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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 271 records · Page 15
All sourcesNASA NTRSDOE OSTI
DOE OSTI2021

Spontaneous Strain Buffer Enables Superior Cycling Stability in Single-Crystal Nickel-Rich NCM Cathode

The capacity degredation in layered Ni-rich LiNixCoyMnzO2 (x >= 0.8) cathode largely originated from drastic surface reactions and intergranular cracks in polycrystalline particles. Herein, we report a highly stable single- crystal LiNi0.83Co0.12Mn0.05O2 cathode material, which can deliver a high specific capacity (similar to 209 mAh g(-1) at 0.1 C, 2.8-4.3 V) and meanwhile display excellent cycling stability (>96% retention for 100 cycles and >93% for 200 cycles). By a combination of in situ X-ray diffraction and in situ pair distribution function analysis, an intermediate monoclinic distortion and irregular H3 stack are revealed in the single crystals upon charging-discharging processes. These structural changes might be driven by unique Li-intercalation kinetics in single crystals, which enables an additional strain buffer to reduce the cracks and thereby ensure the high cycling stability.

in situ synchrotron characterization↗
DOE OSTI2021

Atomic Layer Deposition with TiO2 for Enhanced Reactivity and Stability of Aromatic Hydrogenation Catalysts

Hydrogenation of aromatic molecules in fossil- and bio-derived fuels is essential for decreasing emissions of harmful combustion products and addressing growing concerns around urban air pollution. In this work, we used atomic layer deposition to significantly enhance the hydrogenation performance of a conventional supported Pd catalyst by applying an ultrathin coating of TiO2 in a scalable powder coating process. The TiO2-coated catalyst showed substantial gains in the conversion of multiple aromatic molecules, including a 5-fold improvement in turnover frequency versus the uncoated catalyst in the hydrogenation of naphthalene. This activity enhancement was maintained upon scaling the coating synthesis process from 3 to 100 g. Based on the results from Xray photoelectron spectroscopy, X-ray absorption spectroscopy, and computational modeling, the activity enhancement was attributed to ensemble effects resulting from partial TiO2 coverage of the Pd surface rather than fundamental changes to the Pd electronic structure. Additional durability testing confirmed that the TiO2 coating improved the thermal and hydrothermal stability of the catalyst as well as tolerance toward sulfur impurities in the reactant stream. Using an economic model of an industrial deep hydrogenation process, we found that an increase in catalyst activity or lifetime of 2× would justify even a relatively high estimate for the cost of TiO2 atomic layer deposition coatings at scale

atomic layer↗
DOE OSTI2015

Supportless, bismuth-modified palladium nanotubes with improved activity and stability for formic acid oxidation

Palladium nanotubes (PdNTs) were synthesized by templated vapor deposition and investigated for formic acid electrooxidation. Annealed PdNTs are 2.4 times more active (2.19 mA/cm 2 ) than commercial carbon-supported palladium (0.91 mA/cm 2 ) at 0.3 V vs RHE. Bismuth modification improved nanotube performance over 4 times (3.75 mA/cm 2 ) vs Pd/C and nearly 2 times vs unmodified PdNTs. A surface Bi coverage of 80% results in optimal site-specific activity by drastically reducing surface-poisoning CO generation during formic acid electrooxidation. The Bi-modified PdNTs are exceptionally stable, maintaining 2 times the area-normalized current density as Pd/C after 24 h at 0.2 V vs RHE. As a result, we attribute the enhanced activity and stability of the nanotube catalysts to the presence of highly coordinated surfaces, mimicking a flat polycrystal while retaining high surface area geometry.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2019

Understanding Monsoonal Water Cycle Changes in a Warmer Climate in E3SMv1 Using a Normalized Gross Moist Stability Framework

Abstract One of the grand challenges of climate science is understanding the changes of the tropical rain belts and monsoon systems owing to CO 2 ‐induced warming. A promising path forward links the fluxes of energy and moisture to tropical circulation features. To this end, we make use of the Energy Exascale Earth System Model version 1, where the divergence of moist static energy and moisture have been calculated online, and employ a normalized gross moist stability (NGMS) diagnostic framework to understand the linkages between changes in the flow of energy and moisture within the monsoons. We focus on the Asian Summer Monsoon system and utilize a series of atmosphere‐land and atmosphere‐land‐ocean simulations to understand the connection between fluxes and monsoons. Uncoupled simulations with prescribed sea surface temperatures indicate that decreases in NGMS over land are important in explaining precipitation increases in response to both sea surface temperature and CO 2 increases. In fully coupled experiments, NGMS decreases remain an important contributor to the increase in P‐E, but the coupled simulations highlight the importance of consistent ocean and land responses in interpreting the monsoon changes. This study indicates that transient eddy fluxes play an important role in NGMS decreases and that a time‐mean view of the monsoon circulations is insufficient to quantify the link between future changes in the fluxes of energy and moisture. Compensation between dynamic and thermodynamic components of vertical moist static energy advection occurs, with the thermodynamic contribution dominating. The compensation is shown to be sensitive to relative humidity, with higher relative humidity leading to a stronger thermodynamic component.

Harrop, Bryce E.↗
DOE OSTI2017

Atomistic structural ensemble refinement reveals non-native structure stabilizes a sub-millisecond folding intermediate of CheY

The dynamics of globular proteins can be described in terms of transitions between a folded native state and less-populated intermediates, or excited states, which can play critical roles in both protein folding and function. Excited states are by definition transient species, and therefore are difficult to characterize using current experimental techniques. We report an atomistic model of the excited state ensemble of a stabilized mutant of an extensively studied flavodoxin fold protein CheY. We employed a hybrid simulation and experimental approach in which an aggregate 42 milliseconds of all-atom molecular dynamics were used as an informative prior for the structure of the excited state ensemble. The resulting prior was then refined against small-angle X-ray scattering (SAXS) data employing an established method (EROS). The most striking feature of the resulting excited state ensemble was an unstructured N-terminus stabilized by non-native contacts in a conformation that is topologically simpler than the native state. We then predict incisive single molecule FRET experiments, using these results, as a means of model validation. Our study demonstrates the paradigm of uniting simulation and experiment in a statistical model to study the structure of protein excited states and rationally design validating experiments.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2017

Effective strategies for stabilizing sulfur for advanced lithium–sulfur batteries

The lithium-ion battery, with a relatively small energy density of similar to 250 W h kg(-1), has dominantly powered many devices requiring small energy demands. However, there remains a need for a cheaper and smaller type of battery with higher energy density for energy-intensive storage purposes in the automotive, aircraft, and household energy sectors. With its higher specific capacity (1675 mA h g(-1)) and lower costs, the lithium-sulfur (Li-S) battery represents the most promising next generation battery. The main focus of scientific inquiry surrounding Li-S batteries lies at the cathode, where sulfur chemically bonds to lithium. Current challenges pertaining to the high performance cathode such as the dissolution of sulfur into the electrolyte and electrode volume changes are highlighted. This review focuses on recent developments in the last three years of various sulfur integration methods at the cathode that result in improved electrochemical performance, increased energy density, cyclic stability, and a higher capacity over the mainstream lithium-ion battery. In particular, the most recent approaches were systematically examined and compared including the use of carbon and non-carbon composites to stabilize sulfur. Ideal material hosts for sulfur atoms in the cathode for outstanding Li-S batteries were outlined and thoroughly discussed. Critical understanding and relevant knowledge were summarized aiming to provide general guidance for rational design of high-performance cathodes for advanced Li-S batteries.

Ogoke, Ogechi↗
DOE OSTI2017

Sub-Doppler infrared spectroscopy of resonance-stabilized hydrocarbon intermediates: ν 3 / ν 4 CH stretch modes and CH 2 internal rotor dynamics of benzyl radical

Highly reactive benzyl radicals are generated by electron dissociative attachment to benzyl chloride doped into a neon–hydrogen–helium discharge and immediately cooled to T rot = 15 K in a high density, supersonic slit expansion environment. The sub-Doppler spectra are fit to an asymmetric-top rotational Hamiltonian, thereby yielding spectroscopic constants for the ground (v = 0) and first excited (v = 1, ν 3 , ν 4 ) vibrational levels of the ground electronic state. The rotational constants obtained for the ground state are in good agreement with previous laser induced fluorescence measurements (LIF), with vibrational band origins (ν 3 = 3073.2350 ± 0.0006 cm –1 , ν 4 = 3067.0576 ± 0.0006 cm –1 ) in agreement with anharmonically corrected density functional theory calculations. Furthermore, to assist in detection of benzyl radical in the interstellar medium, we have also significantly improved the precision of the ground state rotational constants through combined analysis of the ground state IR and LIF combination differences. Of dynamical interest, there is no evidence in the sub-Doppler spectra for tunneling splittings due to internal rotation of the CH 2 methylene subunit, which implies a significant rotational barrier consistent with partial double bond character in the CC bond. This is further confirmed with high level ab initio calculations at the CCSD(T)-f12b/ccpVdZ-f12 level, which predict a zero-point energy corrected barrier to internal rotation of ΔE tun ≈ 11.45 kcal mol –1 or 4005 cm –1 . In summary, the high-resolution infrared spectra are in excellent agreement with simple physical organic chemistry pictures of a strongly resonance-stabilized benzyl radical with a nearly rigid planar structure due to electron delocalization around the aromatic ring.

Kortyna, A.↗
DOE OSTI2013

Fast ion confinement and stability in a neutral beam injected reversed field pinch

The behavior of energetic ions is fundamentally important in the study of fusion plasmas. While well-studied in tokamak, spherical torus, and stellarator plasmas, relatively little is known in reversed field pinch plasmas about the dynamics of fast ions and the effects they cause as a large population. These studies are now underway in the Madison Symmetric Torus with an intense 25 keV, 1 MW hydrogen neutral beam injector (NBI). Measurements of the time-resolved fast ion distribution via a high energy neutral particle analyzer, as well as beam-target neutron flux (when NBI fuel is doped with 3–5% D{sub 2}) both demonstrate that at low concentration the fast ion population is consistent with classical slowing of the fast ions, negligible cross-field transport, and charge exchange as the dominant ion loss mechanism. A significant population of fast ions develops; simulations predict a super-Alfvénic ion density of up to 25% of the electron density with both a significant velocity space gradient and a sharp radial density gradient. There are several effects on the background plasma including enhanced toroidal rotation, electron heating, and an altered current density profile. The abundant fast particles affect the plasma stability. Fast ions at the island of the core-most resonant tearing mode have a stabilizing effect, and up to 60% reduction in the magnetic fluctuation amplitude is observed during NBI. The sharp reduction in amplitude, however, has little effect on the underlying magnetic island structure. Simultaneously, beam driven instabilities are observed as repetitive ∼50 μs bursts which coincide with fast particle redistribution; data indicate a saturated core fast ion density well below purely classical predictions.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗