PdCu Alloy Research Articles

Surface Energy Modulation of PdCu Nanocatalysts Via the Crystal Structure Change for Lithium-Oxygen Battereis

Palladium-copper (PdCu) alloys have two representative crystal structures; one is body-centered cubic (bcc), the other is face-centered cubic (fcc) even though both Pd and Cu originally have fcc crystal. The fcc PdCu alloys have disordered structure within which Pd and Cu have solid-solution in fcc lattice, whereas the bcc PdCu alloys have ordered structure which consists of alternative layers with either Pd or Cu atoms. In particular, bcc PdCu alloys have occasionally shown superior performance to fcc PdCu alloys since the unique ordered structure of bcc has isolated Pd on the surface. Most of bcc PdCu alloys have been synthesized for structural transformation by annealing or seed-growth method of fcc PdCu alloys with inevitable grain growth, uneven surface structure and particle size distribution. Despite these limitations, the Pd on the bcc surface which is provided charge flow from Cu serves as an active site for catalytic reaction, which is highly favorable for lithium-oxygen battery. However, the same size of fcc and bcc PdCu alloys is quite difficult to be obtained since the crystallites larger than 20 nm favor the ordered bcc structure with lower symmetry. Thus, bcc PdCu alloys in nanoscale have been rarely reported, consequently fcc and bcc PdCu nanoparticles (NPs) have never been properly compared until now. In this study, we successfully synthesize fcc and bcc PdCu alloys in nanoscale through precisely adjusting the driving force for reducing organometallic complex. The bcc PdCu NPs with higher surface energy govern the growth thermodynamics of discharge product and greatly improved battery performance based on density functional theory calculation and experimental proof. This study provides critical descriptor on material design in the perspective of modulating surface structure via crystal structure to tune its intrinsic properties.

PdCu nanoalloy immobilized in ZIF-derived N-doped carbon/graphene nanosheets: Alloying effect on catalysis

Reducing toxic Cr(VI) to Cr(III) by formic acid attracts much interest for chromium remediation but still needs efficient catalysts to boost its sluggish kinetics. Herein, PdCu nanoalloy (∼3 nm) was uniformly immobilized in N-doped carbon/graphene (NCG) porous nanosheets that were derived from the sandwich-like ZIF-8/graphene oxide precursor. The resulting PdCu/NCG showed a high specific area (SBET) of 656.1 m2 g−1 and a superior activity (kn) of 38.2 min−1 mg−1 for the Cr(VI) reduction with formic acid as reductant, which outperformed its monometallic counterparts and most of noble-metal catalysts. The catalytic performance highly depended on the composition of PdCu nanoalloy and NCG support. DFT calculation and XPS analysis proved the presence of electron transfer from Cu to Pd upon alloying, which induced an upshift of d-band center (εd) of PdCu metals with respect to Fermi energy. The elevated εd facilitated the chemisorption and C–H breakage of formic acid to produce active H species on the catalyst. Such alloying-induced electronic modification of PdCu alloy and porous feature of NCG nanosheets both accounted for the catalytic enhancement.

Synthesis of uniform bulk nanoporous palladium with tunable structure

This work presents systematic investigations on the synthesis of hierarchical nanoporous Pd via electrochemical dealloying of CuPd alloys in sulfuric acid. The impact of electrode potential, dealloying temperature, and additional annealing on microstructure and morphology is explored. Dealloying Cu85Pd15 in 1M sulfuric acid at elevated temperature provides a facile strategy to produce bulk nanoporous Pd samples which are uniform, hierarchically nanoporous, and free of macro-scale cracks. The question “Why will one-step template-free dealloying yield a hierarchical and not unimodal nanoporous structure?” is discussed. The impact of passivation and of a percolating Cu-rich cluster on the pore structure is inspected. A structural instability concept for dealloying of dilute master alloys is preferred as the underlying mechanism. Nanoporous Pd with classical, unimodal pore structure and tunable ligament size ranging from 80 to 270 nm emerges when the as-prepared hierarchical nanoporous Pd is annealed. The material of this study may provide a model system that complements nanoporous Au for studies of bulk nanoscale metal networks as functional and structural materials.

The mechanism of Pd distribution in the process of FAB formation during Pd-coated Cu wire bonding

The palladium (Pd) distribution over the free air ball (FAB) and its effect on the ball’s shear strength were investigated in the Pd-coated copper (Cu) wire bonding process. It was found that for the same FAB/wire diameter ratio of 1.5, the bigger the electrical flame-off (EFO) current was, the larger would be the exposed Cu regions over FAB without Pd distribution. Combining experimental observations, a model of Pd distribution over FAB was first proposed by changing the EFO current and firing time. As the firing time increased, the coated Pd element could be dissolved into the Cu base to form a PdCu alloy at the FAB surface, to protect the bonded ball from corrosion. The Pd-coated Cu wire has higher bonding shear strength than the bare Cu wire. However, the FAB with the largest Pd coverage had the smallest ball shear strength, which revealed that the control of Pd distribution over FAB is very critical for a high-quality bonding interface.

Bowl-Like and Apple-Like PdCu Hollow Microparticles with Mesoporous Nanoshells: Synthesis, Characterization, and Electrocatalytic Performance

Novel bowl-like, apple-like, and spherical PdCu alloy hollow microparticles with mesoporous nanoshells are synthesized through a simple disproportionation reaction route using a spherical Cu2O template with increasing H2PdCl4 ratio. The diameter of hollow particles is about 1 μm, and the thickness of mesoporous shells is about 50 nm. The obtained bowl-like PdCu alloy hollow microparticles with mesoporous nanoshells exhibit the highest electrocatalytic activity among the apple-like and spherical PdCu hollow microparticles and commercial Pd/C electrocatalysts toward methanol anodic oxidation for fuel cells. The remarkably excellent electrocatalytic performance of bowl-like PdCu alloy electrocatalysts might be attributed to the unique bowl-like hollow architecture with highly mesoporous nanoshells which are constructed by self-supported PdCu nanoparticles. The strategy presented here might help pave the way for the synthesis of novel nano-/microcomplex hollow materials with mesoporous nanoshells.

PdCu Alloy Flower-like Nanocages with High Electrocatalytic Performance for Methanol Oxidation

PdCu alloy flower-like nanocages are synthesized through corner-etched Cu2O octahedra as templates by galvanic reaction and disproportionation reaction. PdCu alloy nanocages are obtained with the molar ratio of H2PdCl4/Cu2O = 1:1, and the Pd nanoparticles are prepared with the molar ratio of H2PdCl4/Cu2O = 2:1. The PdCu alloy flower-like nanocages display the highest catalytic activity compared with Pd nanoparticles toward methanol oxidation reaction in alkaline medium, which is 2.7 times than that of commercial Pd/C. In addition, PdCu alloy nanocages also show high poison-tolerance and good stability. The superior electrocatalytic performance of PdCu flower-like nanocages may be attributed to the unique flower-like nanocage structure with high surface area and the synergic effect of Pd and Cu.

CO2 hydrogenation to methanol on Pd-Cu bimetallic catalysts: H2/CO2 ratio dependence and surface species

Our laboratory has observed a strong bimetallic promoting effect on SiO2-supported Pd-Cu catalysts for CH3OH formation from CO2 hydrogenation when the Pd/(Pd + Cu) atomic ratio lied within 0.25–0.34. In the present study, the activities of bimetallic and monometallic catalysts were comparatively evaluated at H2/CO2 = 1, and the origin for the bimetallic promoting effect was sought by a kinetic study and in situ DRIFTS analysis. The bimetallic promoting effect was retained at H2/CO2 = 1, although both the activity and CH3OH selectivity decreased, indicating the significant role of hydrogen partial pressure in the CO2 hydrogenation. Kinetic study provided insights into the strong dependence of CH3OH synthesis on H2/CO2 ratios and roles of Pd-Cu alloys in the observed CH3OH promotion, wherein the alloys could tune the surface sites balance of adsorbed species, and enabled the reduction of activation barrier for CH3OH synthesis. Temperature-programmed reduction results corroborated the strong interaction between Pd and Cu and its impact on the alloy structuring and reducibility. In situ DRIFTS analysis identified formate and carbonyl species were dominant on the surface during the reaction. The surface coverage of formate species was dependent on the catalyst composition, and appeared to correlate to the methanol promotion, implying its key role in the CH3OH synthesis on Pd-Cu catalysts.

Growth morphology and structure of PdCu ion-plasma condensate in the pores of SiO2 and Al2O3 amorphous matrices

The features of the growth morphology and structure of ion-plasma palladium-copper condensate both on the surface and in the pores of amorphous SiO2 and Al2O3 matrices were studied by scanning electron microscopy and high resolution transmission electron microscopy. Differences in the morphology and crystal structure of the metallic ion-plasma condensate obtained by magnetron sputtering deposition of the PdCu alloy on the surface and in a limited pore volume were shown and substantiated. The main regularities of the ion-plasma condensates formation on a developed surface with a high open porosity were discussed.

Cost-effective nitrogen-doped carbon black supported PdCu alloy nanocatalyst for green Suzuki-Miyaura reactions under mild conditions

A nitrogen-doped carbon black (NCB) supported PdCu alloy nanocatalyst is fabricated via a facile one-pot soft chemistry route. The PdCu nanoparticles are uniformly dispersed on the NCB surface with an average size of 3.51 nm. The PdCu/NCB catalyst exhibits superior catalytic activity and significantly improved durability towards the Suzuki-Miyaura coupling reaction in ethanol/water system under mild conditions without a protective atmosphere. Particularly, the Pd5Cu5/NCB catalyst can efficiently catalyzed the SMC reaction with the yield up to 94% in 1.5 h, 7-fold higher than that by the pristine Pd/NCB catalyst (13%). Compared with the carbon black supported PdCu catalyst, nitrogen-doping can lead to better dispersion of the PdCu alloy nanoparticles on the NCB surface with a smaller particle size. The excellent catalytic performance can be attributed to the unique nanostructure of the catalyst and concerted effect of the individual components. Notably, alloying Pd with Cu can effectively reduce the cost of the catalyst.

Photocatalytic Sonogashira reaction over silicon carbide supported Pd–Cu alloy nanoparticles under visible light irradiation

PdCu alloy nanoparticles supported on SiC can efficiently catalyze the Sonogashira reaction by visible light irradiation under ligand-free and mild conditions. The superior catalytic activity of PdCu catalysts was caused by the synergistic effect of PdCu alloy nanoparticles.

Flower-like PdCu catalyst with high electrocatalytic properties for ethylene glycol oxidation

A highly efficient PdCu alloy nanocatalyst has been designed and synthesized, which exhibited excellent selectivity and activity toward ethylene glycol (EG) oxidation reaction with a low loading of electrocatalyst. The results of characterization show that the atom ratio of 1:1 (Pd:Cu) as well as the addition of polyvinyl pyrrolidone (PVP) and potassium bromide (KBr) contributed to the unique morphology of the as-prepared PdCu catalyst. Owing to the flower-like nanostructure and the synergistic effect between Pd and Cu, PdCu electrocatalyst has distinct enhancement in electrocatalytic performance whose forward peak current density is almost 3.2 and 4.3 times higher than that of pure Pd and commercial Pd/C electrocatalysts. We put forward that the prepared PdCu catalyst may have promising and alternative applications in direct EG alkaline fuel cells.

Influence of temperature and pressure on surface modified Pd-Cu alloy foils for hydrogen purification applications

The surface of as-received Pd60Cu40wt% foil samples was modified by depositing a Pd thin film onto one side. X-ray diffraction analysis revealed that the as-received Pd60Cu40wt% foil contained only the disordered face centred cubic (FCC) phase. Three different Pd thin film thicknesses (100, 800 and 1400nm) were deposited using magnetron sputtering onto the as-received Pd60Cu40wt% foil to produce the surface modified foil samples. X-ray diffraction and X-ray photoelectron spectroscopy analysis of these samples showed a strong indication that Cu interdiffusion occurred between the bulk Pd-Cu foil and Pd thin film during the deposition process.For the first time, variable temperature X-ray diffraction analysis has been performed on the surface modified foil samples between 30 and 700°C under 100 and 445kPa of hydrogen pressure in order to investigate the effects of these conditions on Cu interdiffusion. In general, it was found that under 445kPa of hydrogen pressure the palladium hydride (β-PdH) phase present in the thin film is stable up to relatively higher temperatures (225°C) when compared to 100kPa of hydrogen pressure (150 to 175°C). In all cases, it was observed that the interstitial solid solution (α-PdH) phase present within the thin film is stable under a significantly narrower temperature range under 445kPa of hydrogen pressure when compared to 100kPa of hydrogen pressure.

Cu assisted synthesis of self-supported PdCu alloy nanowires with enhanced performances toward ethylene glycol electrooxidation

Self-supported PdCu alloy nanowires fabricated by a facile one-pot method have been reported, which copper assists in the morphological transformation from graininess to nanowires. The copper incorporated with palladium to form alloy structures cannot only cut down the usage of noble metal but also enhance their catalytic performances. The catalysts with self-supported structure and proper ratio of palladium to copper show great activity and long-term stability for the electrooxidation of ethylene glycol in alkaline solution. Especially for Pd43Cu57, its mass activity reaches to 5570.83mAmg−1, which is 3.12 times as high as commercial Pd/C. This study highlights an accessible strategy to prepare self-supported PdCu alloy nanowires and their potential applications in renewable energy fields.

Exploratory studies of the Cu–Pd–Se system at 650°C, 550°C, 400°C, and 300°C

The condensed-phase system Cu–Pd–Se was investigated by means of dry syntheses from elements in evacuated silica glass tubes at 650 °C, 550 °C, 400 °C, and 300 °C. Synthetized phases were analysed by electron microprobe and textural studies in polished sections. At 650 °C an extensive selenide liquid field covers central portions of the system, coexisting with a limited choice of Pd selenides, Cu 2– x Se, alloys, and a (Cu,Pd)Se 2 solid solution. The selenide melt recedes to the Pd side of the system at 550 °C and its remnants persist at 400 °C. At the lower temperature, the gamut of Pd selenides becomes richer, and especially Pd 4 Se and Pd 17 Se 15 display significant solubility of Cu. The composition range of (Cu,Pd)Se 2 broadens and moves towards Cu-richer compositions as temperature decreases; CuSe and CuSe 2 appear at 300 °C. The synthetic analogue of jagueite, Cu 2 Pd 3 Se 4 , is present at 400 °C and 300 °C, at Se concentrations above the Cu 2– x Se–Pd 17 Se 15 line. At all examined temperatures, the individualized CuPd alloy dissolves Se, up to ∼5 at% at low temperatures.

Electrochemical studies of Pd-doped Cu and Pd-doped Cu-Al intermetallics for understanding corrosion behavior in wire-bonding packages

This study investigated the electrochemical characterizations in the field of wire metallurgy (Pd concentration) and molding compound chemistry (chloride concentration) to find ways to reduce metallic entities' susceptibility to corrosion at ball-pad interfaces. The open circuit potentials and potentiodynamic polarization curves of various metallic entities found in a Cu(Pd)-Al bonding interface were obtained in near-neutral electrolytes of 100ppm, 20ppm, and 1ppm of NaCl in high-purity water. From X-ray diffraction spectra, it was found that Pd could be homogeneously incorporated into Cu9Al4, the Cu-rich intermetallic compound (IMC) also referred to as γ but not into CuAl2, the Al-rich IMC also referred to as θ for arc-melted specimens. For Cu-Pd alloys, at a given chloride concentration, increasing Pd concentration causes the value of open-circuit potential (Eoc) to increase and corrosion current density (icorr) to decrease. Likewise, for a given amount of Pd in Cu-Pd alloy, decrease in the NaCl concentration causes the value of Eoc to increase and icorr to decrease. Interestingly, for high concentration of Pd as in the case of Cu-9Pd, Eoc and icorr became less sensitive to the NaCl concentrations investigated. This can be attributed to the Pd enrichment on the corroding surface that reduces the anodic dissolution rate of Cu. For Pd-doped γ intermetallics, increasing Pd concentration causes a systemic increase in the value of Eoc, but at a lower concentration of Pd, the value of icorr was increased. The addition of Pd to γ causes an increase in the cathodic current density due to the high cathodic activity of Pd, while the passivation of Al in γ reduces the extent of the anodic current density reduction due to the addition of Pd, which leads to a higher value of icorr at a low Pd concentration. This is true even when the NaCl concentration is as low as 1ppm. On the other hand, the influence of NaCl concentration on the Eoc and icorr of γ IMC was always observed, even with Pd addition.

Optimization of the Pd/Cu ratio in Pd-Cu-Zn/SiC catalysts for the CO2 hydrogenation to methanol at atmospheric pressure

PdCuZn/SiC catalysts were synthesized with different Pd:Cu:Zn molar compositions and tested in the hydrogenation of carbon dioxide to methanol at atmospheric pressure. Trimetallic catalysts were compared with the corresponding bimetallic ones (PdZn/SiC, CuZn/SiC and PdCu/SiC). Catalysts were characterized by N2 adsorption/desorption, temperature-programed reduction (TPR), X-ray diffraction (XRD), transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS). The Pd0 active sites were related to carbon monoxide formation via reverse water-gas-shift (RWGS), whereas the PdZn alloys catalyzed methanol synthesis. The role of copper in trimetallic catalysts was to inhibit the deposition of metallic palladium by forming a PdCu alloy that proved to be less active to CO formation. Moreover, the active sites of trimetallic catalysts were smaller and better dispersed than those of the corresponding bimetallic ones, probably due to a synergistic effect between the three metals. The catalyst with a molar composition of 37.5:12.5:50 Pd:Cu:Zn (mol.%) was selected as the most active for the methanol synthesis, as this sample showed the highest activity and selectivity to methanol. The role of copper was also shown to be crucial in trimetallic catalyst by comparing the best example with an equivalent bimetallic PdZn/SiC with a Pd:Zn molar ratio of 37.5:62.5.

The interaction of CO with PdCu hydrogen separation membranes: An operando infrared spectroscopy study

Abstract Pd and PdCu alloy membranes are promising candidates for separating hydrogen from mixed gas streams due in part to their infinite selectivity to hydrogen separation. However, other gases such as CO can inhibit hydrogen transport across Pd-based membranes. In this work, the mechanism by which CO inhibits hydrogen transport across a 25 μm-thick Pd47Cu53 (mol%) membrane is investigated by operando infrared-reflection absorption spectroscopy (IRAS) in the 373–533 K temperature range. In the absence of hydrogen, CO adsorbs on three different sites on the PdCu surface: (1) bridging between contiguous Pd atoms, (2) on top of isolated Pd atoms surrounded by Cu atoms, and (3) on top of oxidized Cu atoms. CO induces agglomeration of isolated Pd atoms on the PdCu surface, which is driven by the higher stability of CO adsorbed on bridging sites between Pd atoms than on isolated Pd atoms surrounded by Cu atoms. The rate of hydrogen permeation across the PdCu alloy membrane decreases with increasing CO concentration in the feed gas, and the poisoning effect of CO is more severe at lower temperatures. CO inhibits hydrogen transport across the membrane by adsorbing only on Pd sites on the PdCu surface and blocking H2 dissociation on these sites. Due to the weaker interaction of CO with PdCu alloy surfaces than with Pd, the PdCu alloy is more resistant to CO poisoning than pure Pd.

Glycerol hydrodeoxygenation to 1,2-propanediol catalyzed by CuPd/TiO2-Na

Copper-palladium bimetallic catalysts supported on TiO2 were developed for the aqueous phase hydrodeoxygenation (HDO) of glycerol. Na-promoted bimetallic catalysts had higher activity than monometallic catalysts while maintaining high 1,2-propanediol (1,2-PDO) selectivity (76–93%) characteristic of Cu catalysts. The best results were obtained with CuPd/TiO2-Na. At 220°C and 0.7MPa H2 the initial turnover frequency (TOF based on Cu+Pd sites) was 0.14s−1; the selectivity to 1,2-PDO reached 85%. Characterization of the samples was performed by H2-temperature programed reduction (H2-TPR), X-ray diffraction and high-resolution electron microscopy (HRTEM) plus selected area electron diffraction (SAED), and their results were consistent with the formation of CuPd alloy nanoparticles with their surface enriched in Cu, hence explaining the high selectivity to 1,2-PDO of the bimetallics. The increased activity of the Pd-Cu bimetallic catalysts stems from the significantly smaller average diameter of the CuPd alloy nanoparticles when compared with the Cu or Pd nanoparticles of the monometallic catalysts. Besides the effect upon the nanoparticle structure, Pd promoted HDO in part by the activation of glycerol aqueous phase reforming to produce H2 at the surface level. Cu was stabilized in the bimetallic samples by the formation of the alloy with Pd and by the presence of Na in the catalyst. As a result, CuPd/TiO2-Na can be reused while maintaining high stable activity and 1,2-PDO selectivity. The HDO reaction proceeds through the formation of 1-hydroxy-2-propanone (acetol), followed by its hydrogenation to form 1,2 PDO. Formation of acetol or an acetol-like surface intermediate presumably occurs on support sites, whereas the hydrogenation to 1,2-PDO occurs on the metal sites. The first step is enhanced when basic sites are added to the support, while the hydrogenation step on Cu sites is improved by raising the H2 pressure and/or by the formation of H2 via reforming on Pd sites.

Low-temperature stability of body-centered cubic PdCu membranes

Concerns about limited durability at ambient temperatures are a major obstacle for the utilization of Pd-type membranes for H2 purification in local, on-demand H2 production. It is clear that pure Pd membranes are not suitable for applications that involve fast regular start-up and shut-down of purification systems but knowledge remains sparse about the performance of Pd alloy membranes in such situations. Here we investigated the stability of thin-layered, supported PdCu membranes with body-centered cubic (bcc) structure between room temperature and 673K at H2 pressure differences ΔPH2 up to 1MPa. Three PdCu layers with 46–50% Pd have been prepared by alternating electrodeposition of multiple Cu and Pd layers onto metallized ceramic membranes and subsequent alloying at 673–773K. The H2 permeation rates of all membranes can be described by single permeation laws in the entire investigated temperature range. The nominal H2 permeability of a Pd48Cu52 membrane amounted to 2.3 × 10−9molm−1s−1Pa−0.5 at 673K and ΔPH2 = 100kPa with an ideal H2/N2 selectivity of 3382. The H2 fluxes and N2 leak rates of the three membranes were not affected by cycling between room temperature and 673K under up to 1.1MPa H2 which included more than a dozen H2/N2 exchanges at 298K. These fluxes remained also stable through 100h continuous operation in H2 at that temperature. The excellent low-temperature tolerance of these membranes is attributed to the marginal hydrogen solubility in bcc PdCu alloys rendering them promising membrane materials for H2 purification involving everyday operation at ambient temperatures.

Synthesis of Ultrathin PdCu Alloy Nanosheets Used as a Highly Efficient Electrocatalyst for Formic Acid Oxidation.

Inspired by the unique properties of ultrathin 2D nanomaterials and excellent catalytic activities of noble metal nanostructures for renewable fuel cells, a facile method is reported for the high-yield synthesis of ultrathin 2D PdCu alloy nanosheets under mild conditions. Impressively, the obtained PdCu alloy nanosheet after being treated with ethylenediamine can be used as a highly efficient electrocatalyst for formic acid oxidation. The study implicates that the rational design and controlled synthesis of an ultrathin 2D noble metal alloy may open up new opportunities for enhancing catalytic activities of noble metal nanostructures.