Au-Pd Alloy Research Articles

CO2-Mediated Hydrogen Energy Release-Storage Enabled by High-Dispersion Gold-Palladium Alloy Nanodots.

Developing and fabricating a heterogeneous catalyst for efficient formic acid (FA) dehydrogenation coupled with CO2 hydrogenation back to FA is a promising approach to constructing a complete CO2-mediated hydrogen release-storage system, which remains challenging. Herein, a facile two-step strategy involving high-temperature pyrolysis and wet chemical reduction processes can synthesize efficient pyridinic-nitrogen-modified carbon-loaded gold-palladium alloy nanodots (AuPd alloy NDs). These NDs exhibit a prominent electron synergistic effect between Au and Pd components and tunable alloy-support interactions. The pyridinic-N dosage in carbon substrate improves the surface electron density of the alloy catalyst, thus regulating the chemical adsorption of FA molecules. Specifically, the engineered Au3Pd7/CN0.25 demonstrates an outstanding room-temperature FA dehydrogenation efficiency, achieving ≈100% conversion and an initial turnover frequency (TOF) of up to 9049h-1. The versatile AuPd alloy NDs also show the ability to convert CO2, one of the products of FA dehydrogenation, into FA (formate) with a 90.8% yield under mild conditions. Moreover, in-depth insights into the unique alloyed microstructure, structure-activity relationship, key intermediates, and the alloy-driven five-step reaction mechanism involving the rate-determining step of C─H bond cleavage from critical *HCOO species via D-labeled isotope, in situ infrared spectroscopy, and theoretical calculations are investigated.

Surface properties of PdAu and PdNi alloys under dynamic conditions: NAP-XPS study

Electroless-deposited PdAu and PdNi alloy samples were analyzed using near-ambient X-ray photoelectron Spectroscopy (NAP-XPS) under H2, CO, and CO2-containing streams. Gold enrichment in the near-surface region was evidenced in the PdAu sample under all the analyzed conditions, while palladium increment to the surface was observed in the PdNi alloy. The appearance of a new contribution on the Pd 3d core-level region evidenced the formation of PdHx species on the surface. Competitive CO adsorption and the formation of CHx species at the surface led to the partial blocking of hydrogen adsorption sites, thereby decreasing the PdHx formation. Methane production was detected under CO/H2 and CO2/H2 mixtures in both PdAu and PdNi alloy samples. Our findings demonstrate that both competitive adsorption and the formation of CHx or carbide species on the surface of PdAu and PdNi alloys can negatively influence hydrogen permeation through Pd-based membranes.

Wheatstone Bridge MEMS Hydrogen Sensor with ppb-Level Detection Limit Based on the Palladium-Gold Alloy.

On some occasions, such as new energy clinics, monitoring the trace hydrogen at the ppb level is necessary. The traditional resistive hydrogen sensors based on the Pd alloys are very difficult to realize such an extremely low detection limit. To achieve a detection limit at the ppb level and also ensure good stability, a MEMS hydrogen sensor was designed in a suspended Wheatstone bridge structure, with all four resistive arms defined on a sputtered Pd-Au alloy thin film. For the Wheatstone bridge sensor, absolute response (Ra) and relative response (Rs) are defined to describe the sensitivity of the sensor, and the effect of annealing temperature on baseline drift is investigated using the baseline zero drift parameter (DBZD). By testing the sensors across a hydrogen concentration range of 20 ppb to 3 v/v%, the optimal annealing temperature (250 °C) and operating temperature (60 °C) were identified. Under these conditions, the sensor exhibited a detection limit as low as 20 ppb with a power consumption of only 4.6 mW. At the same time, the response and recovery times of the sensor were 6 and 19 s, respectively, toward 3 v/v% hydrogen. After testing over a 100-day period, Ra fluctuated only 0.0026%, indicating that the hydrogen sensor had good long-term stability for low-concentration detection. More results also showed that the sensor has good repeatability, selectivity, and humidity resistance. With the wide measurement range (20 ppb to 3 v/v%), the sensor has the potential to meet hydrogen detection requirements in multiple scenarios.

Satellite Pd Single-Atom Embraced AuPd Alloy Nanoclusters for Enhanced Hydrogen Evolution.

The fabrication of hybrid active sites that synergistically contain nanoclusters and single atoms (SAs) is vital for electrocatalysts to achieve excellent activity and durability. Herein, we develop a ligand-assisted pyrolysis strategy using nanoclusters (Au4Pd2(SC2H4Ph)8) with alloy cores and protected ligands to build AuPd cluster sites embraced by satellite Pd SAs. In the thermal drive control process, different thermodynamic properties of the alloy atoms and the confinement effects of organic ligands allow for the mild spillover of the single-component metal Pd, resulting in the formation of AuPd alloy nanoclusters tightly encompassed by isolated Pd atoms. Experiments and theoretical calculations indicated that the satellite Pd atoms can optimize the electronic structure of the AuPd nanoclusters and Au sites in the alloy to facilitate the adsorption and dissociation of H2O, thus enhancing the hydrogen evolution reaction (HER) activity. The optimal AuPdNCs/PdSAs-600 exhibits outstanding electrocatalytic activity toward HER, with overpotentials of 21 and 38 mV at 10 mA cm-2 in acidic and alkaline media, respectively. Moreover, the mass activity and turnover frequency of AuPdNCs/PdSAs-600 are one order of magnitude higher than those of commercial Pd/C and Pt/C catalysts. This facile strategy for constructing hybrid catalytic centers using ligand-protected nanoclusters provides efficient insights for the further design of nanocluster-based electrocatalysts synergized by SAs.

Optimizing H-adsorption affinity on electron-enriched Pdδ- active sites for efficient photocatalytic H2 evolution

Noble metal Pd is a promising H2-evolution cocatalyst and has attracted expansive attention in photocatalytic water splitting. However, the present H2-production rate of Pd cocatalysts is still limited due to its strong hydrogen adsorption on Pd active sites, resulting in poor hydrogen evolution kinetics. In this work, an electron-enriched Pdδ- modulation strategy is developed to weaken the hydrogen adsorption on Pd active sites by producing PdAu alloy, resulting in an increased H2-production rate. In this case, the PdAu homogeneous alloy with a particle size of 9–20 nm is uniformly deposited on the TiO2 surface to produce PdAu-modified TiO2 photocatalysts (TiO2/PdAu). It is found that the prepared TiO2/Pd79Au21 sample achieves the maximal photocatalytic H2-production performance of 31.98 mmol g-1 h−1, which is 1.53 times higher than that of TiO2/Pd photocatalyst. Experimental and theoretical studies show that in addition to the promoted transfer of photogenerated carriers, the PdAu alloy can spontaneously induce the electron transfer from Au to Pd to form electron-enriched Pdδ- sites, which prominently weakens the Pd-Hads bonds and thus improve the H2-production efficiency. This study provides further insight into the rational optimization of active sites to facilitate the design of efficient photocatalysts.

Change of composition and surface plasmon resonance of Pd/Au core/shell nanoparticles triggered by CO adsorption.

Controlling composition and plasmonic response of bimetallic nanoparticles (NPs) is of great relevance to tune their catalytic activity. Herein, we demonstrate reversible composition and plasmonic response transitions from a core/shell to a bimetallic alloyed palladium/gold NP triggered by CO adsorption and sample temperature. The use of self-organized growth on alumina template film allows scrutinizing the impact of core size and shell thickness onto NP geometry and plasmonic response. Topography, molecular adsorption, and plasmonic response are addressed by scanning tunneling microscopy, vibrational sum frequency generation (SFG) spectroscopy, and surface differential reflectance spectroscopy, respectively. Modeling CO dipolar interaction and optical reflectivity corroborate the experimental findings. We demonstrate that probing CO adsorption sites by SFG is a remarkably sensitive and relevant method to investigate shell composition and follow in real-time Pd atom migration between the core and the shell. Pd-Au alloying is limited to the first two monolayers of the shell and no plasmonic response is found, while for a thicker shell, a plasmonic response is observed, concomitant with a lower Pd concentration in the shell. Above 10-4mbar, at room temperature, CO adsorption triggers the shell restructuration, forming a Pd-Au alloy that weakens the plasmonic response via Pd migration from the core to the shell. NP annealing at 550K, after pumping CO, leads to the desorption of remaining CO and gives enough mobility for Pd to migrate back inside the core and recover a pure gold shell with its original plasmonic response. This work demonstrates that surface stoichiometry and plasmonic response can be tuned by using CO adsorption and NP annealing.

Nanoparticles of PdAu Alloys on BiOBr Nanosheets for Highly Efficient Photocatalytic Suzuki–Miyaura Reactions

Nanoparticles of PdAu Alloys on BiOBr Nanosheets for Highly Efficient Photocatalytic Suzuki–Miyaura Reactions

Dynamics of Dilute Nanoalloy Catalysts.

Capturing the dynamic character of metal nanoparticles under the reaction conditions is one of the major challenges within heterogeneous catalysis. The role of nanoparticle dynamics is particularly important for metal alloys as the surface composition responds sensitively to the gas environment. Here, a first-principles-based kinetic Monte Carlo method is developed to compare the dynamics of dilute PdAu alloy nanoparticles in inert and CO-rich atmospheres, corresponding to reaction conditions for catalyst deactivation and activation. CO influences the dynamics of the activation by facilitating the formation of vacancies and mobile Au-CO complexes, which are needed to obtain CO-stabilized Pd monomers on the surface. The structure of the catalyst and the location of the Pd monomers determine the rate of deactivation. The rate of catalyst deactivation is slow at low temperatures, which suggests that metastable structures determine the catalyst activity at typical operating conditions. The developed method is general and can be applied to a range of metal catalysts and reactions.

Synergy of alloy and ligand for CO2 hydrogenation to formic acid on PdAu/HPC-AP

Formic acid (FA) is of great significance given its extensive applications in various industrial fields. At present, methanol carbonylation is the main industrial production process of FA. However, this process uses two kinds of raw materials from fossil fuels and emits a large amount of CO2. Alternatively, converting CO2 into FA can not only achieve the production of value-added chemicals but also effectively address environmental issues caused by CO2 emission. To improve the low reactivity of CO2, homogeneous and heterogeneous catalytic systems have been widely evaluated, among which heterogeneous catalytic systems are attracting ever-increasing attention owing to their great industrialization prospects. However, some of these heterogeneous catalysts suffer from low catalytic performance. Herein, PdAu alloy nanoparticles anchored on amine-functionalized hierarchical porous carbon (PdAu/HPC-AP) were constructed to drive efficient converting of CO2 into FA. Characterization and testing results demonstrated that the introduced Au atoms caused lattice distortion and charge redistribution on the surface of the bimetallic catalyst, facilitating the adsorption and activation of reaction molecules. Furthermore, the modification of HPC with an appropriate amount of amine ligands was found important to the chemical adsorption of CO2 and the dispersion of PdAu NPs. The Pd60Au40/HPC-AP catalyst with the optimum synergy of alloy and ligand demonstrated excellent activity for the target reaction with a TOF value of 486 h–1 at 100 °C. Moreover, it can even catalyze the reaction at room temperature with a TOF value of 13 h–1.

Facile interfacial synthesis of thin AuPd alloy nanowires for plasmon-enhanced selective photocatalytic oxidation of benzyl alcohol

Bimetallic AuPd plasmonic photocatalyst is a promising candidate for catalyzing selective oxidation of aromatic alcohol. However, developing a simple one-step method for the preparation of free-standing AuPd nanostructures with excellent photocatalytic performance remains a huge challenge. Here, a facile liquid–liquid interface route was exploited to one-pot prepare free-standing AuPd alloy nanowires (NWs) under mild conditions. Specifically, Au1Pd1 NWs are grown via oriented attachment at chloroform-water interface and 40 °C with Na2PdCl4 and HAuCl4 as precursors and 1-naphthol as reductant. Au1Pd1 NWs possess many advantages, such as thin diameter (4.0 nm), large aspect ratio, abundant defects and strong Au-Pd electronic interaction. During benzyl alcohol oxidation to benzaldehyde, Au1Pd1 NWs exhibit excellent photocatalytic activity and durability. At 40 min of visible light illumination, 98 % conversion of benzyl alcohol and 100 % selectivity to benzaldehyde are finished. After five cycles, Au1Pd1 NWs still maintain high photocatalytic activity. Compared to pure Au NWs, alloying Pd with Au in Au1Pd1 NWs dramatically enhances photocatalytic activity. The results indicate that the generated abundant •O2– under illumination play an important role in significantly improving benzyl alcohol oxidation to benzaldehyde.

Facile synthesis of highly active PdAu alloy nanochains for alcohol oxidation electrocatalysis

An efficacious strategy to enhance the activity and stability of electrocatalysts for alcohol oxidation reactions is the formation of alloys of palladium with oxygenophilic metals. In this study, Palladium nano chains with an average diameter of approximately 4.4 nm were synthesized via a one-step hydrothermal approach, employing creatine as the structural guide. The one-dimensional structure yielded a huge electrochemically active area (84.5 m2 g−1) and good electrical conductivity. the mass activity of Pd87Au13 NCs for alkaline ethanol oxidation reaction was 4050 mA mgPd+Au−1, which is 7.32 times higher thancommercial Pd/C, and also maintains a high residual current density after 20000 s stability test. In addition, the excellent performance of the material was demonstrated during the oxidation of ethylene glycol and glycerol. The improved catalytic performance is owed to the interconnected chain shape providing fast electron transport channels, and the Au doping not only optimizes the electronic structure of Pd but also has a bifunctional effect, which effectively removes the carbon-containing intermediates generated by Pd during alcohol oxidation, thus improving its resistance to poisoning and stability.

Refining laser-induced dewetting for bimetallic Au–Pd nanoparticle synthesis on ZnO thin films: Optimizing fluence for substrate integrity

We report the fabrication of metal alloy Au–Pd nanoparticles on semiconductor thin film substrates (ZnO) by laser-induced dewetting. Employing a UV excimer laser, a single pulse was directed onto a three-layer film stack on a glass substrate: glass/ZnO/Au/Pd and glass/ZnO/Pd/Au. We simulated the temperature attained by the thin films enabling the prediction of energy thresholds required for melting the metal films but avoiding modifying the ZnO film. A specific range is reported of the pulse energy conducive to nanoparticle formation and the energy threshold required to modify the ZnO film beneath them. Depending on the pulse energy applied, the mean diameter of the nanoparticles varied from approximately 150 to around 70 nm. Notably, higher fluences resulted in smaller particles but also induced surface cracks in the ZnO film. Additionally, we observed a reduction in nanoparticle size with increased Pd content. Our results show that laser-induced dewetting can produce bimetallic alloy nanoparticles and, at the same time, ensure the preservation of the optical properties of the ZnO film. This approach opens avenues for tailoring material characteristics and expanding the range of applications of metal nanoparticles on semiconductor-based systems.

Laser Irradiation Synthesis of AuPd Alloy with Decreased Alloying Degree for Efficient Ethanol Oxidation Reaction.

The preparation of electrocatalysts with high performance for the ethanol oxidation reaction is vital for the large-scale commercialization of direct ethanol fuel cells. Here, we successfully synthesized a high-performance electrocatalyst of a AuPd alloy with a decreased alloying degree via pulsed laser irradiation in liquids. As indicated by the experimental results, the photochemical effect-induced surficial deposition of Pd atoms, combined with the photothermal effect-induced interdiffusion of Au and Pd atoms, resulted in the formation of AuPd alloys with a decreased alloying degree. Structural characterization reveals that L-AuPd exhibits a lower degree of alloying compared to C-AuPd prepared via the conventional co-reduction method. This distinct structure endows L-AuPd with outstanding catalytic activity and stability in EOR, achieving mass and specific activities as high as 16.01 A mgPd-1 and 20.69 mA cm-2, 9.1 and 5.2 times than that of the commercial Pd/C respectively. Furthermore, L-AuPd retains 90.1% of its initial mass activity after 300 cycles. This work offers guidance for laser-assisted fabrication of efficient Pd-based catalysts in EOR.

Engineering of bimetallic Au–Pd alloyed particles on nitrogen defects riched g-C3N4 for efficient photocatalytic hydrogen production

The application of metal catalysis has gained prominence as a study area in recent years. In this work, we use adsorptive reduction and calcination to create Au–Pd alloy catalysts on COCN-2 with varying metal loadings. The plasma resonance effect of the alloys increases the photoresponse of the catalysts, and the engineering of nitrogen defects strengthens the strong bonds between Au–Pd alloy particles and carbon nitride graphite, optimizing the electronic structure, encouraging electron-directed migration, and increasing the efficiency of the reduction reaction. As a result, the efficiency of hydrogen generation by the Au–Pd0.6/COCN-2 catalyst is 5.089 mmol g−1 h−1, which is 2367 times higher than that of the g-C3N4 catalyst. Our findings highlight the crucial part that flaws play in strengthening the strong bonds that exist between the metal and the support, which enhances photocatalytic hydrogen generation. This work offers insightful information about creating effective photocatalysts.

Ultrasmall metal alloy nanozymes mimicking neutrophil enzymatic cascades for tumor catalytic therapy

Developing strategies that emulate the killing mechanism of neutrophils, which involves the enzymatic cascade of superoxide dismutase (SOD) and myeloperoxidase (MPO), shows potential as a viable approach for cancer therapy. Nonetheless, utilizing natural enzymes as therapeutics is hindered by various challenges. While nanozymes have emerged for cancer treatment, developing SOD-MPO cascade in one nanozyme remains a challenge. Here, we develop nanozymes possessing both SOD- and MPO-like activities through alloying Au and Pd, which exhibits the highest cascade activity when the ratio of Au and Pd is 1:3, attributing to the high d-band center and adsorption energy for superoxide anions, as determined through theoretical calculations. The Au1Pd3 alloy nanozymes exhibit excellent tumor therapeutic performance and safety in female tumor-bearing mice, with safety attributed to their tumor-specific killing ability and renal clearance ability caused by ultrasmall size. Together, this work develops ultrasmall AuPd alloy nanozymes that mimic neutrophil enzymatic cascades for catalytic treatment of tumors.

Direct formate anion exchange membrane fuel cells with a PdAu bimetallic nanoparticle anode electrocatalyst obtained by metal vapor synthesis

Renewable energy can be stored in liquid e-fuels such as formate. Here Pd–Au alloy nanoparticles prepared by metal vapor synthesis show enhanced activity and efficiency for the re-transformation to electrical energy in direct formate fuel cells.

Continuous flow oxidation of HMF using a supported AuPd-alloy

An AuPd catalyst supported on activated carbon for HMF oxidation in continuous flow: achieving 68 molFDCA molAuPd−1 h−1, surpassing existing benchmarks. Robust stability over 90 h ToS suggests AuPd alloys as viable catalysts for continuous oxidation.

Selective photocatalytic oxidation of methane to methanol by enhancing H2O2 utilization over Au-Pd/In2O3

Hydrogen peroxide (H2O2) is widely used as an oxidant for photocatalytic oxidation of methane to value-added chemicals under mild conditions, but suffers from low utilization efficiency. Herein, we propose a comprehensive strategy for the proper amount of hydroxyl radicals (•OH) generation from H2O2 by regulating the Pd/Au molar ratios and the total Au-Pd contents loaded on In2O3. For the photocatalytic oxidation of methane at ambient temperature, the yield and selectivity of CH3OH over the optimized 1.0% AuPd0.5/In2O3 catalyst were as high as 2187.0 μmol g−1 h−1 and 94.0% respectively, exceeding most reported literatures. Mechanism investigations revealed that the formation of Au-Pd alloys may contribute to the homolytic cleavage of H2O2 into •OH radicals and improve the selectivity of •OH generation. This work provides some guidance for the delicate design of photocatalysts to manipulate selective H2O2 activation and efficient photocatalytic methane oxidation.

Heterogeneously catalyzed thioether metathesis by a supported Au-Pd alloy nanoparticle design based on Pd ensemble control.

C-S bond metathesis of thioethers has gained attention as a new approach to the late-stage diversification of already existing useful thioethers with molecular frameworks intact. However, direct or indirect thioether metathesis is scarcely reported, and heterogeneously catalyzed systems have not been explored. Here, we develop heterogeneously catalyzed direct thioether metathesis using a supported Au-Pd alloy nanoparticle catalyst with a high Au/Pd ratio. The Au-diluted Pd ensembles suppress the strong π-adsorption of diaryl thioethers on the nanoparticles and promote transmetalation via thiolate spill-over onto neighboring Au species, enabling an efficient direct thioether metathesis.

In Ukrainian

The review material reveals the question of the influence of impurities on the physical properties of alloys, as well as the influence of gases on processes in alloys. It has been established that the presence of hydrogen affects diffusion in alloys, and gases have a significant effect on the thermoelectromotive force of metals. The paper describes the addition of a third element to binary systems, which can expand or narrow the domain of existence of an ordered phase. The above examples of adding an impurity of vanadium or molybdenum to an alloy of iron and chromium increase the ordering temperature. It has been established that gases can have a significant effect on the thermoelectromotive force of metals and increase the hardness and reduce the ductility of metals, as well as cause their brittleness and delamination. It has been established that hydrogen (H2) in alloys (for example, Fe-Ni and Au-Cu) affects diffusion and atomic ordering processes. Also, a small concentration of hydrogen, as an impurity, can change the electrical resistance of alloys (for example, in a Pd-Au alloy). It has been established that the addition of a third element to binary systems can change the state diagram, which must be taken into account when solving problems for the production of heat treatment modes for alloys, determining the conditions for phase equilibrium, etc. The paper considers the dependence of hydrogen solubility on temperature in metals (Cu, Fe and Al) and establishes the dependence of hydrogen solubility in a metal on the concentration of impurity metals. The temperature dependence of hydrogen solubility in Fe-V alloys is also shown. The shift of the density of state is studied for different distributions of impurity atoms in the alloy in the order-disorder system, and the dependence of the density of states of disordered and ordered solid solutions is studied. The dependence of the relative solubility of atoms introduced into the pores of alloys with an fcc structure (of the Cu3Au type) is indicated, taking into account the solubility, on the parameter χ, which is proportional to the degree of long-range order in the octahedral and tetrahedral pores of the alloys. The dependence of the relative solubility of intercalated atoms in octahedral pores of alloys with a bcc structure (such as CuZn and Fe3Al) is considered. A plot of the dependence of the concentration of dissolved impurity atoms on the degree of order is shown for substitutional alloys with a bcc lattice, where the M2 coefficient is introduced, which does not depend on the degree of order. The effect of pressure as a measure of long-range order is also studied, where its step decreases or increases, or decreases and then increases and vice versa (order-disorder phase transition). An equally important result is the graphic dependence of solubility (c) on pressure (P) in disordered and ordered alloys.