Palladium Alloy Research Articles

(Invited) Time-Resolved Dissolution Analysis of Precious Metals Using a Solution Flow Cell Combined with ICP-MS

Introduction Platinum (Pt), palladium (Pd), and Pt-Pd alloys exhibit excellent catalytic activity for oxygen reduction reaction;1 thus, they are expected to be used as cathode catalyst in polymer electrolyte fuel cell (PEFC). However, one of the problems is their dissolution under PEFC operating condition. A measurement system, an inductively coupled plasma-mass spectrometer (ICP-MS) combined with solution flow cell, is proposed to detect dissolved ions, and time and potential-resolved measurement for metals could be possible under potential cycling using this system.2 Even though the trivial dissolution of Pt and Pd lead to a performance loss of PEFC, improvement of detection sensitivity is required for the system. In this study, we firstly developed a new system, ICP-MS combined with the commercially available flow cell, to improve detection sensitivity. Then the time-resolved measurement of dissolution rates of Pt and Pd was conducted with high detection sensitivity. Experimental Cross-flow cell (BAS Inc.) was employed for the experiments. Pt or Pd as a working electrode and glassy carbon as a counter electrode were embedded in the cell together. Screw type Ag/AgCl electrode (RE-3VT, BAS Inc.) was used as a reference electrode. A silicon gasket was used to form the flow circuit whose shape is elliptical with a 100 μm thickness, and a test solution (0.5 M H2SO4) flew in the circuit at a rate of 110 μL min-1. The outlet of the cell directly connected ICP-MS (7700x, Agilent Technology), and time-resolved measurements of Pt and Pd were conducted under potentiostatic polarization and potential cycling. Detection limits of Pt and Pd using this system were confirmed to be 0.13, 0.39 pg cm‒2 s‒1, which was lower than those using the previous system. 2 Results and Discussion Firstly, Pt or Pd was polarized to 1.4 V (vs. standard hydrogen electrode) to confirm the system operation. Pt or Pd dissolved immediately after polarization as the following reactions:Pt → Pt2+ + 2e- ,Pd → Pd2+ + 2e- .After polarization, Pt or Pd dissolution detected by ICP-MS after around 20 s. Thus, we should consider this delay time in the time-resolved measurements, and the potential step from open circuit potential to 1.4 V was applied to WE for the calibration of delay time before every experiment. Pt and Pd were subjected to potential cycling between 0.05 – 1.4 V at 10 mV s-1, onset potentials for Pt and Pd dissolution were around 1.0 V and 0.73 V in the anodic scan, respectively. These values were more negative than those decided by the previous system.2 Thus we successfully detected a trivial amount of dissolved Pt and Pd using the developed system. Acknowledgments The authors acknowledge Open Facility Center, Materials Analysis Division, Tokyo Institute of Technology, for assistance with the ICP-MS analysis. References Song, Z. Liang, K. Nagamori, H. Igarashi, M. B. Vukmirovic, R. R. Adzic and K. Sasaki, ACS Catal., 10 4290 (2020).A. Topalov, I. Katsounaros, M. Auinger, S. Cherevko, J. C. Meier, S. O. Klemm and K. J. Mayrhofer, Angew. Chem. Int. Ed. Engl., 51 12613 (2012).

Synthesis of Pt-zeolite coated palladium alloys as catalytic membranes for hydrogen production

PdAu composite membranes were applied for the preparation of PtNaA-PdAu catalytic membranes for hydrogen production from the water gas shift reaction. In the first stage, the deposition of NaA zeolite on top of the PdAu alloys was optimized. Functionalization employing a 1.0 v/v % 3-aminopropyltriethoxysilane solution prior to both seeding and hydrothermal synthesis allowed obtaining a homogeneous and complete PdAu alloy surface coverage. Even though the NaA zeolite coverage decreased the pure hydrogen permeance at 623 K and 50 kPa in comparison with a PdAu membrane, the resistance to a CO containing stream was higher. From direct incorporation of Pt during the zeolite synthesis, a homogeneous, well-intergrown PtNaA zeolite coverage on top of a PdAu alloy membrane was obtained. PtNaA catalytic tubular membranes were evaluated in the water gas shift reaction at 673 K. The membranes were active and stable under reaction conditions, without evidence of methane formation.

Electrodeposition of Pd alloys from choline chloride/urea deep eutectic solvents

In this study, the electrodeposition of palladium alloys was investigated in a choline chloride/urea based deep eutectic solvent containing sulfosalicylic acid dihydrate as organic additive and Pd(II) + Ag(I), Pd(II) + Pt (II), or Pd(II) + Pt (II) + Ag(I) as metal components. The electrochemical behavior of the electrolytes was characterised by cyclic voltammetry. The electrodeposition processes require nucleation overpotential. Energy-dispersive X-ray data indicated that the layer thickness and composition of the produced Pd–Ag, Pd–Pt, and Pd–Pt–Ag films could be varied by changing the deposition mode. Additions of Ag(I) to the Pd and Pd–Pt electrolytes enhanced the overall metal deposition rate. Scanning electron micrographs of the electrodeposits showed that in general, the Pd alloys deposited by pulse current were nodular and relatively compact, whereas the films deposited by potentiostatic deposition were less dense and covered with dendrite-like and sharp-edged crystallites. Data collected from X-ray diffraction (XRD) experiments proved the existence of metallic alloys.

Effects of intermetallic compounds on the thermophysical properties of uranium –palladium alloys

The formation and migration of high-yield lanthanide fission products during reactor operation and fuel reprocessing stages continues to be a critical area of concern for evaluating the performance of metallic fast-reactor nuclear fuels, particularly the formation of lanthanide-Fe eutectic compounds at the fuel-clad interface. Palladium has been shown to be an effective fuel additive for reducing fuel-clad chemical interaction (FCCI) by binding up lanthanide fission products and preventing their interaction with cladding materials, yet very little data exists for thermodynamic and thermal transport properties of actinide-palladium alloys. To better understand the effect of U–Pd intermetallic compounds on the thermophysical properties of metallic uranium, the phase transition temperatures (Ttr) and enthalpies (ΔHtr), specific heat capacities (Cp), thermal diffusivities (D), and the densities (ρ) as a function of temperature were experimentally measured or calculated for a series of alloys in the U–Pd binary system in a temperature range from 300 to 1173 K. These values were used to calculate the thermal conductivity (k) as a function of temperature for each composition and are reported in this paper. The addition of Pd led to an increased weight fraction of UPd3 as well as a substantial reduction in both D and ρ, and a small decrease in Cp at most temperatures measured. Consequently, the addition of 5 and 10 wt % Pd to U lead to a net decrease in k values of 23 and 40%, respectively, across the entire temperature range.

Fast Exact Computation of the k Most Abundant Isotope Peaks with Layer-Ordered Heaps.

Computation of the isotopic distribution of compounds is crucial to applications of mass spectrometry, particularly as machine precision continues to improve. In the past decade, several tools have been created for doing so. In this paper we present a novel algorithm for calculating either the most abundant k isotopologue peaks of a compound or the minimal set of isotopologue peaks which have a combined total abundance of at least p. The algorithm uses Serang's optimal method of selection on Cartesian products. The method is significantly faster than the state-of-the-art on large compounds (e.g., Titin protein) and on compounds whose elements have many isotopes (e.g., palladium alloys).

Aging Effect on Structure, Hardness, Roughness Behavior and Bacterial Adhesion on Silver- Palladium Dental Alloy

Aging in normal saliva for different interval times make a change in internal structure (Formed phases and started base line) of Sliver- Palladium (Ag-Pd) dental alloy. Also aging in saliva for one, two and three weeks decreased Vickers hardness value, calculated maximum shear stress (τm) and roughness parameters for Sliver- Palladium alloy. Microbiological studies show the Candida spp. stuck on Sliver- Palladium alloy surface and their growth dependent on aging times.

Multiplexable intrinsic Fabry-Perot interferometric fiber sensors for multipoint hydrogen gas monitoring.

This Letter presents an approach to produce multiplexable optical fiber chemical sensor using an intrinsic Fabry-Perot interferometer (IFPI) array via the femtosecond laser direct writing technique. Using the hydrogen-sensitive palladium (Pd) alloy as a functional sensory material, Pd alloy coated IFPI devices can reproducibly and reversibly measure hydrogen concentrations with a detection limit of 0.25% at room temperature. Seven IFPI sensors were fabricated in one fiber and performed simultaneous temperature and hydrogen measurements at seven different locations. This Letter demonstrates a simple yet effective approach to fabricate multiplexable fiber optical chemical sensors for use in harsh environments.

Study of the Stress-Strain State of the Process of Drawing Wire from an Alloy of Palladium with Nickel

This article present the results of studies of the process of wire drawing from the PdNi-5 alloy, performed using computer simulation in the DEFORM 3D software package. В качестве материала для исследований использовали сплав с содержанием 95% палладия и 5% никеля. An alloy with a content of 95% palladium and 5% nickel was a material for research. The patterns of changes in the stress-strain state for the current processing mode determined, and a more rational drawing mode with a redistribution of drawing coefficients along transitions proposed. For the proposed regime, using the created model, the values of drawing stresses, drawing forces and Cockcroft-Latham criterion determined. It was found that the stress distribution in the deformation zone corresponds to the generally accepted laws of their change, and their maximum values are realized in the metal located in the calibrating zone of the drawing die. In addition was revealed that the stresses in the current mode have limit values at the second and fourth passes. The redistribution of deformation indicators in the proposed mode allowed reduce the magnitude of these stresses and, thereby, reduce the likelihood of wire breaks. The maximum value of the Cockcroft-Latham criterion is achieved in the last transitions, but at the same time, destruction will not occur, since they do not exceed the limit value. The drawing force also decreases with the implementation of the proposed mode and does not exceed the permissible values regulated by the technical characteristics of the equipment. Since it is the proposed mode of wire drawing, it is characterized by a decrease in energy power indicators and the likelihood of wire breakage in the process of metal deformation it can be recommend it for implementation in existing production.

Peculiarities of Pressure Welding of Pd Foil to Stainless Steel

The peculiarities of joining a palladium alloy foil to 12Cr18Ni10Ti stainless steel by diffusion and resistance welding are considered. It is shown that both technologies can be realized only using an intermediate nickel layer with a thickness of 0.1 mm, which provides uniform strength and joint tightness and also prevents the formation of brittle intermetallic compounds. Diffusion welding allows one to obtain high-quality joints of palladium alloy to stainless steel, but this process proceeds at relatively high (950°C) temperatures and takes a long time. Resistance welding does not have these disadvantages, but the outcome significantly depends on the correct choice of welding conditions, upon which the spot weld nugget must be displaced as much as possible toward the stainless steel and the intermediate nickel layer. The connection of the palladium alloy to the intermediate layer occurs owing to mutual diffusion occurring during the passage of the welding pulse.

Pt Nanoparticle Sensitized PdNi Nanofibers As Highly Sensitive and Selective Hydrogen Gas Sensor

Detection of different gases in power transformer oil is essential to accurately examine and understand different problems and faults in the transformer system. Especially, during situations like corona discharge and arcing, evolution of hydrogen gas can be hazardous due to its highly flammable and explosive nature. Therefore, development of high-performance gas sensors targeted for hydrogen gas over a wide range of concentrations is very important.We suggest a facile and effective fabrication method of hydrogen sensing composite material based on palladium and nickel alloy with nanofiber structures originated from electrospinning. PdNi alloy, with further decoration with platinum nanoparticles as catalysts via apo-ferritin templating, shows greatly enhanced sensitivity and response time. Conventionally, Palladium is widely used as hydrogen sensors due to its well-known phase transition to PdHx, α-PdHx at hydrogen concentration below 1%, and β-PdHx at hydrogen concentration above 2%. However, huge volume expansion associated from this transformation limits its lifetime and reduces its long-term performance. In this work, nickel alloying effectively decreases the lattice parameters of the alloy, while increasing the stability during repetitive exposure to high concentration to hydrogen gas. Furthermore, formation of grain boundaries to compensate the lattice contraction induced by nickel alloying, high surface area from its nanofiber structure and gas dissociation and activation properties of platinum nanoparticles improves the sensor’s sensitivity toward hydrogen gas [1]. Nickel in the lattice also acts as pinning points to effectively suppress the grain growth of the alloy during high temperature annealing and reduction processes, which further improves its sensitivity and response time. This facile fabrication and decoration methods allow us to produce a highly sensitive and rapidly responding hydrogen gas sensor with enhanced long-term stability compared to the conventional Pd based hydrogen gas sensors. Reference [1] D. H. Kim, ACS Nano 13, 6071–6082 (2011); doi:10.1021/acsnano.9b02481

Tuning Binding Energy in Nanoporous Core Shell Alloys of Palladium to Suppress CO Poisoning in Electrochemical Reduction of CO2

Electrochemical CO2 reduction reaction (CO2RR) has been extensively explored for conversion of dissolved CO2 into useful carbon based products e.g CO, formate/formic acid, alcohols etc. Formate/formic acid as a CO2RR product is drawing focus because of its high energy density and utility as a chemical precursor. Traditional formate producing metals e.g. Co, In, Bi, Sn etc. require high overpotentials, limiting their energy effectiveness. Pd on the other hand, originally known to produce CO at overpotentials above 600 mV RHE, has recently shown substantial formate FE’s at overpotentials below 200 mV. The gradual poisoning of Pd-based CO2RR electrocatalysts through the slow production of CO, even at near unity formate FEs, results in deactivation of the catalyst surface and limits the viability of Pd for sustained electrolysis. Here, we report synthesis of core-shell nanoporous multimetallic Pd (np-PdX, where X = Co, Ni, Cu, Ag, Cu-Sn, Cu-Ti) alloys that show suppressed CO deactivation based on the subsurface composition of the alloy electrocatalysts. The Pd skinned nanoporous alloys have been obtained by electrochemical dealloying where the presence of less noble metal/alloy under the Pd shell changes the electronic structure of the Pd and consequently alters the CO adsorption strengths and subsequent catalyst deactivation. The tortuous pores (pore size: 5 – 10 nm) give rise to roughness factors above 200 which generates high geometric formate partial current densities (> 30 mA/cm2). Furthermore, the np-Pd electrodes are free standing and obviate the use of any binder and/or support which otherwise causes extra overpotential losses and morphological instability. The suppression of surface poisoning is explained on the basis of weakening of CO binding strengths due to electronic interactions of the alloying component that shifts the d-band center of Pd, as well as changes to the near surface hydrogen solubility which can also affect the adsorption strength of active/inactive intermediates and reaction selectivity.

Process simulation and integration of IGCC systems with novel mixed ionic and electronic conducting membrane-based water gas shift membrane reactors for CO2 capture

A mixed ionic and electronic conducting (MIEC) membrane provides an alternative to the palladium alloy membrane for water gas shift membrane reactor. It exhibits much better sulfur resistance performance than the palladium alloy membrane. In this paper, the thermodynamic performance of the integrated gasification combined cycle (IGCC) system with MIEC membrane reactor is predicted for the first time. The effects of reactor operation parameters on system flowsheet and performance are investigated and illustrated by sensitive analysis. When the reactor operation temperature is 900 °C and the H2O decomposition ratio is 0.5, the system net efficiency is about 38.90%, which is 2.6% points higher than that of the IGCC with Selexol. The system net efficiency increases with the decrease of operation temperature. With the net efficiency of the conventional system as the reference, the minimum H2O decomposition ratios at different operating temperatures are provided.

Permeator Simulations for the EU-DEMO Fuel Cycle

Palladium alloy permeators are foreseen for the retrieval of hydrogen in the fusion fuel cycle of the European DEMO power plant. Driven by a pressure gradient, unburned fuel permeates through a thin-walled metallic membrane within the permeator while other gases cannot pass this barrier. With a theoretically unlimited selectivity with regard to nonhydrogenic species, a very high proportion of unburned fuel can be recovered in a continuous process from the exhaust gas and reused after a very short time. A potential candidate for the design of such a permeator consists of a tube (l = 500 mm, d = 10 mm) with a 125-μm-thick, self-supporting membrane made of a palladium-silver alloy all combined in the shape of a so-called finger-type design. A two-stage process then connects several of these permeators in parallel and in series to match the required throughput of DEMO during plasma operation at a given degree of separation. As the first design point in the scope of the current preconceptual design phase, a model was developed using the commercial software ASPEN Custom Modeler to estimate important parameters such as the tritium inventory and the scale of the permeator unit. How the hydrogen pressure profile is calculated over the length of a permeator using the Sieverts’ Law and the Finite Volume Method is thoroughly described. As a result, the integral performance of the combined permeators is presented as well as all important boundary conditions and assumptions that led to it. For the current DEMO baseline scenario, the total number of permeators of the abovementioned shape is found to be about 50.

Functionalized PdAu Alloy on Nanocones Fabricated on Optical Fibers for Hydrogen Sensing

This paper reports the development of fiber optical hydrogen sensors using palladium and gold alloy nanostructures as sensor materials for hydrogen measurements using a D-shaped fiber as a platform. Using a maskless reactive ion etching technique, silica nanocone structures were formed on the surface of the D-shaped fiber. Palladium and gold alloys were deposited on the surface of nanostructured D-shaped fiber to form a nano-alloy sensor film. Evanescent interaction between guided light propagated in the fiber core and nano-alloy enabled highly sensitive hydrogen detection from concentrations that ranged from 0.25% to 10% in atmosphere pressure. The formation of nanostructured alloy enabled by the nanocone surface led to more than 3 times faster in sensor response time and significant improvements in sensor sensitivity and reversibility. The work presented here demonstrates that highly controllable VLSI microfabrication schemes can be applied to produce nanostructured sensor films on optical fibers for high-sensitivity chemical sensing.

Мембраны из сплавов палладия для получения особочистого водорода

In the present study, using the improved technology, high-quality vacuum-tight foils 10 – 20 µm in thickness were prepared from effective Pd – 6 wt. % In – 0.5 wt. % Ru, Pd – 6 wt. % Ru, Pd – 40 wt. % Cu palladium alloys. Using a combination of deformation and annealing modes, the Pd – 40 wt. % Cu alloy foil consisting of the ordered β-phase (97%) with the CsCl-type structure that exhibits the maximum hydrogen permeability in this system. The mechanical properties and hydrogen permeability of the prepared foils were studied and compared with those of alloy foils 50 µm thickness. The thermal concentration dilatation in hydrogen was studied at different temperatures. Data on the dilatation of palladium-based membranes are of primary importance for designing membrane filtering elements and selection of optimal conditions for their operation, since these data determine the operation life membranes. Based on the Pd – 6 wt. % In – 0.5 wt. % Ru alloy, the Pd – 6 wt. % In – 0.5 wt. % Ru – 1.25 wt. % Co alloy was developed; it is characterized by increased strength characteristics and lower α ↔ β hydride transition temperature.

Synthesis of Imines by Selective Oxidation of Amines on alloy nanoparticles of palladium and gold under visible light irradiation at ambient temperatures

Imines are important intermediates in organic synthesis. To avoid derivatives, the research on direct oxidized amines as an alternative method is imminent. The gold (Au)–palladium (Pd) alloy nanoparticles (NPs) catalyst shows a favourable activity and high selectivity on benzylamine oxidation reaction under light irradiation. The yield of the reaction on the alloy NPs with a Au:Pd ratio of 1:1.86 in the dark was 36% at 45 °C, while the yield increased to 95% under light illumination. The study demonstrates different properties from alloy NP to pure Au NP and Pd NP catalysts which may be caused by increased surface charge heterogeneity in the alloy system. The conversion rate of the reaction can also be enhanced by light irradiation and heat. The light energy which utilized by Localized Surface Plasmon Resonance effect of gold in alloy system can highly enhanced the efficiency of reaction. These findings provide useful guidelines for designing efficient alloy catalysts with a plasmonic metal and a catalytically active transition metal for various organic syntheses driven by sunlight.

Development of multi‐parameter online monitoring equipment for EHV transformer bushing

To diagnose the running state of bushing and avoid serious power grid accidents, online multi-parameter monitoring equipment for dissolved hydrogen, oil pressure and temperature in bushing oil was developed. The equipment includes three units: signal acquisition, control cabinet and data analysis. A new hydrogen sensor without oil–gas separation membrane and based on palladium alloy film technology was developed. A three-in-one sensor for hydrogen, oil temperature and pressure monitoring has been developed, which has the advantages of miniaturisation, lightweight and easy installation. Test results show the hydrogen measurement range of the sensor is 0–5000 ppm, and the accuracy can reach 10% or 15 ppm (with larger values). The pressure measurement range is 0–1.0 MPa, the resolution is 0.1 kPa, and the accuracy can reach 0.25 grade. The temperature measurement range is −40 to 105°C, and the accuracy is ±1°C. The measurement performance of the device fully meets the requirement of online monitoring of transformer bushing. The equipment has been put into operation in a 330 kV substation, which can monitor the bushing status online and help eliminate the early latent fault of bushing in the weak budding state.

Structural trends in the dehydrogenation selectivity of palladium alloys.

Alloying is well-known to improve the dehydrogenation selectivity of pure metals, but there remains considerable debate about the structural and electronic features of alloy surfaces that give rise to this behavior. To provide molecular-level insights into these effects, a series of Pd intermetallic alloy catalysts with Zn, Ga, In, Fe and Mn promoter elements was synthesized, and the structures were determined using in situ X-ray absorption spectroscopy (XAS) and synchrotron X-ray diffraction (XRD). The alloys all showed propane dehydrogenation turnover rates 5–8 times higher than monometallic Pd and selectivity to propylene of over 90%. Moreover, among the synthesized alloys, Pd3M alloy structures were less olefin selective than PdM alloys which were, in turn, almost 100% selective to propylene. This selectivity improvement was interpreted by changes in the DFT-calculated binding energies and activation energies for C–C and C–H bond activation, which are ultimately influenced by perturbation of the most stable adsorption site and changes to the d-band density of states. Furthermore, transition state analysis showed that the C–C bond breaking reactions require 4-fold ensemble sites, which are suggested to be required for non-selective, alkane hydrogenolysis reactions. These sites, which are not present on alloys with PdM structures, could be formed in the Pd3M alloy through substitution of one M atom with Pd, and this effect is suggested to be partially responsible for their slightly lower selectivity.

Electroless Plating of Palladium Membranes on Porous Substrates for Hydrogen Separation and the Effects of Process Factors on Plating Rate and Efficiency: A Review

The electroless plating of palladium and palladium alloy membranes is fast becoming an important and enabling technology. This is more so when juxtaposed with the rising demand for high purity hydrogen for applications particularly in proton exchange membrane fuel cells (PEMFC). The effect of process factors such as sensitization and activation during surface modification, concentration of the reducing agent, plating temperature, time, pH, additives, air aeration on plating efficiency, quality of the palladium film and deposit morphology is reviewed with the aim of identifying areas requiring further investigation. The paper also reviews how these process factors could be optimised for better plating efficiency and overall membrane quality. The concentration of the reducing agent has been identified as the limiting factor on plating efficiency albeit other process factors separately impact on the plating efficiency. Furthermore, bulk precipitation caused by concentration of the reducing agent has been identified as a major problem during electroless plating with hydrazine based plating baths. To ameliorate this problem, a multi step addition of the hydrazine reducer in separate portions has been recommended.

Platinum–palladium alloy nanotetrahedra with tuneable lattice-strain for enhanced intrinsic activity

Understanding how to regulate lattice strain of PtPd NTDs and the correlation of PtPd NTDs between the compositions, tuneable lattice strain and the electrocatalytic properties.