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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 OSTI2022

High gradient off-axis coupled C-band Cu and CuAg accelerating structures

Here, we report the high gradient testing results of two single-cell off-axis coupled standing wave accelerating structures. Two brazed standing wave off-axis coupled structures with the same geometry were tested: one made of pure copper (Cu) and one made of a copper–silver (CuAg) alloy with a silver concentration of 0.08%. A peak surface electric field of 450 MV/m was achieved in the CuAg structure for a klystron input power of 14.5 MW and a 1 μs pulse length, which was 25% higher than the peak surface electric field achieved in the Cu structure. The superb high gradient performance was achieved because of the two major optimizations in the cavity's geometry: (1) the shunt impedance of the cavity was maximized for a peak surface electric field to accelerating gradient ratio of ~2 for a fully relativistic particle, and (2) the peak magnetic field enhancement due to the input coupler was minimized to limit pulse heating. These tests allow us to conclude that C-band accelerating structures can operate at peak fields similar to those at higher frequencies while providing a larger beam iris for improved beam transport.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2023

Mechanistic Insights into Aldehyde Production from Electrochemical CO 2 Reduction on CuAg Alloy via Operando X-ray Measurements

CO 2 electrolysis converts the greenhouse gas CO 2 into valuable fuels and chemicals, such as carbon monoxide, ethylene, ethanol, etc. Currently, Cu is the only known monometallic catalyst capable of producing multicarbon products from electrochemical CO 2 reduction reaction (eCO2RR), while the poor selectivity limits its further use. It has been found that introducing Ag atoms into the Cu lattice can modulate product preference. However, the synergistic effects between Cu and Ag, and thus, the catalytic performance, are strongly influenced by catalyst morphology, electrolyzer configuration, reaction conditions, etc. Operando measurements can provide explicit information on the catalyst dynamic variation during the reaction, but their operation and analysis are challenging. Herein, we prepared CuAg multiphase alloy catalysts by magnetron sputtering, which allowed for investigating the intrinsic interaction between Cu and Ag. eCO2RR performance exhibited an improved selectivity toward carbonyls at the expense of hydrogen and hydrocarbons. The partially alloyed Cu and Ag phases were confirmed by operando X-ray diffraction. By means of combining operando X-ray measurements and density functional theory (DFT) calculations, the preferred carbonyl production is attributed to the reduced electron density and compressive strain of Cu due to Ag incorporation, which leads to a deeper d-band center and therefore weakened intermediate adsorption and oxophilicity. In conclusion, this work provides evidence of the intrinsic structural and electronic interaction between Cu and Ag during eCO2RR. The obtained information will facilitate the design of bi/multi-phase metallic or alloy electrocatalysts.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

Materials Data on CuAgS by Materials Project

AgCuS crystallizes in the orthorhombic Pnma space group. The structure is three-dimensional. Ag1+ is bonded in a bent 150 degrees geometry to two equivalent S2- atoms. There are one shorter (2.50 Å) and one longer (2.51 Å) Ag–S bond lengths. Cu1+ is bonded in a trigonal planar geometry to three equivalent S2- atoms. There are two shorter (2.25 Å) and one longer (2.33 Å) Cu–S bond lengths. S2- is bonded in a 5-coordinate geometry to two equivalent Ag1+ and three equivalent Cu1+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on CuAgS by Materials Project

AgCuS crystallizes in the orthorhombic Cmcm space group. The structure is three-dimensional. Ag1+ is bonded in a linear geometry to two equivalent S2- atoms. Both Ag–S bond lengths are 2.46 Å. Cu1+ is bonded in a trigonal planar geometry to three equivalent S2- atoms. There are two shorter (2.27 Å) and one longer (2.30 Å) Cu–S bond lengths. S2- is bonded in a 5-coordinate geometry to two equivalent Ag1+ and three equivalent Cu1+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on CuAgS by Materials Project

AgCuS crystallizes in the orthorhombic Cmc2_1 space group. The structure is three-dimensional. Ag1+ is bonded in a linear geometry to two equivalent S2- atoms. There are one shorter (2.47 Å) and one longer (2.49 Å) Ag–S bond lengths. Cu1+ is bonded in a trigonal planar geometry to three equivalent S2- atoms. There are two shorter (2.25 Å) and one longer (2.36 Å) Cu–S bond lengths. S2- is bonded in a 5-coordinate geometry to two equivalent Ag1+ and three equivalent Cu1+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on CuAg(AsO4)2 by Materials Project

AgCu(AsO4)2 crystallizes in the monoclinic P2_1/c space group. The structure is three-dimensional. Ag3+ is bonded in a 7-coordinate geometry to seven O2- atoms. There are a spread of Ag–O bond distances ranging from 2.17–2.83 Å. Cu3+ is bonded in a distorted rectangular see-saw-like geometry to four O2- atoms. There is one shorter (1.85 Å) and three longer (1.90 Å) Cu–O bond length. There are two inequivalent As5+ sites. In the first As5+ site, As5+ is bonded in a tetrahedral geometry to four O2- atoms. There are a spread of As–O bond distances ranging from 1.71–1.77 Å. In the second As5+ site, As5+ is bonded in a tetrahedral geometry to four O2- atoms. There are a spread of As–O bond distances ranging from 1.69–1.77 Å. There are eight inequivalent O2- sites. In the first O2- site, O2- is bonded in a distorted bent 120 degrees geometry to one Ag3+ and one As5+ atom. In the second O2- site, O2- is bonded in a bent 120 degrees geometry to one Cu3+ and one As5+ atom. In the third O2- site, O2- is bonded in a distorted bent 120 degrees geometry to one Ag3+, one Cu3+, and one As5+ atom. In the fourth O2- site, O2- is bonded in a distorted bent 120 degrees geometry to one Ag3+, one Cu3+, and one As5+ atom. In the fifth O2- site, O2- is bonded in a single-bond geometry to one Ag3+ and one As5+ atom. In the sixth O2- site, O2- is bonded in a 2-coordinate geometry to one Ag3+, one Cu3+, and one As5+ atom. In the seventh O2- site, O2- is bonded in a bent 120 degrees geometry to one Ag3+ and one As5+ atom. In the eighth O2- site, O2- is bonded in a distorted bent 120 degrees geometry to one Ag3+ and one As5+ atom.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Ab-initio Cu alloy design for high-gradient accelerating structures

Operation of normal conducting accelerator structures at high accelerating gradients is beneficial for many accelerator applications in basic science, industry, medicine, and National Security. RF breakdown is the major factor that limits the achievable accelerating gradients. Previous experiments on copper (Cu) have demonstrated that RF breakdown probability can be significantly decreased by hardening the material and alloying Cu with solutes such as silver (Ag). In this paper, we propose a figure-of-merit (FOM) that characterizes the ability of Cu alloys to withstand high-gradients. The FOM represents a trade-off between hardening through solid solution strengthening and the additional thermal stress induced by incremental RF pulse heating resulting from changes in electronic properties induced by alloying. We performed high-throughput ab initio calculations and computed the FOM for a large number of binary Cu alloys. Several promising candidate alloys for high-gradient accelerating structures were identified, such as CuAg, CuCd, CuHg, CuAu, CuIn, and CuMg. CuAg alloys have previously exhibited low RF breakdown rates in experiments. The results provide guidance for selecting alloys for the future high-gradient normal conducting accelerating structures operating at very high gradients.

36 MATERIALS SCIENCE↗
DOE OSTI2025

In-situ/operando study of Cu-based nanocatalysts for CO 2 electroreduction using electrochemical liquid cell TEM

The structure of a nanocatalyst during electrocatalytic reactions often deviates from its pristine structure due to intrinsic properties, or physical and chemical adsorption at the catalytic surfaces. Taking Cu-based catalysts for CO 2 electroreduction reactions (CO 2 RR) as an example, they often experience segregation, leaching, and alloying during reactions. With the recent breakthrough development of high-resolution polymer electrochemical liquid cells, in-situ electrochemical liquid cell transmission electron microscopy (EC-TEM) alongside other advanced microscopy techniques, has become a powerful platform for revealing electrocatalysts restructuring at the atomic level. Considering the complex reactions involving electrified solid-liquid interfaces and catalyst structural evolution with intermediates, systematic studies with multimodal approaches are crucial. In this article, we demonstrate a research protocol for the study of electrocatalysts structural evolution during reactions using the in-situ EC-TEM platform. Using Cu and CuAg nanowire catalysts for CO 2 RR as model systems, we describe the experimental procedures and findings. We highlight the platform’s crucial role in elucidating atomic-scale pathways of nanocatalyst restructuring and identifying catalytic active sites, as well as avoiding potential artifacts to ensure unbiased conclusions. Using the multimodal characterization toolbox, we provide the opportunity to correlate the structure of a working catalyst with its performance. Finally, we discuss advancements as well as the remaining gap in elucidating the structural-performance relationship of working catalysts. We expect this article will assist in establishing guidelines for future investigations of complex electrochemical reactions, such as CO 2 RR and other catalytic processes, using the in-situ EC-TEM platform.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗