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At least 73 records · Page 4
All sourcesNASA NTRSDOE OSTI
DOE OSTI2022

Evidence for superionic H 2 O and diffusive He–H 2 O at high temperature and high pressure

In this work, we present the evidence of superionic phase formed in H 2 O and, for the first time, diffusive H 2 O–He phase, based on time-resolved x-ray diffraction experiments performed on ramp-laser-heated samples in diamond anvil cells. The diffraction results signify a similar bcc-like structure of superionic H 2 O and diffusive He–H 2 O, while following different transition dynamics. Based on time and temperature evolution of the lattice parameter, the superionic H 2 O phase forms gradually in pure H 2 O over the temperature range of 1350–1400 K at 23 GPa, but the diffusive He–H 2 O phase forms abruptly at 1300 K at 26 GPa. We suggest that the faster dynamics and lower transition temperature in He–H 2 O are due to a larger diffusion coefficient of interstitial-filled He than that of more strongly bound H atoms. This conjecture is then consistent with He disordered diffusive phase predicted at lower temperatures, rather than H-disordered superionic phase in He–H 2 O.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2025

Experimental determination of hydrogen isotopic equilibrium in the system H 2 O (l) -H 2(g) from 3 to 90 °C

Molecular hydrogen (H 2 ) is found in a variety of settings on and in the Earth from low-temperature sediments to hydrothermal vents, and is actively being considered as an energy resource for the transition to a green energy future. The hydrogen isotopic composition of H 2 , given as D/H ratios or δD, varies in nature by hundreds of per mil from ∼−800 ‰ in hydrothermal and sedimentary systems to ∼+450 ‰ in the stratosphere. This range reflects a variety of processes, including kinetic isotope effects associated with formation and destruction and equilibration with water, the latter proceeding at fast (order year) timescales at low temperatures (<100 °C). At isotopic equilibrium, the D/H fractionation factor between liquid water and hydrogen ( D α H2O(l)-H2(g) ) is a function of temperature and can thus be used as a geothermometer for H 2 formation or re-equilibration temperatures. Multiple studies have produced theoretical calculations for hydrogen isotopic equilibrium between H 2 and water vapor. However, only three published experimental calibrations used in geochemistry exist for the H 2 O-H 2 system: two between 51 and 742 °C for H 2 O (g) -H 2(g) (Suess, 1949, Cerrai et al., 1954), and one in the H 2 O (l) -H 2(g) system for temperatures <100 °C (Rolston et al., 1976). Despite these calibrations existing, there is uncertainty on their accuracy at low temperatures (<100 °C; e.g., Horibe and Craig, 1995).

08 HYDROGEN↗
NASA NTRS1982

Charge transfer in H/+/-H and H/+/-D collisions within the energy range 0.1-150 eV

Absolute charge-transfer cross sections for collisions of protons with hydrogen and deuterium atoms have been measured within the energy range 0.1 to 150 eV using the merging-beams technique. The results are in excellent agreement with a fully quantum-mechanical treatment of this reaction. Earlier measurements which extended down to about 10 eV lie somewhat above the present values.

Newman, J. H.↗
DOE OSTI2025

Trigonal Planar Bis (carbene)Cu(I) Complexes Enable Divergent H 2 Activation with H 2 O for Accelerated Olefin Hydrogenation

CuH-catalyzed olefin hydrogenation is rare compared to those of carbonyl-derived substrates. Olefin insertion into Cu–H to form Cu-alkyl is ubiquitous; however, subsequent H 2 activation remains unknown to our knowledge. Herein, we investigated the transformations of β-H elimination, H 2 cleavage, and catalytic olefin hydrogenation in a series of linear and trigonal planar Cu(I)-alkyl complexes supported by monodentate N-heterocyclic carbene and bidentate naphthyridine- bis (carbene) ligands, respectively. Contrary to unreactive linear species, trigonal planar variants promote β-H elimination, hydrogenolysis, and catalytic hydrogenation of unactivated alkenes at mild temperatures and H 2 pressure. The rare isolation of a naphthyridine- bis (carbene)CuH monomer further affirms two predominant competing pathways for H 2 cleavage of metal–ligand cooperativity at Cu(I)-alkyl or internal electrophilic substitution at Cu(I)-OH. Employing either isolated or in situ generated Cu(I)-OH complex, via protonolysis of alkyl precatalyst by adventitious water, significantly accelerated catalysis compared to that operating primarily by the metal–ligand cooperativity pathway. DFT calculations and energy decomposition analysis on the disparate β-H elimination reactivity between linear and trigonal planar tert-butyl complexes and the mechanism of H 2 activation at a hydroxide complex, indicate that coordination geometry at Cu(I) and properties of the naphthyridine- bis (carbene) ligand are integral to the transformations reported here.

ALMO-EDA↗
DOE OSTI2022

High-performance of CrOx/HZSM-5 catalyst on non-oxidative dehydrogenation of C 2 H 6 to C 2 H 4 : Effect of supporting materials and associated mechanism

Ethane (C 2 H 6 ) is an important inexpensive and widely available fuel resource. High-value use of C 2 H 6 has become increasingly important. Catalytic dehydrogenation of C 2 H 6 to ethylene (C 2 H 4 ) has attracted much attention in recent years due to its high energy efficiency. The direct non-oxidative ethane dehydrogenation (EDH) to ethylene is a promising strategy to produce ethylene and hydrogen at the same time. In this research, Cr/HZSM-5 catalyst with superior stability was synthesized and exhibited an C 2 H 6 converting activity of 1.47 µmol/(g·s) with the corresponding C 2 H 6 conversion and C 2 H 4 selectivity of 37.3% and 90%, respectively. Herein, the synergistic effects of Si and Al in supporting materials were investigated by comparing Cr/HZSM-5 with SBA-15, SiO 2 and Al 2 O 3 supported ones, which contains either Al or Si with different structures. Characterization results indicated that the intimate interactions between Cr and support significantly improved the catalytic performance. The presence of Al in the support promoted the formation of more active Cr 6+ species by forming the aluminum-chromium-chromate (Cr-O-Al) structures which were more efficient to active C-H bond and form (Cr, Al)-OH groups during the reaction. Meanwhile, the formation of internal silanol group with the dissociative adsorbed H* could stabilized the active Cr phase to achieve a stable dehydrogenation activity.

03 NATURAL GAS↗
DOE OSTI2022

Neutron vibrational spectroscopic evidence for short H∙∙∙H contacts in the RNiInH 1.4; 1.6 (R = Ce, La) metal hydride

Intermetallic metal hydrides are critical materials for hydrogen storage applications, however, metal hydrides with greater storage capacities are still needed. Within metal hydrides, the volumetric storage capacities are limited by the number of hydrogen-accommodating interstitial sites which can be simultaneously occupied given a minimum hydride nearest-neighbor distance of ~2.1 A, according to the Switendick-Westlake criterion. To date, violations of this criterion are rare. Perhaps the most well studied compounds violating this criterion are the RNiInHx compounds (R = Ce, La, Nd). Previous neutron diffraction studies on the deuterated species revealed the presence of Ni-D∙∙∙D-Ni-D∙∙∙D-Ni chains with anomalously close D∙∙∙D contacts of ~1.6 A. Yet there are no neutron vibrational spectroscopic investigations reported for these atypical hydrides. Here we use neutron vibrational spectroscopy (NVS) measurements to probe the hydrogen dynamics in LaNiInHx (x = 0.67, 1.6) and CeNiInH 1.4 . For x > 0.67, the presence of close H...H contacts yields two related features in the vibrational spectrum centered near ~90 meV corresponding to the oscillations of paired H atoms simultaneously occupying neighboring R 3 Ni tetrahedra. Notably, these features are energetically distinct from comparable vibrational motions for "unpaired" H atoms when x = 0.67. To compare, we also present powder neutron diffraction and NVS measurements for the newly characterized, chemically similar Sn compounds CeNiSnH, CeNiSnH 2 , and CeNiSnD 2 . These compounds also contain R 3 Ni tetrahedra, however, the H-occupied tetrahedra are well separated from each other with the closest H∙∙∙H distances exceeding 2.1 A, and the Switendick-Westlake criterion is not violated. Consequently, the spectral signature of the close H∙∙∙H contacts is absent in these hydrides.

08 HYDROGEN↗
DOE OSTI2026

Correlating binding energies of adsorbed CO and H on model surfaces with CO/H 2 selectivity from co-electrolysis of CO 2 and H 2 O over copper–palladium bimetallic catalysts

Binding energies of adsorbed CO and H are key descriptors governing the activity and selectivity of the co-electrolysis of CO 2 and H 2 O to produce syngas with desired CO/H 2 ratios. Palladium hydride (PdH), which forms in situ at negative overpotentials, has been identified as the active Pd phase for CO 2 reduction to syngas. Herein, binding energies of CO and H are determined using temperature programmed desorption (TPD) of CO and H 2 from Pd(111), PdH/Pd(111), and Cu/PdH/Pd(111) under ultra-high vacuum (UHV) conditions. TPD results reveal that desorption of H 2 from subsurface PdH occurs at 460 K, while desorption from surface PdH is more facile at 320 K. CO desorption temperatures shift 20 K lower on PdH/Pd(111) compared to on Pd(111). The presence of 0.7 ML Cu further increases the desorption temperature of H 2 by 30 K while simultaneously reducing CO desorption temperatures by 70 K. Density functional theory (DFT) calculations show that CO adsorption onto Pd sites is hindered on the 0.7 ML Cu/PdH/Pd(111) surface while the kinetic barrier for H 2 desorption is increased. The trends in the binding energies of CO and H on model surfaces are consistent with electrochemical measurements of CuPd powder catalysts in a membrane electrode assembly (MEA), where H 2 evolution is reduced while CO production is enhanced compared to unmodified Pd catalysts. Overall, the results from model surface studies (TPD and DFT) provide a prediction and explanation for the activity and CO/H 2 ratios observed in electrochemical experiments. This study also demonstrates that CuPd is a promising catalyst with reduced Pd-loading to produce CO-rich syngas.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Thermodynamics and kinetics of H adsorption and intercalation for graphene on 6 H -SiC(0001) from first-principles calculations

Previous experimental observations for H intercalation under graphene on SiC surfaces motivate the clarification of configuration stabilities and kinetic processes related to intercalation. From first-principles density-functional-theory calculations, we analyze H adsorption and intercalation for graphene on a 6H-SiC(0001) surface, where the system includes two single-atom-thick graphene layers: the top-layer graphene (TLG) and the underling buffer-layer graphene (BLG) above the terminal Si layer. Our chemical potential analysis shows that in the low-H coverage regime (described by a single H atom within a sufficiently large supercell), intercalation into the gallery between TLG and BLG or into the gallery underneath BLG is more favorable thermodynamically than adsorption on top of TLG. However, intercalation into the gallery between TLG and BLG is most favorable. We obtain energy barriers of about 1.3 and 2.3 eV for a H atom diffusing on and under TLG, respectively. From an additional analysis of the energy landscape in the vicinity of a step on the TLG, we assess how readily one guest H atom on the TLG terrace can directly penetrate the TLG into the gallery between TLG and BLG versus crossing a TLG step to access the gallery. Finally, we also perform density functional theory calculations for higher H coverages revealing a shift in favorability to intercalation of H underneath BLG and characterizing the variation with H coverage in interlayer spacings.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Observation of Directed Flow of Hypernuclei $^3_Λ\text{H}$ and $^4_Λ\text{H}$ in $\sqrt{s_{\text{NN}}}$ = 3 GeV Au + Au Collisions at RHIC

We report here the first observation of directed flow ($v_1$) of the hypernuclei $^3_Λ\text{H}$ and $^4_Λ\text{H}$ in mid-central Au + Au collisions at $\sqrt{s_{\text{NN}}}$ = 3 GeV at RHIC. These data are taken as part of the beam energy scan program carried out by the STAR experiment. From 165 × 10 6 events in 5%–40% centrality, about 8400 $^3_Λ\text{H}$ and 5200 $^4_Λ\text{H}$ candidates are reconstructed through two- and three-body decay channels. In this work, we observe that these hypernuclei exhibit significant directed flow. Comparing to that of light nuclei, it is found that the midrapidity $v_1$ slopes of $^3_Λ\text{H}$ and $^4_Λ\text{H}$ follow baryon number scaling, implying that the coalescence is the dominant mechanism for these hypernuclei production in the 3 GeV Au + Au collisions.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2024

Search for h c → π + π − J / ψ via ψ ( 3686 ) → π 0 h c

Using ( 2712.4 ± 14.3 ) × 10 6 ψ ( 3686 ) events collected with the BESIII detector operating at the BEPCII collider, we search for the hadronic transition h c → π + π − J / ψ via ψ ( 3686 ) → π 0 h c . No significant signal is observed. We set the most stringent upper limits to date on the branching fractions B ( ψ ( 3686 ) → π 0 h c ) × B ( h c → π + π − J / ψ ) and B ( h c → π + π − J / ψ ) at the 90% confidence level, which are determined to be 6.7 × 10 − 7 and 9.4 × 10 − 4 , respectively. Published by the American Physical Society 2024

Ablikim, M.↗
DOE OSTI2023

Rational Design and Reticulation of Infinite qbe Rod Secondary Building Units into Metal–Organic Frameworks through a Global Desymmetrization Approach for Inverse C 3 H 8 /C 3 H 6 Separation

Abstract The development of reticular chemistry has enabled the construction of a large array of metal–organic frameworks (MOFs) with diverse net topologies and functions. However, dominating this class of materials are those built from discrete/finite secondary building units (SBUs), yet the designed synthesis of frameworks involving infinite rod‐shaped SBUs remain underdeveloped. Here, by virtue of a global linker desymmetrization approach, we successfully targeted a novel Cu‐MOF (Cu‐ASY) incorporating infinite Cu‐carboxylate rod SBUs with its structure determined by micro electron diffraction (MicroED) crystallography. Interestingly, the rod SBU can be simplified as a unique cylindric sphere packingqbetubule made of [4 3 .6 2 ] tiles, which further connect the tritopic linkers to give a newly discovered 3,5‐connectedgfcnet. Cu‐ASY is a permanent ultramicroporous material featuring 1D channels with highly inert surfaces and shows a preferential adsorption of propane (C 3 H 8 ) over propene (C 3 H 6 ). The efficiency of C 3 H 8 selective Cu‐ASY is validated by multicycle breakthrough experiments, giving C 3 H 6 productivity of 2.2 L/kg. Density functional theory (DFT) calculations reveal that C 3 H 8 molecules form multiple C−H⋅⋅⋅π and atypical C−H⋅⋅⋅ H−C van der Waals interactions with the inner nonpolar surfaces. This work therefore highlights the linker desymmetrization as an encouraging and intriguing strategy for achieving unique MOF structures and properties.

Chemistry↗
DOE OSTI2021

Structural and Electronic Influences on Rates of Tertpyridine-Amine Co III -H Formation During Catalytic H 2 Evolution in an Aqueous Environment

In this paper, the differences in catalytic performance for a series of Co hydrogen evolution catalysts with different pentadentate polypyridyl ligands (L), have been rationalized by examining elementary steps of the catalytic cycle using a combination of electrochemical and transient pulse radiolysis (PR) studies in aqueous solution. Solvolysis of the [Co II -Cl] + species results in the formation of [Co II (κ 4 -L)(OH 2 )] 2+ . Further reduction produces [Co I κ 4 -L)(OH 2 )] + , which undergoes a rate-limiting structural rearrangement to [Co I (κ 5 -L)] + before being protonated to form [Co III -H] 2+ . The rate of [Co III -H] 2+ formation is similar for all complexes in the series. Using E 1/2 values of various Co species and pKa values of [Co III -H] 2+ estimated from PR experiments, we found that while the protonation of [Co III -H] 2+ is unfavorable, [CoII-H]+ reacts with protons to produce H 2 . The catalytic activity for H 2 evolution tracks the hydricity of the [Co II -H] + intermediate.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

Projections of H-mode access and edge pedestal in the SPARC tokamak

In order to inform core performance projections and divertor design, the baseline SPARC tokamak plasma discharge is evaluated for its expected H-mode access, pedestal pressure and edge-localized mode (ELM) characteristics. A clear window for H-mode access is predicted for full field DT plasmas, with the available 25 MW of design auxiliary power. Additional alpha heating is likely needed for H-mode sustainment. Pressure pedestal predictions in the developed H-mode are surveyed using the EPED model. The projected SPARC pedestal would be limited dominantly by peeling modes and may achieve pressures in excess of 0.3 MPa at a density of approximately 3 × 10 20 m -3 . High pedestal pressure is partially enabled by strong equilibrium shaping, which has been increased as part of recent design iterations. Edge-localized modes (ELMs) with >1 MJ of energy are projected, and approaches for reducing the ELM size, and thus the peak energy fluence to divertor surfaces, are under consideration. The high pedestal predicted for SPARC provides ample margin to satisfy its high fusion gain (Q) mission, so that even if ELM mitigation techniques result in a 2x reduction of the pedestal pressure, Q > 2 is still predicted.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2023

Direct Transformation of SiH 4 to a Molecular L(H) 2 Co=Si=Co(H) 2 L Silicide Complex

The synthesis of bimetallic molecular silicide complexes is reported, based on the use of multiple Si–H bond activations in SiH 4 at the metal centers of 14-electron LCo I fragments (L = Tp", HB(3,5-diisopropylpyrazolyl) 3 – ; [BP 2 tBu Pz], PhB(CH 2 P t Bu 2 ) 2 (pyrazolyl)). Upon exposure of (Tp"Co) 2 (μ-N 2 ) (1) to SiH 4 , a mixture of (Tp"Co) 2 (μ-H) (2) and (Tp"Co) 2 (μ-H) 2 (3) was formed and no evidence for Si–H oxidative addition products was observed. In contrast, [BP 2 tBu Pz]-supported Co complexes led to Si–H oxidative additions with the generation of silylene and silicide complexes as products. Notably, the reaction of ([BP 2 tBu Pz]Co) 2 (μ-N 2 ) (5) with SiH 4 gave the dicobalt silicide complex [BP 2 tBu Pz](H) 2 Co=Si=Co(H) 2 [BP 2 tBu Pz] (8) in high yield, representing the first direct route to a symmetrical bimetallic silicide. Here, the effect of the [BP 2 tBu Pz] ligand on Co–Si bonding in 7 and 8 was explored by analysis of solid-state molecular structures and density functional theory (DFT) investigations. Upon exposure to CO or DMAP (DMAP = 4-dimethylaminopyridine), 8 converted to the corresponding [BP 2 tBu Pz]Co(L) x adducts (L = CO, x = 2; L = DMAP, x = 1) with concomitant loss of SiH 4 , despite the lack of significant Si–H interactions in the starting complex. On heating to 60 °C, 8 underwent reaction with MeCl to produce small quantities of Me x SiH 4–x (x = 1–3), demonstrating functionalization of the μ-silicon atom in a molecular silicide to form organosilanes.

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

2 H -Thiopyran-2-thione sulfine, a compound for converting H 2 S to HSOH/H 2 S 2 and increasing intracellular sulfane sulfur levels

Reactive sulfane sulfur species such as persulfides (RSSH) and H 2 S 2 are important redox regulators and closely linked to H 2 S signaling. However, the study of these species is still challenging due to their instability, high reactivity, and the lack of suitable donors to produce them. Herein we report a unique compound, 2H-thiopyran-2-thione sulfine (TTS), which can specifically convert H 2 S to HSOH, and then to H 2 S 2 in the presence of excess H 2 S. Meanwhile, the reaction product 2H-thiopyran-2-thione (TT) can be oxidized to reform TTS by biological oxidants. The reaction mechanism of TTS is studied experimentally and computationally. TTS can be conjugated to proteins to achieve specific delivery, and the combination of TTS and H 2 S leads to highly efficient protein persulfidation. When TTS is applied in conjunction with established H 2 S donors, the corresponding donors of H 2 S 2 (or its equivalents) are obtained. Cell-based studies reveal that TTS can effectively increase intracellular sulfane sulfur levels and compensate for certain aspects of sulfide:quinone oxidoreductase (SQR) deficiency. These properties make TTS a conceptually new strategy for the design of donors of reactive sulfane sulfur species.

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

Kinematics of the H α and H β broad-line region in an SDSS sample of type-1 AGNs

Here, we investigate the kinematics of the part of the broad-line region (BLR) in active galactic nuclei (AGNs) emitting H β and H α emission lines. We explore the widths and asymmetries of the broad H β and H α emission lines in a sample of high-quality (i.e. high signal-to-noise ratio) spectra of type-1 AGN taken from the Data Release 16 of the Sloan Digital Sky Survey in order to explore possible deviation from the gravitationally bound motion. To find only the broad component of H β and H α, we use the FANTASY (Fully Automated pythoN Tool for AGN Spectra analYsis) code for the multicomponent modelling of the AGN spectra and for careful extraction of the broad emission-line parameters. Here, we show that based on the broad-line profiles widths and asymmetries, the BLR gas emitting H β and H α lines follows similar kinematics, and seems to be virialized in our sample of type-1 AGN.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2021

Effects of Glymes on the Distribution of Mg(B 10 H 10 ) and Mg(B 12 H 12 ) from the Thermolysis of Mg(BH 4 ) 2

We examined the effects of concentrations and identities of various glymes, from monoglyme up to tetraglyme, on H 2 release from the thermolysis of Mg(BH 4 ) 2 at 160–200 °C for 8 h. 11 B NMR analysis shows major products of Mg(B 10 H 10 ) and Mg(B 12 H 12 ); however, their relative ratio is highly dependent both on the identity and concentration of the glyme to Mg(BH 4 ) 2 . Selective formation of Mg(B 10 H 10 ) was observed with an equivalent of monoglyme and 0.25 equivalent of tetraglyme. However, thermolysis of Mg(BH 4 ) 2 in the presence of stoichiometric or greater equivalent of glymes can lead to unselective formation of Mg(B 10 H 10 ) and Mg(B 12 H 12 ) products or inhibition of H 2 release.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗