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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 145 records · Page 8
All sourcesNASA NTRSDOE OSTI
DOE OSTI2015

Phosphorus-Graphene Nanosheet Hybrids as Lithium-Ion Anode with Exceptional High-Temperature Cycling Stability

A red phosphorus-graphene nanosheet hybrid is reported as an anode material for lithium-ion batteries. Graphene nanosheets form a sea-like, highly electronically conductive matrix, where the island-like phosphorus particles are dispersed. Benefiting from this structure and properties of phosphorus, the hybrid delivers high initial capacity and exhibits promising retention at 60 °C.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Exceptional Cycling Performance Enabled by Local Structural Rearrangements in Disordered Rocksalt Cathodes

The capacity of lithium transition-metal (TM) oxide cathodes is directly linked to the magnitude and accessibility of the redox reservoir associated with TM cations and/or oxygen anions, which traditionally decreases with cycling as a result of chemical, structural, or mechanical fatigue. Here, it is shown that a capacity increase over 125% can be achieved upon cycling of high-energy Mn- and F-rich cation-disordered rocksalt oxyfluoride cathodes. This study reveals that in Li 1.2 Mn 0.7 Nb 0.1 O 1.8 F 0.2 , repeated Li extraction/reinsertion utilizing Mn 3+ /Mn 4+ redox along with some degree of O-redox participation leads to local structural rearrangements and formation of domains with off-stoichiometry spinel-like features. The effective integration of these local “structure-domains” within the cubic disordered rocksalt framework promotes better Li diffusion and improves material utilization, consequently increased capacity upon cycling. Finally, this study provides important new insights into materials design strategies to further exploit the rich compositional and structural space of Mn chemistry for developing sustainable, high-energy cathode materials.

25 ENERGY STORAGE↗
DOE OSTI2020

The Exceptional Diversity of Homoleptic Uranium–Methyl Complexes

Abstract Homoleptic σ‐bonded uranium–alkyl complexes have been a synthetic target since the Manhattan Project. The current study describes the synthesis and characterization of several unprecedented uranium–methyl complexes. Amongst these complexes, the first example of a homoleptic uranium–alkyl dimer, [Li(THF) 4 ] 2 [U 2 (CH 3 ) 10 ], as well as a seven‐coordinate uranium–methyl monomer, {Li(OEt 2 )Li(OEt 2 ) 2 UMe 7 Li} n were both crystallographically identified. The diversity of complexes reported herein provides critical insight into the structural diversity, electronic structure and bonding in uranium–alkyl chemistry.

Sears, Jeffrey D.↗
DOE OSTI2016

Mesoporous Fluorinated Metal-Organic Frameworks with Exceptional Adsorption of Fluorocarbons and CFCs

Two mesoporous fluorinated metal–organic frameworks (MOFs) were synthesized from extensively fluorinated tritopic carboxylate- and tetrazolate-based ligands. The tetrazolate-based framework MOFF-5 has an accessible surface area of 2445 m 2 g -1 , the highest among fluorinated MOFs. Crystals of MOFF-5 adsorb hydrocarbons, fluorocarbons, and chlorofluorocarbons (CFCs)—the latter two being ozone-depleting substances and potent greenhouse species—with weight capacities of up to 225%. The material exhibits an apparent preference for the adsorption of non-spherical molecules, binding unusually low amounts of both tetrafluoromethane and sulfur hexafluoride.

Chen, Teng-Hao↗
DOE OSTI2020

The Exceptional Diversity of Homoleptic Uranium–Methyl Complexes

Homoleptic σ-bonded uranium–alkyl complexes have been a synthetic target since the Manhattan Project. The current study describes the synthesis and characterization of several unprecedented uranium–methyl complexes. Amongst these complexes, the first example of a homoleptic uranium–alkyl dimer, [Li(THF) 4 ] 2 [U 2 (CH 3 ) 10 ], as well as a seven-coordinate uranium–methyl monomer, {Li(OEt 2 )Li(OEt 2 ) 2 UMe 7 Li} n were both crystallographically identified. We report the diversity of complexes reported herein provides critical insight into the structural diversity, electronic structure and bonding in uranium–alkyl chemistry.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2016

Exceptionally High Rates of Biological Hydrogen Production by Biomimetic In Vitro Synthetic Enzymatic Pathways

Hydrogen production by water splitting energized by biomass sugars is one of the most promising technologies for distributed green H 2 production. Direct H 2 generation from NADPH, catalysed by an NADPH-dependent, soluble [NiFe]-hydrogenase (SH1) is thermodynamically unfavourable, resulting in slow volumetric productivity. We designed the biomimetic electron transport chain from NADPH to H 2 by the introduction of an oxygen-insensitive electron mediator benzyl viologen (BV) and an enzyme (NADPH rubredoxin oxidoreductase, NROR), catalysing electron transport between NADPH and BV. The H 2 generation rates using this biomimetic chain increased by approximately five-fold compared to those catalysed only by SH1. The peak volumetric H 2 productivity via the in vitro enzymatic pathway comprised of hyperthermophilic glucose 6-phosphate dehydrogenase, 6-phosphogluconolactonase, and 6-phosphogluconate dehydrogenase, NROR, and SH1 was 310 mmol H 2 /L h -1 , the highest rate yet reported. The concept of biomimetic electron transport chains could be applied to both in vitro and in vivo H 2 production biosystems and artificial photosynthesis.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2016

Implications of Exceptional Material Kinetics on Thermochemical Fuel Production Rates

Abstract Production of chemical fuels by solar‐driven thermochemical cycling has recently generated significant interest for its potential as a highly efficient method of storing solar energy. Of particular interest is the thermochemical process using non‐stoichiometric oxides, such as ceria. In this process a reactive oxide is cyclically exposed to an inert gas, typically at 1500 °C to induce the partial reduction of the oxide, and then exposed to an oxidizing gas of either H 2 O or CO 2 at a temperature between 800–1500 °C to oxidize the oxide and release H 2 or CO. Conventional wisdom has held that material kinetics limit the fuel production rates. Herein we demonstrate that, instead, at 1500 °C the rates of both reduction and oxidation of ceria, and hence also the global fuel production rate, are limited only by thermodynamic considerations for any reasonable set of operating conditions. Thus, in terms of materials design, significant room exists for sacrificing material kinetics in favor of thermodynamic characteristics.

Davenport, Timothy C.↗
DOE OSTI2022

Exceptional scalar theories in de Sitter space

The special galileon and Dirac-Born-Infeld (DBI) theories are effective field theories of a single scalar field that have many interesting properties in flat space. These theories can be extended to all maximally symmetric spaces, where their algebras of shift symmetries are simple. We study aspects of the curved space versions of these theories: for the special galileon, we find a new compact expression for its Lagrangian in de Sitter space and a field redefinition that relates it to the previous, more complicated formulation. This field redefinition reduces to the well-studied galileon duality redefinition in the flat space limit. For the DBI theory in de Sitter space, we discuss the brane and dilaton formulations of the theory and present strong evidence that these are related by a field redefinition. We also give an interpretation of the symmetries of these theories in terms of broken diffeomorphisms of de Sitter space.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2020

Three exceptions to the Grossman-Nir bound

A bstract We show that the Grossman-Nir (GN) bound, Br( K L → $$ {\pi}^0\nu \overline{\nu} $$ π 0 ν ν ¯ ) ≤ 4 . 3 Br( K + → $$ {\pi}^{+}\nu \overline{\nu} $$ π + ν ν ¯ ), can be violated in the presence of light new physics with flavor violating couplings. We construct three sample models in which the GN bound can be violated by orders of magnitude, while satisfying all other experimental bounds. In the three models the enhanced branching ratio Br( K L → π 0 + inv) is due to K L → π 0 Φ 1, K L → π 0 Φ 1 Φ 1 , K L → $$ {\pi}^0{\psi}_1{\overline{\psi}}_1 $$ π 0 ψ 1 ψ ¯ 1 transitions, respectively, where Φ 1 ( ψ 1 ) is a light scalar (fermion) that escapes the detector. In the three models Br( K + → π + + inv) remains very close to the SM value, while Br( K L → π 0 + inv) can saturate the present KOTO bound. Besides invisible particles in the final state (which may account for dark matter) the models require additional light mediators around the GeV-scale.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2021

On the conformal symmetry of exceptional scalar theories

The DBI and special galileon theories exhibit a conformal symmetry at unphysical values of the spacetime dimension. We find the Lagrangian form of this symmetry. The special conformal transformations are non-linearly realized on the fields, even though conformal symmetry is unbroken. Commuting the conformal transformations with the extended shift symmetries, we find new symmetries, which when taken together with the conformal and shift symmetries close into a larger algebra. For DBI this larger algebra is the conformal algebra of the higher dimensional bulk in the brane embedding view of DBI. For the special galileon it is a real form of the special linear algebra. We also find the Weyl transformations corresponding to the conformal symmetries, as well as the necessary improvement terms to make the theories Weyl invariant, to second order in the coupling in the DBI case and to lowest order in the coupling in the special galileon case.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗