Pd Core Shell Nanoparticles Research Articles

Solids at the liquid–liquid interface: Electrocatalysis with pre-formed nanoparticles

The catalytic activity of Au and Au–Pd core–shell nanoparticles is investigated at the liquid–liquid interface. The particles are shown to catalyse a process which is attributed to interfacial oxygen reduction. The Au–Pd particles are shown to be more active and correlations made between the catalytic activity and particle radius, surface area and concentration give insight into the mechanism of the catalytic process. Comparison is also made with an analogous bipolar configuration, formed by making contact between the liquid half-cells using a gold wire.

Thermal Stability and Shape Evolution of Tetrahexahedral Au–Pd Core–Shell Nanoparticles with High-Index Facets

Nanosized metallic particles with high-index facets have exhibited excellent electrocatalytic activity and thus attracted intense interests over the past few years. Moreover, bimetallic particles with high-index facets could further enhance the catalytic activity by the synergy effects of high-index facets and electronic structures of the alloy. In this article, we employed atomistic simulations to investigate the thermal stability and shape evolution of tetrahexahedral Au–Pd core–shell nanoparticles respectively enclosed by {210} and {310} facets. The ground-state energy calculations indicated that the {210} faceted nanoparticles are more structurally stable than the {310} faceted ones. More importantly, it has been discovered that the former possess better thermal and shape stabilities than the latter. The Lindemann index was introduced to shed light on the melting mechanism, and the atomic distribution function was adopted to describe the diffusion tendency. For these two high-index terminated Au–Pd bimetallic nanoparticles, the core and the shell exhibit different thermal evolution as they are heated to melting, though the melting generally proceeds from the shell into the core. Beyond the overall melting, Au atoms prefer to aggregate near the surface to favor the minimization of the total energy. These results are helpful for understanding the composition, shape, and thermodynamic properties of high-index faceted nanoparticles and therefore could be of great importance to the development of bimetallic core–shell nanocatalysts with both high reactivity and excellent stability.

New Experimental Evidences of Pt–Pd Bimetallic Nanoparticles with Core–Shell Configuration and Highly Fine-Ordered Nanostructures by High-Resolution Electron Transmission Microscopy

In our facile synthesis method, poly(vinylpyrrolidone)-protected Pt and Pt–Pd bimetallic nanoparticles with controllable polyhedral core–shell morphologies are precisely synthesized by the reduction of Pt and Pd precursors at a certain temperature in ethylene glycol with silver nitrate as structure-controlling agent. The Pt nanoparticles exhibited well-shaped polyhedral morphology with highly fine and specific nanostructures in the size range of 20 nm. Important evidences of core–shell configurations of the Pt–Pd core–shell nanoparticles were clearly characterized by high-resolution transmission electron microscopy (HRTEM) measurements. The results of HRTEM images showed that the core–shell Pt–Pd nanoparticles in the size range of 25 nm with polyhedral morphology were synthesized with the thin Pd shells of ∼3 nm in thickness as the atomic Pd layers grown on the Pt cores. Very interesting characteristics of surface structure of Pt nanostructures and Pt–Pd core–shell nanostructures with surface defects were observed. The high-resolution TEM images of Pt–Pd bimetallic nanoparticles showed that the Frank–van der Merwe and Stranski–Krastanov growth modes coexist in the nucleation and growth of the Pd shells on the as-prepared Pt cores. It is predicted that the FM growth becomes the main favorable growth compared with the SK growth in the formation of the thin Pd shells of Pt–Pd core–shell nanoparticles. The experimental evidence of the deformations of lattice fringes and lattice-fringe patterns was found in Pt and Pt–Pd core–shell nanoparticles. The interesting renucleation and recrystallization at the attachments between the nanoparticles are revealed to form a good lattice match. In addition, our novel ideas of the largest surface-area superlattices and promising utilization of them are proposed for next generations of various fuel cells with low cost. Finally, the products of Pt–Pd core–shell nanoparticles can be potentially utilized as highly efficient catalysts in the realization of polymer electrolyte membrane fuel cell and direct methanol fuel cell using the very low Pt loading with better cost-effective design.

Two-Stage Melting in Core–Shell Nanoparticles: An Atomic-Scale Perspective

Microscopic understanding of thermodynamic behaviors of metallic nanoparticles is of significance for their applications in nanoscale catalysis and thermal energy storage. In this article, molecular dynamics simulations are used to investigate the thermal stabilities of Pt–Pd core–shell nanoparticles with different core sizes and shell thicknesses. Our study shows that a distinct two-stage melting occurs during the continuous heating of bimetallic nanoparticles. It has experienced a much broader temperature range compared with the melting of monometallic nanoparticles, although they have both developed from surface into interior. The temperature width for the two-stage melting is dependent not only on the bulk melting points of two component metals but also on the ratio of the shell thickness and core size. Furthermore, due to the melting of the Pd shell beforehand, the melting point of the Pt core is lower than that of the same size Pt nanoparticle not encapsulated by the Pd shell. This study provides a ...

Catalytic CO oxidation by Au–Pd core–shell nanoparticles: A first-principles study

We applied density-functional theory to investigate the CO oxidation catalyzed by the Au38, Au32/Pd6, Pd32/Au6 and Pd38 nanoparticles. Our calculations show that the formation of peroxo-type (OOCO) complex on Au and Au-shell/Pd-core nanoparticles is more favorable than that on Pd and Pd-shell/Au-core nanoparticles, while the cleavage of the O–O bond of –OOCO– intermediate occurs more easily on Pd and Pd-shell/Au-core nanoparticles. Compared to Au(111) and Au(321) surfaces, the [Pd](Au) and/or [Au](Pd) core–shell nanoparticles are predicted to show intrinsically more reactivity for CO oxidation.

Effect of Carbon Supports on Electrocatalytic Reactivity of Au–Pd Core–Shell Nanoparticles

The role of particle-substrate interactions on the reactivity of bimetallic nanostructures is investigated in the case of Au–Pd core–shell nanoparticles supported on Vulcan XC-72R (Vulcan). Core–shell nanostructures (CS) featuring 19 nm Au cores and Pd shells with thicknesses between ca. 1 and 10 nm were synthesized by controlled colloidal methods and subsequently incorporated in the carbon support. X-ray diffraction, energy dispersive X-ray analysis, and high resolution transmission electron microscopy confirmed the CS nature of the nanostructures, which remain unaffected upon incorporation onto the carbon matrix. Their electrochemical properties toward CO and HCOOH electro-oxidation were studied, using cyclic voltammetry and chronoamperometry. The results show that the CO stripping potential becomes independent of the average Pd lattice strain in the case of Vulcan supported CS. This behavior is significantly different to the trend observed in CS assemblies at In-doped SnO2 electrodes. Formic acid oxida...

Electrochemical performance of Pd and Au–Pd core–shell nanoparticles on surface tailored carbon black as catalyst support

The present work studies the influence of the surface chemistry of carbon supports on the electrochemical behaviour of Pd and Au–Pd core–shell (CS) nanoparticles. Vulcan XC-72R was chemically modified by different acid treatments, inducing changes in the volume of the mesopores and surface density of oxygenated species. The CS nanostructures featuring 19 nm Au cores and 10 nm Pd shells were synthesized by colloidal methods and subsequently incorporated to the carbons supports. Pd nanoparticles were prepared by impregnating a Pd precursor into the modified carbons followed by reduction with sodium borohydride. The use of different preparation methods allowed the independent study of the effect of the support on the morphology/distribution of the nanoparticles and on the reactivity of the nanoparticles, through their interaction with organic molecules. The electrocatalysts were characterised by XRD, EDX, Raman spectroscopy and contact angle measurements. CO and formic acid (HCOOH) electro-oxidation were studied using cyclic voltammetry and chronoamperometry. The effect of the carbon support on the electrocatalytic activity was highly dependent on the method of preparation. Pd nanoparticles obtained by impregnation showed higher HCOOH oxidation currents when supported on the highly oxidised Vulcan support. This is due to the generation of smaller particle sizes (2.3 nm) as a result of the high density of oxygenated functional groups. On the other hand, the CS nanostructures are significantly less active in highly oxidised Vulcan as a results of specific chemical interactions which may be related to the formation of oxides. The implication of these findings towards rationalising particle–substrate interactions are briefly discussed.

Au–Pd Core–Shell Nanoparticles Catalyze Suzuki–Miyaura Reactions in Water through Pd Leaching

CNRS; ENS; UPMC in France[UMR 8640]; NSFC in China[20620130427]; Chinese Scholarship Council

Au–Pd Core–Shell Nanoparticles Catalyze Suzuki–Miyaura Reactions in Water through Pd Leaching

Weg von der Oberfläche: Nanopartikel (NPs) aus 16 nm großen Au-Kernen und Pd-Schalen unterschiedlicher Dicke katalysieren Suzuki-Miyaura-Kreuzkupplungen in Wasser bei Raumtemperatur. NPs mit einer Schalendicke von 2–5 Pd-Monoschichten sind katalytisch am aktivsten. Die Katalyse resultiert wohl aus dem Austritt von Pd-Spezies aus den NPs durch die synergistische Wirkung der Carbonatbase und der Arylboronsäure. Detailed facts of importance to specialist readers are published as ”Supporting Information”. Such documents are peer-reviewed, but not copy-edited or typeset. They are made available as submitted by the authors. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.

Synthesis and characterization of Pt–Pd nanoparticles with core-shell morphology: Nucleation and overgrowth of the Pd shells on the as-prepared and defined Pt seeds

In the present research, Pt–Pd core-shell nanoparticles based on the as-prepared and defined Pt-seed cores with well-controlled size and morphology were synthesized. Their characterizations were investigated by using UV–vis spectroscopy, transmission electron microscopy (TEM), and high resolution (HR)TEM measurements. The high resolution elemental mappings were performed in the operation of high angle annular dark field (HAADF) in conjunction with scanning (S)TEM mode and X-ray energy dispersive spectroscopy (XEDS). It is found that not only the Pt–Pd core-shell nanoparticles were formed, but also the nucleation, growth, and the separate formation of single Pd nanoparticles as well. Interestingly, the as-prepared Pt cores without the morphological changes were protected by the overgrowths of the Pd shells during the successive reduction of sodium tetrachloropalladate (II) hydrate. There were the co-existence of the Frank–van der Merwe (FM) layer-by-layer and Stranski–Krastanov (SK) island-on-wetting-layer growth modes of the Pd shells on the as-prepared Pt cores. It is predicted that the SK growth became the favorable growth mode in the formation of the Pd shells in the formation Pt–Pd core-shell nanoparticles.

Shape-controlled synthesis of Pt–Pd core–shell nanoparticles exhibiting polyhedral morphologies by modified polyol method

Pt–Pd core–shell nanoparticles were synthesized by a simple synthetic method. First, Pt nanoparticles were synthesized in a controlled manner via the reduction of chloroplantinic acid hexahydrate in ethylene glycol (EG) at 160 °C in the presence of silver nitrate and the stabilization of polyvinylpyrrolidon. AgNO 3 used acts as a structure-modifying agent to the morphology of the Pt nanoparticles. These Pt nanoparticles function as the seeds for the successive reduction of sodium tetrachloropalladate (II) hydrate in EG under stirring for 15 min at 160 °C in order to synthesize Pt–Pd core–shell nanoparticles. To characterize the as-prepared Pt–Pd nanoparticles, transmission electron microscopy (TEM) and high-resolution TEM are used. The high-resolution elemental mappings were carried out using the combination of scanning TEM and X-ray energy-dispersive spectroscopy. The results also demonstrate the homogeneous nucleation and growth of the Pd metal shell on the definite Pt core. The synthesized Pt–Pd core–shell nanoparticles exhibit a sharp and polyhedral morphology. The epitaxial growth of the controlled Pd shells on the Pt cores via a polyol method was observed. It is suggested that Frank–van der Merwe and Stranski–Krastanov growth modes coexisted in the nucleation and growth of Pt–Pd core–shell nanoparticles.

Study of Au–Pd core–shell nanoparticles by using slow positron beam

Binary Au–Pd nanoparticles were synthesized by ultrasonic irradiation of solutions containing Au 3+ and Pd 2+ ions (the ion ratio from 0.3:0.7 to 0.9:0.1 mM) and cationic surfactant (SDS: sodium dodecyl sulfate). In each case the core–shell structure (Au core, Pd shell) was confirmed by scanning transmission electron microscopy (STEM). The mean diameters of them were all about 9 nm, and the thickness of the Pd shell depends on the ratio of Pd 2+ and Au 3+ ions in solution. In order to study the electronic states of core–shell nanoparticles and their dependence on shell thickness, Doppler broadening measurements were performed for Au–Pd core–shell nanoparticles by using slow positron beam technique. The ratio curves of Au–Pd particles did not match with those of pure Pd and pure Au, but a small difference in the low electron momentum region was observed among nanoparticles depending on Pd shell thickness.

Synthesis and characterization of platinum monolayer oxygen-reduction electrocatalysts with Co–Pd core–shell nanoparticle supports

We synthesized Pt monolayer electrocatalysts for oxygen-reduction using a new method to obtain the supporting core–shell nanoparticles. They consist of a Pt monolayer deposited on carbon-supported Co–Pd core–shell nanoparticles with the diameter of 3–4 nm. The nanoparticles were made using a redox-transmetalation (electroless deposition) method involving the oxidation of Co by Pd cations, yielding a Pd shell around the Co core. The quality of the thus-formed core–shell structure was verified using transmission electron microscopy and X-ray absorption spectroscopy, while cyclic voltammetry was employed to confirm the lack of Co oxidation (dissolution). A Pt monolayer was deposited on the Co–Pd core–shell nanoparticles by the galvanic displacement of a Cu monolayer obtained by underpotential deposition. The total noble metal mass-specific activity of this Pt monolayer electrocatalyst was ca. 3-fold higher than that of commercial Pt/C electrocatalysts.