Pd Nanocubes Research Articles

Anisotropic atom displacement in Pd nanocubes resolved by molecular dynamics simulations supported by x-ray diffraction imaging

Nearly identical Pd nanocubes yield an x-ray powder diffraction pattern with interference fringes affording access to unprecedented structural details of nanocrystal size, shape, and complex atomic displacement for a billion-sized population. The excellent agreement between diffraction data and molecular dynamics (MD) provides strong experimental validation of MD simulations and the proposed data-interpretation paradigm. These results show that individual atomic displacements within the nanocubes are not only a function of disrupted bonds and the crystallographic plane of the adjacent surface, but are complex strain gradients extending across all surfaces of the particle strongly influenced by atomic displacements. This observation of nonuniform surface strain and the manner in which it is affected by different sizes, shapes, and locations within each facet could be the key to understanding many surface related properties of shaped nanocrystals including those associated with important catalysis applications.

Screening of Oligopeptides that Recognize Inorganic Crystalline Facets of Metal Nanoparticles.

Peptides that possess specific affinity to distinct crystal facets have been reported previously. However, their adsorption behavior in terms of the crystal sizes and shapes is less exploited. Herein, we isolate several phage clones that show the strong affinity to {100} of Pd at a neutral pH from the M13 phage library, and among them the phages that have shape selectivity to the cubic structure are identified by eliminating ones that bind randomly shaped Pd nanoparticles (NPs). Since Pd nanocube-binding phages are eluted by lowering pH values in the biopanning process, the selected phages (and their binding peptides displayed on protein pIII) can be released from Pd surfaces through pH changes. We used this feature to modulate the capping density of selected peptides on NPs. For example, when less peptides are capped on Pd nanocubes by lowering the pH values, the shape of the nanocubes is deformed and some evolve into a concave shape, indicating that Pd atoms are released from the less protected {100} facet selectively due to the higher surface energy. This type of crystalline facet-recognizing peptides can be applied for smart capping agents that not only bind target crystalline planes, but also modify their coverage on the specific surfaces with pH changes. The peptide-capping agents could be useful to fabricate NPs with characteristic shapes through etching and adsorption of atoms on specific crystalline planes of seed nanocrystals.

Large-scale synthesis of palladium concave nanocubes with high-index facets for sustainable enhanced catalytic performance.

The catalytic activity of palladium (Pd) nanostructures highly relies on their size and morphology, especially enclosed with high-index facets, which provide more active sites so as to enhance their catalytic performance comparing with their low-index facet counterparts. Herein, Pd concave nanocubes enclosed with {730} facets by a one-pot scalable liquid method, with various high-index facets are synthesized via tuning reduction kinetics. Due to their high-index facets, the Pd concave nanocubes exhibit much higher electrocatalytic activity and stability for methanol oxidation than the Pd nanocubes enclosed by {100} facets and commercial Pd/C. Furthermore, we scale up synthesis of Pd concave nanocubes by expanding the volume of all species to fifty times with high-yield production.

Direct Formic Acid Microfluidic Fuel Cell with Pd Nanocubes Supported on Flow-Through Microporous Electrodes

crystallographicplanes and flow-through microporous electrodes with high surface area. The high performance is attributed to the favorable sizeand shape of the catalyst, the high surface-to-volume ratio, and the high localized mass transport rates inside the flow-throughmicroporous electrodes. These results open up the opportunity to utilize oxygen as oxidant in miniaturized electrochemical cellswithout the constraints imposed by integration of air-breathing cathodes exposed to surrounding air.© The Author(s) 2015. Published by ECS. This is an open access article distributed under the terms of the Creative CommonsAttribution Non-Commercial No Derivatives 4.0 License (CC BY-NC-ND, http://creativecommons.org/licenses/by-nc-nd/4.0/),whichpermitsnon-commercialreuse,distribution,andreproductioninanymedium,providedtheoriginalworkisnotchangedinanyway and is properly cited. For permission for commercial reuse, please email: oa@electrochem.org. [DOI: 10.1149/2.0031504eel]All rights reserved.Manuscript submitted October 29, 2014; revised manuscript received January 26, 2015. Published February 5, 2015.

Controllable synthesis of palladium nanocubes/reduced graphene oxide composites and their enhanced electrocatalytic performance

Homogeneous distribution of cube-shaped Pd nanocrystals on the surface of reduced graphene oxide is obtained via a facile one-step method by employing AA and KBr as the reductant and capping agent, respectively. The experimental factors affecting the morphology and structure of Pd nanoparticles have been systematically investigated to explore the formation mechanism of Pd nanocubes (PdNCs). It is revealed that PdNCs enclosed by active {100} facets with an average side length of 15 nm were successfully synthesized on the surface of reduced graphene oxide. KBr plays the role for facet selection by surface passivation and AA controls the reduction speed of Pd precursors, both of which govern the morphology changes of palladium nanoparticles. In the further electrochemical evaluations, the Pd nanocubes/reduced graphene oxide composites show better electrocatalytic activity and stability towards the electro-oxidation of ethanol than both reduced graphene oxide supported Pd nanoparticles and free-standing PdNCs. It could be attributed to the high electrocatalytic activity of the dominated active {100} crystal facets of Pd nanocubes and the enhanced electron transfer of graphene. The developed approach provide a versatile way for shape-controlled preparation of noble metal nanoparticles, which can work as novel electrocatalysts in the application of direct alcohols fuel cells.

Truncated palladium nanocubes: Synthesis and the effect of OH− concentration on their catalysis of the alkaline oxygen reduction reaction

Small palladium nanocubes (14nm) are successfully synthesized by increasing the amount of reducing agent (ascorbic acid) to improve the nucleation rate. From the results of X-ray diffraction and high-resolution transmission electron microscopy analyses, we conclude that the prepared nanocubes are truncated and contain (100) planes on six facets, with (111) planes appearing at the corners of the nanocubes. Additionally, these truncated nanocubes are used as catalysts for oxygen electroreduction and are compared with conventional Pd nanoparticles. Comparable cyclic voltammograms show that the Pd nanocube surface easily adsorbs OH− ions in a 1M NaOH solution compared with surfaces in a 0.1M NaOH solution. As demonstrated by the results of a rotating ring-disk electrode measurement, the associated Tafel slopes and specific activities in terms of the electrochemical surface area for these Pd nanocubes in both electrolytes show OH− concentration-independent characteristics. Furthermore, at 0.9V (vs. RHE) in the 0.1M NaOH solution, the specific activity of the 14nm Pd nanocubes is 0.52mAcm−2, superior to the value of 0.26mAcm−2 for Pd nanoparticles.

Sub 10-nm Pd Nanocubes and Their Coating with Multi-Armed Pt Shells: Facile Synthesis and Catalysis of Alkaline Oxygen Reduction

Pd nanocubes (∼10 nm) and Pd nanocubes coated with multi-armed Pt shells have been successfully prepared. Their microstructures are determined from their electron diffraction patterns and line scan energy-dispersive X-ray measurements taken on a single particle. These Pd nanocubes and the Pd-Pt nanocubes are applicable as catalysts for the alkaline oxygen reduction reaction. On the basis of the same loading mass of catalyst, the results of rotating ring-disk electrode measurements indicate that the cubic Pd nanoparticles and particles coated by multi-armed Pt shells display activities of 1.47 × 10−2 and 9.22 × 10−3 mA μg−1, respectively. These values are greater than the 6.79 × 10−3 mA μg−1 observed for Pt nanoparticles. The prepared Pd nanocubes and the Pd-Pt core-shell catalysts, as well as Pt nanoparticles, show 98% efficiency in the production of OH− via an approximate four-electron pathway. Additionally, a fair comparison supported by transmission electron microscopy and electrochemical data shows that the shapes of Pd nanocubes coated with multi-armed Pt shells are nearly unchanged by the ORR and that these core-shell catalysts show stabilities superior to Pd nanocubes.

Surface ligand-mediated isolated growth of Pt on Pd nanocubes for enhanced hydrogen evolution activity

Br− ions can affect the growth mode of Pt on a Pd substrate. When Br− ions adsorb on some sites of the Pd cube, the newly formed Pt atoms tended to grow on the Br− free area, facilitating island growth mode. Otherwise, without Br− ions, because of the relatively high diffusion rate between Pt and Pd, Pt atoms can epitaxially deposit on the whole surface of the Pd nanocubes, forming a layered growth mode structure.

Facet-dependent optical properties of Pd-Cu2O core-shell nanocubes and octahedra.

Pd-Cu2O core-shell nanocubes and truncated octahedra with six average sizes for each particle shape have been synthesized from 29 nm Pd nanocubes. The nanocubes have average edge lengths of 64-124 nm, while the truncated octahedra are 107-183 nm in the opposite tip distance. The core and shell composition and lattice orientation have been determined, showing the formation of single-crystalline Cu2O shells. The surface plasmon resonance (SPR) band from the Pd nanocrystal cores is barely visible. However, the Cu2O shells display facet-dependent optical properties. The Cu2O absorption band for smaller Pd-Cu2O cubes is consistently more red-shifted than somewhat larger Pd-Cu2O truncated octahedra. This work again shows that the observed facet-dependent optical phenomenon in metal-Cu2O core-shell nanocrystals is derived from the Cu2O shells. The use of 40 nm Pd cubes as cores gave uniform and size-tunable Pd-Cu2O nanocubes and truncated octahedra that display the Pd SPR band. The Pd SPR band is consistently located at 650 nm for Pd-Cu2O truncated octahedra, and 670 nm for the cubes despite large variation in the shell thickness. Both the Cu2O absorption and the Pd plasmonic band exhibit facet-dependent optical properties.

Visible to near-infrared plasmon-enhanced catalytic activity of Pd hexagonal nanoplates for the Suzuki coupling reaction.

Photocatalytic conversion of solar energy to chemical energy is an efficient process in green chemistry because it facilitates room temperature chemical transformations by generating electronically excited states in photocatalysts. We report here on the robust synthesis, detailed structural characterization, and especially photocatalytic properties of plasmonic Pd hexagonal nanoplates for chemical reactions. The Pd hexagonal nanoplates are twin crystals, and composed of the top and bottom faces enclosed by the {111} planes with stacking faults and the side surfaces bound by mixed six {111} and six {100} planes. The Pd hexagonal nanoplates with well-defined and tunable longitudinal localized surface plasmon resonance (LSPR) have enabled the direct harvesting of visible to near-infrared light for catalytic cross coupling reactions. Upon plasmon excitation, the catalytic Suzuki coupling reactions of iodobenzene and phenylboronic acid accelerate by a plasmonic photocatalytic effect of plasmon induced hot electrons. The turnover frequency (TOF) of the Pd hexagonal nanoplates in a reaction illuminated with a λ = 300-1000 nm Xenon lamp at 176 mW cm(-2) was 2.5 and 2.7 times higher than that of non-plasmonic {111}-enclosed Pd nanooctahedra and {100}-enclosed Pd nanocubes, respectively, and 1.7 times higher than the TOF obtained when the reaction was thermally heated to the same temperature.

Pd nanocube as non-enzymatic glucose sensor

Pd nanocubes enclosed by (100) planes are successfully used as stable catalysts for d-glucose sensors. In this study, a comparison of the specific activities in terms of electrochemical real surface area (ESA) between the Pd nanocubes enclosed by (100) planes and Pd nanoparticles dominated by (111) planes is performed to assess their ability to electrocatalyse glucose oxidation. By measuring activity per ESA, the nanocubes (6.3×10−5Ccm−2) are found to perform 1.45 times better than the nanoparticles (4.32×10−5Ccm−2). The higher specific activity of the nanocubes can be attributed to the higher oxidation power of the anodic glucose oxidation process catalysed by the (100) planes of the nanocubes. Furthermore, the prepared nanocubes show great potential and stability for use as a glucose sensor system as they have a sensitivity of 34μAmM−1cm−2 and a linear range of 1–10mM.

Hollow metal-organic framework nanospheres via emulsion-based interfacial synthesis and their application in size-selective catalysis.

Metal-organic frameworks (MOFs) represent an emerging class of crystalline materials with well-defined pore structures and hold great potentials in a wide range of important applications. The functionality of MOFs can be further extended by integration with other functional materials, e.g., encapsulating metal nanoparticles, to form hybrid materials with novel properties. In spite of various synthetic approaches that have been developed recently, a facile method to prepare hierarchical hollow MOF nanostructures still remains a challenge. Here we describe a facile emulsion-based interfacial reaction method for the large-scale synthesis of hollow zeolitic imidazolate framework 8 (ZIF-8) nanospheres with controllable shell thickness. We further demonstrate that functional metal nanoparticles such as Pd nanocubes can be encapsulated during the emulsification process and used for heterogeneous catalysis. The inherently porous structure of ZIF-8 shells enables encapsulated catalysts to show size-selective hydrogenation reactions.

CO2 hydrogenation with shape-controlled Pd nanoparticles embedded in mesoporous silica: Elucidating stability and selectivity issues

Shape-controlled Pd nanocubes and nanopolyedra particles were embedded in mesoporous silica shells and their catalytic properties for the CO2 hydrogenation were compared to a reference Pd/SiO2 catalyst prepared by wetness impregnation. Whereas the Pd impregnated silica exhibits a strong deactivation, the activity of both embedded solids is remarkably stable. This difference is due to a significant Pd particles sintering in the reference catalyst while no increase of particle size is observed for the core@shell solids. CH4 selectivity is shown to be correlated to the mean coordination number of surface atoms which controls the adsorption strength of CO as intermediate species.

Effects of Pd nanocube size of Pd nanocube-graphene hybrid on hydrogen sensing properties

Palladium (Pd) nanocubes-loaded graphene were synthesized by a simple chemical method for hydrogen sensing. Pd nanocubes of 25, 40, 55, 70 and 85nm sizes were synthesized in colloidal state by a chemical route in two-steps (seed-mediated growth) and then, simply reduced into graphene flakes by hydrazine in a simple one-step process. The hydrogen-sensing and electrocatalyst properties of the new Pd nanocube-graphene hybrid were investigated in detail. The resistivity-type sensor that used the Pd cube-graphene hybrid had a detectable range from 10,000 to 10ppm with good response and linearity at room temperature. Our experiment showed that the Pd cube-graphene hybrid with bigger Pd nanocubes not only showed better response to H2 gas molecules but also maintained its excellent H2 sensing properties even with increases in working temperature. The effects of Pd nanocube size on the H2 sensing performance of the Pd cube-graphene hybrid was explained by both spillover mechanism and influence of Pd size on hybrid state of two materials.

Ninety Second Electrosynthesis of Palladium Nanocubes on ITO Surface and Its Application in Electrosensing of Cefotaxime

AbstractWe describe ninety second electrosynthesis of uniform palladium nanocubes on ITO without any surfactants, templates or premodifications of ITO surfaces. The electrodeposition potential and concentration of palladium precursor are varied for the formation of Pd nanocubes. Electrosynthesized palladium nanocubes have been characterized by various techniques. Further electrosynthesized palladium nanocubes are employed in electrosensing of cefotaxime drug without using any redox mediator or enzyme. The developed amperometric electrochemical sensor under the optimum conditions is convenient and applicable for the determination of cefotaxime drug with a sensitivity of 2.724 µA/µM and 0.062 µM limit of detection at S/N (signal‐to‐noise ratio):3.

In-Situ Studies of Thermal Stability of Core–Frame Cubic Pd–Rh Nanocrystals at Elevated Temperatures

Nanosize metallic particles have long been recognized as important heterogeneous catalytic materials. Recent studies show that the atomic characteristics of metallic nanoparticles, including particle size, shape and surface composition, are critical to catalytic activity and selectivity. It has been proven that the catalytic activities of noble metals are highly dependent on their surface structures. Given that the surface structures of nanocrystals have a strong correlation with their morphologies, the control of nanocrystal morphology has become a central theme of research with an ultimate goal to tune the nanocrystal catalytic performance. Bimetallic nanocubes synthesized by seed-mediated growth have the advantage of coupling the catalytic properties of one metal with those of another metal and form multifunctional nanocrystals. Herein, we demonstrate a potential method to enhance the thermal stability of Pd-Rh core-frame nanocubes investigated by in-situ heating transmission electron microscopy. Pd-Rh bimetallic nanocubes were synthesized by site-specific growth. [1] Transmission electron microscopy (TEM), high-angle annular dark-field scanning (HAADF)-scanning transmission electron microscopy (STEM) and energy dispersive X-ray (EDS) mapping were performed in a JEOL ARM200F with a STEM aberration (Cs) corrector operated at 200 kV. In-situ heating experiments were performed using a MEMS-based localized heating specimen holder (by Protochips). Pd-Rh cubes obtained at different stages of a synthesis were investigated at elevated temperatures. Since the Pd nanocubes start to dramatically degrade at 500 °C, changing into spherical-like shape, we choose 500 °C as the heating treatment temperature to investigate the thermal stability of Pd-Rh core-frame nanocubes. [2] Figure 1 presents the results of the Pd-Rh nanocubes obtained in the initial stage of synthesis. Figures 1a-1c show in-situ HAADF-STEM images of Pd-Rh core-frame nanocubes recorded from the same region at room temperature (RT) and 500°C. The Pd-Rh nanocubes maintained the cubic shape very well up to annealing at 500 °C for 1 hour. The thermal stability of Pd nanocubes is significantly enhanced by coating high melting point metal (Rh) on the corners and edges. Figure 1d and 1e show the atomic HAADF-STEM images of typical nanocubes at RT and 500°C annealing 1 hr, respectively. The atomic numbers of Pd and Rh are 46 and 45, respectively. They are very close. Thus, there is no distinct contrast difference between core Pd and frame Rh in the HAADF images, as shown in Figure 1d-1e. STEM/EDS mapping was used to determine the distributions Pd and Rh in the nanocubes at RT and 500 °C. In summary, using in-situ heating transmission electron microscopy, we have demonstrated one effective approach to enhance thermal stability of Pd nanocubes at elevated temperatures by coating high melting point metal Rh on corners and edges to form core-frame bimetallic nanocubes. The Pd-Rh core-frame cubes maintained cubic shape after annealing 1 hour at 500 °C. Surface pre-melting of Pd is

Synthesis and Electrocatalytic Properties of Uniform Palladium Nanocubes by using Graphene Oxide as Surfactant and Support

Clean and uniform: Pd nanocubes dispersed on graphene oxide are prepared by the reduction of PdCl42−. The as-prepared Pd nanocube/graphene oxidecatalyst exhibitsenhanced electrocatalytic activity and stability for methanol and formic acid oxidation.

Pt-coated Pd nanocubes as catalysts for alkaline oxygen reduction activity

Pt-coated Pd nanocubes enclosed with (100) planes were successfully synthesized using an epitaxial approach. Their microstructures were determined on the basis of their electron diffraction patterns and line scan energy-dispersive X-ray measurements by spotting on a single nanocube. These bimetallic nanocubes can be used as catalysts for an alkaline oxygen reduction reaction. The results of the rotating ring-disk electrode measurements indicated that these nanocubes displayed a 2.6 times greater specific activity than Pt nanoparticles.

Pd–Rh Nanocrystals with Tunable Morphologies and Compositions as Efficient Catalysts toward Suzuki Cross-Coupling Reactions

Delicate elaboration of the nanostructures of multimetal catalytic materials with well-defined shapes and compositions to reveal their potential use as heterogeneous nanocatalysts for organic synthetic reactions with the combined merits of heterogeneous and homogeneous catalysis is both scientifically and technologically important, but this type of investigation has remained rarely pursued. In this work, we demonstrated a facile hydrothermal approach toward the one-pot shape-selective syntheses of Pd–Rh nanocrystals with tunable compositions and morphologies, including hollow nanocubes (NCs), nanoicosahedrons (NIs), and nanotruncated octahedrons (NTOs), using poly(vinylpyrrolidone) as both reductant and capping agent and halide anions (Br–/I–) as shape control agents. The formation of Pd–Rh hollow NCs was induced by an iodine adsorbate-induced reconstruction mechanism with KI, whereas the formation of Pd–Rh NIs and NTOs were realized by controlling the selective nucleation of twinned seeds or single crystal seeds and their relative growth rates along different facets (e.g., (111) and (100) facets) through finely adjusting the Pd/Rh ratio and the amount of KBr added in the absence of KI. Due to the great significance of Pd-catalyzed organic reactions, the catalytic performances of Pd–Rh nanocrystals for Suzuki cross-coupling reactions with different reactants were evaluated. The measured turnover frequencies (TOFs) suggested that Pd–Rh hollow NCs held considerably enhanced catalytic activities (at least 3 times) than other Pd-based solid nanocrystals including Pd–Rh NIs, Pd–Rh NTOs, Pd–Rh NCs, Pd NCs, and commercial Pd/C, with iodobenzene as the reactant. In addition, even for more inert reactants such as bromobenzene or 4-bromotoluene, the catalytic activities of Pd–Rh hollow NCs were still impressive (showing similar TOFs to those of other shapes for reactions with iodobenzene as the reactant), indicating the promising application of Pd-based nanocatalysts for other powerful Pd-catalyzed organic synthesis reactions. Meanwhile, Pd-based solid NCs, enclosed with (100) facets only, showed better catalytic performance than NIs as well as NTOs, which had a larger fraction of (111) facets other than (100) ones, further suggesting that morphology differences were vitally significant to tune the catalytic performances of bimetallic nanocatalysts.

One-pot synthesis and electrocatalytic properties of Pd@Pt core-shell nanocrystals with tailored morphologies.

Pd@Pt core-shell nanocrystals consisting of well-defined Pd nanocube cores and dendritic Pt shells were prepared by a new facile aqueous one-pot synthetic method. The prepared Pd@Pt nanocrystals exhibited efficient catalytic activity and stability toward methanol electrooxidation, and their catalytic function was highly dependent on their Pt shell thickness due to the different synergism between Pt and Pd.