Au Pd Core Shell Research Articles

Synthesis and catalytic activity of core-shell gold-palladium nanoworms towards the catalytic reduction of 4-nitrophenol and methyl orange

The Au-Pd core–shell nanostructures have gained attention as a promising catalyst and exhibit outstanding stability and selectivity in pivotal chemical reactions. This work demonstrates a facile seed-mediated approach for depositing the shell of Pd on worm-shaped Au nanostructures. The control over Pd content on Au nanoworms (NWs) was achieved by adjusting the concentration of tetrachloropalladic acid (H2PdCl4) in the deposition solution. The bent morphology, surface roughness, and polycrystalline structure of the Au NWs ensured that at lower H2PdCl4 concentrations, Pd formed an island-like structure on the Au NWs’ surface. In contrast, increasing the H2PdCl4 concentration led to the formation of a complete Pd shell encasing the Au NWs. The catalytic activity of the Au-Pd core–shell (Pd@Au) NWs exhibited a significant improvement compared to uncoated Au NWs, which has been attributed to the synergetic effect of the two metals. However, it was observed that an optimum Pd-coating was necessary to obtain the best catalytic performance and a further increase in Pd content led to the degradation of the catalytic activity. Specifically, the rate constant of the reduction reactions of 4-nitrophenol (4-NP) and methyl orange (MO) was increased by 6.3 and 3.1 folds, respectively, for the optimized Pd@Au NWs.

Facile construction of core-shell AuPd nanochain networks in one-pot for ethanol oxidation

Palladium (Pd)-based catalysts have been extensively investigated in direct ethanol fuel cells (DEFCs) since the urgent energy and environmental problems. Rational design Pd-based catalyst with outstanding structure can optimize its electrocatalytic performance for ethanol oxidation reaction (EOR) catalyst. In this work, a facile strategy was proposed to prepare AuPd nanochain networks (NNWs) with core-shell structure by adjusting the reduction rate by slowly dropping the acidic reducing agent to the alkaline precursor solution system. The resulting catalysts exhibit a porous self-supporting structure with twisted features, exposing a large number of active sites. The optimized AuPd NNWs catalyst displays much-improved activity (3289.62 mA mg−1 Pd) and greatly enhanced electrocatalytic stability for EOR in comparison with that of commercial Pd/C catalysts. This enhanced activity can be attributed to the synergic effect of the Pd shell with the Au core as well as the twisted and self-supporting structure which can expose much more active sites and provide rich mass and electron transfer channels.

AuPd nanoparticles functionalized core–shell Co3O4/ZnO@ZnO for ultra-sensitive toluene detection

In this work, core–shell AuPd nanoparticles (NPs) sensitized Co3O4/ZnO@ZnO ellipsoid nanoparticles was successfully synthesized via a simple liquid phase synthesis method. SEM and TEM characterization results showed that the as-prepared samples have core–shell ellipsoid morphology and the size of the nanoparticles were uniform. Systematic gas sensing characterization was carried out to obtain the gas sensing property of AuPd NPs decorated Co3O4/ZnO@ZnO. It was found that the gas sensing property could be significantly enhanced after noble metal decoration with Au, Pd and AuPd NPs, respectively. The optimal gas sensing performance was achieved by AuPd NPs functionalized Co3O4/ZnO@ZnO based gas sensor. The maximum response reached 256–100 ppm toluene at 250 °C, which is 50 °C lower than pure ZnO. The detection limit of AuPd functionalized Co3O4/ZnO@ZnO was as low as 100 ppb. The enhanced sensing mechanism was mainly attributed to the synergistic effect of Au and Pd, which was detailly discussed in gas sensing mechanism part.

Plasmonic Au–Pd Bimetallic Nanocatalysts for Hot-Carrier-Enhanced Photocatalytic and Electrochemical Ethanol Oxidation

Gold–palladium (Au–Pd) bimetallic nanostructures with engineered plasmon-enhanced activity sustainably drive energy-intensive chemical reactions at low temperatures with solar simulated light. A series of alloy and core–shell Au–Pd nanoparticles (NPs) were prepared to synergistically couple plasmonic (Au) and catalytic (Pd) metals to tailor their optical and catalytic properties. Metal-based catalysts supporting a localized surface plasmon resonance (SPR) can enhance energy-intensive chemical reactions via augmented carrier generation/separation and photothermal conversion. Titania-supported Au–Pd bimetallic (i) alloys and (ii) core–shell NPs initiated the ethanol (EtOH) oxidation reaction under solar-simulated irradiation, with emphasis toward driving carbon–carbon (C–C) bond cleavage at low temperatures. Plasmon-assisted complete oxidation of EtOH to CO2, as well as intermediary acetaldehyde, was examined by monitoring the yield of gaseous products from suspended particle photocatalysis. Photocatalytic, electrochemical, and photoelectrochemical (PEC) results are correlated with Au–Pd composition and homogeneity to maintain SPR-induced charge separation and mitigate the carbon monoxide poisoning effects on Pd. Photogenerated holes drive the photo-oxidation of EtOH primarily on the Au-Pd bimetallic nanocatalysts and photothermal effects improve intermediate desorption from the catalyst surface, providing a method to selectively cleave C–C bonds.

Bimetallic Au-Pd nanoparticles supported on silica with a tunable core@shell structure: enhanced catalytic activity of Pd(core)-Au(shell) over Au(core)-Pd(shell).

A facile ligand-assisted approach of synthesizing bimetallic Au–Pd nanoparticles supported on silica with a tunable core@shell structure is presented. Maneuvering the addition sequence of metal salts, both Aucore–Pdshell (Au@Pd–SiO2) and Pdcore–Aushell (Pd@Au–SiO2) nanoparticles were synthesized. The structures and compositions of the core–shell materials were confirmed by probe-corrected HRTEM, TEM-EDX mapping, EDS line scanning, XPS, PXRD, BET, FE-SEM-EDX and ICP analysis. The synergistic potentials of the core–shell materials were evaluated for two important reactions viz. hydrogenation of nitroarenes to anilines and hydration of nitriles to amides. In fact, in both the reactions, the Au–Pd materials exhibited superior performance over monometallic Au or Pd counterparts. Notably, among the two bimetallic materials, the one with Pdcore–Aushell structure displayed superior activity over the Aucore–Pdshell structure which could be attributed to the higher stability and uniform Au–Pd bimetallic interfaces in the former compared to the latter. Apart from enhanced synergism, high chemoselectivity in hydrogenation, wide functional group tolerance, high recyclability, etc. are other advantages of our system. A kinetic study has also been performed for the nitrile hydration reaction which demonstrates first order kinetics. Evaluation of rate constants along with a brief investigation on the Hammett parameters has also been presented.

One pot in situ synthesis of nano Au–Pd core-shells embedded on reduced graphene oxide for the oxygen reduction reaction

The core–shell nanoparticles embedded on reduced graphene oxide (rGO) nanosheets usually exhibit enhanced catalytic activity because of their lattice strain effect. In this study, rGO supported core–shell Au–Pd nanoparticles (Au@Pd/rGO) were synthesized by a facile one pot sonochemical method and studied for their enhanced catalytic activity. The ultrasonic liquid processor at the frequency of 20 kHz and the power of 40 W (with an amplitude of 35%) was used to perform the synthesis. The existence of the spherical shaped Au core and size controlled Au-Pd core–shell nanoparticles incorporated into the rGO nanosheets were identified using high resolution transmission electron microscopy (HR-TEM) and high angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) analyzes. The ordered nature and the elemental presence of Au@Pd/rGO and the mapping were studied using Raman, X-ray photoelectron (XPS) and energy dispersive X-ray (EDS) spectroscopic analyses, respectively. The electrode modified with Au@Pd/rGO deliberately showed an improved electrocatalytic activity for the oxygen reduction reaction (ORR). The kinetics involved in the ORR was intensively studied using the rotating disk electrode (RDE) and identified as the developed Au@Pd/rGO possessed a better catalytic activity compared to Au/rGO and analogous activity with the other standard ORR catalysts such as Pd20/C and Pt20/C. The number of electron exchanged for the reaction was calculated as four using Koutecky–Levich (K–L) plot.

Au–Pd core–shell nanoparticle film for optical detection of hydrogen gas

Hydrogen use, as a clean and almost infinite energy source, has an economic impact in many industries. The problem is that this gas cannot be used like any gas because of its explosiveness at 4% in the air, hence the need to know its concentration any time for security reasons. The permanent detection of hydrogen leaks is essential to monitor and to control the hydrogen concentration to prevent any possible risk. In our current research, we have developed hydrogen ultrasensitive sensors by depositing a thin film of Au–Pd core–shell nanoparticles (NPs) on a transparent glass substrate in order to detect hydrogen in its gaseous form. The colloidal Au–Pd core–shell NPs were synthesized according to a multi-reduction step method. The structural characterizations, the nature, and the density of Au–Pd core–shell NPs have been characterized by scanning electron microscopy and transmission electron microscopy. The morphology, size, and structure of Au–Pd core–shell NPs can be controlled under synthesis conditions. The size of the core–shell studied in this work is 13 nm for gold NP diameter and 0 nm–2.3 nm for palladium thicknesses. The physical properties of NPs, such as the optical absorbance response under hydrogen, strongly depend on the nature of the shell and the ratio between the core and the shell. At different hydrogen concentrations ranging from 1% to 4%, the optical response changes in the position of the surface plasmon resonance peak on the absorbance spectrum after the first loading/unloading hydrogen cycle.

Electrocatalytical Performance of Au-Pd Cubic and Octahedral Core-Shell Nanostructures in the Formic Acid Oxidation Reaction

AuPd cubic and octahedral core-shell nanostructures were synthesized by seed growth method and its performance was evaluated in the formic acid oxidation reaction (FAOR). The core-shell nanostructure shapes were confirmed by SEM in Figure 1. The electrochemical surface areas were obtained by CO stripping. The electrocatalytic activity in the FAOR was evaluated in a 0.5 M HClO4 and 1 M HCOOH electrolyte by cyclic voltammetry in Figure 1. The cubic nanostructure showed the best current density for the direct route in the FAOR. The AuPd core-shell encouraged the FAOR direct or indirect route by the CO adsorption-desorption processes on the surface of each shape. Figure 1

Enhancing Catalytic Activity and Selectivity by Plasmon-Induced Hot Carriers.

SummaryPlasmon-assisted chemical transformation holds great potential for solar energy conversion. However, simultaneous enhancement of reactivity and selectivity is still challenging and the mechanism remains mysterious. Herein, we elucidate the localized surface plasmon resonance (LSPR)-induced principles underlying the enhanced activity (∼70%) and selectivity of photoelectrocatalytic redox of nitrobenzene (NB) on Au nanoparticles. Hot carriers selectively accelerate the conversion rate from NB to phenylhydroxylamine (PHA) by ∼14% but suppress the transformation rate from PHA to nitrosobenzene (NSB) by ∼13%. By adding an electron accepter, the as-observed suppression ratio is substantially enlarged up to 43%. Our experiments, supported by in situ surface-enhanced Raman spectroscopy and density functional theory simulations, reveal such particular hot-carrier-induced selectivity is conjointly contributed by the accelerated hot electron transfer and the corresponding residual hot holes. This work will help expand the applications of renewable sunlight in the directional production of value-added chemicals under mild conditions.

Optimization of gold-palladium core-shell nanowires towards H2O2 reduction by adjusting shell thickness.

Designable bimetallic core–shell nanoparticles exhibit superb performance in many fields including industrial catalysis, energy conversion and chemical sensing, due to their outstanding properties associated with their tunable electronic structure. Herein, Au–Pd core–shell (AurichPd@AuPdrich) nanowires (NWs) were synthesized through a one-pot facile chemical reduction method in the presence of cetyltrimethyl ammonium bromide (CTAB) surfactant. The thickness of the Pd shell could be adjusted by directly controlling the Au/Pd feeding ratio while maintaining the nanowire morphology. The as-obtained Au75Pd25 core–shell NWs with a thin Pdrich shell showed significantly enhanced activities towards the reduction of hydrogen peroxide with the sensitivity reaching 338 μA cm−2 mM−1 and a linear range up to 10 mM. In sum, Pd shell thickness could be used to adjust the electronic structure, thereby optimizing the catalytic activity.

Compressive Strain in Core-Shell Au-Pd Nanoparticles Introduced by Lateral Confinement of Deformation Twinnings to Enhance the Oxidation Reduction Reaction Performance.

In this work, quasi-spherical, uniform gold nanoparticles with rich deformation twinning (Audt NPs) were first synthesized with the assistance of copper(II) ions. Then, these Audt NPs were used as the cores for the fabrication of core-shell (CS) Audt-Pd NPs with ultrathin Pd layers, which also can bear compressive strain because of the formation of corrugated structured Pd shells led by the lateral confinement imposed by deformation twinning in the Au cores. The presence of compressive strain in the CS Audt-Pd NPs can result in the widening of the d-band width of the Pd shell and further the downshift of their d-band center, which can then improve the desorption ability of intermediates and still maintain the adsorption ability of the reactants because of the broad adsorption potential range. Taking the oxidation reduction reaction and the ethanol oxidation reaction as examples, the as-prepared Audt-Pd NPs indeed exhibited superior catalytic performances because of the synergism of compressive strain and the electronic effect. Thus, our work opens a new way to introduce compressive strain in the Pd-based CS NP catalysts, which can achieve the enhancement in the electrocatalytic performance by combining the merit of compressive strain and the electronic effect.

Formic acid oxidation on AuPd core-shell electrocatalysts: Effect of surface electronic structure

AuPd core-shell electrocatalysts were synthesized with cubic, cuboctahedric and octahedral shapes to study the electronic effects of these nanostructures on the formic acid oxidation reaction, FAOR. The morphology and the surface electronic structure of the different AuPd core-shell were examined by high-resolution transmission electron microscopy, HRTEM, and X-ray photoelectron spectroscopy, XPS, respectively. The FAOR was analyzed by the binding energy of the d-band center of each core-shell nanostructure and its electrocatalytic behavior. The octahedron shape presents better affinity for the CO adsorption-desorption processes and higher overpotentials than the other electrocatalyst. Therefore, the FAOR indirect route is encouraged. Contrariwise, the cubic nanostructure favors the FAOR direct route due to its exchange current density of 1.741 mA cm−2 that suggest a fast kinetic associated with the lowest d-band binding energy among all the core-shell nanostructures.

(Invited) Composition Dependent Performance of Au-Pd Core-Shell Nanocatalysts for CO2 Electrochemical Reduction

Electrochemical reduction of CO2 (CO2RR) to produce valuable chemicals is promising in simultaneously controlling the CO2 concentration and storing renewable energy. However, its wide adoption still needs highly selective and reactive catalysts. In this study, Au-Pd core-shell (CS) nanoparticles consisting of a Au-rich core and Pd-rich shell were synthesized by wet methods. The nanoparticle composition and shell thickness were adjusted to evaluate their impacts on CO2-to-CO electrocatalytic conversion performance. The CS nanoparticles have a uniform morphology with an average size between 7 to 9 nm. As compared to pure Pd and Au nanoparticles with a similar size, all the synthesized CS nanoparticles exhibited a significantly increased CO selectivity (Figure 1). The CS nanoparticles also have superior mass and specific activities, which are highly dependent on the composition and structure. The best catalyst showed an ultrahigh mass activity of 99.8 mA mg-1 at -0.5 V along with a superior CO faradaic efficiency of 94.7%. In situ infrared spectroscopic studies with an attenuated total reflection configuration (ATR) and density functional theory calculations (DFT) were conducted to reveal the combined structure and composition impacts on the activity. It was found that the scaling relation between *COOH and *CO binding strength was broken on the core-shell nanoparticles and led to the high selectivity and activity toward CO production. The authors acknowledge the support from Hong Kong Research Grant Council (26206115 and 16309418). Figure 1. Faradaic efficiency of CO measured on synthesized Au-Pd core-shell, Pd and Au nanoparticles. Figure 1

Self-limiting synthesis of Au–Pd core–shell nanocrystals with a near surface alloy and monolayer Pd shell structure and their superior catalytic activity on the conversion of hexavalent chromium

In eliminating environmental chromium pollution, hexavalent chromium (Cr(VI)) reduction by HCOOH on Pd-based bimetallic/multimetallic nanocatalysts is attracting an increasing attention. However, it is still a challenge by precisely controlling the surface interface structure of the nanocrystals (NCs) to obtain highly efficient nanocatalysts on Cr(VI)) conversion. Here, a simple and robust synthesis method for Au-Pd core-shell NCs with a special interface structure has been developed by a novel self-limiting strategy. This interesting structure has a near surface alloy (NSA) of AuPd layer on Au core with outer surface of monolayer (ML) of Pd shell (denoted as NSA/ML), which is achieved only by one-pot synthesis. The self-limiting strategy is developed based on the unique catalysis reduction reaction of Au core, with which the growth of Pd shell is internally regulated by the surface Au atoms until the Au–Pd NCs with NSA/ML structure i.e. Au@AuPd@PdML NCs are formed. Furthermore, the Au–Pd core–shell NCs with the shell from NSA to NSA/ML structure can be simply obtained by adjusting the added amount of Pd precursor. More importantly, the catalytic activities of Au–Pd NCs for the conversion of Cr(VI) to Cr(III) present a notable difference for the Pd in Au@AuPd and Au@AuPd@PdML structures, and the Au@AuPd@PdMLNCs exhibited the superior catalytic activity for the conversion of Cr(VI). The present study demonstrates the core@NSA@shellML is an efficient nanostructure to promote the catalytic performance of core–shell NCs for practical applications.

Direct Observation of Early Stages of Growth of Multilayered DNA-Templated Au-Pd-Au Core-Shell Nanoparticles in Liquid Phase.

We report here on direct observation of early stages of formation of multilayered bimetallic Au-Pd core-shell nanocubes and Au-Pd-Au core-shell nanostars in liquid phase using low-dose in situ scanning transmission electron microscopy (S/TEM) with the continuous flow fluid cell. The reduction of Pd and formation of Au-Pd core-shell is achieved through the flow of the reducing agent. Initial rapid growth of Pd on Au along <111> direction is followed by a slower rearrangement of Pd shell. We propose the mechanism for the DNA-directed shape transformation of Au-Pd core-shell nanocubes to adopt a nanostar-like morphology in the presence of T30 DNA and discuss the observed nanoparticle motion in the confined volume of the fluid cell. The growth of Au shell over Au-Pd nanocube is initiated at the vertices of the nanocubes, leading to the preferential growth of the {111} facets and resulting in formation of nanostar-like particles. While the core-shell nanostructures formed in a fluid cell in situ under the low-dose imaging conditions closely resemble those obtained in solution syntheses, the reaction kinetics in the fluid cell is affected by the radiolysis of liquid reagents induced by the electron beam, altering the rate-determining reaction steps. We discuss details of the growth processes and propose the reaction mechanism in liquid phase in situ.

Composition-dependent CO2 electrochemical reduction activity and selectivity on Au–Pd core–shell nanoparticles

Au–Pd core–shell nanoparticles can convert CO2 into CO with a high selectivity and mass activity due to the more balanced *COOH/*CO adsorption.

Enhanced catalytic activity of Au core Pd shell Pt cluster trimetallic nanorods for CO2 reduction.

Herein, Au core Pd shell Pt cluster nanorods (Au@Pd@Pt NRs) with enhanced catalytic activity were rationally designed for carbon dioxide (CO2) reduction. The surface composition and Pd–Pt ratios significantly influenced the catalytic activity, and the optimized structure had only a half-monolayer equivalent of Pt (θPt = 0.5) with 2 monolayers of Pd, which could enhance the catalytic activity for CO2 reduction by 6 fold as compared to the Pt surface at −1.5 V vs. SCE. A further increase in the loading of Pt actually reduced the catalytic activity; this inferred that a synergistic effect existed among the three different nanostructure components. Furthermore, these Au NRs could be employed to improve the photoelectrocatalytic activity by 30% at −1.5 V due to the surface plasmon resonance. An in situ SERS investigation inferred that the Au@Pd@Pt NRs (θPt = 0.5) were less likely to be poisoned by CO because of the Pd–Pt bimetal edge sites; due to this reason, the proposed structure exhibited highest catalytic activity. These results play an important role in the mechanistic studies of CO2 reduction and offer a new way to design new materials for the conversion of CO2 to liquid fuels.

Au Core–Pd Shell Bimetallic Nanoparticles Immobilized within Hyper-Cross-Linked Polystyrene for Mechanistic Study of Suzuki Cross-Coupling: Homogeneous or Heterogeneous Catalysis?

The synthesis of catalytically active bimetallic Au–Pd nanoparticles stabilized in hyper-cross-linked polystyrene (HPS) for Suzuki cross-coupling of 4-bromoanisole (4-BrAn) and phenylboronic acid is presented. The core–shell structure with a thin (less than 1 nm) Pd shell and a Au core was proven by X-ray diffraction and high-angle annular dark-field scanning transmission electron microscopy combined with energy-dispersive X-ray spectroscopy. More than a 2-fold increase in 4-BrAn conversion was found in comparison with monometallic Pd/HPS. Moreover, when the Suzuki reaction was carried out under visible-light irradiation, the product yield further increased by about 1.3 times (from 56.1% up to 73.7%). This effect was assigned to a local surface plasmon resonance arising in the Au core that allowed electron transfer to the extremely thin Pd layer due to intimate contact with gold. The results suggest that the rate-limiting step of the catalytic cycle takes place on the surface of the Pd shell, serving as e...

Direct growth of ultrasmall bimetallic AuPd nanoparticles supported on nitrided carbon towards ethanol electrooxidation

Bimetallic nanoparticles (NPs) show interesting synergy to enhance the activity and durability in electrocatalytic alcohol oxidation compared to single-component metal NPs. The synthesis of bimetallic NPs often carried out in solution brings challenges in separating, loading and dispersing these NPs on conductive carbon supports. We herein report the direct growth of well-defined AuPd bimetallic NPs in the size range of 2–5 nm on nitrided carbon support. Our method is based on a seed-mediated growth method using Au seeds (1.8 ± 0.3 nm) supported on nitrided carbon. We show that the sizes and surface compositions of bimetallic NPs are precisely controllable. The resultant core-shell AuPd bimetallic NPs are thermally stable and they can be converted to alloyed AuPd NPs when subjected to thermal activation at 250 °C for 1 h. The chemical compositions of the AuPd alloyed NPs have been investigated by combining electron microscopy dispersive X-ray analysis, X-ray photoelectron spectroscopy and surface oxygen desorption using electrochemical reduction of catalysts. The catalytic activity, stability, poisoning tolerance and charge transfer resistance of AuPd alloyed NPs for the ethanol electrooxidation are largely enhanced compared to single-component NPs. Au0.45Pd0.55-5 nm exhibited the superior specific activity of 1.11 mA/cm2 and mass activity of >0.4 A/mgmetal toward ethanol oxidation, approximately 5 times more active than commercial Pd/C. We expect that this synthetic method will be of interest to prepare metallic electrocatalysts having defined nanostructures and compositions directly on conductive carbon for applications in fuel cells and batteries.

Carbon black supported Au–Pd core-shell nanoparticles within a dihexadecylphosphate film for the development of hydrazine electrochemical sensor

An amperometric method for the determination of hydrazine (HDZ) using a glassy carbon (GC) electrode modified with carbon black supported Au–Pd core–shell structured nanoparticles (Au@Pd/CB) within dihexadecylphosphate (DHP) film (Au@Pd/CB-DHP/GCE) is proposed. Au@Pd nanoparticles were synthesized by chemical reduction of AuCl3 and PdCl2 using ethylene glycol as a reducing agent, and the nanoparticles supported on CB were characterized by scanning electron microscopy, transmission electron microscopy, energy dispersive X-ray spectroscopy and X-ray diffraction techniques. The proposed Au@Pd/CB-DHP/GCE and CB-DHP/GCE (without Au@Pd) electrodes were used to investigate the electrochemical behavior of HDZ using cyclic voltammetry. When the Au@Pd/CB-DHP/GCE was used, an electrocatalytic effect was observed, the analytical signal was substantially increased (87%) and the oxidation potential decreased, i.e. in 728mV. Additionally, the apparently heterogeneous electron-transfer rate constant (k0) obtained for the Au@Pd/CB-DHP/GCE (0.15cms−1) was about two orders of magnitude greater than that obtained using the CB-DHP/GCE (0.068cms−1). Under the optimized conditions for the amperometric technique, a linear analytical curve for HDZ was obtained in the range of 2.50–88.0μmolL−1, with a limit of detection of 0.23μmolL−1 (0.0074ppm). The proposed method was satisfactorily applied to determine the concentration of HDZ in natural lake and tap water samples.