Pd Shell Research Articles

Core–shell Pd–P@Pt nanoparticles as efficient catalysts for electrooxidation of formic acid

Tailoring the composition and structure is an effective approach for improving the properties of electrocatalysts in fuel cells. In this study, the core–shell Pd–P@Pt nanoparticles were synthesized using a seed-mediated growth method and applied to the formic acid oxidation reaction like electrocatalysts. The core–shell structure was confirmed by transmission electron microscopy, elemental mapping analyses, energy-dispersive X-ray spectroscopy line scan, inductively coupled plasma mass spectrometry, and X-ray photoelectron spectroscopy. The catalytic activity and durability were evaluated by cyclic voltammetry, electrochemically active surface area loss, and chronoamperometry. The obtained particles exhibit higher catalytic activity and durability compared to those of Pt/C and Pt black commercial reference catalysts due to the synergistic effect between the Pd–P core and the Pt shell. In addition, the Pt shell inhibits the corrosion of Pd in the acidic solution, resulting in good stability.

Core/shell FePd/Pd catalyst with a superior activity to Pt in oxygen reduction reaction

Developing high-efficient non-platinum (Pt) catalysts for oxygen reduction reaction (ORR) is the key to reduce the usage of Pt and the palladium (Pd)-based catalyst is a promising alternative. Here, we presented a facile approach to core/shell FePd/Pd nanoparticle (NP) catalyst with the FePd core in chemically ordered face-centered tetragonal (fct-) structure and the shell in controlled thickness from 0.32 to 0.81nm via the thermal annealing of FePd NP followed by an electro-anodization process. With a 0.71nm-thick Pd shell, the fct-FePd/Pd shows a robust catalytic activity and durability for ORR with the mass activities at 0.85 and 0.90V reaching 453 and 96.7A/mgPd, respectively, which are about 3.0 and 2.1 times higher than those of commercial Pt in alkaline media. This work presents a new class of non-Pt catalyst with superior performance to Pt for ORR catalysis, and the strategy demonstrated here can be extended to design high-efficient catalysts for other chemical reactions.

Hydride formation in core–shell alloyed metal nanoparticles

The model and analysis presented are focused on hydride formation in nanoparticles with a Pd shell and a core formed by another metal. The arrangement of metal atoms is assumed to be coherent (no dislocations). The lattice strain distribution, elastic energy, and chemical potential of hydrogen atoms are scrutinized. The slope of the chemical potential (as a function of hydrogen uptake) is demonstrated to decrease with increasing the core volume, and accordingly the critical temperature for hydride formation and the corresponding hysteresis loops are predicted to decrease as well.

Surface plasmon resonance promoted photoelectrocatalyst by visible light from Au core Pd shell Pt cluster nanoparticles

The need for alternative energy sources utilizing visible light is growing stronger due to the increasing energy demand. The UV light is widely used in photoelectrocatalysis, however, it is still difficult to use the visible light efficiently to enhance the catalytic activity. Here we design a surface plasmon resonance (SPR) promoted photoelectrocatalyst taking advantage of visible light by tailoring a Au core Pd shell Pt mushroom trimetallic structure nanoparticles to enhance the catalytic activity of the direct methanol fuel cells (DMFCs). The Au core is used to provide the SPR effect utilizing visible light to enhance the catalytic activity. The combination of the Pd and Pt provides a synergistic effect to enhance the catalytic activity. The photoelectrocatalytic and photothermal effect generated from SPR is proved and quantitatively calculated. These results provide a novel design of photoelectrocatalyst based on the SPR effect.

Palladium modified gold nanoparticles as electrocatalysts for ethanol electrooxidation

Resemblin, g core-shell electrocatalysts consisting of a Au core and Pd shell (Au@Pd) are synthesized via a Cu underpotential deposition (UPD)-Pd-displacement method. The Pd shell is non-uniform consisting of tiny Pd clusters with a coverage of 0.5–0.6. The ethanol oxidation reaction (EOR) activity of this kind of structure is much higher than Pd/C in an alkaline solution. The forward peak current density of Au@Pd is 5.4 times higher than that of Pd/C. Furthermore, the onset potential for EOR of the former is ∼100 mV more negative. An interesting particle size dependent EOR activity is also observed. With increasing the Au particle size (2.9, 5.8 and 6.5 nm), the EOR activity increases. The strain and ligand effects from the Au core, together with the bifunctional reaction mechanism in the Au–Pd system may be reasons for the enhanced activity in Au@Pd catalysts.

Probing the Electronic Structure of Heterogeneous Metal Interfaces by Transition Metal Shelled Gold Nanoparticle-Enhanced Raman Spectroscopy

In heterogeneous catalysis, characterization of heterogeneous metal interfaces of bimetallic catalysts is a crucial step to elucidate the catalytic performance and is a key to develop advanced catalysts. However, analytical techniques such as X-ray photoelectron spectroscopy can only work in vacuum conditions and are difficult to use for in situ analysis. Here, we present efficient and convenient core–shell nanoparticle-enhanced Raman spectroscopy to explore the in situ electronic structures of heterogeneous interfaces (Au@Pd and Au@Pt core–shell NPs) by varying the shell thickness. The experimental observations reported here clearly show that Pd donates electrons to Au, while Pt accepts electrons from Au at the heterogeneous interfaces. This conclusion gains further support from ex situ X-ray photoelectron spectroscopy results. The Au core greatly affects the electronic structures of both the Pd and Pt shells as well as catalytic behaviors. Finally, the as-prepared core–shell nanoparticles were used to d...

Cage-bell Pt-Pd nanostructures with enhanced catalytic properties and superior methanol tolerance for oxygen reduction reaction.

Precisely tailoring the structure and fully making use of the components of nanoparticles are effective to enhance their catalytic performance for a given reaction. We herein demonstrate the design of cage-bell structured Pt-Pd nanoparticles, where a Pd shell is deliberately selected to enhance the catalytic property and methanol tolerance of Pt for oxygen reduction reaction. This strategy starts with the synthesis of core-shell Pt@Ag nanoparticles, followed by galvanic replacement reaction between the Ag shell and Pd2+ ions to form core-shell-shell Pt@Ag@Ag-Pd nanoparticles with a Pt core and double shells composed of Ag at inner and alloy Ag-Pd at outer, respectively. Then, the core-shell-shell templates are agitated with saturated NaCl solution to eliminate the Ag component from the double shells, leading to the formation of bimetallic Pt-Pd nanoparticles with a cage-bell structure, defined as a movable Pt core enclosed by a porous Pd shell, which show enhanced catalytic activity for oxygen reduction compared with that of the Pt seeds due to the additional catalysis from Pd shell. In addition, owing to the different diffusion behavior of methanol and oxygen molecules in the porous Pd shell, the Pt-Pd cage-bell nanostructures also exhibit superior methanol tolerant property in catalyzing the oxygen reduction.

Porous dandelion-like gold@ palladium core-shell nanocrystals in-situ growth on reduced graphene oxide with improved electrocatalytic properties

A one-pot wet-chemical co-reduction route is designed for preparation of porous dandelion-like Au@Pd core-shell nanostructures in-situ grown on reduced grapheneoxide (Au@Pd/rGO) without using any premade seed. Cetyltrimethylammonium chloride (CTAC) and iodide ion (I−) play important roles in this synthetic procedure. Particularly, the Pd shell thickness, particle size, composition and catalytic activity can be tuned by adjusting the concentrations of I−. The effects of composition and structure of the as-synthesized nanocomposites on the catalytic performance are investigated. The dandelion-like Au@Pd/rGO exhibited higher catalytic activity and stronger tolerance to carbonaceous species poisoning for methanol oxidation reaction (MOR) in contrast with Pd/rGO and commercial Pd/C catalysts in alkaline media. This strategy offers a new approach for controlled synthesis of novel nanocatalysts with enhanced catalytic performances in fuel cell.

Electrochemical Reduction of Carbon Dioxide at Gold‐Palladium Core–Shell Nanoparticles: Product Distribution versus Shell Thickness

AbstractThe electrocatalytic reduction of CO2 at carbon‐supported Au‐Pd core–shell nanoparticles is investigated systematically as a function of the Pd shell thickness. Liquid‐ and gas‐phase products were determined by off‐line 1H NMR spectroscopy and on‐line electrochemical mass spectrometry. Our results uncover the relationship between the nature of the products generated and the Pd shell thickness. CO and H2 are the only products generated at 1 nm thick shells, whereas shells of 5 and 10 nm produced HCOO−, CH4 and C2H6. The concentration of HCOO− detected in the electrolyte was dependent on the applied potential and reached a maximum Faradaic efficiency of 27 % at −0.5 V versus the reversible hydrogen electrode for 10 nm thick shells. We conclude that collisions between absorbed hydrogen at relaxed Pd lattices and strongly bound “CO‐like” intermediates promote the complete hydrogenation to C1 and C2 alkanes without the generation of other products, such as alcohols and aldehydes.

Acetylene hydrogenation over structured Au-Pd catalysts.

AuPd nanoparticles were prepared following a methodology designed to produce core-shell structures (an Au core and a Pd shell). Characterisation suggested that slow addition of the shell metal favoured deposition onto the pre-formed core, whereas more rapid addition favoured the formation of a monometallic Pd phase in addition to some nanoparticles with the core-shell morphology. When used for the selective hydrogenation of acetylene, samples that possessed monometallic Pd particles favoured over-hydrogenation to form ethane. A sample prepared by the slow addition of a small amount of Pd resulted in the formation of a core-shell structure but with an incomplete Pd shell layer. This material exhibited a completely different product selectivity with ethylene and oligomers forming as the major products as opposed to ethane. The improved performance was thought to be as a result of the absence of Pd particles, which are capable of forming a Pd-hydride phase, with enhanced oligomer selectivity associated with reaction on uncovered Au atoms.

Photochemical Synthesis of Au@Pd Core-Shell Nanoparticles for Methanol Oxidation Reaction: the Promotional Effect of the Au Core

A novel method for synthesizing Au@Pd core-shell nanoparticles was proposed based on photochemistry. By irradiating the mixture of Au (III) and Pd (II) ions using ultraviolet light, the Au@Pd core-shell nanoparticles were prepared. The size of the nanoparticles and the thickness of the Pd shell could be efficiently adjusted by changing the molar ratio of Au (III) to Pd (II) ion. In this way, nanoparticles with diameter in the range of 5.6~4.6 nm were obtained. The core-shell structure of the synthesized nanoparticles was showed by the characterization using UV-Vis, TEM/HR-TEM and XPS. The paper investigated the electrocatalysis performance of Au@Pd nanoparticles in the methanol catalytic oxidation reaction, as well as the electron donating effect of Au core to Pd shell and the promotion of this effect on the catalytic activity of Pd shell. The experimental results provided reference for the development of non-platinum catalysts of low-temperature fuel cell anode.

"Flash" preparation of strongly coupled metal nanoparticle clusters with sub-nm gaps by Ag+ soldering: toward effective plasmonic tuning of solution-assembled nanomaterials.

Noble metal nanoparticle oligomers are important in applications including plasmonics, catalysis, and molecular sensing. These nanostructural units featuring abundant inter-particle junctions are helpful for a physical/chemical understanding of structure-activity relationships of self-assembled metamaterials. A simple, rapid, and potentially general strategy for the preparation of monodisperse nanoparticle clusters in a homogeneous solution is highly desired for fundamental research toward liquid metamaterials and chemical/biological applications, but this is however very challenging. Here we report an Ag+ soldering strategy to prepare strongly coupled plasmonic (Au) and catalytic (Pt, Au@Pd (Au core with a Pd shell)) nanoparticle clusters almost instantly (<1 min) in a solution without special synthetic efforts, complicated surface decorations, or structure-directing templates. The resulting clusters are isolatable by agarose gel electrophoresis, resulting in mechanically stable products in high purity. The optical extinctions of Au nanodimers (the simplest and most basic form of a coupled structure) exhibit prominent longitudinal plasmonic coupling for nanoparticles down to 13.3 nm in diameter. Theoretical simulations attribute the strong coupling to the existence of a sub-nm gap (c.a. 0.76 nm) between soldered particles, suggesting an ideal (stable, soluble, monodisperse, and weakly passivated) substrate for surface enhanced Raman scattering (SERS) applications.

Sandwich-structured Au@polyallylamine@Pd nanostructures: tuning the electronic properties of the Pd shell for electrocatalysis

We report herein the synthesis of core–shell sandwich Au@polyallylamine@Pd nanostructures, in which the electronic structure of the Pd shell can be strongly tuned by the medial polyallylamine layers.

Construction of polydopamine-coated gold nanostars for CT imaging and enhanced photothermal therapy of tumors: an innovative theranostic strategy.

The advancement of biocompatible nanoplatforms with dual functionalities of diagnosis and therapeutics has been strongly demanded in biomedicine in recent years. In this work, we report the synthesis and characterization of polydopamine (pD)-coated gold nanostars (Au NSs) for computed tomography (CT) imaging and enhanced photothermal therapy (PTT) of tumors. Au NSs were firstly formed via a seed-mediated growth method and then stabilized with thiolated polyethyleneimine (PEI-SH), followed by deposition of pD on their surface. The formed pD-coated Au NSs (Au-PEI@pD NSs) were well characterized. We show that the Au-PEI@pD NSs are able to convert the absorbed near-infrared laser light into heat, and have strong X-ray attenuation properties. Due to the co-existence of Au NSs and pD, the light to heat conversion efficiency of the NSs can be significantly enhanced. These very interesting properties allow them to be used as a powerful theranostic nanoplatform for efficient CT imaging and enhanced phtotothermal therapy of cancer cells in vitro and the xenografted tumor model in vivo. Due to their easy functionalization nature enabled by the coated pD shell, the developed pD-coated Au NSs may be used as a versatile nanoplatform for targeted CT imaging and PTT of different types of cancers.

A core–shell Pd1Ru1Ni2@Pt/C catalyst with a ternary alloy core and Pt monolayer: enhanced activity and stability towards the oxygen reduction reaction by the addition of Ni

A core–shell structured catalyst exhibits high activity and stability.

Shape Transformation of Bimetallic Au–Pd Core–Shell Nanocubes to Multilayered Au–Pd–Au Core–Shell Hexagonal Platelets

Transformation of metallic or bimetallic (BM) nanoparticles (NPs) from one shape to another desired shape is of importance to nanoscience and nanotechnology, where new morphologies of NPs lead to enhancement of their exploitable properties. In this report, we present the shape transformation of Au octahedral NPs to Au–Pd core–shell nanocubes, followed by their transformation to nanostars and finally to multilayered Au–Pd–Au core–shell hexagonal platelets in the presence of T30 DNA. The weaker binding affinity of T30 DNA directs the growth to favor the formation of lower energy {111} facets, changing the morphology from nanocubes to nanostar. The nanostars, exhibiting unusual intermediate morphologies, are comprised two sets of shell layers and have Au core, Pd intermediate shell, and Au outer shell. Similarly, the hexagonal platelets, which also have Au core and inner Pd shell, are encased in an external gold shell. The formation of multilayered Au–Pd–Au core–shell hexagonal platelets from Au–Pd core–shell nanocubes via the multilayered nanostars is monitored using scanning/transmission electron microscopy analysis.

A Strategy for the Formation of Gold–Palladium Supra-Nanoparticles from Gold Nanoparticles of Various Shapes and Their Application to High-Performance H2O2 Sensing

We present a new approach for the synthesis of gold (Au)–palladium (Pd) bimetallic supra-nanoparticles in which densely packed anisotropic Pd nanostructures surround a central Au nanoparticle (rod, sphere, cubic shape). They were obtained by means of Pd crystal growth on Au nanoparticle surfaces which are modified with a mixture of cetyltrimethylammonium bromide (CTAB) and 5-bromosalicylic acid (5-BrSA). From a comparative study with a Au nanorod (NR) as a seed, the use of the CTAB/5-BrSA mixture plays a pivotal role in obtaining such unique supra-structures; the Au NR capped with only CTAB resulted in Au core–continuous Pd shell nanoparticles instead. The Au–Pd supra-nanoparticles provide active surface area for electrocatalytic activities higher than that of the Au@Pd continuous shell nanoparticles, displaying outstanding performance for mediator-free electrochemical detection of H2O2.

A Pathway for the Growth of Core–Shell Pt–Pd Nanoparticles

The aging of both Pt–Pd nanoparticles and core–shell Pt–Pd nanoparticles has been reported to result in alloying of Pt with Pd. In comparison to monometallic Pt catalysts, the growth of Pd–Pt bimetallics is slower; however, the mechanism of growth of particles and the mechanism by which Pd improves the hydrothermal durability of bimetallic Pd–Pt particles remains uncertain. In our work on hydrothermal aging of core–shell Pt–Pd nanoparticles, synthesized by solution methods, with varying Pd:Pt ratio of 1:4, 1:1, and 4:1, we compare the growth of core–shell Pt–Pd nanoparticles and find that particles grow by migrating and joining together. The unique feature of the observed growth is that Pd shells from both particles open up and join, thereby allowing the cores to merge. At high temperatures, alloying occurs in good agreement with reports by other workers.

Core/Shell Face-Centered Tetragonal FePd/Pd Nanoparticles as an Efficient Non-Pt Catalyst for the Oxygen Reduction Reaction.

We report the synthesis of core/shell face-centered tetragonal (fct)-FePd/Pd nanoparticles (NPs) via reductive annealing of core/shell Pd/Fe3O4 NPs followed by temperature-controlled Fe etching in acetic acid. Among three different kinds of core/shell FePd/Pd NPs studied (FePd core at ∼8 nm and Pd shell at 0.27, 0.65, or 0.81 nm), the fct-FePd/Pd-0.65 NPs are the most efficient catalyst for the oxygen reduction reaction (ORR) in 0.1 M HClO4 with Pt-like activity and durability. This enhanced ORR catalysis arises from the desired Pd lattice compression in the 0.65 nm Pd shell induced by the fct-FePd core. Our study offers a general approach to enhance Pd catalysis in acid for ORR.

Enhanced Selectivity to H2 Formation in Decomposition of HCOOH on the Ag19@Pd60 Core-Shell Nanocluster from First-Principles.

In this study, using spin-polarized density functional theory calculation we examined the origin of enhanced catalytic activity toward H2 production from HCOOH in Ag19@Pd60 core-shell nanoclusters (a 79-atom truncated octahedral cluster models). First, we find that the Pd monolayer shell on the Ag core can greatly enhance the selectivity to H2 formation via HCOOH decomposition compared to the pure Pd79 cluster by substantially reducing the binding energy of key intermediate HCOO and in turn the barrier for dehydrogenation. This activity enhancement is related to the modification of d states in the Pd monolayer shell by the strong ligand effect between Ag core and Pd shell, rather than the tensile strain effect by Ag core. In particular, the absence of dz2-r2 density of states near the Fermi level in the Pd monolayer shell (which originated from the substantial charge transfer from Ag to Pd) is the main reason for the increased H2 production from HCOOH decomposition.