Pd Matrix Research Articles

Evolution of helium bubbles induced by helium irradiation in polycrystalline palladium: An insight into tritium aging

Essential insight into evolution principles of helium (He) bubbles within Palladium (Pd), a prominent hydrogen isotope storage and tritium handling material, is of great importance to understand the service performance of such transition metal in the field of nuclear industry. Particularly, the features of He bubbles and their evolution details have long been attracting broad interests. Herein, He bubbles with different structural features and corresponding distinct evolving processes within polycrystalline Pd were investigated by transmission electron microscopy (TEM), elastic recoil detection (ERD) and thermal desorption spectroscopy (TDS). He bubbles were induced and regulated by irradiation conditions. Comprehensive characterizing results indicate that bubbles with small sizes, spherical shape and uniform distribution, realized by low-fluence irradiation, are inclined to be stable in Pd matrix, while coarsened bubbles with faceted shape and regional distribution in the high-fluence condition are prone to release at relatively low temperatures. Meanwhile the evolving processes of He bubbles including migration, coarsening and releasing within polycrystalline Pd were analyzed. The impact of the structural characteristics such as surfaces or grain boundaries of Pd, acted as “fast path” for bubble diffusion, coarsening and release, was systematically discussed. Moreover, the correlation between tuned irradiation and actual tritium aging was discussed by analyzing He concentrations and bubble sizes in both processes. The study reveals important features of He bubble evolution in Pd, which will provide positive reference for understanding correlative behaviors in other irradiation conditions, especially tritium aging. • He bubbles with different features were obtained by tuning fluence and energy of He + irradiation. • Evolution behaviors of He bubbles including nucleation, migration and coarsening were studied by TEM, ERD and TDS. • The stability of He bubble is closely related to the size that small one inclines to stabilize while large one tends to release. • Trapping and coarsening of He bubbles are promoted in grain boundaries and structural defects. • Different evolution periods of He bubble in this study were analyzed for the purpose to offering an analogous reference for tritium aging.

Magnetism of Co-rich clusters embedded in nanoporous Pd prepared by electrochemical dealloying — Influence of thermal annealing

Nanoporous palladium samples containing superparamagnetic Co-rich clusters were prepared by electrochemical dealloying and the magnetic properties were subsequently varied by thermal annealing at different temperatures. It is shown that in this way porous magnetic nanomaterials exhibiting various magnetic characteristics can be obtained. The as-dealloyed, unannealed sample is ferromagnetic at 4.2 K and superparamagnetic at 300 K, with a blocking temperature TB of 100 K. The observed general decrease of the magnetization with increased annealing temperature is explained by the redistribution of Co from the Co-rich superparamagnetic clusters into the Pd matrix, leading to a shrinkage of the clusters and the formation of a diluted Co–Pd alloy phase. As a consequence of the smaller magnetic cluster size a down-shift of TB occurs for annealing temperatures of 373 K and 573 K. After annealing at 773 K the stronger dissolution of Co from the clusters into the Pd-matrix reduces TB further down to 35 K. Additionally, a second blocked magnetic phase with much higher TB emerges, which leads to ferromagnetic behavior at room temperature. The occurrence of this phase is attributed to the formation of larger magnetic entities consisting of Co-rich clusters lying close together and a Co–Pd alloy phase with relatively high Co concentration in between these clusters. After high temperature annealing at 973 K a weakly ferromagnetic phase is obtained at 4.2 K and at 300 K, which can be explained by the nearly completed dissolution of the Co in the Pd matrix.

Accelerating Pd Electrocatalysis for CO2-to-Formate Conversion across a Wide Potential Window by Optimized Incorporation of Cu.

Electrochemical reduction of carbon dioxide (CO2) to formate is a viable way to reduce CO2 emissions and realize a carbon-neutral energy cycle. Although Pd can convert CO2 to formate with a high Faradaic efficiency at minimal overpotentials, it suffers from a limited and narrow potential window. Alloying is an important strategy for the catalyst design and tuning the electronic structures. Here, we report a series of PdCu bimetallic alloy catalysts with tunable compositions based on dendritic architectures. Optimal introduction of Cu atoms into the Pd matrix facilitates formate production and suppresses CO generation. In 0.1 M KHCO3 aqueous solution, our best candidate, Pd82Cu18 catalyst, delivered a high formate Faradaic efficiency of 96.0% at -0.3 V versus RHE. More interestingly, the high selectivity (>90%) toward formate maintained an enlarged electrochemical potential window of 600 mV. The ensemble effect with electronic coupling between Pd and Cu upon alloying and its induced moderate surface O-containing configuration were found to enhance the formate formation and suppress CO poisoning during CO2 reduction.

Amperometric Oxygen Sensor Based on Bimetallic Pd-Cu/C Electrocatalysts

A laminated Pd-Cu alloy/C/Nafion multilayer was prepared to sense O2 atmosphere in a metal-air structure. As a matrix, palladium was doped with various amounts of copper to conduct a preliminary test with optimum response, and four compositions, Pd, Pd8Cu2, Pd6Cu4, and Pd5Cu5, were selected as the candidate electrodes. It was found that the Pd6Cu4/C electrode showed higher sensitivity for all the electrodes. According to the phase identification of X-ray diffraction and X-ray photoelectron spectroscopy tests, the high sensitivity was attributed to the doped Cu, which was merged into the Pd matrix to repel the Pd out of the matrix as a Pd-skin layer on the surface. In the Pd-Cu alloy, the Cu site served as a template reaction site to break the O-O bond and reduce the interaction force of adsorbated oxygen on the Pd site. During the oxygen reduction reaction, not only did the decomposition of O2 molecules occur on the electrode, but the electrode itself proceeded with a phase transformation to high valance of oxide, PdO3. The sensing potential for O2 sensing was determined by polarization curves in which the flat region resulting from a diffusion-control was adopted. Chronoamperometric measurements were employed to construct calibration curves for the selected electrodes. A successive response was measured to test the endurance, which showed appreciable sensitivity decay. We also tested the selectivity by introducing a series of disturbance gases, CO, SO2, and NO2, in which the Pd6Cu4 electrode prevailed over the other electrodes.

Investigation of cadmium and lead contents of boron minerals and boron waste by electrothermal atomic absorption spectrometer

In this study, Cd and Pb were determined and investigated in the most abundant boron minerals such as colemanite, tincal, ulexite and boron waste existed in Turkey using electrothermal atomic absorption spectrometer. Graphite furnace temperature program for Cd and Pb determinations in samples was optimized in the absence or presence of palladium (Pd) and nickel (Ni) + Pd matrix modifier mixture. Pd + Ni modifier mixture was found to be more suitable for both Cd and Pb. The ashing temperatures for Cd and Pb obtained 600 °C and 1100 °C, respectively, in the presence of Ni + Pd mixture. Limits of detection and limits of quantification values for Cd and Pb in the absence or presence of Ni + Pd modifier mixture were determined. Accuracy and precision of the method proposed were checked by analyzing the standard reference materials (Montana Soil 2711 and Estuarine 1646a). Cd and Pb in boron minerals were performed under optimized experimental conditions.

Epigenetic Alteration of Cupreous Gold in the Au–Ag–Cu–Pd Exsolution Texture

The exsolution texture of the Au–Ag–Cu–Pt solid solution is represented by numerous lamellae of cupreous gold in the Ag–Au–Pd matrix. On average, the lamellae contain Au–87.1 wt %, Cu–10.3 wt %, Pd–1.8 wt %, and Ag–1.1 wt %, which corresponds to the Au3Cu mineral phase. We revealed for the first time that cupreous gold lamellae were selectively replaced by high-grade gold (98 wt % Au), with a very precise inheritance of the exsolution texture. The substitution occurred due to the impact of epigenetic solutions on native gold with the removal of relatively mobile components.

The Hybrids of Core‐Shell Chain‐like Nanostructure of Au@Porous Pd with Graphene for Energy Conversion Application

AbstractIn this report, a slick aqueous method of synthesis for Au@ porous Pd core‐shell structure on graphene support is formulated. The as‐synthesized materials have been thoroughly characterized by different characterization techniques to reveal their discrete nanoscale arrangements. The performance of the as‐prepared nanostructures has been evaluated for the oxidation of methanol (MOR) and oxygen reduction reaction (ORR). The combined effect of Au and graphene, as well as the unique nano chain‐like structures of Au@ porous Pd, exploits the enhanced electrocatalytic activity towards MOR and ORR for an energy conversion application. This report reveals the determining part of gold (Au) and graphene synergistic effect on the palladium (Pd) matrix towards the energy conversion application for the fuel cell.

Preparation and Application of Palladium Nanoparticle Impregnated Chloromethylated Polysulfone Matrix as an Efficient Catalytic Membrane for Oxidation of Alcohols

Abstract The use of palladium nanoparticles embedded in a chloromethylated Polysulfone (CMPSf) matrix was developed for highly efficient oxidation of primary and secondary alcohols to corresponding aldehyde and ketone in organic solvent free condition. Pd (Π)/bis (2, 4-dihydroxybenzaldehyde) chelate chemically incorporated onto CMPSf was used to prepare beneficial catalytic membranes. Chemical structure and thermal properties of resulting membranes were characterized via FTIR, 1HNMR, UV-vis, TGA and DSC techniques. Morphology and particle distribution throughout the catalytic membranes was elucidated using FE-SEM. An average particle size of Pd nanoparticles was estimated about 20 nm by XRD technique. ICP technique proved that no Pd particles were leached out of the membrane into the solutions; hence the as-prepared catalytic membranes could be used several times without significant loss in their activities. This is in good accordance with formation of chemical bond between Pd and polymer matrix.

Fabrication of palladium nanoparticles anchored polypyrrole functionalized reduced graphene oxide nanocomposite for antibiofilm associated orthopedic tissue engineering

Two-dimensional reduced graphene oxide (rGO) was used as a scaffold for bone tissue engineering application. To advance the biological properties including biocompatibility, osteoproliferation, and prevent bacterial infection, the rGO was non-covalently functionalized with polypyrrole (PPy) and palladium (Pd) nanoparticles (NPs). The results propose that PPy and Pd in the Pd/PPy/rGO nanocomposite (NC) create the surface functionalities and binding sites to enhance the physicochemical properties of rGO for biomedical applications. X-ray diffraction (XRD) and transmission electron microscopy (TEM) analysis confirmed the highly dispersed 2–5 nm-sized Pd NPs distributed and anchored on the PPy/rGO surface. The Fourier-transform infrared (FTIR) spectrum shows a peak at 1672 cm−1 corresponds to Pd-nitrogen stretching band which is caused by the interaction between Pd and PPy matrix. Moreover, X-ray photoelectron spectroscopy (XPS) approves the zero oxidation state of Pd (Pd0) NPs. It successfully prevents bacterial biofilms caused by E. coli, B. subtilis, P. aeruginosa, and K. pneumoniae. Therefore the NC may be used to build a bone implant material that ensures prevention from colonizing, adhering, and forming microbial biofilms on the substrates of such materials. In the future, Pd/PPy/rGO NC can be a promising material for pharmaceutical applications such as drug-delivery, anticancer and wound healing agents.

Magneto-Ionic Switching of Superparamagnetism.

Electrochemical reactions represent a promising approach to control magnetization via electric fields. Favorable reaction kinetics have made nanoporous materials particularly interesting for magnetic tuning experiments. A fully reversible ON and OFF switching of magnetism in nanoporous Pd(Co) at room temperature is demonstrated, triggered by electrochemical hydrogen sorption. Comprehensive magnetic characterization in combination with high-resolution scanning transmission electron microscopy reveals the presence of Co-rich, nanometer-sized clusters in the nanoporous Pd matrix with distinct superparamagnetic behavior. The strong magneto-ionic effect arises from coupling of the magnetic clusters via a Ruderman-Kittel-Kasuya-Yoshida-type interaction in the Pd matrix which is strengthened upon hydrogen sorption. This approach offers a new pathway for the voltage control of magnetism, for application in spintronic or microelectromagnetic devices.

Visualizing Formation of Intermetallic PdZn in a Palladium/Zinc Oxide Catalyst: Interfacial Fertilization by PdHx

AbstractControllable synthesis of well‐defined supported intermetallic catalysts is desirable because of their unique properties in physical chemistry. To accurately pinpoint the evolution of such materials at an atomic‐scale, especially clarification of the initial state under a particular chemical environment, will facilitate rational design and optimal synthesis of such catalysts. The dynamic formation of a ZnO‐supported PdZn catalyst is presented, whereby detailed analyses of in situ transmission electron microscopy, electron energy‐loss spectroscopy, and in situ X‐ray diffraction are combined to form a nanoscale understanding of PdZn phase transitions under realistic catalytic conditions. Remarkably, introduction of atoms (H and Zn in sequence) into the Pd matrix was initially observed. The resultant PdHx is an intermediate phase in the intermetallic formation process. The evolution of PdHx in the PdZn catalyst initializes at the PdHx/ZnO interfaces, and proceeds along the PdHx ⟨111⟩ direction.

Visualizing Formation of Intermetallic PdZn in a Palladium/Zinc Oxide Catalyst: Interfacial Fertilization by PdHx.

Controllable synthesis of well-defined supported intermetallic catalysts is desirable because of their unique properties in physical chemistry. To accurately pinpoint the evolution of such materials at an atomic-scale, especially clarification of the initial state under a particular chemical environment, will facilitate rational design and optimal synthesis of such catalysts. The dynamic formation of a ZnO-supported PdZn catalyst is presented, whereby detailed analyses of in situ transmission electron microscopy, electron energy-loss spectroscopy, and in situ X-ray diffraction are combined to form a nanoscale understanding of PdZn phase transitions under realistic catalytic conditions. Remarkably, introduction of atoms (H and Zn in sequence) into the Pd matrix was initially observed. The resultant PdHx is an intermediate phase in the intermetallic formation process. The evolution of PdHx in the PdZn catalyst initializes at the PdHx /ZnO interfaces, and proceeds along the PdHx ⟨111⟩ direction.

Ab initio study of the theoretical strength and magnetism of the Fe−Pd, Fe−Pt and Fe−Cu nanocomposites

We studied the Fe−Pd, Fe−Pt and Fe−Cu nanocomposites formed by Fe nanowires embedded in the fcc Pd, Pt or Cu matrix. The Fe atoms form nanowires oriented along the [0 0 1] crystallographic direction. They replace second nearest neighbor atoms in the matrix. By means of varying the distance between the nanowires we arrived to the chemical compositions X15Fe, X8Fe and X7Fe where X stands for Pd, Pt and Cu. The mechanical and magnetic properties of the nanocomposites were obtained by ab initio simulations. We performed tensile and compressive tests along the [0 0 1] direction and compared the results with the deformation behavior of the fcc matrix and the known intermetallic compounds FePd3 and FePt3. It turned out that the maximum attainable stress for the Fe−Pd and Fe−Pt nanocomposites is higher than the stress attainable for the Pd and Pt matrices. The maximum stress increased with the increasing Fe content. The increase was due to the enhanced stability in the nanocomposites described by the C11−C12 > 0 condition. This effect was particularly pronounced in the Fe−Pt nanocomposites. On the contrary, the Fe nanowires in the Fe−Cu nanocomposites do not enhance the stability and strength of the Cu matrix. They even make the Cu matrix more compliant to compression. Regarding the magnetic ground states, the Fe−Pd and Fe−Pt nanocomposites prefer a ferromagnetic configuration where the spins of all Fe atoms are oriented in parallel manner. On the other hand, the Fe−Cu nanocomposites exhibit an antiferromagnetic configuration where the spins of all Fe atoms assigned to a particular nanowire are oriented parallel, but antiparallel to the spins of a neighboring Fe nanowire. The Young modulus E001 along the [0 0 1] crystallographic direction increases linearly with the Fe content in both the Fe−Pd and Fe−Pt nanocomposites.

First principles investigation on the electronic structure and magnetism of dilute Fe impurity in [formula omitted][formula omitted] alloys

Employing the all electron augmented plane wave + local orbital (APW + lo) method based on the density function theory (DFT), we have performed ab initio calculations of electronic structure and magnetic properties of dilute Fe impurity in PdHx alloys (0⩽x⩽1.0). Here we present our results for the H induced changes in the density of state (DOS), local magnetic moment and the macroscopic magnetic properties. The calculations performed for PdHx without the Fe impurity reveal H concentration dependent lattice expansion and Pd-H bonding which results in large change in electronic band structure and the DOS at the Fermi energy. The nonmagnetic DOS calculated for Fe doped PdHx is analyzed within Stoner model and the condition for local moment formation is found to hold for all concentrations of H. With an increase of the H content in the Pd matrix, the local moment of Fe declines from 3.43μB at x = 0 to 2.72μB at x = 1.0. More significantly, the giant magnetic moment, associated with the Fe impurity in Pd, progressively decreases with H concentration as the positive spin polarization of Pd-4d band electrons diminish and crossover to negative sign for x > 0.75. We show that H induced changes in s-d and d-d hybridization plays a crucial role on the magnetic properties of Fe doped PdHx alloys. In particular, we suggest that the rapid decline of the giant moment in PdHx alloys results from the weakening of ferromagnetic d-d exchange interaction between Fe-3d and Pd-d band electrons caused by changes in density of states arising from H induced filling up of the Pd-4d band.

Cost effective and energy efficient catalytic support of Co and Ni in Pd matrix toward ethanol oxidation reaction: Product analysis and mechanistic interpretation

The present investigation deals with the comparative analysis of electro-catalytic behaviour of Pt, Pd and ternary combinations of Co and Ni with Pd NPs, supported on vulcan XC72 as the anode component in direct ethanol fuel cell (DEFC) operating in alkaline environment. Catalyst NPs were synthesized by ethylene glycol reduction method and their structure, composition and surface morphology were determined through XRD, EDAX and TEM techniques. The superb catalytic efficiency of PdCoNi/C toward ethanol oxidation reaction (EOR) is ascribed to the catalytic intervention of transition metal ad atoms and their surface oxides, culminating to enhanced electrochemical surface area, preferred OH− adsorption on the surface and remarkable yield of oxidation products (CH3CO2− and CO32 −) estimated by ion chromatography. The performance output parameters collectively substantiate not only to the catalytic superiority of the PdCoNi/C catalyst but also affordability to a considerable extent over both the Pt/C and Pd/C catalysts.

Magnetic anisotropy of ultrathin Pd 4 Co(111) film by first-principles calculations

Abstract The Pd–Co alloy is a suitable candidate for the perpendicular magnetic recording and related applications. However, no research is available to clarify influences of local structures on the magnetic anisotropy of the Pd–Co alloy. Therefore, in this work, we studied the effects of Co arrangement on the magnetic anisotropy of ultrathin Pd4Co(111) film with 20% Co content by using the density functional theory calculations. We found that a Co monolayer in the surface layer of the ultrathin film offers a large in-plane magnetic anisotropy while the Co atoms mixed inside the Pd matrix exhibit the perpendicular magnetic anisotropy. Notably, a Co monolayer beneath the surface layer of the Pd matrix maximizes the perpendicular magnetic anisotropy up to 1.85 erg/cm2. Electronic properties were also analyzed to clarify the magnetic anisotropy of the ultrathin film.

Spin fluctuation and local magnetism of isolated Fe impurities in Pd1−xVx alloys studied by time differential perturbed angular distribution spectroscopy

The magnetic moment and spin fluctuation temperature of isolated Fe impurity atoms in Pd1−xVx (0 ≤ x ≤ 0.15) alloys have been studied by time differential perturbed angular distribution (TDPAD) technique. With increasing V content in Pd matrix, a large non-linear reduction of the local magnetic moment accompanied with an exponential increase of the spin fluctuation temperature TSF has been observed. At and beyond x = 0.12, the Fe atoms are found to be nonmagnetic. As an important new feature, TSF is observed to vary quadratically with composition dependent changes in host spin polarization.

Thermodynamics of Hydrogen Solution and Diffusion in Oxidized and Unoxidized Pd–W Alloys

Equilibrium hydrogen isotherms have been measured from 423 to 523 K for two fcc Pd–W alloys, Pd0.98W0.02 and Pd0.96W0.04, over H content ranges available up to pH2 ≈ 0.10 MPa. ΔHH and ΔSH values have been determined from the H2 isotherms as a function of the H content of the alloys. After measurement of the isotherms, the Pd0.98W0.02 and Pd0.96W0.04 alloys were internally oxidized. The H2 solubilities in the internally oxidized alloys were measured and evidence is given for the formation of H-bronzes, HxWO3, from the nanosized WO3 precipitates within the Pd matrix. Pd–W alloy membranes prepared for H diffusion measurements were partially internally oxidized in order to improve their resistance toward gaseous contaminants. An equation has been derived to obtain the H diffusion constant for the inner, unoxidized alloy layer within the three layer membrane resulting from internal oxidation. This equation has been applied to data for the two internally oxidized Pd–W alloys. Activation energies and pre-exponen...

Annealing-dependent growth and nonlinear electrical properties of fractal Ge nanojoints based on Pd matrix

The Pd/Ge bilayer films with interesting fractal Ge nanojoints were successfully prepared by high-vacuum thermal evaporation techniques. It was found that Ge nanojoints embedded in Pd matrix showed fascinating fractal morphologies with average size of fractal clusters at 3.5μm and fractal dimension at 1.77 when the films were annealed at 550°C for 15min. The fractal clusters formed Ge nanojoints with average size at 80nm in width and 450nm in length. The annealing-dependent growth model responsible for the fractal Ge nanojoints is discussed reasonably. The electrical measurements confirmed that the annealed Pd/Ge film with interesting fractal clusters showed a nonlinear voltage–current behavior.

Structure and magnetism in Fe/FexPd1−x core/shell nanoparticles formed by alloying in Pd-embedded Fe nanoparticles

We have investigated atomic structure and magnetism in Fe nanoparticles with a diameter of 2 nm embedded in a Pd matrix. The samples for these studies were prepared directly from the gas phase by co-deposition, using a gas aggregation source and an MBE-type source for the Fe nanoparticles and Pd matrix respectively. Extended absorption fine structure (EXAFS) measurements indicate that there is an appreciable degree of alloying at the nanoparticle/matrix interface; at dilute nanoparticle concentrations, more than half of the Fe atoms are alloyed with Pd. This leads to a core/shell structure in the embedded nanoparticles, with an FexPd1−x shell surrounding a reduced pure Fe core. Magnetism in the nanocomposite samples was probed by means of magnetometry measurements, which were interpreted in the light of their atomic structure. These point to a magnetized cloud of Pd atoms surrounding the embedded nanoparticles which is significantly larger than around single Fe atoms in Pd. The coercivities in the Fe/Pd nanocomposite samples are larger than in FexPd1−x atomic alloys of corresponding composition, which is consistent with exchange coupling between the magnetically harder and softer regions in the nanocomposite samples.