Pd Nanowires Research Articles

Metal Bromide Controlled Interfacial Aromatization Reaction for Shape-Selective Synthesis of Palladium Nanostructures with Efficient Catalytic Performances.

Herein, the effect of diverse metal bromides for the shape evolution of palladium nanostructures (Pd NS) has been demonstrated. Aromaticity-driven reduction of bromopalladate(II) is optimized to reproducibly obtain different Pd NS at the water/organic layer interface. In this soft interfacial strategy, a redox potential driven reaction has been performed, forming the thermodynamically more stable (>10(4) -fold) PdBr4 (2-) precursor from PdCl4 (2-) by adding extra metal bromides. In the process, the reductant, Hantzsch dihydropyridine ester (DHPE), is aromatized. Interestingly, alkali metal bromides devoid of coordination propensity exclusively evolve Pd nanowires (Pd NWs), whereas in the case of transition metal bromides the metal ions engage the 'N' donor of DHPE at the interface, making the redox reaction sluggish. Hence, controlled Pd nanoparticles growth is observed, which evolves Pd broccolis (Pd NBRs) and Pd nanorods (Pd NRs) at the interface in the presence of NiBr2 and CuBr2 , respectively, in the aqueous solution. Thus, the effect of diverse metal bromides in the reaction mixture for tailor-made growth of the various Pd NS is reported. Among the as-synthesized materials, the Pd NWs stand to be superior catalysts and their efficiency is almost 6 and 2.5 times higher than commercial 20 % Pd/C in the electrooxidation of ethanol and Cr(VI) reduction reaction by formic acid, respectively.

Self-Assembly Fabrication of Coaxial Te@poly(3,4-ethylenedioxythiophene) Nanocables and Their Conversion to Pd@poly(3,4-ethylenedioxythiophene) Nanocables with a High Peroxidase-like Activity.

Here, we report a simple one-step procedure to fabricate coaxial Te@poly(3,4-ethylenedioxythiophene) (PEDOT) nanocables via a self-assembly redox polymerization between 3,4-ethylenedioxythiophene monomer and the oxidant of sodium tellurite without the assistance of any templates and surfactants. The as-synthesized Te@PEDOT coaxial nanocables have diameters of center cores in the range of 5-10 nm, and the size of the outer shell from several nanometers to 15 nm. More interestingly, the as-prepared Te@PEDOT nanocables can be converted to Pd@PEDOT nanocables via a galvanic replacement reaction. The center core of the Pd nanowire exhibits a high crystallinity. The application of the synthesized Pd@PEDOT nanocables as peroxidase-like catalysts for the colorimetric detection of H2O2 is reported. The synergistic effect between the Pd nanowire and electrically conducting PEDOT enhances the catalytic activity toward the oxidation of the peroxidase substrate 3,3',5,5'-tetramethylbenzidine in the presence of H2O2. A detection limit toward H2O2 is as low as 4.83 μM, and a linear range from 10 to 100 μM has been achieved. This work offers a potential versatile route for the fabrication of cable-like nanocomposites with conducting polymers and other active components, which display great promise in applications such as catalysis, nanoelectronic devices, and energy storage and conversion.

Facile synthesis of Pd nanostructures with enhanced electrocatalytic performance for ethanol oxidation by a bio-based method

A facile method was developed for the controlled synthesis of well-defined Pd nanoparticles and nanowires, with the assistance of polyhedrin as a growth-directing agent.

Controlled Structure of Electrochemically Deposited Pd Nanowires in Ion-Track Templates.

Understanding and controlling structural properties of the materials are crucial in materials research. In this paper, we report that crystallinity and crystallographic orientation of Pd nanowires can be tailored by varying the fabrication conditions during electrochemical deposition in polycarbonate ion-track templates. By changing the deposition temperature during the fabrication process, the nanowires with both single- and poly-crystallinities were obtained. The wires with preferred crystallographic orientations along [111], [100], and [110] directions were achieved via adjusting the applied voltage and temperature during electrochemical deposition.

Fabrication of palladium nanowire array electrode for biofuel cell application

Bioelectrocatalysis was demonstrated with palladium (Pd) nanowire array electrode via nonenzymatic and enzymatic methods for glucose, which was validated by the generation of anodic current in the presence of glucose. The vertically standing Pd nanowires used for the fabrication of the electrodes were on average 5.6μm in length and 64nm in diameter. In comparison, the nonenzymatic bioanode exhibited lower current densities and required the application of larger overpotential which resulted in a large cell voltage drop (Voc=13.5mV) and limited power production when assembled as a biofuel cell under physiological conditions (pH7, 0.1M phosphate buffer saline) with laccase covalently bounded to Pd nanowires as the biocathode. The glucose/O2 biofuel cell was studied in phosphate buffer saline using the enzymatic bioanode that was developed with the co-immobilization of catalase and glucose oxidase on Pd nanowires and the laccase-Pd as the biocathode. The biofuel cell exhibited an open-circuit voltage of 0.506V, delivered a maximum power density of 72μWcm−2 at a cell voltage of 0.25V and a short-circuit current density of 411μAcm−2 when operating in 10mM glucose. Such low-cost lightweight glucose/O2 biofuel cells have a great promise to be optimized, miniaturized to power bio-implantable devices.

Magnetization-Switching Study of fcc Fe–Pd Nanowire and Nanowire Arrays Studied by In-Field Magnetic Force Microscopy

Using electrodeposition into anodic aluminum oxide (AAO) membranes, we have successfully fabricated near-equiatomic Fe48±3Pd52±3 nanowires (NWs) with the diameter of $\approx 200$ nm and the length of $\approx 3.5~\mu{\rm m}$ . X-ray diffraction and transmission electron microscopy/selected-area electron diffraction analyses revealed that the as-deposited NWs are isotropic and polycrystalline with an average crystal size of 5 nm and have an fcc crystal structure. Magnetic force microscopy (MFM) on a single Fe–Pd NW revealed its single-domain behavior with the easy axis of magnetization along the long axis of the NW. The magnetizationswitching behavior of a single Fe–Pd NW studied with the MFM suggested a square-shaped magnetization curve $(M/Ms = 1)$ with $H_{C\Vert} \approx 3.2$ kA/m. In addition, using in-field MFM techniques, the effects of dipolar interactions in an Fe–Pd array of NWs still embedded in the AAO were determined. It was found that the dipolar interactions greatly reduce the parameters of the magnetization hysteresis loop, such as the coercivity, the remanence, and the switching-field distribution of the Fe–Pd NW array.

Magnetic Anisotropy in Bicomponent Self-Assembled Ni and Ni-Pd Nanowires Studied by Magnetic Resonance Spectroscopy

Self-ordered arrays of Ni, Ni(50)Pd(50), and Ni(78)Pd(22) nanowires were synthesized by simultaneous electrochemical deposition of Ni and Pd components into porous templates of anodic aluminum oxide using alternating current. This paper is focused on the interplay of structure and chemical composition of Ni and Ni–Pd bicomponent nanowires arrays and the peculiarities of its magnetic anisotropy.

The release behavior of helium in palladium nanowire: A molecular dynamics study

Molecular dynamics (MD) simulation is employed to investigate the release behavior of helium and its effect on the mechanical properties of palladium (Pd) nanowire. The results indicate that the helium atom can assemble easily to form a helium bubble, which effectively degrade the mechanical properties of Pd nanowire as the bubble size increases. Then, the development propensities of the helium bubble pressure is discussed with the helium atoms continuously releasing, which shows that the relationship between the pressure and the volume of the helium bubble is in well agreement with the description of the state equation. On the basis, it is further found that the release rate of helium has a tight connection with the variation of the bubble pressure in nanowire. Finally, the inherent mechanism of helium releasing from the Pd nanowire is analyzed in detail.

Ethylenediaminetetraacetic acid mediated synthesis of palladium nanowire networks and their enhanced electrocatalytic performance for the hydrazine oxidation reaction

ABSTRACT Noble metal network nanostructures with three-dimensionally (3D) interconnected architectures are attracting much attention because of their unique catalytic, electrical, and optical properties. In this work, we report a facile ethylenediaminetetraacetic acid (EDTA) mediated chemical reduction route for the synthesis of high-quality palladium (Pd) nanowire networks (Pd-NWNWs). During the synthesis, EDTA interacts with PdCl2 to generate EDTA-PdII complex, which efficiently decreases the reduction potential of PdII precursor. The slow reduction rate is crucial for the generation of Pd nanowires. The morphology, composition, and structure of Pd-NWNWs are fully investigated by various physical characterizations. The electrocatalytic activity of Pd-NWNWs for the hydrazine oxidation reaction (HOR) is also studied by cyclic voltammetry, electrochemical impedance spectroscopy, and chronoamperometry, etc. Compared to commercial Pd black, Pd-NWNWs exhibit remarkably improved electrocatalytic activity and stability for the HOR.

Potentiostatically Electrodeposited Hard-Magnetic Fe–Pd-Based Nanowires

Near equiatomic Fe52±3Pd48±3 nanowires (NWs) with the length of 3.5 $\mu \text{m}$ and diameter of $\approx 200$ nm were potentiostatically deposited at −1.1 V for 900 s into a porous anodic aluminum oxide template. Cylindrical NWs with a consistent composition along their length were obtained after introducing two additional steps prior to the electrodeposition (ED) of the Fe–Pd NWs, i.e., template wetting and pre-ED of Au NWs. The as-deposited Fe–Pd NWs were isotropic and nanocrystalline with an fcc crystal structure and were magnetically soft. The influence on the development of the coercivity with annealing temperature and time due to the $ {L}1_{\mathrm { {0}}}$ transformation was investigated. For this purpose, the as-deposited NWs were annealed at temperatures from 400 °C to 700 °C for 1-5 h in Ar + H2 and the phase transformation, microstructure and magnetic properties were analyzed. The coercivity was found to increase by increasing the annealing temperature, as the $ {L}1_{\mathrm { {0}}}$ ordering becomes more complete. A maximum in the coercivity of $ {H}_{{{ {C}\vert \vert }}} = 267$ kA/m and $ {M}_{{{ {r}}}} / {M}_{{{ {s}\vert \vert }}}=0.85$ was achieved upon annealing at 600 °C for 4 h. The high remanence is attributed to the exchange coupling between the nanosized grains and/or the coupling between the soft [ $\alpha $ -Fe, $\gamma $ -(Fe,Pd), fcc-FePd] and hard $ {L}1_{\mathrm { {0}}}$ phases. The effect of the deposited Au NWs prior to the Fe–Pd NWs’ deposition on the $ {L}1_{\mathrm { {0}}}$ ordering was evaluated as well; however, the magnetic properties were significantly decreased due to the formation of soft-magnetic phases, i.e., (Au, Fe) and (Au, Pd).

Magnetic hysteresis in small-grained CoxPd1−x nanowire arrays

Co–Pd nanowires with small grain size are fabricated by AC electrodeposition into hexagonally ordered alumina pores, 20–35nm in diameter and about 1µm long. The effects of the alloy composition, the nanowire diameter and the grain size on the hysteresis properties are considered. X-ray diffraction indicates that the nanowires are single phase, a fcc Co–Pd solid solution; electron microscopy results show that they are polycrystalline, with randomly oriented grains (7–12nm), smaller than the wire diameter. Nanowire arrays are ferromagnetic, with an easy magnetization axis parallel to the nanowire long axis. Both, the coercive field and the loop squareness monotonously increase with the Co content and with the grain size, but no clear correlation with the wire diameter is found. The Co and Co-rich nanowire arrays exhibit coercive fields and reduced remanence values quite insensitive to temperature in the range 4K–300K; on the contrary, in Pd-rich nanowires both magnitudes are smaller and they largely increase during cooling below 100K. These behaviors are systematized by considering the strong dependences displayed by the magneto-crystalline anisotropy and the saturation magnetostriction on composition and temperature. At low temperatures the effective anisotropy value and the domain-wall width to grain size ratio drastically change, promoting less cooperative and harder nucleation modes.

Scalable Bromide-Triggered Synthesis of Pd@Pt Core-Shell Ultrathin Nanowires with Enhanced Electrocatalytic Performance toward Oxygen Reduction Reaction.

This article reports a novel scalable method to prepare ultrathin and uniform Pd@Pt nanowires (NWs) with controllable composition and shell thickness, high aspect ratio, and smooth surface, triggered by bromide ions via a galvanic replacement reaction between PtCl6(2-) and Pd NWs. It was found that bromide ions played a vital role in initiating and promoting the galvanic reaction. The bromide ions served as capping and oxidized etching agents, counterbalancing the Pt deposition and Pd etching on the surface to give final Pd@Pt core-shell nanostructures. Such a counterbalance and the formation PtBr6(2-) with lower redox potential could lower the reaction rate and be responsible for full coverage of a smooth Pt shell. The full coverage of Pt deposited on Pd NWs is important for the enhancement of the activity and stability, which depend strongly on the Pt content and Pt shell thickness. Significantly, the Pd@Pt NWs with Pt content of 21.2% (atomic ratio) exhibited the highest mass activity (810 mA mg(-1)(Pt)) and specific activity (0.4 mA cm(-2)). Interestingly, the mass activity (1560 mA mg(-1)(Pt)) and specific activity (0.98 mA cm(-2)) of Pd@Pt (21.2%) NWs increased to 2.45 and 1.95 times the initial values after 60k cycles tests, 8.5 and 9.0 times greater than those of Pt/C catalysts. In addition, these ultrathin NW electrocatalysts with large aspect ratio are easy to form into a freestanding film, which improves the mass transport, electrical conductivity, and structure stability.

(Invted) Catalytically Accelerated Hydrogen Gas Detection at Electrodeposited Pd@Pt Nanowires

Platinum (Pt)-modified palladium (Pd) nanowires (or Pd@Pt nanowires) are prepared with control of the Pt coverage. These Pd@Pt nanowires are used as resistive gas sensors for the detection of hydrogen gas in air, and the influence of the Pt surface layer is assessed. Pd nanowires with dimensions of 60 nm(h) × 200 nm(w) × 20 μm(l) are first prepared using lithographically-patterned nanowire electrodeposition (LPNE). A thin Pt surface layer is elec- trodeposited conformally onto a Pd nanowire at coverages, θPt , of 0.10 monolayer (ML), 1.0 ML, and 10 ML. X-ray photoelectron spectroscopy coupled with scanning electron microscopy and electrochemical measurements are consistent with a layer-by-layer deposition mode for Pt on the Pd nanowire surface. The resistance of a single Pd@Pt nanowire is measured during the exposure of these nanowires to pulses of hydrogen gas in air at concentrations ranging from 0.04 to 5.0 vol%. Both Pd nanowires and Pd@Pt nanowires show a prompt increase in resistance upon exposure to H2 in air, caused by the conversion of Pd to more resistive PdHx. The Pt surface layer present at Pd@Pt nanowires modifies the response to H2 in two ways: First, the amplitude of the resistance change is reduced as θPt is increased, and second, the rate at which the nanowire resistance attains a new steady-state value upon a change in the H2 concentration - characterized by the response time and the recovery time - is accelerated. An optimum Pt coverage of θPt = 1.0 ML is seen for which nanowire response is accelerated by a factor of 2-3 while the recovery from H2 exposure is faster by an order of magnitude as compared to a pure Pd nanowire operating at the same elevated temperature.

Eshelby twist and correlation effects in diffraction from nanocrystals

Molecular dynamics simulations were used to model the Eshelby dislocation inside Pd and Ir nanowires and to predict the powder diffraction pattern using the Debye scattering equation. We find that the ideal dislocation solution by Eshelby is in good agreement with the observed twist angle and deviatoric strain, even though it ignores both the splitting of the Eshelby dislocation into two partials and surface stress. Surface stress plays a significant role only for nanorods with small aspect ratio (∼1:1). We also find that Wilson's prediction on the diffraction peak broadening for the Eshelby dislocation is overestimated because it ignores the fact that the Eshelby twist relaxes the deviatoric strain. Moreover, the twist loosens the correlation along the nanorod, causing additional line profile broadening, which is read by diffraction as a decrease of coherent domain size when the total twist angle is bigger than 1.5°. Overall, our findings suggest a novel way to predict and analyze the dislocations as well as the resulting strain fields in the twisted nanocrystalline rods.

Colorimetric detection of the flux of hydrogen peroxide released from living cells based on the high peroxidase-like catalytic performance of porous PtPd nanorods.

One-dimensional PtPd porous nanorods (PtPd PNRs) were successfully synthesized through a bromide-induced galvanic replacement reaction between Pd nanowires and K2PtCl6. The PtPd PNRs were porous and alloy-structured with Pt/Pd atomic ratio up to 1:1 which were demonstrated by spectroscopic methods. We had also proved that the nanorods could function as peroxidase mimetic for the detection of H2O2, with the detection limit of 8.6 nM and the linear range from 20 nM to 50 mM. The result demonstrated that PtPd PNRs exhibited much higher affinity to H2O2 over other peroxidase mimetics due to synergistically integrating highly catalytic activity of two metals. On the basis of the peroxidase-like activity, the PtPd PNRs were used as a signal transducer to develop a novel and simple colorimetric method for the study of the flux of H2O2 released from living cell. By using 3,3,5,5-tetramethylbenzidine as substrate, the H2O2 concentration could be distinguished by naked-eye observation without any instrumentation or complicated design. The method developed a new platform for a reliable collection of information on cellular reactive oxygen species release. And the nanomaterial could be used as a power tool for a wide range of potential applications in biotechnology and medicine.

Highly efficient reduction of hexavalent chromium on amino-functionalized palladium nanowires

Palladium (Pd) nanostructures are attracting much attention due to their intriguing optical, electrical, and catalytic properties. Pd-catalytic hydrogenation is an effective route for remediating organic and inorganic contaminants. In this work, a simple formate-mediated chemical reduction method is used to synthesize the polyallylamine functionalized Pd nanowire networks (Pd-NWWs). The morphology, structure, and surface composition of Pd-NWWs are investigated in detail. The formation mechanism of Pd-NWWs is defined in accordance with the experimental observation and discussion. Physical characterization shows the as-synthesized products are a three-dimensionally interconnected network with one-dimensional Pd nanowires as building blocks, and the Pd nanowires grow from the primary spherical Pd nanocrystals via the oriented attachment. In comparison with commercial Pd black, the amino-functionalized Pd-NWWs exhibit remarkably improved catalytic activity for the hexavalent chromium reduction at room temperature.

Temperature balanced hydrogen sensor system with coupled palladium nanowires

A temperature compensated hydrogen sensor was designed and made capable of detecting H2 within a broad range of 100–10.000ppm while compensating instantaneously for large (±25°C) temperature variations. Two related operational constraints have been simultaneously addressed: (1) Selective, and sensitive detection under large temperature changes, (2) Fast warning at low and increasing H2 levels. Accurate measurements of hydrogen concentrations were enabled by matching relevant time-constants. This was achieved with a microchip having two temperature coupled palladium nanowires. One of the H2 sensitive Pd nanowires was directly exposed to hydrogen, whilst the other nanowire was used as a temperature sensor and as a reference. A drop forging technique was used to passivate the second Pd wire against H2 sensing. Temperature effects could be substantially reduced with a digital signal processing algorithm. Measurements were done in a test chamber, enabling the hydrogen concentration to be controlled over short and long periods. An early response for H2 sensing is attainable in the order of 600 milliseconds and an accurate value for the absolute hydrogen concentration can be obtained within 15s.

Catalytically activated palladium@platinum nanowires for accelerated hydrogen gas detection.

Platinum (Pt)-modified palladium (Pd) nanowires (or Pd@Pt nanowires) are prepared with controlled Pt coverage. These Pd@Pt nanowires are used as resistive gas sensors for the detection of hydrogen gas in air, and the influence of the Pt surface layer is assessed. Pd nanowires with dimensions of 40 nm (h) × 100 nm (w) × 50 μm (l) are first prepared using lithographically patterned nanowire electrodeposition. A thin Pt surface layer is electrodeposited conformally onto a Pd nanowire at coverages, θPt, of 0.10 monolayer (ML), 1.0 ML, and 10 ML. X-ray photoelectron spectroscopy coupled with scanning electron microscopy and electrochemical measurements is consistent with a layer-by-layer deposition mode for Pt on the Pd nanowire surface. The resistance of a single Pd@Pt nanowire is measured during the exposure of these nanowires to pulses of hydrogen gas in air at concentrations ranging from 0.05 to 5.0 vol %. Both Pd nanowires and Pd@Pt nanowires show a prompt and reversible increase in resistance upon exposure to H2 in air, caused by the conversion of Pd to more resistive PdHx. Relative to a pure Pd nanowire, the addition of 1.0 ML of Pt to the Pd surface alters the H2 detection properties of Pd@Pt nanowires in two ways. First, the amplitude of the relative resistance change, ΔR/R0, measured at each H2 concentration is reduced at low temperatures (T = 294 and 303 K) and is unaffected at higher temperatures (T = 316, 344, and 376 K). Second, response and recovery rates are both faster at all temperatures in this range and for all H2 concentrations. For higher θPt = 10 ML, sensitivity to H2 is dramatically reduced. For lower θPt = 0.1 ML, no significant influence on sensitivity or the speed of response/recovery is observed.

Highly sensitive hydrogen gas sensor based on a suspended palladium/carbon nanowire fabricated via batch microfabrication processes

We present a highly sensitive H2 sensor based on a single Pd-functionalized carbon nanowire suspended ∼10μm above a substrate while monolithically bridging two carbon posts. The carbon nanowire and posts were fabricated using a batch carbon-microelectromechanical system (MEMS) process consisting of photolithography and pyrolysis. The pyrolysis process resulted in a significant volume reduction in which the nanowire diameter was reduced to ∼120nm from the original 1μm×1.5μm photoresist wire. Because of SiO2 eaves formed by isotropic etching of the Si substrate, as well as the suspended geometry of the carbon nanowire, a single palladium evaporation process enabled selective palladium coating on the carbon nanowire without any nano-patterning processes. The electrical conductivity of the carbon nanowire was modulated by varying the pyrolysis temperature so that the electrical resistance along the suspended Pd/C nanowire was affected predominantly by hydrogen chemisorption onto the thin Pd layer enclosing the carbon core. The suspended functionalized wire showed better sensing capability compared to a Pd nanowire fabricated on the substrate with similar dimensions, because of enhanced mass transport. The suspended nanowire-based H2 sensor quantified from 10 to 500ppm H2 with percentile resistance changes of 5.9–129%.

Electrochemical behaviors and simultaneous determination of guanine and adenine based on highly ordered Pd-nanowire arrays-modified glassy carbon electrode

A novel electrochemical sensor based on a Pd nanowire arrays (Pd NWAs) electrode for the simultaneous detection of guanine (G) and adenine (A).