Pd-Ag Alloy Research Articles

Morphology Engineering of Au/(PdAg alloy) Nanostructures for Enhanced Electrocatalytic Ethanol Oxidation

AbstractNoble metal nanostructures are promising electrocatalysts with their performance determined by their size, shape, and architecture. This study reports the facile preparation of Au/(PdAg alloy) electrocatalysts with diverse architectures, including nanodumbbells, yolk/shell nanoframes, and yolk/shell nanoboxes, from Au nanorod core/Ag shell bimetallic nanostructures. The fine tuning of the nanostructure architecture is realized by combining galvanic replacement reaction, etching/growth, Ostwald ripening, and coreduction processes. The adding sequence of surfactants and Pd precursors, and the Ag shell thicknesses of the starting core/shell nanocrystals, determine the growth routines and therefore the architectures of the obtained Au/(PdAg alloy) nanostructures. Electrocatalytic performances of all Au/(PdAg alloy) nanostructures toward ethanol oxidation reaction (EOR) in alkaline are examined. Compared with the commercial Pd/C electrocatalyst, the nanodumbbells (Au19Pd19Ag62) display 6.3 times higher specific activity and 4.25 times higher mass activity. The nanoframes (Au14Pd14Ag72) are superior as well, with their specific and mass activities 4.4 and 5.5 times higher than those of the Pd/C electrocatalyst, respectively. The nanoboxes also show slight improvement in electrocatalysis. Moreover, the nanodumbbells exhibit greatly improved stability toward EOR in comparison to the Pd/C electrocatalyst. These results can enrich the manufacturing techniques of noble metal nanostructure catalysts and promote their development for fuel cell applications.

Mechanism of the Electromigration in Ag-Pd Alloy Bonding Wires

The failure mechanism of the electromigration in Ag-Pd bonding wires was investigated through stressing with a current density of 1.23 × 105 A/cm2 at temperatures of 150 °C to 300 °C. It was found that the grains of the wire materials grew rapidly during current stressing for 100 minutes at various temperatures. In contrast, the grain structure remained almost unchanged after storage at these temperatures for 100 minutes without current stressing. The mean-time-to-failure (MTF) for various current-stressed Ag-Pd alloy wires decreased with increases in Pd content. The activation energy for the electromigration of these wire materials was measured, and the results indicated that the main driving force was surface diffusion of Ag.

Catalytically Active Pd-Ag Alloy Nanoparticles Synthesized in Microemulsion Template.

This work investigates the possibility to form catalytically active bimetallic Pd-Ag nanoparticles synthesized in the water pools of a reversed microemulsion using methanol, a more environmental- and user-friendly reductant compared to hydrazine or sodium borohydride, which are commonly used for this type of synthesis. The nanoparticles were characterized with regards to crystallinity and size by X-ray diffraction and transmission electron microscopy. CO chemisorption and oxidation followed by in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) was used for investigating the elemental composition of the surface and catalytic activity, respectively. Moreover, the structural composition of the bimetallic particles was determined by scanning transmission electron microscopy coupled with energy-dispersive X-ray spectroscopy. The particles were shown to be crystalline nanoalloys of around 5-12 nm. CO adsorption followed by in situ DRIFTS suggests that the particle surfaces are composed of the same Pd-Ag ratios as the entire particles, regardless of elemental ratio (i.e., no core-shell structures can be detected). This is also shown by numerical simulations using a Monte Carlo based model. Furthermore, CO oxidation confirms that the synthesized particles are catalytically active.

PdAg@Pd core-shell nanotubes: Superior catalytic performance towards electrochemical oxidation of formic acid and methanol

The catalytic activity of alloy nanomaterials can be well modulated through the electrochemical dissolution of the more active component from alloy nanomaterials. In this paper, PdAg alloy nanotubes of diverse Pd to Ag ratio are prepared by galvanic displacement electrochemical reaction. The Ag-leached PdAg nanotubes are characterized by cyclic voltammetric scans, high-angle annular dark-field scanning transmission electron spectroscopy, energy dispersive X-ray elemental mapping and X-ray photoelectron spectroscopy measurements and demonstrate the formation of PdAg@Pd core-shell nanotubes structure with roughed surface and largely enhanced electrochemical surface area. The PdAg@Pd core-shell nanotubes show significantly enhanced catalytic activities and durability towards electro-oxidation of formic acid and methanol than the as-prepared PdAg nanotubes, with the mass activity and specific activity of 1.93 A mg−1 and 2.67 mA cm−2 towards formic acid respectively, which are 7.8 and 4.8 times that of Pd/C. The increased catalytic performance is ascribed to the unique surface and electronic structure of PdAg@Pd core-shell nanotubes.

Hydrogen Permeability of a Foil of Pd–Ag Alloy Modified with a Nanoporous Palladium Coating

Thin films with the composition Pd–23% Ag are obtained via magnetron sputtering. The magnetron sputtering of Pd–50% Zn films with subsequent diffusion annealing and etching of the active component is used to modify the surfaces of palladium–silver films to improve their hydrogen permeability. Modifying the surfaces of the resulting Pd–Ag films using a nanoporous palladium coating with a predominant distribution of particles ranging from 0 to 50 nm allows a hydrogen flux density of up to 0.4 mmol s−1 m−2 to be achieved for sufficiently thin palladium membranes (<10 μm) under conditions of low temperature (<90°C) and pressure (<0.6 MPa). Experimental evidence is gathered that under these conditions, the velocity of hydrogen transport is limited by dissociative–associative processes at membrane boundaries and can be greatly (by an order of magnitude) increased, due to acceleration of the limiting stage of the process via the formation of a palladium nanoporous coating on the film’s surface.

Selective hydrogenation of the C[dbnd]C bond in cinnamaldehyde over an ultra-small Pd-Ag alloy catalyst

Hydrocinnamaldehyde (HCAL) is a crucial intermediate in the manufacture of perfumes and pharmaceuticals, but highly selective hydrogenation of cinnamaldehyde (CALD) to hydrocinnamaldehyde with a good conversion rate is a challenging. We report that the incorporation of Ag into Pd-based catalysts promotes their catalytic activity and HCAL selectivity (HCAL selectivity of 98.6% with >99.9% CALD conversion for Pd-0.3Ag/MCM-41) for CALD hydrogenation compared to those of catalysts with no Ag, e.g., HCAL selectivity of 84.5% for Pd/MCM-41and 77.3% for Pd/AC (activated carbon). The Pd-0.3Ag/MCM-41 catalyst shows an outstanding stability during five cycles of use. The excellent performance of the Pd-0.3Ag/MCM-41 catalyst in CALD hydrogenation is due to the ultra-small size of the Pd nanoparticles (Pd-Ag alloy, a geometric and electronic modification of Pd).

Surface Engineering of a Supported PdAg Catalyst for Hydrogenation of CO2 to Formic Acid: Elucidating the Active Pd Atoms in Alloy Nanoparticles.

The hydrogenation of carbon dioxide (CO2) to formic acid (FA; HCOOH), a renewable hydrogen storage material, is a promising means of realizing an economical CO2-mediated hydrogen energy cycle. The development of reliable heterogeneous catalysts is an urgent yet challenging task associated with such systems, although precise catalytic site design protocols are still lacking. In the present study, we demonstrate that PdAg alloy nanoparticles (NPs) supported on TiO2 promote the efficient selective hydrogenation of CO2 to give FA even under mild reaction conditions (2.0 MPa, 100 °C). Specimens made using surface engineering with atomic precision reveal a strong correlation between increased catalytic activity and decreased electron density of active Pd atoms resulting from a synergistic effect of alloying with Ag atoms. The isolated and electronically promoted surface-exposed Pd atoms in Pd@Ag alloy NPs exhibit a maximum turnover number of 14 839 based on the quantity of surface Pd atoms, which represents a more than 10-fold increase compared to the activity of monometallic Pd/TiO2. Kinetic and density functional theory (DFT) calculations show that the attack on the C atom in HCO3- by a dissociated H atom over an active Pd site is the rate-determining step during this reaction, and this step is boosted by PdAg alloy NPs having a low Pd/Ag ratio.

Acetylene Adsorption on Pd–Ag Alloys: Evidence for Limited Island Formation and Strong Reverse Segregation from Monte Carlo Simulations

Restructuring of alloy surfaces induced by strongly bound adsorbates is a well-established phenomenon occurring in catalysis and membrane science. In catalytic processes, this restructuring can have profound effects because it alters the ensemble distribution between the as-prepared state of the catalyst and the catalytic surface under operando conditions. This work assesses the restructuring of Pd–Ag alloys induced by adsorption of acetylene in the framework of the ensemble formalism. A detailed Ising-type model Hamiltonian of the (111) surface plane is fitted to extensive density functional theory computations. The equilibrium distributions under a realistic environment are then evaluated by a Monte Carlo approach as a function of temperature and alloy composition. Acetylene induces a strong reverse segregation within the relevant range of temperature. Therefore, the surface of Pd–Ag catalysts is almost entirely covered by Pd for bulk ratios <0.8 Ag–Pd, which is, in general, detrimental to the selectivity of Pd–Ag catalysts. Despite the very strong vertical segregation, acetylene only induces marginal in-plane ordering, that is, the surface triangular ensembles follow random distributions as a function of the surface layer Ag fraction quite closely. This can be explained by two factors: first, triangular sites are not sufficient to fully capture the diversity of acetylene binding energies on Pd–Ag alloy surfaces. Rather, an extended environment including the first coordination sphere is necessary and leads to an overlap in terms of binding energy between weakly binding Pd3 ensembles and strongly binding Pd2Ag ensembles. The second critical aspect is related to lateral interactions, which preclude adsorption of acetylene molecules on nearest neighbor triangular sites. Therefore, in a Pd3 island, roughly two thirds of Pd3 sites would be lost. Our study suggests that the equilibrium structure of these alloy catalysts under operando conditions is far from the state targeted by the catalyst design, revealing a nearly unavoidable reason for loss of selectivity of the catalyst with time of operation.

A quantitative experimental phantom study on MRI image uniformity.

Our goal was to assess MR image uniformity by investigating aspects influencing said uniformity via a method laid out by the National Electrical Manufacturers Association (NEMA). Six metallic materials embedded in a glass phantom were scanned (i.e. Au, Ag, Al, Au-Ag-Pd alloy, Ti and Co-Cr alloy) as well as a reference image. Sequences included spin echo (SE) and gradient echo (GRE) scanned in three planes (i.e. axial, coronal, and sagittal). Moreover, three surface coil types (i.e. head and neck, Brain, and temporomandibular joint coils) and two image correction methods (i.e. surface coil intensity correction or SCIC, phased array uniformity enhancement or PURE) were employed to evaluate their effectiveness on image uniformity. Image uniformity was assessed using the National Electrical Manufacturers Association peak-deviation non-uniformity method. Results showed that temporomandibular joint coils elicited the least uniform image and brain coils outperformed head and neck coils when metallic materials were present. Additionally, when metallic materials were present, spin echo outperformed gradient echo especially for Co-Cr (particularly in the axial plane). Furthermore, both SCIC and PURE improved image uniformity compared to uncorrected images, and SCIC slightly surpassed PURE when metallic metals were present. Lastly, Co-Cr elicited the least uniform image while other metallic materials generally showed similar patterns (i.e. no significant deviation from images without metallic metals). Overall, a quantitative understanding of the factors influencing MR image uniformity (e.g. coil type, imaging method, metal susceptibility, and post-hoc correction method) is advantageous to optimize image quality, assists clinical interpretation, and may result in improved medical and dental care.

Enhanced Chemical Stability of Ag Nanowires by Slight Surface Modification with Pd

AbstractThe chemical stability of Ag nanowires (NWs) can be addressed by introducing a layer of noble metal alloy, in particular Ag–Pd alloy, on the Ag NW surface. Due to the high cost of noble metals, it is practically important to use the least amount of noble metals as possible while achieving the chemical and electrical properties required for the electrode. To minimize the amount of Pd added to Ag NWs, the electrode performance should be correlated with the elemental distribution of Pd in the Ag NW. In this study, the amount of Pd deposited on Ag NWs is varied and the 3D elemental distribution of Pd is characterized using atom probe tomography (APT). The results indicate that chemical stability against oxidation can be achieved when the surface layer contains a very small amount of Pd (≈5 at%), thereby maintaining the good electrical and mechanical properties of the pristine Ag NW electrode. This study demonstrates the suitability of Pd‐treated Ag NWs as electrodes for electro‐chemiluminescence involving corrosive oxidation reactions.

Toxicity of porcelain-fused-to-metal substrate to zebrafish (Danio rerio) embryos and larvae

AimsPorcelain-fused-to-metal (PFM) crowns are a standard restoration technique in dentistry, but toxicity of PFM in vivo has not been systematically evaluated. The present study evaluated the effects of various metal alloy shells of PFM crowns on the development of zebrafish embryos and larvae in order to determine the safety of these materials. Main methodsGold palladium (Au-Pd), silver palladium (Ag-Pd), Nickel chromium (Ni-Cr), cobalt chromium (Co-Cr), titanium (Ti) alloy porcelain crowns were immersed in artificial saliva for 1, 4, and 7 weeks, and the leach solution was collected and used to treat zebrafish embryos at 4–144 h PFM. Toxicity was assessed based on mortality, spontaneous movement, heart rate, hatchability, malformation, and swimming behavior. Key findingsThe 1-week leachates of the five PFMs were not toxic to zebrafish. The rates of mortality and malformation of zebrafish in the Ni-Cr alloy group were increased whereas spontaneous movement, heart rate, and swimming behavior were decreased for 4- and 7-week leachates. SignificanceAmong metal substrates commonly used in dental work, Ni-Cr alloy was most toxic, followed by Co-Cr and Ag-Pd alloys. Ti and Au-Pd alloys showed good biocompatibility and are therefore the most suitable materials for clinical applications.

MEMS based highly sensitive dual FET gas sensor using graphene decorated Pd-Ag alloy nanoparticles for H2 detection

A low power, dual-gate field-effect transistor (FET) hydrogen gas sensor with graphene decorated Pd-Ag for hydrogen sensing applications was developed. The FET hydrogen sensor was integrated with a graphene-Pd-Ag-gate FET (GPA-FET) as hydrogen sensor coupled with Pt-gate FET as a reference sensor on a single sensor platform. The sensing gate electrode was modified with graphene by an e-spray technique followed by Pd-Ag DC/MF sputtering. Morphological and structural properties were studied by FESEM and Raman spectroscopy. FEM simulations were performed to confirm the uniform temperature control at the sensing gate electrode. The GPA-FET showed a high sensing response to hydrogen gas at the temperature of 25~254.5 °C. The as-proposed FET H2 sensor showed the fast response time and recovery time of 16 s, 14 s, respectively at the operating temperature of 245 °C. The variation in drain current was positively related with increased working temperature and hydrogen concentration. The proposed dual-gate FET gas sensor in this study has potential applications in various fields, such as electronic noses and automobiles, owing to its low-power consumption, easy integration, good thermal stability and enhanced hydrogen sensing properties.

Thiol Treatment Creates Selective Palladium Catalysts for Semihydrogenation of Internal Alkynes

Summary Surface and interfacial engineering of heterogeneous metal catalysts is effective and critical for optimizing selective hydrogenation for fine chemicals. By using thiol-treated ultrathin Pd nanosheets as a model catalyst, we demonstrate the development of stable, efficient, and selective Pd catalysts for semihydrogenation of internal alkynes. In the hydrogenation of 1-phenyl-1-propyne, the thiol-treated Pd nanosheets exhibited excellent catalytic selectivity (>97%) toward the semihydrogenation product (1-phenyl-1-propene). The catalyst was highly stable and showed no obvious decay in either activity or selectivity for over ten cycles. Systematic studies demonstrated that a unique Pd-sulfide/thiolate interface created by the thiol treatment was crucial to the semihydrogenation. The high catalytic selectivity and activity benefited from the combined steric and electronic effects that inhibited the deeper hydrogenation of C=C bonds. More importantly, this thiol treatment strategy is applicable to creating highly active and selective practical catalysts from commercial Pd/C catalysts for semihydrogenation of internal alkynes.

Electrolytic Migration of Ag-Pd Alloy Wires with Various Pd Contents

During Ag ion migration in an aqueous water drop covering a pair of parallel Ag-Pd wires under current stressing, hydrogen bubbles form first from the cathode, followed by the appearance of pure Ag dendrites on the cathodic wire. In this study, Ag dendrites with a diameter of 0.2–0.4 μm grew toward the anodic wire. The growth rate (v) of these dendrites decreased with the Pd content (c) with a linear relationship of: $$ v = 10.02 - 0.43 \, c $$ . Accompanying the growth of pure Ag dendrites was the formation of a continuous layer of crystallographic Ag2O particles on the surface of the anodic wire. The deposition of such insulating Ag2O products did not prevent the contact of Ag dendrites with the anodic Ag-Pd wire or the short circuit of the wire couple.

One-pot synthesis of Ag-rich AgPd alloy nanoactiniae and their enhanced electrocatalytic activity toward oxygen reduction

Abstract The electro-catalytic properties can be effectively optimized by designing bimetallic alloy nanoparticles with high-content less-active metal to enhance the competence of more-active noble metal. Herein, a one-pot hydrothermal approach is demonstrated for the controllable synthesis of Ag-rich Ag9Pd1 alloy nanoactiniae with obviously enhanced electro-catalytic activity (2.23 mA cm−2 at 0.85 V) and stability for oxygen reduction reaction. In alkaline solution, the ORR onset potential and half-wave potential of the Ag9Pd1 alloy nanoactiniae can reach a value of 1.02 V and 0.89 V, respectively, which origin from strong ligand and ensemble effects between Pd element and Ag element. The nanocrystals are uniformly alloyed, displaying a Ag9Pd1 combination, as displayed by an assembly of X-ray diffraction (XRD) spectrum, energy dispersive X-ray (EDX) analysis, and cyclic voltammetry (CV). This concept of tuning bimetallic alloy nanocrystals with low concentrations of more precious metal may be a promising approach to be applicable to a wide range of alloy nanocrystals.

Innovative joining of Pd-Ag permeator tubes

Pd-alloy membrane tubes are used for hydrogen isotopes separation in the fusion fuel cycle. The efficiency of these separation processes has been significantly increased by the adoption of thin-walled self-supported membrane tubes that exhibit high permeance and infinite selectivity to hydrogen. A critical aspect in the realization of Pd-based membrane devices (both separators and membrane reactors) is related to the joining of the thin-walled tubes to the membrane module. In this work, an innovative fitting of thin-walled tubes has been obtained by coupling two special stainless steel joints (a weld adapter and a sealing insert) that tighten the flared edge of the tube. In particular, the design of the compression fitting relies on the elastic deformation reserve of the conical edge of the sealing insert that is capable: i) to ensure the sealing of the joining also in presence of the expansion/contraction of the Pd-Ag alloy during the hydrogenation cycling, and ii) to compensate small irregularities of the thin-walled tube (thickness, circularity, etc.). The effectiveness of the new joining technique in terms of both hydrogen perm-selectivity and stability has been verified in preliminary permeations tests.

Improving the Sensitivity of Palladium-Based Fiber Optic Hydrogen Sensors

This paper reports on the sensitivity improvement of palladium (Pd)-based fiber optic hydrogen sensors. The expansion of Pd undergoing hydrogen absorption transduces strain in a suitable sensing element. The sensors reported here are based on fiber Bragg grating (FBG) strain sensors with a Pd foil hydrogen sensing element. The hydrogen sensitivity is dependent upon; strain sensor sensitivity, the Pd body geometry, the volumetric expansion of Pd, and the strain transfer between Pd and the sensor element. We have investigated three options to improve the sensitivity: First, improve the strain transfer by decreasing the bond line thickness with new manufacturing methods. Second, increasing the volumetric expansion by using a Pd silver (Ag) alloy (Pd75/Ag25) foil with increased hydrogen solubility. Third, concentrating the strain of the expanding Pd on an FBG by using a new sensor concept. All sensors were tested in hydrogen concentrations of 2,500, 10,000, and 50,000 ppm at 90 °C and 1060 mbar. Using new manufacturing methods, the strain transfer is improved by up to 72% compared to previously reported sensors and the sensitivity is 0.062 pm/ppm. With the PdAg alloy foil, the sensitivity is amplified by a factor of 17 compared to pure palladium foil sensor and the sensitivity is 0.77 pm/ppm. With the new sensor concept with strain concentration, the signal is amplified by a factor 2.5 compared to sensors without strain concentration and the sensitivity is 0.18 pm/ppm.

Clinical effects of full crown prosthesis on anterior teeth

Objective To evaluate the clinical effects of anterior teeth repair of three different restorations made of Co-Cr alloy, Ag-Pd alloy and all-ceramic crowns. Methods 90 cases who needed the both maxillary and mandibular anterior teeth restarations were selected and treated respectively with Co-Cr alloy porcelain fused to metal crowns (PFM)(60 teeth), Ag-Pd alloy PFM (46 teeth)and IPS e. max Press Porcelain full crown (38 teeth). Gingival index was observed before restoration and in 6 and 12 months after restoration. Meanwhile, clinical indicators of two restorations were evaluated as cervical margin's coloration, margin fitness degree, color of restorations, fracture of restorations and contour of restorations, etc. Results The healthy condition of gingiva in groups of Ag-Pd alloy PFM and IPS e. max Press Porcelain full crown were superior to the group of Co-Cr alloy PFM (P<0.05). There was no cervical margin's coloration in groug of all-ceramic PFM. The color and contour of this group was superior to the group of Co-Cr alloy PFM (P<0.05). The significant difference between group of Co-Cr alloy and group of Ag-Pd alloy was cervical margin's coloration and marginal density of the restoration (P<0.05). Conclusions The clinical effects of both groups of Ag-Pd alloy PFM and IPS e. max Press Porcelain full crown is superior to the group of Co-Cr alloy PFM. The IPS e. max Press Porcelain full crown group works best. Key words: CO-Cr alloy PFM; Ag-Pd alloy PFM; IPS e. max Press Porcelain full crown; Anterior teeth

2D PdAg Alloy Nanodendrites for Enhanced Ethanol Electroxidation.

The development of highly active and stable electrocatalysts for ethanol electroxidation is of decisive importance to the successful commercialization of direct ethanol fuel cells. Despite great efforts invested over the past decade, their progress has been notably slower than expected. In this work, the facile solution synthesis of 2D PdAg alloy nanodendrites as a high-performance electrocatalyst is reported for ethanol electroxidation. The reaction is carried out via the coreduction of Pd and Ag precursors in aqueous solution with the presence of octadecyltrimethylammonium chloride as the structural directing agent. Final products feature small thickness (5-7 nm) and random in-plane branching with enlarged surface areas and abundant undercoordinated sites. They exhibit enhanced electrocatalytic activity (large specific current ≈2600 mA mgPd-1) and excellent operation stability (as revealed from both the cycling and chronoamperometric tests) for ethanol electroxidation. Control experiments show that the improvement comes from the combined electronic and structural effects.

Polydopamine-coated halloysite nanotubes supported AgPd nanoalloy: An efficient catalyst for hydrolysis of ammonia borane

AgPd alloy nanoparticles (NPs) supported on halloysite nanotubes (HNTs) coated polydopamine (PDA) successfully synthesized by one-pot hydrothermal route. XRD, TEM and XPS were employed to verify the alloy structure of the obtained AgPd NPs. The HAADF-STEM result revealed that the thickness of PDA coating was ∼10 nm, which could be formed on the surface of HNTs, and the existence of PDA was beneficial to deposit AgPd alloys with high dispersibility on the surface of HNTs. AgPd/PDA-HNT nanocomposites were effective catalysts for the hydrolysis of ammonia borane at room temperature, and the reaction was completed within 160 s using Ag3Pd2/PDA-HNT as catalysts, with a high total turnover frequency (TOF) value of 90 molH2 molcatalyst−1 min−1 and a low apparent activation energy (Ea) of 22.7 kJ mol−1. After the sixth cycle, Ag3Pd2/PDA-HNT catalyst retained 72% of its initial activity and 100% conversion. The excellent catalytic properties, good durability and reusability, enabled Ag3Pd2/PDA-HNT to be an ideal catalyst in the practical applications.