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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 523 records · Page 29
All sourcesNASA NTRSDOE OSTI
DOE OSTI2024

Initial-site characterization of hydrogen migration following strong-field double-ionization of ethanol

Abstract An essential problem in photochemistry is understanding the coupling of electronic and nuclear dynamics in molecules, which manifests in processes such as hydrogen migration. Measurements of hydrogen migration in molecules that have more than two equivalent hydrogen sites, however, produce data that is difficult to compare with calculations because the initial hydrogen site is unknown. We demonstrate that coincidence ion-imaging measurements of a few deuterium-tagged isotopologues of ethanol can determine the contribution of each initial-site composition to hydrogen-rich fragments following strong-field double ionization. These site-specific probabilities produce benchmarks for calculations and answer outstanding questions about photofragmentation of ethanol dications; e.g., establishing that the central two hydrogen atoms are 15 times more likely to abstract the hydroxyl proton than a methyl-group proton to form H $${}_{3}^{+}$$ 3 + and that hydrogen scrambling, involving the exchange of hydrogen between different sites, is important in H 2 O + formation. The technique extends to dynamic variables and could, in principle, be applied to larger non-cyclic hydrocarbons.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2024

Molecular-scale insights into the electrical double layer at oxide-electrolyte interfaces

The electrical double layer (EDL) at metal oxide-electrolyte interfaces critically affects fundamental processes in water splitting, batteries, and corrosion. However, limitations in the microscopic-level understanding of the EDL have been a major bottleneck in controlling these interfacial processes. Herein, we use ab initio-based machine learning potential simulations incorporating long-range electrostatics to unravel the molecular-scale picture of the EDL at the prototypical anatase TiO 2 -electrolyte interface under various pH conditions. Our large-scale simulations, capable of capturing interfacial water dissociation/recombination reactions and electrolytic proton transport, provide unprecedented insights into the detailed structure of the EDL. Moreover, the larger capacitance of the EDL under basic relative to acidic conditions, originating from the higher affinity of the cations for the oxide surface, is found to give rise to distinct charging mechanisms on negative and positive surfaces. Our results are validated by the agreement between the computed EDL capacitance and experimental data.

Chemical physics↗
DOE OSTI2025

Symmetry-mediated quantum coherence of W 5+ spins in an oxygen-deficient double perovskite

Elucidating the factors limiting quantum coherence in real materials is essential to the development of quantum technologies. Here we report a strategic approach to determine the effect of lattice dynamics on spin coherence lifetimes using oxygen deficient double perovskites as host materials. In addition to obtaining millisecond T 1 spin-lattice lifetimes at T ~ 10 K, measurable quantum superpositions were observed up to room temperature. We determine that T 2 enhancement in Sr 2 CaWO 6-δ over previously studied Ba 2 CaWO 6-δ is caused by a dynamically-driven increase in effective site symmetry around the dominant paramagnetic site, assigned as W 5+ via electron paramagnetic resonance spectroscopy. Further, a combination of experimental and computational techniques enabled quantification of the relative strength of spin-phonon coupling of each phonon mode. This analysis demonstrates the effect of thermodynamics and site symmetry on the spin lifetimes of W 5+ paramagnetic defects, an important step in the process of reducing decoherence to produce longer-lived qubits.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Doubling down on borophene electronics

The discovery of graphene, an atomic-thick carbon layer that can be exfoliated off a bulk graphite, has demonstrated various surprising properties and inspired a fervent quest for other new quasi-two-dimensional materials. Many analogues have been discovered, including borophene, silicene, germanene, stanene, phosphorene, arsenene, antimonene and bismuthine — one-atom-thick sheets of boron, silicon, germanium, tin, phosphorus, arsenic, antimony and bismuth, respectively. Borophene is a prototype for a synthetic two-dimensional (2D) material that does not have bulk layered counterparts. Furthermore, the growth of borophene often requires interfacial coupling with the metal substrate to stabilize its 2D form. Despite realizing rich polymorphs, the synthesized borophene is currently limited to only single atomic layers. Now, writing in Nature Materials, Xiaolong Liu and colleagues report the synthesis of double-layer (DL) borophene, which offers another degree of freedom to tune borophene structures and physical properties for electronic applications.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2020

A high-energy and long-cycling lithium–sulfur pouch cell via a macroporous catalytic cathode with double-end binding sites

Lithium-sulfur batteries are attractive alternatives to lithium-ion batteries because of their high theoretical specific energy and natural abundance of sulfur. However, the practical specific energy and cycle life of Li-S pouch cells are significantly limited by the use of thin sulfur electrodes/flooded electrolytes and polysulfides shuttle/Li metal degradation, respectively. In this work we propose a cathode design concept to achieve good Li-S pouch cell performances. The cathode is composed of uniformly embedded ZnS nanoparticles and Co-N-C single-atom catalyst to form double-end biding sites inside a highly oriented macroporous host, which can effectively immobilize and catalytically convert polysulfides intermediates during cycling, thus eliminating the shuttle effect and lithium metal corrosion. The ordered macropores enhance ionic transport under high sulfur loading by forming sufficient catalyst/conductive support/electrolyte triple-phase boundaries. This prevents the formation of inactive sulfur (dead sulfur). Our cathode structure shows improved performances in a pouch cell configuration under high sulfur loading and lean electrolyte operation. An Ah-level pouch cell with only 100% lithium excess can deliver a cell specific energy of > 300 Wh kg –1 with a Coulombic efficiency >95% for 80 cycles.

25 ENERGY STORAGE↗
DOE OSTI2021

Moiré nematic phase in twisted double bilayer graphene

Graphene moiré superlattices display electronic flat bands. At integer fillings of these flat bands, energy gaps due to strong electron-electron interactions are generally observed. However, the presence of other correlation-driven phases in twisted graphitic systems at non-integer fillings is unclear. Here, we report the existence of threefold rotational symmetry breaking in twisted double bilayer graphene. Using spectroscopic imaging over large and uniform areas to characterize the direction and degree of C 3 symmetry breaking, we find it to be prominent only at energies corresponding to the flat bands and nearly absent in the remote bands. We demonstrate that the magnitude of the rotational symmetry breaking does not depend on the degree of the heterostrain or the displacement field, being instead a manifestation of an interaction-driven electronic nematic phase. We show that the nematic phase is a primary order that arises from the normal metal state over a wide range of doping away from charge. Furthermore, our modelling suggests that the nematic instability is not associated with the local scale of the graphene lattice, but is an emergent phenomenon at the scale of the moiré lattice.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2020

Double-pulse speckle contrast correlations with near Fourier transform limited free-electron laser light using hard X-ray split-and-delay

Abstract The ability to deliver two coherent X-ray pulses with precise time-delays ranging from a few femtoseconds to nanoseconds enables critical capabilities of probing ultra-fast phenomena in condensed matter systems at X-ray free electron laser (FEL) sources. Recent progress made in the hard X-ray split-and-delay optics developments now brings a very promising prospect for resolving atomic-scale motions that were not accessible by previous time-resolved techniques. Here, we report on characterizing the spatial and temporal coherence properties of the hard X-ray FEL beam after propagating through split-and-delay optics. Speckle contrast analysis of small-angle scattering measurements from nanoparticles reveals well-preserved transverse coherence of the beam. Measuring intensity fluctuations from successive X-ray pulses also reveals that only single or double temporal modes remain in the transmitted beam, corresponding to nearly Fourier transform limited pulses.

42 ENGINEERING↗
DOE OSTI2025

Peatland fires in Alaska will double by the end of the century

During recent summers, warm and dry conditions have increased the occurrence of wildfires and potentially peat-fires across Alaska. Limitations in resolving the fine-scale distribution of peatlands and climate observations have constrained our ability to accurately predict peat-fire dynamics. Using a new high-resolution peatland map of Alaska, we evaluated the climate and environmental controls of past and future peat-fire activity. Ensemble machine learning models identified reduced soil moisture, higher temperatures, and evapotranspiration as key predictors of annual total burned peatland area (tenfold CV R 2 = 0.62, RMSE = 221.1 km 2 ). By the end of the twenty-first century, models forced with climate datasets from representative concentration pathways (RCPs) 4.5, 6.0, and 8.5 emission scenarios project a statewide doubling of burned peatlands (increasing 61–121%), with regional increases ranging from 25–165% in polar, 61–95% in boreal, and 102–106% in maritime ecoregions. These projections indicate that wildfires will progressively encroach further into organic-rich moist and wet peaty soils, potentially amplifying soil carbon release across Alaska.

climate-change ecology↗
DOE OSTI2022

Long-lived period-doubled edge modes of interacting and disorder-free Floquet spin chains

Floquet spin chains have been a venue for understanding topological states of matter that are qualitatively different from their static counterparts by, for example, hosting π edge modes that show stable period-doubled dynamics. However the stability of these edge modes to interactions has traditionally required the system to be many-body localized in order to suppress heating. In contrast, here we show that even in the absence of disorder, and in the presence of bulk heating, π edge modes are long lived. Their lifetime is extracted from exact diagonalization and is found to be non-perturbative in the interaction strength. A tunneling estimate for the lifetime is obtained by mapping the stroboscopic time-evolution to dynamics of a single particle in Krylov subspace. In this subspace, the π edge mode manifests as the quasi-stable edge mode of an inhomogeneous Su-Schrieffer-Heeger model whose dimerization vanishes in the bulk of the Krylov chain.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2022

Observation of nonlocal Josephson effect on double InAs nanowires

Short-range coherent coupling of two Josephson junctions (JJs) are predicted to generate a supercurrent in one JJ nonlocally modulated by the phase difference in the other. We report on observation of the nonlocal Josephson effect on double InAs nanowires as experimental evidence of the coherent coupling. We measure one JJ sharing one superconducting electrode with the other JJ and observe switching current oscillation as a control of the nonlocal phase difference. Our result will contribute to engineer novel superconducting phenomena with the short-range coherent coupling.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2021

Promotion of oxygen reduction reaction on a double perovskite electrode by a water-induced surface modification

Highly efficient air electrodes are a key component of reversible fuel cells for energy storage and conversion; however, the development of efficient electrodes that are stable against water vapor remains a grand challenge. Here we report an air–electrode, composed of double perovskite material PrBa 0.8 Ca 0.2 Co 2 O 5+δ (PBCC) backbone coated with nanoparticles (NPs) of BaCoO 3-δ (BCO), that exhibits remarkable electrocatalytic activity for oxygen reduction reaction (ORR) while maintaining excellent tolerance to water vapor. When tested in a symmetrical cell exposed to wet air with 3 vol% H 2 O at 750 °C, the electrode shows an area specific resistance of ~0.03 Ω cm 2 in an extended period of time. The performance enhancement is attributed mainly to the electrocatalytic activity of the BCO NPs dispersed on the surface of the porous PBCC electrode. Moreover, in situ Raman spectroscopy is used to probe reaction intermediates (e.g., oxygen species) on electrode surfaces, as the electrochemical properties of the electrodes are characterized under the same conditions. The direct correlation between surface chemistry and electrochemical behavior of an electrode is vital to gaining insight into the mechanisms of the electrocatalytic processes in fuel cells and electrolysers.

25 ENERGY STORAGE↗
DOE OSTI2021

Ellipticity controlled dissociative double ionization of ethane by strong fields

We report the yields of all dissociation channels of ethane dications produced by strong field double ionization were measured. It was found that the branching ratios can be controlled by varying the ellipticity of laser pulses. The CH 3 + formation and H + formation channels show a clear competition, producing the highest and lowest branching ratios at ellipticity of ~0.6, respectively. With the help of theoretical calculations, such a control was attributed to the ellipticity dependent yields of different sequential ionization pathways.

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

Hexanitrato complexes and hybrid double perovskites of Am 3+ and Cm 3+

The synthesis and structures of the homoleptic hexanitrato complexes of Am(III) and Cm(III), [(CH 3 ) 4 N] 2 KAn(NO 3 ) 6 are reported. These compounds form a double perovskite structure type, A 2 B'BX 6 , crystallizing in the cubic space group $Fm$$\bar{3}$$m$. Furthermore, their electronic properties, as calculated using the Quantum Theory of Atoms in Molecules, are reported and compared to their lanthanide homologues Eu(III) and Gd(III).

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

Accurate core excitation and ionization energies from a state-specific coupled-cluster singles and doubles approach

Here, we investigate the use of orbital-optimized references in conjunction with single-reference coupled-cluster theory with single and double substitutions (CCSD) for the study of core excitations and ionizations of 18 small organic molecules, without the use of response theory or equation-of-motion (EOM) formalisms. Three schemes are employed to successfully address the convergence difficulties associated with the coupled-cluster equations, and the spin contamination resulting from the use of a spin symmetry-broken reference, in the case of excitations. In order to gauge the inherent potential of the methods studied, an effort is made to provide reasonable basis set limit estimates for the transition energies. Overall, we find that the two best-performing schemes studied here for ΔCCSD are capable of predicting excitation and ionization energies with errors comparable to experimental accuracies. The proposed ΔCCSD schemes reduces statistical errors against experimental excitation energies by more than a factor of two when compared to the frozen-core core–valence separated (FC-CVS) EOM-CCSD approach – a successful variant of EOM-CCSD tailored towards core excitations.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2023

Energetics of formation and stability in high pressure steam of barium lanthanide cobaltite double perovskites

Here, this study concerns energetics of formation and the stability in high water partial pressure of BaLnCo 2 O 6-δ , (Ln = La, Pr, Nd, and Gd) (BLnC) and BaGd 1-x La x Co 2 O 6-δ , where x = 0.2, 0.5, and 0.7 (BGLC) double perovskite cobaltites. Those materials are extensively studied due to their potential applications as a positrode in electrochemical devices. Therefore, their stability under such conditions is a key issue. All investigated materials are thermodynamically stable relative to binary oxides and exhibit strongly exothermic enthalpies of formation. Moreover, BaGd 0.3 La 0.7 Co 2 O 6-δ and BaGd 0.8 La 0.2 Co 2 O 6-δ remain the main perovskite structure up to 3 bars of water vapor at 400 °C. At higher steam pressure, reaching 10 bar at 300 °C, the partial decomposition to constituent oxides and hydroxides was observed. The BGLC compounds exhibit higher negative formation enthalpies in comparison to single-Ln compositions, which does not translate into higher chemical stability under high steam pressures since the BLnC series retained the main perovskite structure at higher temperatures as well as in higher water vapor pressures.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗