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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 307 records · Page 17
All sourcesNASA NTRSDOE OSTI
DOE OSTI2023

Fast and Non‐equilibrium Uptake of Hydrogen by Pd Icosahedral Nanocrystals

Abstract We report for the first time that Pd nanocrystals can absorb H via a “single‐phase pathway” when particles with a proper combination of shape and size are used. Specifically, when Pd icosahedral nanocrystals of 7‐ and 12‐nm in size are exposed to H atoms, the H‐saturated twin boundaries can divide each particle into 20 smaller single‐crystal units in which the formation of phase boundaries is no longer favored. As such, absorption of H atoms is dominated by the single‐phase pathway and one can readily obtain PdH x with anyx in the range of 0–0.7. When switched to Pd octahedral nanocrystals, the single‐phase pathway is only observed for particles of 7 nm in size. We also establish that the H‐absorption kinetics will be accelerated if there is a tensile strain in the nanocrystals due to the increase in lattice spacing. Besides the unique H‐absorption behaviors, the PdH x ( x =0–0.7) icosahedral nanocrystals show remarkable thermal and catalytic stability toward the formic acid oxidation due tothe decrease in chemical potential for H atoms in a Pd lattice under tensile strain.

Zhou, Siyu↗
DOE OSTI2023

Fast and Non‐equilibrium Uptake of Hydrogen by Pd Icosahedral Nanocrystals

Abstract We report for the first time that Pd nanocrystals can absorb H via a “single‐phase pathway” when particles with a proper combination of shape and size are used. Specifically, when Pd icosahedral nanocrystals of 7‐ and 12‐nm in size are exposed to H atoms, the H‐saturated twin boundaries can divide each particle into 20 smaller single‐crystal units in which the formation of phase boundaries is no longer favored. As such, absorption of H atoms is dominated by the single‐phase pathway and one can readily obtain PdH x with anyx in the range of 0–0.7. When switched to Pd octahedral nanocrystals, the single‐phase pathway is only observed for particles of 7 nm in size. We also establish that the H‐absorption kinetics will be accelerated if there is a tensile strain in the nanocrystals due to the increase in lattice spacing. Besides the unique H‐absorption behaviors, the PdH x (x=0–0.7) icosahedral nanocrystals show remarkable thermal and catalytic stability toward the formic acid oxidation due tothe decrease in chemical potential for H atoms in a Pd lattice under tensile strain.

Chemistry↗
DOE OSTI2020

Probing the Li 4 Ti 5 O 12 Interface Upon Lithium Uptake by Operando Small Angle Neutron Scattering

The formation of a solid–electrolyte interphase (SEI) on the surface of Li 4 Ti 5 O 12 (LTO) has become a highly controversial topic, with arguments for it and against it. However, prior studies supporting the formation of an SEI layer have typically suggested that a layer forms upon cycling of a cell, although the layer is probed after disassembling. In this study, cubic mesostructured LTO is synthesized with crystallite domain sizes between 3 and 4 nm and uniform pores with diameters ≤8 nm. The mean pore size is controlled between 4–8 nm through the use of a triblock amphipathic copolymer with a tunable hydrophobic block as template and by thermal treatment. The LTO morphology obtained is spherical and evolves upon heat treatment. We report these materials show excellent electrochemical performance, including high rate capability and capacity retention. The LTO material is subjected to operando small-angle neutron scattering and X-ray photoelectron spectroscopy experiments, which reveal that the highly debated SEI forms at potentials as high as 2.2 V, first as a LiF-rich layer and subsequently by the growth of a carbonaceous layer. These SEI products form first on the smaller pores before forming on the mesopores.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

An in-situ 3D micro-XRD investigation of water uptake by alkali-silica-reaction (ASR) product

The ASR products in concrete have various chemical compositions. It is yet unclear whether and how these products develop micro-expansion upon moisture ingress. This paper presents a 3D in-situ observation of the crystallography and volume change of an ASR-product-filled vein under varying relative-humidity (R.H.). The vein was observed to contain two layered nano-crystalline phases with distinct basal spacings, and was distributed heterogeneously in space. When R.H. changed from 10% to >38%, the basal spacing increased from 7.43 Å to 8.89 Å for one phase, whereas it remained constant (~10.9 Å) for the other. This is the first time that an ASR product is observed in-situ to exhibit crystal structural expansion during wetting process. However, the product-filled vein exhibited no noticeable swelling when R.H. varied from 10% to 97%. Our findings provide the first direct evidence that the moisturization-induced crystal structural change of ASR product may not be a plausible explanation to the macroscale concrete expansion.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Sectoral and growth rate control on elemental uptake by individual calcite crystals

Heterogeneous distribution of trace elements (impurities) within individual calcite crystals is a phenomenon commonly observed in natural and laboratory systems. Changes in thermodynamic intensive parameters (mostly chemical potential and temperature) cannot always explain the inhomogeneous impurity patterns in calcite crystals and it has been suggested that growth rate and crystallographic orientation may exert strong effects on elemental incorporation into calcite. In addition, there are a number of experimental studies on micro-scale element (E) distribution between non-equivalent pairs of calcite vicinal faces (known as sectoral zoning); however, the variability of partition coefficients (e.g., K E = (E/Ca) calcite /(E/Ca) fluid ) within individual crystals remains undetermined. In this study, we have extended the work on elemental distribution between crystal sectors to evaluation of partition coefficients of trace and minor elements (Li, B, Mg, and Sr) in calcite crystal faces (10–14) and (01-12), whose growth rates were assessed. Growth entrapment model (GEM) and lattice strain theory were applied to explain K E heterogeneity by varying near-surface diffusivity of Mg and Sr and by varying surface enrichment factor for Li, B, Mg, and Sr. Decoupling of sectoral and growth rate effects reveals that sectoral zoning plays a key role in elemental distribution. More specifically, K Li and K B vary by more than one order of magnitude and K Mg varies by a factor of two within individual crystal faces. Strontium sectoral distribution is different from those of Li, B, and Mg and K Sr varies by up to a factor of two. Finally, these behaviors likely reflect different mechanisms of incorporation of Li, B, Mg, and Sr into calcite.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗