Pd-Ag Alloy Research Articles

Stretched-to-compressed-exponential crossover observed in the electrical degradation kinetics of some spinel-metallic screen-printed structures

Thermally-induced (170 °C) degradation-relaxation kinetics is examined in screen-printed structures composed of spinel Cu0.1Ni0.1Co1.6Mn1.2O4ceramics with conductive Ag or Ag-Pd layered electrodes. Structural inhomogeneities due to Ag and Ag-Pd diffusants in spinel phase environment play a decisive role in non-exponential kinetics of negative relative resistance drift. If Ag migration in spinel is inhibited by Pd addition due to Ag-Pd alloy, the kinetics attains stretched exponential behavior with ∼0.58 exponent, typical for one-stage diffusion in structurally-dispersive media. Under deep Ag penetration into spinel ceramics, as for thick films with Ag-layered electrodes, the degradation kinetics drastically changes, attaining features of two-step diffusing process governed by compressed-exponential dependence with power index of ∼1.68. Crossover from stretched- to compressed-exponential kinetics in spinel-metallic structures is mapped on free energy landscape of non-barrier multi-well system under strong perturbation from equilibrium, showing transition with a character downhill scenario resulting in faster than exponential decaying.

Molecular Dynamics Study on Hydrogen Diffusion in Pd and Pd-Ag Alloys

Hydrogen diffusion in Pd with various H concentrations and Pd-Ag alloys with various Ag and H concentrations is investigated using molecular dynamics simulations. At H concentration of 0.5 in Pd, the miscibility gap caused by the spinodal decomposition is observed. The diffusion coefficient of H in Pd is kept constant at H concentration less than 0.1, then increases with increasing H concentration until the phase transition occurs, and after reaching a maximum it decreases with increasing H concentration. The simulations of varying a temperature predict the activation energy for H diffusion of 0.163 eV at H concentration of 0.05, which agrees well with that reported in the literature, and minimum activation energy of 0.144 eV at H concentration of 0.5. Moreover, our results indicate that the addition of Ag to Pd leads to the dissipation of the miscibility gap. The diffusion coefficient of H in Pd-Ag alloys significantly decreases with increasing Ag concentration. The minimum activation energy for H diffusion in Pd-Ag alloys is estimated to be 0.135 eV when Ag and H concentration are 0.1 and 0.5, respectively.

Electrochemical deposition and characterization of AgPd alloy layers

The AgPd alloys were electrodeposited onto Au and glassy carbon disc electrodes from the solution containing 0.001 mol dm-3 PdCl2 + 0.04 mol dm-3 AgCl + 0.1 mol dm-3 HCl + 12 mol dm-3 LiCl under the non-stationary diffusion (quiescent electrolyte) and convective diffusion (? = 1000 rpm) to the different amounts of charge and at different current densities. Electrodeposited alloy layers were characterized by the anodic linear sweep voltammetry (ALSV), scanning electron microscopy, energy dispersive X-ray spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS). The compositions of the AgPd alloys determined by the EDS were almost identical to the theoretically predicted ones, while the compositions obtained by XPS and ALSV analysis were similar to each other, but different from those obtained by EDS. Deviation from the theoretically predicted values (determined by the ratio jL(Pd)/j(Ag)) was more pronounced at lower current densities and lower charges of AgPd alloys electrodeposition, due to the lower current efficiencies for alloys electrodeposition. The ALSV analysis indicated the presence of Ag and Pd, expressed by two ALSV peaks, and in some cases the presence of the additional peak, which was found to correspond to the dissolution of large AgPd crystals, formed at thicker electrodeposits (higher electrodeposition charge), indicating, for the first time, that besides the phase structure, the morphology of alloy electrodeposit could also influence the shape of the ALSV response. In addition to Ag and Pd, the XPS analysis confirmed the presence of AgCl at the surface of samples electrodeposited to low thicknesses (amounts of charge).

Biosynthesis of Ag-Pd bimetallic alloy nanoparticles through hydrolysis of cellulose triggered by silver sulfate.

We report a simple but efficient biological route based on the hydrolysis of cellulose to synthesize Ag–Pd alloy nanoparticles (NPs) under hydrothermal conditions. X-ray powder diffraction, ultraviolet-visible spectroscopy and scanning transmission electron microscopy-energy dispersive X-ray analyses were used to study and demonstrate the alloy nature. The microscopy results showed that well-defined Ag–Pd alloy NPs of about 59.7 nm in size can be biosynthesized at 200 °C for 10 h. Fourier transform infrared spectroscopy indicated that, triggered by silver sulfate, cellulose was hydrolyzed into saccharides or aldehydes, which served as both reductants and stabilizers, and accounted for the formation of the well-defined Ag–Pd NPs. Moreover, the as-synthesized Ag–Pd nanoalloy showed high activity in the catalytic reduction of 4-nitrophenol by NaBH4.

One-pot reductive amination of aldehydes with nitroarenes using formic acid as the hydrogen donor and mesoporous graphitic carbon nitride supported AgPd alloy nanoparticles as the heterogeneous catalyst

A facile one-pot protocol has been developed for the synthesis of secondary amines via a tandem reductive amination of aldehydes with nitroaromatics.

Enhanced and Synergistic Catalysis of Green Synthesized Pd-Ag Alloy Nanoparticles for Anodic Oxidation of Propan-2-ol in Alkali

Bimetallic PdxAgy alloy along with monometallic Pd, Ag nanoparticle were synthesized in a single pot using a green synthetic protocol in absence of any capping agent. X-ray diffraction and microscopic studies of synthesized material demonstrate the formation of nanoballs with radius of ca 25 nm of face centred cubic metals and alloys. The electrochemical studies of as-synthesized materials loaded on carbon support reveal that the Pd4Ag nanoparticles exhibit the best and synergistic electro-catalytic activity in reference to oxidation of propan-2-ol in alkali. The most active Pd4Ag nanoparticles show higher peak current (124.54mAmg-1) in comparison to that (92.54mAmg-1) of Pd in cyclic voltammetric study (CV). The electrode shows the highest exchange current density (0.284mAmg-1of Pd) for propan-2-ol oxidation reaction. CV studies of reaction product reveal that Ag accelerates the formation of acetone rather than carbonate elucidating the plausible mechanism of the reaction. These findings have important implications for further fine-tuning of the Pd nano alloys toward highly active and selective catalysts for alcohol fuel cells.

Investigation on the morphological and optical evolution of bimetallic Pd-Ag nanoparticles on sapphire (0001) by the systematic control of composition, annealing temperature and time.

Multi-metallic alloy nanoparticles (NPs) can offer additional opportunities for modifying the electronic, optical and catalytic properties by the control of composition, configuration and size of individual nanostructures that are consisted of more than single element. In this paper, the fabrication of bimetallic Pd-Ag NPs is systematically demonstrated via the solid state dewetting of bilayer thin films on c-plane sapphire by governing the temperature, time as well as composition. The composition of Pd-Ag bilayer remarkably affects the morphology of alloy nanostructures, in which the higher Ag composition, i.e. Pd0.25Ag0.75, leads to the enhanced dewetting of bilayers whereas the higher Pd composition (Pd0.75Ag0.25) hinders the dewetting. Depending on the annealing temperature, Pd-Ag alloy nanostructures evolve with a series of configurations, i.e. nucleation of voids, porous network, elongated nanoclusters and round alloy NPs. In addition, with the annealing time set, the gradual configuration transformation from the elongated to round alloy NPs as well as size reduction is demonstrated due to the enhanced diffusion and sublimation of Ag atoms. The evolution of various morphology of Pd-Ag nanostructures is described based on the surface diffusion and inter-diffusion of Pd and Ag adatoms along with the Ag sublimation, Rayleigh instability and energy minimization mechanism. The reflectance spectra of bimetallic Pd-Ag nanostructures exhibit various quadrupolar and dipolar resonance peaks, peak shifts and absorption dips owing to the surface plasmon resonance of nanostructures depending on the surface morphology. The intensity of reflectance spectra is gradually decreased along with the surface coverage and NP size evolution. The absorption dips are red-shifted towards the longer wavelength for the larger alloy NPs and vice-versa.

Kinetics models describing degradation-relaxation effects in nanoinhomogeneous substances

The mathematical models of degradation-relaxation kinetics are considered for jammed systems composed of screen-printed spinel Cu0.1Ni0.1Co1.6Mn1.2O4 and conductive Ag or Ag-Pd alloys. Structurally-intrinsic nanoinhomogeneities due to Ag and Ag-Pd diffusants embedded in spinel phase environment are shown to define governing kinetics of thermally-induced degradation obeying an obvious non-exponential behaviour in the resistance drift. The stretched-to-compressed exponential crossover is detected for degradation-relaxation kinetics in these systems with conductive contacts made of Ag-Pd and Ag alloys. Under essential migration of conductive phase, the resulting kinetics is though to be considerable two-step diffusing process originated from Ag penetration deep into spinel ceramics.

Methanol Steam Reforming over ZrO2-Supported Catalysts in Conventional and Membrane Reactors

Results of a study of the methanol steam reforming (MSR) catalytic process in conventional flow and membrane reactors in the presence of Ni0.2–Cu0.8 and Ru0.5–Rh0.5 catalysts supported on ZrO2 with a monoclinic, tetragonal, and cubic structure have been described. The cubic structure of zirconia has been stabilized with ceria. The samples have been characterized by X-ray diffraction analysis, transmission electron microscopy, and the BET method. It has been shown that the catalytic activity of the composites depends on the type of the metals and the structure of the support. It has been found that the Ru–Rh/Ce0.1Zr0.9O2–δ catalyst exhibits the highest activity, whereas Cu–Ni/Ce0.1Zr0.9O2–δ is the most selective. A comparative study of the MSR process in conventional and membrane reactors with Pd–Ru and modified Pd–Ag membranes has been conducted. The membrane process with a membrane based on a Pd–Ag alloy in the presence of the Ru–Rh/Ce0.1Zr0.9O2–δ catalyst provides a ~50% increase in the hydrogen yield.

Synthesis of Pd-Ag Membranes by Electroless Plating for H 2 Separation

Both sequential-deposition and co-deposition based on electroless plating method for the preparation of Pd-Ag composite membranes were investigated. The morphology, phase structure, compositional homogeneity and compactness of the prepared membranes were compared. The results show that Pd-Ag membranes prepared by co-deposition are dendritic, inhomogeneous, and poorly compact, while those by multilayer sequential deposition are more homogeneous and compact. The multi-layer sequential deposition requires higher temperature and longer time for annealing to form Pd-Ag alloy. The Pd particles size is decreased by separate Ag layer and the surface of Pd-Ag membrane is smoother.

Hydrogen and Deuterium Solubility in Commercial Pd–Ag Alloys for Hydrogen Purification

Pd–Ag alloys with compositions close to 23–25% Ag are considered as a benchmark for hydrogen permeability. They are used in small scale reactors for hydrogen separation and purification. Permeability and solubility are strictly mathematically correlated, and the temperature dependence of solubility can provide useful information about the physical state of the material, the hydrogenation enthalpy, and the occurrence of different thermodynamic states. While the permeability of Pd–Ag alloys has been largely investigated, solubility measurements are available only in a restricted temperature range. In this paper, we extend solubility measurements up to 7 bar for Pd77Ag23 in the temperature range between 25 °C and 400 °C and for Pd30Ag70 for temperatures between 190 °C and 300 °C. The occurrence of solid solutions or hydride phases is discussed, and the hydrogenation enthalpy is calculated.

Hollow Pd-Ag Composite Nanowires for Fast Responding and Transparent Hydrogen Sensors.

Pd based alloy materials with hollow nanostructures are ideal hydrogen (H2) sensor building blocks because of their double-H2 sensing active sites (interior and exterior side of hollow Pd alloy) and fast response. In this work, for the first time, we report a simple fabrication process for preparing hollow Pd-Ag alloy nanowires (Pd@Ag HNWs) by using the electrodeposition of lithographically patterned silver nanowires (NWs), followed by galvanic replacement reaction (GRR) to form palladium. By controlling the GRR time of aligned Ag NWs within an aqueous Pd2+-containing solution, the compositional transition and morphological evolution from Ag NWs to Pd@Ag HNWs simultaneously occurred, and the relative atomic ratio between Pd and Ag was controlled. Interestingly, a GRR duration of 17 h transformed Ag NWs into Pd@Ag HNWs that showed enhanced H2 response and faster sensing response time, reduced 2.5-fold, as compared with Ag NWs subjected to a shorter GRR period of 10 h. Furthermore, Pd@Ag HNWs patterned on the colorless and flexible polyimide (cPI) substrate showed highly reversible H2 sensing characteristics. To further demonstrate the potential use of Pd@Ag HNWs as sensing layers for all-transparent, wearable H2 sensing devices, we patterned the Au NWs perpendicular to Pd@Ag HNWs to form a heterogeneous grid-type metallic NW electrode which showed reversible H2 sensing properties in both bent and flat states.

Three-dimensional finite element analysis of glass fiber and cast metal posts with different alloys for reconstruction of teeth without ferrule

The aim of this study was to evaluate different materials for restoration of teeth without ferrule by three-dimensional (3D) finite element analysis (FEA). Five models simulating the maxillary central incisor and surrounding bone were simulated according to the type of post: glass fibre post (GFP) or cast metal post (CMP) with different alloys such as gold (Au), silver–palladium (AgPd), copper–aluminum (CuAl) and nickel–chromium (NiCr). Models were designed using Invesalius and Rhinoceros. FEAs were made using FEMAP and NeiNastran, with an applied axial force of 100 N and oblique occlusal load at 45°. Stress distribution among groups was analysed by two-way analysis of variance (ANOVA), followed by post-hoc Tukey’s test. The GFP showed the best stress distribution in the post, followed by CMP with Au, AgPd, CuAl and NiCr alloys, respectively (p < .001). No statistically significant difference in the stress distribution in teeth was found under application of axial load (p > .05). Under oblique load, the GFP generated the highest values of tension among the models, followed by the CMP with NiCr alloy than other models (p < .001). The use of GFP resulted in a lower stress concentration in the post, but increased stress in the tooth without ferrule. The CMP with NiCr alloy exhibited the highest stress distribution among other CMP. To avoid higher stress in teeth, alloys of Au, AgPd and CuAl, respectively, are recommended.

Catalytic Pd–Ag nanoparticles immobilized on fiber glass by surface self-propagating thermal synthesis

Pd–Ag nanoparticles with different Pd/Ag ratio were deposited onto fiber glass by using the technique of surface self-propagating thermal synthesis (SSTS) and characterized by X-ray photoelectron spectroscopy (XPS), atomic absorption spectroscopy (ААS), and EXAFS spectroscopy. The samples reduced in hydrogen exhibited the formation of Pd–Ag alloy whose tentative structure and composition were suggested. Thermally scheduled reduction of Pd–Ag catalysts in hydrogen made the Ag atoms partially oxidized. Reported are the catalytic properties of synthesized Pd–Ag samples in selective hydrogenation of acetylene.

Potentiodynamic polarization study of the corrosion behavior of palladium-silver dental alloys

Statement of problemAlthough palladium-silver alloys have been marketed for over 3 decades for metal-ceramic restorations, understanding of the corrosion behavior of current alloys is incomplete; this understanding is critical for evaluating biocompatibility and clinical performance. PurposeThe purpose of this in vitro study was to characterize the corrosion behavior of 3 representative Pd-Ag alloys in simulated body fluid and oral environments and to compare them with a high-noble Au-Pd alloy. The study obtained values of important electrochemical corrosion parameters, with clinical relevance, for the rational selection of casting alloys. Material and methodsThe room temperature in vitro corrosion characteristics of the 3 Pd-Ag alloys and the high-noble Au-Pd alloy were evaluated in 0.9% NaCl, 0.09% NaCl, and Fusayama solutions. After simulated porcelain firing heat treatment, 5 specimens of each alloy were immersed in the electrolytes for 24 hours. For each specimen, the open-circuit potential (OCP) was first recorded, and linear polarization was then performed from –20 mV to +20 mV (versus OCP) at a rate of 0.125 mV/s. Cyclic polarization was subsequently performed on 3 specimens of each alloy from –300 mV to +1000 mV and back to –300 mV (versus OCP) at a scanning rate of 1 mV/s. The differences in OCP and corrosion resistance parameters (zero-current potential and polarization resistance) among alloys and electrolyte combinations were compared with the 2-factor ANOVA (maximum-likelihood method) with post hoc Tukey adjustments (α=.05). ResultsThe 24-hour OCPs and polarization resistance values of the 3 Pd-Ag alloys and the Au-Pd alloy were not significantly different (P=.233 and P=.211, respectively) for the same electrolyte, but significant differences were found for corrosion test results in different electrolytes (P<.001 and P=.032, respectively). No significant interaction was found between the factors of alloy and electrolyte (P=.249 and P=.713, respectively). The 3 Pd-Ag silver alloys appeared to be resistant to chloride ion corrosion, and passivation and de-alloying were identified for these alloys. ConclusionsThe Pd-Ag alloys test results showed excellent in vitro corrosion resistance and were equivalent to those of the high-noble Au-Pd alloy in simulated body fluid and oral environments. Passivation, de-alloying, and formation of a AgCl layer were identified as possible corrosion mechanisms for Pd-Ag alloys.

Selective hydrogenation of mixed alkyne/alkene streams at elevated pressure over a palladium sulfide catalyst

The Pd4S phase of palladium sulfide is known to be a highly selective alkyne hydrogenation catalyst at atmospheric pressure. Results presented here demonstrate that high selectivity can be retained at the elevated pressures required in industrial application. For example, in a mixed acetylene/ethylene feed, 100% conversion of acetylene was attained with a selectivity to ethylene in excess of 80% at 18bar pressure. Similarly, almost 85% selectivity can be obtained with mixed C3 feeds containing methyl acetylene, propadiene, propylene and propane at 18bar pressure. Using a low loaded sample (0.1wt% Pd) it was possible to estimate the TOF to be 27s−1. High selectivity was related to the crystal structure of Pd4S with the unique spatial arrangement thought to favour Pd atoms acting in isolation from one another. Based on these results, it is proposed that this catalyst could be a potential replacement for PdAg alloys currently used by industry.

Green synthesis of silver and palladium nanoparticles using Lithodora hispidula (Sm.) Griseb. (Boraginaceae) and application to the electrocatalytic reduction of hydrogen peroxide

Biosynthesis of silver and palladium nanoparticles was carried out by using Lithodora hispidula (Sm.) Griseb. Leaf extract as a reducing agent. The silver and palladium nanoparticles (NPs) were characterized by UV-Visible spectroscopy, inductively coupled Plasma-Mass Spectrometer, X-ray diffraction, scanning electron microscopy and energy-dispersive X-ray analysis. UV-Vis spectra of biosynthesized silver nanoparticles showed an absorption band at 425 nm. The formation of palladium nanoparticles was confirmed by the disappeared absorption band at 410 nm. Scanning electron microscopy analysis showed that Ag, AgPd spherical and Pd nanoparticle morphology were rod in shape. The electrochemical behaviour of Ag, Pd and AgPd alloy nanoparticles were investigated by cyclic voltammetry. Modified glassy carbon electrodes were constructed by using Ag, Pd and AgPd nanoparticles and used in electrocatalytic reduction of hydrogen peroxide in phosphate buffer medium (pH = 6.5), in potential range of 0.0 and -0.8 V vs. Ag/AgCl at 100 mV/s scan rate. The AgPdNPs-GCE based sensor could detect the H2O2 in the linear range of 0.02–5.0 mM with a detection limit of 0.52 μM. The AgPdNPs-GCE showed a good repeatability and stability for detection of H2O2. Furthermore, it exhibited no interference with some biological species such as glucose, ascorbic acid and uric acid.

Characterization Microstructural and Electrochemical of AgPd Alloy Bimetallic Nanoparticles

ABSTRACTBimetallic nanoparticles are of special interest for their potential applications to fuel cells, among the bimetallic systems, AuPd bimetallic nanoparticles have received great interest as they can be widely used as effective catalysts for various electrochemical reactions. Monodisperse AgPd alloy nanoparticles were synthesized by polyol method using silver nitrate and potassium tetrachloropalladate(II) in ethylene glycol as the reducing agent at 160 °C. Structural, compositional and electrochemical characterizations of synthesized bimetallic nanoparticles were investigated. High-angle annular dark field scanning/transmission electron microscopy (HAADF-STEM) images and parallel beam X-ray diffraction (XRD) of the bimetallic nanoparticles were obtained. XRD and the contrast of the HAADF-STEM images show that the bimetallic nanoparticles have an alloy structure. Cyclic voltammetry was carried out in order to confirm the electrochemical responses of the AgPd/C electrocatalysts for methanol oxidation. Thanks to the narrow size distribution of the AgPd alloy bimetallic nanoparticles (9.15 nm) the supported AgPd/C electrocatalysts have high catalytic activity toward methanol electro-oxidation.

Decoration of Carbon Nitride Surface with Bimetallic Nanoparticles (Ag/Pt, Ag/Pd, and Ag/Au) via Galvanic Exchange for Hydrogen Evolution Reaction

Here, we propose the synthesis of AgPt, AgPd, and AgAu bimetallic nanoparticles (NPs) on a carbon nitride (C3N4) surface via a galvanic exchange technique for the hydrogen evolution reaction (HER). Prior to the synthesis of C3N4/AgPt, AgPd, and AgAu, Ag NPs were synthesized on a C3N4 surface. For the synthesis of Ag NPs, initially Ag+ ions were adsorbed and then reduced by NaBH4 resulting in the decoration of Ag NPs. These Ag NPs were then subjected to galvanic exchange where sacrificial Ag was replaced by Pt2+, Pd2+, and Au3+ to fabricate AgPt, AgPd, and AgAu NPs. The galvanic exchange reaction occurs on a solid substrate, which favored slow exchange of Ag and resulted in the transformation of Ag into AgPt, AgPd, and AgAu alloys. The synthesized heterostructures were characterized with the help of PXRD, XPS, TEM, FESEM, and EDS techniques. All the materials were applied for hydrogen evolution using 0.5 M H2SO4 solution. C3N4/AgPt shows efficient electrocatalytic activity as it requires only −150 mV poten...

Mechanical property and hydrogen permeability of ultrafine-grained Pd–Ag alloy processed by high-pressure torsion

A process of high-pressure torsion (HPT) was used to produce an ultrafine-grained Pd–Ag alloy, and to improve mechanical property and hydrogen permeability simultaneously. Hardness values of the HPT-processed sample were much higher than those of a cold-rolled sample which is strengthened by dislocation accumulation. Additionally, in contrast to the degradation of hydrogen permeability in the cold-rolled sample due to a high density of dislocations which act as trapping sites of hydrogen atoms, the hydrogen permeability in the HPT-processed sample was improved due to a high density of high-angle grain boundaries which act as a fast diffusion path. The ultrafine-grained structure in the Pd–Ag alloy was retained during permeation testing at 300 °C due to the addition of silver.