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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 487 records · Page 27
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Iridium-Doped Nanosized Zn–Al Layered Double Hydroxides as Efficient Water Oxidation Catalysts

Layered double hydroxides (LDHs) are an ideal platform to host catalytic metal centers for water oxidation (WO) owing to the high accessibility of water to the interlayer region, which makes all centers potentially reachable and activated. In this paper, we report the syntheses of three iridium-doped zinc–aluminum LDHs (Ir-LDHs) nanomaterials (1–3, with about 80 nm of planar size and a thickness of 8 nm as derived by field emission scanning electron microscopy and powder X-ray diffraction studies, respectively), carried out in the confined aqueous environment of reverse micelles, through a very simple and versatile procedure. These materials exhibit excellent catalytic performances in WO driven by NaIO 4 at neutral pH and 25 °C, with an iridium content as low as 0.5 mol % (~0.8 wt %), leading to quantitative oxygen yields (based on utilized NaIO 4 , turnover number up to ~10,000). Nanomaterials 1–3 display the highest ever reported turnover frequency values (up to 402 min –1 ) for any heterogeneous and heterogenized catalyst, comparable only to those of the most efficient molecular iridium catalysts, tested under similar reaction conditions. The boost in activity can be traced to the increased surface area and pore volume (>5 times and 1 order of magnitude, respectively, higher than those of micrometric materials of size 0.3–1 μm) estimated for the nanosized particles, which guarantee higher noble metal accessibility. X-ray absorption spectroscopy (XAS) studies suggest that 1–3 nanomaterials, as-prepared and after catalysis, contain a mixture of isolated, single octahedral Ir(III) sites, with no evidence of Ir–Ir scattering from second-nearest neighbors, excluding the presence of IrO 2 nanoparticles. The combination of the results obtained from XAS, elemental analysis, and ionic chromatography strongly suggests that iridium is embedded in the brucite-like structure of LDHs, having four hydroxyls and two chlorides as first neighbors. These results demonstrate that nanometric LDHs can be successfully exploited to engineer efficient WOCs, minimizing the amount of iridium used, consistent with the principle of the noble-metal atom economy.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Europium-doped barium chloride storage phosphor plate synthesized by pulsed laser deposition

In computed radiography, scattering of the stimulation light by the storage phosphor crystals in the imaging plates negatively impacts spatial resolution. Storage phosphor plates with thinner phosphor layers have been developed to reduce scattering distance and increase spatial resolution, although at the expense of reduced x-ray absorption. The authors hypothesize that a transparent or translucent nanostructured film, containing a much higher percentage of storage phosphor crystals than achievable in bulk glass-ceramic materials made by conventional methods, may have acceptable photostimulated luminescence efficiency and imaging performance characteristics greater than commercial imaging plates. Films were produced via pulsed laser deposition by alternating target materials of the storage phosphor BaCl 2 :Eu 2+ and either silica or silicon. X-ray diffraction and photoluminescence characterization were conducted to confirm the presence of BaCl 2 :Eu 2+ crystallites. The films were able to store optical data and be read out to produce x-ray radiographs demonstrating 50-mu m spatial resolution. The performance of the experimental storage phosphor plates was compared to commercially available imaging plates. The authors demonstrate for the first time the synthesis of a glass-ceramic imaging plate for computed radiography by pulsed laser deposition.

36 MATERIALS SCIENCE↗
NASA NTRS1981

Sound diffraction around screens and wedges for arbitrary point source locations

A development is presented for the Green's function for a point source in the vicinity of a rigid wedge. The diffraction contributions to the Green's function for arbitrary source and listener location is expressed in a form which can be readily evaluated using the Laguerre technique for numerical integration. The present approach offers the advantages of efficient numerical evaluation and of relatively straightforward reduction to well-known analytical approximations in limiting cases. Comparisons with previously obtained experimental and numerical results obtained by Ambaud and Bergassoli (1972) are presented. The comparison with the experimental results is excellent; the advantages of the present numerical technique, vis a vis that of Ambaud and Bergassoli, are pointed out.

Hadden, W. J., Jr.↗
NASA NTRS1983

Large space antenna communications systems: Integrated Langley Research Center/Jet Propulsion Laboratory development activities. 2: Langley Research Center activities

The electromagnetic analysis activities at the Langley Research Center are resulting in efficient and accurate analytical methods for predicting both far- and near-field radiation characteristics of large offset multiple-beam multiple-aperture mesh reflector antennas. The utilization of aperture integration augmented with Geometrical Theory of Diffraction in analyzing the large reflector antenna system is emphasized.

Cambell, T. G.↗
NASA NTRS1988

An efficient high-frequency analysis of modal reflection and transmission coefficients for a class of waveguide discontinuities

A high-frequency analysis of electromagnetic modal reflection and transmission coefficients is presented for waveguide discontinuities formed by joining different waveguide sections. The analysis uses an extended version of the concept of geometrical theory of diffraction based equivalent edge currents in conjunction with the reciprocity theorem to describe interior scattering effects. If the waveguide modes and their associated modal rays can be found explicitly, general two- and three-dimensional waveguide geometries can be analyzed. Expressions are developed for two-dimensional reflection and transmission coefficients. Numerical results are given for a flanged, semi-infinite parallel plate waveguide and for the junction between two linearly tapered waveguides.

Pathak, P. H.↗
DOE OSTI2021

Role of peracetic acid on the disruption of lignin packing structure and its consequence on lignin depolymerisation

Peracetic acid (PAA) is an effective oxidant capable of solubilising lignin and efficiently depolymerising it to selective phenolic compounds; however, the specific role by which PAA initiates the depolymerisation is still elusive. Herein, interaction between PAA and the lignin macromolecule and the consequent structural changes of the latter were studied by characterising the lignin packing structure and its associated changes during the oxidation process. While the lignin packing structure and its changes associated with the PAA-mediated oxidation were probed by X-ray diffraction, the impact of the PAA on different chemical functionalities present in the lignin structure was established by 13 C and 1 H– 13 C heteronuclear single-quantum coherence nuclear magnetic resonance (NMR) spectroscopy. Further, combining the NMR spectroscopy results, and the product distribution, we conclude that the predominant reaction pathway for the oxidative depolymerisation of lignin with PAA is the Baeyer–Villiger oxidation of the ketone formed by the oxidation of the benzylic hydroxyl group adjacent to the β-O-4 linkage. The experimental evidence provided herein corroborated that PAA instigates oxygen insertion to the lignin macromolecule resulting in disruption of its packing structures and facilitates depolymerisation. We also investigated various metal oxide and mixed metal oxide catalysts to identify effective catalysts that further enhance the efficiency of PAA-mediated depolymerisation of lignin and produce selective monomeric phenolic compounds. Techno-economic analysis was also conducted to identify the key parameters associated with this oxidative process that need to be considered for possible commercial application.

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

Stepwise allomorphic transformations by alkaline and ethylenediamine treatments on bamboo crystalline cellulose for enhanced enzymatic digestibility

Efficient modification and decrystallization of cellulose Iβ in lignocellulosic biomass are potential ways to overcome biomass recalcitrance and facilitates enzymatic degradation. Herein, we have treated moso bamboo and microcrystalline cellulose separately by either alkali or ethylenediamine (EDA) treatments, as well as using both in succession. The pretreatments successfully transformed the initial cellulose Iβ allomorph into cellulose II, III I , and cellulose III II . Crystal structures and crystallinities were determined by Rietveld X-ray diffraction and CP/MAS 13 C NMR. Comparatively, the samples that were sequentially treated by EDA and NaOH had low crystallinity (~50%), larger d-spacings of ~4.4 Å for the hydrophobic (110) planes, and less condensed microfibrillar aggregation. The factors simultaneously contributed to as high enzymatic hydrolysis yield as 89.5% and 91.7% respectively, followed by the yields of mercerized cellulose II and cellulose III II allomorph. Here, the stepwise allomorphic transformations may provide new strategies on improving efficiency of saccharification process and biomass utilization.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2023

Well-Defined Iron Sites in Crystalline Carbon Nitride

Carbon nitride materials can be hosts for transition metal sites, but Mössbauer studies on iron complexes in carbon nitrides have always shown a mixture of environments and oxidation states. Here we describe the synthesis and characterization of a crystalline carbon nitride with stoichiometric iron sites that all have the same environment. The material (formula C 6 N 9 H 2 Fe 0.4 Li 1.2 Cl, abbreviated PTI/FeCl 2 ) is derived from reacting poly(triazine imide)·LiCl (PTI/LiCl) with a low-melting FeCl 2 /KCl flux, followed by anaerobic rinsing with methanol. X-ray diffraction, X-ray absorption and Mössbauer spectroscopies, and SQUID magnetometry indicate that there are tetrahedral high-spin iron(II) sites throughout the material, all having the same geometry. As a result, the material is active for electrocatalytic nitrate reduction to ammonia, with a production rate of ca. 0.1 mmol cm –2 h –1 and Faradaic efficiency of ca. 80% at −0.80 V vs RHE.

Anions↗
DOE OSTI2021

Room temperature crystallography of human acetylcholinesterase bound to a substrate analogue 4K-TMA: Towards a neutron structure

Acetylcholinesterase (AChE) catalyzes hydrolysis of acetylcholine thereby terminating cholinergic nerve impulses for efficient neurotransmission. Human AChE (hAChE) is a target of nerve agent and pesticide organophosphorus compounds that covalently attach to the catalytic Ser203 residue. Reactivation of inhibited hAChE can be achieved with nucleophilic antidotes, such as oximes. Understanding structural and electrostatic (i.e. protonation states) determinants of the catalytic and reactivation processes is crucial to improve design of oxime reactivators. Here we report X-ray structures of hAChE conjugated with a reversible covalent inhibitor 4K-TMA (4K-TMA:hAChE) at 2.8 Å resolution and of 4K-TMA:hAChE conjugate with oxime reactivator methoxime, MMB4 (4K-TMA:hAChE:MMB4) at 2.6 Å resolution, both at physiologically relevant room temperature, as well as cryo-crystallographic structure of 4K-TMA:hAChE at 2.4 Å resolution. 4K-TMA acts as a substrate analogue reacting with the hydroxyl of Ser203 and generating a reversible tetrahedral hemiketal intermediate that closely resembles the first tetrahedral intermediate state during hAChE-catalyzed acetylcholine hydrolysis. Structural comparisons of room temperature with cryo-crystallographic structures of 4K-TMA:hAChE and published mAChE complexes with 4K-TMA, as well as the effect of MMB4 binding to the peripheral anionic site (PAS) of the 4K-TMA:hAChE complex, revealed only discrete, minor differences. The active center geometry of AChE, already highly evolved for the efficient catalysis, was thus indicative of only minor conformational adjustments to accommodate the tetrahedral intermediate in the hydrolysis of the neurotransmitter acetylcholine (ACh). To map protonation states in the hAChE active site gorge we collected 3.5 Å neutron diffraction data paving the way for obtaining higher resolution datasets that will be needed to determine locations of individual hydrogen atoms.

4K-TMA↗
DOE OSTI2021

Simple but tricky: Investigations of terephthalic acid purity obtained from mixed PET waste

In this study, we report for the first time, the basic depolymerization of mixed waste-polyethylene terephthalate (PET) by hydrolysis and subsequent terephthalic acid monomer recovery at high purity using benign reaction conditions. Several conditions were tested for depolymerization such as PET chips size, concentration of aqueous sodium hydroxide (20 or 30%), organic co-solvent (ethylene glycol or ethanol), temperature at which the reaction was run and duration of the heating. More importantly, several batches of PET were utilized as starting materials including a commercial PET, chopped PET obtained from clean bottles whose caps and labels were removed and the purity of the product from each condition was evaluated via nuclear magnetic resonance (1HNMR and 13CNMR), differential scanning calorimetry (DSC) and powder Xray diffraction (XRD). Unsurprisingly, the conversion of PET is dependent on the particle size varying from 100% conversion for fine powder to 73% conversion for (300 µm, mesh 6 – 20 or mesh 14-20). Ethanol appears to be more efficient as a co-solvent than ethylene glycol, with higher PET depolymerization conversions (94% versus 75-80%), shorter reaction times (2h versus 6h) and lower temperatures (80 °C versus 110 °C). The terephthalic acid (TPA) recovered appeared to have only subtle differences among the batches, most notably a pink color when the reaction was run in ethanol/base. The DSC of the compounds produced in ethylene glycol water appear to display a melting point (280-288 °C) while the samples prepared in ethanol as well as a commercial sample did not. Overall, the purity of the various TPA batches is comparable, and similar to commercial TPA, demonstrating the utility of the method to depolymerize realistic waste streams. The method is simple, demonstrated on multigram scale (15-30g) and allows for the complete removal of waste other than PET unaffected by alkaline conditions.

Cosimbescu, Lelia↗
DOE OSTI2020

In Situ Strain Evolution on Pt Nanoparticles during Hydrogen Peroxide Decomposition

Fundamental understanding of structural changes during catalytic reactions is crucial to understanding the underlying mechanisms and optimizing efficiencies. Surface energy and related catalytic mechanisms are widely studied. However, the catalyst lattice deformation induced by catalytic processes is not well understood. Here, we study the strain in an individual platinum (Pt) nanoparticle (NP) using Bragg coherent diffraction imaging under in situ oxidation and reduction reactions. When Pt NPs are exposed to H 2 O 2 , a typical oxidizer and an intermediate during the oxygen reduction reaction process, alternating overall strain distribution near the surface and inside the NP is observed at the (111) Bragg reflection. In contrast, relatively insignificant changes appear in the (200) reflection. Density functional theory calculations are employed to rationalize the anisotropic lattice strain in terms of induced stress by H 2 O 2 adsorption and decomposition on the Pt NP surface. Our study provides deeper insight into the activity-structure relationship in this system.

3D imaging↗
DOE OSTI2021

MnSn 2 and MnSn 2 –TiO 2 nanostructured anode materials for lithium-ion batteries

The high theoretical lithium storage capacity of Sn makes it an enticing anode material for Li-ion batteries (LIBs); however, its large volumetric expansion during Li–Sn alloying must be addressed. Combining Sn with metals that are electrochemically inactive to lithium leads to intermetallics that can alleviate volumetric expansion issues and still enable high capacity. Here, we present the cycling behavior of a nanostructured MnSn 2 intermetallic used in LIBs. Nanostructured MnSn 2 is synthesized by reducing Sn and Mn salts using a hot injection method. The resulting MnSn 2 is characterized by x-ray diffraction and transmission electron microscopy and then is investigated as an anode for LIBs. The MnSn 2 electrode delivers a stable capacity of 514 mAh g -1 after 100 cycles at a C/10 current rate with a Coulombic efficiency >99%. Unlike other Sn-intermetallic anodes, an activation overpotential peak near 0.9 V versus Li is present from the second lithiation and in subsequent cycles. We hypothesize that this effect is likely due to electrolyte reactions with segregated Mn from MnSn 2 . To prevent these undesirable Mn reactions with the electrolyte, a 5 nm TiO 2 protection layer is applied onto the MnSn 2 electrode surface via atomic layer deposition. The TiO 2 -coated MnSn 2 electrodes do not exhibit the activation overpotential peak. The protection layer also increases the capacity to 612 mAh g -1 after 100 cycles at a C/10 current rate with a Coulombic efficiency >99%. This higher capacity is achieved by suppressing the parasitic reaction of Mn with the electrolyte, as is supported by x-ray photoelectron spectroscopy analysis.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
NASA NTRS1974

Skylab program payload integration. TO27 sample array

The objective of the TO27 sample array was to determine the change in optical properties of various transmissive windows, mirrors, and diffraction gratings caused by the deposition of contaminants found about the orbital assembly. The expected information to be obtained from the total TO27 sample array program is as follows: (1) effect of space contaminants on transmittance, reflectance, grating efficiency, and polarization; (2) variations in deposition of contaminants due to substrate, solar radiation, period of exposure, direction of exposure, and geometry effects; (3) identification of contaminants and source of evolution; (4) time of contaminant evolution and lingering time; and (5) guidelines for a model of spacecraft contamination.

Muscari, J. A.↗
DOE OSTI2022

Self-Adjusting Metal–Organic Framework for Efficient Capture of Trace Xenon and Krypton

The capture of the xenon and krypton from nuclear reprocessing off-gas is essential to the treatment of radioactive waste. Although various porous materials have been employed to capture Xe and Kr, the development of high-performance adsorbents capable of trapping Xe/Kr at very low partial pressure as in the nuclear reprocessing off-gas conditions remains challenging. Herein, we report a self-adjusting metal-organic framework based on multiple weak binding interactions to capture trace Xe and Kr from the nuclear reprocessing off-gas. The self-adjusting behavior of ATC-Cu and its mechanism have been visualized by the in-situ single-crystal X-ray diffraction studies and theoretical calculations. The self-adjusting behavior endows ATC-Cu unprecedented uptake capacities of 2.65 and 0.52 mmol g -1 for Xe and Kr respectively at 0.1 bar and 298 K, as well as the record Xe capture capability from the nuclear reprocessing off-gas. Further, our work not only provides a benchmark Xe adsorbent but proposes a new route to construct smart materials for efficient separations.

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

Understanding three-dimensionally interconnected porous oxide-derived copper electrocatalyst for selective carbon dioxide reduction

In this study, we have investigated a hierarchical CuO-derived inverse opal (CuO-IO) catalyst with high CO selectivity up to 80–90% and minimal H 2 evolution at moderate potentials for CO 2 electroreduction. The three-dimensionally (3D) structured, porous catalyst was composed of small CuO nanoparticles and exhibited a peak CO faradaic efficiency (FE) of 72.5% (±1.8), complete suppression of H 2 formation, and good stability over 24 hours operation at –0.6 V versus the reversible hydrogen electrode (RHE). In situ Raman, X-ray absorption spectroscopy and X-ray diffraction measurements indicated reduction of the catalyst into metallic Cu0 oxidation state with dominant Cu(111) orientation under electrocatalytic conditions. We suggest that rapid depletion of CO 2 and protons at the highly roughened catalyst surface likely increased the local pH during the electrolysis. The combination of C 1 favoring Cu(111) surfaces and reduced local proton/CO 2 availability facilitated selective conversion of CO 2 into CO and reduced H 2 and C 2 products. Our work provides additional understanding of the structure–property relationships of 3D porous electrocatalysts for CO 2 reduction applications by evaluating the crystallographic orientation, oxidation state, and crystallite size of a CO-selective CuO-IO catalyst under realistic working conditions.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Strategies for on-chip digital data compression for X-ray pixel detectors

Here, the continued desire for X-ray pixel detectors with higher frame rates will stress the ability of application-specific integrated circuit (ASIC) designers to provide sufficient off-chip bandwidth to reach continuous frame rates in the 1 MHz regime. To move from the current 10 kHz to the 1 MHz frame rate regime, ASIC designers will continue to pack as many power-hungry high-speed transceivers at the periphery of the ASIC as possible. In this paper, however, we present new strategies to make the most efficient use of the off-chip bandwidth by utilizing data compression schemes for X-ray photon-counting and charge-integrating pixel detectors. In particular, we describe a novel in-pixel compression scheme that converts from analog to digital converter units to encoded photon counts near the photon Poisson noise level and achieves a compression ratio of >1.5x independent of the dataset. In addition, we describe a simple yet efficient zero-suppression compression scheme called "zeromask" (ZM) located at the ASIC's edge before streaming data off the ASIC chip. ZM achieves average compression ratios of >4x, >7x, and >8x for high-energy X-ray diffraction, ptychography, and X-ray photon correlation spectroscopy datasets, respectively. We present the conceptual designs, register-transfer level block diagrams, and the physical ASIC implementation of these compression schemes in 65 nm CMOS. When combined, these two digital compression schemes could increase the effective off-chip bandwidth by a factor of 6-12x.

47 OTHER INSTRUMENTATION↗