Ptau Bimetallic Heteronanostructures Made by Post-synthesis Modification of Pt-on-au Nanoparticles

imetallic PtAu heteronanostructures have been synthesized from Pt-on-Au nanoparticles, which were made from platinum acetylacetonate and gold nanoparticles. Using the Pt-on-Au nanoparticles as precursors, Ptsurface rich PtAu bimetallic heteronanostructures can be produced through controlled thermal treatments, as confirmed by field emission high-resolution transmission electron microscopy (HR-TEM) and elemental mapping using a high-angle annular dark-field scanning transmission electron microscope (HAADF-STEM). Oxidation of formic acid was used as a model reaction to demonstrate the effects of varying composition and surface structure on the catalytic performance of PtAu bimetallic nanostructures. Cyclic voltammetry (CV) showed that these carbon-supported PtAu heteronanostructures were much more active than platinum in catalyzing the oxidation of formic acid, judging by the mass current density. The results showed that postsynthesis modification can be a very useful approach to the control of composition distributions in alloy nanostructures

Platinum Lead Nnostructures: Formation, Phase Behavior, and Electrocatalytic Properties

This paper describes the synthesis and crystal phase behavior of platinum lead nanorods. Both face-centered cubic (fcc) Pt100−xPbx (x \u3c 50) and hexagonally close-packed (hcp) Pt50Pb50 nanostructures are synthesized at mild reaction temperatures (180–200 °C). The crystal phase and composition of these PtPb nanorods can be controlled by changing the reaction time and temperature. A mechanism for the formation of either kinetically or thermodynamically stable PtPb nanorods is discussed. The approach developed for controlling crystal phases at fairly low temperatures can be important for the design of alloy or intermetallic nanostructures for a broader range of applications

Truncated Octahedral Pt3ni Oxygen Reduction Reaction Electrocatalysts

This communication describes the preparation of carbon-supported truncated-octahedral Pt3Ni nanoparticle catalysts for the oxygen reduction reaction. Besides the composition, size, and shape controls, this work develops a new butylamine-based surface treatment approach for removing the long-alkane-chain capping agents used in the solution-phase synthesis. These Pt3Ni catalysts can have an area-specific activity as high as 850 μA/cm2Pt at 0.9 V, which is ∼4 times better than the commercial Pt/C catalyst (∼0.2 mA/cm2Pt at 0.9 V). The mass activity reached 0.53 A/mgPt at 0.9 V, which is close to a factor of 4 increase in mass activity, the threshold value that allows fuel-cell power trains to become cost-competitive with their internal-combustion counterparts. Our results also show that the mass activities of these carbon-supported Pt3Ni nanoparticle catalysts strongly depend on the (111) surface fraction, which validates the results of studies based on Pt3Ni extended-single-crystal surfaces, suggesting that further development of catalysts with still higher mass activities is highly plausible

Composition-dependent Formation of Platinum Silver Nanowires

The understanding of shape control of colloidal nanoparticles is still rather limited even after well over a decade of intensive research efforts. While surface capping agents can greatly influence the growth habit of nanocrystals in solution, the formation of certain morphology can hardly be understood based on both experimental data and simulations. Without a good understanding of the origins for shape formation, deterministic approaches to the synthesis of nanostructures can be hard to realize. In this paper, we describe the synthesis and formation of PtAg alloy nanowires in the presence of oleylamine and oleic acid through the oriented attachment. Transmission electron microscopy study shows the formation of wormlike nanowires occurs largely at the composition around Pt50Ag50. Both Pt and Ag rich alloy nanostructures form sphere-like or faceted nanoparticles under the same reaction conditions. Density functional theory calculation is used to understand the interactions between the functional groups of capping agents and low index planes of PtAg alloys. The structural order of interfaces after collision between primary particles is obtained by molecular dynamic simulation. The results indicate that the formation of alloy nanowires is mostly driven by the interplay between the binding energy of capping agents on alloy surfaces and the diffusion of atoms at the interface upon the collision of primary nanoparticles

Effects of the Synthesis Parameters on the Size and Composition of Pt--sn Nanoparticles Prepared by the Polyalcohol Reduction Method

Platinum–tin alloy nanoparticles with cubic and hexagonal structure have been prepared by the “heating up” method using metal–acetylacetonates as precursors and 1,2-hexadecanediol as the reducing agent dissolved in dioctyl ether containing oleyl amine and oleic acid as capping agents. The influence of the principal reaction parameters—the concentration of the capping agents, final reaction temperature, reaction time, and ratio of metal precursors—on the size and composition of the Pt–Sn nanoparticles was investigated. Transmission electron microscopy and X-ray diffraction results show that decreasing the amount of capping agents increases not only the size of the nanoparticles but also the extent of alloying. It is proposed that the reaction between the metal precursors is the primary step of the nucleation process leading to Pt–Sn bimetallic particles. In a competitive reaction that depends on the concentration of capping agents, metal oleate complexes are formed. The balance between the rates of these processes affects the relative rates of particle nucleation and growth as well as the composition of the bimetallic nanoparticles. The preparation method described is suitable for controlled formation of Pt–Sn nanoparticles with cubic and hexagonal crystalline structure, which are excellent candidates for investigation of the structure–activity relationship for a number of catalyzed reactions

Direct Oxidation of Methanol on Pt Nanostructures Supported on Electrospun Nanofibers of Anatase

This letter reports an electrocatalytic study of electrospun anatase nanofibers decorated with Pt catalysts in the form of nanoparticles or nanowires. We decorated the surface of nanofibers with Pt through a polyol process, in which nanoparticles of 2−5 nm in size were formed with different densities depending on the reaction time. By adding Fe(III) ions to the polyol process, we also obtained Pt nanowires of ∼7 nm in diameter and up to 125 nm in length. We then studied the effects of both the coverage and morphology of the Pt nanostructures on the methanol oxidation reaction. Nanofibers with a submonolayer of Pt nanoparticles were found to display improved catalytic durability over commercial Pt/C as determined by chronoamperometry owing to a synergistic effect of the underlying anatase surface and the Pt nanostructures with well-defined facets. Improvement in catalytic activity and durability were also observed for Pt nanowires, indicating that the additional catalytic facets on the nanowires can enhance both catalytic ability and robustness

Growing Pt Nanowires as a Densely Packed Array on Metal Gauze

This paper describes the synthesis of single-crystal nanowires of Pt directly on the surface of metal gauze made of Pt or W and demonstrates a more attractive approach for the growth of Pt nanowires on functional solid supports. There is evidence that the growth mechanism of the nanowires is correlated to the concentration of the Pt precursor and the surface roughness of the substrate. Electrochemical measurements indicate that the active surface area of the Pt nanowire-coated gauze is about 2−3 orders of magnitude greater than the pristine gauze. The results described herein demonstrate a new type of conductive support that can be used as active components for fuel cell applications and as an ideal 3D model catalyst

Electrocatalytic Properties of Pt Nanowires Supported on Pt and W Gauzes

This paper describes the preparation of Pt- or W-supported Pt nanowires by directly growing them on the surface of Pt or W gauze. The growth direction of the nanowires was determined to be along the \u3c111\u3e axis. Electrochemical measurements were performed to investigate their catalytic performance toward methanol oxidation. It was found from cyclic voltammetry that the Pt nanowires supported on Pt gauze had the largest electrochemically active surface area with the greatest activity toward methanol oxidation reaction. They also exhibited a slightly slower current decay over time, indicating a higher tolerance to CO-like intermediates. Furthermore, electrochemical impedance spectroscopy measurements showed that the catalytic performance of the supported Pt nanowires prepared with a H2PtCl6 precursor concentration of 40 mM is significantly better for methanol oxidation than the samples prepared at a concentration of 80 mM. This was due partially to the incomplete removal of poly(vinyl pyrrolidone) (PVP) from the more concentrated sample. In contrast, the Pt nanowires supported on W gauze performed the worst

Electrochemical Synthesis and Catalytic Property of Sub-10 Nm Platinum Cubic Nanoboxes

We report an electrochemical synthesis of ultrafine Pt cubic nanoboxes from Pt-on-Ag heteronanostructures. These cubic nanoboxes have an average edge length of about 6 nm and a wall thickness of 1.5 nm. Several reaction parameters including the profile of applied potentials were examined to develop an optimal procedure for controlling the size, shape, and surface morphology of the nanoboxes. A strong shape-dependent catalytic property is observed for Pt cubic nanoboxes, which is 1.5 times more active than hollow spheres in terms of turn over frequency for catalytic oxidation of methanol

Supportless Oxygen Reduction Electrocatalysts of Cocupt Hollow Nanoparticles

This paper describes a facile solution route to the synthesis of CoCuPt hollow nanoparticles that readily form chain-like structures in solution. The formation of porous CoCuPt nanostructure is through galvanic replacement with cobalt-containing cores as the templates. This approach does not require the further removal of templates and greatly simplifies the synthetic procedures. These porous CoCuPt nanoparticles can be used as supportless electrocatalysts that exhibit enhanced mass- and area-specific activities in the oxygen reduction reaction (ORR) over commercial Pt black catalysts. The highest ORR specific activity achieved so far for this ternary Pt-alloy catalyst is 0.37 mA cm(-2)(Pt) which is more than double that for Pt black