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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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8 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2021

Tuning the electronic structure of Ag-Pd alloys to enhance performance for alkaline oxygen reduction

Alloying is a powerful tool that can improve the electrocatalytic performance and viability of diverse electrochemical renewable energy technologies. Herein, we enhance the activity of Pd-based electrocatalysts via Ag-Pd alloying while simultaneously lowering precious metal content in a broad-range compositional study focusing on highly comparable Ag-Pd thin films synthesized systematically via electron-beam physical vapor co-deposition. Cyclic voltammetry in 0.1 M KOH shows enhancements across a wide range of alloys; even slight alloying with Ag (e.g. Ag 0.1 Pd 0.9 ) leads to intrinsic activity enhancements up to 5-fold at 0.9 V vs. RHE compared to pure Pd. Based on density functional theory and x-ray absorption, we hypothesize that these enhancements arise mainly from ligand effects that optimize adsorbate–metal binding energies with enhanced Ag-Pd hybridization. This work shows the versatility of coupled experimental-theoretical methods in designing materials with specific and tunable properties and aids the development of highly active electrocatalysts with decreased precious-metal content.

25 ENERGY STORAGE↗
DOE OSTI2020

Synthesis and Characterization of Pd-based Nanomaterials

Bimetallic nanoparticles (BNPs) consist of two different types of metals or alloys that are bonded together. Unique properties such as optical, electronic, thermal, and catalytic effects differ for each type of BNP. Important BNPs range from Au-Pd, Ag- Pt, Au-Pt, and Ag-Ni. Pd bimetallic nanoparticles are of interest due to their many applications such as catalysis and sensing. Bimetallic catalysts have increase reaction rates and have improved catalyst stability through the geometry and ligand distribution. Pd nanoparticles are considered to be a strong catalyst due to their high activity at low temperatures and high tolerance to moisture. The catalytic properties of bimetallic nanoparticles depend on the structural properties such as size and shape. Core-shell, hollow structure, and multi-shell alloy are three possible structures nanoparticles can form as bimetallic catalysts. BNPs can be synthesized through different methods to control the size, shape, and structure. To obtain different morphologies, a variety of methods can be performed. Different methods can range from the usage of the glancing angle deposition (GLAD) to the galvanic replacement reaction, but the methods all depend on the properties of the metals. The galvanic displacement reaction was the method used to obtain Pd-based nanoparticles. This reaction is best know for obtaining hollow shaped NPs. To determine what redox process was preformed, the activity series of metals was used. From the activity series of metals, silver (Ag) was selected to preform Pd-based nanoparticles. Objectives: Synthesize Ag nanoparticles and Ag-Pd nanoparticles to understand the morphology. Characterize the synthesized nanoparticles using scanning electron microscopy (SEM), phase analysis light scattering (PALS), dynamic light scattering (DLS), energy dispersive X-ray spectroscopy (EDS), and UV-Vis spectroscopy. Results: In the UV-Vis spectrum, the Ag-Pd bimetallic NP's plasmon band decreased as the volume of palladium increased. The surface charge increases as the concentration of palladium increases. The Pd{sup 2+} ions interact with the sodium citrate surface, and decrease the negative charge. Conclusion: Ag-Pd nanoparticles were successfully created and stabilized with sodium citrate. The addition of Pd decreased the prominent plasmon band of the Ag nanoparticles. The SEM analysis showed that Ag nanoparticles had a well-defined structure, while the Ag-Pd nanoparticles showed hollow and rough structure. The EDX analysis confirmed the presence of silver and palladium. This material can be used in many industrial and research fields such as organic synthesis, fuel cells, and environmental sensing and remediation.

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2023

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

Rapid translation of catalysts from fundamental studies to high-performance devices could facilitate the process of developing and commercializing anion-exchange membrane fuel cells (AEMFCs). Traditionally, translation from material screening in three-electrode rotating disk electrode (RDE) cells to AEMFCs is complicated by differences in microenvironments, e.g. solid ionomer/membrane vs liquid electrolyte. Herein, we introduce a platform for translation to devices that utilizes ionomerless ultra-low-loading Ag-Pd alloy electrocatalyst cathodes synthesized by co-physical vapor deposition (PVD). Our ionomerless cathodes allow for systematic H 2 -O 2 AEMFC experiments while demonstrating comparable activity trends to those in three-electrode cells. Furthermore, here we show that our Ag 10 Pd 90 -based AEMFC reaches a peak power density of ~1 W cm$_{geo}^{-2}$ and ~10 W mg$_{PGM Cathode}^{-1}$ satisfying the U.S. Department of Energy’s platinum-group-metal (PGM) loading and cost targets. Our approach shows promise in facilitating the rapid translation between three-electrode studies and AEMFCs, offering a simple and effective design for decreasing PGM loadings.

25 ENERGY STORAGE↗
NASA NTRS1990

Kinetics and thermodynamics of ceramic/metal interface reactions related to high T(sub c) superconducting applications

Superconducting ceramic materials, no matter what their form, size or shape, must eventually make contact with non-superconducting materials in order to accomplish current transfer to other parts of a real operating system, or for testing and measurement of properties. Thus, whether the configuration is a clad wire, a bulk superconducting disc, tape, or a thick or thin superconducting film on a substrate, the physical and mechanical behavior of interface (interconnections, joints, etc.) between superconductors and normal conductor materials of all kinds is of extreme importance to the technological development of these systems. Fabrication heat treatments associated with the particular joining process allow possible reactions between the superconducting ceramic and the contact to occur, and consequently influence properties at the interface region. The nature of these reactions is therefore of great broad interest, as these may be a primary determinant for the real capability of these materials. Research related both to fabrication of composite sheathed wire products, and the joining contacts for physical property measurements, as well as, a review of other related literature in the field are described. Comparison are made between 1-2-3, Bi-, and Tl-based ceramic superconductors joined to a variety of metals including Cu, Ni, Fe, Cr, Ag, Ag-Pd, Au, In, and Ga. The morphology of reaction products and the nature of interface degradation as a function of time will be highlighted.

Notis, Michael R.↗
NASA NTRS2020

Ag isotopic and chalcophile element evolution of the terrestrial and martian mantles during accretion: new constraints from Bi, Pd, and Ag metal-silicate partitioning.

The Earth’s timing of accretion and acquisition of moderately volatile compounds is uncertain. Hafnium-W and Mn-Cr isotopic data can bracket the timing of early planetary differentiation and core formation. The Ag-Pd system has also been utilized but its application has been limited by a lack of high pressure and temperature metal-silicate partitioning for Pd and Ag. Be-cause Ag (and Bi) are volatile chalcophile siderophile elements, understanding their early distribution can constrain the origin of volatile elements in differentiated bodies and planets. Unfortunately, neither Ag or Bi have been studied across the wide range of pressure and temperature conditions that are relevant to accretion and core-mantle differentiation. Here, new high-pressure and temperature multi-anvil metal-silicate equilibrium experiments for Bi and Ag have been carried out at conditions relevant to planetary accretion and metal silicate differentiation that allow a more refined and complete understanding of element partitioning during core formation. The new metal-silicate partitioning data utilized to predict the distributions of Bi, Pd, and Ag at conditions of accretion for Earth and Mars and show that the Pd/Ag ratio is significantly fractionated during accretion, allowing for the production of detectable 107Ag anomalies produced while 107Pd (half life = 6.5 M.y.) was still extant. Application of the new partitioning results to Earth shows that D(Bi) and D(Ag) (D = metal/silicate concentration ratio) are lowered due to the effect of pressure and Si alloyed in the metallic liquid, resulting in higher predicted mantle Bi and Ag abundances than in the bulk silicate Earth (BSE), as well as high and variable Pd/Ag. The unradiogenic Ag isotopic composition of the BSE could have been generated by early accretion of volatile-poor (high Pd/Ag) precursors, followed by later accretion of volatile–rich (low Pd/Ag) material, in agreement with earlier studies of Pd-Ag and Mn-Cr (Schönbächler et al., 2010). However, these main accretion phases would have to be followed by segregation of a sulfide liquid (at least 1.5% of magma ocean) at high pressures (>30 GPa), to explain the PUM Bi, Pd, and Ag, as well as Au, Pt, Cu and Ni concentrations as proposed previously. If the early accreted bulk Earth was volatile depleted with high Pd/Ag ratios, portions of the mantle may contain ancient domains that developed positive 107Ag isotopic anomalies (as also argued by noble gases, Nd, W, and Os isotopes). In comparison, Bi, Pd, and Ag concentrations in the martian mantle could have been set by simple metal-silicate equilibrium. Mars accreted and differentiated relatively rapidly, while also developing a deep magma ocean with a high Pd/Ag ratio that could have evolved positive 107Ag anomalies, in contrast to Earth. Measurements on shergottites may reveal these predicted Ag isotopic anomalies.

accretion↗
DOE OSTI2020

Materials Data on Ag3Pd by Materials Project

PdAg3 is beta Cu3Ti-like structured and crystallizes in the tetragonal I4/mmm space group. The structure is three-dimensional. Pd is bonded to twelve Ag atoms to form PdAg12 cuboctahedra that share corners with four equivalent PdAg12 cuboctahedra, corners with eight equivalent AgAg8Pd4 cuboctahedra, edges with eight equivalent PdAg12 cuboctahedra, edges with sixteen equivalent AgAg8Pd4 cuboctahedra, faces with four equivalent PdAg12 cuboctahedra, and faces with fourteen AgAg8Pd4 cuboctahedra. There are eight shorter (2.90 Å) and four longer (2.91 Å) Pd–Ag bond lengths. There are two inequivalent Ag sites. In the first Ag site, Ag is bonded to four equivalent Pd and eight Ag atoms to form AgAg8Pd4 cuboctahedra that share corners with twelve equivalent AgAg8Pd4 cuboctahedra, edges with eight equivalent PdAg12 cuboctahedra, edges with sixteen AgAg8Pd4 cuboctahedra, faces with four equivalent PdAg12 cuboctahedra, and faces with fourteen AgAg8Pd4 cuboctahedra. There are four shorter (2.90 Å) and four longer (2.91 Å) Ag–Ag bond lengths. In the second Ag site, Ag is bonded to four equivalent Pd and eight equivalent Ag atoms to form AgAg8Pd4 cuboctahedra that share corners with four equivalent AgAg8Pd4 cuboctahedra, corners with eight equivalent PdAg12 cuboctahedra, edges with twenty-four AgAg8Pd4 cuboctahedra, faces with six equivalent PdAg12 cuboctahedra, and faces with twelve AgAg8Pd4 cuboctahedra.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on AgPd by Materials Project

PdAg crystallizes in the trigonal R-3m space group. The structure is three-dimensional. there are two inequivalent Pd sites. In the first Pd site, Pd is bonded to six equivalent Pd and six Ag atoms to form PdAg6Pd6 cuboctahedra that share corners with twelve PdAg6Pd6 cuboctahedra, edges with twelve PdAg6Pd6 cuboctahedra, edges with twelve AgAg6Pd6 cuboctahedra, faces with six equivalent PdAg6Pd6 cuboctahedra, and faces with twelve AgAg6Pd6 cuboctahedra. All Pd–Pd bond lengths are 2.87 Å. All Pd–Ag bond lengths are 2.86 Å. In the second Pd site, Pd is bonded to ten equivalent Pd and six Ag atoms to form PdAg6Pd10 cuboctahedra that share corners with ten AgAg6Pd6 cuboctahedra, corners with twelve PdAg6Pd6 cuboctahedra, edges with eight AgAg6Pd6 cuboctahedra, edges with sixteen PdAg6Pd6 cuboctahedra, faces with sixteen equivalent PdAg6Pd10 cuboctahedra, and faces with eighteen AgAg6Pd6 cuboctahedra. There are a spread of Pd–Pd bond distances ranging from 2.87–5.74 Å. All Pd–Ag bond lengths are 2.86 Å. There are three inequivalent Ag sites. In the first Ag site, Ag is bonded to six equivalent Pd and six equivalent Ag atoms to form AgAg6Pd6 cuboctahedra that share corners with twelve AgAg6Pd6 cuboctahedra, edges with twelve equivalent PdAg6Pd6 cuboctahedra, edges with twelve AgAg6Pd6 cuboctahedra, faces with six equivalent AgAg6Pd6 cuboctahedra, and faces with twelve equivalent PdAg6Pd6 cuboctahedra. All Ag–Ag bond lengths are 2.87 Å. In the second Ag site, Ag is bonded to six Pd and six equivalent Ag atoms to form AgAg6Pd6 cuboctahedra that share corners with five equivalent PdAg6Pd10 cuboctahedra, corners with twelve AgAg6Pd6 cuboctahedra, edges with ten PdAg6Pd6 cuboctahedra, edges with twelve AgAg6Pd6 cuboctahedra, faces with six equivalent AgAg6Pd6 cuboctahedra, and faces with fifteen PdAg6Pd6 cuboctahedra. All Ag–Pd bond lengths are 2.86 Å. All Ag–Ag bond lengths are 2.87 Å. In the third Ag site, Ag is bonded to six Pd and six equivalent Ag atoms to form AgAg6Pd6 cuboctahedra that share corners with five equivalent PdAg6Pd10 cuboctahedra, corners with twelve AgAg6Pd6 cuboctahedra, edges with ten PdAg6Pd6 cuboctahedra, edges with twelve AgAg6Pd6 cuboctahedra, faces with six equivalent AgAg6Pd6 cuboctahedra, and faces with fifteen PdAg6Pd6 cuboctahedra. All Ag–Ag bond lengths are 2.87 Å.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on AgPd by Materials Project

PdAg crystallizes in the hexagonal P-6m2 space group. The structure is three-dimensional. Pd is bonded to six equivalent Pd and six equivalent Ag atoms to form PdAg6Pd6 cuboctahedra that share corners with eighteen equivalent PdAg6Pd6 cuboctahedra, edges with six equivalent PdAg6Pd6 cuboctahedra, edges with twelve equivalent AgAg6Pd6 cuboctahedra, faces with eight equivalent PdAg6Pd6 cuboctahedra, and faces with twelve equivalent AgAg6Pd6 cuboctahedra. All Pd–Pd bond lengths are 2.86 Å. All Pd–Ag bond lengths are 2.87 Å. Ag is bonded to six equivalent Pd and six equivalent Ag atoms to form AgAg6Pd6 cuboctahedra that share corners with eighteen equivalent AgAg6Pd6 cuboctahedra, edges with six equivalent AgAg6Pd6 cuboctahedra, edges with twelve equivalent PdAg6Pd6 cuboctahedra, faces with eight equivalent AgAg6Pd6 cuboctahedra, and faces with twelve equivalent PdAg6Pd6 cuboctahedra. All Ag–Ag bond lengths are 2.86 Å.

36 MATERIALS SCIENCE↗