be poisoned when exposed to a CO saturated solution for periods exceeding 0.5 h. The results for PtBi are discussed within the framework of the dual-path mechanism for the electrocatalytic oxidation of formic acid, which involves formation of a reactive intermediate and a poisoning pathway. PMID:12619419

  9. Calorimetry, activity, and micro-FTIR analysis of CO chemisorption, titration, and oxidation on supported Pt

    NASA Technical Reports Server (NTRS)

    Sermon, Paul A.; Self, Valerie A.; Vong, Mariana S. W.; Wurie, Alpha T.

    1990-01-01

    The value of in situ analysis on CO chemisorption, titration and oxidation over supported Pt catalysts using calorimetry, catalytic and micro-FTIR methods is illustrated using silica- and titania-supported samples. Isothermal CO-O and O2-CO titrations have not been widely used on metal surfaces and may be complicated if some oxide supports are reduced by CO titrant. However, they can illuminate the kinetics of CO oxidation on metal/oxide catalysts since during such titrations all O and CO coverages are scanned as a function of time. There are clear advantages in following the rates of the catalyzed CO oxidation via calorimetry and gc-ms simultaneously. At lower temperatures the evidence they provide is complementary. CO oxidation and its catalysis of CO oxidation have been extensively studied with hysteresis and oscillations apparent, and the present results suggest the benefits of a combined approach. Silica support porosity may be important in defining activity-temperature hysteresis. FTIR microspectroscopy reveals the chemical heterogeneity of the catalytic surfaces used; it is interesting that the evidence with regard to the dominant CO surface species and their reactivities with regard to surface oxygen for present oxide-supported Pt are different from those seen on graphite-supported Pt.

  10. Creating single-atom Pt-ceria catalysts by surface step decoration

    NASA Astrophysics Data System (ADS)

    Dvořák, Filip; Farnesi Camellone, Matteo; Tovt, Andrii; Tran, Nguyen-Dung; Negreiros, Fabio R.; Vorokhta, Mykhailo; Skála, Tomáš; Matolínová, Iva; Mysliveček, Josef; Matolín, Vladimír; Fabris, Stefano

    2016-02-01

    Single-atom catalysts maximize the utilization of supported precious metals by exposing every single metal atom to reactants. To avoid sintering and deactivation at realistic reaction conditions, single metal atoms are stabilized by specific adsorption sites on catalyst substrates. Here we show by combining photoelectron spectroscopy, scanning tunnelling microscopy and density functional theory calculations that Pt single atoms on ceria are stabilized by the most ubiquitous defects on solid surfaces--monoatomic step edges. Pt segregation at steps leads to stable dispersions of single Pt2+ ions in planar PtO4 moieties incorporating excess O atoms and contributing to oxygen storage capacity of ceria. We experimentally control the step density on our samples, to maximize the coverage of monodispersed Pt2+ and demonstrate that step engineering and step decoration represent effective strategies for understanding and design of new single-atom catalysts.

  11. Creating single-atom Pt-ceria catalysts by surface step decoration.

    PubMed

    Dvořák, Filip; Farnesi Camellone, Matteo; Tovt, Andrii; Tran, Nguyen-Dung; Negreiros, Fabio R; Vorokhta, Mykhailo; Skála, Tomáš; Matolínová, Iva; Mysliveček, Josef; Matolín, Vladimír; Fabris, Stefano

    2016-01-01

    Single-atom catalysts maximize the utilization of supported precious metals by exposing every single metal atom to reactants. To avoid sintering and deactivation at realistic reaction conditions, single metal atoms are stabilized by specific adsorption sites on catalyst substrates. Here we show by combining photoelectron spectroscopy, scanning tunnelling microscopy and density functional theory calculations that Pt single atoms on ceria are stabilized by the most ubiquitous defects on solid surfaces--monoatomic step edges. Pt segregation at steps leads to stable dispersions of single Pt(2+) ions in planar PtO4 moieties incorporating excess O atoms and contributing to oxygen storage capacity of ceria. We experimentally control the step density on our samples, to maximize the coverage of monodispersed Pt(2+) and demonstrate that step engineering and step decoration represent effective strategies for understanding and design of new single-atom catalysts. PMID:26908356

  12. Magnetic-field- and temperature-dependent Fermi surface of CeBiPt

    NASA Astrophysics Data System (ADS)

    Wosnitza, J.; Goll, G.; Bianchi, A. D.; Bergk, B.; Kozlova, N.; Opahle, I.; Elgazzar, S.; Richter, Manuel; Stockert, O.; Löhneysen, H. v.; Yoshino, T.; Takabatake, T.

    2006-09-01

    The half-Heusler compounds CeBiPt and LaBiPt are semimetals with very low charge-carrier concentrations as evidenced by Shubnikov de Haas (SdH) and Hall-effect measurements. Neutron-scattering results reveal a simple antiferromagnetic structure in CeBiPt below TN = 1.15 K. The band structure of CeBiPt sensitively depends on temperature, magnetic field and stoichiometry. Above a certain, sample-dependent, threshold field (B>25 T), the SdH signal disappears and the Hall coefficient reduces significantly. These effects are absent in the non-4f compound LaBiPt. Electronic-band-structure calculations can well explain the observed behaviour by a 4f-polarization-induced Fermi-surface modification.

  13. Quantification of primary versus secondary C-H bond cleavage in alkane activation: Propane on Pt

    SciTech Connect

    Weinberg, W.H.; Sun, Yongkui )

    1991-08-02

    The trapping-mediated dissociative chemisorption of three isotopes of propane (C{sub 3}H{sub 8}, CH{sub 3}, CD{sub 2}CH{sub 3}, and C{sub 3}D{sub 8}) has been investigated on the Pt(110)-(1 {times} 2) surface, and both the apparent activation energies and the preexponential factors of the surface reaction rate coefficients have been measured. In addition, the probabilities of primary and secondary C-H bond cleavage for alkane activation on a surface were evaluated. The activation energy for primary C-H bond cleavage was 425 calories per mole greater than that of secondary C-H bond cleavage, and the two true activation energies that embody the single measured activation energy were determined for each of the three isotopes. Secondary C-H bond cleavage is also preferred on entropic grounds, and the magnitude of the effect was quantified.

  14. Synthesis of Pt-Mo-N Thin Film and Catalytic Activity for Fuel Cells

    SciTech Connect

    Miura, Akira; Tague, Michele E.; Gregoire, John M.; Wen, Xiao-Dong; van Dover, R. Bruce; Abruña, Héctor D.; DiSalvo, Francis J.

    2010-05-13

    Pt-Mo-N composition gradient film was synthesized by combining thin-film deposition techniques and subsequent thermal nitridation. A ternary platinum-based nitride, Pt2Mo3N, showed catalytic activities for fuel cell applications and higher electrochemical stability when it was compared with a PtMo alloy with the same Pt:Mo ratio.

  15. Direct Visualization of Catalytically Active Sites at the FeO-Pt(111) Interface.

    PubMed

    Kudernatsch, Wilhelmine; Peng, Guowen; Zeuthen, Helene; Bai, Yunhai; Merte, Lindsay R; Lammich, Lutz; Besenbacher, Flemming; Mavrikakis, Manos; Wendt, Stefan

    2015-08-25

    Within the area of surface science, one of the "holy grails" is to directly visualize a chemical reaction at the atomic scale. Whereas this goal has been reached by high-resolution scanning tunneling microscopy (STM) in a number of cases for reactions occurring at flat surfaces, such a direct view is often inhibited for reaction occurring at steps and interfaces. Here we have studied the CO oxidation reaction at the interface between ultrathin FeO islands and a Pt(111) support by in situ STM and density functional theory (DFT) calculations. Time-lapsed STM imaging on this inverse model catalyst in O2 and CO environments revealed catalytic activity occurring at the FeO-Pt(111) interface and directly showed that the Fe-edges host the catalytically most active sites for the CO oxidation reaction. This is an important result since previous evidence for the catalytic activity of the FeO-Pt(111) interface is essentially based on averaging techniques in conjunction with DFT calculations. The presented STM results are in accord with DFT+U calculations, in which we compare possible CO oxidation pathways on oxidized Fe-edges and O-edges. We found that the CO oxidation reaction is more favorable on the oxidized Fe-edges, both thermodynamically and kinetically. PMID:26027877

  16. Direct Visualization of Catalytically Active Sites at the FeO-Pt(111) Interface

    SciTech Connect

    Kudernatsch, Wilhelmine; Peng, Guowen; Zeuthen, Helene; Bai, Yunhai; Merte, L. R.; Lammich, Lutz; Besenbacher, Fleming; Mavrikakis, Manos; Wendt, Stefen

    2015-08-25

    Within the area of surface science, one of the “holy grails” is to directly visualize a chemical reaction at the atomic scale. Whereas this goal has been reached by high-resolution scanning tunneling microscopy (STM) in a number of cases for reactions occurring at flat surfaces, such a direct view is often inhibited for reaction occurring at steps and interfaces. Here we have studied the CO oxidation reaction at the interface between ultrathin FeO islands and a Pt(111) support by in situ STM and density functional theory (DFT) calculations. Time-lapsed STM imaging on this inverse model catalyst in O2 and CO environments revealed catalytic activity occurring at the FeO-Pt(111) interface and directly showed that the Fe-edges host the catalytically most active sites for the CO oxidation reaction. This is an important result since previous evidence for the catalytic activity of the FeO-Pt(111) interface is essentially based on averaging techniques in conjunction with DFT calculations. The presented STM results are in accord with DFTþU calculations, in which we compare possible CO oxidation pathways on oxidized Fe-edges and O-edges. We found that the CO oxidation reaction is more favorable on the oxidized Fe-edges, both thermodynamically and kinetically.

  17. Preparation and characterization of Pt-CeO2/C and Pt-TiO2/C electrocatalysts with improved electrocatalytic activity for methanol oxidation

    NASA Astrophysics Data System (ADS)

    Hameed, R. M. Abdel; Amin, R. S.; El-Khatib, K. M.; Fetohi, Amani E.

    2016-03-01

    Pt-TiO2/C and Pt-CeO2/C electrocatalysts were synthesized by solid state reaction of TiO2/C and CeO2/C powders using intermittent microwave heating, followed by chemical reduction of platinum ions using mixed reducing agents of ethylene glycol and sodium borohydride. The crystal structure, surface morphology and chemical composition of prepared electrocatalysts were investigated using X-ray diffraction (XRD), transmission electron microscopy (TEM) and energy dispersive X-ray analysis (EDX). The phase angle values of different Pt diffraction planes in Pt-TiO2/C and Pt-CeO2/C were shifted in the positive direction relative to those in Pt/C. Pt particles with diameter values of 3.06 and 2.78 nm were formed in Pt-TiO2/C and Pt-CeO2/C, respectively. The electrochemical performance of prepared electrocatalysts was examined using cyclic voltammetry, chronoamperometry and electrochemical impedance spectroscopy. Pt-CeO2/C showed an enhanced oxidation current density when compared to Pt/C. Long time oxidation test at Pt-TiO2/C and Pt-CeO2/C revealed their improved stability. Lower charge transfer resistance values were estimated at Pt-metal oxide/C electrocatalysts.

  18. The origin of high activity but low CO(2) selectivity on binary PtSn in the direct ethanol fuel cell.

    PubMed

    Jin, Jia-Mei; Sheng, Tian; Lin, Xiao; Kavanagh, Richard; Hamer, Philip; Hu, Peijun; Hardacre, Christopher; Martinez-Bonastre, Alex; Sharman, Jonathan; Thompsett, David; Lin, Wen-Feng

    2014-05-28

    The most active binary PtSn catalyst for direct ethanol fuel cell applications has been studied at 20 °C and 60 °C, using variable temperature electrochemical in situ FTIR. In comparison with Pt, binary PtSn inhibits ethanol dissociation to CO(a), but promotes partial oxidation to acetaldehyde and acetic acid. Increasing the temperature from 20 °C to 60 °C facilitates both ethanol dissociation to CO(a) and then further oxidation to CO2, leading to an increased selectivity towards CO2; however, acetaldehyde and acetic acid are still the main products. Potential-dependent phase diagrams for surface oxidants of OH(a) formation on Pt(111), Pt(211) and Sn modified Pt(111) and Pt(211) surfaces have been determined using density functional theory (DFT) calculations. It is shown that Sn promotes the formation of OH(a) with a lower onset potential on the Pt(111) surface, whereas an increase in the onset potential is found upon modification of the (211) surface. In addition, Sn inhibits the Pt(211) step edge with respect to ethanol C-C bond breaking compared with that found on the pure Pt, which reduces the formation of CO(a). Sn was also found to facilitate ethanol dehydrogenation and partial oxidation to acetaldehyde and acetic acid which, combined with the more facile OH(a) formation on the Pt(111) surface, gives us a clear understanding of the experimentally determined results. This combined electrochemical in situ FTIR and DFT study provides, for the first time, an insight into the long-term puzzling features of the high activity but low CO2 production found on binary PtSn ethanol fuel cell catalysts. PMID:24722871

  19. Comparison of sulfur interaction with hydrogen on Pt(1 1 1), Ni(1 1 1) and Pt 3Ni(1 1 1) surfaces: The effect of intermetallic bonding

    NASA Astrophysics Data System (ADS)

    Pillay, D.; Johannes, M. D.

    2008-08-01

    Adsorption strengths of hydrogen and sulfur both individually and together as co-adsorbates were investigated on Pt(1 1 1), Ni(1 1 1) and Pt 3Ni(1 1 1) surfaces using density functional theory in order to determine the effect of metal alloying on sulfur tolerance. The adsorption strengths of H and S singly follow the same trend: Ni(1 1 1) > Pt(1 1 1) > Pt 3Ni(1 1 1), which correlates well with the respective d-band center positions of each surface. We find that the main effect of alloying is to distort both the sub-layer structure and the Pt overlayer resulting in a lowered d-band. For all three surfaces, the d-band shifts downward non-linearly as a function of S coverage. Nearly identical decreases in d-band position were calculated for each surface, leading to an expectation that subsequent adsorption of H would scale with surface type similarly to single species adsorption. In contradiction to this expectation, there was no clearly discernable difference between the energies of coadsorbed H on Pt(1 1 1) and Ni(1 1 1) and only a slightly lowered energy on Pt 3Ni(1 1 1). This provides evidence that coadsorbed species in close proximity interact directly through itinerant mobile electrons and through electrostatic repulsion rather than solely through the electronic structure of the surface. The combination of the lowered d-band position (arising from distorted geometry) and direct co-adsorbate interactions on Pt 3Ni(1 1 1) leads to a lower energy barrier for H 2S formation on the surface compared to pure Pt(1 1 1). Thus, alloying Pt with Ni both decreases the likelihood of S adsorption and favors S removal through H 2S formation.

  20. The influence of carbon support porosity on the activity of PtRu/Sibunit anode catalysts for methanol oxidation

    NASA Astrophysics Data System (ADS)

    Rao, V.; Simonov, P. A.; Savinova, E. R.; Plaksin, G. V.; Cherepanova, S. V.; Kryukova, G. N.; Stimming, U.

    In this paper we analyse the promises of homemade carbon materials of Sibunit family prepared through pyrolysis of natural gases on carbon black surfaces as supports for the anode catalysts of direct methanol fuel cells. Specific surface area ( SBET) of the support is varied in the wide range from 6 to 415 m 2 g -1 and the implications on the electrocatalytic activity are scrutinized. Sibunit supported PtRu (1:1) catalysts are prepared via chemical route and the preparation conditions are adjusted in such a way that the particle size is constant within ±1 nm in order to separate the influence of support on the (i) catalyst preparation and (ii) fuel cell performance. Comparison of the metal surface area measured by gas phase CO chemisorption and electrochemical CO stripping indicates close to 100% utilisation of nanoparticle surfaces for catalysts supported on low (22-72 m 2 g -1) surface area Sibunit carbons. Mass activity and specific activity of PtRu anode catalysts change dramatically with SBET of the support, increasing with the decrease of the latter. 10%PtRu catalyst supported on Sibunit with specific surface area of 72 m 2 g -1 shows mass specific activity exceeding that of commercial 20%PtRu/Vulcan XC-72 by nearly a factor of 3.

  1. Nanoparticle cluster gas sensor: Pt activated SnO2 nanoparticles for NH3 detection with ultrahigh sensitivity.

    PubMed

    Liu, Xu; Chen, Nan; Han, Bingqian; Xiao, Xuechun; Chen, Gang; Djerdj, Igor; Wang, Yude

    2015-09-28

    Pt activated SnO2 nanoparticle clusters were synthesized by a simple solvothermal method. The structure, morphology, chemical state and specific surface area were analyzed by X-ray powder diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and N2-sorption studies, respectively. The SnO2 nanoparticle cluster matrix consists of tens of thousands of SnO2 nanoparticles with an ultra-small grain size estimated to be 3.0 nm. And there are abundant random-packed wormhole-like pores, caused by the inter-connection of the SnO2 nanoparticles, throughout each cluster. The platinum element is present in two forms including metal (Pt) and tetravalent metal oxide (PtO2) in the Pt activated SnO2 nanoparticle clusters. The as-synthesized pure and Pt activated SnO2 nanoparticle clusters were used to fabricate gas sensor devices. It was found that the gas response toward 500 ppm of ammonia was improved from 6.48 to 203.44 through the activation by Pt. And the results indicate that the sensor based on Pt activated SnO2 not only has ultrahigh sensitivity but also possesses good response-recovery properties, linear dependence, repeatability, selectivity and long-term stability, demonstrating the potential to use Pt activated SnO2 nanoparticle clusters as ammonia gas sensors. At the same time, the formation mechanisms of the unique nanoparticle clusters and highly enhanced sensitivity are also discussed. PMID:26289622

  2. Linking morphology with activity through the lifetime of pretreated PtNi nanostructured thin film catalysts

    SciTech Connect

    Cullen, David A.; Lopez-Haro, Miguel; Bayle-Guillemaud, Pascale; Debe, Mark; Steinbach, Andrew J.; Guetaz, L.

    2015-04-10

    In this study, the nanoscale morphology of highly active Pt3Ni7 nanostructured thin film fuel cell catalysts is linked with catalyst surface area and activity following catalyst pretreatments, conditioning and potential cycling. The significant role of fuel cell conditioning on the structure and composition of these extended surface catalysts is demonstrated by high resolution imaging, elemental mapping and tomography. The dissolution of Ni during fuel cell conditioning leads to highly complex, porous structures which were visualized in 3D by electron tomography. Quantification of the rendered surfaces following catalyst pretreatment, conditioning, and cycling shows the important role pore structure plays in surface area, activity, and durability.

  3. Nanoporous bimetallic Pt-Au alloy nanocomposites with superior catalytic activity towards electro-oxidation of methanol and formic acid.

    PubMed

    Zhang, Zhonghua; Wang, Yan; Wang, Xiaoguang

    2011-04-01

    We present a facile route to fabricate novel nanoporous bimetallic Pt-Au alloy nanocomposites by dealloying a rapidly solidified Al(75)Pt(15)Au(10) precursor under free corrosion conditions. The microstructure of the precursor and the as-dealloyed sample was characterized using X-ray diffraction, scanning electron microscopy, transmission electron microscopy, high-resolution transmission electron microscopy, and energy dispersive X-ray (EDX) analysis. The Al(75)Pt(15)Au(10) precursor is composed of a single-phase Al(2)(Au,Pt) intermetallic compound, and can be fully dealloyed in a 20 wt.% NaOH or 5 wt.% HCl aqueous solution. The dealloying leads to the formation of the nanoporous Pt(60)Au(40) nanocomposites (np-Pt(60)Au(40) NCs) with an fcc structure. The morphology, size and crystal orientation of grains in the precursor can be conserved in the resultant nanoporous alloy. The np-Pt(60)Au(40) NCs consist of two zones with distinct ligament/channel sizes and compositions. The formation mechanism of these np-Pt(60)Au(40) NCs can be rationalized based upon surface diffusion of more noble elements and spinodal decomposition during dealloying. Electrochemical measurements demonstrate that the np-Pt(60)Au(40) NCs show superior catalytic activity towards the electro-oxidation of methanol and formic acid in the acid media compared to the commercial JM-Pt/C catalyst. This material can find potential applications in catalysis related areas, such as direct methanol or formic acid fuel cells. Our findings demonstrate that dealloying is an effective and simple strategy to realize the alloying of immiscible systems under mild conditions, and to fabricate novel nanostructures with superior performance. PMID:21311802

  4. On the adsorption and formation of Pt dimers on the CeO2(111) surface

    NASA Astrophysics Data System (ADS)

    Bruix, Albert; Nazari, Fariba; Neyman, Konstantin M.; Illas, Francesc

    2011-12-01

    The direct adsorption of Pt2 dimers on CeO2(111) and their formation from isolated adsorbed Pt atoms have been studied using periodic slab model calculations based on density functional theory and including the so-called on-site Hubbard parameter (GGA + U). In the most stable configuration Pt2 is found to be almost parallel to the surface; the electronic ground state is closed shell and there is no evidence of charge transfer towards or from the surface. The formation of Pt2 from two single adsorbed Pt atoms involves a rather small energy barrier of ˜0.10 eV only. On the contrary, dissociation of adsorbed Pt2 requires to overcome a considerable barrier of ˜1.43 eV. This indicates that once Pt2 is formed it will remain on the surface, thus likely triggering the growth of larger supported Pt particles.

  5. Enhanced Oxygen Reduction Activity on Pt/C for Nafion-free, Thin, Uniform Films in Rotating Disk Electrode Studies

    SciTech Connect

    Shinozaki, Kazuma; Pivovar, Bryan S.; Kocha, Shyam S.

    2013-01-01

    Commercially available nanoparticle platinum on high surface area carbon black (Pt/HSC) electrocatalysts were characterized in rotating disk electrode (RDE) setups using varying ink formulations and film drying techniques in an attempt to obtain thin, uniform films and reproducible activity. Electrodes prepared from Nafion-free inks that were dried under an isopropyl alcohol (IPA) atmosphere produced uniform, thin films at low electrocatalyst loadings of ~4.5 mg/cm2 Pt. These Nafion-free/IPA-dried electrodes were found to exhibit oxygen reduction reaction (ORR) activities higher than conventional Nafion-based/Air-dried electrodes by a factor of ~2.8. The magnitude of mass and specific activities were determined to be im ~771 ±56 mA/mgPt and is~812 ±59 mA/cm2Pt respectively and appear to be the highest values reported for RDE measurements on Pt/HSC in 0.1M HClO4 at 20 mV/s and 25°C. Electrochemical diagnostics including ORR I-V profiles, cyclic voltammograms and electrochemical impedance spectroscopy (EIS) studies were conducted to investigate the thin film Pt/HSC electrodes and correlate results to film morphology and electrochemical activity.

  6. Pt surface modification of SnO2 nanorod arrays for CO and H2 sensors.

    PubMed

    Huang, Hui; Ong, C Y; Guo, J; White, T; Tse, M S; Tan, O K

    2010-07-01

    Uniform SnO(2) nanorod arrays were deposited on a 4 inch SiO(2)/Si wafer by plasma-enhanced chemical vapor deposition (PEVCD) at low deposition temperature of around 300 degrees C. The SnO(2) nanorods were connected at the roots, thus the nanorod sensors could be fabricated by a feasible way compatible with microelectronic processes. The surface of the sensors was modified by Pt nanoparticles deposited by dip coating and sputtering, respectively. The sensing properties of the Pt-modified SnO(2) nanorod sensors to CO and H(2) gases were comparatively studied. After surface modification of Pt, the sensing response to CO and H(2) gases increased dramatically. The 2 nm Pt-modified SnO(2) nanorod sensors by sputtering showed the best sensing performance. By increasing Pt thickness from 2 nm up to 20 nm, the optimal working temperature decreased by 30 degrees C while the sensing response also decreased by about 4 times. Comparing these two Pt modification approaches by dip coating and sputtering, both could achieve comparable promotion effect if the Pt thickness can be controlled around its optimal value. The deposition technique of SnO(2) nanorod arrays by PECVD has good potential for scale-up and the fabrication process of nanorod sensors possesses simplicity and good compatibility with contemporary microelectronics-based technology. PMID:20648350

  7. Impact of magnetic surface anisotropy on the precessional switching of magnetization in Pt-alloy nanofilms

    NASA Astrophysics Data System (ADS)

    Daniel, M.; Arun, R.; Sabareesan, P.

    2012-09-01

    Precessional switching of magnetization in CoPt and FePt nanofilms is investigated by solving the Landau-Lifshitz-Gilbert (LLG) equation analytically and numerically. Switching in these films occurs only above a critical value of the magnetic field, and it further depends on the magnetocrystalline anisotropy and saturation magnetization of the film. The presence of magnetic surface anisotropy in these films reduces the switching time significantly. Also, the switching time in the case of Pt-alloys of Co and Fe is low compared to that in the case of pure Co and Fe films.

  8. The control of Pt and Ru nanoparticle size on high surface area supports.

    PubMed

    Liu, Qiuli; Joshi, Upendra A; Über, Kevin; Regalbuto, John R

    2014-12-28

    Supported Ru and Pt nanoparticles are synthesized by the method of strong electrostatic adsorption and subsequently treated under different steaming-reduction conditions to achieve a series of catalysts with controlled particle sizes, ranging from 1 to 8 nm. While in the case of oxidation-reduction conditions, only Pt yielded particles ranging from 2.5 to 8 nm in size and a loss of Ru was observed. Both Ru and Pt sinter faster in air than in hydrogen. This methodology allows the control of particle size using a "production-scalable" catalyst synthesis method which can be applied to high surface area supports with common metal precursors. PMID:25200960

  9. Enhanced electrocatalytic activity of the Au-electrodeposited Pt nanoparticles-coated conducting oxide for the quantum dot-sensitized solar cells

    SciTech Connect

    Yoon, Yeung-Pil; Kim, Jae-Hong; Ahn, Kwang-Soon; Kang, Soon-Hyung; Kim, Hyunsoo; Choi, Chel-Jong; Kim, Kyong-Kook

    2014-08-25

    Au was electrodeposited potentiostatically at 0.3 V for 5 min on nanoporous Pt nanoparticle-coated F-doped SnO{sub 2} (FTO/Pt) substrates. For comparison, Au-electrodeposited FTO (FTO/Au) and Au-uncoated FTO/Pt were prepared. FTO/Au showed large-sized Au clusters dispersed sparsely over FTO, which resulted in lower electrocatalytic activity than FTO/Pt. In contrast, FTO/Pt exhibited poor stability unlike FTO/Au due to poisoning by the adsorption of sulfur species. The Au-electrodeposited FTO/Pt (FTO/Pt/Au) consisted of small Au clusters deposited over the entire area of Pt due to the effective Au nucleation provided by nanoporous metallic Pt. FTO/Pt/Au exhibited enhanced electrocatalytic activity and excellent stability because the small Au particles well-dispersed over the nanoporous metallic Pt network provided numerous electrochemical reaction sites, and the Pt surface was not exposed to the electrolyte. When FTO/Pt/Au was used as the counter electrode (CE) of a quantum dot-sensitized solar cell, the significantly enhanced electrocatalytic activity of the FTO/Pt/Au CE facilitated the reduction reaction of S{sub n}{sup 2− }+ 2e{sup −} (CE) → S{sub n−1}{sup 2−} + S{sup 2−} at the CE/electrolyte interface, resulting in a significantly hindered recombination reaction, S{sub n}{sup 2− }+ 2e{sup −} (TiO{sub 2} in the photoanode) → S{sub n-1}{sup 2−} + S{sup 2−}, and significantly improved overall energy conversion efficiency.

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

    DOE PAGESBeta

    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

  11. Magnetization Reversal and Thermal Activation in Co/Pt Multilayers

    NASA Astrophysics Data System (ADS)

    Meldrim, J. Mark; Kirby, Roger; Sellmyer, David

    2000-03-01

    Co/Pt multilayers not only display interesting intrinsic magnetic properties such as perpendicular anisotropy but also have technological applications. As grain sizes become smaller and smaller, the role of thermal activation becomes important in understanding magnetization reversal [1,2]. We have prepared [Co 3 Å/Pt 9 Å] x N thin films where N ranges from 6 to 24 by DC magnetron sputtering at various Ar pressures. As the sputtering gas pressure is changed, we find the lateral grain size changes from 20 nm to 45 nm. At the same time, the hysteresis loops become less square and the coercivity increases from a few hundred Oe to above 5 kOe. Activation volumes were determined for the samples both by the field sweep rate method and viscosity measurements. These results will be discussed in terms of simple models of thermally assisted magnetization reversal. This work is supported by NFS grant DMR 9623992 and CMRA. [1] J. S. Shen, R. D. Kirby, K. Wierman, Z. S. Shan, and D. J. Sellmyer, J. App. Phys. 73, 6418 (1993). [2] X. Chen and M. H. Kryder. J. App. Phys. 85, 5006 (1999).

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

    DOE PAGESBeta

    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

  13. Activation of C-H Bonds in Pt(+) + x CH4 Reactions, where x = 1-4: Identification of the Platinum Dimethyl Cation.

    PubMed

    Wheeler, Oscar W; Salem, Michelle; Gao, Amanda; Bakker, Joost M; Armentrout, P B

    2016-08-11

    Activation of C-H bonds in the sequential reactions of Pt(+) + x(CH4/CD4), where x = 1-4, have been investigated using infrared multiple photon dissociation (IRMPD) spectroscopy and theoretical calculations. Pt(+) cations are formed by laser ablation and exposed to controlled amounts of CH4/CD4 leading to [Pt,xC,(4x-2)H/D](+) dehydrogenation products. Irradiation of these products in the 400-2100 cm(-1) range leads to CH4/CD4 loss from the x = 3 and 4 products, whereas PtCH2(+)/PtCD2(+) products do not decompose at all, and x = 2 products dissociate only when formed from a higher order product. The structures of these complexes were explored theoretically at several levels of theory with three different basis sets. Comparison of the experimental and theoretical results indicate that the species formed have a Pt(CH3)2(+)(CH4)x-2/Pt(CD3)2(+)(CD4)x-2 binding motif for x = 2-4. Thus, reaction of Pt(+) with methane occurs by C-H bond activation to form PtCH2(+), which reacts with an additional methane molecule by C-H bond activation to form the platinum dimethyl cation. This proposed reaction mechanism is consistent with theoretical explorations of the potential energy surface for reactions of Pt(+) with one and two methane molecules. PMID:27438025

  14. In situ measurements of change in work function of Pt, Pd and Au surfaces during desorption of oxygen by using photoemission yield spectrometer in air

    NASA Astrophysics Data System (ADS)

    Yamashita, Daisuke; Ishizaki, Atsushi

    2016-02-01

    We investigated the change in work function of Pt, Pd and Au surfaces during desorption of oxygen by using a photoemission yield spectrometer with an open counter. Oxygen coverage was formed by UV/ozone treatment, and then continuous change in work function with exposure to air was observed at various temperatures. Work function of Pt, Pd and Au surfaces decreased during desorption of oxygen, and finally returned to the initial value of untreated surfaces. Furthermore, temperature dependence on the change in work function was found. These characteristics were explained using chemical kinetics scheme. The exponential decay of work function was well reproduced by the first-order reaction rate equation, and it was confirmed that the order of rate constant, kr, is kr(Au) < kr(Pd) < kr(Pt). The activation energy was estimated to be 36, 38 and 28 kJ/mol for Pt, Pd, Au, respectively.

  15. Ammonia decomposition activity on monolayer Ni supported on Ru, Pt and WC substrates

    NASA Astrophysics Data System (ADS)

    Hansgen, Danielle A.; Vlachos, Dionisios G.; Chen, Jingguang G.

    2011-12-01

    Catalyst design for specific reactions currently involves using atomic or molecular descriptors to identify promising catalysts. In this paper, we explore three surfaces that have similar computed nitrogen binding energies, which is a descriptor for the ammonia decomposition reaction. The surfaces studied include a monolayer of Ni on Pt(111), Ru(0001) and tungsten monocarbide (WC). The activity of these surfaces toward the ammonia decomposition reaction was compared using density functional theory and temperature programmed desorption. It was found that while the NHx-H bond scission is similar on each of the surfaces, the temperature of nitrogen desorption is very different. The differences are explained and the implications for ammonia decomposition activity and catalyst design are discussed.

  16. TiO2-modified CNx nanowires as a Pt electrocatalyst support with high activity and durability for the oxygen reduction reaction.

    PubMed

    Tang, J; Meng, H M

    2016-01-21

    A Pt/TiO2-modified carbon nitride nanofiber (Pt/TiO2-CNx) catalyst has been synthesized by a chemical method for the oxygen reduction reaction (ORR). The material characteristics confirmed by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM) and high resolution transmission electron microscopy (HRTEM) have indicated that the TiO2-CNx nanowires have a diameter of about 35-85 nm, the TiO2 nanoparticles are embedded in CNx nanowires and Pt nanoparticles are about 2.21 nm in size. The X-ray photoelectron spectra (XPS) show that Ti has a shift in the binding energy of Ti 2p, implying suboxide formation. Pt/0.2 g TiO2-CNx has about 3% loss in the (electrochemical surface area) ESA after 1000 cycles, however, the Pt/C catalyst has about 50.8% loss in the ESA. Pt/0.2 g TiO2-CNx has much better activity than Pt/C, which is proposed to be due to the high total surface area of Pt. The durability test shows that the Pt/0.2 g TiO2-CNx catalyst has no loss of activity after 5000 cycles. After 5000 cycles, the average size of Pt nanoparticles and the peaks of Pt 4f almost remain unchanged. The high durability of Pt/0.2 g TiO2-CNx is attributed to the corrosion-resistance of 0.2 g TiO2-CNx nanowires support and the good interaction between the 0.2 g TiO2-CNx support and the Pt nanoparticles. PMID:26660293

  17. Tuning the activity of Pt alloy electrocatalysts by means of the lanthanide contraction.

    PubMed

    Escudero-Escribano, María; Malacrida, Paolo; Hansen, Martin H; Vej-Hansen, Ulrik G; Velázquez-Palenzuela, Amado; Tripkovic, Vladimir; Schiøtz, Jakob; Rossmeisl, Jan; Stephens, Ifan E L; Chorkendorff, Ib

    2016-04-01

    The high platinum loadings required to compensate for the slow kinetics of the oxygen reduction reaction (ORR) impede the widespread uptake of low-temperature fuel cells in automotive vehicles. We have studied the ORR on eight platinum (Pt)-lanthanide and Pt-alkaline earth electrodes, Pt5M, where M is lanthanum, cerium, samarium, gadolinium, terbium, dysprosium, thulium, or calcium. The materials are among the most active polycrystalline Pt-based catalysts reported, presenting activity enhancement by a factor of 3 to 6 over Pt. The active phase consists of a Pt overlayer formed by acid leaching. The ORR activity versus the bulk lattice parameter follows a high peaked "volcano" relation. We demonstrate how the lanthanide contraction can be used to control strain effects and tune the activity, stability, and reactivity of these materials. PMID:27034369

  18. Linking morphology with activity through the lifetime of pretreated PtNi nanostructured thin film catalysts

    DOE PAGESBeta

    Cullen, David A.; Lopez-Haro, Miguel; Bayle-Guillemaud, Pascale; Debe, Mark; Steinbach, Andrew J.; Guetaz, L.

    2015-04-10

    In this study, the nanoscale morphology of highly active Pt3Ni7 nanostructured thin film fuel cell catalysts is linked with catalyst surface area and activity following catalyst pretreatments, conditioning and potential cycling. The significant role of fuel cell conditioning on the structure and composition of these extended surface catalysts is demonstrated by high resolution imaging, elemental mapping and tomography. The dissolution of Ni during fuel cell conditioning leads to highly complex, porous structures which were visualized in 3D by electron tomography. Quantification of the rendered surfaces following catalyst pretreatment, conditioning, and cycling shows the important role pore structure plays in surfacemore » area, activity, and durability.« less

  19. Nanoporous PtRu Alloys with Unique Catalytic Activity toward Hydrolytic Dehydrogenation of Ammonia Borane.

    PubMed

    Zhou, Qiuxia; Xu, Caixia

    2016-03-01

    Nanoporous (NP) PtRu alloys with three different bimetallic components were straightforwardly fabricated by dealloying PtRuAl ternary alloys in hydrochloric acid. Selective etching of aluminum from source alloys generates bicontinuous network nanostructures with uniform size and structure. The as-made NP-PtRu alloys exhibit superior catalytic activity toward the hydrolytic dehydrogenation of ammonia borane (AB) than pure NP-Pt and NP-Ru owing to alloying platinum with ruthenium. The NP-Pt70 Ru30 alloy exhibits much higher specific activity toward hydrolytic dehydrogenation of AB than NP-Pt30 Ru70 and NP-Pt50 Ru50 . The hydrolysis activation energy of NP-Pt70 Ru30 was estimated to be about 38.9 kJ mol(-1) , which was lower than most of the reported activation energy values in the literature. In addition, recycling tests show that the NP-Pt70 Ru30 is still highly active in the hydrolysis of AB even after five runs, which indicates that NP-PtRu alloy accompanied by the network nanoarchitecture is beneficial to improve structural stability toward the dehydrogenation of AB. PMID:26573746

  20. Highly Effective Pt-Based Water-Gas Shift Catalysts by Surface Modification with Alkali Hydroxide Salts

    SciTech Connect

    Kusche, Matthias; Bustillo, Karen; Agel, Friederike; Wasserscheid, Peter

    2015-01-29

    Here, we describe an economical and convenient method to improve the performance of Pt/alumina catalysts for the water–gas shift reaction through surface modification of the catalysts with alkali hydroxides according to the solid catalyst with ionic liquid layer approach. The results are in agreement with our findings reported earlier for methanol steam reforming. This report indicates that alkali doping of the catalyst plays an important role in the observed catalyst activation. In addition, the basic and hygroscopic nature of the salt coating contributes to a significant improvement in the performance of the catalyst. During the reaction, a partly liquid film of alkali hydroxide forms on the alumina surface, which increases the availability of H2O at the catalytically active sites. Kinetic studies reveal a negligible effect of the KOH coating on the rate dependence of CO and H2O partial pressures. In conclusion, TEM studies indicate an agglomeration of the active Pt clusters during catalyst preparation; restructuring of Pt nanoparticles occurs under reaction conditions, which leads to a highly active and stable system over 240h time on stream. Excessive pore fillings with KOH introduce a mass transfer barrier as indicated in a volcano-shaped curve of activity versus salt loading. The optimum KOH loading was found to be 7.5wt%.

  1. Highly Effective Pt-Based Water-Gas Shift Catalysts by Surface Modification with Alkali Hydroxide Salts

    DOE PAGESBeta

    Kusche, Matthias; Bustillo, Karen; Agel, Friederike; Wasserscheid, Peter

    2015-01-29

    Here, we describe an economical and convenient method to improve the performance of Pt/alumina catalysts for the water–gas shift reaction through surface modification of the catalysts with alkali hydroxides according to the solid catalyst with ionic liquid layer approach. The results are in agreement with our findings reported earlier for methanol steam reforming. This report indicates that alkali doping of the catalyst plays an important role in the observed catalyst activation. In addition, the basic and hygroscopic nature of the salt coating contributes to a significant improvement in the performance of the catalyst. During the reaction, a partly liquid filmmore » of alkali hydroxide forms on the alumina surface, which increases the availability of H2O at the catalytically active sites. Kinetic studies reveal a negligible effect of the KOH coating on the rate dependence of CO and H2O partial pressures. In conclusion, TEM studies indicate an agglomeration of the active Pt clusters during catalyst preparation; restructuring of Pt nanoparticles occurs under reaction conditions, which leads to a highly active and stable system over 240h time on stream. Excessive pore fillings with KOH introduce a mass transfer barrier as indicated in a volcano-shaped curve of activity versus salt loading. The optimum KOH loading was found to be 7.5wt%.« less

  2. Highly Effective Pt-Based Water–Gas Shift Catalysts by Surface Modification with Alkali Hydroxide Salts

    PubMed Central

    Kusche, Matthias; Bustillo, Karen; Agel, Friederike; Wasserscheid, Peter

    2015-01-01

    Herein, we describe an economical and convenient method to improve the performance of Pt/alumina catalysts for the water–gas shift reaction through surface modification of the catalysts with alkali hydroxides according to the solid catalyst with ionic liquid layer approach. The results are in agreement with our findings reported earlier for methanol steam reforming. This report indicates that alkali doping of the catalyst plays an important role in the observed catalyst activation. In addition, the basic and hygroscopic nature of the salt coating contributes to a significant improvement in the performance of the catalyst. During the reaction, a partly liquid film of alkali hydroxide forms on the alumina surface, which increases the availability of H2O at the catalytically active sites. Kinetic studies reveal a negligible effect of the KOH coating on the rate dependence of CO and H2O partial pressures. TEM studies indicate an agglomeration of the active Pt clusters during catalyst preparation; restructuring of Pt nanoparticles occurs under reaction conditions, which leads to a highly active and stable system over 240 h time on stream. Excessive pore fillings with KOH introduce a mass transfer barrier as indicated in a volcano-shaped curve of activity versus salt loading. The optimum KOH loading was found to be 7.5 wt %. PMID:26413174

  3. Enhanced activity and stability of Pt/TiO2/carbon fuel cell electrocatalyst prepared using a glucose modifier

    NASA Astrophysics Data System (ADS)

    Odetola, Christopher; Trevani, Liliana; Easton, E. Bradley

    2015-10-01

    Two TiO2-C composite materials were prepared through a conventional sol gel synthesis using Vulcan XC-72 carbon black. The carbon was initially functionalised to form acid treated Vulcan (ATV) prior to TiO2 deposition. In one composite, the ATV was further modified through glucose adsorption (G-ATV) in order to facilitate the growth of small and uniform TiO2 nanoparticles on the carbon surface. Platinum nanoparticles were deposited on TiO2/G-ATV and TiO2/ATV supports through reduction of H2PtCl6 with NaBH4 at 0 °C. The electrochemical properties of the two composite catalysts were compared with in house Pt/C catalyst. We observed a three-fold increase in TiO2 loading (14 wt%) on glucose doped carbon surface compared with just acid treated support (5 wt%). The beginning of life (BOL) electrochemical active surface area (ECSA) of Pt/14 wt%TiO2/G-ATV catalyst was 40.4 m2 g-1 compared to 37.1 m2 g-1 obtained for Pt on 5 wt% TiO2/ATV despite increased TiO2 loadings on the former. Furthermore these composite catalysts showed enhanced oxygen reduction activity and better durability during accelerated stress tests which was attributed to an electronic interaction between Pt and the TiO2 on the support.

  4. Surface chemistry on bimetallic alloy surfaces: adsorption of anions and oxidation of CO on Pt3Sn(111).

    PubMed

    Stamenković, Vojislav R; Arenz, Matthias; Lucas, Christopher A; Gallagher, Mark E; Ross, Philip N; Marković, Nenad M

    2003-03-01

    The microscopic structure of the Pt(3)Sn(111) surface in an electrochemical environment has been studied by a combination of ex situ low-energy electron diffraction (LEED), Auger electron spectroscopy (AES), and low-energy ion scattering (LEIS) and in situ surface X-ray scattering (SXS) and Fourier transform infrared (FTIR) spectroscopy. In ultrahigh vacuum (UHV) the clean-annealed surface produces a p(2 x 2) LEED pattern consistent with the surface composition, determined by LEIS, of 25 at. % Sn. SXS results show that the p(2 x 2) structure can be "transferred" from UHV into 0.5 M H(2)SO(4) and that the surface structure remains stable from 0.05 to 0.8 V. At 0.05 V the expansion of Pt surface atoms, ca. +2% from the bulk lattice spacing, is induced by adsorption of underpotential-deposited (UPD) hydrogen. At 0.5 V, where Pt atoms are covered by (bi)sulfate anions, the topmost layer is contracted relative to 0.05 V, although Sn atoms expand significantly, ca. 8.5%. The p(2 x 2) structure is stable even in solutions containing CO. In contrast to the Pt(111)-CO system, no ordered structures of CO are formed on the Pt(3)Sn(111) surface and the topmost layer expands relatively little (ca. 1.5%) from the bulk lattice spacing upon the adsorption of CO. The binding site geometry of CO on Pt(3)Sn(111) is determined by FTIR. In contrast to the near invariant band shape of a-top CO on Pt(111), changes in band morphology (splitting of the band) and vibrational properties (increase in the frequency mode) are clearly visible on the Pt(3)Sn(111) surface. To explain the line shape of the CO bands, we suggest that in addition to alloying effects other factors, such as intermolecular repulsion between coadsorbed CO and OH species, are controlling segregation of CO into cluster domains where the local CO coverage is different from the coverage expected for the CO-CO interaction on an unmodified Pt(111) surface. PMID:12603163

  5. Highly accessible Pt nanodots homogeneously decorated on Au nanorods surface for sensing.

    PubMed

    Feng, Xun; Li, Xin; Shi, Hongyan; Huang, Hao; Wu, Xiaochun; Song, Wenbo

    2014-12-10

    Some nanostructures are reported to possess enzyme-mimetic activities similar to those of natural enzymes. Herein, highly-dispersed Pt nanodots on Au nanorods (HD-PtNDs@AuNRs) with mimetic peroxidase activity were designed as an active electrode modifier for fabrication of a hydrogen peroxide (H2O2) electrochemical sensor. The HD-PtNDs@AuNRs were synthesized by a seed-mediated growth approach and confirmed by scanning electron microscopy, transmission electron microscopy, energy dispersive X-ray spectroscopy, and UV-vis spectroscopy. The electrochemical and catalytical performances of HD-PtNDs@AuNRs towards H2O2 reduction were investigated in detail by cyclic voltammetry and amperometry. The HD-PtNDs@AuNRs modified electrode displayed a high catalytic activity to H2O2 at -0.10 V (versus SCE), a rapid response within 5 s, a wide linear range of 2.0-3800.0 μM, a detection limit of 1.2 μM (S/N=3), and a high sensitivity of 181 μA mM(-1) cm(-2). These results suggested a promising potential of fabricating H2O2 electrochemical sensor using HD-PtNDs@AuNRs. PMID:25441877

  6. Response of a Pt-polyyne membrane in surface acoustic wave sensors: Experimental and theoretical approach

    NASA Astrophysics Data System (ADS)

    Caliendo, Cinzia; Fratoddi, Ilaria; Russo, Maria Vittoria; Lo Sterzo, Claudio

    2003-06-01

    A surface acoustic wave (SAW) sensor, based on a polymeric sensitive membrane, has been realized for sensor applications and materials characterization. A platinum-containing rigid-rod organometallic polymer [-Pt(PPh3)2(-C≡C-pC6H2(2,5-OC16H33)2-C≡C-)]n (Pt-P-HDOB), obtained by the reaction of cis-[Pt(PPh3)2Cl2] with 1,4-diethynyl-2,5-dihexadeciloxybenzene (HDOB) by means of the recently assessed "Extended one pot" polymerization route, was here studied. The chemical structure and chain length of Pt-P-HDOB polymer were defined by spectroscopic techniques and gel permeation chromatography measurements. The acoustic characterization of the Pt-P-HDOB film was developed with the aid of the perturbation theory applied to different polymer-coated-piezoelectric substrates and the shear modulus of Pt-P-HDOB film have been estimated. A SAW delay line has been implemented on ZnO/Si substrate and a thin polymeric film has been spin deposited on the device surface to realize a chemical sensor. The sensor has been exposed to different chemicals and its response has been measured for different chemical concentrations. High sensitivity and reproducibility of the sensor response to relative humidity and methanol vapors were found.

  7. Effect of metal support interaction on surface segregation in Pd Pt nanoparticles

    NASA Astrophysics Data System (ADS)

    De Sarkar, A.; Menon, Mahesh; Khanra, Badal C.

    2001-10-01

    In this work, we present the results of our Monte Carlo (MC) simulation studies for the segregation behavior of supported, clean and gas-covered Pd-Pt nanoparticles as a function of the metal-support interaction. For preferential Pd-support interaction, the base of the nanoparticle is found to get enriched with Pd atoms; while for preferential interaction of Pt atoms with the support the base gets enriched in Pt. The composition of the rest of the particle changes slightly with the metal-support interaction. The presence of oxygen and hydrogen atoms does not influence the role of the metal-support interaction on the surface composition of Pd-Pt nanoparticles. The simulation results are found to be in total agreement with the known experimental results.

  8. Correlation Between Surface Chemistry and Electrocatalytic Properties of Monodisperse Pt(x)Ni(1-x) Nanoparticles

    SciTech Connect

    Wang, Chao; Chi, Miaofang; Wang, Guofeng; Van der Vliet, Dennis; Li, Dongguo; More, Karren Leslie; Wang, Hsien-Hua; Schlueter, John; Markovic, Nenad; Stamenkovic, Vojislav

    2011-01-01

    Monodisperse and homogeneous Pt{sub x}Ni{sub 1-x} alloy nanoparticles of various compositions are synthesized via an organic solution approach in order to reveal the correlation between surface chemistry and their electrocatalytic properties. Atomic-level microscopic analysis of the compositional profile and modeling of nanoparticle structure are combined to follow the dependence of Ni dissolution on the initial alloy composition and formation of the Pt-skeleton nanostructures. The developed approach and acquired knowledge about surface structure-property correlation can be further generalized and applied towards the design of advanced functional nanomaterials.

  9. Antagonistic Activities of Novel Peptides from Bacillus amyloliquefaciens PT14 against Fusarium solani and Fusarium oxysporum.

    PubMed

    Kim, Young Gwon; Kang, Hee Kyoung; Kwon, Kee-Deok; Seo, Chang Ho; Lee, Hyang Burm; Park, Yoonkyung

    2015-12-01

    Bacillus species have recently drawn attention due to their potential use in the biological control of fungal diseases. This paper reports on the antifungal activity of novel peptides isolated from Bacillus amyloliquefaciens PT14. Reverse-phase high-performance liquid chromatography revealed that B. amyloliquefaciens PT14 produces five peptides (PT14-1, -2, -3, -4a, and -4b) that exhibit antifungal activity but are inactive against bacterial strains. In particular, PT14-3 and PT14-4a showed broad-spectrum antifungal activity against Fusarium solani and Fusarium oxysporum. The PT14-4a N-terminal amino acid sequence was identified through Edman degradation, and a BLAST homology analysis showed it not to be identical to any other protein or peptide. PT14-4a displayed strong fungicidal activity with minimal inhibitory concentrations of 3.12 mg/L (F. solani) and 6.25 mg/L (F. oxysporum), inducing severe morphological deformation in the conidia and hyphae. On the other hand, PT14-4a had no detectable hemolytic activity. This suggests PT14-4a has the potential to serve as an antifungal agent in clinical therapeutic and crop-protection applications. PMID:26496638

  10. Propylene on Pt(111)I. Characterization of surface species by infra-red spectroscopy

    NASA Astrophysics Data System (ADS)

    Zaera, Francisco; Chrysostomou, Demetrius

    2000-06-01

    The adsorption of propylene on Pt(111) single-crystal surfaces was characterized by reflection-absorption infra-red spectroscopy (RAIRS). The uptake of propylene on the surface at 90 K results in the development of at least four adsorption species as a function of coverage. Significant rehybridization of the CC double bond of propylene takes place at low coverages, so the molecule primarily interacts with the metal via two σ metalcarbon bonds. Below half-saturation, the molecule mainly bonds through the central carbon atom, but at higher coverage, the CC bond becomes flat, and the terminal methyl group tilts towards a more vertical orientation. Further dosing of propylene after saturation of the di-σ state leads to the build-up of a flat π-bonded second layer. Ultimately, a layer of condensed propylene could be grown on the surface under the vacuum conditions of the experiment as long as the temperature was kept below 80 K. Annealing of the low-temperature propylene-saturated Pt(111) surface first induces the desorption of the weakly held π species, and later, between 230 and 250 K, to the dehydrogenation and rearrangement of the remaining di-σ species to propylidyne (Pt 3CCH 2CH 3). The details of the conversion of propylene to propylidyne change somewhat with the conditions under which this transformation is carried out, and appear to involve a stable and identifiable intermediate [2-propyl, CH 3CH(Pt)CH 3, and/or propylidene, Pt 2CHCH 2CH 3]. Propylene π-bonding is also possible on propylidyne-saturated Pt(111) surfaces under vacuum.

  11. Photo-enhanced activity of Pt and Pt-Ru catalysts towards the electro-oxidation of methanol

    NASA Astrophysics Data System (ADS)

    Arulmani, Dheevesh V.; Eastcott, Jennie I.; Mavilla, Stephanie G.; Easton, E. Bradley

    2014-02-01

    Electrocatalyst materials, consisting of Pt or Pt-Ru supported on carbon with and without TiO2, are evaluated for their activity towards the methanol oxidation reaction (MOR) in 1.0 M H2SO4 at 25 °C in the presence and absence of visible light irradiation. Electrochemical studies showed that enhanced MOR activity is achieved upon irradiation with visible light for each catalyst, in both the presence and absence of TiO2. Irradiation leads to no improvement in activity towards the formic acid oxidation reaction (FAOR) indicating that irradiation aids in the removal of adsorbed intermediate species, such as CO, during MOR. While the presence of a TiO2 support does lead to an increase in activity upon irradiation, about 50% of the improvements arise solely from the irradiation of the metal-containing electrocatalysts themselves.

  12. Preparation and characterization of Pt supported on graphene with enhanced electrocatalytic activity in fuel cell

    NASA Astrophysics Data System (ADS)

    Xin, Yuchen; Liu, Jian-guo; Zhou, Yong; Liu, Wenming; Gao, Jian; Xie, Yun; Yin, Ying; Zou, Zhigang

    Pt nanoparticles are deposited onto graphene sheets via synchronous reduction of H 2PtCl 6 and graphene oxide (GO) suspension using NaBH 4. Lyophilization is introduced to avoid irreversible aggregation of graphene (G) sheets, which happens during conventional drying process. Pt/G catalysts reveal a high catalytic activity for both methanol oxidation and oxygen reduction reaction compared to Pt supported on carbon black (Pt/C). The performance of Pt/G catalysts is further improved after heat treatment in N 2 atmosphere at 300 °C for 2 h, and the peak current density of methanol oxidation for Pt/G after heat treatment is almost 3.5 times higher than Pt/C. Transmission electron microscope (TEM) images show that the Pt particles are uniformly distributed on graphene sheets. X-ray photoelectron spectroscopy (XPS) results demonstrate that the interaction between Pt and graphene is enhanced during annealing. It suggests that graphene has provided a new way to improve electrocatalytic activity of catalyst for fuel cell.

  13. Porous Pt Nanotubes with High Methanol Oxidation Electrocatalytic Activity Based on Original Bamboo-Shaped Te Nanotubes.

    PubMed

    Lou, Yue; Li, Chunguang; Gao, Xuedong; Bai, Tianyu; Chen, Cailing; Huang, He; Liang, Chen; Shi, Zhan; Feng, Shouhua

    2016-06-29

    In this report, a facile and general strategy was developed to synthesize original bamboo-shaped Te nanotubes (NTs) with well-controlled size and morphology. On the basis of the as-prepared Te NTs, porous Pt nanotubes (NTs) with excellent property and structural stability have been designed and manufactured. Importantly, we avoided the use of surface stabilizing agents, which may affect the catalytic properties during the templated synthesis process. Furthermore, Pt NTs with different morphology were successfully prepared by tuning the experimental parameters. As a result, transmission electron microscopy (TEM) study shows that both Te NTs and Pt NTs have uniform size and morphology. Following cyclic voltammogram (CV) testing, the as-prepared porous Pt NTs and macroporous Pt NTs exhibited excellent catalytic activities toward electrochemical methanol oxidation reactions due to their tubiform structure with nanoporous framework. Thus, the as-prepared Pt NTs with specific porous structure hold potential usage as alternative anode catalysts for direct methanol fuel cells (DMFCs). PMID:27310183

  14. Production of 191Pt radiotracer with high specific activity for the development of preconcentration procedures

    NASA Astrophysics Data System (ADS)

    Parent, M.; Strijckmans, K.; Cornelis, R.; Dewaele, J.; Dams, R.

    1994-04-01

    A radiotracer of Pt with suitable nuclear characteristics and high specific activity (i.e. activity to mass ratio) is a powerful tool when developing preconcentration methods for the determination of base-line levels of Pt in e.g. environmental and biological samples. Two methods were developed for the production of 191Pt with high specific activity and radionuclidic purity: (1) via the 190Pt(n, γ) 191Pt reaction by neutron irradiation of enriched Pt in a nuclear reactor at high neutron fluence rate and (2) via the 191Ir(p, n) 191Pt reaction by proton irradiation of natural Ir with a cyclotron, at an experimentally optimized proton energy. For the latter method it was necessary to separate Pt from the Ir matrix. For that reason either liquid-liquid extraction with dithizone or adsorption chromatography were used. The yields, the specific activities and the radionuclidic purities were experimentally determined as a function of the proton energy and compared to the former method. The half-life of 191Pt was accurately determined to be 2.802 ± 0.025 d.

  15. 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

  16. 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

  17. Reversible hydrogenation of surface N atoms to form NH on Pt(111).

    PubMed

    Herceg, Eldad; Mudiyanselage, Kumudu; Trenary, Michael

    2005-02-24

    The formation and dissociation chemistry of the NH species on Pt(111) was characterized with reflection absorption infrared spectroscopy and temperature programmed desorption. Irradiation of a chemisorbed bilayer of ammonia with a 100 eV electron beam at 85 K leads to a mixture of NH, N, and H on the surface. Annealing to temperatures in the range of 200-300 K leads to reaction of N and H to form additional NH. The NH species has an intense and narrow NH stretch peak at 3320 cm(-1), while no peak due to the PtNH bend is observed above 800 cm(-1). The NH species is stable up to a temperature of approximately 400 K. The surface N atoms produced from NH dissociation are readily hydrogenated back to NH by exposure of the surface to H2. However, NH cannot be further hydrogenated to generate adsorbed NH2 or to NH3 under the conditions used here. Exposure of the NH/Pt(111) surface to D2 at 380 K produces the ND species. Comparison with the results of density functional theory calculations based on small Pt clusters indicates that NH occupies three-fold hollow sites with the molecular axis perpendicular to the surface. PMID:16851294

  18. Pt5Gd as a highly active and stable catalyst for oxygen electroreduction.

    PubMed

    Escudero-Escribano, María; Verdaguer-Casadevall, Arnau; Malacrida, Paolo; Grønbjerg, Ulrik; Knudsen, Brian P; Jepsen, Anders K; Rossmeisl, Jan; Stephens, Ifan E L; Chorkendorff, Ib

    2012-10-10

    The activity and stability of Pt(5)Gd for the oxygen reduction reaction (ORR) have been studied, using a combination of electrochemical measurements, angle-resolved X-ray photoelectron spectroscopy (AR-XPS), and density functional theory calculations. Sputter-cleaned, polycrystalline Pt(5)Gd shows a 5-fold increase in ORR activity, relative to pure Pt at 0.9 V, approaching the most active in the literature for catalysts prepared in this way. AR-XPS profiles after electrochemical measurements in 0.1 M HClO(4) show the formation of a thick Pt overlayer on the bulk Pt(5)Gd, and the enhanced ORR activity can be explained by means of compressive strain effects. Furthermore, these novel bimetallic electrocatalysts are highly stable, which, in combination with their enhanced activity, makes them very promising for the development of new cathode catalysts for fuel cells. PMID:22998588

  19. Adsorption and ring-opening of lactide on the chiral metal surface Pt(321){sup S} studied by density functional theory

    SciTech Connect

    Franke, J.-H.; Kosov, D. S.

    2015-01-28

    We study the adsorption and ring-opening of lactide on the naturally chiral metal surface Pt(321){sup S}. Lactide is a precursor for polylactic acid ring-opening polymerization, and Pt is a well known catalyst surface. We study, here, the energetics of the ring-opening of lactide on a surface that has a high density of kink atoms. These sites are expected to be present on a realistic Pt surface and show enhanced catalytic activity. The use of a naturally chiral surface also enables us to study potential chiral selectivity effects of the reaction at the same time. Using density functional theory with a functional that includes the van der Waals forces in a first-principles manner, we find modest adsorption energies of around 1.4 eV for the pristine molecule and different ring-opened states. The energy barrier to be overcome in the ring-opening reaction is found to be very small at 0.32 eV and 0.30 eV for LL- and its chiral partner DD-lactide, respectively. These energies are much smaller than the activation energy for a dehydrogenation reaction of 0.78 eV. Our results thus indicate that (a) ring-opening reactions of lactide on Pt(321) can be expected already at very low temperatures, and Pt might be a very effective catalyst for this reaction; (b) the ring-opening reaction rate shows noticeable enantioselectivity.

  20. Kinetics of optically excited charge carriers at the GaN surface: Influence of catalytic Pt nanostructures

    NASA Astrophysics Data System (ADS)

    Winnerl, Andrea; Pereira, Rui N.; Stutzmann, Martin

    2015-10-01

    In this work, we use GaN with different deposited Pt nanostructures as a controllable model system to investigate the kinetics of photo-generated charge carriers in hybrid photocatalysts. We combine conductance and contact potential difference measurements to investigate the influence of Pt on the processes involved in the capture and decay of photo-generated charge carriers at and close to the GaN surface. We found that in the presence of Pt nanostructures the photo-excitation processes are similar to those found in Pt free GaN. However, in GaN with Pt nanostructures, photo-generated holes are preferentially trapped in surface states of the GaN covered with Pt and/or in electronic states of the Pt and lead to an accumulation of positive charge there, whereas negative charge is accumulated in localized states in a shallow defect band of the GaN covered with Pt. This preferential accumulation of photo-generated electrons close to the surface is responsible for a dramatic acceleration of the turn-off charge transfer kinetics and a stronger dependence of the surface photovoltage on light intensity when compared to a Pt free GaN surface. Our study shows that in hybrid photocatalysts, the metal nanostructures induce a spatially inhomogeneous surface band bending of the semiconductor that promotes a lateral drift of photogenerated charges towards the catalytic nanostructures.

  1. Kinetics of optically excited charge carriers at the GaN surface: Influence of catalytic Pt nanostructures

    SciTech Connect

    Winnerl, Andrea Pereira, Rui N.; Stutzmann, Martin

    2015-10-21

    In this work, we use GaN with different deposited Pt nanostructures as a controllable model system to investigate the kinetics of photo-generated charge carriers in hybrid photocatalysts. We combine conductance and contact potential difference measurements to investigate the influence of Pt on the processes involved in the capture and decay of photo-generated charge carriers at and close to the GaN surface. We found that in the presence of Pt nanostructures the photo-excitation processes are similar to those found in Pt free GaN. However, in GaN with Pt nanostructures, photo-generated holes are preferentially trapped in surface states of the GaN covered with Pt and/or in electronic states of the Pt and lead to an accumulation of positive charge there, whereas negative charge is accumulated in localized states in a shallow defect band of the GaN covered with Pt. This preferential accumulation of photo-generated electrons close to the surface is responsible for a dramatic acceleration of the turn-off charge transfer kinetics and a stronger dependence of the surface photovoltage on light intensity when compared to a Pt free GaN surface. Our study shows that in hybrid photocatalysts, the metal nanostructures induce a spatially inhomogeneous surface band bending of the semiconductor that promotes a lateral drift of photogenerated charges towards the catalytic nanostructures.

  2. Surface and electronic structure of epitaxial PtLuSb (001) thin films

    SciTech Connect

    Patel, Sahil J.; Kawasaki, Jason K.; Logan, John; Schultz, Brian D.; Adell, J.; Thiagarajan, B.; Mikkelsen, A.; Palmstrøm, Chris J.

    2014-05-19

    The surface and electronic structure of single crystal thin films of PtLuSb (001) grown by molecular beam epitaxy were studied. Scanning tunneling spectroscopy (STS), photoemission spectroscopy, and temperature dependent Hall measurements of PtLuSb thin films are consistent with a zero-gap semiconductor or semi-metal. STS and photoemission measurements show a decrease in density of states approaching the Fermi level for both valence and conduction bands as well as a slight shift of the Fermi level position into the valence band. Temperature dependent Hall measurements also corroborate the Fermi level position by measurement of p-type carriers.

  3. CO Oxidation on supported single Pt atoms - Experimental and Ab Initio density functional studies of CO interaction with Pt atom on theta-alumina(010) surface

    SciTech Connect

    Narula, Chaitanya Kumar; Debusk, Melanie Moses; Yoon, Mina; Allard Jr, Lawrence Frederick; Mullins, David R; Wu, Zili; Yang, Xiaofan; Veith, Gabriel M; Stocks, George Malcolm

    2013-01-01

    Although there are only a few known examples of supported single atoms, they are unique because they bridge the gap between homogenous and heterogeneous catalysis. The metal center is single supported atoms can be isoelectronic with their homogenous catalyst counterpart and may allow mechanistic pathways normally seen in homogenous catalysts. Here, we report CO oxidation activity of mono-disperse single Pt atoms supported on an inert substrate, -alumina (Al2O3), in the presence of stoichiometric oxygen. Since CO oxidation on single Pt atoms cannot occur via a conventional Langmuir-Hinshelwood scheme (L-H scheme) which requires at least one Pt-Pt bond, we have carried out a first principles density functional theoretical study of a proposed pathway which is a variation on the conventional L-H scheme and is inspired by organometallic chemistry of platinum. We find that a single supported Pt atom prefers to bond to O2 over CO. The CO then bonds with the oxygenated Pt atom and forms a carbonate which dissociates to liberate CO2, leaving an oxygen atom on Pt. A subsequent reaction with another CO molecule regenerates the single atom catalyst. An in-situ diffuse reflectance infrared study of CO adsorption on the catalyst s supported single atoms has been carried out to infer information on CO absorption modes and compare the observed spectra with calculated ones for intermediates in the proposed CO oxidation pathway. Our results clearly show that supported Pt single atoms are catalytically active and that this catalytic activity can occur without involving the substrate. Characterization by electron microscopy and X-ray absorption studies of the mono-disperse Pt/ -Al2O3, synthesized by solution methods, are also presented.

  4. Nanoparticle cluster gas sensor: Pt activated SnO2 nanoparticles for NH3 detection with ultrahigh sensitivity

    NASA Astrophysics Data System (ADS)

    Liu, Xu; Chen, Nan; Han, Bingqian; Xiao, Xuechun; Chen, Gang; Djerdj, Igor; Wang, Yude

    2015-09-01

    Pt activated SnO2 nanoparticle clusters were synthesized by a simple solvothermal method. The structure, morphology, chemical state and specific surface area were analyzed by X-ray powder diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and N2-sorption studies, respectively. The SnO2 nanoparticle cluster matrix consists of tens of thousands of SnO2 nanoparticles with an ultra-small grain size estimated to be 3.0 nm. And there are abundant random-packed wormhole-like pores, caused by the inter-connection of the SnO2 nanoparticles, throughout each cluster. The platinum element is present in two forms including metal (Pt) and tetravalent metal oxide (PtO2) in the Pt activated SnO2 nanoparticle clusters. The as-synthesized pure and Pt activated SnO2 nanoparticle clusters were used to fabricate gas sensor devices. It was found that the gas response toward 500 ppm of ammonia was improved from 6.48 to 203.44 through the activation by Pt. And the results indicate that the sensor based on Pt activated SnO2 not only has ultrahigh sensitivity but also possesses good response-recovery properties, linear dependence, repeatability, selectivity and long-term stability, demonstrating the potential to use Pt activated SnO2 nanoparticle clusters as ammonia gas sensors. At the same time, the formation mechanisms of the unique nanoparticle clusters and highly enhanced sensitivity are also discussed.Pt activated SnO2 nanoparticle clusters were synthesized by a simple solvothermal method. The structure, morphology, chemical state and specific surface area were analyzed by X-ray powder diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and N2-sorption studies, respectively. The SnO2 nanoparticle cluster matrix consists of tens of thousands of SnO2 nanoparticles with an ultra-small grain size estimated to be 3.0 nm. And there are abundant random-packed wormhole-like pores, caused by the inter

  5. Surface structure and relaxation at the Pt3Sn(111)/electrolyte interface

    SciTech Connect

    Gallagher, Mark E.; Lucas, Chris A.; Stamenkovic, Vojislav; Markovic, Nenad M.; Ross, Philip N.

    2004-07-29

    In situ surface X-ray scattering (SXS) measurements have been performed to determine the surface structure of Pt3Sn(111) in sulfuric acid electrolyte. Potentiodynamic measurements indicate that the ultra high vacuum (UHV) prepared p(2 x 2) alloy surface structure is stable upon transfer to electrolyte and remains stable during subsequent cycling of the applied potential. A detailed structural study by crystal truncation rod (CTR) analysis shows that the surface layer of Pt and Sn atoms undergoes an expansion of {approx} 2 percent of the (111) layer spacing at low potential (0.05 V vs. reversible hydrogen electrode) in CO-free electrolyte. At 0.55 V the expansion of the Pt atoms is reduced to {approx} 0.6 percent, whereas the Sn atoms are expanded by {approx} 6 percent of the layer spacing. The potential-induced buckling of the surface layer is also observed in CO-saturated electrolyte and is a precursor to Sn dissolution which occurs at {approx} 1.0 V, causing irreversible roughening of the surface.

  6. Oxidation mechanism of formic acid on the bismuth adatom-modified Pt(111) surface.

    PubMed

    Perales-Rondón, Juan Victor; Ferre-Vilaplana, Adolfo; Feliu, Juan M; Herrero, Enrique

    2014-09-24

    In order to improve catalytic processes, elucidation of reaction mechanisms is essential. Here, supported by a combination of experimental and computational results, the oxidation mechanism of formic acid on Pt(111) electrodes modified by the incorporation of bismuth adatoms is revealed. In the proposed model, formic acid is first physisorbed on bismuth and then deprotonated and chemisorbed in formate form, also on bismuth, from which configuration the C-H bond is cleaved, on a neighbor Pt site, yielding CO2. It was found computationally that the activation energy for the C-H bond cleavage step is negligible, which was also verified experimentally. PMID:25188779

  7. Understanding the electronic band structure of Pt-alloys for surface reactivity

    NASA Astrophysics Data System (ADS)

    Jung, Jongkeun; Kim, Beomyoung; Hong, Ji Sook; Jin, Tae Won; Shim, Ji Hoon; Nemsak, Slavomir; Denlinger, Jonathan D.; Masashi, Arita; Kenya, Shimada; Kim, Changyoung; Mun, Bongjin Simon

    In polymer exchange membrane fuel cell (PEMFC), the oxygen reduction reaction (ORR) at cathode side has been continuously investigated due to its critical importance in performance of fuel cell. So far, even with best industrial catalyst made with Pt, the performance of ORR is too far below from the commercial purpose. In 2007, Stamenkovic et al. showed that Pt alloys with 3- dtransition metal exhibited significantly improved ORR performance and pointed out the altered electronic structure of surface as the major contributing factor for enhanced ORR. Since 1990, with the advance of DFT calculation, the trend of surface chemical reactivity is explained with the analysis of d-band structures, known as d-band model. While d-band provides valid insight on surface chemical reactivity based on the valence band DOS, the relation between surface work function and DOS has not been well understood. The element-specific local electronic band structure of Pt alloys are identified by ARPES measurement, and the correlation between surface work function and local charge density is investigated.

  8. Preparation and enhanced visible-light photocatalytic H2-production activity of CdS-sensitized Pt/TiO2 nanosheets with exposed (001) facets.

    PubMed

    Qi, Lifang; Yu, Jiaguo; Jaroniec, Mietek

    2011-05-21

    CdS-sensitized Pt/TiO(2) nanosheets with exposed (001) facets were prepared by hydrothermal treatment of a Ti(OC(4)H(9))(4)-HF-H(2)O mixed solution followed by photochemical reduction deposition of Pt nanoparticles (NPs) on TiO(2) nanosheets (TiO(2) NSs) and chemical bath deposition of CdS NPs on Pt/TiO(2) NSs, successively. The UV and visible-light driven photocatalytic activity of the as-prepared samples was evaluated by photocatalytic H(2) production from lactic acid aqueous solution under UV and visible-light (λ ≥ 420 nm) irradiation. It was shown that no photocatalytic H(2)-production activity was observed on the pure TiO(2) NSs under UV and/or visible-light irradiation. Deposition of CdS NPs on Pt/TiO(2) NSs caused significant enhancement of the UV and visible-light photocatalytic H(2)-production rates. The morphology of TiO(2) particles had also significant influence on the visible-light H(2)-production activity. Among TiO(2) NSs, P25 and the NPs studied, the CdS-sensitized Pt/TiO(2) NSs show the highest photocatalytic activity (13.9% apparent quantum efficiency obtained at 420 nm), exceeding that of CdS-sensitized Pt/P25 by 10.3% and that of Pt/NPs by 1.21%, which can be attributed to the combined effect of several factors including the presence of exposed (001) facets, surface fluorination and high specific surface area. After many replication experiments of the photocatalytic hydrogen production in the presence of lactic acid, the CdS-sensitized Pt/TiO(2) NSs did not show great loss in the photocatalytic activity, confirming that the CdS/Pt/TiO(2) NSs system is stable and not photocorroded. PMID:21678582

  9. Enhancement of oxygen reduction reaction activities by Pt nanoclusters decorated on ordered mesoporous porphyrinic carbons

    DOE PAGESBeta

    Sun-Mi Hwang; Choi, YongMan; Kim, Min Gyu; Sohn, Young-Jun; Cheon, Jae Yeong; Joo, Sang Hoon; Yim, Sung-Dae; Kuttiyiel, Kurian A.; Sasaki, Kotaro; Adzic, Radoslav R.; et al

    2016-03-08

    The high cost of Pt-based membrane electrode assemblies (MEAs) is a critical hurdle for the commercialization of polymer electrolyte fuel cells (PEFCs). Recently, non-precious metal-based catalysts (NPMCs) have demonstrated much enhanced activity but their oxygen reduction reaction (ORR) activity is still inferior to that of Pt-based catalysts resulting in a much thicker electrode in the MEA. For the reduction of mass transport and ohmic overpotential we adopted a new concept of catalyst that combines an ultra-low amount of Pt nanoclusters with metal–nitrogen (M–Nx) doped ordered mesoporous porphyrinic carbon (FeCo–OMPC(L)). The 5 wt% Pt/FeCo–OMPC(L) showed a 2-fold enhancement in activities comparedmore » to a higher loading of Pt. Our experimental results supported by first-principles calculations indicate that a trace amount of Pt nanoclusters on FeCo–OMPC(L) significantly enhances the ORR activity due to their electronic effect as well as geometric effect from the reduced active sites. Finally, in terms of fuel cell commercialization, this class of catalysts is a promising candidate due to the limited use of Pt in the MEA.« less

  10. Structure and Activity of Pt-Ni Catalysts Supported on Modified Al2O3 for Ethanol Steam Reforming.

    PubMed

    Navarro, R M; Sanchez-Sanchez, M C; Fierro, J L G

    2015-09-01

    Modification of alumina with La-, Ce-, Zr- and Mg-oxides was studied with the aim to use them as supports of bimetallic Pt-Ni catalysts for the steam reforming of ethanol. Activity results showed that modifications of Al2O3 support with the incorporation of La, Ce, Zr or Mg oxides play an essential role in the catalytic behaviour of PtNi catalysts. Bimetallic PtNi catalyst supported on bare Al2O3 showed evolution of the reaction products with time on stream consisting in the increase of C2H4 production with concomitant decrease of CH4 and CO2 production. The addition of Mg or Zr to γ-A1203 did not inhibit the appearance of ethylene but delayed its production. In the case of Ce- or La-supported catalysts, the product selectivities were stable with time-on-stream, with no changes being observed in the product distribution for 24 h. Characterization results showed that La- and Ce-containing supports improves the Pt and Ni metal exposure values. The better stability achieved for Ce and La containing catalysts was inferred to be related with a participation/assistance of lanthanum and cerium entities in the gasification of coke deposits together with a modification of Pt and Ni dispersion which lower the probability of the nucleation of coke precursors on their surfaces. PMID:26716216

  11. Effect of Sb Segregation on Conductance and Catalytic Activity at Pt/Sb-Doped SnO2 Interface: A Synergetic Computational and Experimental Study.

    PubMed

    Fu, Qiang; Colmenares Rausseo, Luis César; Martinez, Umberto; Dahl, Paul Inge; García Lastra, Juan Maria; Vullum, Per Erik; Svenum, Ingeborg-Helene; Vegge, Tejs

    2015-12-23

    Antimony-doped tin dioxide (ATO) is considered a promising support material for Pt-based fuel cell cathodes, displaying enhanced stability over carbon-based supports. In this work, the effect of Sb segregation on the conductance and catalytic activity at Pt/ATO interface was investigated through a combined computational and experimental study. It was found that Sb-dopant atoms prefer to segregate toward the ATO/Pt interface. The deposited Pt catalysts, interestingly, not only promote Sb segregation, but also suppress the occurrence of Sb(3+) species, a charge carrier neutralizer at the interface. The conductivity of ATO was found to increase, to a magnitude close to that of activated carbon, with an increment of Sb concentration before reaching a saturation point around 10%, and then decrease, indicating that Sb enrichment at the ATO surface may not always favor an increment of the electric current. In addition, the calculation results show that the presence of Sb dopants in ATO has little effect on the catalytic activity of deposited three-layer Pt toward the oxygen reduction reaction, although subsequent alloying of Pt and Sb could lower the corresponding catalytic activity. These findings help to support future applications of ATO/Pt-based materials as possible cathodes for proton exchange membrane fuel cell applications with enhanced durability under practical applications. PMID:26615834

  12. Synthesis of Pt-Ni/graphene via in situ reduction and its enhanced catalyst activity for methanol oxidation.

    PubMed

    Li, Lihong; Wu, Yuen; Lu, Jun; Nan, Caiyun; Li, Yadong

    2013-09-01

    A simple in situ reduction approach was used to obtain Pt3Ni/reduced graphene oxide (rGO) with dominant {111} facets. The catalytic activity of Pt-Ni/rGO toward methanol electro-oxidation was studied by performing cyclic voltammetry. The Pt3Ni/rGO nanocatalysts exhibited improved catalytic activity and durability. PMID:23863973

  13. Pt-M (M = Cu, Fe, Zn, etc.) bimetallic nanomaterials with abundant surface defects and robust catalytic properties.

    PubMed

    Mao, Junjie; Chen, Yuanjun; Pei, Jiajing; Wang, Dingsheng; Li, Yadong

    2016-05-21

    Herein, we exploit two typical crystal growth modes, namely, "stacking" and "carving" routes, to synthesize Pt-based bimetallic nanomaterials with defect-rich surface structures, which exhibit enhanced electrocatalytic properties toward both methanol oxidation reaction (MOR) and oxygen reduction reaction (ORR) compared with commercial Pt/C. PMID:27063415

  14. Fabrication of cubic PtCu nanocages and their enhanced electrocatalytic activity towards hydrogen peroxide

    PubMed Central

    2014-01-01

    Cubic PtCu nanocages (NCs) were successfully synthesized through a redox reaction using cuprous oxide (Cu2O) as a sacrificial template and reducing agent. The porous PtCu NCs were composed of amounts of PtCu nanograins with an average particle size of 2.9 nm. The electrocatalytic performance of the PtCu NC electrode towards H2O2 was studied by cyclic voltammetry (CV) and chronoamperometry. The prepared PtCu NC electrode exhibited excellent electrocatalytic activity towards H2O2, with a wide liner range from 5 μM to 22.25 mM, a relatively high sensitivity of 295.3 μA mM-1 cm-2, and a low detection limit of 5 μM (S/N = 3). The hollow porous nanostructure has potential applications in biosensors. PMID:24512566

  15. Nitride stabilized PtNi core-shell nanocatalyst for high oxygen reduction activity.

    PubMed

    Kuttiyiel, Kurian A; Sasaki, Kotaro; Choi, Yongman; Su, Dong; Liu, Ping; Adzic, Radoslav R

    2012-12-12

    We describe a route to the development of novel PtNiN core-shell catalysts with low Pt content shell and inexpensive NiN core having high activity and stability for the oxygen reduction reaction (ORR). The PtNiN synthesis involves nitriding Ni nanoparticles and simultaneously encapsulating it by 2-4 monolayer-thick Pt shell. The experimental data and the density functional theory calculations indicate nitride has the bifunctional effect that facilitates formation of the core-shell structures and improves the performance of the Pt shell by inducing both geometric and electronic effects. Synthesis of inexpensive NiN cores opens up possibilities for designing of various transition metal nitride based core-shell nanoparticles for a wide range of applications in energy conversion processes. PMID:23194259

  16. Clean Ir(111) and Pt(111) electronic surface states: A first-principle fully relativistic investigation

    NASA Astrophysics Data System (ADS)

    Dal Corso, Andrea

    2015-07-01

    We present a first-principle investigation of the fully relativistic electronic surface states and resonances of clean Pt(111) and Ir(111) and compare them with those of Au(111). Our calculations are based on a recently introduced fully relativistic projector augmented-wave (PAW) approach that includes spin-orbit coupling and allows us to access both the relativistic energy splittings and the spin polarization of the surface states. The maps of the electronic structure of the two surfaces are critically discussed in comparison with previous calculations and with some of the available angle-resolved photoelectron spectroscopy data.

  17. A thermodynamically consistent surface reaction mechanism for CO oxidation on Pt

    SciTech Connect

    Mhadeshwar, A.B.; Vlachos, D.G.

    2005-08-01

    The thermodynamic inconsistency of catalytic combustion reaction mechanisms has been a long-standing, fundamental, and practical problem. Here, we develop a thermodynamically consistent catalytic reaction mechanism for CO oxidation on Pt. First, we propose a modification of the bond index of the unity bond index-quadratic exponential potential (UBI-QEP) semiempirical framework for calculation of the activation energy of the Langmuir-Hinshelwood-type bimolecular surface reaction between co-adsorbed CO{sup *} and O{sup *}. Thermodynamic consistency is then ensured in the reaction mechanism by combining the semiempirical UBI-QEP theory, statistical mechanics, and constraint-based optimization against experimental data. Atmospheric pressure ignition and ultrahigh vacuum molecular beam experiments are selected as targets for optimization. The optimized mechanism is validated against redundant experiments, including temperature-programmed desorption, temperature-programmed reaction, and molecular beam experiments. Our microkinetic model is able to capture multiple types of data while being thermodynamically consistent over a wide range of conditions.

  18. 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.

  19. A novel Pt-Co alloy hydrogen anode catalyst with superlative activity, CO-tolerance and robustness.

    PubMed

    Shi, G Y; Yano, H; Tryk, D A; Watanabe, M; Iiyama, A; Uchida, H

    2016-08-01

    PtCo nanoparticles, having two atomic layers of stabilized Pt skin, supported on carbon black (Pt2AL-PtCo/C), exhibited superlative mass activity for the CO-tolerant hydrogen oxidation reaction (HOR), together with high robustness with respect to air exposure, as a novel anode catalyst in reformate gas-based polymer electrolyte fuel cells. The high area-specific HOR activity and CO tolerance are consistent with DFT calculations. PMID:26952735

  20. Coherent heavy quasiparticles in a CePt5 surface alloy.

    PubMed

    Klein, M; Nuber, A; Schwab, H; Albers, C; Tobita, N; Higashiguchi, M; Jiang, J; Fukuda, S; Tanaka, K; Shimada, K; Mulazzi, M; Assaad, F F; Reinert, F

    2011-05-01

    We report on the results of a high-resolution angle-resolved photoemission study on the ordered surface alloy CePt(5). The temperature dependence of the spectra show the formation of the coherent low-energy heavy-fermion band near the Fermi level. These experimental data are supported by a multiband model calculation in the framework of the dynamical mean-field theory. PMID:21635113

  1. Surface-molecule proton transfer in the scattering of hyperthermal DABCO from H/Pt(111)

    NASA Astrophysics Data System (ADS)

    Kuipers, E. W.; Vardi, A.; Danon, A.; Amirav, A.

    1992-01-01

    Hyperthermal DABCO is scattered from H-covered Pt(111). The ionization by electron and proton transfer is measured as a function of the incident molecular kinetic energy and the angle of incidence. The positive ions produced are energy analyzed showing hyperthermal distributions which are dependent on the incident energy. This means that no equilibration occurs at the surface and therefore protonation at hyperthermal energy is an Eley-Rideal reaction. The protonation yield depends linearly on the incident DABCO flux and the H-coverage on the Pt(111) surface. The ionization yield for both electron and proton transfer depends on the incident energy as k( Ei- Etr) n with a similar threshold energy of 1.5 eV. From this we learn that direct protonation occurs by electron transfer and a subsequent binding of an H-atom. Within the error bars we found no difference between H-atom and D-atom transfer. Protonation of other molecules with a high proton affinity such as dimethylaniline at H-covered Pt(111) was measured as well. Analytical applications for both surface analysis and molecular detection are discussed.

  2. Reconstruction of core and surface nanoparticles: The example of Pt55 and Au55

    NASA Astrophysics Data System (ADS)

    da Silva, Juarez L. F.; Kim, Hyoung Gyu; Piotrowski, Maurício J.; Prieto, Maurício J.; Tremiliosi-Filho, Germano

    2010-11-01

    Cuboctahedron (CUB) and icosahedron (ICO) model structures are widely used in the study of transition-metal (TM) nanoparticles (NPs), however, it might not provide a reliable description for small TM NPs such as the Pt55 and Au55 systems in gas phase. In this work, we combined density-functional theory calculations with atomic configurations generated by the basin hopping Monte Carlo algorithm within the empirical Sutton-Chen embedded atom potential. We identified alternative lower energy configurations compared with the ICO and CUB model structures, e.g., our lowest energy structures are 5.22 eV (Pt55) and 2.01 eV (Au55) lower than ICO. The energy gain is obtained by the Pt and Au diffusion from the ICO core region to the NP surface, which is driven by surface compression (only 12 atoms) on the ICO core region. Therefore, in the lowest energy configurations, the core size reduces from 13 atoms (ICO, CUB) to about 9 atoms while the NP surface increases from 42 atoms (ICO, CUB) to about 46 atoms. The present mechanism can provide an improved atom-level understanding of small TM NPs reconstructions.

  3. Active frequency selective surfaces

    NASA Astrophysics Data System (ADS)

    Buchwald, Walter R.; Hendrickson, Joshua; Cleary, Justin W.; Guo, Junpeng

    2013-05-01

    Split ring resonator arrays are investigated for use as active elements for the realization of voltage controllable frequency selective surfaces. Finite difference time domain simulations suggest the absorptive and reflective properties of such surfaces can be externally controlled through modifications of the split ring resonator gap impedance. In this work, such voltage-controlled resonance tuning is obtained through the addition of an appropriately designed high electron mobility transistor positioned across the split ring resonator gap. It is shown that a 0.5μm gate length high electron mobility transistor allows voltage controllable switching between the two resonant conditions associated with a split ring resonator and that of a closed loop geometry when the surface is illuminated with THz radiation. Partial switching between these two resonant conditions is observed at larger gate lengths. Such active frequency selective surfaces are proposed, for example, for use as modulators in THz detection schemes and as RF filters in radar applications when scaled to operate at GHz frequencies.

  4. Promoting effect of vanadium on catalytic activity of Pt/Ce-Zr-O diesel oxidation catalysts.

    PubMed

    Huang, Haifeng; Jiang, Bo; Gu, Lei; Qi, Zhonghua; Lu, Hanfeng

    2015-07-01

    A series of Pt-V/Ce-Zr-O diesel oxidation catalysts was prepared using the impregnation method. The catalytic activity and sulfur resistance of Pt-V/Ce-Zr-O were investigated in the presence of simulated diesel exhaust. The effect of vanadium on the structure and redox properties of the catalysts was also investigated using the Brunauer-Emmett-Teller method, X-ray diffraction, H2 temperature-programmed reduction, CO temperature-programmed desorption, X-ray photoelectron spectroscopy, and Energy Dispersive Spectroscopy. Results showed that the Pt particles were well dispersed on the Ce-Zr-O carrier through the vanadium isolation effect, which significantly improved the oxidation activity toward CO and hydrocarbons. An electron-withdrawing phenomenon occurred from V to Pt, resulting in an increase in the metallic nature of platinum, which was beneficial to hydrocarbon molecular activation. PMID:26141886

  5. Investigation of interaction between the Pt(II) ions and aminosilane-modified silica surface in heterogeneous system

    NASA Astrophysics Data System (ADS)

    Nowicki, Waldemar; Gąsowska, Anna; Kirszensztejn, Piotr

    2016-05-01

    UV-vis spectroscopy measurements confirmed the reaction in heterogeneous system between Pt(II) ions and ethylenediamine type ligand, n-(2-aminoethyl)-3-aminopropyl-trimethoxysilane, immobilized at the silica surface. The formation of complexes is a consequence of interaction between the amine groups from the ligand grafted onto SiO2 and ions of platinum. A potentiometric titration technique was to determine the stability constants of complexes of Pt(II) with immobilized insoluble ligand (SG-L), on the silica gel. The results show the formation of three surface complexes of the same type (PtHSG-L, Pt(HSG-L)2, PtSG-L) with SG-L ligand, in a wide range of pH for different Debye length. The concentration distribution of the complexes in a heterogeneous system is evaluated.

  6. Surface reconstructions and transport of epitaxial PtLuSb (001) thin films grown by MBE

    NASA Astrophysics Data System (ADS)

    Patel, Sahil J.; Logan, John A.; Harrington, Sean D.; Schultz, Brian D.; Palmstrøm, Chris J.

    2016-02-01

    This work presents the surface reconstructions and transport properties of the topological insulator PtLuSb grown on Al0.1In0.9Sb/GaAs (001). Two stable surface reconstructions, (1×3) and c(2×2), were observed on PtLuSb (001) surfaces. Antimony-dimerization was determined to be the nature of the (1×3) surface reconstruction as evidenced by chemical binding energy shifts in the antimony 4d core-level for surface bonding components. The two surface reconstructions were studied as a function of Sb4 overpressure and substrate temperature to create a reconstruction phase diagram. From this reconstruction phase diagram, a growth window from 320 °C to 380 °C using an antimony overpressure was identified. Within this window, the highest quality films were grown at a growth temperature of 380 °C. These films exhibited lower p-type carrier concentrations as well as relatively high hole mobilities.

  7. Scaling of submonolayer island sizes in Ag growth on stepped Pt surfaces

    NASA Astrophysics Data System (ADS)

    Ramadan, A.; Picaud, F.; Ramseyer, C.

    2010-09-01

    Simulations based on an atomic description of the growth mechanisms are used to interpret physical behavior of silver adatoms growth on stepped platinum surface. We study in details the influence of atom confinement during the growth process on vicinal Pt surfaces with different terrace widths. The behavior of the mean island density on terraces and steps and their size is analyzed in a general way as a function of the flux F, the diffusion coefficient D and the terrace width using Kinetic Monte-Carlo simulations. Specific scaling factors are found to describe the growth near the defects or on the terraces depending on the confinement.

  8. Graphene growth on a Pt(111) substrate by surface segregation and precipitation

    NASA Astrophysics Data System (ADS)

    Gao, Jian-Hua; Sagisaka, Keisuke; Kitahara, Masayo; Xu, Ming-Sheng; Miyamoto, Satoru; Fujita, Daisuke

    2012-02-01

    We report on the fabrication of a sizable graphene sheet on a carbon-doped Pt(111) substrate through surface segregation and precipitation. Scanning Auger electron spectroscopy (AES) reveals that the graphene covered more than 98% of the substrate surface. Our graphene consists of single-layer graphene across the substrate with fractions of several micrometer wide bi- and tri-layer graphene islands. We also show that the number of graphene layers can be precisely determined by analyzing AES data. While Raman spectroscopy is usually used to study graphene on SiO2, we show that AES is a powerful tool to characterize graphene grown on metal substrates.

  9. [Hydrogen induced C-C, C-N, and C-S bond activities on Pi and Ni surfaces]: Summary

    SciTech Connect

    Gland, J.L.

    1994-12-31

    This document summarizes research applied to chemical bond activation studies. Topics summarized include: Carbon nitrogen bonds experimentation with aniline on Ni(111), Mi(100), and Pt(111) surfaces; carbon sulfur bonds experimentation with methanethiol, phenylthiol, and dimethyl disulfide on Pt(111) and Ni(111) surfaces; carbon-carbon bonds experimentation on Ni(100), Ni(111) and Pt(111) surfaces; and in-situ fluorescence yield near edge spectroscopy.

  10. NiPt/Rh(111): A stable surface alloy with enhanced magnetic moments

    NASA Astrophysics Data System (ADS)

    Imam, Mighfar; Marathe, Madhura; Narasimhan, Shobhana

    2009-04-01

    We have performed ab initio density functional theory calculations to investigate the miscibility and magnetic properties of pseudomorphically grown monolayers of Ni xPt 1- x surface alloys on a Rh(111) substrate. We find that the formation of this alloy is energetically favored over phase-segregated forms, and its magnetic moment is also enhanced. A significant contribution to this enhanced magnetic moment is found to come from the induced moments on the otherwise non-magnetic elements Pt and Rh. A low concentration of Ni gives rise to a high magnetic moment per Ni atom. We find that a low effective coordination and a high non-spin-polarized density of states at the Fermi level are responsible for these enhanced moments.

  11. Rapid synthesis of a PtRu nano-sponge with different surface compositions and performance evaluation for methanol electrooxidation

    NASA Astrophysics Data System (ADS)

    Xiao, Meiling; Feng, Ligang; Zhu, Jianbing; Liu, Changpeng; Xing, Wei

    2015-05-01

    A rapid strategy to synthesize a highly active PtRu alloy nano-sponge catalyst system for methanol electro-oxidation is presented. The greatly increased Pt utilization, anti-CO poisoning ability and electronic effect resulting from the porous nano-sponge structure could account for the performance improvement.

  12. Rapid synthesis of a PtRu nano-sponge with different surface compositions and performance evaluation for methanol electrooxidation.

    PubMed

    Xiao, Meiling; Feng, Ligang; Zhu, Jianbing; Liu, Changpeng; Xing, Wei

    2015-06-01

    A rapid strategy to synthesize a highly active PtRu alloy nano-sponge catalyst system for methanol electro-oxidation is presented. The greatly increased Pt utilization, anti-CO poisoning ability and electronic effect resulting from the porous nano-sponge structure could account for the performance improvement. PMID:25966842

  13. Investigation of the contrast inversion effect on hydrophilic surfaces using Pt/C whisker probes in a scanning force microscope

    NASA Astrophysics Data System (ADS)

    Zhukov, M. V.; Mukhin, I. S.; Levichev, V. V.; Golubok, A. O.

    2015-02-01

    We compare the spatial resolution and image contrast of an erythrocyte surface obtained by means of scanning force microscopy (SFM) with conventional hydrophobic Si probes and probes modified by hydrophilic Pt/C whisker probes. It is shown that probes with Pt/C nanowhiskers provide a higher spatial resolution and contrast when imaging relief on the surface of erythrocytes. The contrast inversion is revealed in some areas of the SFM images when replacing Si probes by probes with Pt/C nanowhiskers. The origin of this inversion in the tapping and contact modes is discussed.

  14. Adsorption of polyiodobenzene molecules on the Pt(111) surface using van der Waals density functional theory

    NASA Astrophysics Data System (ADS)

    Johnston, Karen; Pekoz, Rengin; Donadio, Davide

    2016-02-01

    Adsorption of aromatic molecules on surfaces is widely studied due to applications in molecular electronics. In this work, the adsorption of iodobenzene molecules on the Pt(111) surface has been studied using density functional theory. Iodobenzene molecules, with various numbers of iodine atoms, have two non-dissociative adsorption minima. One structure exhibits chemisorption between the ring and the surface (short-range) and the other structure exhibits chemisorption between the iodine ions and the surface (long-range). Both structures have a strong van der Waals interaction with the surface. In general, the adsorption energy increases as the number of iodine atoms increases. The dissociated structure of monoiodobenzene was investigated, and the dissociation barrier and the barrier between the short- and long-range states were compared.

  15. Understanding Electrocatalytic Activity Enhancement of Bimetallic Particles to Ethanol Electro-oxidation: (1) Water Adsorption and Decomposition on PtnM (n=2,3 and 9; M=Pt, Ru, Sn)

    PubMed Central

    Wang, Yixuan; Mi, Yunjie; Redmon, Natalie; Holiday, Jessica

    2009-01-01

    The fundamental assumption of the bi-functional mechanism for PtSn alloy to catalyze ethanol electro-oxidation reaction (EER) is that Sn facilitates water dissociation and EER occurs over Pt site of the PtSn alloy. To clarify this assumption and achieve a good understanding about the EER, H2O adsorption and dissociation over bimetallic clusters PtM (M=Pt, Sn, Ru, Rh, Pd, Cu and Re) are systematically investigated in the present work. To discuss a variety of effects, PtnM (n=2, and 3; M=Pt, Sn and Ru), one-layer Pt6M (M=Pt, Sn and Ru), and two-layer (Pt6M)Pt3 (M=Pt, Sn, Ru, Rh, Pd, Cu and Re) clusters are used to model the PtM bimetallic catalysts. Water exhibits atop adsorption on Pt and Ru sites of the optimized clusters PtnM (n=2, and 3; M=Pt and Ru), yet bridge adsorption on Sn sites of Pt2Sn as well as distorted tetrahedral Pt3Sn. However, in the cases of one-layer Pt6M and two-layer Pt9M cluster models water preferentially binds to all of investigated central atom M of surface layer in atop configuration with the dipole moment of water almost parallel to the cluster surface. Water adsorption on the Sn site of PtnSn (n=2 and 3) is weaker than those on the Pt site of Ptn (n=3 and 4) and the Ru site of PtnRu (n=2 and 3), while water adsorptions on the central Sn atom of Pt6Sn and Pt9Sn are enhanced so significantly that they are even stronger than those on the central Pt and Ru atoms of PtnM (n=6 and 9; M=Pt and Ru). For all of the three cluster models, energy barrier (Ea) for the dissociation of adsorbed water over Sn is lower than over Ru and Pt atoms (e.g., Ea: 0.78 vs 0.96 and 1.07 eV for Pt9M), which also remains as external electric fields were added. It is interesting to note that the dissociation energy on Sn site is also the lowest (Ediss: 0.44 vs 0.61 and 0.67eV). The results show that from both kinetic and thermodynamic viewpoints Sn is more active to water decomposition than pure Pt and the PtRu alloy, which well supports the assumption of the bi

  16. 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.

  17. Segmented Pt/Ru, Pt/Ni, and Pt/RuNi nanorods as model bifunctional catalysts for methanol oxidation.

    PubMed

    Liu, Fang; Lee, Jim Yang; Zhou, Wei Jiang

    2006-01-01

    Five-segment (Pt-Ru-Pt-Ru-Pt, Pt-Ni-Pt-Ni-Pt, and Pt-RuNi-Pt-RuNi-Pt) nanorods with the same overall rod length and the same total Pt segment length were prepared by sequential electrodeposition of the metals into the pores of commercially available anodic aluminum oxide (AAO) membranes. Field-emission scanning electron microscopy (FESEM) showed that the nanorods were about 210 nm in diameter and about 1.5 microm in length. The alternating Pt and oxophilic metal(s) segments could be easily differentiated in backscattered-electron images. X-ray diffraction (XRD) analysis of the nanorods indicated that Pt and Ni were polycrystalline with fcc structures, Ru was hcp, and the co-deposited RuNi adopted the nickel fcc structure with some negative shifts in the Bragg angles. The chemical states of Pt, Ru, and Ni on the nanorod surface were assayed by X-ray photoelectron spectroscopy (XPS), and the presence of Pt(0), Pt(II), Pt(IV), Ru(0), Ru(VI), Ni(0), and Ni(II) was observed. The nanorods were catalytically active for the room-temperature electrooxidation of methanol in acidic solutions. The relative rates of reaction showed the Pt-RuNi pair sites as having the lowest overpotential to dissociate water, the highest catalytic activity in methanol oxidation, and the strongest CO-tolerance in the potential window employed. The use of segmented nanorods with identifiable Pt-oxophilic metal(s) interfaces removes many of the ambiguities in the interpretation of experimental data from conventional alloy catalysts, thereby enabling a direct comparison of the activities of various types of pair sites in methanol oxidation. PMID:17193567

  18. Tuning the surface enhanced Raman scattering and catalytic activities of gold nanorods by controlled coating of platinum.

    PubMed

    Sharma, Vipul; Sinha, Niraj; Dutt, Sunil; Chawla, Mohit; Siril, Prem Felix

    2016-02-01

    Galvanic replacement of silver (Ag) by platinum (Pt) on bi-metallic nanorods (NRs) having gold (Au) core and silver shell (Au@Ag) resulted in discontinuous coating of Pt over Au (Au@Pt-DC) NRs. However, a novel method has been developed in this work for the preparation of Au NRs having smooth and continuous coating of Pt (Au@Pt-C NRs) using galvanic replacement reaction of Au@Ag NRs in presence of sulphuric acid. Selective blocking by the bisulfate ions that are adsorbed on Pt surface, preventing Pt on Pt deposition seems to be the mechanism of formation of Au@Pt-C NRs. Effect of the nature of Pt shell (i.e. whether continuous or discontinuous) on SERS activity of the NRs was investigated with methylene blue (MB) as a reporter molecule. The specific enhancement of the Raman signals were in the order Au@ Pt-C NRsPt-DC NRs. Catalytic reduction of MB by NaBH4 using the NRs also followed a similar trend with Au@Pt-DC NRs showing almost three times better activity than Au and Au@Pt-C NRs. PMID:26520825

  19. Homogeneous Pt-bimetallic Electrocatalysts

    SciTech Connect

    Wang, Chao; Chi, Miaofang; More, Karren Leslie; Markovic, Nenad; Stamenkovic, Vojislav

    2011-01-01

    Alloying has shown enormous potential for tailoring the atomic and electronic structures, and improving the performance of catalytic materials. Systematic studies of alloy catalysts are, however, often compromised by inhomogeneous distribution of alloying components. Here we introduce a general approach for the synthesis of monodispersed and highly homogeneous Pt-bimetallic alloy nanocatalysts. Pt{sub 3}M (where M = Fe, Ni, or Co) nanoparticles were prepared by an organic solvothermal method and then supported on high surface area carbon. These catalysts attained a homogeneous distribution of elements, as demonstrated by atomic-scale elemental analysis using scanning transmission electron microscopy. They also exhibited high catalytic activities for the oxygen reduction reaction (ORR), with improvement factors of 2-3 versus conventional Pt/carbon catalysts. The measured ORR catalytic activities for Pt{sub 3}M nanocatalysts validated the volcano curve established on extended surfaces, with Pt{sub 3}Co being the most active alloy.

  20. 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

  1. Synthesis, Characterization, and Catalytic Oxygen Electroreduction Activities of Carbon-Supported PtW Nanoparticle Catalysts

    SciTech Connect

    Xiong, Liufeng; More, Karren Leslie; He, Ting

    2010-01-01

    Carbon-supported PtW (PtW/C) alloy nanoparticle catalysts with well-controlled particle size, dispersion, and composition uniformity, have been synthesized by wet chemical methods of decomposition of carbonyl cluster complexes, hydrolysis of metal salts, and chemical reactions within a reverse microemulsion. The synthesized PtW/C catalysts were characterized by X-ray diffraction, high-resolution transmission electron microscopy, and energy-dispersive spectroscopy. The catalytic oxygen electroreduction activities were measured by the hydrodynamic rotating disk electrode technique in an acidic electrolyte. The influence of the synthesis method on PtW particle size, size distribution, composition uniformity, and catalytic oxygen electroreduction activity, have been investigated. Among the synthesis methods studied, PtW/C catalysts prepared by the decomposition of carbonyl cluster complexes displayed the best platinum mass activity for oxygen reduction reaction under the current small scale production; a 3.4-fold catalytic enhancement was achieved in comparison to a benchmark Pt/C standard.

  2. Lignin-derived oxygenate reforming on a bimetallic surface: The reaction of benzaldehyde on Zn/Pt(111)

    NASA Astrophysics Data System (ADS)

    Shi, Daming; Vohs, John M.

    2016-08-01

    Temperature programmed desorption (TPD) and high-resolution electron energy loss spectroscopy (HREELS) were used to characterize the adsorption and reaction of benzaldehyde (C6H5CHO) on hydrogen-covered Pt(111) and Zn-modified Pt(111) surfaces. Benzaldehyde was found to interact with Pt(111) via both the phenyl ring and carbonyl of the aldehyde group. This bonding configuration facilitates unselective decomposition of the benzaldehyde to produce CO, H2, and small hydrocarbon fragments at relatively low temperatures. On the other hand, benzaldehyde was found to bond to Zn-decorated Pt(111) surface exclusively via the carbonyl group in an η2(C, O) configuration, with the phenyl ring tilted away from the surface. This configuration weakens Csbnd O bond in the carbonyl facilitating its cleavage and helps prevent hydrogenation of the phenyl ring.

  3. Genesis and Evolution of Surface Species during Pt Atomic Layer Deposition on Oxide Supports Characterized by in Situ XAFS Analysis and Water-Gas Shift Reaction

    SciTech Connect

    Setthapun, Worajit; Williams, W. Damion; Kim, Seung Min; Feng, Hao; Elam, Jeffrey W.; Rabuffetti, Federico A.; Poeppelmeier, Kenneth R.; Stair, Peter C.; Stach, Eric A.; Ribeiro, Fabio H.; Miller, Jeffrey T.; Marshall, Christopher L.

    2010-06-03

    Platinum atomic layer deposition (ALD) using MeCpPtMe₃ was employed to prepare high loadings of uniform-sized, 1-2 nm Pt nanoparticles on high surface area Al₂O₃, TiO₂, and SrTiO₃ supports. X-ray absorption fine structure was utilized to monitor the changes in the Pt species during each step of the synthesis. The temperature, precursor exposure time, treatment gas, and number of ALD cycles were found to affect the Pt particle size and density. Lower-temperature MeCpPtMe₃ adsorption yielded smaller particles due to reduced thermal decomposition. A 300 °C air treatment of the adsorbed MeCpPtMe₃ leads to PtO. In subsequent ALD cycles, the MeCpPtMe₃ reduces the PtO to metallic Pt in the ratio of one precursor molecule per PtO. A 200 °C H₂ treatment of the adsorbed MeCpPtMe₃ leads to the formation of 1-2 nm, metallic Pt nanoparticles. During subsequent ALD cycles, MeCpPtMe₃ adsorbs on the support, which, upon reduction, yields additional Pt nanoparticles with a minimal increase in size of the previously formed nanoparticles. The catalysts produced by ALD had identical water-gas shift reaction rates and reaction kinetics to those of Pt catalysts prepared by standard solution methods. ALD synthesis of catalytic nanoparticles is an attractive method for preparing novel model and practical catalysts.

  4. Kinetically induced irreversibility in electro-oxidation and reduction of Pt surface

    NASA Astrophysics Data System (ADS)

    Jinnouchi, Ryosuke; Kodama, Kensaku; Suzuki, Takahisa; Morimoto, Yu

    2015-05-01

    A mean field kinetic model was developed for electrochemical oxidations and reductions of Pt(111) on the basis of density functional theory calculations, and the reaction mechanisms were analyzed. The model reasonably describes asymmetric shapes of cyclic voltammograms and small Tafel slopes of relevant redox reactions observed in experiments without assuming any unphysical forms of rate equations. Simulations using the model indicate that the oxidation of Pt(111) proceeds via an electrochemical oxidation from Pt to PtOH and a disproportionation reaction from PtOH to PtO and Pt, while its reduction proceeds via two electrochemical reductions from PtO to PtOH and from PtOH to Pt.

  5. Formation and Stabilization of Nano-Sized Pt Clusters on TiO2 Surfaces

    SciTech Connect

    Baer, Donald R.; Liang, Yong; Gan, Shupan

    2000-09-30

    This paper reports experiments related to the stability and size distributions of platinum (Pt) clusters on TiO2 surfaces. Efforts to enhance the efficiency and reliability of microsystems will likely use components or elements with at least one dimension smaller than a micron. The ability to design and fabricate elements at submicron dimensions-nanotechnology-is a rapidly growing area of science and technology. In this paper we describe experiments using newly generated knowledge of surfaces and the nanodimensional information provided by scanning probe microscopy (SPM) that are designed to assist development of a new generation of catalysts for application in microchemical systems. Critical questions for the design of a new catalyst is the ability to fabricate metal clusters of different sizes and their temperature stability. We report on the investigation of nucleation, growth, and temperature stability of self-organized nanoscale Pt clusters on different TiO2 surfaces using scanning tunneling microscopy (STM) and x-ray photoelectron spectroscopy (XPS). Surfaces examined include anatase (001) and rutile (110), both (1x1) and reconstructed (1x2) forms.

  6. Synthesis of surface roughed Pt nanowires and their application as electrochemical sensors for hydrogen peroxide detection.

    PubMed

    Gao, Fan; Li, Zhiyang; Ruan, Dajiang; Gu, Zhiyong

    2014-09-01

    In this paper, platinum nanowires with roughed surface textures were fabricated by a galvanostatic electrodeposition method for electrochemical sensors toward hydrogen peroxide detection. The electrochemical behavior of the glassy carbon electrode modified with these nanowires has been studied for oxidation of hydrogen peroxide by using cyclic voltammetry and amperometry in phosphate buffer solution. Surface roughness was found to enhance the sensitivity of the Pt nanowire based electrochemical sensor towards H2O2. The Pt nanowires with rough surfaces displayed higher electrocatalytic response compared to nanowires with smooth surfaces, with a sensitivity of 171 μA mM(-1) cm(-2), and linear dynamic range up to 35 mM. The nanowire concentration effect on the sensing behavior was investigated with the best sensitivity output found at a nanowire concentration of roughly 8.6 x 10(7) number of nanowires/cm2. The new sensor also showed good anti-interference property and exhibited high accuracy when a real water sample containing H2O2 was measured. PMID:25924305

  7. Light-controlled propulsion, aggregation and separation of water-fuelled TiO2/Pt Janus submicromotors and their ``on-the-fly'' photocatalytic activities

    NASA Astrophysics Data System (ADS)

    Mou, Fangzhi; Kong, Lei; Chen, Chuanrui; Chen, Zhihong; Xu, Leilei; Guan, Jianguo

    2016-02-01

    In this work, water-fuelled TiO2/Pt Janus submicromotors with light-controlled motions have been developed by utilizing the asymmetrical photocatalytic water redox reaction over TiO2/Pt Janus submicrospheres under UV irradiation. The motion state, speed, aggregation and separation behaviors of the TiO2/Pt Janus submicromotor can be reversibly, wirelessly and remotely controlled at will by regulating the ``on/off'' switch, intensity and pulsed/continuous irradiation mode of UV light. The motion of the water-fuelled TiO2/Pt Janus submicromotor is governed by light-induced self-electrophoresis under the local electrical field generated by the asymmetrical water oxidation and reduction reactions on its surface. The TiO2/Pt Janus submicromotors can interact with each other through the light-switchable electrostatic forces, and hence continuous and pulsed UV irradiation can make the TiO2/Pt Janus submicromotors aggregate and separate at will, respectively. Because of the enhanced mass exchange between the environment and active submicromotors, the separated TiO2/Pt Janus submicromotors powered by the pulsed UV irradiation show a much higher activity for the photocatalytic degradation of the organic dye than the aggregated TiO2/Pt submicromotors. The water-fuelled TiO2/Pt Janus submicromotors developed here have some outstanding advantages as ``swimming'' photocatalysts for organic pollutant remediation in the macro or microenvironment (microchannels and microwells in microchips) because of their small size, long-term stability, wirelessly controllable motion behaviors and long life span.In this work, water-fuelled TiO2/Pt Janus submicromotors with light-controlled motions have been developed by utilizing the asymmetrical photocatalytic water redox reaction over TiO2/Pt Janus submicrospheres under UV irradiation. The motion state, speed, aggregation and separation behaviors of the TiO2/Pt Janus submicromotor can be reversibly, wirelessly and remotely controlled at will by

  8. Highly Durable and Active PtFe Nanocatalyst for Electrochemical Oxygen Reduction Reaction.

    PubMed

    Chung, Dong Young; Jun, Samuel Woojoo; Yoon, Gabin; Kwon, Soon Gu; Shin, Dong Yun; Seo, Pilseon; Yoo, Ji Mun; Shin, Heejong; Chung, Young-Hoon; Kim, Hyunjoong; Mun, Bongjin Simon; Lee, Kug-Seung; Lee, Nam-Suk; Yoo, Sung Jong; Lim, Dong-Hee; Kang, Kisuk; Sung, Yung-Eun; Hyeon, Taeghwan

    2015-12-16

    Demand on the practical synthetic approach to the high performance electrocatalyst is rapidly increasing for fuel cell commercialization. Here we present a synthesis of highly durable and active intermetallic ordered face-centered tetragonal (fct)-PtFe nanoparticles (NPs) coated with a "dual purpose" N-doped carbon shell. Ordered fct-PtFe NPs with the size of only a few nanometers are obtained by thermal annealing of polydopamine-coated PtFe NPs, and the N-doped carbon shell that is in situ formed from dopamine coating could effectively prevent the coalescence of NPs. This carbon shell also protects the NPs from detachment and agglomeration as well as dissolution throughout the harsh fuel cell operating conditions. By controlling the thickness of the shell below 1 nm, we achieved excellent protection of the NPs as well as high catalytic activity, as the thin carbon shell is highly permeable for the reactant molecules. Our ordered fct-PtFe/C nanocatalyst coated with an N-doped carbon shell shows 11.4 times-higher mass activity and 10.5 times-higher specific activity than commercial Pt/C catalyst. Moreover, we accomplished the long-term stability in membrane electrode assembly (MEA) for 100 h without significant activity loss. From in situ XANES, EDS, and first-principles calculations, we confirmed that an ordered fct-PtFe structure is critical for the long-term stability of our nanocatalyst. This strategy utilizing an N-doped carbon shell for obtaining a small ordered-fct PtFe nanocatalyst as well as protecting the catalyst during fuel cell cycling is expected to open a new simple and effective route for the commercialization of fuel cells. PMID:26670103

  9. Preparation, characterization of Au (or Pt)-loaded titania nanotubes and their photocatalytic activities for degradation of methyl orange

    NASA Astrophysics Data System (ADS)

    Zhao, Qian; Li, Mei; Chu, Jinyu; Jiang, Tingshun; Yin, Hengbo

    2009-01-01

    TiO 2 nanotubes were prepared by hydrothermal method and Au (or Pt) was loaded on TiO 2 nanotubes by photodeposition method. The photocatalysts were characterized by powder X-ray diffraction (XRD), transmission electron microscopy (TEM), UV-vis diffuse reflectance spectroscopy (DRS), X-ray photoelectron spectroscopy (XPS) and N 2 adsorption technique, respectively. The photocatalytic properties of the samples were also investigated. The results show that TiO 2 nanotubes with uniform diameter were prepared, and they have specific surface areas over 400 m 2/g. The specific surface areas of TiO 2 nanotubes decrease with the increasing of calcining temperature, and crystalline phase of TiO 2 in the wall of nanotubes was transformed from anatase into rutile phase in calcination process. The photocatalytic activities of TiO 2 nanotubes are higher than that of nanosized TiO 2, and the photocatalytic activities of TiO 2 nanotubes were enhanced after loading Au (or Pt). After irradiation for 40 min under a 300 W of middle-pressure mercury lamp (MPML), the degradation rate of methyl orange solution using the Au/TiNT-500 (or Pt/TiNT-500) as a catalyst can reach 96.1% (or 95.1%). On the other hand, Au-loaded sample has evident adsorption peak in visible range, indicating that Au-loaded TiO 2 nanotubes are hopeful to become visible light photocatalyst.

  10. Synthesis of PtCu nanowires in nonaqueous solvent with enhanced activity and stability for oxygen reduction reaction

    NASA Astrophysics Data System (ADS)

    Chen, Bing; Cheng, Daojian; Zhu, Jiqin

    2014-12-01

    Pt-based core-shell electrocatalysts with one-dimensional (1D) nanostructure show a great opportunity to improve the catalytic activity and durability of pure Pt catalyst for oxygen reduction reaction (ORR). Here, we synthesize Cu@CuPt core@shell nanowires (NWs) with 1D nanostructure by using Cu NWs as templates in organic solvent medium. The ORR mass activity and specific activity of PtCu NWs are 0.216 A mgpt-1 and 0.404 mA cm-2 at 0.9 V, respectively, which are 3.1 and 3.7 times larger than that of the commercial Pt/C catalyst (0.07 A mgpt-1 and 0.110 mA cm-2, respectively). Theoretical studies suggest that the electronic effect of the Cu substrate on the Pt monolayer could be the main reason for the higher activity of PtCu NWs than that of the commercial Pt/C catalyst. In addition, the PtCu NWs show much better durability than the commercial Pt/C catalyst after stability test. It is expected that the as-synthesized PtCu NWs in organic solvent medium could be excellent candidates as high performance catalysts for ORR.

  11. Excited state lifetime during photostimulated desorption of no from a Pt surface

    NASA Astrophysics Data System (ADS)

    Magkoev, T. T.

    1998-07-01

    We analyze the rotational energy distribution N(J) for NO molecules desorbed from a Pt (111) surface, taking into account the valence electron excitations, using a simple impulse model. We find a linear dependence between ln N(J) and (Er)1/2, where Er is the rotational energy of the desorbed molecules. The excited state lifetime and the critical residence time in the excited state, evaluated from the given dependences, are close to each other, and in order of magnitude are 10-15 s. We also estimate the frequency and amplitude of the tilting vibrations of the adsorbed molecules in the excited state.

  12. Density functional theory study of the adsorption of MeOH and EtOH on the surface of Pt-decorated graphene

    NASA Astrophysics Data System (ADS)

    Rad, Ali Shokuhi

    2016-09-01

    The adsorption energies and orientation of single alcohol molecule (methanol and ethanol) on the surface of Pt-decorated graphene (PtG) were determined from first-principles density functional (DFT) calculations. We found the same adsorption energies as well as connecting distances upon adsorption of MeOH and EtOH on PtG surface, in which at their relaxed structures, the O atom of alcohol is closed to the Pt of PtG surface. We found high adsorption energies, low connecting distances, and high orbital hybridizing upon adsorption of EtOH and MeOH molecules on PtG surface. There are significant shifts in the location of both the HOMO and LUMO, in addition to variation in the charge transfer when the MeOH and EtOH are adsorbed on PtG surface.

  13. Relationship between the catalytic activity of Pt/alumina and the relaxation process of the photoexcited electrons

    NASA Astrophysics Data System (ADS)

    Ito, Junji; Hanaki, Yasunari; Shen, Qing; Toyoda, Taro

    2012-12-01

    In order to decrease the consumption of precious metals used in the catalytic converters used in automobiles, we studied the relationship between the catalytic activity of Pt/alumina (Pt/Al2O3) and the relaxation process of photoexcited electrons. Firstly, we studied the relationship between the size of the Pt particles in Pt/Al2O3 and catalytic performance. Secondly, the relationship between the size of the Pt particles in Pt/Al2O3 and the decay time of the excited electrons was studied using an improved transient grating (TG) technique. The results showed that faster decay of the excited electrons leads to greater oxidation rates. The decay time obtained with the improved TG technique gives an indication of the time that the exited electrons take to return to the ground state. According to studies utilizing FT-IR, one of the processes necessary for quickly generating CO2 with Pt is that the electron in the Ptsbnd O bond moves to the Pt side and that the Pt+ becomes Pt metal. Thus, the decay time obtained with the improved TG technique corresponds to the process whereby Pt+ returns to Pt metal. Thus, we found that the consumption of precious metals can be reduced by increasing the speed of the decay of the excited electrons.

  14. Enhancing the available specific surface area of carbon supports to boost the electroactivity of nanostructured Pt catalysts.

    PubMed

    Holade, Yaovi; Morais, Claudia; Servat, Karine; Napporn, Teko W; Kokoh, K Boniface

    2014-12-14

    We report increasing improvements in the available specific surface area of the commonly used Vulcan XC 72R and Ketjenblack EC-600JD carbons by simple thermal pre-treatment. The treated Vulcan and Ketjenblack substrates have a specific surface area of 322 and 1631 m(2) g(-1), respectively, instead of 262 and 1102 m(2) g(-1) for the as-received materials, which is a 23 and 48% improvement. Subsequently, when used as platinum nanoparticle (3 nm) supports, the electrochemical active surface area is enhanced by factors of 2.2 and 1.2 for treated Vulcan and Ketjenblack carbons, respectively. Furthermore, electrochemical investigations have highlighted a surprisingly improved catalytic activity for the pre-treated Vulcan XC 72R and Ketjenblack EC-600JD supported Pt nanoparticles. In fact, the synthesized nanostructures from the so-called "Bromide Anion Exchange" method exhibit good catalytic activity toward glucose electrooxidation, both in the alkaline medium and the phosphate buffered solution at pH 7.4. More importantly, the present catalysts are four times more active than those in the literature prepared under similar conditions for glucose dehydrogenation at low potential (0.27 V vs. Reversible Hydrogen Electrode). Consequently, these remarkable trends uncovered herein provide ample new strategic routes for the pre-treatment of Vulcan XC 72R and Ketjenblack carbons for widespread uses. PMID:25351933

  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. 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.

  17. 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.

  18. The effect of the particle size on the kinetics of CO electrooxidation on high surface area Pt catalysts.

    PubMed

    Arenz, Matthias; Mayrhofer, Karl J J; Stamenkovic, Vojislav; Blizanac, Berislav B; Tomoyuki, Tada; Ross, Phil N; Markovic, Nenad M

    2005-05-11

    Using high-resolution transmission electron microscopy (TEM), infrared reflection-absorption spectroscopy (IRAS), and electrochemical (EC) measurements, platinum nanoparticles ranging in size from 1 to 30 nm are characterized and their catalytic activity for CO electrooxidation is evaluated. TEM analysis reveals that Pt crystallites are not perfect cubooctahedrons, and that large particles have "rougher" surfaces than small particles, which have some fairly smooth (111) facets. The importance of "defect" sites for the catalytic properties of nanoparticles is probed in IRAS experiments by monitoring how the vibrational frequencies of atop CO (nu(CO)) as well as the concomitant development of dissolved CO(2) are affected by the number of defects on the Pt nanoparticles. It is found that defects play a significant role in CO "clustering"on nanoparticles, causing CO to decrease/increase in local coverage, which yields to anomalous redshift/blueshift nu(CO) frequency deviations from the normal Stark-tuning behavior. The observed deviations are accompanied by CO(2) production, which increases by increasing the number of defects on the nanoparticles, that is, 1 < or = 2 < 5 < 30 nm. We suggest that the catalytic activity for CO adlayer oxidation is predominantly influenced by the ability of the surface to dissociate water and to form OH(ad) on defect sites rather than by CO energetics. These results are complemented by chronoamperometric and rotating disk electrode (RDE) data. In contrast to CO stripping experiments, we found that in the backsweep of CO bulk oxidation, the activity increases with decreasing particle size, that is, with increasing oxophilicity of the particles. PMID:15869305

  19. Photoemission and reaction study of mass-selected Pt clusters on TiO2(110) surface

    NASA Astrophysics Data System (ADS)

    Isomura, Noritake; Watanabe, Yoshihide

    2008-03-01

    Metal cluster has been speculated to have strong size dependence in catalytic activity. The clusters on surfaces would give further specificity because of the interaction between the clusters and the surface. Catalytic properties of mass-selected metal clusters on well-defined oxide surfaces have been investigated using the new ultra high vacuum cluster deposition apparatus. In this study, we have examined catalytic and electronic properties of platinum clusters used as a composition of automotive exhaust catalysts, and used titanium dioxide as the support. Pt cluster ions were produced by a DC magnetron-sputter cluster ion source [1] with an ion funnel [2], mass-selected by a quadrupole mass filter, and then deposited on TiO2(110) single crystal surfaces. The catalytic oxidation of CO on Ptn/TiO2 (n<10) was investigated using the high-pressure reaction cell with quartz linings, which was connected to the external recirculation loop with a stainless steel bellows pump. The catalytic activity was suggested to be dependent on the size (n) of Ptn clusters. It was expected to be due to the electronic properties of the clusters. The size specificity will be discussed with the results of photoemission spectroscopy. [1] H. Haberland et al., J. Vac. Sci. Technol. A 10, 3266 (1992). [2] S.A. Shaffer el al., Rapid Commun. Mass Spectrom. 11, 1813 (1997).

  20. Synthesis and Antiproliferative Activity of Steroidal Thiosemicarbazone Platinum (Pt(II)) Complexes.

    PubMed

    Huang, Yanmin; Kong, Erbin; Gan, Chunfang; Liu, Zhiping; Lin, Qifu; Cui, Jianguo

    2015-01-01

    Steroidal compounds exhibit particular physiological activities. In this paper, some steroidal thiosemicarbazones platinum (Pt(II)) complexes were synthesized by the condensation of steroidal ketones with thiosemicarbazide using estrone, chenodeoxycholic acid, and 7-deoxycholic acid as starting materials and complexation of steroidal thiosesemicarbazones with Pt(II). The complexes were characterized by IR, NMR, and MS, and their antiproliferative activities were evaluated. The results showed that some steroidal thiosemicarbazones platinum (Pt(II)) complexes displayed moderate cytotoxicity to HeLa and Bel-7404 cells. Thereinto, complex 6 showed an excellent inhibited selectivity to HeLa cells with an IC50 value of 9.2 μM and SI value of 21.7. At the same time, all compounds were almost inactive to HEK293T (normal kidney epithelial cells). The information obtained from the studies may be useful for the design of novel chemotherapeutic drugs. PMID:26635511

  1. Synthesis and Antiproliferative Activity of Steroidal Thiosemicarbazone Platinum (Pt(II)) Complexes

    PubMed Central

    Huang, Yanmin; Kong, Erbin; Gan, Chunfang; Liu, Zhiping; Lin, Qifu; Cui, Jianguo

    2015-01-01

    Steroidal compounds exhibit particular physiological activities. In this paper, some steroidal thiosemicarbazones platinum (Pt(II)) complexes were synthesized by the condensation of steroidal ketones with thiosemicarbazide using estrone, chenodeoxycholic acid, and 7-deoxycholic acid as starting materials and complexation of steroidal thiosesemicarbazones with Pt(II). The complexes were characterized by IR, NMR, and MS, and their antiproliferative activities were evaluated. The results showed that some steroidal thiosemicarbazones platinum (Pt(II)) complexes displayed moderate cytotoxicity to HeLa and Bel-7404 cells. Thereinto, complex 6 showed an excellent inhibited selectivity to HeLa cells with an IC50 value of 9.2 μM and SI value of 21.7. At the same time, all compounds were almost inactive to HEK293T (normal kidney epithelial cells). The information obtained from the studies may be useful for the design of novel chemotherapeutic drugs. PMID:26635511

  2. An orally active antitumor cyclohexanediamine-Pt(IV) complex: trans,cis,cis-bis(n-valerato)(oxalato)(1R,2R-cyclohexane diamine)Pt(IV).

    PubMed

    Kizu, R; Nakanishi, T; Miyazaki, M; Tashiro, T; Noji, M; Matsuzawa, A; Eriguchi, M; Takeda, Y; Akiyama, N; Kidani, Y

    1996-05-01

    In order to develop orally active antitumor platinum complexes, several cyclohexanediamine-Pt(IV) complexes of a general formula trans,cis,cis-[Pt(IV) (OCOCnHn+1)2 (oxalato)(1R,2R-cyclohexanediamine)] were synthesized by derivatizing oxaliplatin [Pt(II)(oxalato)(1R,2R-cyclohexanediamine), I-OHP], which is a potent antitumor cyclohexanediamine-Pt(II) complex we have prepared and now undergoing clinical trials. The I-OHP derivatives were found to be stable, lipophilic and reduced to yield I-OHP, an active species, quantitatively by ascorbate in vitro. All the derivatives were antitumor active against mouse lymphocytic leukemia L1210 when given i.p. In particular, trans-bis-valerato-oxalato-1R,2R-dach-Pt(IV), C5-OHP, showed markedly high activity. C5-OHP also exhibited significant antitumor activity against L1210 when orally administered. C5-OHP was considered to be a suitable candidate for the oral cancer chemotherapy agent to be developed. PMID:8791997

  3. Infrared-active quadruple contrast FePt nanoparticles for multiple scale molecular imaging.

    PubMed

    Chou, Shang-Wei; Liu, Chien-Liang; Liu, Tzu-Ming; Shen, Yu-Fang; Kuo, Lun-Chang; Wu, Cheng-Ham; Hsieh, Tsung-Yuan; Wu, Pei-Chun; Tsai, Ming-Rung; Yang, Che-Chang; Chang, Kai-Yao; Lu, Meng-Hua; Li, Pai-Chi; Chen, Shi-Ping; Wang, Yu-Hsin; Lu, Chen-Wen; Chen, Yi-An; Huang, Chih-Chia; Wang, Churng-Ren Chris; Hsiao, Jong-Kai; Li, Meng-Lin; Chou, Pi-Tai

    2016-04-01

    A single nanomaterial with multiple imaging contrasts and functions is highly desired for multiscale theragnosis. Herein, we demonstrate single 1-1.9 μm infrared-active FePt alloy nanoparticles (FePt NPs) offering unprecedented four-contrast-in-one molecular imaging - computed tomography (CT), magnetic resonance imaging (MRI), photoacoustic (PA) imaging, and high-order multiphoton luminescence (HOMPL) microscopy. The PA response of FePt NPs outperforms that of infrared-active gold nanorods by 3- to 5.6-fold under identical excitation fluence and particle concentrations. HOMPL (680 nm) of an isolated FePt NP renders spatial full-width-at-half-maximum values of 432 nm and 300 nm beyond the optical diffraction limit for 1230-nm and 920-nm excitation, respectively. The in vivo targeting function was successfully visualized using HOMPL, PA imaging, CT, and MRI, thereby validating FePt as a single nanomaterial system covering up to four types (Optical/PA/CT/MRI) of molecular imaging contrast, ranging from the microscopic level to whole-body scale investigation. PMID:26854391

  4. Preparation of Pt/{PDDA-GN/PSS-GN}n multilayer films and their electrocatalytic activity regarding methanol oxidation.

    PubMed

    Huang, Xiaomei; Li, Zhongshui; Zhang, Xiaofeng; He, Xiaolei; Lin, Shen

    2013-03-01

    The stable aqueous dispersion solutions of polymer-modified graphene were prepared by reduction with hydrazine hydrate in situ from exfoliated graphite oxides in the presence of poly (diallyldimethylammonium chloride) (PDDA) and poly(sodium 4-styrenesulfonate) (PSS), respectively. The multilayer films consisting of PDDA-GN and PSS-GN were fabricated on the substrate by layer-by-layer self-assembly technique and characterized by ultraviolet-visible spectroscopy (UV-vis). The multilayer films were used as a novel catalyst support for electrodeposition of Pt nanoparticle clusters in situ. X-ray photoelectron spectroscopy (XPS), field emission scanning electron microscope (FE-SEM), and X-ray diffraction (XRD) analysis demonstrated that Pt particles had been immobilized on the surface of {PDDA-GN/PSS-GN}(n) multilayer films. Cyclic voltammetry and chronoamperometric curves were used to study electrocatalytic activity of Pt/{PDDA-GN/PSS-GN}(n) multilayer films regarding methanol oxidation. The results indicated good electrocatalytic activity of the titled multilayer composites toward methanol oxidation in the 0.5 M H(2)SO(4). PMID:23200343

  5. Activation of Homolytic Si-Zn and Si-Hg Bond Cleavage, Mediated by a Pt(0) Complex, via Novel Pt-Zn and Pt-Hg Compounds.

    PubMed

    Kratish, Yosi; Molev, Gregory; Kostenko, Arseni; Sheberla, Dennis; Tumanskii, Boris; Botoshansky, Mark; Shimada, Shigeru; Bravo-Zhivotovskii, Dmitry; Apeloig, Yitzhak

    2015-09-28

    The thermally stable [(tBuMe2 Si)2 M] (M=Zn, Hg) generate R3 Si(.) radicals in the presence of [(dmpe)Pt(PEt3 )2 ] at 60-80 °C. The reaction proceeds via hexacoordinate Pt complexes, (M=Zn (2 a and 2 b), M=Hg (3 a and 3 b)) which were isolated and characterized. Mild warming or photolysis of 2 or 3 lead to homolytic dissociation of the Pt-MSiR3 bond generating silyl radicals and novel unstable pentacoordinate platinum paramagnetic complexes (M=Zn (5), Hg (6)) whose structures were determined by EPR spectroscopy and DFT calculations. PMID:26288342

  6. Highly active nanoporous Pt-based alloy as anode and cathode catalyst for direct methanol fuel cells

    NASA Astrophysics Data System (ADS)

    Chen, Xiaoting; Jiang, Yingying; Sun, Junzhe; Jin, Chuanhong; Zhang, Zhonghua

    2014-12-01

    In this paper, we explore nanoporous PtPdAlCu (np-PtPdAlCu) quaternary alloy through ball-milling with the subsequent two-step dealloying strategy. The microstructure and catalytic performance of the np-PtPdAlCu catalyst have been characterized by X-ray diffraction (XRD), field-emission scanning electron microscopy (SEM), transmission electron microscopy (TEM), and electrochemical measurements. The np-PtPdAlCu catalyst exhibits an open bi-continuous interpenetrating ligament/channel structure with a length scale of 2.3 ± 0.5 nm. The np-PtPdAlCu catalyst shows 2 and 3.5 times enhancement in the mass activity and area specific activity towards methanol oxidation at anode respectively, compared to the Johnson Matthey (JM) Pt/C (40 wt.%) catalyst. Moreover, the CO stripping peak of np-PtPdAlCu is 0.49 V (vs. SCE), indicating a 180 mV negative shift in comparison with the Pt/C catalyst (0.67 V vs. SCE). In addition, the np-PtPdAlCu catalyst also shows an enhanced oxygen reduction reaction (ORR) activity at cathode compared to Pt/C. The present study provides a facile and effective route to design high-performance catalysts for direct methanol fuel cells (DMFCs).

  7. Ground state of Ho atoms on Pt(111) metal surfaces: Implications for magnetism

    NASA Astrophysics Data System (ADS)

    Karbowiak, M.; Rudowicz, C.

    2016-05-01

    We investigated the ground state of Ho atoms adsorbed on the Pt(111) surface, for which conflicting results exist. The density functional theory (DFT) calculations yielded the Ho ground state as | Jz=±8 > . Interpretation of x-ray absorption spectroscopy and x-ray magnetic circular dichroism spectra and the magnetization curves indicated the ground state as | Jz=±6 > . Superposition model is employed to predict the crystal-field (CF) parameters based on the structural data for the system Ho/Pt(111) obtained from the DFT modeling. Simultaneous diagonalization of the free-ion (HFI) and the trigonal CF Hamiltonian (HCF) within the whole configuration 4 f10 of H o3 + ion was performed. The role of the trigonal CF terms, neglected in the pure uniaxial CF model used previously for interpretation of experimental spectra, is found significant, whereas the sixth-rank CF terms may be neglected in agreement with the DFT predictions. The results provide substantial support for the experimental designation of the | Jz=±6 > ground state, albeit with subtle difference due to admixture of other | Jz> states, but run against the DFT-based designation of the | Jz=±8 > ground state. A subtle splitting of the ground energy level with the state (predominantly), | Jz=±6 > is predicted. This paper provides better insight into the single-ion magnetic behavior of the Ho/Pt(111) system by helping to resolve the controversy concerning the Ho ground state. Experimental techniques with greater resolution powers are suggested for direct confirmation of this splitting and C3 v symmetry experienced by the Ho atom.

  8. 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.

  9. Face-related segregation reversal at Pt 50Ni 50 surfaces studied with the embedded atom method

    NASA Astrophysics Data System (ADS)

    Deurinck, P.; Creemers, C.

    1999-11-01

    The segregation to the three low-index surfaces of a Pt50Ni50 single crystal is modelled by Monte Carlo simulations combined with the embedded atom method (EAM). Using the best fit EAM parameters from the literature for the six transition metals of the Ni and Cu groups does not yield satisfactory results. In this work the EAM parameters are recalculated and optimised exclusively for the Pt-Ni alloy system under study. Only then does EAM reliably reproduce the driving forces for segregation. The experimental results [Y. Gauthier et al., Phys. Rev. B 31 (1985) 6216; Y. Gauthier et al., Phys. Rev. B 35 (1987) 7867; S.M. Foiles, in: P.A. Dobson, A. Miller (Eds.), Surface Segregation Phenomena, CRC Press, Boca Raton, FL, 1990, p. 79] reveal a face-related segregation reversal for the Pt50Ni50 single crystal. It appears from the simulations that this is caused by a relatively small difference in surface energy in close competition with the elastic strain release. At the open (110) surface the difference in surface energy dominates causing Ni segregation. At the (100) and (111) surfaces the difference in surface energy is overpowered by the elastic strain leading to Pt segregation. The simulations are in good agreement with the experimental results and reproduce quantitatively the Ni segregation to the (110) surface and the Pt segregation to the (100) and (111) surfaces. Only at the (110) surface significant relaxations are predicted in good agreement with experimental evidence. Atomic vibrations can be included by allowing a large number of very small displacements or with a more classical treatment of vibrational entropy. Both approaches yield the same results and show that the inclusion of atomic vibrations is important only for the (110) surface and tend to attenuate the Ni segregation profile.

  10. Superior anti-CO poisoning capability: Au-decorated PtFe nanocatalysts for high-performance methanol oxidation.

    PubMed

    Cai, Zhao; Lu, Zhiyi; Bi, Yongmin; Li, Yaping; Kuang, Yun; Sun, Xiaoming

    2016-03-11

    Herein we demonstrate a surface engineering strategy, namely, decorating Au on the surface of bimetallic PtFe nanocatalysts, to effectively decrease the adsorption energy of CO on the Pt center, which promotes the electrocatalytic activity towards methanol oxidation, far better than those of PtFe and commercial Pt/C catalysts. PMID:26833455

  11. Analysis of spin-orbit coupling effects in the Pt-Si nanowires on Si(110) surface

    NASA Astrophysics Data System (ADS)

    Oh, Sehoon; Lee, Hyungjun; Choi, Hyoung Joon

    2014-03-01

    We study Pt-induced nanowires on Si(110) surface by using an ab-initio pseudopotential density-functional method. A thick slab of Si atoms is considered with Pt atoms added on the Si surface. Atomic structures of Pt-induced nanowires are determined by the total-energy minimization. We calculate surface band structures near the Fermi level and simulate scanning tunneling microscopy (STM) images and angle-resolved photoemission spectra (ARPES). We analyze the effects of the spin-orbit interaction on the electronic structure qualitatively as well as quantitatively. This work was supported by NRF of KOREA (Grant No. 2011-0018306) and KISTI supercomputing center (Project No. KSC-2013-C3-008).

  12. Oxidation of CO on a Pt-Fe alloy electrode studied by surface enhanced infrared reflection--absorption spectroscopy

    SciTech Connect

    Watanabe, Masahiro; Zhu, Yimin; Uchida, Hiroyuki

    2000-03-02

    To clarify the CO-tolerant mechanism at Pt-based alloy anode catalysts, surface-enhanced infrared reflection-absorption spectroscopy with the attenuated total reflection technique (ATR-SEIRAS), coupled with CV measurement, was used to observe the oxidation process of adsorbed CO on a typical Pt-Fe (Pt-Fe = 0.27/0.73) alloy. The alloy electrode exhibits a lower saturated coverage of CO ({theta}{sub co} = 0.55) than that of pure Pt ({theta}{sub co} = 1.0). The dominating linear CO is observed around 2,000 cm{sup {minus}1} when the equilibrium adlayer of CO covers the alloy electrode; however, linear and bridged CO and also COOH were found at the pure Pt electrode at the same CO coverage in the non-steady-state. On the basis of previous results that a Pt skin is formed during the repetitive potential cycling due to the dissolution of Fe on the alloy surface and the skin exhibits less electronic density in the d band, it can be explained that the lowered linear CO coverage and almost no bridged CO are obtained as the result of the lowered back-donation of d electrons from the Pt skin to adsorbates on the alloy surface. The wavenumber shift of the linear CO stretching to a lower value at the alloy, which is not simple predicted by the lowering of the back-donation of the electron, is ascribed to the weakening of the C -Pt bond. As a presumable effect of the electronic structure change at the Pt skin, the dissociation-oxidation of adsorbed water as well as a formation of adsorbed HOOH species are clearly observed beyond 0.6 V in the electrolyte solution without CO, which is different from that at the pure Pt electrode. Carbonate species can also be detected around 1,300--1,450 cm{sup {minus}1}, which are possibly produced by the surface reaction of CO{sub 2} with water.

  13. High viscosity to highly dispersed PtPd bimetallic nanocrystals for enhanced catalytic activity and stability.

    PubMed

    Ying, Jie; Hu, Zhi-Yi; Yang, Xiao-Yu; Wei, Hao; Xiao, Yu-Xuan; Janiak, Christoph; Mu, Shi-Chun; Tian, Ge; Pan, Mu; Van Tendeloo, Gustaaf; Su, Bao-Lian

    2016-07-01

    A facile high-viscosity-solvent method is presented to synthesize PtPd bimetallic nanocrystals highly dispersed in different mesostructures (2D and 3D structures), porosities (large and small pore sizes), and compositions (silica and carbon). Further, highly catalytic activity, stability and durability of the nanometals have been proven in different catalytic reactions. PMID:27222099

  14. Adsorption states of NO on the Pt(1 1 1) step surface

    NASA Astrophysics Data System (ADS)

    Tsukahara, N.; Mukai, K.; Yamashita, Y.; Yoshinobu, J.; Aizawa, H.

    2006-09-01

    Using infrared reflection absorption spectroscopy (IRAS) and scanning tunneling microscopy (STM), we investigated the adsorption states of NO on the Pt(9 9 7) step surface. At 90 K, we observe three N-O stretching modes at 1490 cm -1, 1631 cm -1 and 1700 cm -1 at 0.2 ML. The 1490 cm -1 and 1700 cm -1 peaks are assigned to NO molecules at fcc-hollow and on-top sites of the terrace, respectively. The 1631 cm -1 peak is assigned to the step NO species. In the present STM results, we observed that NO molecules were adsorbed at the bridge sites of the step as well as fcc-hollow and on-top sites of the terrace. To help with our assignments, density functional theory calculations were also performed. The calculated results indicate that a bridge site of the step is the most stable adsorption site for NO, and its stretching frequency is 1607 cm -1. The interactions between NO species at different sites on Pt(9 9 7) are also discussed.

  15. Flower like Bi structures on Pt surface facilitating effective cholesterol biosensing.

    PubMed

    V C, Soorya; Berchmans, Sheela

    2016-07-01

    This work demonstrates effective biosensing of cholesterol with the help of an efficient inorganic H2O2 transducer based on Pt-Bi combined with the organic enzyme platform. It could be shown that the Bi (bismuth) adatoms modified Pt (platinum) surface displays enhanced catalytic oxidation of H2O2 at neutral pH and the catalytic oxidation of H2O2 occurs at a lower potential of 0.25V vs NCE (normal calomel electrode). The sensing platform is highly sensitive and shows linear response towards [H2O2] in the absence of any redox mediator or enzyme. The H2O2 sensing platform, further modified with cholesterol oxidase led to cholesterol biosensing with a sensitivity of 3.41μAmM(-1)cm(-2). The apparent Michaelis-Menten constant (Km(app)) was calculated to be 0.43mM which indicates high binding affinity with the substrate. The cholesterol biosensor does not suffer from the interferences due to other common electroactive species and is highly stable. PMID:27127043

  16. Enhanced methanol oxidation activity and stability of Pt particles anchored on carbon-doped TiO2 nanocoating support

    NASA Astrophysics Data System (ADS)

    Qin, Yuan-Hang; Li, Yunfeng; Lv, Ren-Liang; Wang, Tie-Lin; Wang, Wei-Guo; Wang, Cun-Wen

    2015-03-01

    In this work, carbon-doped TiO2 nanocoating (TiO2-C) was prepared by a sol-gel process and employed as the support of Pt nanoparticles for methanol oxidation reaction (MOR). The obtained Pt/TiO2-C catalyst was characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and electrochemical measurements. XRD characterization shows that the average crystallite sizes of Pt particles and TiO2-C support are 2.7 and 6.5 nm, respectively. TEM characterizations show that Pt particles are highly dispersed on TiO2 nanocoating, which preserves its nanoscale structure without no apparent sintering after carbon doping. XPS characterization shows that the Pt particles anchored on TiO2-C exhibit positively shifted binding energies of Pt 4f. Cyclic voltammetry (CV) and chronoamperometry (CA) characterizations show that TiO2-C has a greatly enhanced electrical conductivity and Pt/TiO2-C catalyst has better electrocatalytic activity and stability than Pt/C catalyst for MOR, which could be attributed to the high dispersion of Pt particles on TiO2-C support, the strong metal-support interactions between Pt particles and TiO2-C support, and the rich active -OH species on TiO2-C support.

  17. Preparation of Pt-Ru-Ni ternary nanoparticles by microemulsion and electrocatalytic activity for methanol oxidation

    SciTech Connect

    Zhang Xin . E-mail: xzhang@stu.edu.cn; Zhang Feng; Guan Renfeng; Chan, K.-Y.

    2007-02-15

    Ternary platinum-ruthenium-nickel nanoparticles are prepared by water-in-oil reverse microemulsions of water/Triton X-100/propanol-2/cyclohexane. Nanoparticles formed in the microemulsions are characterized by transmission electron microscopy (TEM), electron diffraction (ED), X-ray diffractometry (XRD), energy dispersive X-ray analysis (EDX). These resulting materials showed a homogenous alloy structure, the mono-dispersion and an average diameter of 2.6 {+-} 0.3 nm with a narrow particle size distribution. The composition and particle size of ternary Pt-Ru-Ni nanoparticles can be controlled by adjusting the initial metal salt solution and preparation conditions. Pt-Ru-Ni ternary metallic nanoparticles showed an enhanced catalytic activity towards methanol oxidation compared to Pt-Ru bimetallic nanoparticles.

  18. Nickel-doped ceria nanoparticles for promoting catalytic activity of Pt/C for ethanol electrooxidation

    NASA Astrophysics Data System (ADS)

    Tan, Qiang; Du, Chunyu; Sun, Yongrong; Du, Lei; Yin, Geping; Gao, Yunzhi

    2014-10-01

    This paper reports the facile synthesis of monodispersed nickel-doped ceria nanoparticles by a thermal decomposition method, which is used to promote catalytic properties of Pt/C. The Pt/Ni-doped CeO2/C catalyst obtained exhibits remarkably high activity and stability towards the ethanol electrooxidation in acidic media. This is attributed to higher oxygen releasing capacity and stronger interaction of Ni-doped CeO2 with Pt than pure CeO2 nanoparticles that contribute positively to the removal of poisoning intermediates. We believe that the design concept and synthetic strategy of metal doped oxides used for fuel cell catalysts can be potentially extended to other catalytic fields.

  19. Influence of surface capping on oxygen reduction catalysis: A case study of 1.7 nm Pt nanoparticles

    NASA Astrophysics Data System (ADS)

    Liu, Wen; Wang, Hailiang

    2016-06-01

    Organic and polymer capping agents are prevailingly used in the synthesis of metal nanocrystals to render size and shape controls for desirable catalytic properties. A general assumption in the electrocatalysis field is that the capping agents block active sites and hinder catalytic turnover. However there have been a number of experimental results suggesting otherwise. Investigation of the fundamental correlations between the surface capping and the catalytic kinetics of metal nanoparticles is of paramount importance yet still remains challenging in large part due to structural changes induced by capping agent removal or synthesis using different capping agents. Our approach involves a unique catalyst system comprising of 1.7 nm Pt nanoparticles with and without various surface capping. We find that surface capping affects both activity and selectivity of electrocatalytic oxygen reduction reaction. The influences can be positive, neutral or negative. The five capping agents studied fall into three groups. Polyacrylic acid (PAA) and polyvinylpyrrolidone (PVP) cappings do not change the onset potential or product selectivity, but increase the catalytic current density. Sodium dodecyl sulfate (SDS) and tetradecyltrimethylammonium bromide (TTAB) cappings do not change the onset potential or product selectivity, but slightly decrease the catalytic current density. Oleylamine (OA) capping significantly decreases the onset potential and the catalytic current density as well as change the product selectivity by favoring a high percentage of 2-electron reduction.

  20. Responsivity enhancement of ZnO/Pt/MgZnO/SiO2 and MgZnO/Pt/ZnO/SiO2 structured ultraviolet detectors by surface plasmons in Pt nanoparticles

    NASA Astrophysics Data System (ADS)

    Sun, Long; Jiang, Dayong; Zhang, Guoyu; Liu, Rusheng; Duan, Qian; Qin, Jieming; Liang, Qingcheng; Gao, Shang; Hou, Janhua; Zhao, Jianxun; Liu, Wanqiang; Shen, Xiande

    2016-01-01

    The structured (ZnO/Pt/MgZnO/SiO2) ultraviolet detector was fabricated and demonstrated to investigate how metallic nanoparticles localized surface plasmons contribute when the two different dielectrics surrounded simultaneously. After sandwiching the Pt nanoparticles between the double layers of MgZnO and ZnO, the extinction was increased largely. Meanwhile, by examining the dependence of MgZnO and ZnO peak responsivity enhancement ratio, we found that MgZnO was significantly larger than ZnO. The interpretation by considering is that the localized surface plasmons of energy match with MgZnO which is superior to ZnO. In order to validate this conclusion and make it more accurate, we also fabricated the MgZnO/Pt/ZnO/SiO2 structure. Our work suggests that rational integration of double-layer and metal nanoparticles is a viable approach to perceive localized surface plasmons with double-layer ultraviolet detectors, which may help to advance optoelectronic devices.

  1. Trimetallic Au/Pt/Rh Nanoparticles as Highly Active Catalysts for Aerobic Glucose Oxidation

    NASA Astrophysics Data System (ADS)

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

    2015-02-01

    This paper reports the findings of an investigation of the correlations between the catalytic activity for aerobic glucose oxidation and the composition of Au/Pt/Rh trimetallic nanoparticles (TNPs) with average diameters of less than 2.0 nm prepared by rapid injection of NaBH4. The prepared TNPs were characterized by UV-Vis, TEM, and HR-TEM. The catalytic activity of the alloy-structured TNPs for aerobic glucose oxidation is several times higher than that of Au monometallic nanoparticles with nearly the same particle size. The catalytic activities of the TNP catalysts were dependent not only on the composition, but also on the electronic structure. The high catalytic activities of the Au/Pt/Rh TNPs can be ascribed to the formed negative-charged Au atoms due to electron donation of Rh neighboring atoms acting as catalytically active sites for aerobic glucose oxidation.

  2. Effects of Nanowire Length and Surface Roughness on the Electrochemical Sensor Properties of Nafion-Free, Vertically Aligned Pt Nanowire Array Electrodes.

    PubMed

    Li, Zhiyang; Leung, Calvin; Gao, Fan; Gu, Zhiyong

    2015-01-01

    In this paper, vertically aligned Pt nanowire arrays (PtNWA) with different lengths and surface roughnesses were fabricated and their electrochemical performance toward hydrogen peroxide (H₂O₂) detection was studied. The nanowire arrays were synthesized by electroplating Pt in nanopores of anodic aluminum oxide (AAO) template. Different parameters, such as current density and deposition time, were precisely controlled to synthesize nanowires with different surface roughnesses and various lengths from 3 μm to 12 μm. The PtNWA electrodes showed better performance than the conventional electrodes modified by Pt nanowires randomly dispersed on the electrode surface. The results indicate that both the length and surface roughness can affect the sensing performance of vertically aligned Pt nanowire array electrodes. Generally, longer nanowires with rougher surfaces showed better electrochemical sensing performance. The 12 μm rough surface PtNWA presented the largest sensitivity (654 μA·mM⁻¹·cm⁻²) among all the nanowires studied, and showed a limit of detection of 2.4 μM. The 12 μm rough surface PtNWA electrode also showed good anti-interference property from chemicals that are typically present in the biological samples such as ascorbic, uric acid, citric acid, and glucose. The sensing performance in real samples (river water) was tested and good recovery was observed. These Nafion-free, vertically aligned Pt nanowires with surface roughness control show great promise as versatile electrochemical sensors and biosensors. PMID:26404303

  3. Effects of Nanowire Length and Surface Roughness on the Electrochemical Sensor Properties of Nafion-Free, Vertically Aligned Pt Nanowire Array Electrodes

    PubMed Central

    Li, Zhiyang; Leung, Calvin; Gao, Fan; Gu, Zhiyong

    2015-01-01

    In this paper, vertically aligned Pt nanowire arrays (PtNWA) with different lengths and surface roughnesses were fabricated and their electrochemical performance toward hydrogen peroxide (H2O2) detection was studied. The nanowire arrays were synthesized by electroplating Pt in nanopores of anodic aluminum oxide (AAO) template. Different parameters, such as current density and deposition time, were precisely controlled to synthesize nanowires with different surface roughnesses and various lengths from 3 μm to 12 μm. The PtNWA electrodes showed better performance than the conventional electrodes modified by Pt nanowires randomly dispersed on the electrode surface. The results indicate that both the length and surface roughness can affect the sensing performance of vertically aligned Pt nanowire array electrodes. Generally, longer nanowires with rougher surfaces showed better electrochemical sensing performance. The 12 μm rough surface PtNWA presented the largest sensitivity (654 μA·mM−1·cm−2) among all the nanowires studied, and showed a limit of detection of 2.4 μM. The 12 μm rough surface PtNWA electrode also showed good anti-interference property from chemicals that are typically present in the biological samples such as ascorbic, uric acid, citric acid, and glucose. The sensing performance in real samples (river water) was tested and good recovery was observed. These Nafion-free, vertically aligned Pt nanowires with surface roughness control show great promise as versatile electrochemical sensors and biosensors. PMID:26404303

  4. DFT study of hydrogen fluoride and sulfur trioxide interactions on the surface of Pt-decorated graphene

    NASA Astrophysics Data System (ADS)

    Rad, Ali Shokuhi

    2016-08-01

    In this study, we investigate the adsorption properties of hydrogen florid (HF) and sulfur trioxide (SO3) on the surface of platinum decorated graphene (PtG) using density functional theory. We found one optimized configuration for HF and two ones for SO3 upon adsorption on the surface of PtG. Our result show significant adsorption on PtG with calculated energy adsorption of -73.6 (-54.2 BSSE) kJ/mol for HF at its only position and -172.4 (-144.8 BSSE) and -62.7 (-53.7 BSSE) kJ/mol for SO3 at its two positions; P1 and P2, respectively), whereas there is weak physisorption of these analytes on pristine graphene (PG). Results of charge analyses reveled interesting net charge transfer; while the direction of charge is from HF to PtG, reverse direction is found for SO3 for its two configurations. To deep understand the concept of adsorption properties, we used orbital analyses including density of states for interaction of mentioned analytes on the surface of PtG.

  5. Electrospun TiC/C nano-felt surface-decorated with Pt nanoparticles as highly efficient and cost-effective counter electrode for dye-sensitized solar cells

    NASA Astrophysics Data System (ADS)

    Zhao, Yong; Thapa, Amit; Feng, Quan; Xi, Min; Qiao, Qiquan; Fong, Hao

    2013-11-01

    Electrospun nano-felt consisting of overlaid TiC/C composite nanofibers was surface-decorated with Pt nanoparticles (Pt NPs) for use as highly efficient and cost-effective counter electrode (CE) in dye-sensitized solar cells (DSSCs). In the nanofibers, the self-generated TiC crystallites (~70 wt%) with sizes of ~20 nm were randomly embedded in carbon (~30 wt%). Upon surface-decoration, most Pt NPs were distributed on TiC crystallites, leading to substantial enhancement in the electrocatalytic activity/efficiency of Pt due to the strong interaction between Pt and TiC as well as the resulting synergetic effect on electrocatalysis. Electrochemical measurements indicated that the TiC/C-Pt CE exhibited low charge transfer resistance (Rct), large capacitance (C), and fast reaction rate towards the reduction of I3- ions, and the prototype DSSC exhibited a performance comparable to that with conventional Pt CE in terms of short circuit current density (Jsc), open circuit voltage (Voc), fill factor (FF), and energy conversion efficiency (η).

  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. New insights into the surface structure of Pt-Pd core-shell nanoparticles as revealed by Cs-corrected STEM

    NASA Astrophysics Data System (ADS)

    Khanal, Subarna; Casillas, Gilberto; Velazquez-Salazar, J. Jesus; Ponce, Arturo; Yacaman, Miguel Jose

    2012-10-01

    Bimetallic nanoparticles of Pt-Pd core-shell structures have been found to possess significant applications in fuel cells, hydrogen storage, catalysis, etc. However, the cost of Pt makes it unpractical to use in big quantities; therefore, one of the big challenges is to very small catalysts with only a few layers of the active metal in the shell in order to maximize the efficiency in their use. In this work the modified polyol method was used to synthesize Pt-Pd core-shell nanoparticles in the size range of 20 nm and characterized them by Cs-corrected scanning transmission electron microscopy. This technique allowed us to probe the structure at the atomic level of these nanoparticles revealing new structural information. We determined the structure of the three main polyhedral morphologies obtained in the synthesis: octahedral, decahedral and triangular plates. These final shapes of the core-shell structures were determined by the seed morphology. In addition the STEM energy dispersive X-ray spectroscopy (EDS) chemical analysis can be better identified the chemical composition of the nanocrystals. The overgrowth of the thin Pd shells on the Pt cores due to the epitaxial growth modes was observed. In this work, we have been able to observed Shockley partial dislocations, stacking faults, and adatoms at the surfaces of the nanoparticles.

  8. Adsorptions of SO2, SOF2, and SO2F2 on Pt-modified anatase (1 0 1) surface: Sensing mechanism study

    NASA Astrophysics Data System (ADS)

    Zhang, Xiaoxing; Chen, Qinchuan; Hu, Weihua; Zhang, Jinbin

    2015-10-01

    The type and severity of faults occurring in gas-insulated switchgear (GIS) can be assessed by detecting SF6 decomposed gases, which is significant for fault diagnosis and online condition monitoring of GIS. Characteristic decomposition components of SF6 under partial discharge or overheating faults and first-principle density functional theory calculations are adopted to analyze the adsorption of SO2, SOF2, and SO2F2 on Pt-modified anatase (1 0 1) surface and to examine further the sensing mechanism of Pt-modified anatase-based gas sensor used to detect SO2, SOF2, and SO2F2. Results show that SO2F2 molecule more easily decomposes upon adsorption on the active Pt nanoparticle than SOF2 molecule. Meanwhile, SO2 molecule does not decompose. This finding explains the phenomenon in the sensing experiment of Pt-modified TiO2 nanotube array gas sensor, wherein the response of SO2F2 is higher than that of SOF2 at the optimal temperature of the sensor. Moreover, the responses of SO2F2 and SOF2 significantly change at the optimal temperature, whereas the response of SO2 is nearly unchanged.

  9. Effect of Ni(111) surface alloying by Pt on partial oxidation of methane to syngas: A DFT study

    NASA Astrophysics Data System (ADS)

    Zhang, Minhua; Yang, Kuiwei; Zhang, Xiaohang; Yu, Yingzhe

    2014-12-01

    Density functional theory calculations were performed to study the adsorption and dissociation of methane as well as syngas formation over Ni(111) and NiPt(111) aiming to gain insight into the effect of Ni(111) surface alloying on partial oxidation of methane (POM). Results show that Pt-doped Ni(111) surface is beneficial to the adsorption of CHx and H species while unfavorable to the desorption of H2. The process of CH → C + H is found to be the rate-limiting step of successive dehydrogenation of methane on NiPt(111). Especially, the processes of CH4 → CH3 + H and CH3 → CH2 + H proceed more easily on NiPt(111) than on Ni(111). Three potential pathways for CO formation in the POM process were proposed and calculations identified that CH + O → CHO → CO + H are likely to be the main routes for CO formation on Ni(111) with CH + O → CHO as the rate-limiting step. Further calculations reveal that the formation of CO and H2 may be more difficult on NiPt(111) than on Ni(111).

  10. Chemical corrosion of PtRuCu6/C for highly efficient methanol oxidation

    NASA Astrophysics Data System (ADS)

    Huang, Meihua; Wu, Chuxin; Guan, Lunhui

    2016-02-01

    Until now, Pt is commonly used as anode catalyst for methanol oxidation in direct methanol fuel cells. Here we report that chemical corrosion of PtRuCu6/C, which was prepared by microwave-polyol technique, promotes the activity of Pt for methanol oxidation. The PtRuCu6/C is chemically corroded, and the obtained sample is denoted as PtRuCu6-A/C. The PtRuCu6-A/C contains a Pt-Ru-Cu core and Pt-Ru shell with surface defects. The PtRuCu6-A/C has surface activity and mass activity 10.6 and 6.0 times higher than those of Pt/C for methanol oxidation. And the surface activity and mass activity of PtRuCu6-A/C are 3.3 and 3.9 times higher than those of PtRu/C for methanol oxidation. The enhanced activity of PtRuCu6-A/C is attributed to the surface defects and the stronger electronic modification of Pt. This facile preparation strategy provides a new route of synthesizing highly active catalysts for methanol oxidation.

  11. Surface-initiated growth of ionomer films from pt-modified gold electrodes.

    PubMed

    Berron, Brad J; Faulkner, Christopher J; Fischer, Remington E; Payne, P Andrew; Jennings, G Kane

    2009-11-01

    The ability to chemically wire ionomer films to electrode surfaces can promote transport near interfaces and impact a host of energy-related applications. Here, we demonstrate proof-of-concept principles for the surface-initiated ring-opening metathesis polymerization (SI-ROMP) of norbornene (NB), 5-butylnorbornene (NBH4), and 5-perfluorobutylnorbornene (NBF4) from Pt-modified gold substrates and the subsequent sulfonation of olefins along the polymer backbones to produce ultrathin sulfonated polymer films. Prior to sulfonation, the films are hydrophobic and exhibit large barriers against ion transport, but sulfonation dramatically reduces the resistance of the films by providing pathways for proton diffusion. Sulfonated films derived from NBF4 and NBH4 yield more anodic potentials for oxygen reduction than those derived from NB or unfunctionalized electrodes. These improvements are consistent with hydrophobic structuring by the fluorocarbon or hydrocarbon side groups to minimize interfacial flooding and generate pathways for enhanced O(2) permeation near the interface. Importantly, we demonstrate that the sulfonated polymer chains remain anchored to the surface during voltammetry for oxygen reduction whereas short-chain thiolates that do not tether polymer are removed from the substrate. This approach, which we extend to unmodified gold electrodes at neutral pH, presents a method of cleaning the ionomer/electrode interface to remove molecular components that may hamper the performance of the electrode. PMID:19637878

  12. Surface profile control of FeNiPt/Pt core/shell nanowires for oxygen reduction reaction

    SciTech Connect

    Zhu, Huiyuan; Zhang, Sen; Su, Dong; Jiang, Guangming; Sun, Shouheng

    2015-03-18

    The ever-increasing energy demand requires renewable energy schemes with low environmental impacts. Electrochemical energy conversion devices, such as fuel cells, combine fuel oxidization and oxygen reduction reactions and have been studied extensively for renewable energy applications. However, their energy conversion efficiency is often limited by kinetically sluggish chemical conversion reactions, especially oxygen reduction reaction (ORR). [1-5] To date, extensive efforts have been put into developing efficient ORR catalysts with controls on catalyst sizes, compositions, shapes and structures. [6-12] Recently, Pt-based catalysts with core/shell and one-dimensional nanowire (NW) morphologies were found to be promising to further enhance ORR catalysis. With the core/shell structure, the ORR catalysis of a nanoparticle (NP) catalyst can be tuned by both electronic and geometric effects at the core/shell interface. [10,13,14] With the NW structure, the catalyst interaction with the conductive support can be enhanced to facilitate electron transfer between the support and the NW catalyst and to promote ORR. [11,15,16]

  13. Surface profile control of FeNiPt/Pt core/shell nanowires for oxygen reduction reaction

    DOE PAGESBeta

    Zhu, Huiyuan; Zhang, Sen; Su, Dong; Jiang, Guangming; Sun, Shouheng

    2015-03-18

    The ever-increasing energy demand requires renewable energy schemes with low environmental impacts. Electrochemical energy conversion devices, such as fuel cells, combine fuel oxidization and oxygen reduction reactions and have been studied extensively for renewable energy applications. However, their energy conversion efficiency is often limited by kinetically sluggish chemical conversion reactions, especially oxygen reduction reaction (ORR). [1-5] To date, extensive efforts have been put into developing efficient ORR catalysts with controls on catalyst sizes, compositions, shapes and structures. [6-12] Recently, Pt-based catalysts with core/shell and one-dimensional nanowire (NW) morphologies were found to be promising to further enhance ORR catalysis. With themore » core/shell structure, the ORR catalysis of a nanoparticle (NP) catalyst can be tuned by both electronic and geometric effects at the core/shell interface. [10,13,14] With the NW structure, the catalyst interaction with the conductive support can be enhanced to facilitate electron transfer between the support and the NW catalyst and to promote ORR. [11,15,16]« less

  14. One-Step Synthesis of Pt/Graphene Composites from Pt Acid Dissolved Ethanol via Microwave Plasma Spray Pyrolysis.

    PubMed

    Jo, Eun Hee; Chang, Hankwon; Kim, Sun Kyung; Choi, Ji-Hyuk; Park, Su-Ryeon; Lee, Chong Min; Jang, Hee Dong

    2016-01-01

    Pt nanoparticles-laden graphene (Pt/GR) composites were synthesized in the gas phase from a mixture of ethanol and Pt precursor by microwave plasma spray pyrolysis. The morphology of Pt/GR composites has the shape of wrinkled sheets of paper, while Pt nanoparticles (Pt NPs) that are less than 2.6 nm in the mean diameter are uniformly well deposited on the surface of GR sheets stacked in only three layers. The Pt/GR composite prepared with 20 wt% of Pt had the highest specific surface area and electrochemical surface area of up to 402 m(2) g(-1) and 77 m(2) g(-1) (Pt), respectively. In addition, the composite showed superior electrocatalytic activity compared with commercial Pt-carbon black. The excellent electrocatalytic activity was attributed to the high specific surface area and electrochemical surface area of the Pt/GR composite directly produced by microwave plasma spray pyrolysis. Thus, it is clearly expected that the Pt/GR composite is a promising material for DMFC catalysts. PMID:27622908

  15. The preparation of large surface area lanthanum based perovskite supports for AuPt nanoparticles: tuning the glycerol oxidation reaction pathway by switching the perovskite B site.

    PubMed

    Evans, Christopher D; Kondrat, Simon A; Smith, Paul J; Manning, Troy D; Miedziak, Peter J; Brett, Gemma L; Armstrong, Robert D; Bartley, Jonathan K; Taylor, Stuart H; Rosseinsky, Matthew J; Hutchings, Graham J

    2016-07-01

    Gold and gold alloys, in the form of supported nanoparticles, have been shown over the last three decades to be highly effective oxidation catalysts. Mixed metal oxide perovskites, with their high structural tolerance, are ideal for investigating how changes in the chemical composition of supports affect the catalysts' properties, while retaining similar surface areas, morphologies and metal co-ordinations. However, a significant disadvantage of using perovskites as supports is their high crystallinity and small surface area. We report the use of a supercritical carbon dioxide anti-solvent precipitation methodology to prepare large surface area lanthanum based perovskites, making the deposition of 1 wt% AuPt nanoparticles feasible. These catalysts were used for the selective oxidation of glycerol. By changing the elemental composition of the perovskite B site, we dramatically altered the reaction pathway between a sequential oxidation route to glyceric or tartronic acid and a dehydration reaction pathway to lactic acid. Selectivity profiles were correlated to reported oxygen adsorption capacities of the perovskite supports and also to changes in the AuPt nanoparticle morphologies. Extended time on line analysis using the best oxidation catalyst (AuPt/LaMnO3) produced an exceptionally high tartronic acid yield. LaMnO3 produced from alternative preparation methods was found to have lower activities, but gave comparable selectivity profiles to that produced using the supercritical carbon dioxide anti-solvent precipitation methodology. PMID:27074316

  16. Hot-Electron-Induced Highly Efficient O2 Activation by Pt Nanoparticles Supported on Ta2O5 Driven by Visible Light.

    PubMed

    Sakamoto, Hirokatsu; Ohara, Tomoyuki; Yasumoto, Naoki; Shiraishi, Yasuhiro; Ichikawa, Satoshi; Tanaka, Shunsuke; Hirai, Takayuki

    2015-07-29

    Aerobic oxidation on a heterogeneous catalyst driven by visible light (λ >400 nm) at ambient temperature is a very important reaction for green organic synthesis. A metal particles/semiconductor system, driven by charge separation via an injection of "hot electrons (e(hot)(-))" from photoactivated metal particles to semiconductor, is one of the promising systems. These systems, however, suffer from low quantum yields for the reaction (<5% at 550 nm) because the Schottky barrier created at the metal/semiconductor interface suppresses the e(hot)(-) injection. Some metal particle systems promote aerobic oxidation via a non-e(hot)(-)-injection mechanism, but require high reaction temperatures (>373 K). Here we report that Pt nanoparticles (∼5 nm diameter), when supported on semiconductor Ta2O5, promote the reaction without e(hot)(-) injection at room temperature with significantly high quantum yields (∼25%). Strong Pt-Ta2O5 interaction increases the electron density of the Pt particles and enhances interband transition of Pt electrons by absorbing visible light. A large number of photogenerated e(hot)(-) directly activate O2 on the Pt surface and produce active oxygen species, thus promoting highly efficient aerobic oxidation at room temperature. PMID:26158296

  17. Genesis and evolution of surface species during Pt atomic layer deposition on oxide supports characterized by in-situ XAFS analysis and water-gas shift reaction.

    SciTech Connect

    Setthapun, W.; Williams, W.; Kim, S.; Feng, H.; Elam, J.; Rabuffetti, F.; Poeppelmeier, K.; Stair, P.; Stach, E.; Ribeiro, F.; Miller, J.; Marshall, C.; Northwestern Univ.; Purdue Univ.

    2010-06-03

    Platinum atomic layer deposition (ALD) using MeCpPtMe{sub 3} was employed to prepare high loadings of uniform-sized, 1-2 nm Pt nanoparticles on high surface area Al{sub 2}O{sub 3}, TiO{sub 2}, and SrTiO{sub 3} supports. X-ray absorption fine structure was utilized to monitor the changes in the Pt species during each step of the synthesis. The temperature, precursor exposure time, treatment gas, and number of ALD cycles were found to affect the Pt particle size and density. Lower-temperature MeCpPtMe{sub 3} adsorption yielded smaller particles due to reduced thermal decomposition. A 300 C air treatment of the adsorbed MeCpPtMe{sub 3} leads to PtO. In subsequent ALD cycles, the MeCpPtMe{sub 3} reduces the PtO to metallic Pt in the ratio of one precursor molecule per PtO. A 200 C H{sub 2} treatment of the adsorbed MeCpPtMe{sub 3} leads to the formation of 1-2 nm, metallic Pt nanoparticles. During subsequent ALD cycles, MeCpPtMe{sub 3} adsorbs on the support, which, upon reduction, yields additional Pt nanoparticles with a minimal increase in size of the previously formed nanoparticles. The catalysts produced by ALD had identical water-gas shift reaction rates and reaction kinetics to those of Pt catalysts prepared by standard solution methods. ALD synthesis of catalytic nanoparticles is an attractive method for preparing novel model and practical catalysts.

  18. 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

  19. A novel Pt-Co alloy hydrogen anode catalyst with superlative activity, CO-tolerance and robustness

    NASA Astrophysics Data System (ADS)

    Shi, G. Y.; Yano, H.; Tryk, D. A.; Watanabe, M.; Iiyama, A.; Uchida, H.

    2016-07-01

    PtCo nanoparticles, having two atomic layers of stabilized Pt skin, supported on carbon black (Pt2AL-PtCo/C), exhibited superlative mass activity for the CO-tolerant hydrogen oxidation reaction (HOR), together with high robustness with respect to air exposure, as a novel anode catalyst in reformate gas-based polymer electrolyte fuel cells. The high area-specific HOR activity and CO tolerance are consistent with DFT calculations.PtCo nanoparticles, having two atomic layers of stabilized Pt skin, supported on carbon black (Pt2AL-PtCo/C), exhibited superlative mass activity for the CO-tolerant hydrogen oxidation reaction (HOR), together with high robustness with respect to air exposure, as a novel anode catalyst in reformate gas-based polymer electrolyte fuel cells. The high area-specific HOR activity and CO tolerance are consistent with DFT calculations. Electronic supplementary information (ESI) available: Experimental details, TEM images and particle size distribution histograms of all catalysts, and details of the DFT calculations. See DOI: 10.1039/c6nr00778c

  20. Electrostatic Self-Assembly of Pt-around-Au Nanocomposite with High Activity towards Formic Acid Oxidation

    SciTech Connect

    Zhang, Sheng; Shao, Yuyan; Yin, Geping; Lin, Yuehe

    2010-03-01

    Pt-around-Au nanocomposite is synthesized using the electrostatic selfassembly method. This catalyst shows significantly improved activity towards formic acid oxidation. The possible reason is the efficient spillover of HCOO from Au to the surrounding Pt NPs, where HCOO is further oxidized to CO2.

  1. Structural and chemical characteristics of atomically smooth GaN surfaces prepared by abrasive-free polishing with Pt catalyst

    NASA Astrophysics Data System (ADS)

    Murata, Junji; Sadakuni, Shun; Okamoto, Takeshi; Hattori, Azusa N.; Yagi, Keita; Sano, Yasuhisa; Arima, Kenta; Yamauchi, Kazuto

    2012-06-01

    This paper reports the structural and chemical characteristics of atomically flat gallium nitride (GaN) surfaces prepared by abrasive-free polishing with platinum (Pt) catalyst. Atomic force microscopy revealed regularly alternating wide and narrow terraces with a step height equivalent to that of a single bilayer on the flattened GaN surfaces, which originate from the differences in etching rate of two neighboring terraces. The material removal characteristics of the method for GaN surfaces were investigated in detail. We confirmed that an atomically smooth GaN surface with an extremely small number of surface defects, including pits and scratches, can be achieved, regardless of the growth method, surface polarity, and doping concentration. X-ray photoelectron spectroscopy showed that the flattening method produces clean GaN surfaces with only trace impurities such as Ga oxide and metallic Ga. Contamination with the Pt catalyst was also evaluated using total-reflection X-ray fluorescence analysis. A wet cleaning method with aqua regia is proposed, which markedly eliminates this Pt contamination without affecting the surface morphology.

  2. Tuning the surface structure of supported PtNi(x) bimetallic electrocatalysts for the methanol electro-oxidation reaction.

    PubMed

    Zhang, Bingsen; Niu, Yiming; Xu, Junyuan; Pan, Xiaoli; Chen, Cheng-Meng; Shi, Wen; Willinger, Marc-Georg; Schlögl, Robert; Su, Dang Sheng

    2016-03-11

    The structures of PtNix nanoalloy particles were modified through thermal annealing in different atmospheres. The evolution of surface structures was uncovered by advanced transmission electron microscopy, and the structure-function correlation in methanol electro-oxidation was probed. It provided new insights into the design and synthesis of highly efficient electrocatalysts. PMID:26871308

  3. High-activity mesoporous Pt/Ru catalysts for methanol oxidation.

    PubMed

    Franceschini, Esteban A; Bruno, Mariano M; Williams, Federico J; Viva, Federico A; Corti, Horacio R

    2013-11-13

    High activity mesoporous Pt/Ru catalysts with 2D-hexagonal structure were synthesized using a triblock poly(ethylene oxide)-b-poly(propylene oxide)-b-poly(ethylene oxide) copolymer (Pluronic F127) template. The normalized mass activities for the methanol oxidation reaction (MOR) of the Pt/Ru catalysts with a regular array of pores is higher than those reported for nanoparticulated Pt/Ru catalysts. Different kinetic parameters, as Tafel slope and activation energy, were obtained for the MOR on the mesoporous catalysts. Results indicated that catalysts performance depends on pore size. Mass activities and the CO2 conversion efficiency for large pore size mesoporous catalysts (10 nm) are greater than those reported for smaller pore size mesoporous catalysts with similar composition. The effect of pore size on catalysts performance is related to the greater accessibility of methanol to the active areas inside large pores. Consequently, the overall residence time of methanol increases as compared with mesoporous catalyst with small pores. PMID:24083938

  4. Correlating the chemical composition and size of various metal oxide substrates with the catalytic activity and stability of as-deposited Pt nanoparticles for the methanol oxidation reaction

    SciTech Connect

    Megan E. Scofield; Wong, Stanislaus S.; Koenigsmann, Christopher; Bobb-Semple, Dara; Tao, Jing; Tong, Xiao; Wang, Lei; Lewis, Crystal S.; Vuklmirovic, Miomir; Zhu, Yimei; Adzic, Radoslav R.

    2015-12-09

    The performance of electrode materials in conventional direct alcohol fuel cells (DAFC) is constrained by (i) the low activity of the catalyst materials relative to their overall cost, (ii) the poisoning of the active sites due to the presence of partially oxidized carbon species (such as but not limited to CO, formate, and acetate) produced during small molecule oxidation, and (iii) the lack of catalytic stability and durability on the underlying commercial carbon support. Therefore, as a viable alternative, we have synthesized various metal oxide and perovskite materials of different sizes and chemical compositions as supports for Pt nanoparticles (NPs). Our results including unique mechanistic studies demonstrate that the SrRuO3 substrate with immobilized Pt NPs at its surface evinces the best methanol oxidation performance as compared with all of the other substrate materials tested herein, including commercial carbon itself. In addition, data from electron energy loss spectroscopy (EELS) and X-ray photoelectron spectroscopy (XPS) confirmed the presence of electron transfer from bound Pt NPs to surface Ru species within the SrRuO3 substrate itself, thereby suggesting that favorable metal support interactions are responsible for the increased methanol oxidation reaction (MOR) activity of Pt species with respect to the underlying SrRuO3 composite catalyst material.

  5. Correlating the chemical composition and size of various metal oxide substrates with the catalytic activity and stability of as-deposited Pt nanoparticles for the methanol oxidation reaction

    DOE PAGESBeta

    Megan E. Scofield; Wong, Stanislaus S.; Koenigsmann, Christopher; Bobb-Semple, Dara; Tao, Jing; Tong, Xiao; Wang, Lei; Lewis, Crystal S.; Vuklmirovic, Miomir; Zhu, Yimei; et al

    2015-12-09

    The performance of electrode materials in conventional direct alcohol fuel cells (DAFC) is constrained by (i) the low activity of the catalyst materials relative to their overall cost, (ii) the poisoning of the active sites due to the presence of partially oxidized carbon species (such as but not limited to CO, formate, and acetate) produced during small molecule oxidation, and (iii) the lack of catalytic stability and durability on the underlying commercial carbon support. Therefore, as a viable alternative, we have synthesized various metal oxide and perovskite materials of different sizes and chemical compositions as supports for Pt nanoparticles (NPs).more » Our results including unique mechanistic studies demonstrate that the SrRuO3 substrate with immobilized Pt NPs at its surface evinces the best methanol oxidation performance as compared with all of the other substrate materials tested herein, including commercial carbon itself. In addition, data from electron energy loss spectroscopy (EELS) and X-ray photoelectron spectroscopy (XPS) confirmed the presence of electron transfer from bound Pt NPs to surface Ru species within the SrRuO3 substrate itself, thereby suggesting that favorable metal support interactions are responsible for the increased methanol oxidation reaction (MOR) activity of Pt species with respect to the underlying SrRuO3 composite catalyst material.« less

  6. Self-assembly growth of alloyed NiPt nanocrystals with holothuria-like shape for oxygen evolution reaction with enhanced catalytic activity

    NASA Astrophysics Data System (ADS)

    Ding, Tao; Wang, Wenliang; Zhou, Xiaoli; Zhang, Li; Wang, Chunde; Jiang, Jun; Yang, Weilai; Yang, Qing

    2016-01-01

    Self-assembly growth of alloyed NiPt nanocrystals with holothuria-like wire shape has been achieved via a facile and moderate hydrothermal process at 120 °C for 1 h from the reaction of nickel nitrate and chloroplatinic acid in alkaline solution in the presence of ethanediamine and hydrazine hydrate. The holothuria-like alloyed NiPt wires are Ni-rich in composition (Ni23.6Pt) and uniform in diameter with many tiny tips outstretched from the wires surface. The holothuria-like wires are assembled from granular subunits with the assistance of capping molecular of ethanediamine and the wires display an improved oxygen evolution reaction catalytic activity.

  7. 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.

  8. Selectivity of Chemisorbed Oxygen in C–H Bond Activation and CO Oxidation and Kinetic Consequences for CH₄–O₂ Catalysis on Pt and Rh Clusters

    SciTech Connect

    Chin, Ya-Huei; Buda, Corneliu; Neurock, Matthew; Iglesia, Enrique

    2011-10-06

    Rate measurements, density functional theory (DFT) within the framework of transition state theory, and ensemble-averaging methods are used to probe oxygen selectivities, defined as the reaction probability ratios for O* reactions with CO and CH₄, during CH₄–O₂ catalysis on Pt and Rh clusters. CO₂ and H₂O are the predominant products, but small amounts of CO form as chemisorbed oxygen atoms (O*) are depleted from cluster surfaces. Oxygen selectivities, measured using ¹²CO–¹³CH₄–O₂ reactants, increase with O₂/ CO ratio and O* coverage and are much larger than unity at all conditions on Pt clusters. These results suggest that O* reacts much faster with CO than with CH₄, causing any CO that forms and desorbs from metal cluster surfaces to react along the reactor bed with other O* to produce CO₂ at any residence time required for detectable extents of CH₄ conversion. O* selectivities were also calculated by averaging DFTderived activation barriers for CO and CH₄ oxidation reactions over all distinct surface sites on cubo-octahedral Pt clusters (1.8 nm diameter, 201 Pt atoms) at low O* coverages, which are prevalent at low O₂ pressures during catalysis. CO oxidation involves non-activated molecular CO adsorption as the kinetically relevant step on exposed Pt atoms vicinal of chemisorbed O* atoms (on *–O* site pairs). CH₄ oxidation occurs via kinetically relevant C–H bond activation on *–* site pairs involving oxidative insertion of a Pt atom into one of the C–H bonds in CH₄, forming a three-centered HC₃–Pt–H transition state. C–H bond activation barriers reflect the strength of Pt–CH₃ and Pt–H interactions at the transition state, which correlates, in turn, with the Pt coordination and with CH₃ * binding energies. Ensemble-averaged O* selectivities increase linearly with O₂/CO ratios, which define the O* coverages, via a proportionality constant. The proportionality constant is given by the ratio of rate

  9. A RHEED study of 1 × n reconstructions of the Pt(110) surface

    NASA Astrophysics Data System (ADS)

    Stock, M.; Risse, J.; Korte, U.; Meyer-Emsen, G.

    1990-07-01

    1 × n ( n = 2-5) reconstructions of Pt(110) which have been partly observed with LEED previously were investigated with RHEED. Using Ino's photographic beam rocking method, Patterson-like one-dimensional distribution functions were obtained from averaged intensities. The distributions for 1 × 2 and 1 × 3 are consistent with the accepted missing-row and facetting models, respectively, which exhibit small (111) facets. They reveal further that 1 × 4 is a modified 1 × 2 structure. 1 × 5 is a periodic mixing of 1 × 2 and 1 × 3. Therefore facets larger than for 1 × 3 as have been assumed so far in stability considerations for higher order reconstructions of noble metals are improbable. Increasing Ca concentrations (in the % region) are found with AES in the sequence 1 × 2, 1 × 5, 1 × 3, where 1 × 2 and 1 × 4 are the only structures observed on a clean surface. This correlates with the mean facet size of the structures. A fully dynamical evaluation of diffracted fractional order beams for the 1× 2 surface was carried out using an efficient algorithm for the simultaneous fit of several parameters. Relaxations of the first and second layer ( R1 = -27%, R2 = 5%), pairing the second ( P 2 = 0.08 Å) and buckling of the third layer ( B 3 = 0.18 Å peak to peak) were determined. These are compatible with some LEED and MEIS results.

  10. Adsorption of halide anions at the Pt(111)-solution interfacestudied by in situ surface x-ray scattering

    NASA Astrophysics Data System (ADS)

    Lucas, C. A.; Marković, N. M.; Ross, P. N.

    1997-03-01

    In this paper we present x-ray scattering results of iodide, bromide, and chloride adsorption onto the Pt(111) surface in solution. Iodide forms two commensurate adlayer structures, a (7×7)R19.1° phase and a hexagonal (3×3) phase, which coexist on the Pt surface. Formation of the (3×3) phase appears to be kinetically limited, whereas the 7 phase shows a hysteretic effect as a function of the electrode potential, associated with an order-disorder transition. Bromide forms a series of high-order commensurate structures on Pt(111) that are poorly ordered unless the size of the unit cell is small. No ordered structures for chloride adsorption are observed and specular x-ray reflectivity results suggest that the chloride coverage at low potential is too small to form a close-packed monolayer on the surface. The differences between the structures formed by the adsorbed anions, and the differences between results for Pt(111) and Au(111), are discussed in terms of the strength of the metal-halide interaction.

  11. CO oxidation of Pt nanostructures supported by TiO2/Ti.

    PubMed

    Kim, Kwang-Dae; Tai, Wei Sheng; Kim, Young Dok

    2010-01-01

    This study examined the CO oxidation reactivity of Pt deposited on TiO2. The Pt catalysts were prepared by the evaporation of Pt on Ti foils covered with TiO2, and their surface structures were characterized by scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). Separate Pt nanoparticles could be observed with lower amounts of deposited Pt (<2 nm). With increasing Pt thickness, these Pt nanoparticles appeared to agglomerate into more complicated nanostructures. When approximately 5 nm of Pt was deposited, the TiO2 surface was almost completely covered by Pt. Additional deposition of Pt on these complete Pt-layers resulted in the deposition of small nanoparticles (approximately 5 nm) on top of the Pt underlayer. The CO oxidation reactivity at 160 degrees C, normalized with respect to the Pt thickness, initially decreased with increasing amount of Pt. This was attributed mainly to the decrease in the surface-to-volume ratio. However, the reactivity increased when the amount of Pt exceeded 5 nm, which can be rationalized in part by the unique structural properties of Pt-films according to SEM imaging. We also suggest that a stronger influence of the metal-support interactions at lower Pt coverages results in reduced catalytic activity. PMID:20352865

  12. Europa's Active Surface

    NASA Technical Reports Server (NTRS)

    1996-01-01

    A newly discovered impact crater can be seen just right of the center of this image of Jupiter's moon Europa returned by NASA's Galileo spacecraft camera. The crater is about 30 kilometers (18.5 miles) in diameter. The impact excavated into Europa's icy crust, throwing debris (seen as whitish material) across the surrounding terrain. Also visible is a dark band, named Belus Linea, extending east-west across the image. This type of feature, which scientists call a 'triple band,' is characterized by a bright stripe down the middle. The outer margins of this and other triple bands are diffuse, suggesting that the dark material was put there as a result of possible geyser-like activity which shot gas and rocky debris from Europa's interior. The curving 'X' pattern seen in the lower left corner of the image appears to represent fracturing of the icy crust and infilling by slush which froze in place. The crater is centered at about 2 degrees north latitude by 239 degrees west longitude. The image was taken from a distance of 156,000 kilometers (about 96,300 miles) on June 27, 1996, during Galileo's first orbit around Jupiter. The area shown is 860 by 700 kilometers (530 by 430 miles), or about the size of Oregon and Washington combined. The Galileo mission is managed by NASA's Jet Propulsion Laboratory.

  13. Control of crystallographic texture and surface morphology of Pt/Tio2 templates for enhanced PZT thin film texture.

    PubMed

    Fox, Austin J; Drawl, Bill; Fox, Glen R; Gibbons, Brady J; Trolier-McKinstry, Susan

    2015-01-01

    Optimized processing conditions for Pt/TiO2/SiO2/Si templating electrodes were investigated. These electrodes are used to obtain [111] textured thin film lead zirconate titanate (Pb[ZrxTi1-x ]O3 0 ≤ x ≤ 1) (PZT). Titanium deposited by dc magnetron sputtering yields [0001] texture on a thermally oxidized Si wafer. It was found that by optimizing deposition time, pressure, power, and the chamber pre-conditioning, the Ti texture could be maximized while maintaining low surface roughness. When oxidized, titanium yields [100]-oriented rutile. This seed layer has as low as a 4.6% lattice mismatch with [111] Pt; thus, it is possible to achieve strongly oriented [111] Pt. The quality of the orientation and surface roughness of the TiO2 and the Ti directly affect the achievable Pt texture and surface morphology. A transition between optimal crystallographic texture and the smoothest templating surface occurs at approximately 30 nm of original Ti thickness (45 nm TiO2). This corresponds to 0.5 nm (2 nm for TiO2) rms roughness as determined by atomic force microscopy and a full-width at half-maximum (FWHM) of the rocking curve 0002 (200) peak of 5.5/spl degrees/ (3.1/spl degrees/ for TiO2). A Pb[Zr0.52Ti 0.48]O3 layer was deposited and shown to template from the textured Pt electrode, with a maximum [111] Lotgering factor of 87% and a minimum 111 FWHM of 2.4/spl degrees/ at approximately 30 nm of original Ti. PMID:25585390

  14. 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.

  15. Creating single-atom Pt-ceria catalysts by surface step decoration

    PubMed Central

    Dvořák, Filip; Farnesi Camellone, Matteo; Tovt, Andrii; Tran, Nguyen-Dung; Negreiros, Fabio R.; Vorokhta, Mykhailo; Skála, Tomáš; Matolínová, Iva; Mysliveček, Josef; Matolín, Vladimír; Fabris, Stefano

    2016-01-01

    Single-atom catalysts maximize the utilization of supported precious metals by exposing every single metal atom to reactants. To avoid sintering and deactivation at realistic reaction conditions, single metal atoms are stabilized by specific adsorption sites on catalyst substrates. Here we show by combining photoelectron spectroscopy, scanning tunnelling microscopy and density functional theory calculations that Pt single atoms on ceria are stabilized by the most ubiquitous defects on solid surfaces—monoatomic step edges. Pt segregation at steps leads to stable dispersions of single Pt2+ ions in planar PtO4 moieties incorporating excess O atoms and contributing to oxygen storage capacity of ceria. We experimentally control the step density on our samples, to maximize the coverage of monodispersed Pt2+ and demonstrate that step engineering and step decoration represent effective strategies for understanding and design of new single-atom catalysts. PMID:26908356

  16. Influence of the oxidative/reductive treatments on the activity of Pt/Ce 0.67Zr 0.33O 2 catalyst

    NASA Astrophysics Data System (ADS)

    Fan, Jun; Wu, Xiaodong; Ran, Rui; Weng, Duan

    2005-05-01

    A Pt/Ce 0.67Zr 0.33O 2 powder catalyst was prepared by sol-gel method. The as-received sample was successively oxidized, reduced and re-oxidized. The samples were characterized by XRD, XPS, TPR and three-way catalytic activity evaluation. The results supported the re-organization of the support and the occurrence of a strong metal-support interaction (SMSI) effect between platinum and ceria-zirconia mixed oxides. The oxidative/reductive atmosphere affected the structure and performance of the catalyst by the SMSI. It was suggested that a migration of Ce 4+ from the bulk to the surface of the support took place during the reductive treatment, resulting in a formation of ceria-rich phase on the surface. The diffusion process was reversed when the atmosphere was switched to an oxidative one. The status of decoration or encapsulation of Pt by ceria-rich phase changed with the atmosphere, and hereby affected the activity of the catalyst. At temperatures below 300 °C, the re-oxidized sample exhibited the best activity while the reduced one behaved the worst on the conversion of NO and CO, and the as-received one showed the worst on the oxidation of HC. After then the activity of the four samples tends to be the similar. The surface and interfacial Pt 0 sites were both considered as the effective factors. Models were constructed to describe the diffusion of ions and oxygen vacancies as well as the possible surface structure serving as the carrier of Pt 0 site which impacted on the catalytic activity remarkably.

  17. Photocatalytic activity of Pt-TiO2 films supported on hydroxylated fly ash cenospheres under visible light

    NASA Astrophysics Data System (ADS)

    Wang, Bing; Yang, Zewei; An, Hao; Zhai, Jianping; Li, Qin; Cui, Hao

    2015-01-01

    TiO2 was coated on the surface of hydroxylated fly ash cenospheres (FACs) by the sol-gel method. Platinum (Pt) was then deposited on these TiO2/FAC particles by a photoreduction method to form PTF photocatalyst. The photocatalytic activity of PTF for the degradation of methylene blue (MB) under visible-light irradiation was determined. The PTF sample that was calcined at 450 °C and had a Pt/TiO2 mass ratio of 1.5% exhibited the optimal photocatalytic activity for degradation of MB with a catalyst concentration of 3 g L-1. MB was photodecomposed by PTF in aqueous solution more effectively at alkali pH than at acidic pH, because more MB molecules were adsorbed on the surface of PTF under alkaline conditions than that under acidic. The effect of various inorganic anions (HCO3-, F-, SO42-, NO3-, and Cl-) on the photodegradation of MB by PTF was also investigated. Addition of anions with a concentration of 5 mM enhanced the photocatalytic efficiency of PTF because of the improved adsorption of MB. This effect weakened as the anion concentration was increased, which was attributed to the ability of the anions to scavenge hydroxyl radicals and holes. Our results indicated that the photodegradation of MB took place mainly on the catalyst surface. The generation of hydroxyl radicals in the photocatalytic reaction was measured by the fluorescence method. KI was used to determine the participation of holes in the photocatalytic reaction. Both hydroxyl radicals and valence-band holes were detected in the PTF system. Recycling tests revealed that calcination of the used PTF helped to regain its photocatalytic activity.

  18. Electro-oxidation of ethanol on ternary non-alloyed Pt-Sn-Pr/C catalysts

    NASA Astrophysics Data System (ADS)

    Corradini, Patricia G.; Antolini, Ermete; Perez, Joelma

    2015-02-01

    Ternary Pt-Sn-Pr/C (70:10:20), (70:15:15) and (45:45:10) electro-catalysts were prepared by a modified formic acid method, and their activity for the ethanol oxidation reaction (EOR) was compared with that of Pt-Pr/C catalysts prepared by the same methods and that of commercial Pt-Sn/C (75:25) and Pt/C catalysts. Among all the catalysts, the Pt-Sn-Pr/C (45:45:10) catalyst presented both the highest mass activity and the highest specific activity. The steady state electrochemical stability of ternary Pt-Sn-Pr catalysts increased with the surface Sn/Pt atomic ratio. Following repetitive potential cycling (RPC), the activity for ethanol oxidation of Pt-Sn-Pr/C catalysts with high surface Sn/Pt atomic ratio was considerably higher than that of the corresponding as-prepared catalysts, and increased with increasing the Sn/Pt ratio. The increase of the EOR mass activity following RPC was ascribed to the increase of either the specific activity (for the Pt-Sn-Pr/C (70:15:15) catalyst) or the electrochemically active surface area (for the Pt-Sn-Pr/C (45:45:10) catalyst). Dissolution of Sn and Pr oxides from Pt-Sn-Pr/C catalyst surface was observed following RPC.

  19. Ultrahigh methanol electro-oxidation activity of PtRu nanoparticles prepared on TiO2-embedded carbon nanofiber support

    NASA Astrophysics Data System (ADS)

    Ito, Yudai; Takeuchi, Taizo; Tsujiguchi, Takuya; Abdelkareem, Mohammad Ali; Nakagawa, Nobuyoshi

    2013-11-01

    A TiO2-embedded carbon nanofiber (TECNF) was proposed as a promising support of the PtRu nanocatalyst for the methanol oxidation reaction. The nanofiber support was prepared by the electrospinning of polyacrylonitrile (PAN) with TiO2 nanoparticles followed by carbonization and steam activation of the nanofiber, and lastly, the PtRu nanoparticles deposition. Cyclic voltammetry (CV) revealed a significantly high MOR activity for the PtRu/TECNF compared to that of the PtRu nanoparticles deposited on different supports, i.e., carbon black (C), TiO2 nanoparticles (TiO2), a mixture of these nanoparticles (C + TiO2) and carbon nanofiber (CNF). The MOR activity was high in the order of PtRu/TECNF > PtRu/CNF > PtRu/(C + TiO2) > PtRu/C >> PtRu/TiO2. The activity of PtRu/TECNF increased with an increase in the weight ratio of Ti/C for TECNF up to 1.0 and then decreased. The MOR mass activity of PtRu/TECNF at the optimum Ti/C ratio was 4 times higher than that of PtRu/C. The ultrahigh catalytic activity of PtRu/TECNF is attributed to the metal-support interaction, which efficiently occurs at the PtRu/TECNF structure. The ultrahigh catalytic activity was also confirmed by the two-times higher DMFC power output using PtRu/TECNF, in spite of quarter the PtRu loading on the electrode, compared to that using the commercial PtRu/C.

  20. Effect of calcination temperature on the structure of a Pt/TiO2 (B) nanofiber and its photocatalytic activity in generating H2.

    PubMed

    Lin, Chiu-Hsun; Chao, Jiunn-Hsing; Liu, Chun-Hsuan; Chang, Jui-Chun; Wang, Feng-Chieh

    2008-09-01

    Hydrogen trititanate (H 2Ti 3O 7) nanofibers were prepared by a hydrothermal method in 10 M NaOH at 403 K, followed by acidic rinsing and drying at 383 K. Calcining H 2Ti 3O 7 nanofibers at 573 K led to the formation of TiO 2 (B) nanofibers. Calcination at 673 K improved the crystallinity of the TiO 2 (B) nanofibers and did not cause any change in the morphology and dimensions of the nanofibers. TiO 2 (B) and H 2Ti 3O 7 nanofibers are 10-20 nm in diameter and several micrometers long, but FE-SEM reveals that several of these nanofibers tend to bind tightly to each other, forming a fiber bundle. Calcination at 773 K transformed TiO 2 (B) nanofibers into a TiO 2 (B)/anatase bicrystalline mixture with their fibrous morphology remaining intact. Upon increasing the calcination temperature to 873 K, most of the TiO 2 (B) nanofibers were converted into anatase nanofibers and small anatase particles with smoother surfaces. In the photocatalytic dehydrogenation of neat ethanol, 1% Pt/TiO 2 (B) nanofiber calcined at 673 K was the most active catalyst and generated about the same amount of H 2 as did 1% Pt/P-25. TPR indicated that the calcination of 1% Pt/TiO 2 (B) nanofiber at 573 K produced a poor Pt dispersion and poor activity. Calcination at a temperature higher than 773 K (in ambient air) resulted in an SMSI effect similar to that observed over TiO 2 in the reductive atmosphere. As suggested by XPS, such an SMSI effect decreased the surface concentration of Pt metal and created Pt (delta) sites, preventing Pt particles from functioning as a Schottky barrier and leading to a lower activity. Because of the synergetic effect between TiO 2 (B) and anatase phases, the bicrystalline mixture, produced by calcining at 773 K, was able to counter negative effects such as the reduction in surface area and the SMSI effect and maintained its photocatalytic activity. PMID:18690728

  1. The effect of H2O and pretreatment on the activity of a Pt/SnO2 catalyst

    NASA Technical Reports Server (NTRS)

    Vannorman, John D.; Brown, Kenneth G.; Schryer, Jacqueline; Schryer, David R.; Upchurch, Billy T.; Sidney, Barry D.

    1990-01-01

    CO oxidation catalysts with high activity at 25 C to 100 C are important for long-life, closed-cycle operation of pulsed CO2 lasers. A reductive pretreatment with either CO or H2 has been shown to significantly enhance the activity of a commercially available platinum on tin (IV) oxide (Pt/SnO2) catalyst relative to an oxidative or inert pretreatment or no pretreatment. Pretreatment at temperatures of 175 C and above causes an initial dip in the observed CO2 yield before the steady-state yield is attained. This dip has been found to be caused by dehydration of the catalyst during pretreatment and is readily eliminated by humidifying the catalyst or the reaction gas mixture. It is hypothesized that the effect of humidification is to increase the concentration of OH groups on the catalyst surface which play a role in the reaction mechanism.

  2. Electrocatalytic and photocatalytic activity of Pt-TiO2 films on boron-doped diamond substrate

    NASA Astrophysics Data System (ADS)

    Spătaru, Tanţa; Marcu, Maria; Spătaru, Nicolae

    2013-03-01

    In the present work boron-doped diamond (BDD) polycrystalline films were used as support for direct anodic deposition of hydrous titanium oxide, and continuous TiO2 coatings were obtained by appropriately adjusting the deposition charge. The photoelectrochemical activity of the TiO2/BDD electrodes was investigated and it was found that, in terms of charge carriers separation efficiency, conductive diamond is a much better support for TiO2, compared to traditional carbonaceous materials such as glassy carbon. Further electrochemical deposition of platinum particles on the oxide-coated conductive diamond enabled the formation of a composite with enhanced electrochemically active surface area. The electrocatalytic and photocatalytic properties of the Pt/TiO2/BDD electrodes thus obtained were also scrutinized and it appeared that these hybrid systems also exhibit promising features for methanol anodic oxidation.

  3. The Effects of TI/PT Bottom Electrode on Crystallographic and Surface Characteristics of PZT Thick Films

    NASA Astrophysics Data System (ADS)

    Koochekzadeh, Ali; Keshavarz Alamdari, Eskandar; Barzegar, Abdolghafar

    The ceramic lead zirconate titanate (PZT) films near the morphotropic phase boundary are successfully integrated into MEMS devices, especially for applications in microsensors and actuators. The ferro/piezo electric properties of PZT thick films are widely dependent on its surface quality and crystallographic orientation growth. This paper indicates the influences of platinum bottom electrode on the surface and crystallographic properties of PZT. Ti (10nm) and Pt (100nm) thin films have been deposited on silicon substrate by thermal evaporation and electron beam respectively without vacuum breaking. After annealing treatment, the Pt film exhibited (111) preferred orientation. Finally one micron thick PZT (54/46) film was deposited by a RF magnetron sputtering at room temperature in pure Argon followed by a conventional post annealing treatment on silicon substrate. The XRD measurements have shown the provskite structure of PZT films with (100) preferred orientation at annealing temperatures above 600°C and (111) preferred orientation above 650°c. The SEM results demonstrate that whatever the annealing temperature is increased, recrystallization grains and black holes on Pt surface occurs and cause morphological change of PZT surface. The AFM test shows the strong RMS roughness of platinum surface after annealing temperature at 650°C.

  4. Effects of transition metal doping in Pt/M-TiO2 (M = V, Cr, and Nb) on oxygen reduction reaction activity

    NASA Astrophysics Data System (ADS)

    Kim, Jun-Hyuk; Kwon, Gihan; Lim, Hankwon; Zhu, Chenhui; You, Hoydoo; Kim, Yong-Tae

    2016-07-01

    High cost and low durability are unresolved issues that impede the commercialization of proton exchange membrane fuel cells (PEMFCs). To overcome these limitations, Pt/TiO2 is reported as an alternative electrocatalyst for enhancing the oxygen reduction reaction (ORR) activity and/or durability of the system. However, the low electrical conductivity of TiO2 is a drawback that may be addressed by doping. To date, most reports related to Pt/doped-TiO2 focus on changes in the catalyst activity caused by the Pt-TiO2 interaction (metal-support interaction), instead of the effect of doping itself; doping is merely considered to enhance the electrical conductivity of TiO2. In this study, we discuss the variation in the electronic fine structure of Pt caused by the dopant, and its correlation with the ORR activity. More extensive contraction of the Pt lattice in Pt/M-TiO2 (M = V, Cr, and Nb) relative to Pt/TiO2 and Pt/C leads to outstanding ORR specific activity of Pt/M-TiO2. Notably, a fourfold increase of the specific activity is achieved with Pt/V-TiO2 relative to Pt/C. Furthermore, an accelerated durability test (ADT) of Pt/V-TiO2 demonstrates that this system is three times more durable than conventional Pt/C due to the metal-support interaction.

  5. Selectivity loss of Pt/CeO{sub 2} PROX catalysts at low CO concentrations: mechanism and active site study.

    SciTech Connect

    Polster, C. S.; Zhang, R.; Cyb, M. T.; Miller, J. T.; Baertsch, C. D.

    2010-07-01

    CO and H{sub 2} oxidation were studied over a series of Pt/CeO{sub 2} catalysts with differing Pt loadings and dispersions. Kinetic rate analysis confirms the presence of dual Langmuir-Hinshelwood (L-H) and Mars and van Krevelen (M-vK) pathways and is used to explain the loss in CO oxidation selectivity at low CO concentrations. In situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) shows the strong CO coverage dependence on both CO and O{sub 2} concentrations and explains the transition from L-H to M-vK reaction character. Redox site measurements are performed on Pt/CeO{sub 2} catalysts by anaerobic titrations under conditions where the M-vK pathway dominates the reaction rate. Similar redox site densities per interfacial Pt atom suggest that interfacial Pt-O-Ce sites are responsible for M-vK redox activity.

  6. Active particles on curved surfaces

    NASA Astrophysics Data System (ADS)

    Fily, Yaouen; Baskaran, Aparna; Hagan, Michael

    Active systems have proved to be very sensitive to the geometry of their environment. This is often achieved by spending significant time at the boundary, probing its shape by gliding along it. I will discuss coarse graining the microscopic dynamics of self-propelled particles on a general curved surface to predict the way the density profile on the surface depends on its geometry. Beyond confined active particles, this formalism is a natural starting point to study objects that cannot leave the boundary at all, such as cells crawling on a curved substrate, animals running on uneven ground, or active colloids trapped at an interface.

  7. Antitumor activity of [Pt(O,O'-acac)(γ-acac)(DMS)] in mouse xenograft model of breast cancer.

    PubMed

    Muscella, A; Vetrugno, C; Migoni, D; Biagioni, F; Fanizzi, F P; Fornai, F; De Pascali, S A; Marsigliante, S

    2014-01-01

    The higher and selective cytotoxicity of [Pt(O,O'-acac)(γ-acac)(DMS)] toward cancer cell in both immortalized cell lines and in breast cancer cells in primary cultures, stimulated a pre-clinical study so as to evaluate its therapeutic potential in vivo. The efficacy of [Pt(O,O'-acac)(γ-acac)(DMS)] was assessed using a xenograft model of breast cancer developed by injection of MCF-7 cells in the flank of BALB/c nude mice. Treatment of solid tumor-bearing mice with [Pt(O,O'-acac)(γ-acac)(DMS)] induced up to 50% reduction of tumor mass compared with an average 10% inhibition recorded in cisplatin-treated animals. Thus, chemotherapy with [Pt(O,O'-acac)(γ-acac)(DMS)] was much more effective than cisplatin. We also demonstrated enhanced in vivo pharmacokinetics, biodistribution and tolerability of [Pt(O,O'-acac)(γ-acac)(DMS)] when compared with cisplatin administered in Wistar rats. Pharmacokinetics studies with [Pt(O,O'-acac)(γ-acac)(DMS)] revealed prolonged Pt persistence in systemic blood circulation and decreased nefrotoxicity and hepatotoxicity, major target sites of cisplatin toxicity. Overall, [Pt(O,O'-acac)(γ-acac)(DMS)] turned out to be extremely promising in terms of greater in vivo anticancer activity, reduced nephrotoxicity and acute toxicity compared with cisplatin. PMID:24457958

  8. Antitumor activity of [Pt(O,O'-acac)(γ-acac)(DMS)] in mouse xenograft model of breast cancer

    PubMed Central

    Muscella, A; Vetrugno, C; Migoni, D; Biagioni, F; Fanizzi, F P; Fornai, F; De Pascali, S A; Marsigliante, S

    2014-01-01

    The higher and selective cytotoxicity of [Pt(O,O′-acac)(γ-acac)(DMS)] toward cancer cell in both immortalized cell lines and in breast cancer cells in primary cultures, stimulated a pre-clinical study so as to evaluate its therapeutic potential in vivo. The efficacy of [Pt(O,O′-acac)(γ-acac)(DMS)] was assessed using a xenograft model of breast cancer developed by injection of MCF-7 cells in the flank of BALB/c nude mice. Treatment of solid tumor-bearing mice with [Pt(O,O′-acac)(γ-acac)(DMS)] induced up to 50% reduction of tumor mass compared with an average 10% inhibition recorded in cisplatin-treated animals. Thus, chemotherapy with [Pt(O,O′-acac)(γ-acac)(DMS)] was much more effective than cisplatin. We also demonstrated enhanced in vivo pharmacokinetics, biodistribution and tolerability of [Pt(O,O′-acac)(γ-acac)(DMS)] when compared with cisplatin administered in Wistar rats. Pharmacokinetics studies with [Pt(O,O′-acac)(γ-acac)(DMS)] revealed prolonged Pt persistence in systemic blood circulation and decreased nefrotoxicity and hepatotoxicity, major target sites of cisplatin toxicity. Overall, [Pt(O,O′-acac)(γ-acac)(DMS)] turned out to be extremely promising in terms of greater in vivo anticancer activity, reduced nephrotoxicity and acute toxicity compared with cisplatin. PMID:24457958

  9. 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

  10. Reactivity of atomically dispersed Pt(2+) species towards H2: model Pt-CeO2 fuel cell catalyst.

    PubMed

    Lykhach, Yaroslava; Figueroba, Alberto; Camellone, Matteo Farnesi; Neitzel, Armin; Skála, Tomáš; Negreiros, Fabio R; Vorokhta, Mykhailo; Tsud, Nataliya; Prince, Kevin C; Fabris, Stefano; Neyman, Konstantin M; Matolín, Vladimír; Libuda, Jörg

    2016-03-01

    The reactivity of atomically dispersed Pt(2+) species on the surface of nanostructured CeO2 films and the mechanism of H2 activation on these sites have been investigated by means of synchrotron radiation photoelectron spectroscopy and resonant photoemission spectroscopy in combination with density functional calculations. Isolated Pt(2+) sites are found to be inactive towards H2 dissociation due to high activation energy required for H-H bond scission. Trace amounts of metallic Pt are necessary to initiate H2 dissociation on Pt-CeO2 films. H2 dissociation triggers the reduction of Ce(4+) cations which, in turn, is coupled with the reduction of Pt(2+) species. The mechanism of Pt(2+) reduction involves reverse oxygen spillover and formation of oxygen vacancies on Pt-CeO2 films. Our calculations suggest the existence of a threshold concentration of oxygen vacancies associated with the onset of Pt(2+) reduction. PMID:26908194

  11. Biomass-derived oxygenate reforming on Pt(111): A demonstration of surface science using D-glucose and its model surrogate glycolaldehyde

    NASA Astrophysics Data System (ADS)

    McManus, Jesse R.; Yu, Weiting; Salciccioli, Michael; Vlachos, Dionisios G.; Chen, Jingguang G.; Vohs, John M.

    2012-12-01

    Molecules derived from cellulosic biomass, such as glucose, represent an important renewable feedstock for the production of hydrogen and hydrocarbon-based fuels and chemicals. Development of efficient catalysts for their reformation into useful products is needed; however, this requires a detailed understanding of their adsorption and reaction on catalytically active transition metal surfaces. In this paper we demonstrate that the standard surface science techniques routinely used to characterize the reaction of small molecules on metals are also amenable for use in studying the adsorption and reaction of complex biomass-derivatives on single crystal metal surfaces. In particular, Temperature Programmed Desorption (TPD) and High Resolution Electron Energy Loss Spectroscopy (HREELS) combined with Density Functional Theory (DFT) calculations were used to elucidate the adsorption configuration of D-glucose and glycolaldehye on Pt(111). Both molecules were found to adsorb in an η1 aldehyde configuration partially validating the use of simple, functionally-equivalent model compounds for surface studies of cellulosic oxygenates.

  12. Architecturally designed Pt-MoS2 and Pt-graphene composites for electrocatalytic methanol oxidation.

    PubMed

    Patil, Sagar H; Anothumakkool, Bihag; Sathaye, Shivaram D; Patil, Kashinath R

    2015-10-21

    Thin films consisting of platinum nanoparticles (Pt NPs) with uniform size and distribution have been successfully prepared at a liquid-liquid interface. Apart from the usual substrates like glass, Si etc. the films were also deposited on the surfaces of MoS2 thin films and graphene nanosheets (GNS) respectively, by using a layer-by-layer (LbL) deposition technique to form Pt-MoS2 and Pt-GNS composites. The loading concentration of Pt NPs on MoS2 and GNS can be adjusted by selecting the number and sequence of the component layers during LbL deposition. The Pt thin films, Pt-MoS2 and Pt-GNS nanocomposite thin films are characterized using transmission electron microscopy (TEM), high resolution transmission electron microscopy (HRTEM), energy dispersive X-ray spectrometry (EDS), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). TEM results of the composites show that Pt NPs with sizes in the range of 1 to 3 nm are uniformly dispersed on the MoS2/GNS surface. The catalytic activities of Pt and Pt-composites for the reaction of methanol oxidation are studied using cyclic voltammetry and chronoamperometry. Electrochemical studies reveal that both the Pt-MoS2 and Pt-GNS nanocomposites show excellent electrocatalytic activity towards methanol oxidation. Pt-MoS2 and Pt-GNS nanocomposite electrodes show excellent stability for reuse of the catalyst. A probable mechanism of catalysis has been discussed. We propose that the similar architecture reported here would be promising for the synthesis of high performance catalysts for fuel cells, gas phase reactions, and other applications such as sensors. PMID:26377752

  13. Facile synthesis of Ru-decorated Pt cubes and icosahedra as highly active electrocatalysts for methanol oxidation

    NASA Astrophysics Data System (ADS)

    Lin, Zhuoqing; Chen, Wenlong; Jiang, Ying; Bian, Ting; Zhang, Hui; Wu, Jianbo; Wang, Yong; Yang, Deren

    2016-06-01

    PtRu bimetallic particles are well-known commercial catalysts with promising performance for methanol oxidation. However, shape-controlled synthesis of PtRu bimetallic nanocrystals, especially for the platonic structures with {100} (e.g., cubes) or {111} facets (e.g., icosahedra) exposed towards catalysis, has met only limited success due to the different crystal structures of Pt and Ru. Here we report a facile approach to the synthesis of Ru decorated Pt bimetallic cubes and icosahedra in a mixed solvent. We found that the cubes were formed in the solvent containing N,N-dimethylmethanamide (DMF) and oleylamine (OAm) possibly due to the selective adsorption of CO on Pt{100} arising from the decomposition of DMF catalyzed by a Ru salt precursor. When hexadecane was added into the aforementioned solvent, the synthesis became a two-phase interfacial reaction due to the large difference in solvent polarity, thereby retarding the reaction kinetics and promoting the formation of the icosahedra with the composition similar to the cubes. When evaluated as catalysts towards methanol oxidation, the Ru decorated Pt icosahedra showed much better performance in terms of specific and mass activity relative to the corresponding cubes. Specifically, the Ru decorated Pt bimetallic icosahedra achieved a specific activity of 0.76 mA cm-2 and mass activity of 74.43 mA mgPt-1, which is ~6.7 and 2.2 times as high as those of the carbon supported Pt7Ru nanoparticles, respectively. This enhancement can be attributed to a combination of twin-induced strain and facet effects.PtRu bimetallic particles are well-known commercial catalysts with promising performance for methanol oxidation. However, shape-controlled synthesis of PtRu bimetallic nanocrystals, especially for the platonic structures with {100} (e.g., cubes) or {111} facets (e.g., icosahedra) exposed towards catalysis, has met only limited success due to the different crystal structures of Pt and Ru. Here we report a facile approach

  14. Halogen poisoning effect of Pt-TiO2 for formaldehyde catalytic oxidation performance at room temperature

    NASA Astrophysics Data System (ADS)

    Zhu, Xiaofeng; Cheng, Bei; Yu, Jiaguo; Ho, Wingkei

    2016-02-01

    Catalytic decomposition of formaldehyde (HCHO) at room temperature is an important method for HCHO removal. Pt-based catalysts are the optimal catalyst for HCHO decomposition at room temperature. However, the stability of this catalyst remains unexplored. In this study, Pt-TiO2 (Pt-P25) catalysts with and without adsorbed halogen ions (including F-, Cl-, Br-, and I-) were prepared through impregnation and ion modification. Pt-TiO2 samples with adsorbed halogen ions exhibited reduced catalytic activity for formaldehyde decomposition at room temperature compared with the Pt-TiO2 sample; the catalytic activity followed the order of F-Pt-P25, Cl-Pt-P25, Br-Pt-P25, and I-Pt-P25. Characterization results (including XRD, TEM, HRTEM, BET, XPS, and metal dispersion) showed that the adsorbed halogen ions can poison Pt nanoparticles (NPs), thereby reducing the HCHO oxidation activity of Pt-TiO2. The poison mechanism is due to the strong adsorption of halogen ions on the surface of Pt NPs. The adsorbed ions form coordination bonds with surface Pt atoms by transferring surplus electrons into the unoccupied 5d orbit of the Pt atom, thereby inhibiting oxygen adsorption and activation of the Pt NP surface. Moreover, deactivation rate increases with increasing diameter of halogen ions. This study provides new insights into the fabrication of high-performance Pt-based catalysts for indoor air purification.

  15. The structure and reactivity of adsorbates on stepped Rh and Pt surfaces investigated by LEED, HREELS, TPD, XPS and STM

    SciTech Connect

    Batteas, J.D. |

    1995-06-01

    Defects on surfaces such as steps play an important role in surface chemistry. In order to obtain an understanding of the influence of steps in surface chemical reactions, the structure and reactivity of small molecules (O{sub 2}, CO, H{sub 2}S, and C{sub 2}H{sub 4}) on atomically stepped surfaces of RH and Pt have been investigated. The detailed structures of CO and oxygen bonded to the Rh(110) surface were determined. The CO molecules bond near the short bridge sites with the CO molecular axis tilted approximately 24{degree} from the surface normal. Oxygen atoms are bound asymmetrically in the 3-fold fcc hollow-sites to the (111) facets of the steps. The interactions of CO and oxygen on the Rh(311) surface were examined. The reaction of CO with the ordered phases of O shows two distinct reaction channels, a low temperature reaction limited channel (200 K) and a high temperature diffusion limited channel (350 K). Models of the reaction geometry and dynamics are proposed. The thermal decomposition of ethylene was examined on the Rh(311) surface. The stable decomposition species (C{sub 2}H, CH and C{sub 2}) are formed near 300 K, approximately 100 K lower on the stepped Rh(311) than on the flatter Rh(111) surface. The formation of these species at lower temperatures is attributed to the stepped nature of the surface. Finally, in situ STM was used to examine surface structural changes of a stepped Pt(111) crystal under coadsorption of sulfur and CO. This is the first direct evidence for a new mechanism by which a surface covered with an unreactive, strongly chemisorbed overlayer can form new sites, for bonding and reactions to occur, by massive surface restructuring at the step edges. This new surface phenomenon answers some of the puzzles of metal surface catalysis and its implications are described. 278 refs.

  16. Facile synthesis of Ru-decorated Pt cubes and icosahedra as highly active electrocatalysts for methanol oxidation.

    PubMed

    Lin, Zhuoqing; Chen, Wenlong; Jiang, Ying; Bian, Ting; Zhang, Hui; Wu, Jianbo; Wang, Yong; Yang, Deren

    2016-07-01

    PtRu bimetallic particles are well-known commercial catalysts with promising performance for methanol oxidation. However, shape-controlled synthesis of PtRu bimetallic nanocrystals, especially for the platonic structures with {100} (e.g., cubes) or {111} facets (e.g., icosahedra) exposed towards catalysis, has met only limited success due to the different crystal structures of Pt and Ru. Here we report a facile approach to the synthesis of Ru decorated Pt bimetallic cubes and icosahedra in a mixed solvent. We found that the cubes were formed in the solvent containing N,N-dimethylmethanamide (DMF) and oleylamine (OAm) possibly due to the selective adsorption of CO on Pt{100} arising from the decomposition of DMF catalyzed by a Ru salt precursor. When hexadecane was added into the aforementioned solvent, the synthesis became a two-phase interfacial reaction due to the large difference in solvent polarity, thereby retarding the reaction kinetics and promoting the formation of the icosahedra with the composition similar to the cubes. When evaluated as catalysts towards methanol oxidation, the Ru decorated Pt icosahedra showed much better performance in terms of specific and mass activity relative to the corresponding cubes. Specifically, the Ru decorated Pt bimetallic icosahedra achieved a specific activity of 0.76 mA cm(-2) and mass activity of 74.43 mA mgPt(-1), which is ∼6.7 and 2.2 times as high as those of the carbon supported Pt7Ru nanoparticles, respectively. This enhancement can be attributed to a combination of twin-induced strain and facet effects. PMID:27297644

  17. Mild Synthesis of Pt/SnO2 /Graphene Nanocomposites with Remarkably Enhanced Ethanol Electro-oxidation Activity and Durability.

    PubMed

    Qu, Yunteng; Gao, Yunzhi; Wang, Long; Rao, Jiancun; Yin, Geping

    2016-01-01

    We have designed a new Pt/SnO2 /graphene nanomaterial by using L-arginine as a linker; this material shows the unique Pt-around-SnO2 structure. The Sn(2+) cations reduce graphene oxide (GO), leading to the in situ formation of SnO2 /graphene hybrids. L-Arginine is used as a linker and protector to induce the in situ growth of Pt nanoparticles (NPs) connected with SnO2 NPs and impede the agglomeration of Pt NPs. The obtained Pt/SnO2 /graphene composites exhibit superior electrocatalytic activity and stability for the ethanol oxidation reaction as compared with the commercial Pt/C catalyst owing to the close-connected structure between the Pt NPs and SnO2 NPs. This work should have a great impact on the rational design of future metal-metal oxide nanostructures with high catalytic activity and stability for fuel cell systems. PMID:26626713

  18. The SHORT-ROOT-like gene PtSHR2B is involved in Populus phellogen activity.

    PubMed

    Miguel, Andreia; Milhinhos, Ana; Novák, Ondřej; Jones, Brian; Miguel, Célia M

    2016-03-01

    SHORT-ROOT (SHR) is a GRAS transcription factor first characterized for its role in the specification of the stem cell niche and radial patterning in Arabidopsis thaliana (At) roots. Three SHR-like genes have been identified in Populus trichocarpa (Pt). PtSHR1 shares high similarity with AtSHR over the entire length of the coding sequence. The two other Populus SHR-like genes, PtSHR2A and PtSHR2B, are shorter in their 5' ends when compared with AtSHR. Unlike PtSHR1, that is expressed throughout the cambial zone of greenhouse-grown Populus trees, PtSHR2Bprom:uidA expression was detected in the phellogen. Additionally, PtSHR1 and PtSHR2B expression patterns markedly differ in the shoot apex and roots of in vitro plants. Transgenic hybrid aspen expressing PtSHR2B under the 35S constitutive promoter showed overall reduced tree growth while the proportion of bark increased relative to the wood. Reverse transcription-quantitative PCR (RT-qPCR) revealed increased transcript levels of cytokinin metabolism and response-related genes in the transgenic plants consistent with an increase of total cytokinin levels. This was confirmed by cytokinin quantification by LC-MS/MS. Our results indicate that PtSHR2B appears to function in the phellogen and therefore in the regulation of phellem and periderm formation, possibly acting through modulation of cytokinin homeostasis. Furthermore, this work points to a functional diversification of SHR after the divergence of the Populus and Arabidopsis lineages. This finding may contribute to selection and breeding strategies of cork oak in which, unlike Populus, the phellogen is active throughout the entire tree lifespan, being at the basis of a highly profitable cork industry. PMID:26709311

  19. A Strategy for Fabricating Porous PdNi@Pt Core-shell Nanostructures and Their Enhanced Activity and Durability for the Methanol Electrooxidation

    NASA Astrophysics Data System (ADS)

    Liu, Xinyu; Xu, Guangrui; Chen, Yu; Lu, Tianhong; Tang, Yawen; Xing, Wei

    2015-01-01

    Three-dimensionally (3D) porous morphology of nanostructures can effectively improve their electrocatalytic activity and durability for various electrochemical reactions owing to big surface area and interconnected structure. Cyanogel, a jelly-like inorganic polymer, can be used to synthesize various three-dimensionally (3D) porous alloy nanomaterials owing to its double-metal property and particular 3D backbone. Here, 3D porous PdNi@Pt core-shell nanostructures (CSNSs) are facilely synthesized by first preparing the Pd-Ni alloy networks (Pd-Ni ANWs) core via cyanogel-reduction method followed by a galvanic displacement reaction to generate the Pt-rich shell. The as-synthesized PdNi@Pt CSNSs exhibit a much improved catalytic activity and durability for the methanol oxidation reaction (MOR) in the acidic media compared to the commercial used Pt black because of their specific structural characteristics. The facile and mild method described herein is highly attractive for the synthisis of 3D porous core-shell nanostructures.

  20. Dendrimer Templated Synthesis of One Nanometer Rh and Pt Particles Supported on Mesoporous Silica: Catalytic Activity for Ethylene and Pyrrole Hydrogenation.

    SciTech Connect

    Huang, Wenyu; Kuhn, John N.; Tsung, Chia-Kuang; Zhang, Yawen; Habas, Susan E.; Yang, Peidong; Somorjai, Gabor A.

    2008-05-09

    Monodisperse rhodium (Rh) and platinum (Pt) nanoparticles as small as {approx}1 nm were synthesized within a fourth generation polyaminoamide (PAMAM) dendrimer, a hyperbranched polymer, in aqueous solution and immobilized by depositing onto a high-surface-area SBA-15 mesoporous support. X-ray photoelectron spectroscopy indicated that the as-synthesized Rh and Pt nanoparticles were mostly oxidized. Catalytic activity of the SBA-15 supported Rh and Pt nanoparticles was studied with ethylene hydrogenation at 273 and 293 K in 10 torr of ethylene and 100 torr of H{sub 2} after reduction (76 torr of H{sub 2} mixed with 690 torr of He) at different temperatures. Catalysts were active without removing the dendrimer capping but reached their highest activity after hydrogen reduction at a moderate temperature (423 K). When treated at a higher temperature (473, 573, and 673 K) in hydrogen, catalytic activity decreased. By using the same treatment that led to maximum ethylene hydrogenation activity, catalytic activity was also evaluated for pyrrole hydrogenation.

  1. Preparation and Catalytic Activity for Aerobic Glucose Oxidation of Crown Jewel Structured Pt/Au Bimetallic Nanoclusters.

    PubMed

    Zhang, Haijun; Wang, Liqiong; Lu, Lilin; Toshima, Naoki

    2016-01-01

    Understanding of the "structure-activity" relations for catalysts at an atomic level has been regarded as one of the most important objectives in catalysis studies. Bimetallic nanoclusters (NCs) in its many types, such as core/shell, random alloy, cluster-in-cluster, bi-hemisphere, and crown jewel (one kind of atom locating at the top position of another kind of NC), attract significant attention owing to their excellent optical, electronic, and catalytic properties. PVP-protected crown jewel-structured Pt/Au (CJ-Pt/Au) bimetallic nanoclusters (BNCs) with Au atoms located at active top sites were synthesized via a replacement reaction using 1.4-nm Pt NCs as mother clusters even considering the fact that the replacement reaction between Pt and Au(3+) ions is difficult to be occurred. The prepared CJ-Pt/Au colloidal catalysts characterized by UV-Vis, TEM, HR-TEM and HAADF-STEM-EELS showed a high catalytic activity for aerobic glucose oxidation, and the top Au atoms decorating the Pt NCs were about 15 times more active than the Au atoms of Au NCs with similar particle size. PMID:27476577

  2. Preparation of AuPt alloy foam films and their superior electrocatalytic activity for the oxidation of formic acid.

    PubMed

    Liu, Jun; Cao, Ling; Huang, Wei; Li, Zelin

    2011-09-01

    AuPt alloy films with three-dimensional (3D) hierarchical pores consisting of interconnected dendrite walls were successfully fabricated by a strategy of cathodic codeposition utilizing the hydrogen bubble dynamic template. The foam films were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). Due to the special porous structure, the electronic property, and the assembly effect, the AuPt alloy foam films show superior electrocatalytic activity toward the electrooxidation of formic acid in acidic solution, and the prepared 3D porous AuPt alloy films also show high activity and long stability for the electrocatalytic oxidation of methanol, where synergistic effect plays an important role in addition to the electronic effect and assembly effect. These findings provide more insights into the AuPt bimetallic nanomaterials for electrocatalytic applications. PMID:21838240

  3. Activity, short-term stability (poisoning tolerance) and durability of carbon supported Pt-Pr catalysts for ethanol oxidation

    NASA Astrophysics Data System (ADS)

    Corradini, Patricia G.; Antolini, Ermete; Perez, Joelma

    2014-04-01

    Pt-Pr/C electrocatalysts were prepared by a modified formic acid method, and their activity for carbon monoxide and ethanol oxidation, their short term stability and durability were compared to that of commercial Pt/C and Pt-Sn/C (3:1) catalysts. By derivative voltammetry (DV) it was found that ethanol electro-oxidation takes place by two main pathways at different potentials. It was observed that, in the presence of Pr, ethanol electro-oxidation takes place mostly through the pathway at lower potential, which is the most interesting for fuel cell application. The Pt-Pr/C catalysts were less tolerant to poisoning by ethanol oxidation intermediate species than Pt/C. Durability test by a repetitive potential cycling under Ar atmosphere revealed a good structural stability of Pt-Pr/C catalysts. A repetitive potential cycling under CO atmosphere carried out on the Pt-Pr/C (1:1) catalyst, instead, indicated a structural change, likely by formation of a core-shell structure.

  4. Electronic structure of graphene on a reconstructed Pt(100) surface: Hydrogen adsorption, doping, and band gaps

    NASA Astrophysics Data System (ADS)

    Ulstrup, Søren; Nilsson, Louis; Miwa, Jill A.; Balog, Richard; Bianchi, Marco; Hornekær, Liv; Hofmann, Philip

    2013-09-01

    We probe the structure and electronic band structure of graphene grown on a Pt(100) substrate using scanning tunneling microscopy, low energy electron diffraction, and angle-resolved photoemission spectroscopy. It is found that the graphene layer lacks a well-defined azimuthal orientation with respect to the substrate, causing a circular smearing of the π band instead of a well-defined Dirac cone near the Fermi level. The graphene is found to be electron doped placing the Dirac point ˜0.45 eV below the Fermi level, and a gap of 0.15±0.03 eV is found at the Dirac point. We dose atomic hydrogen and monitor the coverage on the graphene by analyzing the impurity-induced broadening of the π-band width. Saturation of graphene on Pt(100) with hydrogen does not expand the band gap, but instead hydrogen-mediated broadening and rehybridization of the graphene sp2 bonds into sp3 leads to a complete disruption of the graphene π band, induces a lifting of the Pt(100) reconstruction, and introduces a dispersing Pt state near the Fermi level. Deposition of rubidium on graphene on Pt(100) leads to further electron doping, pushing the Dirac point to a binding energy of ˜1.35 eV, and increasing the band gap to 0.65±0.04 eV.

  5. Pt interactions with annealed and chemically-etched Nb-doped SrTiO 3(0 0 1) surfaces: Metal/oxide surface chemical effects on band bending behavior

    NASA Astrophysics Data System (ADS)

    Vamala, Chiranjeevi; Manandhar, Sudha; Kelber, Jeff

    2009-01-01

    XPS and LEED have been used to characterize the interaction of sputter-deposited Pt (maximum coverage <5 ML) with Nb-doped SrTiO3(0 0 1) surfaces prepared either by annealing in O2 and then UHV, or by chemical-etching in aqua regia. The annealed surface exhibits an ordered (1 × 1) LEED pattern, with additional diffraction spots and streaks indicating the presence of oxygen vacancies. Increasing Pt coverage results in the decrease of the observed Pt(4f7/2) binding energy and the uniform shift of the Sr(3d), Ti(2p) and O(1s) levels to smaller binding energies, as expected for Pt cluster growth and surface-to-Pt charge donation on an n-type semiconductor. The etched surface is disordered, and exhibits a hydroxylated surface with a contaminant C film of ∼23 Ǻ average thickness. Pt deposition on the etched surface results in an immediate decrease in the intensity of the OH feature in the O(1s) spectrum, and a uniform shift of the Sr(3d), Ti(2p) and O(1s) levels to larger binding energies with increasing Pt coverage. The observed Pt(4f7/2) binding energy on the etched surface (∼72 eV) is independent of Pt coverage, and indicates substantial electronic charge donation from the Pt to surface hydroxyl species. The observation of band bending towards higher binding energies upon Pt deposition (behavior normally associated with p-type semiconductors) demonstrates that sub-monolayer quantities of adsorbates can alter metal/oxide interfacial charge transfer and reverse the direction of band bending, with important consequences for Schottky barrier heights and device applications.

  6. Novel hollow Pt-ZnO nanocomposite microspheres with hierarchical structure and enhanced photocatalytic activity and stability

    NASA Astrophysics Data System (ADS)

    Yu, Changlin; Yang, Kai; Xie, Yu; Fan, Qizhe; Yu, Jimmy C.; Shu, Qing; Wang, Chunying

    2013-02-01

    Noble metal/semiconductor nanocomposites play an important role in high efficient photocatalysis. Herein, we demonstrate a facile strategy for fabrication of hollow Pt-ZnO nanocomposite microspheres with hierarchical structure under mild solvothermal conditions using Zn (CH3COO)2.2H2O and HPtCl4 as the precursors, and polyethylene glycol-6000 (PEG-6000) and ethylene glycol as the reducing agent and solvent, respectively. The as-synthesized ZnO and Pt-ZnO composite nanocrystals were well characterized by powder X-ray diffraction (XRD), nitrogen-physical adsorption, scanning electron microscopy (SEM), energy dispersive X-ray (EDX), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), UV-vis diffuse reflectance spectra (DRS), and photoluminescence (PL) emission spectroscopy. It was found that Pt content greatly influences the morphology of Pt-ZnO composite nanocrystals. Suitable concentration of HPtCl4 in the reaction solution system can produce well hierarchically hollow Pt-ZnO nanocomposite microspheres, which are composed of an assembly of fine Pt-ZnO nanocrystals. Photocatalytic tests of the Pt-ZnO microspheres for the degradation of the dye acid orange II revealed extremely high photocatalytic activity and stability compared with those of pure ZnO and corresponding Pt deposited ZnO. The remarkable photocatalytic performance of hollow Pt-ZnO microspheres mainly originated from their unique nanostructures and the low recombination rate of the e-/h+ pairs by the platinum nanoparticles embedded in ZnO nanocrystals.Noble metal/semiconductor nanocomposites play an important role in high efficient photocatalysis. Herein, we demonstrate a facile strategy for fabrication of hollow Pt-ZnO nanocomposite microspheres with hierarchical structure under mild solvothermal conditions using Zn (CH3COO)2.2H2O and HPtCl4 as the precursors, and polyethylene glycol-6000 (PEG-6000) and ethylene glycol as the reducing agent and solvent, respectively. The as

  7. Preparation and Catalytic Activity for Aerobic Glucose Oxidation of Crown Jewel Structured Pt/Au Bimetallic Nanoclusters

    NASA Astrophysics Data System (ADS)

    Zhang, Haijun; Wang, Liqiong; Lu, Lilin; Toshima, Naoki

    2016-08-01

    Understanding of the “structure-activity” relations for catalysts at an atomic level has been regarded as one of the most important objectives in catalysis studies. Bimetallic nanoclusters (NCs) in its many types, such as core/shell, random alloy, cluster-in-cluster, bi-hemisphere, and crown jewel (one kind of atom locating at the top position of another kind of NC), attract significant attention owing to their excellent optical, electronic, and catalytic properties. PVP-protected crown jewel-structured Pt/Au (CJ-Pt/Au) bimetallic nanoclusters (BNCs) with Au atoms located at active top sites were synthesized via a replacement reaction using 1.4-nm Pt NCs as mother clusters even considering the fact that the replacement reaction between Pt and Au3+ ions is difficult to be occurred. The prepared CJ-Pt/Au colloidal catalysts characterized by UV-Vis, TEM, HR-TEM and HAADF-STEM-EELS showed a high catalytic activity for aerobic glucose oxidation, and the top Au atoms decorating the Pt NCs were about 15 times more active than the Au atoms of Au NCs with similar particle size.

  8. Preparation and Catalytic Activity for Aerobic Glucose Oxidation of Crown Jewel Structured Pt/Au Bimetallic Nanoclusters

    PubMed Central

    Zhang, Haijun; Wang, Liqiong; Lu, Lilin; Toshima, Naoki

    2016-01-01

    Understanding of the “structure-activity” relations for catalysts at an atomic level has been regarded as one of the most important objectives in catalysis studies. Bimetallic nanoclusters (NCs) in its many types, such as core/shell, random alloy, cluster-in-cluster, bi-hemisphere, and crown jewel (one kind of atom locating at the top position of another kind of NC), attract significant attention owing to their excellent optical, electronic, and catalytic properties. PVP-protected crown jewel-structured Pt/Au (CJ-Pt/Au) bimetallic nanoclusters (BNCs) with Au atoms located at active top sites were synthesized via a replacement reaction using 1.4-nm Pt NCs as mother clusters even considering the fact that the replacement reaction between Pt and Au3+ ions is difficult to be occurred. The prepared CJ-Pt/Au colloidal catalysts characterized by UV-Vis, TEM, HR-TEM and HAADF-STEM-EELS showed a high catalytic activity for aerobic glucose oxidation, and the top Au atoms decorating the Pt NCs were about 15 times more active than the Au atoms of Au NCs with similar particle size. PMID:27476577

  9. Graphene nanosheet-tailored PtPd concave nanocubes with enhanced electrocatalytic activity and durability for methanol oxidation

    NASA Astrophysics Data System (ADS)

    Lu, Yizhong; Jiang, Yuanyuan; Chen, Wei

    2014-02-01

    Here, we demonstrate that graphene oxide (GO) can act as a structure-directing agent for the formation of PtPd alloy concave nanocubes enclosed by high index facets. In the presence of GO, PtPd alloy concave nanocubes could be easily tailored by a simple hydrothermal reaction. In sharp contrast, only cubic PtPd alloy nanocrystals were obtained in the absence of GO. Moreover, compared to the unsupported PtPd nanocubes, the composition ratio of Pt to Pd changed significantly from 1 : 1 to 3 : 1. Due to the exposed high-index facets and the strong interaction between catalysts and graphene support, the as-synthesized PtPd concave nanocubes exhibited enhanced electrocatalytic activity and high durability toward methanol oxidation. The present work highlights the unique role of GO in the formation of metal nanocrystals as not only a catalyst support but also a structure- and/or morphology-directing agent, due to the presence of various functional groups on GO sheets. The present GO-assisted approach provides a new avenue to the synthesis of nanocrystals with high-index facets and initiates new opportunities for the exploration of high-performance graphene-based nanocatalysts.Here, we demonstrate that graphene oxide (GO) can act as a structure-directing agent for the formation of PtPd alloy concave nanocubes enclosed by high index facets. In the presence of GO, PtPd alloy concave nanocubes could be easily tailored by a simple hydrothermal reaction. In sharp contrast, only cubic PtPd alloy nanocrystals were obtained in the absence of GO. Moreover, compared to the unsupported PtPd nanocubes, the composition ratio of Pt to Pd changed significantly from 1 : 1 to 3 : 1. Due to the exposed high-index facets and the strong interaction between catalysts and graphene support, the as-synthesized PtPd concave nanocubes exhibited enhanced electrocatalytic activity and high durability toward methanol oxidation. The present work highlights the unique role of GO in the formation of

  10. Thermal phase evolution of Pt-Si intermetallic thin films prepared by the activated adsorption of SiH{sub 4} on Pt(100) and comparison to known structural models

    SciTech Connect

    Bondos, J.C.; Drummer, N.E.; Gewirth, A.A.; Nuzzo, R.G.

    1999-03-24

    The authors have investigated the growth, morphology, and phase evolution of Pt-Si intermetallic thin films using scanning tunneling microscopy (STM), low-energy electron diffraction (LEED), and Auger electron spectroscopy (AES). These materials were formed through an inverted CVD deposition process that involves the exposure of a Pt(100) crystal to silane (SiH{sup 4}) followed by flash annealing treatments. Structural studies performed as a function of the annealing temperature reveal a complicated phase behavior that involves the sequential formation of four atomically ordered phases with multilevel character. The nature of this process is analyzed to obtain information about the primary structure-determining interactions responsible for the phase transformations seen in this system. This report describes the structure-determining influences seen on the Pt(100) surface and provide a comparison with earlier results obtained on Pt(111) and Ni surfaces. The substrate effects are marked and the differences between the results obtained on Pt(100) and Pt(111) are discussed in detail. A model is presented that relates the structure of the phases obtained on the Pt(100) surface to known bulk Pt silicide phases. Of particular interest is the finding that inverted CVD via the thermolytic decomposition of SiH{sub 4} on the Pt(100) substrate yields, upon suitable thermal treatment, a ({radical} 17 x {radical} 17)R14.0{degree} overlayer structure exhibiting two chiral surface domains. This multilayer structure is well described by a termination of the bulk Pt-Si intermetallic phase that is isomorphic with the well-known Ni{sub 12}P{sub 5} structure.

  11. Novel hollow Pt-ZnO nanocomposite microspheres with hierarchical structure and enhanced photocatalytic activity and stability.

    PubMed

    Yu, Changlin; Yang, Kai; Xie, Yu; Fan, Qizhe; Yu, Jimmy C; Shu, Qing; Wang, Chunying

    2013-03-01

    Noble metal/semiconductor nanocomposites play an important role in high efficient photocatalysis. Herein, we demonstrate a facile strategy for fabrication of hollow Pt-ZnO nanocomposite microspheres with hierarchical structure under mild solvothermal conditions using Zn (CH(3)COO)(2)·2H(2)O and HPtCl(4) as the precursors, and polyethylene glycol-6000 (PEG-6000) and ethylene glycol as the reducing agent and solvent, respectively. The as-synthesized ZnO and Pt-ZnO composite nanocrystals were well characterized by powder X-ray diffraction (XRD), nitrogen-physical adsorption, scanning electron microscopy (SEM), energy dispersive X-ray (EDX), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), UV-vis diffuse reflectance spectra (DRS), and photoluminescence (PL) emission spectroscopy. It was found that Pt content greatly influences the morphology of Pt-ZnO composite nanocrystals. Suitable concentration of HPtCl(4) in the reaction solution system can produce well hierarchically hollow Pt-ZnO nanocomposite microspheres, which are composed of an assembly of fine Pt-ZnO nanocrystals. Photocatalytic tests of the Pt-ZnO microspheres for the degradation of the dye acid orange II revealed extremely high photocatalytic activity and stability compared with those of pure ZnO and corresponding Pt deposited ZnO. The remarkable photocatalytic performance of hollow Pt-ZnO microspheres mainly originated from their unique nanostructures and the low recombination rate of the e(-)/h(+) pairs by the platinum nanoparticles embedded in ZnO nanocrystals. PMID:23385557

  12. Role of the Pinning Points in epitaxial Graphene Moiré Superstructures on the Pt(111) Surface

    PubMed Central

    Martínez, José I.; Merino, Pablo; Pinardi, Anna L.; Gonzalo, Otero-Irurueta; López, María F.; Méndez, Javier; Martín-Gago, José A.

    2016-01-01

    The intrinsic atomic mechanisms responsible for electronic doping of epitaxial graphene Moirés on transition metal surfaces is still an open issue. To better understand this process we have carried out a first-principles full characterization of the most representative Moiré superstructures observed on the Gr/Pt(111) system and confronted the results with atomically resolved scanning tunneling microscopy experiments. We find that for all reported Moirés the system relaxes inducing a non-negligible atomic corrugation both, at the graphene and at the outermost platinum layer. Interestingly, a mirror “anti-Moiré” reconstruction appears at the substrate, giving rise to the appearance of pinning-points. We show that these points are responsible for the development of the superstructure, while charge from the Pt substrate is injected into the graphene, inducing a local n-doping, mostly localized at these specific pinning-point positions. PMID:26852920

  13. Growth of cobalt ultra-thin films deposited on Pt(100) surfaces: An Auger electron spectroscopy study

    NASA Astrophysics Data System (ADS)

    Boeglin, C.; Carrière, B.; Deville, J. P.; Heckmann, O.; Leroux, C.; Panissod, P.

    1989-04-01

    To investigate the possibility of building Co/Pt modulated multilayers, attention has been paid to the early stages of interface formation between cobalt and platinum. The growth of cobalt layers less than 10 monolayers thick on Pt(100) surfaces has been studied by Auger electron spectroscopy. Growth kinetics obtained by AES show that two different models of interface formation can be possible: the Volmer-Weber case (cobalt islands) or an interdiffusion process between the two metals (similar to suicide formation). Looking at the fine structure of the low-energy platinum Auger transitions suggests that there is a strong interaction between cobalt and platinum as soon as the equivalent of a cobalt 2 monolayer coverage is deposited. This would favor the interdiffusion process model.

  14. Role of the Pinning Points in epitaxial Graphene Moiré Superstructures on the Pt(111) Surface.

    PubMed

    Martínez, José I; Merino, Pablo; Pinardi, Anna L; Gonzalo, Otero-Irurueta; López, María F; Méndez, Javier; Martín-Gago, José A

    2016-01-01

    The intrinsic atomic mechanisms responsible for electronic doping of epitaxial graphene Moirés on transition metal surfaces is still an open issue. To better understand this process we have carried out a first-principles full characterization of the most representative Moiré superstructures observed on the Gr/Pt(111) system and confronted the results with atomically resolved scanning tunneling microscopy experiments. We find that for all reported Moirés the system relaxes inducing a non-negligible atomic corrugation both, at the graphene and at the outermost platinum layer. Interestingly, a mirror "anti-Moiré" reconstruction appears at the substrate, giving rise to the appearance of pinning-points. We show that these points are responsible for the development of the superstructure, while charge from the Pt substrate is injected into the graphene, inducing a local n-doping, mostly localized at these specific pinning-point positions. PMID:26852920

  15. Design of Pt-CeOx hetero-interface on electrodes in polymer electrolyte membrane fuel cells

    NASA Astrophysics Data System (ADS)

    Mori, T.; Fugane, K.; Chauhan, S.; Ito, M.; Masuda, T.; Noguchi, H.; Uosaki, K.

    2014-03-01

    Pt-CeOx interface on Pt electrodes was prepared for improvement of both oxygen reduction reaction (ORR) activity of Pt cathode and CO tolerance of Pt anode. The surface of Pt-CeOx nano-particle/C electrode mainly consists of metallic Pt, ionized Pt (i.e. Pt2+) and Ce3+ species. The ORR activity on Pt was improved by the formation of Pt-CeOx interface. In-situ XAFS analysis suggests that cerium oxide surface in the Pt-CeOx/C was oxidized instead of Pt surface by electrochemical redox reaction of CeOx at room temperature. This suggests that the Pt-CeOx interface plays key role for improvement of cathode performance. Also, CO tolerance of Pt was improved by the formation of aforementioned interface. The improvement of CO tolerance of Pt was also observed by using in-situ IR analysis. Based on all experimental data, it is concluded that the design of defect structure in Pt-CeOx provides us opportunity to make the breakthrough electrodes for fuel cell application.

  16. Alkyl chain length-dependent surface reaction of dodecahydro-N-alkylcarbazoles on Pt model catalysts

    SciTech Connect

    Gleichweit, Christoph; Amende, Max; Bauer, Udo; Schernich, Stefan; Höfert, Oliver; Lorenz, Michael P. A.; Zhao, Wei; Bachmann, Philipp; Papp, Christian; Müller, Michael; Koch, Marcus; Wasserscheid, Peter; Libuda, Jörg; Steinrück, Hans-Peter

    2014-05-28

    The concept of liquid organic hydrogen carriers (LOHC) holds the potential for large scale chemical storage of hydrogen at ambient conditions. Herein, we compare the dehydrogenation and decomposition of three alkylated carbazole-based LOHCs, dodecahydro-N-ethylcarbazole (H{sub 12}-NEC), dodecahydro-N-propylcarbazole (H{sub 12}-NPC), and dodecahydro-N-butylcarbazole (H{sub 12}-NBC), on Pt(111) and on Al{sub 2}O{sub 3}-supported Pt nanoparticles. We follow the thermal evolution of these systems quantitatively by in situ high-resolution X-ray photoelectron spectroscopy. We show that on Pt(111) the relevant reaction steps are not affected by the different alkyl substituents: for all LOHCs, stepwise dehydrogenation to NEC, NPC, and NBC is followed by cleavage of the C–N bond of the alkyl chain starting at 380–390 K. On Pt/Al{sub 2}O{sub 3}, we discern dealkylation on defect sites already at 350 K, and on ordered, (111)-like facets at 390 K. The dealkylation process at the defects is most pronounced for NEC and least pronounced for NBC.

  17. 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

  18. Surface acoustic load sensing using a face-shear PIN-PMN-PT single-crystal resonator.

    PubMed

    Kim, Kyungrim; Zhang, Shujun; Jiang, Xiaoning

    2012-11-01

    Pb(In(0.5)Nb(0.5))O(3)-Pb(Mg(1/3)Nb(2/3))O(3)-PbTiO(3) (PIN-PMN-PT) resonators for surface acoustic load sensing are presented in this paper. Different acoustic loads are applied to thickness mode, thickness-shear mode, and face-shear mode resonators, and the electrical impedances at resonance and anti-resonance frequencies are recorded. More than one order of magnitude higher sensitivity (ratio of electrical impedance change to surface acoustic impedance change) at the resonance is achieved for the face-shear-mode resonator compared with other resonators with the same dimensions. The Krimholtz, Leedom, and Matthaei (KLM) model is used to verify the surface acoustic loading effect on the electrical impedance spectrum of face-shear PIN-PMN-PT single-crystal resonators. The demonstrated high sensitivity of face-shear mode resonators to surface loads is promising for a broad range of applications, including artificial skin, biological and chemical sensors, touch screens, and other touch-based sensors. PMID:23192819

  19. Effects of surface morphology and anisotropy on the tangential-momentum accommodation coefficient between Pt(100) and Ar

    NASA Astrophysics Data System (ADS)

    Pham, Thanh Tung; To, Quy Dong; Lauriat, Guy; Léonard, Céline; Hoang, Vo Van

    2012-11-01

    In this paper, we study the influence of platinum (100) surface morphology on the tangential-momentum accommodation coefficient with argon using a molecular dynamics method. The coefficient is computed directly by beaming Ar atoms onto the surfaces and measuring the relative momentum changes. The wall is maintained at a constant temperature and its interaction with the gas atoms is governed by the Kulginov potential. To capture correctly the surface effect of the walls and the atoms' trajectories, the quantum Sutton-Chen multibody potential is employed between the Pt atoms. The effects of wall surface morphology, incident direction, and temperature are considered in this work and provide full information on the gas-wall interaction.

  20. Tuning oxygen reduction reaction activity via controllable dealloying: a model study of ordered Cu3Pt/C intermetallic nanocatalysts.

    PubMed

    Wang, Deli; Yu, Yingchao; Xin, Huolin L; Hovden, Robert; Ercius, Peter; Mundy, Julia A; Chen, Hao; Richard, Jonah H; Muller, David A; DiSalvo, Francis J; Abruña, Héctor D

    2012-10-10

    A promising electrocatalyst prototype of low Pt mole fraction, intermetallic nanoparticles of Cu(3)Pt, has been prepared using a simple impregnation-reduction method, followed by a post heat-treatment. Two dealloying methods (electrochemical and chemical) were implemented to control the atomic-level morphology and improve performance for the oxygen reduction reaction (ORR). The morphology and elemental composition of the dealloyed nanoparticles were characterized at angstrom resolution using an aberration-corrected scanning transmission electron microscope equipped with an electron energy loss spectrometer. We found that the electrochemical dealloying method led to the formation of a thin Pt skin of ca. 1 nm in thickness with an ordered Cu(3)Pt core structure, while chemical leaching gave rise to a "spongy" structure with no ordered structure being preserved. A three-dimensional tomographic reconstruction indicated that numerous voids were formed in the chemically dealloyed nanoparticles. Both dealloying methods yielded enhanced specific and mass activities toward the ORR and higher stability relative to Pt/C. The spongy nanoparticles exhibited better mass activity with a slightly lower specific activity than the electrochemically dealloyed nanoparticles after 50 potential cycles. In both cases, the mass activity was still enhanced after 5000 potential cycles. PMID:22954373

  1. Pillared honeycomb nanoarchitectures formed on solid surfaces by the self-assembly of lipid-packaged one-dimensional Pt complexes

    PubMed Central

    Chang-Soo, Lee; Kimizuka, Nobuo

    2002-01-01

    A highly lipophilic polyion complex [Pt(en)2][PtCl2(en)2](1)4 (en, 1,2-diaminoethane) is prepared from one-dimensional mixed valence PtII/PtIV complex and newly designed chiral amphiphile 1. The powdery sample showed purple color, which is a result of the mixed valence absorption of the linear chlorobridged complex (PtII-Cl-PtIV-Cl-)n. When the lipid complex is dispersed in dichloromethane, purple-colored dispersion is obtained at 0°C, whereas the color disappears after heating the solution to 21°C. The observed thermochromism is reversible with respect to the temperature changes and is ascribed to the reversible dissociation and reassembly of the self-assembling inorganic wires. Casting of the 0°C-purple dispersion on solid substrates affords honeycomb nanostructures in addition to the nanowires with the width of about 20 nm. The honeycomb patterns seem to be templated by the condensed water droplets that are formed and aligned on the rapidly evaporating dichloromethane solution. On the other hand, more regular honeycomb structures are exclusively obtained by casting the 21°C-colorless solution. These observations indicate that the ordered honeycomb structures are obtainable on solid surfaces by the self-assembly of molecularly dispersed components [Pt(en)2](1)2 and trans-[PtCl2(en)2](1)2. Very interestingly, formation of double-layered honeycomb nanostructure is observed by scanning electron microscopy. The unit hexagons and pillars of the honeycombs are made of nanowires that are hierarchically assembled from the lipid-packaged PtII/PtIV complexes. The surface self-organization of lipophilic inorganic complexes has a potential to fabricate novel nanoarchitectures with conjugated electronic structures. PMID:11929964

  2. Xe adsorption site distributions on Pt(111), Pt(221) and Pt(531)

    NASA Astrophysics Data System (ADS)

    Gellman, Andrew J.; Baker, L.; Holsclaw, B. S.

    2016-04-01

    The ideal structures of the Pt(111), Pt(221) and Pt(531) surfaces expose adsorption sites that can be qualitatively described as terrace sites on Pt(111), both step and terrace sites on Pt(221), and kink sites on Pt(531). The real surface structures of these surfaces can be complicated by imperfections such as misorientation, reconstruction and thermal roughening, all of which will influence their distributions of adsorption sites. Xe adsorption sites on the Pt(111), Pt(221) and Pt(531) surfaces have been probed using both photoemission of adsorbed Xe (PAX) and temperature programmed desorption (TPD) of Xe. Both PAX and Xe TPD are sensitive to the adsorption sites of the Xe and serve as complementary means of assessing the distributions of adsorption sites on these three Pt surfaces. The adsorption of Xe is sufficiently sensitive to detect the presence of residual steps on the Pt(111) surface at a density of ~ 1.5% step atoms per Pt atom. On the Pt(221) surface, PAX and Xe TPD reveal adsorption at both terrace and step sites simultaneously. Although the ideal structure of the Pt(531) surface has no well-defined steps or terraces, Xe adsorption indicates that its adsorption sites are best described as a distribution of both step and kink sites with roughly twice as many steps sites as kinks.

  3. CO2 Activation and Hydrogenation by PtHn (-) Cluster Anions.

    PubMed

    Zhang, Xinxing; Liu, Gaoxiang; Meiwes-Broer, Karl-Heinz; Ganteför, Gerd; Bowen, Kit

    2016-08-01

    Gas phase reactions between PtHn (-) cluster anions and CO2 were investigated by mass spectrometry, anion photoelectron spectroscopy, and computations. Two major products, PtCO2 H(-) and PtCO2 H3 (-) , were observed. The atomic connectivity in PtCO2 H(-) can be depicted as HPtCO2 (-) , where the platinum atom is bonded to a bent CO2 moiety on one side and a hydrogen atom on the other. The atomic connectivity of PtCO2 H3 (-) can be described as H2 Pt(HCO2 )(-) , where the platinum atom is bound to a formate moiety on one side and two hydrogen atoms on the other. Computational studies of the reaction pathway revealed that the hydrogenation of CO2 by PtH3 (-) is highly energetically favorable. PMID:27363532

  4. Graphene nanosheet-tailored PtPd concave nanocubes with enhanced electrocatalytic activity and durability for methanol oxidation.

    PubMed

    Lu, Yizhong; Jiang, Yuanyuan; Chen, Wei

    2014-03-21

    Here, we demonstrate that graphene oxide (GO) can act as a structure-directing agent for the formation of PtPd alloy concave nanocubes enclosed by high index facets. In the presence of GO, PtPd alloy concave nanocubes could be easily tailored by a simple hydrothermal reaction. In sharp contrast, only cubic PtPd alloy nanocrystals were obtained in the absence of GO. Moreover, compared to the unsupported PtPd nanocubes, the composition ratio of Pt to Pd changed significantly from 1 : 1 to 3 : 1. Due to the exposed high-index facets and the strong interaction between catalysts and graphene support, the as-synthesized PtPd concave nanocubes exhibited enhanced electrocatalytic activity and high durability toward methanol oxidation. The present work highlights the unique role of GO in the formation of metal nanocrystals as not only a catalyst support but also a structure- and/or morphology-directing agent, due to the presence of various functional groups on GO sheets. The present GO-assisted approach provides a new avenue to the synthesis of nanocrystals with high-index facets and initiates new opportunities for the exploration of high-performance graphene-based nanocatalysts. PMID:24519683

  5. One-pot synthesis of single-crystal Pt nanoplates uniformly deposited on reduced graphene oxide, and their high activity and stability on the electrocalalytic oxidation of methanol.

    PubMed

    Hao, Yanfei; Wang, Xudan; Shen, Jianfeng; Yuan, Junhua; Wang, Ai-Jun; Niu, Li; Huang, Shengtang

    2016-04-01

    We demonstrate a one-pot thermoreduction approach towards the preparation of single-crystal Pt nanoplates, which were uniformly deposited on the reduced graphene oxide (RGO) using polyvinylpyrrolidone (PVP) as a stabilizer. The size of Pt nanoplates can be tuned from 6.8 to 10.1 nm by controlling Pt loading. The as-prepared Pt/PVP/RGO catalysts show high stability and activity towards the methanol oxidation reaction (MOR). Their MOR current can reach up to 401 mA mg(-1) Pt and MOR current can maintain 89.4% of its initial value after 10 000 potential cycles. PMID:26906081

  6. A facile reflux procedure to increase active surface sites form highly active and durable supported palladium@platinum bimetallic nanodendrites

    NASA Astrophysics Data System (ADS)

    Wang, Qin; Li, Yingjun; Liu, Baocang; Xu, Guangran; Zhang, Geng; Zhao, Qi; Zhang, Jun

    2015-11-01

    A series of well-dispersed bimetallic Pd@Pt nanodendrites uniformly supported on XC-72 carbon black are fabricated by using different capping agents. These capping agents are essential for the branched morphology control. However, the surfactant adsorbed on the nanodendrites surface blocks the access of reactant molecules to the active surface sites, and the catalytic activities of these bimetallic nanodendrites are significantly restricted. Herein, a facile reflux procedure to effectively remove the capping agent molecules without significantly affecting their sizes is reported for activating supported nanocatalysts. More significantly, the structure and morphology of the nanodendrites can also be retained, enhancing the numbers of active surface sites, catalytic activity and stability toward methanol and ethanol electro-oxidation reactions. The as-obtained hot water reflux-treated Pd@Pt/C catalyst manifests superior catalytic activity and stability both in terms of surface and mass specific activities, as compared to the untreated catalysts and the commercial Pt/C and Pd/C catalysts. We anticipate that this effective and facile removal method has more general applicability to highly active nanocatalysts prepared with various surfactants, and should lead to improvements in environmental protection and energy production.

  7. Synthesis And Characterization of Gamma-Al2O3-Supported Pt Catalysts From Pt(4) And Pt(6) Clusters Formed in Aqueous Solutions

    SciTech Connect

    Siani, A.; Wigal, K.R.; Alexeev, A.S.; Amiridis, M.D.

    2009-05-26

    Highly dispersed Pt catalysts were prepared by deposition of Pt{sub 4} and Pt{sub 6} clusters, initially formed in unprotected and poly(vinyl alcohol) (PVA)-protected colloidal Pt suspensions, onto a {gamma}-Al{sub 2}O{sub 3} surface. These catalysts were characterized by extended X-ray absorption fine structure (EXAFS) and Fourier transform infrared (FTIR) spectroscopies. The EXAFS results indicate that the supported Pt species formed were very similar in structure to those of the original clusters in the corresponding colloidal suspensions. The FTIR results further indicate that the {gamma}-Al{sub 2}O{sub 3}-supported Pt{sub 4} clusters have significantly lower chemisorptive properties compared with larger supported Pt nanoparticles; nevertheless, the Pt{sub 4}/{gamma}-Al{sub 2}O{sub 3} sample was active for the oxidation of CO with no need for additional activation treatment. In fact, treatment of this sample with H{sub 2} at 150--200 {sup o}C led to the formation of Pt aggregates with sizes of 1.0--1.6 nm, demonstrating that the surface Pt4 species readily sintered in this temperature range under reducing conditions.

  8. Zero-point vibration of hydrogen adsorbed on Si and Pt surfaces.

    PubMed

    Fukutani, K; Itoh, A; Wilde, M; Matsumoto, M

    2002-03-18

    Hydrogen atoms adsorbed on Si(111) and Pt(111) were investigated by nuclear reaction analysis (NRA) using 1H(15N,alphagamma)12C. From measurements of the NRA spectrum at normal and tilted ion incidences the zero-point vibrational energies of H on Si(111) in the perpendicular and parallel directions were found to be 123.4+/-4.6 and 44.6+/-6.2 meV, respectively, which are consistent with harmonic potentials. The zero-point energies obtained for Pt(111)-H were 80.8+/-3.9 and 62.1+/-6.0 meV for perpendicular and parallel directions, respectively. These results indicate that the stretching mode is harmonic, while the bending mode is strongly anharmonic. PMID:11909413

  9. Co-Pt core-shell nanostructured catalyst prepared by selective chemical vapor pulse deposition of Pt on Co as a cathode in polymer electrolyte fuel cells

    SciTech Connect

    Seo, Sang-Joon; Chung, Ho-Kyoon; Yoo, Ji-Beom; Chae, Heeyeop; Seo, Seung-Woo; Min Cho, Sung

    2014-01-15

    A new type of PtCo/C catalyst for use as a cathode in polymer electrolyte fuel cells was prepared by selective chemical vapor pulse deposition (CVPD) of Pt on the surface of Co. The activity of the prepared catalyst for oxygen reduction was higher than that of a catalyst prepared by sequential impregnation (IMP) with the two metallic components. This catalytic activity difference occurs because the former catalyst has smaller Pt crystallites that produce stronger Pt-Co interactions and have a larger Pt surface area. Consequently, the CVPD catalyst has a great number of Co particles that are in close contact with the added Pt. The Pt surface was also electronically modified by interactions with Co, which were stronger in the CVPD catalyst than in the IMP catalyst, as indicated by X-ray diffraction, X-ray photoemission spectroscopy, and cyclic voltammetry measurements of the catalysts.

  10. Atomically flat surface of (0 0 1) textured FePt thin films by residual stress control

    NASA Astrophysics Data System (ADS)

    Liu, S. H.; Hsiao, S. N.; Chou, C. L.; Chen, S. K.; Lee, H. Y.

    2015-11-01

    Single-layered Fe52Pt48 films with thickness of 10 nm were sputter-deposited on glass substrates. Rapid thermal annealing with different heating rates (10-110 K/s) was applied to transform as-deposited fcc phase into L10 phase and meanwhile to align [0 0 1]-axis of L10 crystal along plane normal direction. Based on X-ray diffractometry using synchrotron radiation source, the texture coefficient of (0 0 1)-plane increases with increasing heating rate from 10 to 40 K/s, which is correlated with perpendicular magnetic anisotropy and in-plane tensile stress analyzed by asymmetric sin2 ψ method. Furthermore, it was revealed by atomic force microscopy that the dewetting process occurred as heating rate was raised up to 80 K/s and higher. The change in the microstructure due to stress relaxation leads to the degradation of (0 0 1) orientation and magnetic properties. Surface roughness is closely related to the in-plane tensile stress. Enhanced perpendicular magnetic anisotropy and atomically flat surface were achieved for the samples annealed at 40 K/s, which may be suitable for further practical applications. This work also suggests a feasible way for surface engineering by controlling internal stress of the FePt without introducing cap layer.

  11. Self-supported Pt nanoclusters via galvanic replacement from Cu2O nanocubes as efficient electrocatalysts

    NASA Astrophysics Data System (ADS)

    Li, Qing; Xu, Ping; Zhang, Bin; Wu, Gang; Zhao, Hongtao; Fu, Engang; Wang, Hsing-Lin

    2013-07-01

    A novel synthesis method for self-supported Pt nanoclusters (Pt NCs) comprised of interconnected 2-3 nm Pt nanoparticles was developed by employing the galvanic replacement process between Cu2O nanocubes and PtCl42- ions. This discovered synthesis procedure eliminates the use of any polymer capping agents and enables a catalytically clean Pt surface. It is determined that the presence of H+ ions is crucial for initializing the galvanic replacement reaction. The electrocatalytic performances of the Pt NCs were tested for both oxygen reduction and methanol oxidation reactions, which showed higher electrochemical activity and greater long-term durability as compared with commercial Pt materials.A novel synthesis method for self-supported Pt nanoclusters (Pt NCs) comprised of interconnected 2-3 nm Pt nanoparticles was developed by employing the galvanic replacement process between Cu2O nanocubes and PtCl42- ions. This discovered synthesis procedure eliminates the use of any polymer capping agents and enables a catalytically clean Pt surface. It is determined that the presence of H+ ions is crucial for initializing the galvanic replacement reaction. The electrocatalytic performances of the Pt NCs were tested for both oxygen reduction and methanol oxidation reactions, which showed higher electrochemical activity and greater long-term durability as compared with commercial Pt materials. Electronic supplementary information (ESI) available: Fig. S1-S9. See DOI: 10.1039/c3nr02243a

  12. Electronic bands, Fermi surface, and elastic properties of new 4.2 K superconductor SrPtAs with a honeycomb structure from first principles calculations

    NASA Astrophysics Data System (ADS)

    Shein, I. R.; Ivanovskii, A. L.

    2011-10-01

    The hexagonal phase SrPtAs (s.g. P6/ mmm; #194) with a honeycomb lattice structure was recently declared as a new low-temperature ( T C ∼ 4.2 K) superconductor. Here, by means of first-principles calculations the optimized structural parameters, electronic bands, Fermi surface, total and partial densities of states, inter-atomic bonding picture, independent elastic constants, bulk and shear moduli for SrPtAs were obtained for the first time and analyzed in comparison with the related layered superconductor SrPt 2As 2.

  13. LEED crystallography studies of the structure of clean and adsorbate-covered Ir, Pt and Rh crystal surfaces

    SciTech Connect

    Koestner, R.J.

    1982-08-01

    There have only been a few Low Energy Electron Diffraction (LEED) intensity analyses carried out to determine the structure of molecules adsorbed on metal surfaces; most surface crystallography studies concentrated on the structure of clean unreconstructed or atomic adsorbate-covered transition metal faces. The few molecular adsorption systems already investigated by dynamical LEED are CO on Ni(100), Cu(100) and Pd(100) as well as C/sub 2/H/sub 2/ and C/sub 2/H/sub 4/ adsorbed on Pt(111). The emphasis of this thesis research has been to extend the applicability of LEED crystallography to the more complicated unit cells found in molecular overlayers on transition metals or in there constructed surfaces of clean transition metals.

  14. Pt-Au/Al[sub 2]O[sub 3] catalysts: Preparation, characterization, and dehydrogenation activity

    SciTech Connect

    Rouabah, D.; Fraissard, J. )

    1993-11-01

    The physicochemical characteristics of Pt-Au catalysts, such as the dispersion, chemisorption, and thermodesorption of hydrogen, have been studied in terms of gold content. The catalysts were prepared by coimpregnation of a [gamma]-alumina by a mixture of hexachloroplatinic and tetrachloroauric acids, calcination in oxygen and slow reduction in H[sub 2]-He from 25 to 400[degrees]C. The most outstanding result is the very large increase in the dispersion with the gold concentration. For example, with the alloy containing 80% gold more than 70% of the detectable particles are below 10 [angstrom]. In the same way, the activity per site and the selectivity in the dehydrogenation of methylcyclohexane to toluene increase with the gold concentration. 26 refs., 10 figs., 2 tabs.

  15. Dependence of Gas-Phase Crotonaldehyde Hydrogenation Selectivity and Activity on the Size of Pt Nanoparticles (1.7-7.1 nm) Supported on SBA-15

    SciTech Connect

    Grass, Michael; Rioux, Robert; Somorjai, Gabor A.

    2008-08-03

    The selectivity and activity for the hydrogenation of crotonaldehyde to crotyl alcohol and butyraldehyde was studied over a series of Pt nanoparticles (diameter of 1.7, 2.9, 3.6, and 7.1 nm). The nanoparticles were synthesized by the reduction of chloroplatinic acid by alcohol in the presence of poly(vinylpyrrolidone) (PVP), followed by encapsulation into mesoporous SBA-15 silica. The rate of crotonaldehyde hydrogenation and selectivity towards crotyl alcohol both increase with increasing particle size. The selectivity towards crotyl alcohol increased from 13.7 % to 33.9 % (8 Torr crotonaldehyde, 160 Torr H{sub 2} and 353 K), while the turnover frequency increases from 2.1 x 10{sup -2} s{sup -1} to 4.8 x 10{sup -2} s{sup -1} with an increase in the particle size from 1.7 nm to 7.1 nm. The decarbonylation pathway to form propene and CO is enhanced over the higher proportion of coordinatively unsaturated sites on the smaller nanoparticles. The apparent activation energy remains constant ({approx} 16 kcal mol{sup -1} for the formation of butyraldehyde and {approx} 8 kcal mol{sup -1} for the formation of crotyl alcohol) as a function of particle size. In the presence of 130-260 mTorr CO, the reaction rate decreases for all products with a CO reaction order of -0.9 for crotyl alcohol and butyraldehyde over 7.1 nm Pt particles; over 1.7 nm Pt particles, the order in CO is -1.4 and -0.9, respectively. Hydrogen reduction at 673 K after calcination in oxygen results in increased activity and selectivity relative to reduction at either higher or lower temperature; this is discussed with regards to the incomplete removal and/or change in morphology of the polymeric surface stabilizing agent, poly(vinylpyrrolidone) used for the synthesis of the Pt nanoparticles.

  16. Very low amount of TiO2 on N-doped carbon nanotubes significantly improves oxygen reduction activity and stability of supported Pt nanoparticles.

    PubMed

    Zhao, Anqi; Masa, Justus; Xia, Wei

    2015-04-28

    Electrochemical corrosion is a major problem for carbon materials used in electrocatalysis. Highly dispersed TiO2 was deposited on O-functionalized and N-doped carbon nanotubes by chemical vapour deposition to tackle the carbon corrosion problem. Very low Ti loadings of about 1 wt% were applied to minimize the negative influence of TiO2 as a semiconductor on the high conductivity of carbon materials. Both N doping and TiO2 coating facilitate strong metal-support interactions and favour the formation of small Pt particles. N doping improved the intrinsic catalytic activity of the carbon support and enhanced the conductivity due to the removal of surface oxygen groups, while the negative effect of TiO2 on conductivity is counterbalanced by its promoting effect on metal-support interactions leading to enhanced overall catalytic performance. Pt/TiO2/NCNTs showed the highest ORR activity, and significantly outperformed Pt/NCNTs in electrochemical stability tests. PMID:25811122

  17. Highly Active Nanoreactors: Patchlike or Thick Ni Coating on Pt Nanoparticles Based on Confined Catalysis.

    PubMed

    Qi, Xinhong; Li, Xiangcun; Chen, Bo; Lu, Huilan; Wang, Le; He, Gaohong

    2016-01-27

    Catalyst-containing nanoreactors have attracted considerable attention for specific applications. Here, we initially report preparation of PtNi@SiO2 hollow microspheres based on confined catalysis. The previous encapsulation of dispersed Pt nanoparticles (NPs) in hollow silica microspheres ensures the formation of Pt@Ni coreshell NPs inside the silica porous shell. Thus, the Pt NPs not only catalyze the reduction of Ni ions but also direct Ni deposition on the Pt cores to obtain Pt@Ni core-shell catalyst. It is worthy to point out that this synthetic approach helps to form a patchlike or thick Ni coating on Pt cores by controlling the penetration time of Ni ions from the bulk solution into the SiO2 microspheres (0.5, 1, 2, or 4 h). Notably, the Pt@Ni core-shell NPs with a patch-like Ni layer on Pt cores (0.5 and 1 h) show a higher H2 generation rate of 1221-1475 H2 mL min(-1) g(-1)cat than the Pt@Ni NPs with a thick Ni layer (2 and 4 h, 920-1183 H2 mL min(-1) g(-1)cat), and much higher than that of pure Pt NPs (224 H2 mL min(-1) g(-1)cat). In addition, the catalyst possesses good stability and recyclability for H2 generation. The Pt@Ni core-shell NPs confined inside silica nanocapsules, with well-defined compositions and morphologies, high H2 generation rate, and recyclability, should be an ideal catalyst for specific applications in liquid phase reaction. PMID:26725500

  18. The enhanced electrocatalytic activity and stability of supported Pt nanopartciles for methanol electro-oxidation through the optimized oxidation degree of carbon nanotubes

    NASA Astrophysics Data System (ADS)

    Xiao, Meiling; Zhu, Jianbing; Ge, Junjie; Liu, Changpeng; Xing, Wei

    2015-05-01

    Carbon nanotubes (CNTs) with different oxidation degrees are synthesized by the modified Hummer's method and used as the support materials for platinum (Pt) catalysts. The effect of their oxidation degree on the catalytic activity and stability of the supported Pt catalysts for methanol electrooxidation is investigated for the first time. The electrocatalytic activity for methanol oxidation reaction increases with increasing the oxidation degree due to more oxygen-containing species introduced to CNTs, which improves the dispersion of Pt nanoparticles and also modifies the electronic structure of Pt catalysts. However, under more severe oxidation condition, the stability of Pt catalysts decreases due to the destruction of graphitic structure of CNTs. Therefore, the optimized treatment condition for the CNTs is mild oxidation, which provides the supported Pt catalysts with both excellent catalytic activity and stability.

  19. Dissociative chemisorption of methane on Ni and Pt surfaces: mode-specific chemistry and the effects of lattice motion.

    PubMed

    Nave, Sven; Tiwari, Ashwani K; Jackson, Bret

    2014-10-16

    The dissociative chemisorption of methane on metal surfaces is of great practical and fundamental interest. Not only is it the rate-limiting step in the steam re-forming of natural gas, but also the reaction exhibits interesting mode-specific behavior and a strong dependence on the temperature of the metal. Electronic structure methods are used to explore this reaction on various Ni and Pt surfaces, with a focus on how the transition state is modified by motion of the metal lattice atoms. These results are used to construct models that explain the strong variation in reactivity with substrate temperature, shown to result primarily from changes in the dissociation barrier height with lattice motion. The dynamics of the dissociative chemisorption of CH4 on Ni and Pt is explored, using a fully quantum approach based on the reaction path Hamiltonian that includes all 15 molecular degrees of freedom and the effects of lattice motion. Agreement with experiment is good, and vibrational excitation of the molecule is shown to significantly enhance reactivity. The efficacy for this is examined in terms of the vibrationally nonadiabatic couplings, mode softening, mode symmetry, and energy localization in the reactive bond. PMID:25153478

  20. A novel non-enzymatic glucose sensor based on Pt3Ru1 alloy nanoparticles with high density of surface defects.

    PubMed

    Yang, Jiangwei; Liang, Xinyi; Cui, Lan; Liu, Haiyan; Xie, Junbo; Liu, Weixing

    2016-06-15

    A novel non-enzymatic glucose sensor based on a glassy carbon electrode modified with Pt3Ru1 alloy nanoparticles (Pt3Ru1/GCE) was fabricated. Pt3Ru1 alloy nanoparticles were prepared by a reverse microemulsion method at room temperature. The X-ray diffraction (XRD) and energy dispersive X-ray spectroscopy (EDS) demonstrate that Pt3Ru1 nanoparticles are disordered alloy with face central cubic (fcc) structure and the atom ratio of Pt and Ru is 3:1. The high-resolution transmission electron microscopy (HRTEM) images show that Pt3Ru1 alloy nanoparticles were aggregated with a high density of surface defects. Furthermore, the sensor properties of Pt3Ru1/GCE were investigated by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and chronoamperometry (CA) in 0.01 M PBS (pH 7.4). The results indicate that the proposed sensor exhibits a wide linear range of 5 × 10(-7)M to 10(-2)M (R(2)=0.9988) with a low detection limit of 0.3 μM for glucose. Moreover, the sensor demonstrates good sensitivity, stability, reproducibility, and better anti-interference performance toward ascorbic acid (AA), uric acid (UA), and fructose (Fru). PMID:26827147

  1. Preparation of well-defined surfaces at atmospheric pressure: Studies of structural transformations of I, Ag-Adlattices on Pt(111) by leed and electrochemistry

    NASA Astrophysics Data System (ADS)

    Wieckowski, Andrzej; Schardt, Bruce C.; Rosasco, Stephen D.; Stickney, John L.; Hubbard, Arthur T.

    1984-10-01

    Pt(111) surfaces disordered by ion-bombardment or electrochemical oxidation were converted to well-defined, ordered states by annealing in iodine vapor at atmospheric pressure. A structure not obtainable in vacuum was formed, Pt(111)(3 3 × 9 3)R30°-I , containing 0.62 I atoms per surfa ce Pt atom in a slightly distorted hexagonal array. The I-I interatomic distances in this structure, 0.33 and 0.36 nm, were less than the Van der Waals distance, 0.43 nm. Gentle heating of this structure under pure Ar yielded I 2 molecules, I atoms and a series of structures: Pt(111)(3 3 × 9 3)R30°-I ?( 3 × 3)R30°-I ?Pt(111) (clean surface). The Pt(111)( 7 × 7 )R19.1°-I adlattice proved to be identifiable from its distinctive electrochemical behavior in electrodeposition of Ag from aqueous solutions of AgClO 4, which consists of three prominent structural transitions. Kinematic calculations of the directions and qualitative intensities of the LEED beams at selected kinetic energies has led to proposed structures consisting of Ag atoms close-packed in registry with the three-fold sites of Pt but with I atoms substituted for Ag atoms at the ( 3 × 3)R30° positions. Phase boundaries caused by reversals of the two packing sites of the 3 unit mesh at intervals 17 Pt unit vectors divide the surface into hexagonal antiphase domains.

  2. Artist's rendering of Lunar Surface Activities

    NASA Technical Reports Server (NTRS)

    1969-01-01

    Lunar Surface Activities: Instruments erected on the surface are a seismometer to record any subsurface activity of the Moon, a laser reflector, a solar wind collector, and possibly an antenna for improving communications and television picture transmission.

  3. Density Functional Theory Study of the Energetics, Electronic Structure, and Core-Level Shifts of NO Adsorption on the Pt(111) Surface

    SciTech Connect

    Zeng, Z. H.; Da Silva, J. L. F.; Deng, H. Q.; Li, W. X.

    2009-01-01

    In this work, we report a first-principles investigation of the energetics, structures, electronic properties, and core-level shifts of NO adsorption on the Pt(111) surface. Our calculations are based on density functional theory within the framework of the ultrasoft pseudopotential plane-wave and the all-electron projected augmented-wave methods. We found that at 0.25, 0.50, and 0.75 monolayer, NO adsorbs preferentially in the fcc, fcc+top, and fcc+top+hcp sites, respectively. The geometric parameters, adsorption energies, vibrational frequencies, and work-function changes are in good agreement with the experimental data. The interaction between NO and Pt(111) was found to follow a donation-back-donation process, in which the NO {sigma} states donate electrons to the substrate Pt d states, while the substrate Pt d states back donate to the NO {pi} states. Though there is an overall net charge transfer from the substrate to the NO adsorbate regardless of the adsorption sites and coverages, the spatial redistribution of the transferred electron is site dependent. The charge accumulation for NO in the top sites occurs closer to the surface than NO in the hollow sites, which results in the reduction of the Pt(111) surface work function for the top NO but an increase for the hollow NO. The core-level shifts of the topmost surface Pt atoms coordinated with top and hollow NO molecules at different coverages are in excellent agreement with experiments. In contrast, the N 1s core-level shifts between top and hollow NO ({approx}0.7 eV) deviated significantly from the zero shift found in experiments. Our analysis indicates that the difference may come from the thermal vibration and rotation of adsorbed NO on the Pt(111) surface.

  4. Site-specific Pt Deposition and Etching on Electrically and Thermally Isolated SiO2 Micro-disk Surfaces

    SciTech Connect

    Saraf, Laxmikant V.

    2010-03-22

    Electrically and thermally isolated surfaces are often crucial for improving the detection sensitivity of microelectronic sensors. The site specific in-situ growth of Pt nano-rods on thermally and electrically isolated micro-fabricated SiO2 disks using wet chemical etching and focused ion/electron dual-beam (FIB-SEM) is demonstrated in this work. Fabrication of an array of micro-cavities on top of micro-disk is also demonstrated. FIB source is also utilized to fabricate through-holes in the micro-disks. The nature of Ga Gaussian distribution in the Ga-implanted region using a FIB source can naturally create more conducting layer on the sidewalls of through-holes on the micro-disks. Some sensor design concepts based on micro-fabrication of SiO2 micro-disks utilizing thermally and electrically isolated surfaces are discussed from the viewpoint of applications in photonics and bio-sensing.

  5. Mode-selective chemistry on metal surfaces: The dissociative chemisorption of CH4 on Pt(111)

    NASA Astrophysics Data System (ADS)

    Guo, Han; Jackson, Bret

    2016-05-01

    A quantum approach based on an expansion in vibrationally adiabatic eigenstates is used to explore CH4 dissociation on Pt(111). Computed sticking probabilities for molecules in the ground, 1v3 and 2v3, states are in very good agreement with the available experimental data, reproducing the variation in reactivity with collision energy and vibrational state. As was found in similar studies on Ni(100) and Ni(111), exciting the 1v1 symmetric stretch of CH4 is more effective at promoting the dissociative chemisorption of CH4 than exciting the 1v3 antisymmetric stretch. This behavior is explained in terms of symmetry, mode-softening, and nonadiabatic transitions between vibrationally adiabatic states. We find that the efficacies of the bending modes for promoting reaction are reasonably large, and similar to the 1v3 state. The vibrational efficacies for promoting reaction on Ni(111) are larger than for reaction on Pt(111), due to the larger nonadiabatic couplings. Our computed sticking probabilities are in good agreement with results from recent ab initio molecular dynamics and reactive force field studies.

  6. Mode-selective chemistry on metal surfaces: The dissociative chemisorption of CH4 on Pt(111)

    DOE PAGESBeta

    Guo, Han; Jackson, Bret

    2016-05-13

    A quantum approach based on an expansion in vibrationally adiabatic eigenstates is used to explore CH4 dissociation on Pt(111). Computed sticking probabilities for molecules in the ground, 1v3 and 2v3, states are in very good agreement with the available experimental data, reproducing the variation in reactivity with collision energy and vibrational state. As was found in similar studies on Ni(100) and Ni(111), exciting the 1v1 symmetric stretch of CH4 is more effective at promoting the dissociative chemisorption of CH4 than exciting the 1v3 antisymmetric stretch. This behavior is explained in terms of symmetry, mode-softening, and nonadiabatic transitions between vibrationally adiabaticmore » states. We find that the efficacies of the bending modes for promoting reaction are reasonably large, and similar to the 1v3 state. The vibrational efficacies for promoting reaction on Ni(111) are larger than for reaction on Pt(111), due to the larger nonadiabatic couplings. As a result, our computed sticking probabilities are in good agreement with results from recent ab initio molecular dynamics and reactive force field studies.« less

  7. Mode-selective chemistry on metal surfaces: The dissociative chemisorption of CH4 on Pt(111).

    PubMed

    Guo, Han; Jackson, Bret

    2016-05-14

    A quantum approach based on an expansion in vibrationally adiabatic eigenstates is used to explore CH4 dissociation on Pt(111). Computed sticking probabilities for molecules in the ground, 1v3 and 2v3, states are in very good agreement with the available experimental data, reproducing the variation in reactivity with collision energy and vibrational state. As was found in similar studies on Ni(100) and Ni(111), exciting the 1v1 symmetric stretch of CH4 is more effective at promoting the dissociative chemisorption of CH4 than exciting the 1v3 antisymmetric stretch. This behavior is explained in terms of symmetry, mode-softening, and nonadiabatic transitions between vibrationally adiabatic states. We find that the efficacies of the bending modes for promoting reaction are reasonably large, and similar to the 1v3 state. The vibrational efficacies for promoting reaction on Ni(111) are larger than for reaction on Pt(111), due to the larger nonadiabatic couplings. Our computed sticking probabilities are in good agreement with results from recent ab initio molecular dynamics and reactive force field studies. PMID:27179502

  8. Exceptional activity of sub-nm Pt clusters on CdS for photocatalytic hydrogen production: A combined of experimental and first-principles study

    SciTech Connect

    Wu, Qiyuan; Su, Dong; Xiong, Shangmin; Shen, Peichuan; Zhao, Shen; Li, Yan; Orlov, Alexander

    2014-12-24

    In this work we have explored a new concept of substantially increasing photocatalytic activity for H₂ production of conventional semiconductors by modifying them with sub-nm Pt particles. By combining both experimental and theoretical approaches, we have also developed new mechanistic insights into the 17 times increase in photocatalytic activity of Pt modified CdS catalysts.

  9. Synthesis and electrocatalytic activity of Au/Pt bimetallic nanodendrites for ethanol oxidation in alkaline medium.

    PubMed

    Han, Xinyi; Wang, Dawei; Liu, Dong; Huang, Jianshe; You, Tianyan

    2012-02-01

    Gold/Platinum (Au/Pt) bimetallic nanodendrites were successfully synthesized through seeded growth method using preformed Au nanodendrites as seeds and ascorbic acid as reductant. Cyclic voltammograms (CVs) of a series of Au/Pt nanodendrites modified electrodes in 1M KOH solution containing 1M ethanol showed that the electrocatalyst with a molar ratio (Au:Pt) of 3 exhibited the highest peak current density and the lowest onset potential. The peak current density of ethanol electro-oxidation on the Au(3)Pt(1) nanodendrites modified glassy carbon electrode (Au(3)Pt(1) electrode) is about 16, 12.5, and 4.5 times higher than those on the polycrystalline Pt electrode, polycrystalline Au electrode, and Au nanodendrites modified glassy carbon electrode (Au dendrites electrode), respectively. The oxidation peak potential of ethanol electro-oxidation on the Au(3)Pt(1) electrode is about 299 and 276 mV lower than those on the polycrystalline Au electrode and Au dendrites electrode, respectively. These results demonstrated that the Au/Pt bimetallic nanodendrites may find potential application in alkaline direct ethanol fuel cells (ADEFCs). PMID:22071516

  10. Effect of Ce addition on the surface properties and n-dodecane dehydrogenation performance of Pt-Sn/Ce-Al2O3 catalyst

    NASA Astrophysics Data System (ADS)

    Li, Xianru; He, Songbo; Wei, Huangzhao; Luo, Sha; Gu, Bin; Sun, Chenglin

    2015-08-01

    Ce-modified alumina carriers with different Ce content were prepared by vacuum isovolume impregnation method aiming to improve the n-dodecane catalytic dehydrogenation performance of PtSn/Al2O3 catalyst. The support and catalyst were characterized by XRD, N2 adsorption-desorption, NH3-TPD, H2-TPR, CO-pulse adsorption and TG-DTG. Results showed that Ce addition decreased the surface acid amount significantly and inhibited the reduction of SnO x species. Besides, Ce containing catalyst showed higher n-dodecane dehydrogenation activity and stability and lower coke deposition amount and coke burning temperature. In our study, the optimal Ce addition amount for n-dodecane dehydrogenation was 2%.

  11. Enhancing stability of octahedral PtNi nanoparticles for oxygen reduction reaction by halide treatment

    NASA Astrophysics Data System (ADS)

    Choi, Juhyuk; Lee, Youhan; Kim, Jihan; Lee, Hyunjoo

    2016-03-01

    Because a reduction in the amount of Pt catalysts is essential for the commercialization of fuel cells, various approaches have been tested to maximize the mass activity of Pt-based catalysts. Among these, the most successful results so far were obtained using shaped PtNi alloy nanoparticles, preferably with PtNi(111) facets. However, these nanoparticles typically suffer from much lower activity after the durability tests due to the leaching out of the surface Ni during the oxygen reduction reaction (ORR), which leads to the disappearance of the activity-enhancing effect caused by electronic structure modification. Here, we showed that halide treatment of the octahedral PtNi nanoparticles could significantly enhance their durability. Halides are adsorbed on surface Ni more strongly than on surface Pt, and the surface halides are found to preserve the surface Ni that induces the ORR activity enhancement. Especially, Br can preserve the surface Ni effectively. Durability testing by repeating cyclic voltammetry 10,000 times in the 0.6-1.1 V range showed that the mass activity decreased by 52.6% for the as-prepared PtNi octahedral nanoparticles, whereas the mass activity decreased by only 15.0% for the Br-treated PtNi nanoparticles. The simple treatment significantly enhanced the long-term stability of the highly active PtNi alloy nano-octahedra.

  12. Surface-plasmon mediated photoluminescence enhancement of Pt-coated ZnO nanowires by inserting an atomic-layer-deposited Al2O3 spacer layer

    NASA Astrophysics Data System (ADS)

    Ren, Qing-Hua; Zhang, Yan; Lu, Hong-Liang; Chen, Hong-Yan; Zhang, Yuan; Li, De-Hui; Liu, Wen-Jun; Ding, Shi-Jin; Jiang, An-Quan; Zhang, David Wei

    2016-04-01

    Surface-plasmon mediated photoluminescence emission enhancement has been investigated for ZnO nanowire (NW)/Pt nanoparticle (NP) nanostructures by inserting an Al2O3 spacer layer. The thickness of the Al2O3 spacer layer and of the Pt NPs capped on the ZnO NWs are well controlled by atomic layer deposition. It is found that the photoluminescence property of the ZnO NW/Al2O3/Pt hybrid structure is highly tunable with respect to the thickness of the inserted Al2O3 spacer layer. The highest enhancement (˜14 times) of the near band emission of ZnO NWs is obtained with an optimized Al2O3 spacer layer thickness of 10 nm leading to a ultraviolet-visible emission ratio of 271.2 compared to 18.8 for bare ZnO NWs. The enhancement of emission is influenced by a Förster-type non-radiative energy transfer process of the exciton energy from ZnO NWs to Pt NPs as well as the coupling effect between excitons of ZnO NWs and surface plasmons of Pt NPs. The highly versatile and tunable photoluminescence properties of Pt-coated ZnO NWs achieved by introducing an Al2O3 spacer layer demonstrate their potential application in highly efficient optoelectronic devices.

  13. Surface-plasmon mediated photoluminescence enhancement of Pt-coated ZnO nanowires by inserting an atomic-layer-deposited Al₂O₃ spacer layer.

    PubMed

    Ren, Qing-Hua; Zhang, Yan; Lu, Hong-Liang; Chen, Hong-Yan; Zhang, Yuan; Li, De-Hui; Liu, Wen-Jun; Ding, Shi-Jin; Jiang, An-Quan; Zhang, David Wei

    2016-04-22

    Surface-plasmon mediated photoluminescence emission enhancement has been investigated for ZnO nanowire (NW)/Pt nanoparticle (NP) nanostructures by inserting an Al2O3 spacer layer. The thickness of the Al2O3 spacer layer and of the Pt NPs capped on the ZnO NWs are well controlled by atomic layer deposition. It is found that the photoluminescence property of the ZnO NW/Al2O3/Pt hybrid structure is highly tunable with respect to the thickness of the inserted Al2O3 spacer layer. The highest enhancement (∼14 times) of the near band emission of ZnO NWs is obtained with an optimized Al2O3 spacer layer thickness of 10 nm leading to a ultraviolet-visible emission ratio of 271.2 compared to 18.8 for bare ZnO NWs. The enhancement of emission is influenced by a Förster-type non-radiative energy transfer process of the exciton energy from ZnO NWs to Pt NPs as well as the coupling effect between excitons of ZnO NWs and surface plasmons of Pt NPs. The highly versatile and tunable photoluminescence properties of Pt-coated ZnO NWs achieved by introducing an Al2O3 spacer layer demonstrate their potential application in highly efficient optoelectronic devices. PMID:26963868

  14. A highly stable TiB2-supported Pt catalyst for polymer electrolyte membrane fuel cells

    NASA Astrophysics Data System (ADS)

    Yin, Shibin; Mu, Shichun; Pan, Mu; Fu, Zhengyi

    2011-10-01

    Pt nanoparticles supported on TiB2 conductive ceramics (Pt/TiB2) have been prepared through a liquid reduction method, where the TiB2 surfaces are stabilized with perfluorosulfonic acid. The prepared Pt/TiB2 catalyst is characterized with X-ray diffraction (XRD) and TEM techniques, and a rotating disk electrode (RDE) apparatus. The Pt nanoparticles are found to uniformly disperse on the surface of the TiB2 particles with narrow size distribution. The electrochemical stability of Pt/TiB2 is evaluated and found highly electrochemically stable compared to a commercial Pt/C catalyst. Meanwhile, the catalyst also shows comparable performance for oxygen reduction reaction (ORR) to the Pt/C. The mechanism of the remarkable stability and comparable activity for ORR on Pt/TiB2 is also proposed and discussed.

  15. Characterization of Pt-based Transition Metal Alloy Electrodes for PEFC

    SciTech Connect

    Uebayashi, M.; Sato, Y.; Jeyadevan, B.; Tohji, K.; Sawada, Y.; Itoh, T.

    2007-03-20

    Pt metal is generally used as electrocatalyst in polymer electrolyte fuel cells (PEFC). However, the catalytic action of Pt anode is obstructed by the adsorption of CO gas molecules on to their surface and consequently the efficiency of the fuel cell decreases. Moreover, the activity of PEFC deteriorates even if the presence of CO is as low as 100 ppm. In this paper, attempts are being made to replace the Pt with Pt-based transition metal alloys such as PtFe and PtCo to overcome the above problem and also to improve the activity of fuel cells. The PtFe/C and PtCo/C necessary for the preparation of the electrodes were synthesized by depositing PtFe and PtCo particles synthesized using the polyol process on to the surface ketjenblack. From the results of cyclic voltammetry, we could confirm that PtFe/C could be used as an alternate material of Pt/C. However, Fe ions get eluted in the electrolyte. Thus, the study that can control the elution of Fe ion is necessary. Also in case of PtCo/C, we could confirm that Co ion doesn't get to elute, however the hydrogen oxidation reaction current is quite low.

  16. Titanium oxynitride interlayer to influence oxygen reduction reaction activity and corrosion stability of Pt and Pt-Ni alloy.

    PubMed

    Tan, XueHai; Wang, Liya; Zahiri, Beniamin; Kohandehghan, Alireza; Karpuzov, Dimitre; Lotfabad, Elmira Memarzadeh; Li, Zhi; Eikerling, Michael H; Mitlin, David

    2015-01-01

    A key advancement target for oxygen reduction reaction catalysts is to simultaneously improve both the electrochemical activity and durability. To this end, the efficacy of a new highly conductive support that comprises of a 0.5 nm titanium oxynitride film coated by atomic layer deposition onto an array of carbon nanotubes has been investigated. Support effects for pure platinum and for a platinum (50 at %)/nickel alloy have been considered. Oxynitride induces a downshift in the d-band center for pure platinum and fundamentally changes the platinum particle size and spatial distribution. This results in major enhancements in activity and corrosion stability relative to an identically synthesized catalyst without the interlayer. Conversely, oxynitride has a minimal effect on the electronic structure and microstructure, and therefore, on the catalytic performance of platinum-nickel. Calculations based on density functional theory add insight with regard to compositional segregation that occurs at the alloy catalyst-support interface. PMID:25470445

  17. 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.

  18. EFFECT OF PRETREATMENT ON PT-CO/C CATHODE CATALYSTS FOR THE OXYGEN-REDUCTION REACTION

    SciTech Connect

    Fox, E.; Colon-Mercado, H.

    2010-01-19

    Carbon supported Pt and Pt-Co electrocatalysts for the oxygen reduction reaction in low temperature fuel cells were prepared by the reduction of the metal salts with sodium borohydride and sodium formate. The effect of surface treatment with nitric acid on the carbon surface and Co on the surface of carbon prior to the deposition of Pt was studied. The catalysts where Pt was deposited on treated carbon the ORR reaction preceded more through the two electron pathway and favored peroxide production, while the fresh carbon catalysts proceeded more through the four electron pathway to complete the oxygen reduction reaction. NaCOOH reduced Pt/C catalysts showed higher activity that NaBH{sub 4} reduced Pt/C catalysts. It was determined that the Co addition has a higher impact on catalyst activity and active surface area when used with NaBH{sub 4} as reducing agent as compared to NaCOOH.

  19. Quaternary PtMnCuX/C (X = Fe, Co, Ni, and Sn) and PtMnMoX/C (X = Fe, Co, Ni, Cu and Sn) alloys catalysts: Synthesis, characterization and activity towards ethanol electrooxidation

    NASA Astrophysics Data System (ADS)

    Ammam, Malika; Easton, E. Bradley

    2012-10-01

    In this account, two series of quaternary PtMnCuX/C (X = Fe, Co, Ni, and Sn) and PtMnMoX/C (X = Fe, Co, Ni, Cu and Sn) alloys catalysts have been synthesized and characterized by ICP, XRD, XPS, TEM and cyclic voltammetry. XRD spectra of each series illustrated that PtMnCuX/C (X = Fe, Co and Ni) and PtMnMoX/C (X = Fe, Co, Ni and Cu) alloys have been formed without significant free Mn, Cu, Mo or X co-catalysts. For PtMnCuSn/C and PtMnMoSn/C, in addition to alloy formation, significant free Sn-oxides are present in each catalyst. Cyclic voltammetry and chronoamperometry revealed that all quaternary showed superior electrocatalytic activity towards ethanol oxidation compared to the ternary precursor. Also, shift of the onset potential of ethanol oxidation towards less positive values were also recorded with the quaternary alloys, demonstrating a facilitated oxidation with the quaternary alloys compared to ternary alloy precursor. The magnitude of the gain in potential depend on the alloy composition and PtMnMoSn/C was found to be the best of all synthetized quaternary alloys with an onset potential of ethanol oxidation of only 0.059 V vs. Ag/AgCl.

  20. Synthesis of yolk/shell Fe3O4-polydopamine-graphene-Pt nanocomposite with high electrocatalytic activity for fuel cells

    NASA Astrophysics Data System (ADS)

    Huang, Yingqiang; Liu, Yingju; Yang, Zhuohong; Jia, Jinliang; Li, Xin; Luo, Yan; Fang, Yueping

    2014-01-01

    A novel yolk/shell Fe3O4-polydopamine-graphene-Pt (Fe3O4@PDA/RGO/Pt) nanocomposite is synthesized using polydopamine as a moderate modifier for graphene as well as a coupling agent for the assembly of Pt nanoparticles. The morphology and structure of the as-prepared catalysts are characterized by transmission electron microscopy, X-ray photoelectron spectroscopy, X-ray diffraction and Fourier transform infrared spectroscopy. The detailed formation mechanism of such yolk/shell nanocomposite is discussed. Subsequently, its catalytic activity towards the methanol oxidation is evaluated by cyclic voltammetry, chronoamperometry, electrochemical impedance spectra and CO-stripping voltammetry. Results show that such york/shell Fe3O4@PDA/RGO/Pt exhibits higher electrochemical activity and stability to methanol oxidation than Pt/graphene, which is not only attributed to the synergetic cocatalytic effect at the heterojunction interfaces between the Pt nanoparticles and the support, but also due to the high immobilization of Pt nanoparticles by the functional groups of polydopamine. In addition, the separation ability of Pt nanoparticles from the nanocomposite by Fe3O4 can decrease the CO poison from free Pt nanoparticles. Therefore, this unique yolk/shell nanocomposite may be suitable for the production of catalysts with low-cost and high activity.

  1. Long-range influence of steps on water adsorption on clean and D-covered Pt surfaces.

    PubMed

    den Dunnen, Angela; van der Niet, Maria J T C; Badan, Cansin; Koper, Marc T M; Juurlink, Ludo B F

    2015-04-01

    We have examined water desorption from Pt(111) terraces of varying width and its dependence on precoverage by deuterium (D) with temperature programmed desorption studies. We observe distinct water desorption from (100) steps and (111) terraces, with steps providing adsorption sites with a higher binding energy than terraces. Preadsorption of D at the steps causes annihilation of water stabilization at the steps, while it also causes an initial stabilization of water on the (111) terraces. When the (111) terraces also become precovered with D, this water stabilization trend reverses on all surfaces. Destabilization continues for stepped surfaces containing up to 8-atom wide (111) terraces with a (100) step type and these become hydrophobic, in contrast to surfaces with a (110) step type and with the infinite (111) terrace. Our results illustrate how surface defects and a delicate balance between intermolecular forces and the adsorption energy govern hydrophobic vs. hydrophilic behavior, and that the influence of steps on the adsorption of water on nano-structured platinum surfaces has a very long-ranged character. PMID:25268577

  2. Electrochemically Seed-Mediated Synthesis of Sub-10 nm Tetrahexahedral Pt Nanocrystals Supported on Graphene with Improved Catalytic Performance.

    PubMed

    Liu, Shuo; Tian, Na; Xie, Ai-Yun; Du, Jia-Huan; Xiao, Jing; Liu, Li; Sun, Hong-Yu; Cheng, Zhi-Ying; Zhou, Zhi-You; Sun, Shi-Gang

    2016-05-11

    Controlling the surface structure of Pt nanocrystals (NCs), especially creating high-index facets with abundant active step sites, is an effective approach to enhance catalytic performances. However, the available high-index faceted Pt NCs have large particle sizes, which severely impedes their practical applications. In this study, we reported a new electrochemically seed-mediated method, by which sub-10 nm tetrahexahedral Pt NCs (THH Pt NCs) enclosed with {210} high-index facets supported on graphene were synthesized. Pt nanoparticles of ∼3 nm in size as high-density crystal seeds play a key role in the small-sized control. The obtained THH Pt NCs exhibited a higher mass activity than commercial Pt/C catalyst for ethanol electrooxidation. We further demonstrated that this method is also valid for reshaping commercial Pt/C, to create high-index facets on surfaces and thus to improve both mass activity and stability. PMID:27063648

  3. Thermally activated crystallization of Nb2O5 grown on Pt electrode

    NASA Astrophysics Data System (ADS)

    Berger, L.; Mähne, H.; Klemm, V.; Leuteritz, A.; Mikolajick, T.; Rafaja, D.

    2012-08-01

    The influence of the local crystallographic orientation of the polycrystalline bottom platinum electrode on the crystallization of niobium pentoxide thin films during their rapid thermal annealing was investigated by X-ray diffraction, X-ray reflectivity and transmission electron microscopy. The Nb2O5 thin films under study were reactively sputtered in a mixed O2/Ar atmosphere and subsequently subjected to the annealing in argon atmosphere at temperatures ranging from 500 ∘C to 700 ∘C. The X-ray diffraction confirmed a transition from the amorphous niobium oxide to the crystalline orthorhombic Nb2O5 for temperatures between 500 ∘C and 600 ∘C. The X-ray reflectivity measurements showed that the crystallization process was accompanied by a continuous increase of the electron density in Nb2O5 and by a rapid increase of the surface roughness at 700 ∘C. It was further observed by transmission electron microscopy that Nb2O5 crystallizes selectively and that the crystalline domains of Nb2O5 possess a strong orientation relationship to the platinum from the bottom electrode. The orientation relationship (bar{1} 1 1)_{Pt} {allel} (bar{1} bar{6}0)_{Nb2O5} was identified as the most beneficial one for crystallization of Nb2O5.

  4. Distributions of noble metal Pd and Pt in mesoporous silica

    NASA Astrophysics Data System (ADS)

    Arbiol, J.; Cabot, A.; Morante, J. R.; Chen, Fanglin; Liu, Meilin

    2002-10-01

    Mesoporous silica nanostructures have been synthesized and loaded with Pd and Pt catalytic noble metals. It is found that Pd forms small nanoclusters (3-5 nm) on the surface of the mesoporous structure whereas Pt impregnation results in the inclusion of Pt nanostructures within the silica hexagonal pores (from nanoclusters to nanowires). It is observed that these materials have high catalytic properties for CO-CH4 combustion, even in a thick film form. In particular, results indicate that the Pt and Pd dispersed in mesoporous silica are catalytically active as a selective filter for gas sensors.

  5. Ternary Pt-Ru-Ni catalytic layers for methanol electrooxidation prepared by electrodeposition and galvanic replacement

    NASA Astrophysics Data System (ADS)

    Papaderakis, Athanasios; Pliatsikas, Nikolaos; Prochaska, Chara; Papazisi, Kalliopi; Balomenou, Stella; Tsiplakides, Dimitrios; Patsalas, Panagiotis; Sotiropoulos, Sotiris

    2014-06-01

    Ternary Pt-Ru-Ni deposits on glassy carbon substrates, Pt-Ru(Ni)/GC, have been formed by initial electrodeposition of Ni layers onto glassy carbon electrodes, followed by their partial exchange for Pt and Ru, upon their immersion into equimolar solutions containing complex ions of the precious metals. The overall morphology and composition of the deposits has been studied by SEM microscopy and EDS spectroscopy. Continuous but nodular films have been confirmed, with a Pt÷Ru÷Ni % bulk atomic composition ratio of 37÷12÷51 (and for binary Pt-Ni control systems of 47÷53). Fine topographical details as well as film thickness have been directly recorded using AFM microscopy. The composition of the outer layers as well as the interactions of the three metals present have been studied by XPS spectroscopy and a Pt÷Ru÷Ni % surface atomic composition ratio of 61÷12÷27 (and for binary Pt-Ni control systems of 85÷15) has been found, indicating the enrichment of the outer layers in Pt; a shift of the Pt binding energy peaks to higher values was only observed in the presence of Ru and points to an electronic effect of Ru on Pt. The surface electrochemistry of the thus prepared Pt-Ru(Ni)/GC and Pt(Ni)/GC electrodes in deaerated acid solutions (studied by cyclic voltammetry) proves the existence of a shell consisting exclusively of Pt-Ru or Pt. The activity of the Pt-Ru(Ni) deposits towards methanol oxidation (studied by slow potential sweep voltammetry) is higher from that of the Pt(Ni) deposit and of pure Pt; this enhancement is attributed both to the well-known Ru synergistic effect due to the presence of its oxides but also (based on the XPS findings) to a modification effect of Pt electronic properties.

  6. Ternary Pt-Ru-Ni catalytic layers for methanol electrooxidation prepared by electrodeposition and galvanic replacement

    PubMed Central

    Papaderakis, Athanasios; Pliatsikas, Nikolaos; Prochaska, Chara; Papazisi, Kalliopi M.; Balomenou, Stella P.; Tsiplakides, Dimitrios; Patsalas, Panagiotis; Sotiropoulos, Sotiris

    2014-01-01

    Ternary Pt-Ru-Ni deposits on glassy carbon substrates, Pt-Ru(Ni)/GC, have been formed by initial electrodeposition of Ni layers onto glassy carbon electrodes, followed by their partial exchange for Pt and Ru, upon their immersion into equimolar solutions containing complex ions of the precious metals. The overall morphology and composition of the deposits has been studied by SEM microscopy and EDS spectroscopy. Continuous but nodular films have been confirmed, with a Pt ÷ Ru ÷ Ni % bulk atomic composition ratio of 37 ÷ 12 ÷ 51 (and for binary Pt-Ni control systems of 47 ÷ 53). Fine topographical details as well as film thickness have been directly recorded using AFM microscopy. The composition of the outer layers as well as the interactions of the three metals present have been studied by XPS spectroscopy and a Pt ÷ Ru ÷ Ni % surface atomic composition ratio of 61 ÷ 12 ÷ 27 (and for binary Pt-Ni control systems of 85 ÷ 15) has been found, indicating the enrichment of the outer layers in Pt; a shift of the Pt binding energy peaks to higher values was only observed in the presence of Ru and points to an electronic effect of Ru on Pt. The surface electrochemistry of the thus prepared Pt-Ru(Ni)/GC and Pt(Ni)/GC electrodes in deaerated acid solutions (studied by cyclic voltammetry) proves the existence of a shell consisting exclusively of Pt-Ru or Pt. The activity of the Pt-Ru(Ni) deposits toward methanol oxidation (studied by slow potential sweep voltammetry) is higher from that of the Pt(Ni) deposit and of pure Pt; this enhancement is attributed both to the well-known Ru synergistic effect due to the presence of its oxides but also (based on the XPS findings) to a modification effect of Pt electronic properties. PMID:24959530

  7. Low-coordinated surface atoms of CuPt alloy cocatalysts on TiO2 for enhanced photocatalytic conversion of CO2

    NASA Astrophysics Data System (ADS)

    Lee, Sooho; Jeong, Sunil; Kim, Whi Dong; Lee, Seokwon; Lee, Kangha; Bae, Wan Ki; Moon, Jun Hyuk; Lee, Sangheon; Lee, Doh C.

    2016-05-01

    We report the photocatalytic conversion of CO2 to CH4 using CuPt alloy nanoclusters anchored on TiO2. As the size of CuPt alloy nanoclusters decreases, the photocatalytic activity improves significantly. Small CuPt nanoclusters strongly bind CO2 intermediates and have a stronger interaction with the TiO2 support, which also contributes to an increased CH4 generation rate. The alloying and size effects prove to be the key to efficient CO2 reduction, highlighting a strategic platform for the design of photocatalysts for CO2 conversion.We report the photocatalytic conversion of CO2 to CH4 using CuPt alloy nanoclusters anchored on TiO2. As the size of CuPt alloy nanoclusters decreases, the photocatalytic activity improves significantly. Small CuPt nanoclusters strongly bind CO2 intermediates and have a stronger interaction with the TiO2 support, which also contributes to an increased CH4 generation rate. The alloying and size effects prove to be the key to efficient CO2 reduction, highlighting a strategic platform for the design of photocatalysts for CO2 conversion. Electronic supplementary information (ESI) available. See DOI: 10.1039/c6nr02124g

  8. Liquid-phase hydrogenation of citral over Pt/SiO{sub 2} catalysts. 1. Temperature effects on activity and selectivity

    SciTech Connect

    Singh, U.K.; Vannice, M.A.

    2000-04-01

    Liquid-phase hydrogenation of citral (3,7-dimethyl-2,6-octadienal) over Pt/SiO{sub 2} catalysts was studied in the temperature and pressure ranges 298--423 K and 7--21 atm, respectively. The reaction kinetics were shown to be free of artifacts arising from transport limitations and poisoning effects. The reaction rate in hexane at the solvent exhibited an activity minimum at 373 K. The initial turnover frequency for citral disappearance over 1.44% Pt/SiO{sub 2} catalyst at 20 atm H{sub 2} pressure decreased from 0.19 s{sup {minus}1} at 298 K to 0.02 s{sup {minus}1} at 373 K, but exhibited normal Arrhenius behavior between 373 and 423 K with an activation energy of 7 kcal/mol. Reaction at 298 K produced substantial deactivation, with the rate decreasing by more than an order of magnitude during the first 4 h of reaction; however, reaction at temperatures greater than 373 K exhibited negligible deactivation and a constant rate up to citral conversions greater than 70%. These unusual temperature effects were modeled using Langmuir-Hinshelwood kinetics invoking dissociative adsorption of hydrogen, competitive adsorption between hydrogen and the organic compounds, and addition of the second hydrogen atom to each reactant as the rate-determining step. Decomposition of the unsaturated alcohol (either geraniol or nerol) was proposed to occur concurrently with the hydrogenation steps to yield adsorbed CO and carbonaceous species which cause the deactivation, but at higher temperatures these species could be removed from the Pt surface by desorption or rapid hydrogenation, respectively. The activity minimum observed in the present study is attributed to the relative rates of the alcohol decomposition reaction and CO desorption, with the decomposition reaction having an activation barrier lower than that for CO desorption.

  9. Reproducible fabrication of stable small nano Pt with high activity for sensor applications

    NASA Astrophysics Data System (ADS)

    Ye, Pingping; Guo, Xiaoyu; Liu, Guiting; Chen, Huifen; Pan, Yuxia; Wen, Ying; Yang, Haifeng

    2013-07-01

    Pt nanoparticles with an average size of 2-3 nm in diameter were reproducibly synthesized by reduction of H2PtCl6 solution containing inositol hexaphosphate (IP6) as the stabilizing agent. Single crystals with Pt(111) faces of the resulting cubic nanoparticles were revealed by the electron diffraction pattern. The PtNPs-IP6 nanoparticles were used to modify an electrode as a nonenzymatic sensor for H2O2 detection, exhibiting a fast response and high sensitivity. A low detection limit of 2.0 × 10-7 M (S/N = 3) with two linear ranges between 2.4 × 10-7 and 1.3 × 10-3 M (R2 = 0.9987) and between 1.3 × 10-3 and 1.3 × 10-2 M (R2 = 0.9980) was achieved. The attractive electrochemical performance of PtNPs-IP6 enables it to be employed as a promising material for the development of Pt-based analytical systems and other applications.

  10. Effects of culture supernatant from Lactobacillus pentosus strain S-PT84 on autonomic nerve activity in rats.

    PubMed

    Beppu, Yoshinori; Izumo, Takayuki; Horii, Yuko; Shen, Jiao; Fujisaki, Yoshiyuki; Nakashima, Toshihiro; Tsuruoka, Nobuo; Nagai, Katsuya

    2012-01-01

    Intestinal administration of various lactobacilli has been reported to affect autonomic neurotransmission, blood pressure, blood glucose, and body weight in rats, however, the mechanisms of action of the lactobacilli remain to be clarified. Therefore, the effect of the culture supernatant of Lactobacillus pentosus strain S-PT84 on the autonomic nerve activity in urethane-anesthetized rats was investigated. Intraduodenal injection of the low-molecular-weight (LMW) fraction (molecules less than 10,000 Da) of the S-PT84 culture supernatant elevated the brown adipose tissue sympathetic nerve activity and reduced the gastric vagal nerve activity. Moreover, intraoral administration of this LMW fraction increased the body temperature of rats above the interscapular brown adipose tissue. These results suggest that the LMW fraction of the S-PT84 culture supernatant affects the autonomic nerve activity and thermogenesis, and that the change in thermogenesis may be caused by the change in the sympathetic nerve activity of brown adipose tissue. PMID:22523286

  11. Highly Active and Stable Pt-Loaded Ce0.75Zr0.25O2 Yolk-Shell Catalyst for Water-Gas Shift Reaction.

    PubMed

    Shim, Jae-Oh; Hong, Young Jun; Na, Hyun-Suk; Jang, Won-Jun; Kang, Yun Chan; Roh, Hyun-Seog

    2016-07-13

    Multishelled, Pt-loaded Ce0.75Zr0.25O2 yolk-shell microspheres were prepared by a simple spray pyrolysis process for use in the water-gas shift (WGS) reaction. The Pt-loading was optimized, obtaining highly active Pt/Ce0.75Zr0.25O2 yolk-shell nanostructures for the WGS. Of the prepared catalysts, a 2% Pt loading of the Ce0.75Zr0.25O2 yolk-shell microspheres showed the highest CO conversion. The high catalytic activity of the 2% Pt/Ce0.75Zr0.2O2 catalyst was mainly due to its easier reducibility and the maintenance of active catalytic Pt species. The Pt-loaded Ce0.75Zr0.25O2 catalyst microspheres were highly resistant to Pt sintering because of their unique yolk-shell structure. Spray pyrolysis was found to be highly efficient for the production of precious-metal-loaded, multicomponent metal oxide yolk-shell microspheres for catalytic applications. PMID:27315135

  12. Observation of a topologically non-trivial surface state in half-Heusler PtLuSb (001) thin films

    PubMed Central

    Logan, J. A.; Patel, S. J.; Harrington, S. D.; Polley, C. M.; Schultz, B. D.; Balasubramanian, T.; Janotti, A.; Mikkelsen, A.; Palmstrøm, C. J.

    2016-01-01

    The discovery of topological insulators, materials with bulk band gaps and protected cross-gap surface states in compounds such as Bi2Se3, has generated much interest in identifying topological surface states (TSSs) in other classes of materials. In particular, recent theoretical calculations suggest that TSSs may be found in half-Heusler ternary compounds. If experimentally realizable, this would provide a materials platform for entirely new heterostructure spintronic devices that make use of the structurally identical but electronically varied nature of Heusler compounds. Here we show the presence of a TSS in epitaxially grown thin films of the half-Heusler compound PtLuSb. Spin- and angle-resolved photoemission spectroscopy, complemented by theoretical calculations, reveals a surface state with linear dispersion and a helical tangential spin texture consistent with previous predictions. This experimental verification of topological behaviour is a significant step forward in establishing half-Heusler compounds as a viable material system for future spintronic devices. PMID:27346655

  13. Observation of a topologically non-trivial surface state in half-Heusler PtLuSb (001) thin films

    DOE PAGESBeta

    Logan, J. A.; Patel, S. J.; Harrington, S. D.; Polley, C. M.; Schultz, B. D.; Balasubramanian, T.; Janotti, A.; Mikkelsen, A.; Palmstrøm, C. J.

    2016-06-27

    The discovery of topological insulators, materials with bulk band gaps and protected cross-gap surface states in compounds such as Bi2Se3, has generated much interest in identifying topological surface states (TSSs) in other classes of materials. In particular, recent theoretical calculations suggest that TSSs may be found in half-Heusler ternary compounds. If experimentally realizable, this would provide a materials platform for entirely new heterostructure spintronic devices that make use of the structurally identical but electronically varied nature of Heusler compounds. Here we show the presence of a TSS in epitaxially grown thin films of the half-Heusler compound PtLuSb. Spin- and angle-resolvedmore » photoemission spectroscopy, complemented by theoretical calculations, reveals a surface state with linear dispersion and a helical tangential spin texture consistent with previous predictions. As a result, this experimental verification of topological behavior is a significant step forward in establishing half-Heusler compounds as a viable material system for future spintronic devices.« less

  14. Observation of a topologically non-trivial surface state in half-Heusler PtLuSb (001) thin films.

    PubMed

    Logan, J A; Patel, S J; Harrington, S D; Polley, C M; Schultz, B D; Balasubramanian, T; Janotti, A; Mikkelsen, A; Palmstrøm, C J

    2016-01-01

    The discovery of topological insulators, materials with bulk band gaps and protected cross-gap surface states in compounds such as Bi2Se3, has generated much interest in identifying topological surface states (TSSs) in other classes of materials. In particular, recent theoretical calculations suggest that TSSs may be found in half-Heusler ternary compounds. If experimentally realizable, this would provide a materials platform for entirely new heterostructure spintronic devices that make use of the structurally identical but electronically varied nature of Heusler compounds. Here we show the presence of a TSS in epitaxially grown thin films of the half-Heusler compound PtLuSb. Spin- and angle-resolved photoemission spectroscopy, complemented by theoretical calculations, reveals a surface state with linear dispersion and a helical tangential spin texture consistent with previous predictions. This experimental verification of topological behaviour is a significant step forward in establishing half-Heusler compounds as a viable material system for future spintronic devices. PMID:27346655

  15. Observation of a topologically non-trivial surface state in half-Heusler PtLuSb (001) thin films

    NASA Astrophysics Data System (ADS)

    Logan, John; Patel, Sahil; Harrington, Sean; Polley, Craig; Schultz, Brian; Balasubramanian, T.; Janotti, Anderson; Mikkelsen, Anders; Palmstrøm, Chris

    Topological insulators are a recently discovered new quantum state of matter that has a bulk band gap but also possesses cross-gap surface states which are protected by time-reversal symmetry. The experimental realization of topologically non-trivial surface states (TSSs) in materials such as Bi2Se3 has generated widespread interest in identifying other material systems that exhibit TSSs due to their many uses including spintronic devices. In particular, recent theory calculations suggest that TSSs may be found in certain half-Heusler ternary compounds. If experimentally realizable, this would provide an opportunity for the creation of entirely new heterostructure spintronic devices that make use of the structurally-identical but electronically-varied nature of Heusler compounds. Here, we show the presence of a TSS in the half-Heusler compound PtLuSb. Spin and angle-resolved photoemission spectroscopy reveals a surface state with linear dispersion and a helical tangential spin texture consistent with theoretical predictions and the expectation for a topological insulator.

  16. 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.

  17. Surface enhanced vibrational spectroscopy and first-principles study of L-cysteine adsorption on noble trimetallic Au/Pt@Rh clusters.

    PubMed

    Loganathan, B; Chandraboss, V L; Senthilvelan, S; Karthikeyan, B

    2015-09-01

    The Rh shell of the Au/Pt/Rh trimetallic nanoparticles induces a wide variety of interesting surface reactions by allowing the adsorption of amino acids like L-cysteine (L-Cys). We present a snapshot of theoretical and experimental investigation of L-Cys adsorption on the surface of noble trimetallic Au/Pt@Rh colloidal nanocomposites. Density functional theoretical (DFT) investigations of L-Cys interaction with the Rhodium (Rh) shell of a trimetallic Au/Pt@Rh cluster in terms of geometry, binding energy (E(B)), binding site, energy gap (E(g)), electronic and spectral properties have been performed. L-Cys establishes a strong interaction with the Rh shell. It binds to Rh by the S1-site, which makes a stable L-Cys-Rh surface complex. DFT can be taken as a valuable tool to assign the vibrational spectra of the adsorption of L-Cys on trimetallic Au/Pt@Rh colloidal nanocomposites and mono-metallic Rh nanoparticles. Surface-enhanced infrared spectroscopy (SEIRS) with L-Cys on a Rh6 cluster surface has been simulated for the first time. Experimental information on the L-Cys-Rh surface complex is included to examine the interaction. The experimental spectral observations are in good agreement with the simulated DFT results. Characterization of the synthesized trimetallic Au/Pt@Rh colloidal nanocomposites has been done by high-resolution transmission electron microscopy (HR-TEM) with selected area electron diffraction (SAED) pattern, energy dispersive X-ray (EDX) spectroscopy, dynamic light scattering (DLS) measurements, zeta potential, zeta deviation analysis and UV-visible (UV-Vis) spectroscopic studies. PMID:25650352

  18. Monodisperse core/shell Ni/FePt nanoparticles and their con-version to Ni/Pt to catalyze oxygen reduction

    DOE PAGESBeta

    Zhang, Sen; Hao, Yizhou; Su, Dong; Doan-Nguyen, Vicky V. T.; Wu, Yaoting; Li, Jing; Sun, Shouheng; Murray, Christopher B.

    2014-10-28

    We report a size-controllable synthesis of monodisperse core/shell Ni/FePt nanoparticles (NPs) via a seed-mediated growth and their subsequent conversion to Ni/Pt NPs. Preventing surface oxidation of the Ni seeds is essential for the growth of uniform FePt shells. These Ni/FePt NPs have a thin (≈ 1 nm) FePt shell, and can be converted to Ni/Pt by acetic acid wash to yield active catalysts for oxygen reduction reaction (ORR). Tuning the core size allow for optimization of their electrocatalytic activity. The specific activity and mass activity of 4.2 nm/0.8 nm core/shell Ni/FePt reach 1.95 mA/cm² and 490 mA/mgPt at 0.9 Vmore » (vs. reversible hydrogen electrode, RHE), which are much higher than those of benchmark commercial Pt catalyst (0.34 mA/cm² and 92 mA/mgPt at 0.9 V). Our studies provide a robust approach to monodisperse core/shell NPs with non-precious metal core, making it possible to develop advanced NP catalysts with ultralow Pt content for ORR and many other heterogeneous reactions.« less

  19. Monodisperse core/shell Ni/FePt nanoparticles and their con-version to Ni/Pt to catalyze oxygen reduction

    SciTech Connect

    Zhang, Sen; Hao, Yizhou; Su, Dong; Doan-Nguyen, Vicky V. T.; Wu, Yaoting; Li, Jing; Sun, Shouheng; Murray, Christopher B.

    2014-10-28

    We report a size-controllable synthesis of monodisperse core/shell Ni/FePt nanoparticles (NPs) via a seed-mediated growth and their subsequent conversion to Ni/Pt NPs. Preventing surface oxidation of the Ni seeds is essential for the growth of uniform FePt shells. These Ni/FePt NPs have a thin (≈ 1 nm) FePt shell, and can be converted to Ni/Pt by acetic acid wash to yield active catalysts for oxygen reduction reaction (ORR). Tuning the core size allow for optimization of their electrocatalytic activity. The specific activity and mass activity of 4.2 nm/0.8 nm core/shell Ni/FePt reach 1.95 mA/cm² and 490 mA/mgPt at 0.9 V (vs. reversible hydrogen electrode, RHE), which are much higher than those of benchmark commercial Pt catalyst (0.34 mA/cm² and 92 mA/mgPt at 0.9 V). Our studies provide a robust approach to monodisperse core/shell NPs with non-precious metal core, making it possible to develop advanced NP catalysts with ultralow Pt content for ORR and many other heterogeneous reactions.

  20. Incorporation effect of nanosized perovskite LaFe₀.₇Co₀.₃O₃ on the electrochemical activity of Pt nanoparticles-multi walled carbon nanotube composite toward methanol oxidation

    SciTech Connect

    Noroozifar, Meissam; Khorasani-Motlagh, Mozhgan; Khaleghian-Moghadam, Roghayeh; Ekrami-Kakhki, Mehri-Saddat; Shahraki, Mohammad

    2013-05-01

    Nanosized perovskite LaFe₀.₇Co₀.₃O₃ (LFCO) is synthesized through conventional co-precipitation method and characterized by X-ray powder diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive X-ray (EDX) techniques. The incorporation effect of the mentioned perovskite to catalytic activity of the PtNPs-MWCNTs-nafion (or -chitosan) catalyst toward methanol oxidation has been studied by cyclic voltammetry. Based on the electrochemical studies, all MWCNTs-PtNPs-nafion (or chitosan) and MWCNTs-PtNPs-LFCO-nafion (or chitosan) catalysts show a considerable activity for methanol oxidation. However, a synergistic effect is observed when LFCO is added to the catalyst by decreasing the poisoning rate of the Pt catalyst. - Graphical abstract: Nanosized perovskite LaFe₀.₇Co₀.₃O₃ is synthesized and characterized. The incorporation effect of the mentioned perovskite to catalytic activity of the PtNPS-MWCNTs-nafion (or -chitosan) catalyst toward methanol oxidation is studied. Highlights: • Nanocrystalline LaFe₀.₇Co₀.₃O₃ (LFCO) is prepared by a new simple co-precipitation method. • Effect of LFCO to catalytic activity of PtNPS for methanol oxidation is studied. • A synergistic effect is observed when LFCO is added to the Pt catalyst. • Oxygen of LFCO could be considered as active oxygen to remove CO intermediates.

  1. Reexamination of CO formation during formic acid decomposition on the Pt(1 1 1) surface in the gas phase

    NASA Astrophysics Data System (ADS)

    Wang, Yingying; Zhang, Dongju; Liu, Peng; Liu, Chengbu

    2016-08-01

    Existing theoretical results for formic acid (HCOOH) decomposition on Pt(1 1 1) cannot rationalize the easy CO poisoning of the catalysts in the gas phase. The present work reexamined HCOOH decomposition on Pt(1 1 1) by considering the effect of the initial adsorption structure of the reactant on the reactivity. Our calculations present a new adsorption configuration of HCOOH on Pt(1 1 1), from which the formation of CO is found to be competing with the formation of CO2. The newly proposed mechanism improves our understanding for the mechanism of HCOOH decomposition catalyzed by Pt-based catalysts.

  2. 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

  3. Atomic Structure of Pt3Ni Nanoframe Electrocatalysts by in Situ X-ray Absorption Spectroscopy.

    PubMed

    Becknell, Nigel; Kang, Yijin; Chen, Chen; Resasco, Joaquin; Kornienko, Nikolay; Guo, Jinghua; Markovic, Nenad M; Somorjai, Gabor A; Stamenkovic, Vojislav R; Yang, Peidong

    2015-12-23

    Understanding the atomic structure of a catalyst is crucial to exposing the source of its performance characteristics. It is highly unlikely that a catalyst remains the same under reaction conditions when compared to as-synthesized. Hence, the ideal experiment to study the catalyst structure should be performed in situ. Here, we use X-ray absorption spectroscopy (XAS) as an in situ technique to study Pt3Ni nanoframe particles which have been proven to be an excellent electrocatalyst for the oxygen reduction reaction (ORR). The surface characteristics of the nanoframes were probed through electrochemical hydrogen underpotential deposition and carbon monoxide electrooxidation, which showed that nanoframe surfaces with different structure exhibit varying levels of binding strength to adsorbate molecules. It is well-known that Pt-skin formation on Pt-Ni catalysts will enhance ORR activity by weakening the binding energy between the surface and adsorbates. Ex situ and in situ XAS results reveal that nanoframes which bind adsorbates more strongly have a rougher Pt surface caused by insufficient segregation of Pt to the surface and consequent Ni dissolution. In contrast, nanoframes which exhibit extremely high ORR activity simultaneously demonstrate more significant segregation of Pt over Ni-rich subsurface layers, allowing better formation of the critical Pt-skin. This work demonstrates that the high ORR activity of the Pt3Ni hollow nanoframes depends on successful formation of the Pt-skin surface structure. PMID:26652294

  4. Pt-Au Triangular Nanoprisms with Strong Dipole Plasmon Resonance for Hydrogen Generation Studied by Single-Particle Spectroscopy.

    PubMed

    Lou, Zaizhu; Fujitsuka, Mamoru; Majima, Tetsuro

    2016-06-28

    Three anisotropic Pt-covered, Pt-edged, and Pt-tipped Au triangular nanoprisms (TNPs) were prepared by controlling the overgrowth of Pt as photocatalysts for H2 generation. With strong electric field and more interface for the hot electrons transfer, the H2 generation rate of Pt-edged Au TNPs was 3 and 5 times higher than those of Pt-tipped and Pt-covered Au TNPs. Single-particle photoluminescence (PL) spectra and finite-difference-time-domain (FDTD) simulations demonstrated that dipole surface plasmon resonance (DSPR) of Au TNPs enhanced the hot electrons transfer from Au to Pt leading to H2 generation. SPR bands of Au TNPs depending on the size play an important role on the photocatalytic activity of Pt-edged Au TNPs. PMID:27212221

  5. Fraction of Pt surface covered with coke following hydrogenolysis of hexane

    SciTech Connect

    Rivera-Latas, F.J.; Betta, R.A.D.; Boudart, M. )

    1992-05-01

    This paper reports that following hydrogenolysis of n-hexane on an alumina-supported platinum catalyst, the surface of the metal is covered partially with carbonaceous residues or coke. The fraction of surface platinum not covered with coke has been found to be about one half by four independent techniqu3s: titration of preadsorbed oxygen by dihydrogen, chemisorption of carbon monoxide, infrared spectroscopy of chemisorbed carbon monoxide, and hydrogenation rate of ethylene. The first of these techniques suggests itself as the simplest one for further studies of deactivation by coking of platinum catalysts.

  6. (abstract) Optical Scattering and Surface Microroughness of Ion Beam Deposited Au and Pt Thin Films

    NASA Technical Reports Server (NTRS)

    Al-Jumaily, Ghanim A.; Raouf, Nasrat A.; Edlou, Samad M.; Simons, John C.

    1994-01-01

    Thin films of gold and platinum have been deposited onto superpolished fused silica substrates using thermal evaporation, ion assisted deposition (IAD), and ion assisted sputtering. The influence of ion beam flux, thin film material, and deposition rate on the films microroughness have been investigated. Short range surface microroughness of the films has been examined using scanning tunneling microscopy (STM) and atomic force microscopy (AFM). Long range surface microroughness has been characterized using an angle resolved optical scatterometer. Results indicate that ion beam deposited coatings have improved microstructure over thermally evaporated films.

  7. Thermodynamic properties of hydrogen-water adsorption at terraces and steps of Pt(111) vicinal surface electrodes

    NASA Astrophysics Data System (ADS)

    Gómez-Marín, Ana M.; Feliu, Juan M.

    2016-04-01

    In this work, the effect of temperature on the adsorption states of Pt(111) vicinal surface electrodes in perchloric acid is studied through a thermodynamic analysis. The method allows calculating thermodynamic properties of the interface. In this framework, the concept of the generalized isotherm and the statistical thermodynamics description are applied to calculate formal entropies, enthalpies and Gibbs energies, ΔGbari0, of the adsorption processes at two-dimensional terraces and one-dimensional steps. These values are compared with data from literature. Additionally, the effect of the step density on ΔGbari0 and on the lateral interactions between adsorbed species, ωij, at terraces and steps is also determined. Calculated ΔGbari0, entropies and enthalpies are almost temperature-independent, especially at steps, but they depend on the step orientation. In contrast, ΔGbari0 and ωij at terraces depend on the step density, following a linear tendency for terrace lengths larger than 5 atoms. However, while ΔGbari0 increases with the step density, ωij decreases. Results were explained by considering the modification in the energetic surface balance by hydrogen, Hads, and water, H2Oads, co-adsorption on the electrode, which in turn determines the whole adsorption processes on terraces and steps.

  8. 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.

  9. A Compendium of Scale Surface Microstructures: Ni(pt)al Coatings Oxidized at 1150 C for 2000 1-h Cycles

    NASA Technical Reports Server (NTRS)

    Smialek, James L.; Garg, Anita

    2010-01-01

    The surface structure of scales formed on Ni(Pt)Al coatings was characterized by SEM/EDS/BSE in plan view. Two nominally identical {100} samples of aluminide coated CMSX4 single crystal were oxidized at 1150 C for 2000 1-h cycles and were found to produce somewhat disparate behavior. One sample, with less propensity for coating grain boundary ridge deformation, presented primarily alpha-Al2O3 scale structures, with minimal weight loss and spallation. The original scale structure, still retained over most of the sample, consisted of the classic theta-alpha transformation-induced ridge network structure, with approx. 25 nm crystallographic steps and terraces indicative of surface rearrangement to low energy alumina planes. The scale grain boundary ridges were often decorated with a fine, uniform distribution of (Hf,Ti)O2 particles. Another sample, producing steady state weight losses, exhibited much interfacial spallation and a complex assortment of different structures. Broad areas of interfacial spalling, crystallographically-faceted (Ni,Co)(Al,Cr)2O4 spinel, with an alpha-Al2O3 base scale, were the dominant features. Other regions exhibited nodular spinel grains, with fine or (Ta,Ti)-rich (rutile) particles decorating or interspersed with the spinel. While these features were consistent with a coating that presented more deformation at extruded grain boundaries, the root cause of the different behavior between the duplicate samples could not be conclusively identified.

  10. High surface area platinum-titania aerogels: Preparation, structural properties, and hydrogenation activity

    SciTech Connect

    Schneider, M.; Duff, D.G.; Mallat, T.; Wildberger, M.; Baiker, A. )

    1994-06-01

    High surface area platinum-titania aerogels with marked meso-to macroporosity have been synthesized via the sol-gel-aerogel route. An acid-catalyzed titania gel was prepared from tetrabutoxy-titanium(IV) with methanol as solvent. The platinum precursor solutions added after the redispersion of the titania gel were either PtCl[sub 4], (NH[sub 4])[sub 2]PtCl[sub 6] or Pt(acac)[sub 2] dissolved in protic solvents. Platinum metal particles formed upon high-temperature supercritical drying. The platinum-titania aerogels have a BET surface area of 150 to 190 m[sup 2] g[sup [minus]1] after thermal pretreatments up to 673 K and the titania matrix consists of well-developed anatase crystallites of about 8-9 nm mean size. Depending on the platinum precursor used, the volume-weighted-mean particle size, determined by TEM, varies in the range 3.6 to 68 nm, consistent with XRD results for the platinum component. All aerogel samples showed a pronounced stability of both the titania matrix and the platinum particles towards air or hydrogen at temperatures up to 673 K. Thermal analysis, combined with mass spectroscopy, revealed that the untreated catalysts contain a considerable amount of entrapped organic impurities after the high-temperature supercritical drying. For the characterization of the activity and the accessibility of platinum particles the liquid phase hydrogenations of trans-stilbene and benzophenone were used as test reactions. Compared to a commercial alumina-supported platinum catalyst, the untreated 2-5 wt% platinum-titania catalysts derived from (NH[sub 4])[sub 2]PtCl[sub 6]- and especially PtCl[sub 4]-precursor solutions exhibit a markedly higher catalytic activity. In general, air pretreatments at 573 K or above had either no or promoting influence on activity. In contrast, pretreatments in hydrogen produced either no or detrimental activity change. 50 refs., 9 figs., 3 tabs.

  11. Tailoring Catalytic Activity of Pt Nanoparticles Encapsulated Inside Dendrimers by Tuning Nanoparticle Sizes with Subnanometer Accuracy for Sensitive Chemiluminescence-Based Analyses.

    PubMed

    Lim, Hyojung; Ju, Youngwon; Kim, Joohoon

    2016-05-01

    Here, we report the size-dependent catalysis of Pt dendrimer-encapsulated nanoparticles (DENs) having well-defined sizes over the range of 1-3 nm with subnanometer accuracy for the highly enhanced chemiluminescence of the luminol/H2O2 system. This size-dependent catalysis is ascribed to the differences in the chemical states of the Pt DENs as well as in their surface areas depending on their sizes. Facile and versatile applications of the Pt DENs in diverse oxidase-based assays are demonstrated as efficient catalysts for sensitive chemiluminescence-based analyses. PMID:27032992

  12. Correction: Particle shape optimization by changing from an isotropic to an anisotropic nanostructure: preparation of highly active and stable supported Pt catalysts in microemulsions.

    PubMed

    Parapat, Riny Y; Wijaya, Muliany; Schwarze, Michael; Selve, Sören; Willinger, Marc; Schomäcker, Reinhard

    2016-04-01

    Correction for 'Particle shape optimization by changing from an isotropic to an anisotropic nanostructure: preparation of highly active and stable supported Pt catalysts in microemulsions' by Riny Y. Parapat et al., Nanoscale, 2013, 5, 796-805. PMID:26961853

  13. Correction: Particle shape optimization by changing from an isotropic to an anisotropic nanostructure: preparation of highly active and stable supported Pt catalysts in microemulsions

    NASA Astrophysics Data System (ADS)

    Parapat, Riny Y.; Wijaya, Muliany; Schwarze, Michael; Selve, Sören; Willinger, Marc; Schomäcker, Reinhard

    2016-03-01

    Correction for `Particle shape optimization by changing from an isotropic to an anisotropic nanostructure: preparation of highly active and stable supported Pt catalysts in microemulsions' by Riny Y. Parapat et al., Nanoscale, 2013, 5, 796-805.

  14. Role of chemical composition in the enhanced catalytic activity of Pt-based alloyed ultrathin nanowires for the hydrogen oxidation reaction under alkaline conditions

    DOE PAGESBeta

    Megan E. Scofield; Wong, Stanislaus S.; Zhou, Yuchen; Yue, Shiyu; Wang, Lei; Su, Dong; Tong, Xiao; Vukmirovic, Miomir B.; Adzic, Radoslav R.

    2016-05-19

    With the increased interest in the development of hydrogen fuel cells as a plausible alternative to internal combustion engines, recent work has focused on creating alkaline fuel cells (AFC), which employ an alkaline environment. Working in alkaline as opposed to acidic media yields a number of tangible benefits, including (i) the ability to use cheaper and plentiful precious-metal-free catalysts, due to their increased stability, (ii) a reduction in the amount of degradation and corrosion of Pt-based catalysts, and (iii) a longer operational lifetime for the overall fuel cell configuration. However, in the absence of Pt, no catalyst has achieved activitiesmore » similar to those of Pt. Herein, we have synthesized a number of crystalline ultrathin PtM alloy nanowires (NWs) (M = Fe, Co, Ru, Cu, Au) in order to replace a portion of the costly Pt metal without compromising on activity while simultaneously adding in metals known to exhibit favorable synergistic ligand and strain effects with respect to the host lattice. In fact, our experiments confirm theoretical insights about a clear and correlative dependence between measured activity and chemical composition. We have conclusively demonstrated that our as-synthesized alloy NW catalysts yield improved hydrogen oxidation reaction (HOR) activities as compared with a commercial Pt standard as well as with our as-synthesized Pt NWs. The Pt7Ru3 NW system, in particular, quantitatively achieved an exchange current density of 0.493 mA/cm2, which is higher than the corresponding data for Pt NWs alone. In addition, the HOR activities follow the same expected trend as their calculated hydrogen binding energy (HBE) values, thereby confirming the critical importance and correlation of HBE with the observed activities.« less

  15. Intrinsic activity and poisoning rate for HCOOH oxidation on platinum stepped surfaces.

    PubMed

    Grozovski, Vitali; Climent, Víctor; Herrero, Enrique; Feliu, Juan M

    2010-08-21

    Pulsed voltammetry has been used to study formic acid oxidation on platinum stepped surfaces to determine the kinetics of the reaction and the role of the surface structure in the reactivity. From the current transients at different potentials, the intrinsic activity of the electrode through the active intermediate reaction path (j(theta = 0)), as well as the rate constant for the CO formation (k(ads)) have been calculated. The kinetics for formic acid oxidation through the active intermediate reaction path is strongly dependent on the surface structure of the electrode, with the highest activity found for the Pt(100) surface. The presence of steps, both on (100) and (111) terraces, does not increase the activity of these surfaces. CO formation only takes place in a narrow potential window very close to the local potential of zero total charge. The extrapolation of the results obtained with stepped surfaces with (111) terraces to zero step density indicates that CO formation should not occur on an ideal Pt(111) electrode. Additionally, the analysis of the Tafel slopes obtained for the different electrodes suggests that the oxidation of formic acid is strongly affected by the presence of adsorbed anions, hydrogen and water. PMID:20539876

  16. Direct imaging of thermally-activated grain-boundary diffusion in Cu/Co/IrMn/Pt exchange-bias structures using atom-probe tomography

    SciTech Connect

    Letellier, F.; Lardé, R.; Le Breton, J.-M.; Akmaldinov, K.; Auffret, S.; Dieny, B.; Baltz, V.

    2014-11-28

    Magnetic devices are often subject to thermal processing steps, such as field cooling to set exchange bias and annealing to crystallize amorphous magnetic electrodes. These processing steps may result in interdiffusion and the subsequent deterioration of magnetic properties. In this study, we investigated thermally-activated diffusion in Cu/Co/IrMn/Pt exchange biased polycrystalline thin-film structures using atom probe tomography. Images taken after annealing at 400 °C for 60 min revealed Mn diffusion into Co grains at the Co/IrMn interface and along Pt grain boundaries for the IrMn/Pt stack, i.e., a Harrison type C regime. Annealing at 500 °C showed further Mn diffusion into Co grains. At the IrMn/Pt interface, annealing at 500 °C led to a type B behavior since Mn diffusion was detected both along Pt grain boundaries and also into Pt grains. The deterioration of the films' exchange bias properties upon annealing was correlated to the observed diffusion. In particular, the topmost Pt capping layer thickness turned out to be crucial since a faster deterioration of the exchange bias properties for thicker caps was observed. This is consistent with the idea that Pt acts as a getter for Mn, drawing Mn out of the IrMn layer.

  17. Direct imaging of thermally-activated grain-boundary diffusion in Cu/Co/IrMn/Pt exchange-bias structures using atom-probe tomography

    NASA Astrophysics Data System (ADS)

    Letellier, F.; Lechevallier, L.; Lardé, R.; Le Breton, J.-M.; Akmaldinov, K.; Auffret, S.; Dieny, B.; Baltz, V.

    2014-11-01

    Magnetic devices are often subject to thermal processing steps, such as field cooling to set exchange bias and annealing to crystallize amorphous magnetic electrodes. These processing steps may result in interdiffusion and the subsequent deterioration of magnetic properties. In this study, we investigated thermally-activated diffusion in Cu/Co/IrMn/Pt exchange biased polycrystalline thin-film structures using atom probe tomography. Images taken after annealing at 400 °C for 60 min revealed Mn diffusion into Co grains at the Co/IrMn interface and along Pt grain boundaries for the IrMn/Pt stack, i.e., a Harrison type C regime. Annealing at 500 °C showed further Mn diffusion into Co grains. At the IrMn/Pt interface, annealing at 500 °C led to a type B behavior since Mn diffusion was detected both along Pt grain boundaries and also into Pt grains. The deterioration of the films' exchange bias properties upon annealing was correlated to the observed diffusion. In particular, the topmost Pt capping layer thickness turned out to be crucial since a faster deterioration of the exchange bias properties for thicker caps was observed. This is consistent with the idea that Pt acts as a getter for Mn, drawing Mn out of the IrMn layer.

  18. Effect of water and ammonia on surface species formed during NO(x) storage-reduction cycles over Pt-K/Al2O3 and Pt-Ba/Al2O3 catalysts.

    PubMed

    Morandi, Sara; Prinetto, Federica; Castoldi, Lidia; Lietti, Luca; Forzatti, Pio; Ghiotti, Giovanna

    2013-08-28

    The effect of water, in the temperature range 25-350 °C, and ammonia at RT on two different surface species formed on Pt-K/Al2O3 and Pt-Ba/Al2O3 NSR catalysts during NO(x) storage-reduction cycles was investigated. The surface species involved are nitrates, formed during the NO(x) storage step, and isocyanates, which are found to be intermediates in N2 production during reduction by CO. FT-IR experiments demonstrate that the dissociative chemisorption of water and ammonia causes the transformation of the bidentate nitrates and linearly bonded NCO(-) species into more symmetric species that we call ionic species. In the case of water, the effect on nitrates is observable at all the temperatures studied; however, the extent of the transformation decreases upon increasing temperature, consistent with the decreased extent of dissociatively adsorbed water. It was possible to hypothesize that the dissociative chemisorption of water and ammonia takes place in a competitive way on surface sites able to give bidentate nitrates and linearly bonded NCO(-) that are dislocated, remaining on the surface as ionic species. PMID:23860492

  19. Fundamental studies of titanium oxide-Pt(1 0 0) interfaces II. Influence of oxidation and reduction reactions on the surface structure of TiO x films on Pt(1 0 0)

    NASA Astrophysics Data System (ADS)

    Matsumoto, Taketoshi; Batzill, Matthias; Hsieh, Shuchen; Koel, Bruce E.

    2004-11-01

    Chemical reactions of titanium-oxide ultrathin films on Pt(1 0 0) and associated changes in the surface structure have been studied by STM (scanning tunneling microscopy), LEED (low energy electron diffraction), AES (Auger electron spectroscopy) and TPD (temperature programmed desorption). Such reactions and changes have important consequences for understanding and modeling of catalysis of related systems and the oxide structures formed have an additional significance in their subsequent use as masks or templates on Pt(1 0 0) in studies relevant to nanotechnology. In a previous paper [Matsumoto et al., Surf. Sci., submitted] we characterized a monolayer-oxide film exhibiting a (3 × 5) structure on Pt(1 0 0) as due to Ti 2O 3. Herein, we characterize changes that occur in this film during subsequent oxidation and reduction reactions, and propose models for the structures of TiO x films that are formed. O 3 (ozone) or NO 2 (nitrogen dioxide) oxidation of the (3 × 5)-Ti 2O 3 film at 600 K and subsequent annealing to 700-950 K in vacuum produced disordered oxide regions and domains of a (4 × 13) structure that we attribute to a TiO 2 film with a square -Ti-O- net. This film is transformed further after annealing at 1000-1100 K to (3 × 5)-Ti 2O 3 domains and domains exhibiting a (2√2 × 2√2) R45° structure that we attribute to a Ti 5O 8 film. Additional heating of this film to 1200 K forms primarily a (3 × 5)-Ti 2O 3 oxide film. Three dimensional clusters of TiO 2 are also produced by these oxidation and annealing procedures. Initial oxidation of a "flat" (3 × 5) oxide film at 600 K reconstructs this surface to form a multilayer, porous oxide film, and more extensive oxidation eventually forms a much less porous oxide film with pyramidal oxide crystallites. Oxidation of the (3 × 5) structure using NO (nitric oxide) differs from that above in that the (4 × 13) structure was not observed, but oxidation does produce the (2√2 × 2√2) R45° structure due to

  20. Microwave-assisted synthesis of Pt/CNT nanocomposite electrocatalysts for PEM fuel cells.

    PubMed

    Zhang, Weimin; Chen, Jun; Swiegers, Gerhard F; Ma, Zi-Feng; Wallace, Gordon G

    2010-02-01

    Microwave-assisted heating of functionalized, single-wall carbon nanotubes (FCNTs) in ethylene glycol solution containing H(2)PtCl(6), led to the reductive deposition of Pt nanoparticles (2.5-4 nm) over the FCNTs, yielding an active catalyst for proton-exchange membrane fuel cells (PEMFCs). In single-cell testing, the Pt/FCNT composites displayed a catalytic performance that was superior to Pt nanoparticles supported by raw (unfunctionalized) CNTs (RCNTs) or by carbon black (C), prepared under identical conditions. The supporting single-wall carbon nanotubes (SWNTs), functionalized with carboxyl groups, were studied by thermogravimetric analysis (TGA), cyclic voltammetry (CV), and Raman spectroscopy. The loading level, morphology, and crystallinity of the Pt/SWNT catalysts were determined using TGA, SEM, and XRD. The electrochemically active catalytic surface area of the Pt/FCNT catalysts was 72.9 m(2)/g-Pt. PMID:20644806

  1. The interaction of potassium submonolayers adsorbed on Pt(111) with oxygen and the adsorption of ethylene on the resulting modified surfaces: a TDS and UPS study

    NASA Astrophysics Data System (ADS)

    Cassuto, A.; Schmidt, S.; Mane, Mane

    1993-03-01

    UPS shows that K atoms deposited on Pt(111) in the submonolayer range strongly interact with oxygen molecules. At 300 K, oxygen molecules dissociate. Oxygen atoms either attach to potassium atoms or lead to K 2O. At 95 K, depending on the experimental conditions (exposure and pressure), potassium peroxide or potassium Superoxide, as majority species, form. TDS as well as UPS indicate that on these surfaces ethylene is π-bonded as on Pt(111) surfaces, partially covered with K atoms. No ethylene adsorption occurs on surfaces fully covered with oxygen atoms or oxides. Ethylene adsorption therefore occurs on the clean part of the sample and is disturbed by the presence of various species of potassium attached to oxygen.

  2. Titanium surface hydrophilicity enhances platelet activation.

    PubMed

    Alfarsi, Mohammed A; Hamlet, Stephen M; Ivanovski, Saso

    2014-01-01

    Titanium implant surface modification is a key strategy used to enhance osseointegration. Platelets are the first cells that interact with the implant surface whereupon they release a wide array of proteins that influence the subsequent healing process. This study therefore investigated the effect of titanium surface modification on the attachment and activation of human platelets. The surface characteristics of three titanium surfaces: smooth (SMO), micro-rough (SLA) and hydrophilic micro-rough (SLActive) and the subsequent attachment and activation of platelets following exposure to these surfaces were determined. The SLActive surface showed the presence of significant nanoscale topographical features. While attached platelets appeared to be morphologically similar, significantly fewer platelets attached to the SLActive surface compared to both the SMO and SLA surfaces. The SLActive surface however induced the release of the higher levels of chemokines β-thromboglobulin and platelet factor 4 from platelets. This study shows that titanium surface topography and chemistry have a significant effect on platelet activation and chemokine release. PMID:25311339

  3. Elucidating hydrogen oxidation/evolution kinetics in base and acid by enhanced activities at the optimized Pt shell thickness on the Ru core

    DOE PAGESBeta

    Elbert, Katherine; Hu, Jue; Ma, Zhong; Zhang, Yu; Chen, Guangyu; An, Wei; Liu, Ping; Isaacs, Hugh S.; Adzic, Radoslav R.; Wang, Jia X.

    2015-10-05

    Hydrogen oxidation and evolution on Pt in acid are facile processes, while in alkaline electrolytes, they are 2 orders of magnitude slower. Thus, developing catalysts that are more active than Pt for these two reactions is important for advancing the performance of anion exchange membrane fuel cells and water electrolyzers. Herein, we detail a 4-fold enhancement of Pt mass activity that we achieved using single-crystalline Ru@Pt core–shell nanoparticles with two-monolayer-thick Pt shells, which doubles the activity on Pt–Ru alloy nanocatalysts. For Pt specific activity, the two- and one-monolayer-thick Pt shells exhibited enhancement factors of 3.1 and 2.3, respectively, compared tomore » the Pt nanocatalysts in base, differing considerably from the values of 1 and 0.4, respectively, in acid. To explain such behavior and the orders of magnitude difference in activity on going from acid to base, we performed kinetic analyses of polarization curves over a wide range of potential from –250 to 250 mV using the dual-pathway kinetic equation. From acid to base, the activation free energies increase the most for the Volmer reaction, resulting in a switch of the rate-determining step from the Tafel to the Volmer reaction, and a shift to a weaker optimal hydrogen binding energy. Furthermore, the much higher activation barrier for the Volmer reaction in base than in acid is ascribed to one or both of the two catalyst-insensitive factors: slower transport of OH– than H+ in water and a stronger O–H bond in water molecules (HO–H) than in hydrated protons (H2O–H+).« less

  4. Elucidating hydrogen oxidation/evolution kinetics in base and acid by enhanced activities at the optimized Pt shell thickness on the Ru core

    SciTech Connect

    Elbert, Katherine; Hu, Jue; Ma, Zhong; Zhang, Yu; Chen, Guangyu; An, Wei; Liu, Ping; Isaacs, Hugh S.; Adzic, Radoslav R.; Wang, Jia X.

    2015-10-05

    Hydrogen oxidation and evolution on Pt in acid are facile processes, while in alkaline electrolytes, they are 2 orders of magnitude slower. Thus, developing catalysts that are more active than Pt for these two reactions is important for advancing the performance of anion exchange membrane fuel cells and water electrolyzers. Herein, we detail a 4-fold enhancement of Pt mass activity that we achieved using single-crystalline Ru@Pt core–shell nanoparticles with two-monolayer-thick Pt shells, which doubles the activity on Pt–Ru alloy nanocatalysts. For Pt specific activity, the two- and one-monolayer-thick Pt shells exhibited enhancement factors of 3.1 and 2.3, respectively, compared to the Pt nanocatalysts in base, differing considerably from the values of 1 and 0.4, respectively, in acid. To explain such behavior and the orders of magnitude difference in activity on going from acid to base, we performed kinetic analyses of polarization curves over a wide range of potential from –250 to 250 mV using the dual-pathway kinetic equation. From acid to base, the activation free energies increase the most for the Volmer reaction, resulting in a switch of the rate-determining step from the Tafel to the Volmer reaction, and a shift to a weaker optimal hydrogen binding energy. Furthermore, the much higher activation barrier for the Volmer reaction in base than in acid is ascribed to one or both of the two catalyst-insensitive factors: slower transport of OH than H+ in water and a stronger O–H bond in water molecules (HO–H) than in hydrated protons (H2O–H+).

  5. Structural and surface coverage effects on CO oxidation reaction over carbon-supported Pt nanoparticles studied by quadrupole mass spectrometry and diffuse reflectance FTIR spectroscopy.

    PubMed

    Cheah, Seng Kian; Bernardet, Véronique P; Franco, Alejandro A; Lemaire, Olivier; Gelin, Patrick

    2016-06-01

    The CO oxidation reaction on carbon-supported Pt nanoparticles (average size of 2.8 to 7.7 nm) was studied under flowing conditions at atmospheric pressure and temperatures between 300 and 353 K by coupling quadrupole mass spectrometry (QMS) and diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). The Pt loading was varied between 20 and 60 wt%. Gases diluted in He (0.5 mol%) were used together with Ar as a tracer. Reactions with CO and O2 introduced separately onto the samples were studied by QMS, applying successive step changes of the reaction mixtures. Variations in the rate of the reactions were observed and correlated with changes of the calculated coverage of the Pt surface by CO and/or O adspecies at varying steps of the experiment. The transient reaction of CO(g) with adsorbed O (Oad) was fast and mass transport-limited while that of O2(g) with adsorbed CO (COad) was sluggish. Following the same experimental procedures, FTIR spectra of adsorbed CO after varying steps were recorded, confirming the variations of COad and Oad as determined by QMS and indicating changes in the CO distribution over varying types of Pt surface sites. The influence of the adlayer composition (co-adsorption of COad and Oad), the particle size/structure and some possible surface reconstruction effects on the CO oxidation rate were evidenced and discussed. The structure of the Pt nanoparticles supported on carbon appears as an important factor for the efficiency of the so-called O2 bleeding as a CO mitigation strategy in polymer electrolyte membrane fuel cells. PMID:27212705

  6. Structure of Tl adlayers on the Pt(111) electrode surface: Effects of solution pH and bisulfate coadsorption

    SciTech Connect

    Adzic, R.R.; Wang, J.X.; Magnussen, O.M.; Ocko, B.M.

    1996-08-29

    The structure of Tl adlayers deposited at underpotentials on Pt(111) has been investigated in four different electrolyte solutions (HClO{sub 4}, NaClO{sub 4}, NaOH, and H{sub 2}SO{sub 4}) with surface X-ray scattering (SXS) techniques. In all solutions investigated, Tl forms an incommensurate, aligned-hexagonal phase at the most negative potentials prior to its bulk deposition or hydrogen evolution. With decreasing potential the monolayer compresses and thus the Tl coverage increases. Under hydrogen evolution, the close-packed hexagonal Tl monolayer also exists and this reaction causes a slight lowering of the Tl coverage and a significant decrease of the in-plane ordering of the monolayer. In sulfuric acid solution, besides the close-packed hexagonal phase, a commensurate ({radical}3 x {radical}3)R30{degree} phase with a Tl coverage of 1/3 monolayer is formed in coadsorption with bisulfates over a 0.22 V wide potential range. 21 refs., 8 figs.

  7. 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

  8. PtRu/Ti anodes with varying Pt ratio: Ru ratio prepared by electrodeposition for the direct methanol fuel cell.

    PubMed

    Shao, Zhi-Gang; Zhu, Fuyun; Lin, Wen-Feng; Christensen, Paul A; Zhang, Huamin

    2006-06-21

    PtRu/Ti anodes with varying Pt ratio Ru ratio were prepared by electrodeposition of a thin PtRu catalyst layer onto Ti mesh for a direct methanol fuel cell (DMFC). The morphology and structure of the catalyst layers were analyzed by SEM, EDX and XRD. The catalyst coating layer shows an alloy character. The relative activities of the PtRu/Ti electrodes were assessed and compared in half cell and single DMFC experiments. The results show that these electrodes are very active for the methanol oxidation and that the optimum Ru surface coverage was ca. 9 at.% for DMFC operating at 20 degrees C and 11 at.% at 60 degrees C. The PtRu/Ti anode shows a performance comparable to that of the conventional carbon-based anode in a DMFC operating with 0.25 M or 0.5 M methanol solution and atmosphere oxygen gas at 90 degrees C. PMID:16763704

  9. Synthesis of Pt-Ni Octahedra in Continuous-Flow Droplet Reactors for the Scalable Production of Highly Active Catalysts toward Oxygen Reduction.

    PubMed

    Niu, Guangda; Zhou, Ming; Yang, Xuan; Park, Jinho; Lu, Ning; Wang, Jinguo; Kim, Moon J; Wang, Liduo; Xia, Younan

    2016-06-01

    A number of groups have reported the syntheses of nanosized Pt-Ni octahedra with remarkable activities toward the oxygen reduction reaction (ORR), a process key to the operation of proton-exchange membrane fuel cells. However, the throughputs of those batch-based syntheses are typically limited to a scale of 5-25 mg Pt per batch, which is far below the amount needed for commercial evaluation. Here we report the use of droplet reactors for the continuous and scalable production of Pt-Ni octahedra with high activities toward ORR. In a typical synthesis, Pt(acac)2, Ni(acac)2, and W(CO)6 were dissolved in a mixture of oleylamine, oleic acid, and benzyl ether, and then pumped into a polytetrafluoroethylene tube. When the solution entered the reaction zone at a temperature held in the range of 170-230 °C, W(CO)6 quickly decomposed to generate CO gas, naturally separating the reaction solution into discrete, uniform droplets. Each droplet then served as a reactor for the nucleation and growth of Pt-Ni octahedra whose size and composition could be controlled by changing the composition of the solvent and/or adjusting the amount of Ni(acac)2 added into the reaction solution. For a catalyst based on Pt2.4Ni octahedra of 9 nm in edge length, it showed an ORR mass activity of 2.67 A mgPt(-1) at 0.9 V, representing an 11-fold improvement over a state-of-the-art commercial Pt/C catalyst (0.24 A mgPt(-1)). PMID:27135156

  10. Efficient C-C bond splitting on Pt monolayer and sub-monolayer catalysts during ethanol electro-oxidation: Pt layer strain and morphology effects.

    PubMed

    Loukrakpam, Rameshwori; Yuan, Qiuyi; Petkov, Valeri; Gan, Lin; Rudi, Stefan; Yang, Ruizhi; Huang, Yunhui; Brankovic, Stanko R; Strasser, Peter

    2014-09-21

    Efficient catalytic C-C bond splitting coupled with complete 12-electron oxidation of the ethanol molecule to CO2 is reported on nanoscale electrocatalysts comprised of a Pt monolayer (ML) and sub-monolayer (sML) deposited on Au nanoparticles (Au@Pt ML/sML). The Au@Pt electrocatalysts were synthesized using surface limited redox replacement (SLRR) of an underpotentially deposited (UPD) Cu monolayer in an electrochemical cell reactor. Au@Pt ML showed improved catalytic activity for ethanol oxidation reaction (EOR) and, unlike their Pt bulk and Pt sML counterparts, was able to generate CO2 at very low electrode potentials owing to efficient C-C bond splitting. To explain this, we explore the hypothesis that competing strain effects due to the Pt layer coverage/morphology (compressive) and the Pt-Au lattice mismatch (tensile) control surface chemisorption and overall activity. Control experiments on well-defined model Pt monolayer systems are carried out involving a wide array of methods such as high-energy X-ray diffraction, pair-distribution function (PDF) analysis, in situ electrochemical FTIR spectroscopy, and in situ scanning tunneling microscopy. The vibrational fingerprints of adsorbed CO provide compelling evidence on the relation between surface bond strength, layer strain and morphology, and catalytic activity. PMID:25081353

  11. 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

  12. 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

  13. 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.

  14. Intracellular surface-enhanced Raman scattering (SERS) with thermally stable gold nanoflowers grown from Pt and Pd seeds

    NASA Astrophysics Data System (ADS)

    Song, Hyon Min; Deng, Lin; Khashab, Niveen M.

    2013-05-01

    SERS provides great sensitivity at low concentrations of analytes. SERS combined with near infrared (NIR)-resonant gold nanomaterials are important candidates for theranostic agents due to their combined extinction properties and sensing abilities stemming from the deep penetration of laser light in the NIR region. Here, highly branched gold nanoflowers (GNFs) grown from Pd and Pt seeds are prepared and their SERS properties are studied. The growth was performed at 80 °C without stirring, and this high temperature growth method is assumed to provide great shape stability of sharp tips in GNFs. We found that seed size must be large enough (>30 nm in diameter) to induce the growth of those SERS-active and thermally stable GNFs. We also found that the addition of silver nitrate (AgNO3) is important to induce sharp tip growth and shape stability. Incubation with Hela cells indicates that GNFs are taken up and reside in the cytoplasm. SERS was observed in those cells incubated with 1,10-phenanthroline (Phen)-loaded GNFs.SERS provides great sensitivity at low concentrations of analytes. SERS combined with near infrared (NIR)-resonant gold nanomaterials are important candidates for theranostic agents due to their combined extinction properties and sensing abilities stemming from the deep penetration of laser light in the NIR region. Here, highly branched gold nanoflowers (GNFs) grown from Pd and Pt seeds are prepared and their SERS properties are studied. The growth was performed at 80 °C without stirring, and this high temperature growth method is assumed to provide great shape stability of sharp tips in GNFs. We found that seed size must be large enough (>30 nm in diameter) to induce the growth of those SERS-active and thermally stable GNFs. We also found that the addition of silver nitrate (AgNO3) is important to induce sharp tip growth and shape stability. Incubation with Hela cells indicates that GNFs are taken up and reside in the cytoplasm. SERS was observed in

  15. Analysis of Pt/SnO(sub x) during catalysis of CO oxidation

    NASA Technical Reports Server (NTRS)

    Sermon, Paul A.; Self, Valerie A.; Barrett, E. P. S.

    1990-01-01

    Temperature-programmed reduction using 6kPaH2 suggests that a sample consisting of 3 percent Pt supported directly on SnO2 is, under conditions of catalysis of CO oxidation used here, best represented as 3 percent Pt/SnO sub x, since the support is likely to partially reduced, probably in the vicinity of the metal/oxide interface. Catalytic measurements at 421 to 424 K show that this 3 percent Pt/SnO sub x is significantly more active per unit area of Pt than 6 percent Pt/SiO2 in catalyzing the oxidation of CO. In situ micro-FTIR reveals that while the latter has predominantly linearly bound CO on the surface under reaction conditions, the Pt/SnO sub x also has a species absorbing at 2168 cm(exp -1) which may be CO upon Pt in a positive oxidation state or weakly chemisorbed CO on zero-valent Pt. This may be directly involved in the low temperature oxidation of CO on the Pt/SnO sub x, since being weakly held the activation energy for its surface diffusion to the metal/oxide interface will be low; such mobile species could allow the high rates of surface transport and an increase in the fraction of the surface over which the CO oxidation occurs. FTIR also reveals carbonate-type species on the P/SnO sub c surface.

  16. Facet-controlled {100}Rh-Pt and {100}Pt-Pt dendritic nanostructures by transferring the {100} facet nature of the core nanocube to the branch nanocubes

    NASA Astrophysics Data System (ADS)

    Khi, Nguyen Tien; Park, Jongsik; Baik, Hionsuck; Lee, Hyunkyung; Sohn, Jeong-Hun; Lee, Kwangyeol

    2015-02-01

    Facet-controlled dendritic nanostructures are expected to exhibit excellent catalytic properties because both aggregation-free nature and controlled facet-originated activity and selectivity can be accomplished. However, such examples are extremely rare due to the incompatibility of the dendrite formation process with the usage of surface-stabilizing moieties, which are typically used to control facets. Herein, we demonstrate that regiospecific growth on a facet-controlled core nanoparticle can induce the facet-control of the branch nanoparticles. Specifically, facet-controlled dendritic nanostructures of {100}Rh-Pt and {100}Pt-Pt can be conveniently prepared by transferring the crystallographic behaviour of the {100}Pt dendritic core nanocube to the {100}Rh or {100}Pt branch nanocubes.Facet-controlled dendritic nanostructures are expected to exhibit excellent catalytic properties because both aggregation-free nature and controlled facet-originated activity and selectivity can be accomplished. However, such examples are extremely rare due to the incompatibility of the dendrite formation process with the usage of surface-stabilizing moieties, which are typically used to control facets. Herein, we demonstrate that regiospecific growth on a facet-controlled core nanoparticle can induce the facet-control of the branch nanoparticles. Specifically, facet-controlled dendritic nanostructures of {100}Rh-Pt and {100}Pt-Pt can be conveniently prepared by transferring the crystallographic behaviour of the {100}Pt dendritic core nanocube to the {100}Rh or {100}Pt branch nanocubes. Electronic supplementary information (ESI) available. See DOI: 10.1039/c4nr07049f

  17. Platinum-coated copper nanowires with high activity for hydrogen oxidation reaction in base.

    PubMed

    Alia, Shaun M; Pivovar, Bryan S; Yan, Yushan

    2013-09-11

    Platinum (Pt)-coated copper (Cu) nanowires (Pt/CuNWs) are synthesized by the partial galvanic displacement of CuNWs and have a 100 nm diameter and are 25-40 μm length. Pt/CuNWs are studied as a hydrogen oxidation reaction (HOR) catalyst in base along with Cu templated Pt nanotubes (PtNT (Cu)), a 5% Cu monolayer on a bulk polycrystalline Pt electrode (5% ML Cu/BPPt), BPPt, and carbon supported Pt (Pt/C). Comparison of these catalysts demonstrates that the inclusion of Cu benefited the HOR activity of Pt/CuNWs likely by providing compressive strain on Pt; surface Cu further aids in hydroxyl adsorption, thereby improving the HOR activity of Pt/CuNWs. Pt/CuNWs exceed the area and mass exchange current densities of carbon supported Pt by 3.5 times and 1.9 times. PMID:23952885

  18. Immobilization of Active Bacteriophages on Polyhydroxyalkanoate Surfaces.

    PubMed

    Wang, Chanchan; Sauvageau, Dominic; Elias, Anastasia

    2016-01-20

    A rapid, efficient technique for the attachment of bacteriophages (phages) onto polyhydroxyalkanoate (PHA) surfaces has been developed and compared to three reported methods for phage immobilization. Polymer surfaces were modified to facilitate phage attachment using (1) plasma treatment alone, (2) plasma treatment followed by activation by 1-ethyl-3-(3-(dimethylamino)propyl)carbodiimide hydrochloride (EDC) and N-hydroxysulfosuccinimide (sulfo-NHS), (3) plasma-initiated acrylic acid grafting, or (4) plasma-initiated acrylic acid grafting with activation by EDC and sulfo-NHS. The impact of each method on the surface chemistry of PHA was investigated using contact angle analysis and X-ray photoelectron spectroscopy. Each of the four treatments was shown to result in both increased hydrophilicity and in the modification of the surface functional groups. Modified surfaces were immersed in suspensions of phage T4 for immobilization. The highest level of phage binding was observed for the surfaces modified by plasma treatment alone. The change in chemical bond states observed for surfaces that underwent plasma treatment is suspected to be the cause of the increased binding of active phages. Plasma-treated surfaces were further analyzed through phage-staining and fluorescence microscopy to assess the surface density of immobilized phages and their capacity to capture hosts. The infective capability of attached phages was confirmed by exposing the phage-immobilized surfaces to the host bacteria Escherichia coli in both plaque and infection dynamic assays. Plasma-treated surfaces with immobilized phages displayed higher infectivity than surfaces treated with other methods; in fact, the equivalent initial multiplicity of infection was 2 orders of magnitude greater than with other methods. Control samples - prepared by immersing polymer surfaces in phage suspensions (without prior plasma treatment) - did not show any bacterial growth inhibition, suggesting they did not bind

  19. A Novel Activated-Charcoal-Doped Multiwalled Carbon Nanotube Hybrid for Quasi-Solid-State Dye-Sensitized Solar Cell Outperforming Pt Electrode.

    PubMed

    Arbab, Alvira Ayoub; Sun, Kyung Chul; Sahito, Iftikhar Ali; Qadir, Muhammad Bilal; Choi, Yun Seon; Jeong, Sung Hoon

    2016-03-23

    Highly conductive mesoporous carbon structures based on multiwalled carbon nanotubes (MWCNTs) and activated charcoal (AC) were synthesized by an enzymatic dispersion method. The synthesized carbon configuration consists of synchronized structures of highly conductive MWCNT and porous activated charcoal morphology. The proposed carbon structure was used as counter electrode (CE) for quasi-solid-state dye-sensitized solar cells (DSSCs). The AC-doped MWCNT hybrid showed much enhanced electrocatalytic activity (ECA) toward polymer gel electrolyte and revealed a charge transfer resistance (RCT) of 0.60 Ω, demonstrating a fast electron transport mechanism. The exceptional electrocatalytic activity and high conductivity of the AC-doped MWCNT hybrid CE are associated with its synchronized features of high surface area and electronic conductivity, which produces higher interfacial reaction with the quasi-solid electrolyte. Morphological studies confirm the forms of amorphous and conductive 3D carbon structure with high density of CNT colloid. The excessive oxygen surface groups and defect-rich structure can entrap an excessive volume of quasi-solid electrolyte and locate multiple sites for iodide/triiodide catalytic reaction. The resultant D719 DSSC composed of this novel hybrid CE fabricated with polymer gel electrolyte demonstrated an efficiency of 10.05% with a high fill factor (83%), outperforming the Pt electrode. Such facile synthesis of CE together with low cost and sustainability supports the proposed DSSCs' structure to stand out as an efficient next-generation photovoltaic device. PMID:26911208

  20. 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%.