Pd-Ag Alloy Research Articles

Surface segregation on Ag@MNi (M = Pd, Pt, Rh, and Ru) core–shell nanocrystals for enhancing the oxygen reduction performance

Synthesis of cost-effective electrocatalysts for oxygen reduction reaction (ORR) has received wide attention due to their sluggish kinetics, which limits the development and application of fuel cell technique. In this work, we report a versatile synthetic approach to prepare a series of small-sized Ag@MNi (M = Pd, Pt, Rh, Ru) nanocrystals with core–shell structures by a simple solvothermal method. According to characterization analysis, surface segregation of Pd was proved in the outermost layer with the Pd-rich shell layer, which can regulate the adsorption energy of *OH. Electrochemical results show that the onset potential and half-wave potential of Ag@PdNi nanocrystals (Ag@PdNi NCs) are 1.005 and 0.913 V vs. RHE (reversible hydrogen electrode), respectively, with a Tafel slope of 55.31 mV dec-1 and strong ORR catalytic durability, which is similar to Ag@MNi (M = Pt, Rh, Ru) NCs and slightly higher than that of PdAg alloy nanoparticles (PdAg alloy NPs), PdNi alloy nanoparticles (PdNi alloy NPs), commercial Pd black and even commercial Pt/C, in alkaline medium. Density Functional (DFT) calculations show that the presence of Agcore effectively promotes the segregation of Pd atoms to the outer shell surface, where Ni provides better segregated substitution sites for Pd, which significantly improves the ORR activity and durability due to the electronic synergistic effect between Agcore nuclei and Pdshell can reduce the adsorption strength of OHads.

PdAg alloy nanowheats: Facile interfacial synthesis and highly selective catalysis in the hydrogenation of 4-nitrobenzaldehyde

Developing a simple and mild one-step method for the preparation of bimetallic nanomaterials with both free-standing features and excellent catalytic performance is highly desirable but remains technically difficult. Herein, a facile liquid-liquid interface route is exploited to grow the wheat-like PdAg nanostructures at the interface of chloroform and water under mild conditions without the use of any surfactants and supports. To implement this scheme, Na2PdCl4 and AgNO3 as precursors are dissolved in aqueous phase and α-naphthol as reducing agent in chloroform phase to build up the interfacial reaction system. At 40°C, the PdAg nanowheats are orderly grown, fused and assembled by many newly generated nanoparticles at the interface region, which have uniform shapes with the length of about 340 nm and the diameter of about 45 nm, abundant defects and strong electronic interaction between Au and Pd, as well as free-standing features. In the hydrogenation reaction of 4-nitrobenzaldehyde, PdAg-1 nanowheats exhibit excellent catalytic activity, selectivity and durability. Within 60.0 min of reaction at 35°C under atmospheric pressure, 99.8 % conversion of 4-nitrobenzaldehyde and 99.5 % selectivity toward 4-aminobenzaldehyde can be realized. After 5 cycles, 99.4 % conversion of 4-nitrobenzaldehyde and 98.0 % selectivity toward 4-aminobenzaldehyde can be maintained.

HYDROGEN GAS RECOVERY THROUGH THE PERMEATION MEMBRANE BASED BIMETALLIC PALLADIUM ALLOY

Generally, the H2 gas produced from the industrial processes is not in a pure state but is mixed with other compounds. For example, the off-gas produced in the oil refinery process still contains CH4, H2, and other gases. Thus, the process of separating as well as recovering the valuable H2 gas from other gas compounds is of essential process. Currently, the H2 separation process is being developed with relatively low costs with good efficiency, namely using the permeation membranes separation process, in which the compounds with high permeability tends to be more easily separated. Here we report the hydrogen recovery process from the mixed H2/N2 off-gas contains 61 % hydrogen and 39% balancing nitrogen, by using the bimetallic Pd-Ag membrane, where the effect of the gas feed pressure (1 and 2 bar) and operating temperature (373.15, 423.15, 473.15, and 523.15, 573.15 K) on the resulting permeate flux is comprehensively studied. We found that the flux and permeability increased with the increase in the gas feed pressure and temperature. Under the same gas temperature of 373.15 K, the permeation flux at the 2 bar gas feed pressure was found to be 2.047 mol.s-1.m-2, which was 166% greater than that of 1 bar pressure, i.e. 1.204 mol.s-1.m-2. Meanwhile, under the same gas feed pressure of 2 bar, the permeation flux at the operating temperature of 573.15 K was found to be 2.103 mol.s-1.m-2, which is 104,9% greater than that of 373.15 K operating temperature, i.e. 2.047 mol.s-1.m-2. These findings suggest the breakthrough advantages of the Pd-Ag alloy membrane for its high hydrogen permeability at low pressure.

(Invited) Traversing Length Scales for Electrochemical Hydrogen Production and Use: Developing a Platform for Material Design and in Situ Material Characterization of Electrocatalysts

Converting chemical processing to carbon-free or to closed carbon cycle processing (e.g. carbon neutral) will require large quantities of sustainable, and likely electrically produced, fuels and processes. Hydrogen is both a chemical fuel alternative, but also an important commodity for chemical manufacturing e.g. ammonia production for fertilizers. Water electrolyzers (WE) and hydrogen fuel cells (H2FCs) for either making or converting hydrogen to electrical energy will require cheaper and more readily available catalyst materials than the current platinum or iridium based state-of-the-art. Alkaline zero-gap devices (anion exchange membrane, AEM WE or H2FCs) offer a promising landscape for earth abundant materials, however they have traditionally underperformed due to large scale component instabilities, e.g. membranes, ionomer, catalysts, etc. With recent advances in alkaline membrane technology it is imperative that commercializable catalysts are developed. Due to a variety of architectural differences, the dissimilar microenvironments and catalyst-electrolyte-gas interfaces between classical fundamental (e.g. three electrode cell measurements with a rotating disc electrode (RDE) and device studies makes it difficult to translate materials to industrial readiness. It is imperative that these trends translate from the small lab-scale (mA), an environment that engenders rapid catalyst evaluation, to industrial-relevant scales (> A) in multi-variable devices.Herein I will discuss work we have done both on developing a robust a platform for measuring performance trends across length scales and microenvironments and expanding tools for characterizing in situ material stability related primarily to WE and H2FCs. For H2FCs, I will discuss our teams’ recent work translating Ag-Pd catalysts from first principles with density function theory (DFT), to classic fundamental studies with RDEs, and finally to H2FCs with a max ~ 10 W/mgPGM on the cathode.1,2 I will discuss the thin film, ionomer-free system that extended across length scales and microenvironments and how we are currently using this platform to develop Ag-based fully non-platinum group metal catalysts. Comparing both H2FCs and WEs, I will go on to discuss one large component of performance, stability, and our ongoing efforts to develop tools for in situ characterization. On-line inductively coupled plasma mass spectrometry (on-line ICP-MS) and electrochemical mass spectrometry (EC-MS) are emerging tools for monitoring material dissolution and product production, respectively, in real time. By coupling these techniques, looking at Co-based metals we have identified degradation mechanisms as well as windows of stable hydrogen evolution and oxygen reduction catalysis in highly acidic electrolytes. A focus on catalyst activity and nature of the active site across microenvironments and in situ material stability provides insights that could enable the next generation materials and stabilization techniques, e.g. in situ, synthetic, morphology, etc. for improving overall performance across technological length scales. References 1) Zamora Zeledón, J. A.; Stevens, M.B.; Gunasooriya, G.T.K.K.; Gallo, A.; Landers, A.T.; Kreider, M.E.; Hahn, C.; Nørskov, J.K.; Jaramillo, T.F. Tuning the Electronic Structure of Ag-Pd Alloys to Enhance Performance for Alkaline Oxygen Reduction, Nature Comm., 2021, 12, 1-9.2) Douglin, J.C.; Zamora Zeledón, J. A; Keider, M. E; Singh, R.K.; Stevens, M.B. ‡ Jaramillo, T. F. ‡ Dekel, D.R. ‡ High performance anion-exchange membrane fuel cells with ionomerless cathodes employing ultra-low loading Ag-Pd alloy electrocatalysts, Nature Energy, 2023, 1-11.

Nanostructured bi-metallic Pd–Ag alloy films for surface-enhanced Raman spectroscopy-based sensing application

Nanostructured bi-metallic Pd–Ag alloy films for surface-enhanced Raman spectroscopy-based sensing application

Combinatorial Analysis of Silver‐Palladium Alloy Thin Film Libraries

Combinatorial analysis of Ag–Pd alloy thin films shows the formation of a solid solution with the face‐centered cubic structure for all investigated alloy compositions. Using mixed matter theory and the high field model, oxide growth upon applying an anodic potential is indicated. Electrochemical impedance spectroscopy supports the idea of oxide formation based on a change in behavior correlated to a sharp increase in oxide formation as indicated by cyclic voltammetry measurements. After polarization at 4 V, a stable total impedance and increasingly less‐pronounced phase shift are detected in the frequency range of 100 mHz to 10 kHz, which encompasses the common range of application of active implantable medical devices (AIMD). Upon fitting the measured impedance data with the Randles circuit, capacitances are determined in the nF cm−2 range for the investigated alloys and attributed to the formed mixed oxide layer. Charge transfer resistances are found to be in the kΩ cm−2 range. No correlation between alloy composition and capacitance or resistance can be detected so far. These findings indicate a fundamental applicability of Ag–Pd alloys for use in AIMD.

Palladium‐Silver Alloys Deposited on Different Carriers for Dehydrogenation of Formic Acid

AbstractHydrogen (H2) is recognized as a clean energy carrier with great potential for the future energy systems. Given the existing challenges in direct H2 storage and delivery, the current option for utilizing hydrogen energy is to produce hydrogen from its storage carriers on‐site, and the development of a highly active, highly selective, and highly stable catalyst for H2 production is an important part of this. Herein, PdAg alloy was deposited on mesoporous carbon nitride (mpg‐C3N4) as a catalyst for the dehydrogenation of the formic acid (FA). The synergistic effect of Pd and Ag metals for catalysis was explored. The role of the supports on the catalytic performance was also demonstrated by depositing PdAg alloy on several carriers of Silica@Resorcinol‐Formaldehyde Spheres, Carbon Flower Particles and SBA‐15. Pd1Ag1/2/mpg‐C3N4 showed a considerable activity during FA dehydrogenation with a turnover frequency (TOF) value of 887 h−1 at 333 K, demonstrating that carbon nitride as a carrier has a significant enhancement on the catalytic hydrogen production from formic acid.

Theoretical Understanding of Electromigration-Related Surface Diffusion and Current-Induced Force in Ag-Pd Systems.

Electromigration, as a common reason for interconnect failure, is becoming increasingly important in the ongoing decrease in the integrated circuit manufacturing process. A study is being carried out utilizing the ab initio calculational method to gain a deeper understanding of electromigration, with a focus on the atom diffusion process in the Ag-Pd alloy system, a commonly used interconnect material. We begin by establishing that the primary mechanism of diffusion is step-edge diffusion on the (111) surface. Following this, we examine the current-induced force exerted on the migrating Ag atom. The Pd substitutional defect reveals an effect that increases the energy barrier of diffusion and decreases the current-induced force that powers the directional migration.

Fabrication of Microporous Palladium by Selective Anodic Dissolution of Ag-Pd Alloy in Alkali Chlorides Melt

The electrochemical dealloying of Ag40Pd60 alloy in (LiCl)57(CsCl)26(KCl)17 melt with the addition of 3 mol% silver chloride has been studied. Selective anodic dissolution of the alloy was carried out both in the potentiostatic and in galvanostatic regimes at temperatures ranging from 300 to 500 °C. The obtained voltammetry characteristics of the initial alloy, chronoamperograms and chronopotentiogram during the dealloying are presented and discussed. At a temperature near 500 °C, the second maximum was observed in the chronoamperograms at two different values of the set potential. The unusual shape of the current curves is due to the superposition of several diffusion processes, which intensities in this case are greater than at lower temperatures. Bi-continuous structures of practically pure palladium with pores and ligaments of sizes ranging from a few to tens of micrometers were obtained in the potentiostatic regime. As the dealloying temperature increased, the sizes of pores and ligaments increased naturally. The same effect was also caused by the increase in applied potential. In the galvanostatic mode similar metallic structures were obtained, but the residual silver content reached 5%, and, in addition, the effects of samples sintering appeared.

Exploring the Effects Behind the Outstanding Catalytic Performance of PdAg Catalysts Supported on Almond Shell‐Derived Activated Carbon Towards the Dehydrogenation of Formic Acid

AbstractIn this work, highly efficient carbon‐supported Pd‐based catalysts for formic acid dehydrogenation were synthesized by a straightforward wet impregnation‐reduction method. The carbon support was obtained from a biomass residue (almond shell) prepared via H3PO4‐assisted hydrothermal carbonization (HTC) and thermal activation. This carbon support was doped with nitrogen groups to study the effect on the electronic properties and catalytic performance of the catalysts. Investigating the formation of PdAg alloys with varying Pd : Ag molar ratios resulted in catalysts exhibiting enhanced catalytic activity compared to monometallic Pd counterparts. Notably, the Pd1Ag0.5/NAS catalyst displayed outstanding catalytic performance, achieving an initial TOF of 1716 h−1 (calculated in the first 3 minutes of reaction and expressed per mole of Pd) and maintaining substantial activity over 6 consecutive reaction cycles. This work elucidates the successful synthesis of effective catalysts, emphasizing the influence of nitrogen doping and PdAg alloy composition on catalytic behavior and stability.

Evaluation of the effects of an Iraqi phosphate bonded investment and two commercial types on the marginal fitness of porcelain- fused- to- metal copings .

The effect of different phosphate- bonded investments on the marginal fitnessof porcelain- fused—to-metal copings cast by one type of noble alloy and one type ofbase metal alloy was studied. Three types of phosphate—bonded investments (Castorit -Super C, Norvest, and Iraqivest) were used for investing the thirty copings of eachgroup. The marginal fitness of each coping was determined by measuring the verticalmarginal discrepancies between the gingival margin of the coping and the margin ofthe preparation at four reference points on the labial, mesial, palatal and distal aspectsof the die by the aid of light traveling microscope .The statistical analysis of the results showed that there were significantdifferences in marginal fitness among different investments for both Pd- Ag& Ni-Cralloys. The Castorit- Super C and Norvest investments produced comparable resultswith both alloys, while the Iraqivest appeared less compatible with Pd-Ag alloy thanthe other two investments and it had comparable compatibility to Norvest investmentwhen used with Ni- Cr alloy. The Ni- Cr alloy (Heraenium NA) copings revealedsignificantly greater marginal discrepancy than the Pd-Ag alloy (QD) eopingsspecially when using Castorit- Super C and Norvest investments .

Highly efficient and direct recovery of low-pressure hydrogen isotopes from tritium extraction gas by PdY alloy membrane permeator

Low-pressure hydrogen recovery is crucial for the fusion reactor deuterium-tritium fuel cycle, and the usual treatment is achieved through multiple steps of enrichment and separation, which has the drawbacks of complex processes and high energy consumption. In this work, a membrane permeator including 12 sets of Pd92Y8 at% alloy tubes has been investigated for the permeability and extraction of hydrogen in low-pressure mixtures. The hydrogen permeation through dense Pd-based membrane mechanism and corresponding Sieverts’ exponents have been verified. The concentration polarization effect is deducted from the results. Through pure hydrogen permeation test, the cold-rolling 80 μm thick Pd92Y8 at% membrane has hydrogen permeability at 400 °C of 3.43×10−8 mol∙m−1∙s−1∙Pa−0.5, which is higher than that of PdAg alloy membrane under the same conditions. Highly efficient recovery efficiency has been achieved for low hydrogen pressure mixtures, and the PdY alloy membrane permeator with 678 cm2 effective area could reach around 95% hydrogen extraction recovery for 0.1 mol% hydrogen-helium mixture and 97.74% recovery for 0.33 mol% at the rate of 21 standard liter per minute (SLM). It indicates that the PdY alloy membrane permeation can be an alternative solution for efficiently recovering low-pressure hydrogen isotopes in tritium extraction gas.

Mechanisms of aqueous bromate reduction activity enhancement with well-defined bimetallic palladium-based catalysts

Catalytic reduction has been shown to remove bromate (BrO3−) in drinking water without waste stream formation, though most reported catalysts rely on palladium (Pd), a financially and environmentally expensive metal. Emerging efforts show Pd can be partially replaced with less expensive metals in nanoparticle (NP) alloys, with enhanced hydrogenation reactivity. However, it is unclear if novel NP alloys will enhance bromate reduction, and if so whether they can be intelligently designed based on underlying mechanisms of enhancement. Herein, we address this knowledge gap reporting that well-defined alloyed PdCu and PdAg nanoparticles deposited on carbon nanotubes achieve a 3.9-times improvement in catalytic activity versus monometallic Pd catalysts, which further translates to catalysts prepared using straight-forward impregnation methods. Density functional theory results indicate that improved hydrogenation rates are related to optimized BrO3− and H binding on PdM surfaces achieved by electronic effects in PdCu alloys and unique surface ensembles in PdAg alloys. Overall, these catalysts delineate a pathway for improved bromate removal activity at environmentally relevant concentrations.

Bimetallic PdAg clusters loaded on hierarchical self-pillared pentasil zeolite as efficient catalysts for formic acid dehydrogenation

In the present study, siliceous self-pillared pentasil (SPP) zeolite with regular mesopores was synthesized and used as a support for anchoring bimetallic PdAg clusters through a facile impregnation-reduction method. The as-prepared PdAg/SPP catalysts with different Pd/Ag ratios were demonstrated to catalyze formic acid dehydrogenation for hydrogen production. XRD results confirmed the formation of PdAg alloy on the surface of SPP zeolite. The Pd7Ag3/SPP catalyst showed high activity at 80 °C with an initial turn-over frequency (TOF) of 1263.6 h−1, proving the strategy using hierarchical SPP zeolite as carrier is advantageous over bulky zeolites for making highly active formic acid dehydrogenation catalysts.

Asymmetric magnetic nanosnowman loaded with AgPd nanocage toward NIR-enhanced catalytic activity.

Although bimetallic noble nanostructures often possess high activity in nanocatalysis, their controllable fabrication, tunable catalytic activity, and easy separation remain significant challenges. In this study, an Fe3O4@AgPd/Polydopamine (Fe3O4@AgPd/PDA) nanosnowman loaded with an AgPd nanocage was designed by a one-step template-disposition-redox polymerization method. The AgPd nanocage endowed the product with high catalytic activity for the reduction of organic pollutants (4-NP, MO, MB). Interestingly, under near-infrared (NIR) light, the catalytic kinetics of the Fe3O4@AgPd/PDA nanosnowman on catalytic reduction of organic pollutants increased by 2.6, 1.57, and 5.45 times, respectively. The asymmetric nanostructure facilitated the separation of electron-hole pairs, promoted electron transfer, and accelerated the catalytic activity. Density functional theory (DFT) analysis indicated that the electron transfer between the AgPd alloy and the Fe3O4 nanosphere played a critical role on the high catalytic activity. Moreover, Fe3O4@AgPd/PDA also demonstrated excellent catalytic activity in the Heck carbon-carbon coupling reaction with a >95% conversion rate and >99% selectivity. Owing to the well-encapsulated PDA shell and outstanding magnetic properties, the Fe3O4@AgPd/PDA nanosnowman exhibited good cyclic catalytic activity. With its multi-mode catalysis, NIR-enhanced catalytic activity, and easy separation, the Fe3O4@AgPd/PDA nanosnowman exhibits great application potential in nanocatalysis.

Anchoring PdAg alloys on self-crosslinked carbon dots as efficient catalysts for formic acid dehydrogenation under ambient conditions

The optimized Pd0.9Ag0.1/CDs catalyst can catalyze complete dehydrogenation of FA in 9.5 min with a TOF value of 617 h−1 at 298 K. This work provides a simple approach for the fabrication of CDs supported highly distributed PdAg alloy catalysts.

Synergistic effects of Pd-Ag decoration on SnO/SnO2 nanosheets for enhanced hydrogen sensing

Hydrogen, the lightest and most abundant element in the universe, holds immense importance across various fields of application from industry to healthcare. Detecting hydrogen is crucial in medical diagnostics and leak detection, as it helps diagnose gastrointestinal conditions and ensures safety in industrial settings by identifying potential leaks in hydrogen-based systems. In this study, we present the synthesis of tin oxide (SnO/SnO2) nanosheets using a facile hydrothermal method followed by the decoration of Pd-Ag alloy nanoparticles (NPs) for the purpose of hydrogen gas detection. Different combinations of Pd and Ag in Pd-Ag alloy NPs were tested on the surface of the SnO/SnO2 nanosheets in order to optimize their catalytic properties for enhanced hydrogen gas sensing. The Pd-Ag alloy NPs with a ratio of 1:0.5 decorated on SnO/SnO2 nanosheets (Pd1Ag0.50@SnO/SnO2), exhibited the highest response (s = Ra/Rg) of 81.34 at an optimum temperature of 225 °C compared to the bare SnO/SnO2 nanosheets. The fabricated sensor also showed an excellent level of selectivity, repeatability, and a good response time (45 s). The enhanced sensing response of Pd1Ag0.50@SnO/SnO2 towards hydrogen is explained using the spillover and electronic sensitization mechanism. The combined gas sensing mechanism is discussed in detail.

Structural evolutions under surface oxidation of AgPd Alloy: From Orientation, composition and strain effects to catalytic application

The surface oxidation of AgPd alloys can significantly impact their catalytic activity, however, the detailed understanding of such dynamic mechanism and the prediction of catalytic activity is still lacking. Herein, a comprehensive investigation combining ab initio molecular dynamics simulations with experimental observations is performed. The surface oxidation of AgPd alloys is highly dependent on oxygen concentration, where AgOx forms in oxygen-poor environment and PdOx forms in oxygen-rich environment, and shows highly reliance on the orientation, composition and strain state. The oxidation level of Ag, Pd and AgPd alloys follows the trend of (111) < (100) < (110) under 1.0 ML of O coverage. Both Pd single-atom and Ag matrix atoms in PdAg single-atom alloys are susceptible to oxidation under 0.5 ML of O coverage, with the increase of Pd atom number, only AgOx forms. Tensile strain promotes the oxidation of Ag(111) surface by facilitating the inward diffusion of O atoms, while compressive strain promotes the oxidation of Pd(111) and AgPd(111) surfaces by facilitating the outward migration of Ag/Pd atoms. The oxidized AgPd(111) surface with tensile strain under 0.5 ML of O coverage exhibits the optimum electrocatalytic activity toward formate oxidation reaction.

Interfacial electronic structure modulation enables PdAg/NiOx an advanced oxygen evolution electrocatalyst

Hydrogen production by electrolysis of water is one of the solutions to energy problems and environmental pollution. The design of efficient oxygen evolution electrocatalyst remains a challenging. One way to improve catalytic performance is to change the morphology and structure of the catalyst. Herein, a two-dimensional (2D) flake nano-flower heterostructured catalyst was designed on nickel foam (NF) substrate by simple hydrothermal and thermal annealing reactions. Benefiting from the porous nanosheet structure and synergistic effect between PdAg and NiOx, which facilitates electrolyte transport, the PdAg/NiOx nanosheets deliver a low overpotential (253 mV @ 10 mA cm−2) for oxygen evolution reaction (OER) and has excellent stability. In addition, the addition of PdAg alloy regulates the electronic structure of the active component Ni, which also makes for further improving the electrocatalytic OER performance. This work not only offers a promising strategy of in situ anchoring PdAg alloy on NiOx nanosheet but also provide a new way for the application of alloy heterogeneous interfaces to high performance OER catalysts.

High-performance ionomerless cathode anion-exchange membrane fuel cells with ultra-low-loading Ag–Pd alloy electrocatalysts

High-performance ionomerless cathode anion-exchange membrane fuel cells with ultra-low-loading Ag–Pd alloy electrocatalysts