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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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At least 109 records · Page 6
All sourcesNASA NTRSDOE OSTI
DOE OSTI2022

Stabilization of Cu 2 O through Site-Selective Formation of a Co 1 Cu Hybrid Single-Atom Catalyst

Single-atom catalysts (SACs) consist of a low coverage of isolated metal atoms dispersed on a metal substrate, called single-atom alloys (SAAs), or alternatively single metal atoms coordinated to oxygen atoms on an oxide support. We present the synthesis of a new type of Co 1 Cu SAC centers on a Cu 2 O(111) support by means of a site-selective atomic layer deposition technique. Isolated metallic Co atoms selectively coordinate to the native oxygen vacancy sites (Cu sites) of the reconstructed Cu 2 O(111) surface, forming a Co 1 Cu SAA with no direct Co–O x bonds. The centers, here referred to as Co 1 Cu hybrid SACs, are found to stabilize the active Cu + sites of the low-cost Cu 2 O catalyst that otherwise is prone to deactivation under reaction conditions. The stability of the Cu 2 O(111) surface was investigated by synchrotron radiation-based ambient-pressure X-ray photoelectron spectroscopy under reducing CO environment. The structure and reduction reaction are modeled by density functional theory calculations, in good agreement with experimental results.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Thermal expansion and phonon anharmonicity of cuprite studied by inelastic neutron scattering and ab initio calculations

Inelastic neutron scattering measurements were performed with a time-of-flight chopper spectrometer to observe phonons in all parts of the Brillouin zone of a single crystal of cuprite Cu 2 O. We reduced the experimental data to phonon dispersions in the high-symmetry directions, and changes between 10 and 300 K are reported. In this paper, we show ab initio quasiharmonic (QH) and anharmonic (AH) calculations of phonon dispersions. We performed all AH calculations with a temperature-dependent effective potential method. Both QH and AH calculations account for the small negative thermal expansion of cuprite at low temperatures. However, the measured temperature-dependent phonon behavior was predicted more accurately with the AH calculations than the QH ones. Nevertheless, at 300 K, the cubic AH used in this paper did not entirely account for the experimental phonon dispersions in cuprite.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2020

Observation of [VCu1–Ini2+VCu1–] Defect Triplets in Cu-Deficient CuInS2

Copper indium disulfide (CuInS2) is a semiconductor with a direct energy band gap of 1.53 eV, an optimal value for highly efficient thin-film solar cells. But it has reached only ~ 11 % power conversion efficiency, far less than the theoretically achievable value of ~ 30 %. The cause of this low performance is not understood. A single crystal grown from 1 mol% Cu-deficient melt was studied, using atomic resolution high-angle annular dark-field (HAADF) scanning transmission electron microscopy (STEM) and electron dispersive spectroscopy (EDS). While the bulk crystal is exactly stoichiometric CuInS2, it contains nanometer-thick, structurally coherent, Cu-deficient interphases that form along rotational twin boundaries in the {112} plane. Transition zones from bulk crystal to interphase are observed, where In is seen to move from its normal site InIn in the chalcopyrite structure to a tetrahedral interstitial site Ini, while Cu remains in its normal CuCu position. Two InIn rows of the bulk crystal merge into one row of Ini, causing excess Ini in the interphase. The concentrations of CuCu and Ini reflect a ratio of Cu vacancies, VCu, to excess Ini of ~ 2. Their relative lattice positions, and the high electrical resistivity of the crystal, suggests that VCu and excess Ini ‘precipitate’ as self-compensating, electrically neutral, [VCu1- Ini2+ VCu1-] defect triplets. This is the first atomic-level observation of the ordered defect that has been invoked as the basic structural modifier in chalcopyrite compound homologs. The interphases introduce an optical gap of 1.47 eV. Electron trapping in band tail states, evident from a photoconductivity exponent of 0.54, is the likely cause of an unusually low electron mobility of 0.1 cm2V-1s-1. The overall result is that making CuInS2 slightly copper-poor inserts nanometer-thick layers of the interphase into the bulk crystal. This study shows that apparently conflicting results of the effect of Cu deficiency on CuInS2 thin-film solar cells may be resolved by analyzing structure and composition at nanometer spatial resolution.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2025

Dynamic Metal–Support Interaction Dictates Cu Nanoparticle Sintering on Al 2 O 3 Surfaces

Nanoparticle sintering remains a critical challenge in heterogeneous catalysis. In this work, we present a unified deep potential (DP) model based on the Perdew–Burke–Ernzerhof approximation of density functional theory for Cu nanoparticles on three Al 2 O 3 surfaces (γ-Al 2 O 3 (100), γ-Al 2 O 3 (110), and α-Al 2 O 3 (0001)). Using DP-accelerated simulations, we reveal that the nanoparticle size-mobility relationship strongly depends on the supporting surface. The diffusion of nanoparticles on the two γ-Al 2 O 3 surfaces is almost independent of the size of the nanoparticle, while the diffusion on α-Al 2 O 3 (0001) decreases rapidly with increasing size. Interestingly, nanoparticles with fewer than 55 atoms diffuse several times faster on α-Al 2 O 3 (0001) than on γ-Al 2 O 3 (100) at 800 K while expected to be more sluggish based on their larger binding energy at 0 K. The diffusion on α-Al 2 O 3 (0001) is facilitated by dynamic metal–support interaction (MSI), where Al atoms move out of the surface plane to optimize contact with the nanoparticle and relax back to the plane as the nanoparticle moves away. In contrast, the MSI on γ-Al 2 O 3 (100) and on γ-Al 2 O 3 (110) is dominated by more stable and directional Cu–O bonds, consistent with the limited diffusion observed on these surfaces. Our extended MD simulations provide insight into the sintering processes, showing that the dispersity of the nanoparticles strongly influences the coalescence driven by nanoparticle diffusion. We observed that the coalescence of Cu 13 nanoparticles on α-Al 2 O 3 (0001) can occur in a short time (10 ns) at 800 K even with an initial internanoparticle distance increased to 3 nm, while the coalescence on the two γ-Al 2 O 3 surfaces are inhibited significantly by increasing the initial internanoparticle distance. These findings demonstrate that the dynamics of the supporting surface is crucial to understanding the sintering mechanism and offer guidance for designing sinter-resistant catalysts by engineering the support morphology.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2022

Channel Scaling Dependent Photoresponse of Copper-Based Flexible Photodetectors Fabricated Using Laser-Induced Oxidation

Copper (Cu) oxide compounds (Cu x O), which include cupric (CuO) and cuprous (Cu 2 O) oxide, have been recognized as a promising p-channel material with useful photovoltaic properties and superior thermal conductivity. Typically, deposition methods or thermal oxidation can be used to obtain Cu x O. However, these processes are difficult to apply to flexible substrates because plastics have a comparatively low glass transition temperature. Also, additional patterning steps are needed to fabricate applications. In this work, we fabricated a metal–semiconductor–metal photodetector using laser-induced oxidation of thin Cu films under ambient conditions. Raman spectroscopy, scanning electron microscopy–energy-dispersive X-ray spectroscopy, and atomic force microscopy were used to study the composition and morphology of our devices. Moreover, the photoresponse of this device is reported herein. We performed an in-depth analysis of the relationship between the channel size and number of carriers using scanning photocurrent microscopy. The carrier transport behaviors were identified; the photocurrent decreased as the length and width of the channel increased. Furthermore, we verified the suitability of the device as a flexible photodetector using a variety of bending tests. Our in-depth analysis of this Cu-based flexible photodetector could play an important role in understanding the mechanisms of other flexible photovoltaic applications.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Rechargeable Alkaline Zinc/Copper Oxide Batteries

Resurrecting a battery chemistry thought to be only primary, we demonstrate the first example of a rechargeable alkaline zinc/copper oxide battery. With the incorporation of a Bi 2 O 3 additive to stabilize the copper oxide-based conversion cathode, Zn/(CuO–Bi 2 O 3 ) cells are capable of cycling over 100 times at >124 W h/L, with capacities from 674 mA h/g (cycle 1) to 362 mA h/g (cycle 150). The crucial role of Bi 2 O 3 in facilitating the electrochemical reversibility of Cu 2 O, Cu(OH) 2 , and Cu o was supported by scanning and transmission electrochemical microscopy, cyclic voltammetry, and rotating ring-disc electrode voltammetry and monitored via operando energy-dispersive X-ray diffraction measurements. Bismuth was identified as serving two roles, decreasing the cell resistance and promoting Cu(I) and Cu(II) reduction. Additionally, to mitigate the capacity losses of long-term cycling CuO cells, we demonstrate two limited depth of discharge (DOD) strategies. First, a 30% DOD (202 mA h/g) retains 99.9% capacity over 250 cycles. Second, the modification of the CuO cathode by the inclusion of additional Cu metal enables performance at very high areal capacities of ~40 mA h/cm 2 and unprecedented energy densities of ~260 W h/L, with near 100% Coulombic efficiency. This work revitalizes a historically primary battery chemistry and opens opportunity to future works in developing copper-based conversion cathode chemistries for the realization of low-cost, safe, and energy-dense secondary batteries.

25 ENERGY STORAGE↗
DOE OSTI2021

On the interactions between molten aluminum and high entropy alloy particles during aluminum matrix composite processing

The feasibility of adding AlCrTiV high entropy alloy (HEA) particles to molten aluminum to make metal matrix composites was studied. Equiatomic AlCrTiV HEA particles, produced by a solid state reduction process, were dispersed into pure aluminum and 7075 alloy (Al-5.8Zn-2.3Mg-1.4Cu, all weight %) melt and by a ultrasonic dispenser. It was found that the AlCrTiV particles reacted with molten aluminum, leading to the formation of Al 45 (Cr,V) 7 and Al 3 Ti intermetallic phases in the aluminum matrix composites. Although the AlCrTiV HEA particles did not survive in molten aluminum during composite processing, the final composite materials showed significantly improved mechanical properties, due to grain refinement and dispersion strengthening. Finally, the research suggests that the interactions between matrix aluminum alloys and the particles are key in controlling the final microstructure and properties of the composites.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Thermodynamic re-modelling of the Cu–Nb–Sn system: Integrating the nausite phase

Currently available Cu–Nb–Sn phase diagrams lack the recently discovered nausite phase (Cu,Nb)Sn 2 , which is an important intermediate in the course of thermal processing of superconducting Nb 3 Sn wires. Processing decisively determines the resulting microstructure of Nb 3 Sn and, thus, its superconducting properties. Lack of suitable and complete phase diagrams, however, obstructs rational design of such thermal processing procedures. To close this gap and to obtain valid knowledge of homogeneity and stability range of nausite, various Cu–Nb–Sn samples, which are heat-treated between 300 °C and 500 °C, are investigated. By means of energy-dispersive X-ray spectroscopy (EDX), a temperature-dependent homogeneity range of nausite is observed, which covers average mole fractions of Cu between 0.09 and 0.15. This is correlated with a change in the mean atomic volume and can be seen in the lattice parameters determined by X-ray diffraction (XRD). Additionally performed first-principles calculations on different CuSn 2 and NbSn 2 model structures confirm this trend. Furthermore, the peritectic decomposition of nausite to NbSn 2 and liquid at 586 °C is determined by means of in situ XRD and differential scanning calorimetry (DSC). By using the CALPHAD (CALculation of PHase Diagrams) approach, all these findings are used to extend a previous thermodynamic description of the Cu–Nb–Sn system by including the nausite as an additional phase. Finally, with this noteworthy integration, the updated modelling of the Cu–Nb–Sn system can be used for optimizing the multistage heat-treatment steps during processing superconducting Nb 3 Sn wires.

36 MATERIALS SCIENCE↗
NASA NTRS1988

X-ray rocking curve measurements of bent crystals

A three-crystal laboratory X-ray spectrometer is used to measure the Bragg reflection from concave cylindrically curved crystals to be used in the high-resolution X-ray spectrometer of the NASA Advanced X-ray Astrophysics Facility (AXAF). The first two crystals, in the dispersive (1.1) arrangement, select a narrow collimated monochromatic beam in the Cu K-alpha(1) line at 1.5 A (8.1 keV), which illuminates the test crystal. The angular centroids of rocking curves measured along the surface provide a measure of the conformity of the crystal to the desired radius of curvature. Individual and combined rocking-curve widths and areas provide a measure of the resolution and efficiency at 1.54 A. The crystals analyzed included LiF(200), PET, and acid phthalates such as TAP.

Hakim, M. B.↗
DOE OSTI2024

Composition-Dependent Reconstructions of Titanium Oxide Clusters and Cu(111) Support via Cluster-Adatom Interactions

Mass-selected cluster deposition and scanning tunneling microscopy (STM) were used to investigate the surface structure and thermal stability of Ti 3 O y (y = 5, 6) clusters on a Cu(111) surface. STM imaging shows that the substoichiometric Ti 3 O 5 clusters aggregate into large dendritic assemblies at step edges, while the stoichiometric Ti 3 O 6 clusters are highly dispersed as single or small groupings of clusters. Cluster deposition also results in extensive reconstruction of the Cu(111) surface. The Ti 3 O 5 /Cu(111) surface exhibits one Cu-layer deep pits that are ringed by cluster assemblies that nucleate and grow at the perimeter step edges. By comparison, the Ti 3 O 6 /Cu(111) surface consists of irregular step edges and small one Cu-layer islands that are decorated with clusters. The restructuring of the Cu(111) surface is attributed to strong Cu-cluster interactions that release Cu adatoms from the step edges. This mechanism is supported by density functional theory (DFT) calculations, which predict that the Cu adatom attachment to the clusters is energetically favorable. Annealing the surfaces at elevated temperatures (400-700 K) results in higher densities of irregular steps, pits and isolated Cu islands as well as increased cluster aggregation. In conclusion, this work highlights adatom-cluster interactions as another manifestation of strong cluster-support interactions that can significantly alter the nature of the oxide-metal interface.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
NASA NTRS1974

Texturing and residual stress in metals as a result of sliding

Pole figures of the texturing produced by friction in the alloys Cu - 10 at. % Sn, Cu - 10 at. % Si, 440 C stainless steel, and AISI 52100 bearing steel were obtained with an energy-dispersive X-ray diffractometer. While the texturing behavior of these alloys is generally similar to that of pure metals, the 52100 steel and the Cu5Si phase of Cu - 10 at. % Si show no texturing at the loads and speeds used in this experiment. Photographic methods were used in an attempt to measure the uniform residual stress in the wear tracks produced on some pure metals. The stress in copper and iron was, however, below the limit of detectability - about 4.3 x 10 to the 7th power N/sq m (6000 psi). Line broadening under all test conditions in the case of copper and at high load and speed conditions in iron is attributed, at least in part, to the reduction of crystallite size and, perhaps, to nonuniform residual stress, as well.

Wheeler, D. R.↗
DOE OSTI2020

Biomineralization of Cu 2 S Nanoparticles by Geobacter sulfurreducens

Biomineralization of Cu has been shown to control contaminant dynamics and transport in soils. However, very little is known about the role that subsurface microorganisms may play in the biogeochemical cycling of Cu. In this study, we investigate the bioreduction of Cu(II) by the subsurface metal-reducing bacterium Geobacter sulfurreducens. Rapid removal of Cu from solution was observed in cell suspensions of G. sulfurreducens when Cu(II) was supplied, while transmission electron microscopy (TEM) analyses showed the formation of electron-dense nanoparticles associated with the cell surface. Energy-dispersive X-ray spectroscopy (EDX) point analysis and EDX spectrum image maps revealed that the nanoparticles are rich in both Cu and S. This finding was confirmed by X-ray absorption near-edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) analyses, which identified the nanoparticles as Cu 2 S. Biomineralization of Cu x S nanoparticles in soils has been reported to enhance the colloidal transport of a number of contaminants, including Pb, Cd, and Hg. However, formation of these Cu x S nanoparticles has only been observed under sulfate-reducing conditions and could not be repeated using isolates of implicated organisms. As G. sulfurreducens is unable to respire sulfate, and no reducible sulfur was supplied to the cells, these data suggest a novel mechanism for the biomineralization of Cu 2 S under anoxic conditions. The implications of these findings for the biogeochemical cycling of Cu and other metals as well as the green production of Cu catalysts are discussed.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2021

Single-atom catalysts with anionic metal centers: promising electrocatalysts for the oxygen reduction reaction and beyond

Ongoing efforts to develop single-atom catalysts (SACs) for the oxygen reduction reaction (ORR) typically focus on SACs with cationic metal centers, while SACs with anionic metal centers (anionic SACs) have been generally neglected. However, anionic SACs may offer excellent active sites for ORR, since anionic metal centers could facilitate the activation of O2 by back donating electrons to the antibonding orbitals of O2. In this work, we propose a simple guideline for designing anionic SACs: the metal centers should have larger electronegativity than the surrounding atoms in the substrate on which the metal atoms are supported. By means of density functional theory (DFT) simulations, we identified 13 anionic metal centers (Co, Ni, Cu, Ru, Rh, Pd, Ag, Re, Os, Ir, Pt, Au, and Hg) dispersed on pristine or defective antimonene substrates as new anionic SACs, among which anionic Au and Co metal centers exhibit limiting potentials comparable to, or even better than, conventional Pt-based catalysts towards ORR. We also found that anionic Os and Re metal centers on the defective antimonene can electrochemically catalyze the nitrogen reduction reaction (NRR) with a limiting potential close to that of stepped Ru(0001). Overall, our work shows promise towards the rational design of anionic SACs and their utility for applications as electrocatalysts for ORR and other important electrochemical reactions.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Dual-site catalysts featuring platinum-group-metal atoms on copper shapes boost hydrocarbon formations in electrocatalytic CO2 reduction

Abstract Copper-based catalyst is uniquely positioned to catalyze the hydrocarbon formations through electrochemical CO 2 reduction. The catalyst design freedom is limited for alloying copper with H-affinitive elements represented by platinum group metals because the latter would easily drive the hydrogen evolution reaction to override CO 2 reduction. We report an adept design of anchoring atomically dispersed platinum group metal species on both polycrystalline and shape-controlled Cu catalysts, which now promote targeted CO 2 reduction reaction while frustrating the undesired hydrogen evolution reaction. Notably, alloys with similar metal formulations but comprising small platinum or palladium clusters would fail this objective. With an appreciable amount of CO-Pd 1 moieties on copper surfaces, facile CO * hydrogenation to CHO * or CO-CHO * coupling is now viable as one of the main pathways on Cu(111) or Cu(100) to selectively produce CH 4 or C 2 H 4 through Pd-Cu dual-site pathways. The work broadens copper alloying choices for CO 2 reduction in aqueous phases.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
NASA NTRS1991

Electromigration failure in YBa2Cu3O(7-x) thin films

Electromigration failure in highly oriented YBa2Cu3O(7-x) thin films below the superconducting transition temperature is reported here for the first time. The film on SrTiO3 failed at 86 K, 230,000 A/sq cm, while that on LaAlO3 failed at 84 K, 930,000 A/sq cm. Scanning electron microscopy and energy dispersive X-ray analysis of the films after failure shows that Cu migrates preferentially away from the failure region toward the electrode.

Vitta, Satish↗
DOE OSTI2020

Sweeping potential regulated structural and chemical evolution of solid-electrolyte interphase on Cu and Li as revealed by cryo-TEM

A fundamental understanding of solid-electrolyte interphase (SEI) is paramount importance for controlling the cycling performance of rechargeable lithium metal batteries. The structural and chemical evolution of SEI with respect to electrochemical operating condition remains barely established. Here we develop a unique method for imaging the evolution of SEI formed on the Cu foil under sweeping electrochemical potential. By using cryogenic TEM imaging combined with energy dispersive X-ray spectroscopy and X-ray photoelectron spectroscopy electronic structure analyses, we reveal that, for the vinylene carbonate (VC)-free electrolyte, the SEI formed at 1.0 V is a monolithic amorphous structure, which evolves to amorphous matrix embedded with Li 2 O particles as the voltage decreases to 0 V. In the case of VC-containing electrolyte, the SEI is featured by an amorphous matrix with Li 2 O particles from 1.0 V to 0 V. The thickness of SEI formed on Cu foil increases with decreasing voltage. Associated with the localized charge modulation by the surface topographic feature and defects in the Cu foil, the SEI layer shows direct spatial correlation with these structural defects in the Cu. In addition, upon Li deposition, the SEI formed on the Li metal has similar thickness with, but different composition from the SEI formed on the Cu foil at 0 V. Furthermore, those results provide insight toward SEI engineering for enhanced cycling stability of Li metal.

25 ENERGY STORAGE↗
NASA NTRS1997

Microstructure and Mechanical Properties of Vacuum Plasma Sprayed Cu-8Cr-4Nb

This paper compares the tensile properties of Cu-8Cr-4Nb material produced by VPS to material previously produced by extrusion. The microstructure of the VPS material is also presented. The combustion chamber liner of rocket motors represents an extreme materials application. The liner hot wall is exposed to a 2760 C (5000 F) flame while the cold side is exposed to cryogenic hydrogen liquid. Materials for use in the combustion chamber liner require a combination of high temperature strength, creep resistance, and low cycle fatigue resistance along with high thermal conductivity. The hot side is also subject to localized cycles between reducing and oxidizing environments that degrade the liner by a process called blanching. A new Cu-8 at.% Cr-4 at% Nb (Cu-8Cr-4Nb) alloy has been developed at NASA Lewis Research Center as a replacement for the currently used alloy, NARloy-z (Cu-3 wt.% Ag-0.5 wt.% Zr). The alloy is strengthened by a fine dispersion of Cr2Nb particles. The alloy has better mechanical properties than NARloy-Z while retaining most of the thermal conductivity of pure copper. The alloy has been successfully consolidated by extrusion and hot isostatic pressing (HIPing). However, vacuum plasma spraying (VPS) offers several advantages over prior consolidation methods. VPS can produce a near net shape piece with the profile of the liner. In addition, oxidation resistant and thermal barrier coatings can be incorporated as an integral part of the liner hot wall during the VPS deposition. The low oxygen VPS Cu-8Cr-4Nb exhibits a higher strength than Cu-8Cr-4Nb produced by extrusion at elevated temperatures and a comparable strength at room temperature. Moduli and ductility were not significantly different. However, the ability to produce parts to near-net shape and maintain the good elevated temperature tensile properties of the extruded Cu-8Cr-4Nb makes VPS an attractive processing method for fabricating rocket engine combustion liners.

Holmes, Richard↗