Pure Pd Research Articles

Self-standing three-dimensional PdAu nanoflowers for plasma-enhanced photo-electrocatalytic methanol oxidation with a CO-free dominant mechanism

Precise design of high efficacious catalysts and the insight into the mechanism for photo-electrocoupling catalytic methanol oxidation reaction (MOR) are two major issues for the development and practical application of direct methanol fuel cells (DMFCs). Herein, a novel self-standing three-dimensional nanosheet assembly PdAu nanoflower with local surface plasmon resonance effect is fabricated to acquire excellent catalytic performance and explore the photo-electrocatalytic mechanism for MOR. Interestingly, the Pd1Au1 nanoflower electrocatalyst exhibits superior mass activity than pure Pd and Pd/C catalysts thanks to the abundant active sites and efficacious charge transfer. Further on, with the assistance of LSPR effect, the catalytic activity for MOR of Pd1Au1 catalyst (4179.04 mA mg−1Pd) under visible light illumination achieved 2.41-fold than dark conditions (1731.42 mA mg−1Pd). Moreover, the long-term durability of Pd1Au1 catalysts with visible light is also improved compare to dark condition and other mentioned Pd catalyst. More significantly, a photo-electrocoupling CO-free dominant mechanism is proposed to in-depth understand the promotion of catalytic activity and durability for MOR. This contribution provides the rational design of plasma-enhanced high-effective photo-electrocatalyst and reveals a CO-free dominant MOR mechanism for the progress of future liquid direct fuel cells.

Even partially amorphous Pd2Ni2P metallic glass significantly promotes hydrogen evolution electrocatalysis

Metallic glasses are expected to be endowed with higher electrocatalytic activity, with respect to their crystalline counterparts, due to the presence of a high density of under-coordinated sites. However, glasses made of metals, as opposed to metal oxide/sulfides are harder to synthesize, with the challenge increasing with amorphousness. In light of these issues, we calibrate the increase in hydrogen evolution reactivity using the Pd2Ni2P bulk metallic glass composition as a model system. This composition has a good glass-forming ability and is interesting from a catalytic point of view, as Ni and P lie on the opposite leg of the HER volcano plot with respect to Pd. Partially amorphous (PA) Pd2Ni2P alloy displayed a five-fold higher specific electrocatalytic activity on per unit electrochemical surface area (ECSA) basis compared to its crystalline (C) counterpart. This magnitude of specific electrocatalytic activity, which is on par with that for pure Pd, has been achieved with just 40% of the precious metal, leading to a considerable saving in cost. The homogeneous single-phase structure of the highly electro-active partially amorphous alloy leads to higher electrochemical stability than its polycrystalline counterpart. This finding implies that many compositions ignored traditionally due to their poor electrocatalytic activity or stability can now be reconsidered in amorphous forms, thus expanding the material space of valuable catalysts.

Comparative study on the numerical simulation of hydrogen separation through palladium and palladium–copper membranes

The hydrogen (H2) diffusion through palladium (Pd) and Pd–copper (Cu) membranes was numerically investigated by developing a two-dimensional computational fluid dynamics model for predicting the performance of H2 separation. The momentum and mass transport phenomena in the laminar flow conditions were solved at different operating conditions in a vertical cylindrical-type reactor. The effect of feed-gap distance, H2 concentration, and reactor heating temperature on the H2 permeation processes were simulated and compared for both Pd-based membranes. The concentration, velocity, and convective and diffusion mass transfer flux distributions were analyzed using the designed model. The H2 concentration was proportional to the feed-gap distance/cross-sectional area. The smaller the feed-gap distance, the greater the probability of a H2 molecule being adsorbed by the membrane surface and the ionization energy increasing, leading to further H2 dissociation through the Pd-based membranes. It was found that the diffusion flux of all feed concentrations was substantially decreased 50 s after the start of the permeation process. Moreover, the diffusion flux of the Pd–Cu40% membrane was relatively larger than that of the pure Pd membrane under the same operating conditions. The distributions of the convective flux, diffusion mass transfer flux, and concentration of the Pd–Cu40% membrane were substantially increased up to 350 °C, then fell to a lower value at higher temperatures. The simulation results were validated with the experimental results, with analysis indicating a good agreement with the experimental results under the same operating conditions. It can be concluded that the simulation modeling for Pd-based membranes was able to predict the optimum operating conditions at high H2 diffusion rates.

Wireless and Linear Hydrogen Detection up to 4% with High Sensitivity through Phase-Transition-Inhibited Pd Nanowires.

Palladium (Pd) has been drawing increasing attention as a hydrogen (H2) detecting material due to its highly selective sensitivity to H2. However, at H2 concentrations above 2%, Pd undergoes an inevitable phase transition, causing undesirable electrical and mechanical alterations. In particular, nonlinear gas response (ΔR/R0) that accompanies phase transition has been a great bottleneck for detecting H2 in high concentrations, which is especially important as there is a risk of explosion over 4% H2. Here, we propose a phase-transition-inhibited Pd nanowire H2 sensor that can detect up to 4% H2 with high linearity and high sensitivity. Based on the calculation of the change in free energy, we designed Pd nanowires that are highly adhered to the substrate to withstand the stress that leads to phase transition. We theoretically optimized the Pd nanowire dimensions using a finite element method simulation and then experimentally fabricated the proposed sensor by exploiting a developed nanofabrication method. The proposed sensor exhibits a high sensing linearity (98.9%) with high and stable sensitivity (ΔR/R0/[H2] = 875%·bar-1) over a full range of H2 concentrations (0.1-4%). Using the fabricated Pd sensors, we have successfully demonstrated a wireless sensor module that can detect H2 with high linearity, notifying real-time H2 leakage through remote communication. Overall, our work suggests a nanostructuring strategy for detecting H2 with a phase-transition-inhibited pure Pd H2 sensor with rigorous scientific exploration.

Regulating Pd-catalysis for electrocatalytic CO2 reduction to formate via intermetallic PdBi nanosheets

Electrocatalytic CO 2 reduction plays an important role in the reduction of the CO 2 concentration in atmosphere and consequently the mitigation of greenhouse effects. Pd has been extensively investigated as an electrocatalyst for the CO 2 reduction to formate, which is an important raw material in the production of organic chemicals. However, the low selectivity and competitive reaction (hydrogen evolution reaction (HER)) have hindered the performance of monometallic Pd catalysts. In this paper, intermetallic PdBi nanosheets (NSs) are prepared for efficient CO 2 reduction to formate. The highest Faradaic efficiency (FE) of formate on fully ordered PdBi NSs reaches 91.9% at −1.0 V vs . RHE, which outperforms that of the disordered PdBi and pure Pd catalysts. Density functional theory calculations suggest that compared to disordered PdBi NSs, the ordered structure can decrease the free energy barrier of *OCHO (a key intermediate of formate formation) and inhibit H 2 evolution as well, thereby enhancing the activity and selectivity for formate production. Intermetallic PdBi nanosheet with ordered hexagonal phase is developed as electrocatalyst for selective reduction of CO 2 to formate. The ordered-PdBi has a lower free energy barrier of *OCHO and higher energy barrier of *H than disordered-PdBi, enhancing the activity of formate production.

Preparation of Two-Dimensional Pd@Ir Nanosheets and Application in Bacterial Infection Treatment by the Generation of Reactive Oxygen Species.

Noble metal nanozymes have shown great promise in biomedicine; however, developing novel and high-performance noble metal nanozymes is still highly pressing and challenging. Herein, we, for the first time, prepared two-dimensional (2D) Pd@Ir bimetal nanosheets (NSs) with well-defined size and composition by a facile seed-mediated growth strategy. Enzyme-mimicked investigations find that the Pd@Ir NSs possess oxidase (OXD)-, peroxidase (POD)-, and catalase (CAT)-like multienzyme-mimetic activities. Especially, they exhibited much higher OXD- and POD-like activities than individual Pd NSs and Ir nanoparticles (NPs). The density functional theory (DFT) calculations reveal that the adsorption energy of O2 on Pd@Ir NSs is lower than that on the pure Pd NSs, which is more favorable for the conversion of O2 molecules from the triplet state (3O2) into the singlet state (1O2). Finally, based on the outstanding nanozyme activities to yield highly active singlet oxygen (1O2) and hydroxyl radicals (•OH) as well as excellent biosafety, the as-prepared Pd@Ir NSs were applied to treat bacteria-infected wounds, and satisfactory therapeutic outcomes were achieved. We believe that the highly efficient 2D Pd@Ir nanozyme will be an effective therapeutic reagent for various biomedical applications.

Pd/PdO Electrocatalysts Boost Their Intrinsic Nitrogen Reduction Reaction Activity and Selectivity via Controllably Modulating the Oxygen Level.

The electrocatalytic nitrogen reduction reaction (eNRR) is regarded as promising sustainable ammonia (NH3) production alternative to the industrial Haber-Bosch process. However, the current electrocatalytic systems still exhibit a grand challenge to simultaneously boost their eNRR activity and selectivity under ambient conditions. Herein, we construct Pd/PdO electrocatalysts with a controlled oxygen level by a facile electrochemical deposition approach at different gas atmospheres. Theoretical calculation results indicate that the introduction of an oxygen atom into a pure Pd catalyst would modulate the electron density of the Pd/PdO heterojunction and thus influence the adsorption energy for nitrogen and hydrogen. The calculation results and experiments show that the Pd/PdO heterojunction with a moderate oxygen level (O-M) exhibits optimal eNRR performance with a high NH3 yield of 11.0 μg h-1 mgcat-1 and a large Faraday efficiency (FE) of 22.2% at 0.03 V (vs RHE) in a 0.1 M KOH electrolyte. The moderate affinity of Pd to N in the Pd/PdO heterojunction and the inhibition of the hydrogen evolution reaction (HER) can facilitate the breaking of the triple bond of N2 and promote the protonation of N, which is confirmed by ex situ X-ray photoelectron spectroscopy (XPS) and in situ Raman spectroscopy. In situ Fourier transform infrared spectroscopy (FTIR) and density functional theory (DFT) calculations further disclose that the O-M catalysts prefer the distal association pathway during the eNRR process. This work opens a new way to construct heterostructures by controlling the oxygen level in other electrochemical fields.

Theoretical insights on the influence of Au core in Au[formula omitted]@Pd[formula omitted] for improving HCOOH dissociation

The core–shell bimetallic catalysts have unique catalytic activity due to the synergistic effect of the different elements. In this study, HCOOH dissociation on Au3@Pd1 and Au2@Pd2 has been investigated by using the density functional method. The results indicated that compared with pure Pd, the adsorption of the intermediates on the core–shell structures is strengthened by the introduced Au core. Strain effect plays an important role for the adsorption strength, which is also confirmed by the d band center. Compared with Au3@Pd1, Au2@Pd2 has better catalytic activity in the dissociation of HCOOH to produce H2. The rate determining step is bi-HCOO → mono-HCOO, which is also supported by the turnover frequency calculations for H2 production. In addition, the calculated turnover frequency shows that the order of the rate of H2 production is Au2@Pd2 > Au3@Pd1 > Pd(111), in agreement with the order of the catalytic activity from the energy barrier at the rate determining step for the three catalysts. This work provides insights concerning the influence of Au core on the catalytic activity at the atomic level and offers practical guidelines for the design of highly efficient catalysts.

Branch-Regulated Palladium-Antimony Nanoparticles Boost Ethanol Electro-oxidation to Acetate.

Tuning the composition and morphology of bimetallic nanoparticles (NPs) offers an effective strategy to improve their electrocatalytic performance. In this work, we present a facile wet-chemistry procedure to engineer PdSb NPs with controlled morphology. Spherical or branched NPs are produced by tuning the heterogeneous nucleation of Sb on Pd seeds. Compared with pure Pd NPs, the incorporation of Sb not only decreases the amount of Pd used but also results in a significant increase of activity and stability for the electrocatalytic ethanol oxidation reaction (EOR). Best performances are obtained with highly branched PdSb NPs, which deliver a specific activity of 109 mA cm-2 and a mass activity of up to 2.42 A mgPd-1, well above that of a commercial Pd/C catalyst and branched Pd NPs. Moreover, PdSb displays significant stability enhancement of over 10 h for the EOR measurements. Density functional theory calculations reveal that the improved performance of PdSb NPs is related to the role played by Sb in reducing the energy barrier of the EOR rate-limiting step. Interestingly, as a side and value-added product of the EOR, acetate is obtained with 100% selectivity on PdSb catalysts.

Hydrophobically modified Pd membrane for the efficient purification of hydrogen in light alcohols steam reforming process

The ability to selectively remove H2 from the product has made palladium (Pd) membrane reactor a good choice for steam reforming reaction. However, carbonaceous deposited on the surface of Pd membrane during reaction hindered its industrial application. In order to protect Pd membrane from being poisoned by water and light alcohols, a TS-1/Pd composite membrane was prepared by a facile one-step hydrothermal method combined with silane coupling treatment. The zeolite layer acted as a protective armor by keeping poisonous species away from the Pd bulk, and the silanization process increased the hydrophobicity by reducing the hydroxyl density on the surface of TS-1/Pd composite membrane. After 100 h’s exposure in the steam reforming condition, the percentage of carbon content was only 0.95% for the TS-1/Pd membrane, compared with 13.20% for the pure Pd membrane. The H2 permeability and H2/N2 selectivity of the TS-1/Pd remained constant, while that for pure Pd membrane fell by 50% and 80%, respectively. The significantly improved resistance to carbon deposition provides possibility for the large-scale application of Pd membrane reactor in hydrogen production via steam reforming.

Substantial enhancement of hydrogen permeability of Mo2C/V composite membranes by ion beam sputtering

Ion beam sputtering (IBS) was used to deposit Mo 2 C catalytic layers on vanadium (V) foils and to prepare Mo 2 C/V composite membranes for hydrogen separation and purification. It is found that the sputtering temperature during IBS largely affects the structure and catalytic activity of the as-deposited Mo 2 C films. A high sputtering temperature facilitates the growth of cubic Mo 2 C along the catalytically dominant crystal plane, which substantially enhances the hydrogen permeability of Mo 2 C/V. Typically, the Mo 2 C/V membranes prepared by IBS at a sputtering temperature of 600 °C exhibit a significantly high hydrogen permeability of ∼ 6.7 × 10 −8 mol H 2 m −1 s −1 Pa −0.5 at a hydrogen permeation temperature of 600 °C. This is 2.4 times that of Pd and 2.0 times that of Mo 2 C/V membranes prepared by conventional magnetron sputtering. The present work demonstrates that IBS is a promising technique to prepare highly permeable and cost-effective Mo 2 C/V membranes for high temperature hydrogen separation. • Ion beam sputtering is a potential method to prepare Mo 2 C/V for H 2 separation. • The sputtering temperatures largely affect the microstructures of Mo 2 C films. • The cubic Mo 2 C by ion beam sputtering exhibits a preferred growth of (220) plane. • Enhancement of catalytic activity of Mo 2 C leads to high H 2 permeability of Mo 2 C/V. • The highest H 2 permeability of Mo 2 C/V membranes is ∼2.4 times that of pure Pd.

Separation of Pd(II) and Zn(II) by Solvent Extraction using Commercial Extractants from Hydrochloric Acid Leaching Solution of Cemented Pd from Spent Electroplating Solutions

The demand for palladium (Pd) has increased and this has made it necessary to recover pure Pd from diverse secondary resources. To recover the small amount of Pd(II) present in spent electroplating solutions, Pd(II) is concentrated by cementation with zinc metal. In this work, a hydrometallurgical process consisting of leaching and solvent extraction was developed to recover Pd from the cemented Pd. The extraction behavior of Pd(II) and Zn(II) from synthetic HCl solution by commercial extractants such as LIX 63, Cyanex301, DOS, TBP, Alamin 308, Alamine 336 and Aliquat 336 was investigated by varying HCl concentration. The results showed that LIX 63, Cyanex 301 and DOS selectively extracted Pd(II) over Zn(II). These three extractants were employed to separate Pd(II) and Zn(II) from actual leaching solutions with cemented Pd using a mixture of 7.0 M HCl and 0.5% M H2O2 with 2 g/L pulp density at 60oC for 120 min. Cyanex 301 and DOS selectively extracted Pd(II) over Zn(II) from the leaching solution, while a small amount of Zn(II) was co-extracted with Pd(II) by LIX 63. A two stage counter-current extraction of actual leaching solution with LIX 63 resulted in the co-extraction of Zn(II) with Pd(II). The complete stripping of Pd(II) from the loaded Cyanex301 was achieved using either diluted aqua regia or a mixed solution of 5 M HCl and 0.5% NaClO at an A/O ratio of ten. The hydrometallurgical process is proposed to recover a pure Pd(II) solution from cemented Pd.

New PdNiAu ternary alloys as potential material for hydrogen separation processes

Novel PdNiAu ternary samples were successfully developed by sequential electroless deposition of the pure metals. The structure, composition, and morphology of the synthesized samples were analyzed by X-ray diffraction, Scanning Electron Microscopy, and energy-dispersive X-ray Spectroscopy. XRD analysis revealed that the metal deposition order (Ni→Pd→Au or Pd→Ni→Au) strongly affects the formation of a single and homogeneous FCC phase. By means of X-ray Photoelectron Spectroscopy, Pd-enrichment to the surface was evidenced in the sample with lower Ni content. The optimized procedure allowed synthesizing the Ni29Pd64Au7_PSS composite membrane, which exhibited a hydrogen permeance slightly higher than that reported for pure Pd.

Ir Single Atoms Doped Cuboctahedral Pd for Boosted Methanol Oxidation Reaction

AbstractThe construction of binary metal Pd‐based catalysts is an effective strategy to enhance the activity of methanol oxidation reaction. Herein, atomically dispersed Ir single atoms doped to cuboctahedral Pd nanoparticles (Ir‐SAs/Pd) as efficient catalysts for alkaline methanol oxidation are prepared via a simple chemical reduction method. The synthetic Ir‐SAs/Pd catalysts exhibit the outstanding mass activity of about 1717.3 mA mgPd−1 compared with pure Pd and commercial Pd/C in electrooxidation for methanol. Meanwhile, the introduction of Ir single atoms enhances the CO tolerance of Pd nanoparticles to a large extent. On the basis of density functional theory results, the enhanced catalytic performance and CO tolerance rely on the effective improvement of the electron dominance near Fermi level and the negative shift of the d‐band center for Pd as a result of the electron redistribution between Pd and Ir atoms. This article will provide new insight into the design of high‐performance binary metal catalysts for methanol oxidation in alkaline media.

Electronic structure engineering of bimetallic Pd-Au alloy nanocatalysts for improving electrocatalytic hydrodechlorination performance

Regulating the electronic structure of Pd catalyst for promoting electrocatalytic hydrodechlorination is promising but still challenging. Herein, we propose an electronic structure engineering for accelerating the hydrodechlorination process by desigining bimetallic Pd-Au alloy nanoparticles (ANs) with electron-rich Pd as high-efficiency electrocatalysts. The Pd7Au3 ANs exhibits the highest electrocatalytic hydrodechlorination activity, the 4-chlorophenol hydrodechlorination efficiency reaches 98.35 % within 4 h, and the mass activity is 0.47 h−1 mgPd−1, which is 7.83 times as high as that of pure Pd nanoparticles. The experimental characterization and theoretical calculation reveal that Pd atoms “obtain” electrons and gold atoms “lose” electrons in Pd-Au ANs, resulting in the formation of electron-rich Pd, which promotes the desorption of the dechlorination product phenol and accelerates the renewal of active sites. This work provides an electronic structure engineering strategy of Pd-based electrocatalysts for electrocatalytic hydrodechlorination, which opens a new opportunity for rational design and construction of high-performance hydrodechlorination catalysts.

Lattice-Resolution, Dynamic Imaging of Hydrogen Absorption into Bimetallic AgPd Nanoparticles.

Palladium's strong reactivity and absorption affinity to H2 makes it a prime material for hydrogen-based technologies. Alloying of Pd has been used to tune its mechanical stability, catalytic activity, and absorption thermodynamics. However, atomistic mechanisms of hydrogen dissociation and intercalation are informed predominantly by theoretical calculations, owing to the difficulty in imaging dynamic metal-gas interactions at the atomic scale. Here, we use in situ environmental high resolution transmission electron microscopy to directly track the hydrogenation-induced lattice expansion within AgPd triangular nanoprisms. We investigate the thermodynamics of the system at the single particle level and show that, contrary to pure Pd nanoparticles, the AgPd system exhibits α/β coexistence within single crystalline nanoparticles in equilibrium; the nanoparticle system also moves to a solid-solution loading mechanism at lower Ag content than bulk. By tracking the lattice expansion in real time during a phase transition, we see surface-limited β phase growth, as well as rapid reorientation of the α/β interface within individual particles. This secondary rate corresponds to the speed with which the β phase can restructure and, according to our atomistic calculations, emerges from lattice strain minimization. We also observe no preferential nucleation at the sharpest nanoprism corners, contrary to classical nucleation theory. Our results achieve atomic lattice plane resolution─crucial for exploring the role of crystal defects and single atom sites on catalytic hydrogen splitting and absorption.

Iron oxide-Palladium core-shell nanospheres for ferromagnetic resonance-based hydrogen gas sensing

Interfaces of ferromagnetic transition metals such as Iron, Cobalt, and Nickel with non-magnetic palladium are of interest due to their unique magnetic and spintronic properties. These interfaces enable ferromagnetic resonance (FMR) based sensing of hydrogen gas. In the present work, we synthesized Fe3O4–Pd core-shell nanospheres via a one-pot synthesis method using the thermal decomposition of Fe3+ acetylacetonate in the presence of a reducing agent to produce the Fe3O4 core, followed by the reduction of a Pd2+ precursor to form the pure Pd shell. We found that our in-situ synthesized core-shell nanostructure is magnetically active and shows excellent H2 gas sensing properties. The effect of reversible hydrogen gas absorption on the magnetism of Fe3O4–Pd core-shell nanospheres was investigated. The hydrogen-induced ferromagnetic-resonance (FMR) peak shift amounted to 30% of the peak linewidth for the virgin state of the sample. In addition, in the presence of hydrogen gas, we observed a fully reversible decrease in the FMR peak linewidth by about two times. This was accompanied by a nearly doubling of the FMR peak height. Response and recovery times of about 2 and 50 s, respectively, were extracted from the measurements. All the data was collected using a mix of just 3% hydrogen in a nitrogen carrier gas.

Design of Nb-Ti-Fe hydrogen permeable alloys based on the ductile-to-brittle transition-hydrogen concentration region

Nb-based dual-phase alloys are one of the most promising candidates for hydrogen purification. To solve their brittle fracture in hydrogen-containing atmospheres, the ductile-to-brittle transition-hydrogen concentration (DBTC) is a significant reference index, and the dissolved hydrogen concentration should be controlled below the lower limit of the DBTC, i.e., 0.72 H/M (atomic hydrogen to metal ratio). In this study, hydrogen permeable Nb-Ti-Fe alloys were designed and developed by using the above DBTC concept. Four hyper-eutectic Nb-Ti-Fe alloy membranes were prepared, and their hydrogen solubility was systematically analyzed by corresponding pressure-composition isotherms (PCT curves). The results show that all these samples had a linear relationship between the hydrogen concentration and square root of the hydrogen pressure between 0.1 and 0.4 MPa, which is in accordance with the Sieverts’ law. The hydrogen solubility of the specimens containing the primary TiFe phase was lower than 0.72 H/M, but the alloys with the primary Nb phase had a value that was much higher. The latter was completely broken during the test, even if the feed hydrogen pressure was reduced to 0.15 MPa. Based on the above results and DBTC concept, novel insights into the design of Nb-Ti-Fe hydrogen permeable alloys were elucidated; that is, an improvement in both the hydrogen permeability and hydrogen embrittlement resistance can be attained by controlling the hydrogen solubility. Following this concept, a Nb5Ti58Fe35Cu2 alloy was successfully developed that exhibited a high permeability of 4.32 × 10−8 mol H2 m−1 s−1 Pa−0.5 at 673 K, which is 2.7 times than that of a pure Pd membrane under the same test conditions. The present work demonstrated the feasibility and applicability of the DBTC concept in the design of dual-phase Nb-Ti-Fe hydrogen permeable alloy membranes.

Selective precipitation of ammonium hexachloropalladate from leaching solutions of cemented palladium with zinc

Palladium (Pd) present in spent electroplating solutions is concentrated by cementation with zinc (Zn) metal powder. Therefore, it is necessary to recover Pd from the cemented Pd. In this work, recovery of pure Pd(IV) compounds from the leaching solutions of the cemented Pd was investigated by using selective precipitation method. It was found that the existence of Pd(IV) in the aqueous solutions is critical for the precipitation with NH4Cl. Precipitation experiments of Pd(IV) from the synthetic aqua regia solution containing Pd(IV) and Zn(II) was tested. Afterwards, the optimum precipitation conditions were applied to recover Pd(IV) precipitates from the real H2SO4 and HCl leaching solutions containing NaClO as an oxidizing agent. The selective precipitation resulted in the recovery of extra pure (NH4)2PdCl6 from real leaching solutions under the conditions of 1:30 molar ratio of Pd(IV) to NH4Cl at 60oC within 30 min. The precipitation percentage of Pd(IV) from the H2SO4 and HCl solutions was over 99.9 and 98.2%, respectively. A simple hydrometallurgical process consisting of cementation, leaching, and precipitation was proposed for the recovery of pure Pd(IV) compounds from spent electroplating solution.

Resistivity Testing of Palladium Dilution Limits in CoPd Alloys for Hydrogen Storage.

Palladium satisfies most of the requirements for an effective hydrogen storage material with two major drawbacks: it has a relatively low gravimetric hydrogen density and is prohibitively expensive for large scale applications. Pd-based alloys should be considered as possible alternatives to a pure Pd. The question is how much one can dilute the Pd concentration in a variety of candidate materials while preserving the hydrogen absorption capability. We demonstrate that the resistivity measurements of thin film alloy samples can be used for a qualitative high-throughput screening and study of the hydrogen absorbing properties over the entire range of palladium concentrations. Contrary to palladium-rich alloys where additional hydrogen scattering indicates a degree of hydrogen content, the diluted alloy films respond by a decrease in resistance due to their thickness expansion. Evidence of significant hydrogen absorption was found in thin CoPd films diluted to just 20% of Pd.