Pd Shell Research Articles

Seeded Rods with Ag and Pd Bimetallic Tips—Spontaneous Rearrangements of the Nanoalloys on the Atomic Scale

Deposition of metal cocatalysts is a common practice to improve the activity of photocatalysts. The use of nanoalloyed nanoparticles allows the formation of diverse nanostructures, tailored for a specific application. Nevertheless, too often the spontaneous atomic scale phenomena interfere with the initial design to produce a modified structure with undesirable properties. Here, we demonstrate such a process for Pd, Ag, or their combination as metal tips mounted on seeded rods of a CdSe dot in a CdS rod (CdSe@CdS) that serve as hydrogen evolution photocatalysts. Spontaneous radial reconstruction at the metal tip brings both Pd and Ag atoms outward even when a two-stage preparation process is applied to specifically produce a core–shell structure. The diffusion of Pd outward enables hydrogen evolution even when the initial Pd tip is covered by a Ag shell, and in the opposite case, a Pd shell shows reduced activity compared with Pd-only tips, due to the surfacing of Ag atoms. In addition, we show that the tip reconstruction occurs already during synthesis; aberration-corrected high-resolution electron microscopy also reveals other processes, such as cation exchange and small clustering around the seeded rods, all quite invisible using regular TEM techniques. In addition, we studied the size effect of Pd-tipped seeded rods and showed that the %QE of seeded rods with 2.2 Pd tips is as high as 91%. These results are significant in the understanding of the structure–function relationship, as it highlights one possible hidden reconstruction pathway of nanoalloys.

Core-Shell Pd@M (M=Ni, Cu, Co) Nanoparticles/Graphene Ensembles with High Mass Electrocatalytic Activity Toward the Oxygen Reduction Reaction.

Herein, it is demonstrated that pyrene butyric acid (PBA)-stabilized metal nanoparticles with core-shell morphology, Pd@MNPs (M=Ni, Cu, Co), non-covalently supported on graphene (G) sheets, are more active towards oxygen electroreduction in alkaline environments than the benchmark Pd/C catalyst, albeit with a 70 % lower precious metal loading. The PBA-stabilized Pd@MNPs (M=Ni, Cu, Co)/G ensembles were prepared by employing a simple modified polyol method and galvanic replacement and thoroughly characterized with advanced microscopy imaging and complementary spectroscopic techniques. Electrochemical studies revealed that Pd@NiNPs /G presents the optimum performance, exhibiting a 30 mV more positive onset potential and 3.2 times greater mass activity over Pd/C. Moreover, chronoamperometric assays showed the minimum activity loss for Pd@NiNPs /G, not only among its core-shell counterparts but importantly when compared with the benchmark catalyst. The excellent performance of Pd@NiNPs /G was attributed to the (a) presence of PBA as stabilizer, (b) uniform Pd@NiNPs dispersion onto the graphene sheets, (c) efficient intra-ensemble interactions between the two species, (d) existence of the core-shell structure for Pd@NiNPs , and (e) stability of the Ni core metal under the reaction conditions. Last, the oxygen reduction on Pd@NiNPs /graphene occurs by the direct four-electron reduction pathway, showing great potential for use in energy related applications.

Synthesis of Pd/Ru Bimetallic Nanoparticles by Escherichia coli and Potential as a Catalyst for Upgrading 5-Hydroxymethyl Furfural Into Liquid Fuel Precursors.

Escherichia coli cells support the nucleation and growth of ruthenium and ruthenium-palladium nanoparticles (Bio-Ru and Bio-Pd/Ru NPs). We report a method for the synthesis of these monometallic and bimetallic NPs and their application in the catalytic upgrading of 5-hydroxymethyl furfural (5-HMF) to 2,5 dimethylfuran (DMF). Examination using high resolution transmission electron microscopy with energy dispersive X-ray microanalysis (EDX) and high angle annular dark field (HAADF) showed Ru NPs located mainly at the cell surface using Ru(III) alone but small intracellular Ru-NPs (size ∼1–2 nm) were visible only in cells that had been pre-“seeded” with Pd(0) (5 wt%) and loaded with equimolar Ru. Pd(0) NPs were distributed between the cytoplasm and cell surface. Cells bearing 5% Pd/5% Ru showed some co-localization of Pd and Ru but chance associations were not ruled out. Cells loaded to 5 wt% Pd/20 wt% Ru showed evidence of core-shell structures (Ru core, Pd shell). Examination of this cell surface material using X-ray photoelectron spectroscopy (XPS) showed Pd(0) and Pd(II) and Ru(IV) and Ru(III), with confirmation by analysis of bulk material using X-ray absorption near edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) analyses. Both Bio-Ru NPs and Bio-Pd/Ru NPs were active in the conversion of 5-HMF into 2,5-DMF but commercial Ru on carbon catalyst outperformed 5 wt% bio-Ru by fourfold. While 5 wt% Pd/20 wt% Ru achieved 20% yield of DMF the performance of the 5 wt% Pd/5 wt% Ru bio-catalyst was higher and comparable to the commercial 5 wt% Ru/C catalyst in a test reaction using commercial 5-HMF (>50% selectivity). 5-HMF was prepared by thermochemical hydrolysis of starch and cellulose with solvent extraction of 5-HMF into methyltetrahydrofuran (MTHF). Here, with MTHF as the reaction solvent the commercial Ru/C catalyst had little activity (100% conversion, negligible selectivity to DMF) whereas the 5 wt% Pd/5 wt% Ru bio-bimetallic gave 100% conversion and 14% selectivity to DMF from material extracted from hydrolyzates. The results indicate a potential green method for realizing increased energy potential from biomass wastes as well as showing a bio-based pathway to manufacturing a scarcely described bimetallic material.

Facile Synthesis of P25@Pd Core-Shell Catalyst with Ultrathin Pd Shell and Improved Catalytic Performance in Heterogeneous Enantioselective Hydrogenation of Acetophenone

Heterogeneous enantioselective hydrogenation is an ideal method for synthesizing important chiral compounds in pesticides and pharmaceuticals. Up to the present, supported noble-metal catalysts are most widely studied in heterogeneous enantioselective hydrogenations. However, it is found that the weak interactions existing on the surface of support may have negative effects on the enantioselectivity. Herein, a new category of TiO2 (Aeroxide® P25) supported Pd catalyst with ultrathin Pd shell was successfully prepared via a simple strategy based on the reduction of PdI carbonyl complex. Characterization results show that a well-dispersed ultrathin Pd shell with an average thickness of ~1.0 nm and a Pd loading of 36 wt.% was formed over the surface of P25 support. By excluding the negative weak interactions from the support, the P25@Pd core-shell catalyst with unique electronic properties of Pd exhibits higher activity and enantioselectivity than that of Pd/P25 catalyst prepared by the impregnation method and unsupported Pd black catalyst in the enantioselective hydrogenation of acetophenone.

Spherical Sandwich Au@Pd@UIO-67/Pt@UIO- n ( n = 66, 67, 69) Core-Shell Catalysts: Zr-Based Metal-Organic Frameworks for Effectively Regulating the Reverse Water-Gas Shift Reaction.

In this study, spherical sandwich Au@Pd@UIO-67/Pt@UIO- n ( n = 66, 67, 69) core-shell catalysts were assembled. Au nanoparticles (NPs) were used as the core for the epitaxial growth of Pd shells, and Au@Pd core-shell NPs were successfully encapsulated in the center of monodispersed Au@Pd@UIO-67 nanospheres. Pt NPs were fully fixed onto the nanosphere surfaces to obtain Au@Pd@UIO-67/Pt composites; further coating with UIO- n led to Au@Pd@UIO-67/Pt@UIO- n, in which Pt NPs are sandwiched between the Au@Pd@UIO-67 core and the UIO- n shell. The Au@Pd core-shell NPs efficiently controlled the morphology and structure of UIO-67 and enhanced the CO selectivity of the catalyst. Pt NPs increased the CO2 conversion, and the UIO- n component effectively regulated the reverse water-gas shift reaction.

Pt-Mn/C and Pd-Mn/C Nanoparticles As ORR Electrocatalysts

The sluggish kinetics of the oxygen reduction reaction (ORR) at the cathode remains as one of the main challenges for commercial viability of alkaline exchange membrane fuel cells (AEMFCs). It is therefore, of great interest to explore the development of electrocatalysts with superior activity and stability relative to the conventional carbon supported Pt nanoparticles (NPs). In this work we have studied the effects and evolution of structure and surface composition of Pt-Mn and Pd-Mn NPs on their electrocatalytic activity for the ORR in alkaline media. Both Pt-Mn and Pd-Mn NPs were synthesized using solvothermal methods and were supported on C via impregnation. In the case of Pt-Mn an ordered intermetallic phase was obtained by heat treatment, while for Pd-Mn NPs heat treatment did not lead to an ordered alloy. We have investigated the crystalline structure of these NPs using X-ray diffraction (XRD) and their size, morphology and composition using TEM/STEM, EELS and EDX. Cyclic voltammetry (CV) and rotating disk electrode (RDE) voltammetry were used to assess their electrocatalytic activity and stability. The NPs were electrochemically dealloyed in acidic media, through potential cycling, leading to the formation of Pt and Pd shell on PtMn and PdMn core. The dealloyed nanocatalysts exhibited over 400% increase in mass activity and 500% increase in specific activity as compare to Pt/C. The stability of the electrocatalyst was tested after 4,000 potential cycles in alkaline media following the DOE protocol (0.6-1.0 V vs reversible hydrogen electrode). In alkaline media, Mn surface segregation ensued, leading to a lower electrocatalytic activity when compared to the freshly dealloyed catalyst.

Electrocatalytic properties of a Pd0(Pb) composite synthesized by galvanic displacement: activity towards formic acid oxidation

Galvanic displacement of electrodeposited lead by palladium fails to produce Pd shells. The anomalous ratio between formic acid electrooxidation reaction (FAOR) rates on Pd0(Pb) observed in HClO4 and H2SO4 solutions is associated with the reduction of ClO4− anions to chloride ones which inhibit the FAOR.

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.

Golden Palladium Zinc Ordered Intermetallics as Oxygen Reduction Electrocatalysts.

Exploring Pt-free electrocatalysts with high activity and long durability for the oxygen reduction reaction (ORR) has been long pursued by the renewable energy materials community. In this work, we have designed an ordered intermetallic PdZn/C (O-PdZn) with a several atomic-layer Pd shell, which achieved a 3-fold enhancement in ORR mass activities (MA) in alkaline media, relative to Pd/C and Pt/C. Further Au incorporation in O-PdZn/C (Au-O-PdZn/C) yielded a catalyst with superior durability with less than 10% loss in MA after 30000 potential cycles. These effects have attributed to the rationally designed ordered structure and stabilizing effect of Au atoms. Aberration-corrected scanning transmission electron microscopy and synchrotron-based X-ray fluorescence spectroscopy were employed to show that Au not only galvanically replaced Pd and Zn on the surface but also penetrated through the PdZn lattice and distributed uniformly within the particles. Au-O-PdZn/C was also tested as an effective oxygen cathode in broad applications in rechargeable Li-air and Zn-air batteries.

Specific features of galvanic displacement of electrodeposited copper by palladium. Activity of Pd0(Cu) composite in FAOR

Galvanic displacement (GD) of electrodeposited (e.d.) copper by palladium in PdSO4+H2SO4 solutions in the absence (solution I) and in the presence (solution II) of copper ions Cu2+ is carried out. The resulting samples are characterized by several methods (SEM, XPS, AES-ICP, etc.). In is found that on freshly formed Pd0(Cu)-I and Pd0(Cu)-II composites, no Pd shell is formed. The copper content is shown to be 10at.% and higher in the surface layer and 22–27% in the bulk (Pd+Cu=100%). Voltammetric and XPS data allow assuming that the surface layer contains mixed oxides (such as PdCuOx) and copper ions which prevent the formation of the Pd shell. Both freshly formed Pd0(Cu) samples and those subjected to potential cycling (0.3–1.2V, RHE) demonstrate the high specific activity in formic acid electrooxidation reaction (FAOR, 1M HCOOH+0.5M H2SO4) which exceeds the activity of e.d. Pd by a factor of 3–4 at 150mV and 8–10 at 300mV. The possible reasons for the higher FAOR activity of Pd in Pd0(Cu) composites are discussed.

AuPd/C core–shell and alloy nanoparticles with enhanced catalytic activity toward the electro-oxidation of ethanol in alkaline media

Carbon-supported Pd, Au@Pd core–shell and Au1–xPdx-alloyed nanoparticles were prepared by a chemical reduction method and characterized by different experimental techniques, including X-ray powder diffraction, transmission electron microscopy, scanning-transmission electron microscopy using bright-field and high-angle annular dark field detectors and X-ray energy dispersive spectroscopy. The catalytic mass activity toward ethanol oxidation was assessed by cyclic voltammetry and chronoamperometry at room temperature. The measurements showed that the addition of Au enhances remarkably the electrocatalytic activity of the material, due to the bifunctional effect of Au1–xPdx/C alloys, and the synergetic effect on Au@Pd/C, resulting in a dissolution resistance of core–shell catalysts at potentials of 1.5 V versus reversible hydrogen electrode. In situ Fourier transform infrared spectroscopy measurements showed that the mechanism for ethanol oxidation depends on the electrocatalyst structure and morphology. Acetate was identified as the main product of ethanol electro-oxidation on the studied electrocatalysts. However, the presence of a core–shell structure on Au@Pd/C resulted in enhanced ethanol oxidation selectivity toward CO2. The improvement of activity is attributed to the interaction between Pd shell and Au core.

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.

Core-shell structure Ag@Pd nanoparticles supported on layered MnO2 substrate as toluene oxidation catalyst

The silver palladium bimetallic core-shell structure nanoparticles (Ag@Pd NPs) were synthesized by a thin Pd shell slowly generating on the outmost of Ag nanoparticle according to galvanic replacement mechanism. Then, the 2D layered structure manganese dioxide (MnO2) substrate was used to support the as-synthesize Ag@Pd NPs to prepare Ag@Pd/MnO2 catalyst for toluene purification in oxidation reaction. Physicochemical properties of the samples were characterized by a number of different analytical techniques. It is found that the Ag@Pd NPs are homogeneously spherical shape with an average particle diameter size of 7.1 nm. And the MnO2 substrate can not only uniformly disperse Ag@Pd active component on its surface for its high specific surface area and mesopore volume, but also provide the reactive lattice oxygen by its mixed oxidation states of Mn3+/Mn4+. Moreover, the core-shell configuration of Ag@Pd NPs can improve the state phase transformation from Pd0 to PdO2 with the aid of lattice oxygen of MnO2 substrate, because of the lattice oxygen migration controlled strong metal-support interaction (SMSI) effect between palladium active component and MnO2 substrate. So, there would be more exposed PdO2 active sites on the Ag@Pd/MnO2 catalyst relative to monometallic Pd/MnO2 catalyst. Hence, the as-prepared bimetallic core-shell Ag@Pd/MnO2 catalyst exhibits greatly higher toluene oxidation activity at lower reaction temperature than monometallic Pd/MnO2 catalyst, indicating it is a promising catalyst for use in volatile organic compounds (VOCs) purification.

Fully Tensile Strained Pd3Pb/Pd Tetragonal Nanosheets Enhance Oxygen Reduction Catalysis.

While surface strain engineering in shaped and bimetallic nanostructures offers additional variables for manoeuvring the catalysis, manipulating isotropic strain distributions in nanostructures remains a great challenge to reach higher tiers of the catalyst's design. Herein, we report an efficient approach to construct a unique class of core/shell palladium-lead (Pd-Pb)/Pd nanosheets (NSs) and nanocubes (NCs) with homogeneous tensile strain along [001] on both the top-Pd and edge-Pd surfaces for boosting oxygen reduction reaction (ORR). These core/shell Pd-Pb/Pd NSs and Pd-Pb/Pd NCs exhibit over 160% and 140% increases in mass activity and over 114% and 98% increases in specific activity when compared with these unshelled counterparts, respectively. Especially, the Pd3Pb/Pd NSs show the ORR mass and specific activities of 0.57 A/mgPd and 1.31 mA/cm2 at 0.90 V versus reversible hydrogen electrode, which are 8.8 (6.5) and 9.4 (9.8) times higher than those of the commercial Pd/C (Pt/C), respectively. The valence band photoemission spectra and first-principles calculations collectively show that the tensile strained Pd shell results in an upshift of the d-band-center of Pd, weakening the chemisorption of oxygenated species due to the contribution of the antibonding orbital. In addition, the Pd3Pb/Pd NSs and NCs with intermetallic core and homogeneous few layers of Pd shell can sustain at least 20 000 potential cycles with negligible activity decay and composition changes. The present work provides a new direction for the design of highly active and stable catalysts for fuel cells and beyond.

Noble metal (Pt, Au@Pd) nanoparticles supported on metal organic framework (MOF-74) nanoshuttles as high-selectivity CO2 conversion catalysts

The Zn-based metal-organic framework (MOF) catalysts MOF-74, Au@Pd@MOF-74, Pt/MOF-74, and Pt/Au@Pd@MOF-74, were assembled. Core-shell Au@Pd, in which Au nanoparticles (NPs) serve as the core for the epitaxial growth of Pd shells, was encapsulated into MOF-74 nanoshuttles to control the MOF-74 morphology and impart NP functionality. Pt NPs were loaded onto the MOF-74 surface. Pt/MOF-74 catalyzed CO2 conversion at 99.7% CO selectivity in the reverse water-gas shift (RWGS) reaction, and Au@Pd@MOF-74 photocatalyzed CO2 with 100% CO selectivity. Importantly, the catalyst Pt/Au@Pd@MOF-74, not only catalyzed the conversion of CO2 to CO in RWGS with 99.6% selectivity, but also photocatalyzed CO2 to CH4 at low concentration (800 ppm).

Understanding the strain effect of Au@Pd nanocatalysts by in situ surface-enhanced Raman spectroscopy.

A gap-mode configuration was developed for the in situ SERS study of the structure-activity relationship of Au@Pd core-shell nanocatalysts, which show much better performance in the selective oxidation of benzyl alcohol compared to Pd. The in situ SERS results reveal that the tensile strain in the Pd shell could promote the activation of oxygen, thus improving the activity. Such a tensile strain effect decreases with the increase of the Pd shell thickness, leading to a volcano correlation between the activity and the shell thickness.

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.

Core–Shell Engineering of Pd–Ag Bimetallic Catalysts for Efficient Hydrogen Production from Formic Acid Decomposition

To develop high-performance bimetallic catalysts, fine control over both the ligand and strain effects of secondary elements on the catalytic function of primary elements is crucial. Here we introduce an approach to produce Pd–Ag bimetallic core–shell nanocatalysts with synergistic regulation of the ligand and strain effects of Ag. Through precise core–shell engineering, (PdAg alloy core)@(ultrathin Pd shell) nanocrystals with controlled core compositions and shell thicknesses in addition to a well-defined octahedral morphology could be realized. The prepared octahedral PdAg@Pd core–shell nanocrystals exhibited pronounced catalytic performance toward hydrogen production from formic acid decomposition. The maximum catalytic activity was achieved with PdAg@Pd nanocrystals consisting of PdAg alloy cores with an average Pd/Ag atomic ratio of 3.5:1 and 1.1 atomic layer of Pd shells, which showed a record high turnover frequency of 21 500 h–1 at 50 °C. This catalytic function could be attributed to the optimize...

Atomic-Scale Structure and Stress Release Mechanism in Core-Shell Nanoparticles.

Core-shell nanoparticles find applications in catalysts, sensors, and theranostics. The full internal 3D atomic structure, however, cannot be resolved by current imaging and diffraction techniques. We analyzed the atomic positions and stress-release mechanism in a cubic Au-Pd core-shell nanoparticle in approximately 1000 times higher resolution than current experimental techniques using large-scale molecular dynamics simulation to overcome these limitations. The core-shell nanocube of 73 nm size was modeled similarly to solution synthesis by random epitaxial deposition of a 4 nm thick shell of Pd atoms onto a Au core of 65 nm side length using reliable interatomic potentials. The internal structure reveals specific deformations and stress relaxation mechanisms that are caused by the +4.8% lattice mismatch of gold relative to palladium and differential confinement of extended particle facets, edges, and corners by one, two, or three Au-Pd interfaces, respectively. The three-dimensional lattice strain causes long-range, arc-like bending of atomic rows along the faces and edges of the particle, especially near the Au-Pd interface, a bulging deformation of the Pd shell, and stacking faults in the Pd shell at the corners of the particle. The strain pattern and mechanism of stress release were further characterized by profiles of the atomic layer spacing in the principal crystallographic directions. Accordingly, strain in the Pd shell is several times larger in the extended facets than near the edges and corners of the nanoparticle, which likely affects adsorption, optical, and electrochemical properties. The findings are consistent with available experimental data, including 3D reconstructions of the same cubic nanoparticle by coherent diffractive imaging (CDI) and may be verified by more powerful experimental techniques in the future. The stress release mechanisms are representative for cubic core-shell nanoparticles with fcc structure and can be explored for different shapes by the same methods.

One-pot synthesis of PdAu bimetallic composite nanoparticles and their catalytic activities for hydrogen peroxide generation

We report a facile one-pot aqueous-phase synthesis of PdAu bimetallic nanoparticles with different Pd/Au ratio. The synthesis was conducted by co-reduction of Pd and Au precursor using ascorbic acid as a reducing agent and in the presence of polyallylamine hydrochloride (PAH). By high-angle annular dark field scanning transmission electron microscopy (HAADF-STEM) and energy-dispersive X-ray spectrometry (EDS) analyses, we found that the synthesized nanoparticles had an onion-like core/shell/shell/shell structure with Au-rich core, Pd-rich shell, Au-rich shell, and Pd shell, respectively. We also investigated the catalytic performance of the synthesized PdAu nanoparticles toward hydrogen peroxide generation reaction.