Pd-rich Alloys Research Articles

Machine learning search for stable binary Sn alloys with Na, Ca, Cu, Pd, and Ag.

We present our findings of a large-scale screening for new synthesizable materials in five M-Sn binaries, M = Na, Ca, Cu, Pd, and Ag. The focus on these systems was motivated by the known richness of M-Sn properties with potential applications in energy storage, electronics packaging, and superconductivity. For the systematic exploration of the large configuration space, we relied on our recently developed MAISE-NET framework that constructs accurate neural network interatomic potentials and utilizes them to accelerate ab initio global structure searches. The scan of over two million candidate phases at a fraction of the typical ab initio calculation cost has uncovered 29 possible intermetallics thermodynamically stable at different temperatures and pressures (1 bar and 20 GPa). Notable predictions of ambient-pressure materials include a simple hP6-NaSn2 phase, fcc-based Pd-rich alloys, tI36-PdSn2 with a new prototype, and several high-temperature Sn-rich ground states in the Na-Sn, Cu-Sn, and Ag-Sn systems. Our modeling work also involved ab initio (re)examination of previously observed M-Sn compounds that helped explain the entropy-driven stabilization of known Cu-Sn phases. The study demonstrates the benefits of guiding structure searches with machine learning potentials and significantly expands the number of predicted thermodynamically stable crystalline intermetallics achieved with this strategy so far.

Emergent properties from CuPd alloy films under near-infrared excitation

Noble-transition metal alloys offer emergent optical and electronic properties for near-infrared (NIR) optoelectronic devices. We investigate the optical and electronic properties of CuxPd1-x alloy thin films and their ultrafast electron dynamics under NIR excitation. Ultraviolet photoelectron spectroscopy measurements supported by density functional theory calculations show strong d-band hybridization between the Cu 3d and Pd 4d bands. These hybridization effects result in emergent optical properties, most apparent in the dilute Pd case. Time-resolved terahertz spectroscopy with NIR (e.g., 1550nm) excitation displays composition-tunable electron dynamics. We posit that the negative peak in the normalized increment of transmissivity (ΔT/T) below 2ps from dilute Pd alloys is due to non-thermalized hot-carrier generation. On the other hand, Pd-rich alloys exhibit an increase in ΔT/T due to thermalization effects upon ultrafast NIR photoexcitation. CuxPd1-x alloys in the dilute Pd regime may be a promising material for future ultrafast NIR optoelectronic devices.

Effect of composition and thermal history on deformation behavior and cluster connections in model bulk metallic glasses

The compositional dependence and influence of relaxation state on the deformation behavior of a Pt–Pd-based bulk metallic glasses model system was investigated, where platinum is systematically replaced by topologically equivalent palladium atoms. The hardness and modulus increased with rising Pd content as well as by annealing below the glass transition temperature. Decreasing strain-rate sensitivity and increasing serration length are observed in nano indentation with increase in Pd content as well as thermal relaxation. Micro-pillar compression for alloys with different Pt/Pd ratios validated the greater tendency for shear localization and brittle behavior of the Pd-rich alloys. Based on total scattering experiments with synchrotron X-ray radiation, a correlation between the increase in stiffer 3-atom cluster connections and reduction in strain-rate sensitivity, as a measure of ductility, with Pd content and thermal history is suggested.

Effect of the Alloying Metal on the Corrosion Resistance of Pd-Rich Binary Alloys with Pt, Rh, and Ru in Sulfuric Acid.

The paper presents the study of the corrosion resistance of electrodeposited Pd and its binary alloys with Pt, Rh, and Ru on a polycrystalline Au substrate. The corrosion resistance was tested in 0.5 M sulfuric acid at room temperature using potentiodynamic polarization and electrochemical impedance spectroscopy techniques. The morphology/composition and work function values were determined by scanning electron microscopy/energy–dispersive X–ray spectroscopy and scanning Kelvin probe, respectively. The obtained results revealed that the Pd electrode is the most resistant to corrosion, whereas the Pd-Ru electrode is the most susceptible to dissolution. It was found that the corrosion resistance of Pd-binary alloys decrease in the following order: Pd > Pd-Pt > Pd-Rh > Pd-Ru. This effect was assigned mainly to the difference in surface roughness factor of tested electrodes.

Conducting Polymer-Based Nanohybrids for Fuel Cell Application.

Carbon materials such as carbon graphitic structures, carbon nanotubes, and graphene nanosheets are extensively used as supports for electrocatalysts in fuel cells. Alternatively, conducting polymers displayed ultrahigh electrical conductivity and high chemical stability havegenerated an intense research interest as catalysts support for polymer electrolyte membrane fuel cells (PEMFCs) as well as microbial fuel cells (MFCs). Moreover, metal or metal oxides catalysts can be immobilized on the pure polymer or the functionalized polymer surface to generate conducting polymer-based nanohybrids (CPNHs) with improved catalytic performance and stability. Metal oxides generally have large surface area and/or porous structures and showed unique synergistic effects with CPs. Therefore, a stable, environmentally friendly bio/electro-catalyst can be obtained with CPNHs along with better catalytic activity and enhanced electron-transfer rate. The mass activity of Pd/polypyrrole (PPy) CPNHs as an anode material for ethanol oxidation is 7.5 and 78 times higher than that of commercial Pd/C and bulk Pd/PPy. The Pd rich multimetallic alloys incorporated on PPy nanofibers exhibited an excellent electrocatalytic activity which is approximately 5.5 times higher than monometallic counter parts. Similarly, binary and ternary Pt-rich electrocatalysts demonstrated superior catalytic activity for the methanol oxidation, and the catalytic activity of Pt24Pd26Au50/PPy significantly improved up to 12.5 A per mg Pt, which is approximately15 times higher than commercial Pt/C (0.85 A per mg Pt). The recent progress on CPNH materials as anode/cathode and membranes for fuel cell has been systematically reviewed, with detailed understandings into the characteristics, modifications, and performances of the electrode materials.

Magnetic field direction dependence of topological Hall effect like features in synthetic ferromagnetic and antiferromagnetic multilayers

The anomalies in the transverse resistivity are usually thought to be Topological Hall Effects (THEs), which have been considered as the trait of topologically nontrivial spin textures, such as the skyrmion phase. However, the origin of the THE-like features is still under debate. Here, we present the observation of THE-like features in synthetic antiferromagnetic [Pd/Co]/Ru/[Co/Pd] and synthetic ferromagnetic [Pd/Co]/NiO/[Co/Pd] structures. The Pd-rich alloys, which are formed due to the heterogeneous component and the gradual intermixing at the Co/Pd interface, result in a negative anomalous Hall effect coefficient, causing the peak and dip features in transport measurements. By changing the external magnetic field from out-of-plane to in-plane, the magnitude and width of the bump feature in THE curves can be modified, which is caused by the different anisotropy energy of the components in the heterogeneous ferromagnets. The present work broadens the perception of THE-like features and may add a different dimension to understand the magnetization reversal in magnetic multilayers.

Positive vs negative resistance response to hydrogenation in palladium and its alloys

Resistive solid state sensors are widely used in multiple applications, including molecular and gas detection. The absorption or intercalation of the target species varies the lattice parameters and an effective thickness of thin films, which is usually neglected in the analyses of their transport properties in general and the sensor response in particular. Here, we explore the case of palladium-based thin films absorbing hydrogen and demonstrate that the expansion of thickness is an important mechanism determining the magnitude and the very polarity of the resistance response to hydrogenation in high resistivity films. The model of the resistance response that takes into account the modifications of thickness was tested and confirmed in three Pd-based systems with variable resistivity: thin Pd films above and below the percolation threshold, thick Pd–SiO2 granular composite films with different contents of silica, and Pd-rich CoPd alloys where resistivity depends on the Co concentration. The superposition of the bulk resistivity increase due to hydride formation and the decrease in the film resistance due to the thickness expansion provides a consistent explanation of the hydrogenation response in both continuous and discontinuous films with different structures and compositions.

A possibility of Pd based high entropy alloy for hydrogen gas sensing applications

Diffusion of H atoms in Pd-based alloy usually takes place through octahedral voids for face centered cubic (FCC) metals and alloys. Transition metals are preferred as the alloying element for Pd-based alloy because electron removal and addition from Pd, and the number of vacant d-states of Pd can be regulated by lacking the deformation of electronic structure of Pd. In addition, the alloying alters a lattice constant and hydrogen permeability, thereby improving the mechanical, chemical stabilities of Pd-based devices and reduce the expensive cost of Pd raw material. High entropy alloys (HEA) have been investigated as an important contributor in field of microelectronics as a catalyst, diffusion barrier, and anode materials for a solid oxide fuel cell (SOFC). HEA’s of Pd, Ag, Ni, Cu, Au, Rh, Pt and Ir are designed empirically and their lattice constants, corresponding an octahedral void size are analyzed with pure Pd, thus suggesting them as a potential candidate for hydrogen storage applications in the future. The core reason for designing HEA is to overcome the problem of cost and availability of Pd and Pd-rich binary alloys. In this paper, we calculated the lattice parameters using the Vergards law, octahedral void size, lattice distortion and cost for PdAg-based HEA’s of 20 combinations.

Preparation of compact and porous Pd-Ni alloys and study of their performances for ethanol oxidation in alkali

Electrodeposition and galvanic displacement reactions are used to prepare compact and porous Pd-Ni alloys and heterogeneous bilayer structures Pd/Ni or Pd/Pd-Ni. Pd is present in the deposits either as a pure metal or in solid solutions with Ni. Electrode activity in ethanol oxidation and Pd surface area are estimated by cyclic voltammetry. Results show that, in a first approximation, the peak current of ethanol oxidation is simply proportional to the Pd area, regardless of samples morphology, structure and composition, for the entire series of samples. Deviations from the proportionality relation indicate that Pd and Pd-rich alloys are more active than Ni-rich alloys of same Pd surface.

Accuracy of Real Space Cluster Expansion for Total Energies of Pd-rich PdX (X=Rh, Ru) Alloys, based on Full-Potential KKR Calculations for Perfect and Impurity Systems

We study the accuracy and convergence of the real space cluster expansion (RSCE) for the total energies of the Pd-rich PdX (X=Ru, Rh) alloys, which are used to study the phase stability and phase equilibria of the Pd-rich PdX alloys. In the present RSCE, the X atoms of minor element are treated as impurities in Pd. Then-body interaction energies (IEs) among X impurities in Pd, being used in the expansion of the total energies of the Pd-rich PdX alloys, are determined uniquely and successively from the low body to high body, by the full-potential Korringa-Kohn-Rostoker (FPKKR) Green's function method (FPKKR) for the perfect and impurity systems (Pd-host and Xnin Pd,n=1~4), combined with the generalized gradient approximation in the density functional theory. In the previous paper, we showed that the RSCE, in which the perturbed potentials due to the insertion of Xnimpurities in Pd were redetermined self-consistently up to the first-nearest neighboring (nn) host atoms around Xnimpurities, reproduce fairly well (the error of ~ 0.2mRy per atom) the FPKKR-band-calculation result of the ordered Pd3Rh alloy in L12structure, but a little wrongly (the error of ~ 0.7mRy per atom) for the ordered Pd3Ru alloy in L12structure. In the present paper, we show that this small RSCE error for the Pd3Ru alloy is corrected very well (from ~ 0.7mRy to ~ 0.1mRy per atom) by enlarging the self-consistent region for the perturbed potentials up to the 2nd-nn host atoms around Run impurities in Pd. We also clarify the correction for each value of the n-body (n=1~ 4) IEs.

Dihydride formation in the palladium–rhodium alloys under high hydrogen pressure

Palladium, rhodium and their alloys were studied in a diamond anvil cell in a high pressure hydrogen atmosphere up to 20 GPa by X-ray diffraction at room temperature. Formation of a monohydride with H/(Rh + Pd) = 1 ratio was observed for each alloy at hydrogen pressures less than 3 GPa. The corresponding volume expansion of the metal lattice was 2.2–2.8 Å3 per metal atom. A formation of the dihydride with H/(Rh + Pd) = 2 was observed at a hydrogen pressure around 10 GPa for the alloys with rhodium content Rh/(Rh + Pd) ≥ 50 at.%. The dihydride formation is accompanied by a volume expansion of metal lattice by 3.2–3.9 Å3 per metal atom. For Pd-rich alloys with Rh/(Rh + Pd) ≤ 25 at.% and pure Pd the dihydride formation was not observed up to maximum reached hydrogen pressure. All observed phases had a fcc structure of metal lattice.

One-pot synthesis of tailored Pd–Co nanoalloy particles confined in mesoporous carbon

The synthesis of mesoporous carbon with confined PdCo nanoalloy particles by a one-pot soft-template approach is reported herein. The influence of metal precursor type, metal composition and annealing temperature on the carbon@PdCo material characteristics was systematically investigated. Small and homogeneously distributed PdCo nanoparticles in the carbon matrix were achieved. The PdCo particle size could be tuned from 8 to 25 nm and the metal composition proved to be the main parameter controlling the size. When the amount of Pd is low (Pd50Co50) the particle is small and increases with the increase of temperature. On the contrary, for richer Pd contents (Pd75Co25, Pd90Co10) the particle size is larger but they exhibit extremely high stability with no obvious modification of size between 450 and 800 °C. The tuned experimental parameters had less impact on the materials textural characteristics, they exhibit similar surface area and uniform pore size distribution. Among the materials, only the Pd rich alloys (Pd90Co10) are able to form metallic hydride and consequently, showing the highest hydrogen adsorption capacity.

Estimating Bulk-Composition-Dependent H2 Adsorption Energies on CuxPd1–x Alloy (111) Surfaces

The bulk-composition-dependent dissociative adsorption energy of hydrogen on CuPd alloys has been measured experimentally and modeled using density functional theory. The hydrogen adsorption energy cannot be simply defined by a single reactive site or as a composition weighted average of the pure metal components. We developed a modeling approach that uses a basis of active sites weighted by a model site probability distribution to estimate a bulk-composition-dependent adsorption energy. The approach includes segregation under reaction conditions. With this method, we can explain the composition-dependent adsorption energy of hydrogen on Cu-rich alloy surfaces. In Pd-rich alloys, a Pd-hydride phase may form, which results in deviations from trends on the metallic alloy surface.

Characterization of Continuous and Discontinuous Precipitation Phases in Pd-Rich Precious Metal Alloys

Aberration-corrected scanning transmission electron microscopy (AC-STEM), X-ray diffraction (XRD), electron backscatter diffraction, and electron probe microanalysis were applied to characterize continuous and discontinuous phase formation in precious metal alloys used in electrical contacts. The Pd-rich Paliney® (®Paliney is tradename of Deringer-Ney Inc., Bloomfield, CT) alloys contain Pd, Ag, Cu, Au, Pt (and Zn or Ni). With aging at 755 K (482 °C), nanometer-scale chemistry modulation was observed indicating spinodal decomposition. An ordered body-centered tetragonal (bct) structure was also observed with AC-STEM after the 755 K (482 °C) aging treatment and another phase, tentatively identified as β-Cu3Pd4Zn, was found by microscopy and XRD after prolonged holds at higher temperatures. During slow cooling or isothermal holds at high temperature [755 K to 973 K (482 °C to 700 °C)], a two-phase lamellar structure develops along grain boundaries by discontinuous precipitation. XRD and AC-STEM showed that the lamellar structure was comprised of Ag-rich and Cu-rich fcc phases (α 1 and α 2). The phases are discussed in relation to a pseudo-ternary diagram based on Ag-Cu-Pd, which provides a simplified representation of the discontinuous phase compositions in the multi-component alloy system.

Characterization and electrochemical behavior of Pd-rich Pd-Ru alloys

Thin layers (0.1–5μm) of Pd-rich Pd-Ru alloys were prepared by potentiostatic electodeposition from baths containing aqueous solutions of RuCl3 and PdCl2 with HCl. Alloy bulk compositions were determined by atomic emission spectroscopy and energy dispersive analysis of X-rays. The crystal structure of the deposits was examined by X-ray diffraction. Alloy surface morphology was characterized by scanning electron microscopy and atomic force microscopy. Surface compositions were determined by X-ray photoelectron spectroscopy. General electrochemical behavior of Pd-Ru deposits was investigated using cyclic voltammetry. The processes of alloy surface oxidation and hydrogen adsorption/absorption were studied in 0.5M H2SO4 solutions at 298K. It was found that homogeneous fcc alloys were formed by Pd and Ru with the lattice parameter smaller than that of pure Pd.

Aerobic oxidative coupling of alcohols and amines over Au–Pd/resin in water: Au/Pd molar ratios switch the reaction pathways to amides or imines

A facile switch of the reaction pathways of aerobic oxidative coupling of alcohols and amines from amidation to imination was realized for the first time by tuning the Au/Pd ratios in ion-exchange resin supported Au–Pd alloy catalysts (Au–Pd/resin). Amides were obtained with high yields on Au6Pd/resin while imines were obtained over AuPd4/resin. Various alcohols and amines underwent oxidative coupling smoothly in water to afford the desired products with good to excellent yields. Further investigation on the reaction mechanism suggested the synergistic effect between Au and Pd determined the adsorption strength of the aldehyde intermediate, which in turn dictated the reaction pathways. That is, on Au-rich alloys (e.g., Au6Pd) absorbed aldehyde species was formed, followed by further oxidation to yield amides, while on Pd-rich alloys (e.g., AuPd4), free aldehyde was generated, which then underwent condensation with amines to produce imines. The discovery might provide avenues to develop new efficient catalysts for the green synthesis of special chemicals.

Magnetotransport in Pd-Rich PdFe Alloys

The transport properties of Pd-rich PdFe alloys are investigated as a function of the atomic and magnetic orders on the L21 (Cu3Au) lattice. The residual resistivity, anisotropic magnetoresistance (AMR), and anomalous Hall effect are calculated from first-principles as a function of the atomic order. The calculations are based on the relativistic generalization of the transport Kubo–Greenwood approach as formulated in the framework of the first principles TB-LMTO method and Coherent Potential Approximation (CPA). The effect of the thermal magnetic disorder on the resistivity and AMR has been also studied using the disordered local moment approach based on the CPA. Our results are in an overall good agreement with available experimental data.

Effects of atomic and magnetic order on electronic transport in Pd-rich Pd-Fe alloys

The transport properties of Pd-rich PdFe alloys are investigated as a function of the atomic and magnetic order on the L2${}_{1}$ (Cu${}_{3}$Au) lattice. The residual resistivity, anisotropic magnetoresistance (AMR), and anomalous Hall effect are calculated from first principles in their dependence on the degree of atomic order. The calculations are based on the relativistic generalization of the transport Kubo-Greenwood approach as formulated in the framework of the first-principles tight-binding linear muffin-tin orbital (TB-LMTO) method and coherent potential approximation (CPA). The effect of the thermal magnetic disorder on the resistivity (thermal magnetoresistance) and AMR has been also studied using the disordered local moment approach based on the CPA. It is found that the experimentally observed fast decrease of AMR ratio with temperature can be mostly ascribed to the spin disorder effects. Our results are in an overall good agreement with available experimental data.

X-ray Diffraction Study of the Ordered Structures and Phase Relation in Pd-Mn Alloy System

This paper reports the results of structural study on the ordered phases formed in Pd-rich Pd-Mn alloys adopting X-ray powder diffraction method. Formations of the tetragonal D023-type Pd3Mn, orthorhombic Pd2Mn and orthorhombic Pd5Mn3 reported by previous researchers have been confirmed. Rietveld refinement of the diffraction data of the latter two phases has determined precisely the atomic parameters and revealed the significance of the shifts of atoms in Pd2Mn. It is shown that the L10-type phase extends to about 33 at% Mn at high temperatures and Pd2Mn and Pd5Mn3 form via two-step ordering from the L10-type phase. A revised phase diagram on the Pd-rich side has been proposed. Discussion is given on the stability of the relevant ordered phases by making calculation of the total energy by the density functional method.

Biphasic Pd−Au Alloy Catalyst for Low-Temperature CO Oxidation

Low-temperature CO oxidation over a compositional series of Pd-Au nanoalloy catalysts supported on silica fume was studied. Except for the pure metals, these materials invariably showed biphasic separation into palladium- and gold-rich components. Performance was optimal for a catalyst of bulk composition Pd(4)Au(1), a mixture of Pd(90)Au(10) (72.5 at. %) and Pd(31)Au(69) (27.5 at. %), that was remarkably active at 300 K and more stable than a pure Au catalyst. For bulk materials dominated by Pd (Pd:Au = 16:1; 8:1; 4:1), the palladium-rich alloy fraction frequently adopted hollow sphere or annular morphology, while the gold-rich crystals were often multiply twinned. Quantitative powder X-ray diffraction (XRD) showed that under the synthesis conditions used, the Au solubility limit in Pd crystals was approximately 12 at. %, while Pd was more soluble in Au (approximately 31 at. %). This was consistent with X-ray photoelectron spectroscopy (XPS), which revealed that the surfaces of Pd-rich alloys were enriched in gold relative to the bulk composition. In situ Fourier transform infrared spectra collected during CO oxidation contained a new band at 2114 cm(-1) (attributed to linear CO-Au/Au-Pd bonds) and reduced intensity of a band at 2090 cm(-1) (arising from a linear CO-Pd bond) with escalating Au content, indicating that the Pd sites became increasingly obscured by Au. High-resolution electron micrographs (HRTEM) of the Pd-rich alloys revealed atomic scale surface defects consistent with this interpretation. These results demonstrate that gold-containing biphasic Pd nanoalloys may be highly durable alternatives for a range of catalytic reactions.