[Show abstract][Hide abstract] ABSTRACT: Mercaptocarboxylic acids with different carbon chain lengths were used for stabilizing uniform 15 nm copper nanoparticles. The effects of surface chemistry such as ligand type and surface oxidation on the reactive oxygen species (ROS) generated by the copper nanoparticles were examined. Transmission electron microscopy (TEM), powder X-ray diffraction (PXRD), UV-vis spectroscopy, and an acellular ROS assay show that ROS generation is closely related to the surface oxidation of copper nanoparticles. It was found that the copper nanoparticles with longer chain ligands had surfaces that were better protected from oxidation and a corresponding lower ROS generating capacity than did particles with shorter chain ligands. Conversely, the copper nanoparticles with greater surface oxidation also had higher ROS generating capacity.
[Show abstract][Hide abstract] ABSTRACT: Lattice distortion in AgPt nanoparticles was studied using X-ray diffraction and other techniques. These nanoparticles show high catalytic activity in the reduction of p-nitrophenol and had a turn over frequency of 5.4 × 10(2) s(-1).
Full-text · Article · Oct 2011 · Chemical Communications
[Show abstract][Hide abstract] ABSTRACT: This paper describes a new approach to the synthesis of PtAg alloy nanostructures rich in Pt at the surface through a selective electrochemical dissolution of Ag from PtAg alloy nanoparticles that are made from platinum acetylacetonate, Pt(acac)2, and silver stearate, Ag(St). The surface and bulk compositions, size, and architecture of these heterogeneous nanostructures are controlled synergistically by changing the upper limits of cycling potentials in perchloric acid (HClO4) aqueous solution to dissolve Ag deterministically. The structures and elemental distributions of Ag and Pt in the resulting heterogeneous nanoparticles are characterized by high-resolution transmission electron microscopy (HR-TEM), high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) and energy-dispersive X-ray (EDX). These Pt-surface rich PtAg nanostructures exhibit much higher activity than Pt nanoparticles as electrocatalysts in formic acid oxidation reaction (FAOR).
No preview · Article · Nov 2010 · Advanced Functional Materials
[Show abstract][Hide abstract] ABSTRACT: 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.
Full-text · Article · Sep 2010 · Philosophical Transactions of The Royal Society A Mathematical Physical and Engineering Sciences
[Show abstract][Hide abstract] ABSTRACT: The galvanic replacement reaction between Ag nanostructures and aqueous HAuCl4 solution has been widely studied for the purpose of generating noble-metal nanostructures with hollow interiors. Here we explore the galvanic replacement reaction between Cu nanowires and HAuCl4, H2PtCl6, or Na2PdCl4, which also generates hollow metal nanostructures. Compared to the galvanic replacement reaction using Ag nanowires in boiling water, the reaction involving Cu nanowires is relatively mild and can be conducted at room temperature since the reduction potential of Cu2+/Cu is much lower than that of Ag+/Ag. Moreover, the Cu nanowires are inexpensive to prepare, making this approach more practical for large-scale production. In this study, we use electron microscopy to characterize the morphological evolution and final structure of the Au, Pt, and Pd nanotubes. We find that the final structure retains the initial circular morphology of the Cu nanowires and that the surface of the nanotubes is decorated with 20-nm (for Au) or 2-nm pores (for Pt and Pd). Using energy dispersive X-ray spectroscopy (EDX), we find that we can obtain pure Au nanotubes when a stoichiometric amount of HAuCl4 is reacted with the Cu nanowires. We also evaluate the electrocatalytic activity of the Pt nanotubes for formic acid oxidation.
No preview · Article · Aug 2010 · Science of Advanced Materials
[Show abstract][Hide abstract] ABSTRACT: Bimetallic 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.
KeywordsNanostructure-alloy-platinum-gold-formic acid oxidation-electrocatalyst-polymer electrolyte membrane fuel cell (PEMFC)
[Show abstract][Hide abstract] ABSTRACT: 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 Pt(50)Ag(50). 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.
[Show abstract][Hide abstract] ABSTRACT: This communication describes the preparation of carbon-supported truncated-octahedral Pt(3)Ni 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 Pt(3)Ni catalysts can have an area-specific activity as high as 850 muA/cm(2)(Pt) at 0.9 V, which is approximately 4 times better than the commercial Pt/C catalyst ( approximately 0.2 mA/cm(2)(Pt) at 0.9 V). The mass activity reached 0.53 A/mg(Pt) 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 Pt(3)Ni nanoparticle catalysts strongly depend on the (111) surface fraction, which validates the results of studies based on Pt(3)Ni extended-single-crystal surfaces, suggesting that further development of catalysts with still higher mass activities is highly plausible.
No preview · Article · Mar 2010 · Journal of the American Chemical Society
[Show abstract][Hide abstract] ABSTRACT: 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.
[Show abstract][Hide abstract] ABSTRACT: Pt-on-Ag bimetallic nanoparticles were prepared based on a heterogeneous nucleation and growth method. Interestingly, platinum hollow nanoparticles could be obtained by selectively removing the silver cores from Pt-on-Ag nanoparticles. High-resolution transmission electron microscopy (HR-TEM), energy-dispersive X-ray (EDX) analysis with a high-angle annular dark-field scanning transmission electron microscope (HAADF-STEM), and X-ray diffraction (XRD) were used to characterize these nanostructures. The observation that Pt hollows can be produced from Pt-on-Ag nanoparticles through the dissolution of Ag metal cores indicates that particle-on-particle nanodendrites were most likely derived from the products formed through the Stranski−Krastanov (SK) growth. The carbon-supported Pt hollow catalysts, which possessed much higher catalytic activity in oxygen reduction reaction (ORR) than the Pt-on-Ag nanoparticles, were also better than a commercial Pt catalyst (E-tek, 20% Pt). The nanometer-sized textures of the wall of Pt hollow spheres could contribute to the enhancement of the electrocatalytic activity.
No preview · Article · Sep 2009 · Chemistry of Materials
[Show abstract][Hide abstract] ABSTRACT: Platinum-on-palladium bimetallic heterogeneous nanostructures were prepared using a sequential synthetic method, in which 3-nm Pt particles grew on the surfaces of 5-nm Pd nanoparticles. Electrochemical study of carbon-supported Pt-on-Pd heteronanostructures shows not only enhancement in electrocatalytic activity for oxygen reduction reaction (ORR) but also much improved stability in comparison to a commercial platinum catalyst (E-TEK, 20 wt % Pt, diameter: 2.5 nm). The greatly suppressed hydroxyl adsorption on active sites by introducing Pd was attributed to the enhanced activity, while the retention of active surface area, morphology, and composition because of the large overall bimetallic particle size and unique architectures could be the key factors for the much improved stability over 30,000 cycles. Our work shows heterogeneous platinum-on-metal bimetallic nanostructures offer new opportunities to the design of hierarchically ordered multifunctional fuel cell catalysts.
No preview · Article · Jun 2009 · Journal of the American Chemical Society
[Show abstract][Hide abstract] ABSTRACT: Recent advances in the design and preparation of platinum-based nanostructures and their applications as electrocatalysts for low-temperature fuel cells are reviewed. Discussions are focused on the fundamental understanding and new experimental designs in the control of shape, composition and nanoscale structure of platinum and its alloy particles in colloidal systems. We explain the formation of various heteronanostructures using the Frank–van der Merwe (FM), Volmer–Weber (VW) and Stranski–Krastanov (SK) growth modes. Phenomena that exist in nanometer-sized regime, such as the disappearance of miscibility gaps for certain platinum alloys are given special attentions. The relationship between electronic structure or surface atomic arrangement and catalytic properties of platinum-based nanostructures is discussed.
[Show abstract][Hide abstract] ABSTRACT: This article describes an electrochemical study on the use of RuSe2 + δ nanotubes as a catalyst for the oxygenreduction reaction (ORR). Uniform RuSe2 + δ nanotubes were synthesized via a facile template-engaged reaction between Ru(acac)3 and t-Senanowires at 80 °C, followed by selective removal of the unreacted t-Se cores. The resultant RuSe2 + δ nanotubes were 55 nm in outer diameter, together with a wall thickness of 9 nm. These nanotubes were active for ORR and displayed high tolerance to 0.1 M methanol. While the mass-specific ORR activities at 0.7 V were 30 times lower than those reported for commercial Pt/C (TKK) catalysts, no detrimental effect over the ORR activity was observed upon the addition of 0.1 M methanol. In the presence of 0.1 M methanol, the mass-specific ORR activity for RuSe2 + δ was 12 times lower than that for Pt/C (TKK) at 0.7 V. Durability tests by chronoamperometry showed that 0.1 M methanol led to significant performance loss for Pt/C (TKK), while RuSe2 + δ was completely tolerant to 0.1 M methanol even after 1,800 s of operation.
No preview · Article · Feb 2009 · Journal of Materials Chemistry
[Show abstract][Hide abstract] ABSTRACT: High activity, excellent durability and low cost are three key issues in development of advanced fuel cell catalysts. In this context, alloy and intermetallic Pt-based nanoparticles are attractive candidates as their electronic structures and surface atom arrangements can be finely tuned. Herein, we present the synthesis and electrochemical property of alloyed PtAg and intermetallic PtPb nanostructures. PtAg alloyed nanoparticles with compositions in their miscibility gap were obtained through simultaneous reduction of Pt acetylacetonate (Pt(acac)2) and Ag stearate by 1,2-hexadecanediol (HDD) at elevated temperatures using long carbon chain amines and acids as capping reagents. PtPb nanorods were made from Pt(acac)2 and lead acetylacetonate (Pb(acac)2) using tert-butylaminborane (TBAB) complex as the reducants. The electrochemical properties of these nanoparticles were characterized. Both PtAg and PtPb systems showed enhanced electrocatalytic performance in fuel oxidation reaction of small molecules.
[Show abstract][Hide abstract] ABSTRACT: Heterogeneous nanostructures that contain discrete domains of platinum and other metals are attractive candidates as advanced fuel cell catalysts that integrate several different functionalities. In this talk we present the synthesis of platinum-based heterogeneous nanostructures in various non-hydrolytic systems. We show the controls over the nucleation and growth of nanoparticles are possible. Platinum nanoparticles can be deposited on different supports through the reduction of platinum salt precursors at elevated temperatures. Bifunctional long chain surfactants were used as capping and reducing reagents. The electrochemical properties of these nanoparticles were characterized in solutions. These catalysts showed enhanced performances in oxygen reduction reaction (ORR), methanol oxidation reaction (MOR) and formic acid oxidation reaction (FAOR) in comparison with pure Pt catalysts.
[Show abstract][Hide abstract] ABSTRACT: This paper presents several solution phase strategies for shape-controlled synthesis of metal and metal alloy nanostructures. Platinum-based hollow spheres and necklaces are among the interesting morphologies that will be discussed. In this synthesis, cobalt nanoparticles were synthesized by reducing cobalt salts in solution and used as sacrificial templates. We show that these templates can be completely or partially oxidized by platinum-containing ions and form hollow and higher-ordered necklace structures. The as-synthesized necklace nanostructures, presumably formed in situ through the self-assembly, can have an average diameter between 20 and 40 nm and a length of several micrometers. This method can be used to control the composition of the alloys by designing the molar ratios of various metal ions. The method may potentially be extended to the synthesis of other Pt-based alloy nanostructures and scaled up for large scale production.
[Show abstract][Hide abstract] ABSTRACT: 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 <111> 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 H(2)PtCl(6) 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.
[Show abstract][Hide abstract] ABSTRACT: This paper describes the synthesis and crystal phase behavior of platinum lead nanorods. Both face-centered cubic (fcc) Pt100−xPbx (x < 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.
[Show abstract][Hide abstract] ABSTRACT: Silver platinum binary alloys with compositions between about Ag2Pt98 and Ag95Pt5 at < similar to 400 degrees C have largely not been observed in bulk due to the large immiscibility between these two metals. We present in this paper that Ag-Pt alloy nanostructures can be made in a broad composition range. The formation of Ag-Pt nanostructures is studied by powder X-ray diffraction (PXRD) and energy-dispersive X-ray (EDX). Our results indicate that lattice parameter changes almost linearly with composition in these Ag-Pt nanomaterials. In another word, lattice parameter and composition relationship follows the Vegard's law, which is a strong indication for the formation of metal alloys. Our transmission electron microscopy (TEM) study shows that the silver-rich Ag-Pt alloy nanostructures have spherical shape, while the platinum-rich ones possess wire-like morphology. The stability and crystal phase are investigated by annealing the alloy nanostructures directly OF on carbon supports.
No preview · Article · Jul 2008 · Journal of Solid State Chemistry