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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 577 records · Page 32
All sourcesNASA NTRSDOE OSTI
DOE OSTI2024

Coordination-induced O-H/N-H bond weakening by a redox non-innocent, aluminum-containing radical

Abstract Several renewable energy schemes aim to use the chemical bonds in abundant molecules like water and ammonia as energy reservoirs. Because the O-H and N-H bonds are quite strong (>100 kcal/mol), it is necessary to identify substances that dramatically weaken these bonds to facilitate proton-coupled electron transfer processes required for energy conversion. Usually this is accomplished through coordination-induced bond weakening by redox-active metals. However, coordination-induced bond weakening is difficult with earth’s most abundant metal, aluminum, because of its redox inertness under mild conditions. Here, we report a system that uses aluminum with a redox non-innocent ligand to achieve significant levels of coordination-induced bond weakening of O-H and N-H bonds. The multisite proton-coupled electron transfer manifold described here points to redox non-innocent ligands as a design element to open coordination-induced bond weakening chemistry to more elements in the periodic table.

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

Turbulence driven widening of the near-SOL power width in ASDEX Upgrade H-Mode discharges

Divertor heat flux data from infra red (IR) from various tokamaks in H-Mode regime show that the power width, $\lambda_{q}$, scales approximately like 1.6 $(R/a) ρ_{s,pol}$. However, the IR based scaling comes with the restriction that only discharges were considered with attached divertor conditions. Here we set up a new data base covering low edge density data but also including high density plasmas reaching the H-mode density limit. We use Thomson-scattering to measure the electron temperature decay length which will set the near-SOL power width through parallel heat conduction. We present scaling results for the density, temperature and pressure separatrix fall-off lengths. As the principal result we derive a generalized power width scaling which reads as $\lambda_{q}\propto\,\rho_{s,pol}\cdot(1+2.1\alpha_{t}^{1.7})$ where $\alpha_{t}$ describes a normalized collisionality ($\alpha_{t} = 3\cdot\,10^{-18}\,R\,q^2\,n\,Z_{eff}T^{-2}$). The parameter $\alpha_{t}$ describes the relative importance of the interchange effect on drift-wave turbulence as proposed by Scott and is found to be closely linked to the diamagnetic parameter αd introduced by Rogers, Drake and Zeiler (RDZ). The edge operational space for ASDEX Upgrade displays a boundary qualitatively in agreement with the region labelled as density limit in the edge plasma phase space proposed by RDZ. The data base shows in the limit of low edge densities ($\alpha_{t}\simeq\,0.2$) accurate agreement to the IR based power width scaling. At elevated separatrix densities ($\alpha_{t}\simeq\,1$) the power width is broadened by a factor of up to about three accompanied by a reduction of the $\text{H}_{98,y2}$ confinement factor. Finally, plasmas with higher triangularity show higher values for $\text{H}_{98,y2}$ in the same range of normalized collisionality.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2024

Non-linear dependence of ion heat flux on plasma density at the L–H transition of JET NBI-heated deuterium–tritium plasmas

Abstract Recent JET D–T campaigns opened the possibility of unique isotope studies to investigate the L–H transition physics in view of reactor plasmas and to study the origin of the observed power threshold minimum. In the present paper, we characterise L–H transitions in the low and high-density branches of JET NBI-heated D–T plasmas. As discussed in the paper, L–H transition has been hypothesised to be determined by the transport power losses of plasma ions, i.e. the so-called ion heat flux ( Q i ). We present the first power balance analysis of JET NBI-heated D–T plasmas to evaluate the ion heat flux at the transition. Due to the experimental setting being similar to previous JET D experiments, we also directly compare the results, discussing the isotope effect and similarities between datasets. First, we find an isotope effect between D and D–T Q i , with a lower Q i in D–T plasmas. We confirm that the ion heat flux deviates from density linearity compared to the linear trend observed in wave-heated D plasmas of other tokamaks. The deviation we observe in NBI-heated L–H transitions happens at an isotope-dependent density. Plasma edge rotation correlates with Q i deviation from density linearity in the low-density branch. However, further investigations would be required to assess the role of rotation on Q i and the power threshold minimum at JET. At low plasma density, NBI power dominates Q i , while increasing the density makes the equipartition power dominant. We finally compare our results with hypotheses proposed from evidence in other tokamaks to present a complete overview of ion heat flux analyses in D and D–T NBI-heated plasmas at JET.

Vincenzi, P. (ORCID:0000000251564354)↗
DOE OSTI2024

H - Ion Source RF Plasma Testing with 13 MHz and 27 MHz at the Spallation Neutron Source (SNS)

The baseline RF-driven H⁻ ion source configuration at the Spallation Neutron Source (SNS) facility uses a continuous wave (CW) 600 W 13 MHz RF system to ignite and maintain a low-density plasma inside the ion source vacuum chamber. After the continuous low-density 13 MHz plasma has been established, a pulsed (typical 1 ms pulse width and 60 Hz pulse repetition rate) 80 kW 2 MHz RF system is used to increase the plasma density to produce the pulsed H⁻ ion beam. Incremental upgrades and improvements to the SNS ion source systems have resulted in the ability to reliably operate an H⁻ ion source for SNS neutron production run cycles that can last up to four months. Conditions inside the SNS H⁻ ion source evolve throughout a four-month run cycle due to changes in impurity levels, sputtering, and erosion. As the internal ion source conditions change during the run cycle, there can also be changes in plasma stability and the 13 MHz RF power level required to ignite the plasma. This paper presents the preliminary results of testing performed on the SNS Ion Source Test Stand (ISTS) system where we looked at plasma ignition and plasma stability using 27 MHz RF in place of the baseline 13 MHz RF system.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2024

Measurement of Λ b 0 , Λ c + , and Λ Decay Parameters Using Λ b 0 → Λ c + h − Decays

A comprehensive study of the angular distributions in the bottom-baryon decays Λ b 0 → Λ c + h − ( h = π , K ) , followed by Λ c + → Λ h + with Λ → p π − or Λ c + → p K S 0 decays, is performed using a data sample of proton-proton collisions corresponding to an integrated luminosity of 9 fb − 1 collected by the LHCb experiment at center-of-mass energies of 7, 8, and 13 TeV. The decay parameters and the associated charge-parity ( C P ) asymmetries are measured, with no significant C P violation observed. For the first time, the Λ b 0 → Λ c + h − decay parameters are measured. The most precise measurements of the decay parameters α , β , and γ are obtained for Λ c + decays and an independent measurement of the decay parameters for the strange-baryon Λ decay is provided. The results deepen our understanding of weak decay dynamics in baryon decays. © 2024 CERN, for the LHCb Collaboration 2024 CERN

Aaij, R. (ORCID:0000000305331952)↗
DOE OSTI2020

Simplified Two-Stage Model Predictive Control for a Hybrid Multilevel Converter With Floating H-Bridge

This paper proposes a simplified two-stage model predictive control (ST-MPC) for a hybrid multilevel converter, which is an active-neutral-point-clamped converter with floating H-bridge (ANPC-H). The objective of the first stage is to select the voltage vector that has the optimal current tracking performance by using a novel geometrical positioning approach in the complex plane. The second stage selects the best switching state among all the available switching states that belong to the same voltage vector obtained in the first stage, to balance dc capacitor voltages and reduce the common mode voltage. The proposed ST-MPC can dramatically reduce the computational burden and ensure the best current tracking by the two-stage structure, such that the execution time is much shorter compared with the conventional MPC. In addition, the geometrical positioning approach in the first stage is generic and can be applicable for any multilevel converters with N-level output; thus, this ST-MPC can be applied for both sevenand nine-level operation of the hybrid ANPC-H converter under different dc voltage ratios. Both simulation results and experimental results obtained on a silicon carbide hybrid ANPC-H converter prototype validate the feasibility and effectiveness of the proposed ST-MPC strategy.

42 ENGINEERING↗
DOE OSTI2022

Diamond formation kinetics in shock-compressed C$-$H$-$O samples recorded by small-angle x-ray scattering and x-ray diffraction

Extreme conditions inside ice giants such as Uranus and Neptune can result in peculiar chemistry and structural transitions, e.g., the precipitation of diamonds or superionic water, as so far experimentally observed only for pure C$-$H and H 2 O systems, respectively. Here, we investigate a stoichiometric mixture of C and H 2 O by shock-compressing polyethylene terephthalate (PET) plastics and performing in situ x-ray probing. We observe diamond formation at pressures between 72 ± 7 and 125 ± 13 GPa at temperatures ranging from ~3500 to ~6000 K. Combining x-ray diffraction and small-angle x-ray scattering, we access the kinetics of this exotic reaction. The observed demixing of C and H 2 O suggests that diamond precipitation inside the ice giants is enhanced by oxygen, which can lead to isolated water and thus the formation of superionic structures relevant to the planets’ magnetic fields. Moreover, our measurements indicate a way of producing nanodiamonds by simple laser-driven shock compression of cheap PET plastics.

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

Solvent Recovery and Management at the Savannah River Site H-Canyon Facility

NIOWAVE, Inc. is a domestic supplier of medical and industrial isotopes from uranium and radium. The Savannah River National laboratory (SRNL) is currently providing support to NIOWAVE, which plans to deploy a superconducting electron linear accelerator (LINAC) to fission uranium for Mo-99 production without the need for a nuclear reactor or HEU. The uranium from the Mo-99 production targets will be purified using a modified PUREX (Plutonium Uranium Reduction Extraction) solvent extraction process to recover the uranium in the product stream. The uranium will then be precipitated as an oxalate which is calcined to U 3 O 8 to fabricate pellets for new Mo-99 targets. In previous support provided to NIOWAVE, the SRNL demonstrated a solvent washing process to remove degradation products from the tributyl phosphate (TBP) solvent used in the modified PUREX process under development for uranium recovery. To supplement this technology demonstration, NIOWAVE requested the SRNL to provide summary information on the solvent recovery and management activities which are used at the Savannah River Site (SRS) H-Canyon facility. An existing reference document for the reprocessing of irradiated HEU fuels at the SRS was used as the primary reference for the solvent management activities; although, other reference documents were used to provide supplementary information. The information provided includes a brief summary of the solvent degradation issues which have been observed in the H-Canyon solvent extraction cycles and resulting process safety concerns. The solvent recovery processes for the three cycles of solvent extraction used in the H-Canyon were subsequently described including the process equipment which consists of the continuous and batch solvent washers, pumps, and tanks. A final section is provided on the monitoring and analysis of solvent quality based on the previous work performed at the SRNL for NIOWAVE and past research and development activities performed to support the solvent extraction processes in both the SRS F-Canyon and H-Canyon facilities.

07 ISOTOPE AND RADIATION SOURCES↗
DOE OSTI2024

Probing room temperature indirect and minimum direct band gaps of h-BN

Abstract Hexagonal boron nitride (h-BN) has attracted considerable interest as an ultrawide bandgap (UWBG) semiconductor. Experimental studies focused on the detailed near band-edge structure of h-BN at room temperature are still lacking. We report a direct experimental measurement of the near band-edge structure performed on h-BN quasi-bulk wafers via photocurrent excitation spectroscopy (PES). PES resolved the band-to-band transitions near M- and K-points in the Brillion zone (BZ), from which the room temperature indirect band gap of E g M K ∼6.02 eV, minimum direct bandgap at M-point of E g M = 6.36 eV and next lowest direct energy bandgap at K-point of E g K = 6.56 eV , have been simultaneously determined for the first time experimentally. The measured energy differences between K- and M-points in the conduction band minimum (CBM) and valence band maximum (VBM) are Δ E C M K = 0.54 eV and Δ E V M K = 0.34 eV, respectively, in good agreement with the calculation results. Significantly differing from its III-nitride wurtzite counterparts, in which only electrons and holes in the conduction and valence band extremes at the Γ-point are predominantly involved in the optical and transport processes, the results highlighted that charge carriers associated with both M- and K-valleys control to the optical excitation, recombination and charge transport processes in h-BN.

Physics↗
DOE OSTI2021

Significant H i and Metal Differences around the z = 0.83 Lens Galaxy toward the Doubly Lensed Quasar SBS 0909+532

We report a large difference in neutral hydrogen (H i) and metal column densities between the two sight lines probing opposite sides of the lensing galaxy at z {sub lens} = 0.83 toward the doubly lensed quasar SBS 0909+532. Using archival HST-STIS and Keck HIRES spectra of the lensed quasar images, we measure log N {sub H I} = 18.77 ± 0.12 cm{sup −2} toward the brighter image (A) at an impact parameter of r {sub A} = 3.15 kpc and log N {sub H I} = 20.38 ± 0.20 cm{sup −2} toward the fainter image (B) at an impact parameter of r {sub B} = 5.74 kpc. This difference by a factor of ∼41 is the highest difference between sight lines for a lens galaxy in which H i has been measured, suggesting patchiness and/or anisotropy on these scales. We estimate an average Fe abundance gradient between the sight lines to be ≥+0.35 dex kpc{sup −1}. The N {sub Fe II}/N {sub Mg II} ratios for the individual components detected in the Keck HIRES spectra have supersolar values for all components in sight line A and for 11 out of 18 components in sight line B, suggesting that Type Ia supernovae may have contributed to the chemical enrichment of the galaxy’s environment. Additionally, these observations provide complementary information to detections of cold gas in early-type galaxies and the tension between these and some models of cloud survival.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2023

L-H transition studies in tritium and deuterium–tritium campaigns at JET with Be wall and W divertor

The recent deuterium–tritium campaign in JET-ILW (DTE2) has provided a unique opportunity to study the isotope dependence of the L-H power threshold in an ITER-like wall environment (Be wall and W divertor). Here we present results from dedicated L-H transition experiments at JET-ILW, documenting the power threshold in tritium and deuterium–tritium plasmas, comparing them with the matching deuterium and hydrogen datasets. From earlier experiments in JET-ILW it is known that as plasma isotopic composition changes from deuterium, through varying deuterium/hydrogen concentrations, to pure hydrogen, the value of the line averaged density at which the threshold is minimum, ${\bar n_{{\text{e}},{\text{min}}}}$, increases, leading us to expect that ${\bar n_{{\text{e}},{\text{min}}}}$(T) < ${\bar n_{{\text{e}},{\text{min}}}}$(DT) < ${\bar n_{{\text{e}},{\text{min}}}}$(D) < ${\bar n_{{\text{e}},{\text{min}}}}$(H). The new power threshold data confirms these expectations in most cases, with the corresponding ordering of the minimum power thresholds. We present a comparison of this data to power threshold scalings, used for extrapolation to future devices such as ITER and DEMO.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2022

Boosting the H 2 –D 2 Exchange Activity of Dilute Nanoporous Ti–Cu Catalysts through Oxidation–Reduction Cycle–Induced Restructuring

The use of nanoporous metals as catalysts has attracted significant interest in recent years. Their high-curvature, nanoscale ligaments provide not only high surface area but also a high density of undercoordinated step edge and kink sites. However, their long-term stability, especially at higher temperatures, is often limited by thermal coarsening and the associated loss of surface area. Herein, it is demonstrated that the nanoscale morphology of nanoporous Cu can be regenerated by applying oxidation/reduction cycles at 250 °C. Specifically, the morphological evolution and H 2 dissociation activity of hierarchical nanoporous Cu catalysts doped with Ti during structural rearrangement triggered by oxidative and reductive atmospheres at elevated temperatures are studied. In addition to coarsening of the structure at elevated temperatures, oxidation at 400 °C causes an expansion of the ligaments. Further, subsequent reduction at 400 °C leads to the formation of particles and a drop in the H 2 dissociation activity compared the fresh catalyst. However, performing the redox cycle at 250 °C reverses coarsening and boosts the H 2 dissociation activity for the hydrogen–deuterium (H 2 –D 2 ) reaction. Herein, the possibility to reverse coarsening is demonstrated, thereby mitigating the loss of activity frequently observed in nanoporous catalysts.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Regiospecific Incorporation of Acetylene Linker in High‐Electron Mobility Dimerized Acceptors for Organic Solar Cells with High Efficiency (18.8%) and Long 1‐Sun Lifetime (> 5000 h)

Abstract The commercialization of organic solar cells (OSCs) requires both high power conversion efficiency (PCE) and long‐term stability. However, the lifetime of the OSCs containing small‐molecule acceptors (SMA) should be significantly enhanced. In this study, a series of planarity‐controlled is developed, high electron mobility dimerized SMAs (DSMAs) and realize OSCs with high‐performance (PCE = 18.8%) and high‐stability ( t 80% lifetime = 5380 h under 1‐Sun illumination). An acetylene linker with a planar triple bond is designed for dimerization of SMA units to afford the high backbone planarity necessary to achieve high crystallinity and electron mobility. To further engineer the molecular conformation and electron mobility of the DSMAs, different regioisomers of a Y‐based SMA are dimerized to yield three regioisomerically distinct DSMAs, denoted as DYA‐I, DYA‐IO, and DYA‐O, respectively. It is found that the crystallinity, electron mobility, and glass transition temperature of the DSMAs gradually increase in the order of DYA‐O, DYA‐IO, and DYA‐I, which, in turn, enhance the PCE and device stability of the resulting OSCs; DYA‐O (PCE = 16.45% and t 80% lifetime = 3337 h) < DYA‐IO (PCE = 17.54% and t 80% lifetime = 4255 h) < DYA‐I (PCE = 18.83% and t 80% lifetime = 5380 h).

Chemistry↗
DOE OSTI2022

Multiple Roles of Alkanethiolate‐Ligands in Direct Formation of H 2 O 2 over Pd Nanoparticles

Abstract Coadsorbed organic species including thiolates can promote direct synthesis of hydrogen peroxide from H 2 and O 2 over Pd particles. Here, density functional theory based kinetic modeling, augmented with activity measurements and vibrational spectroscopy are used to provide atomistic understanding of direct H 2 O 2 formation over alkylthiolate(RS) Pd. We find that the RS species are oxidized during reaction conditions yielding RSO 2 as the effective ligand. The RSO 2 ligand shows superior ability for proton transfer to the intermediate surface species OOH, which accelerates the formation of H 2 O 2 . The ligands promote the selectivity also by blocking sites for unselective water formation and by modifying the electronic structure of Pd. The work rationalizes observations of enhanced selectivity of direct H 2 O 2 formation over ligand‐funtionalized Pd nanoparticles and shows that engineering of organic surface modifiers can be used to promote desired hydrogen transfer routes.

Chen, Lin↗
DOE OSTI2023

Significant Roles of Surface Hydrides in Enhancing the Performance of Cu/BaTiO 2.8 H 0.2 Catalyst for CO 2 Hydrogenation to Methanol

Abstract Tuning the anionic site of catalyst supports can impact reaction pathways by creating active sites on the support or influencing metal‐support interactions when using supported metal nanoparticles. This study focuses on CO 2 hydrogenation over supported Cu nanoparticles, revealing a 3‐fold increase in methanol yield when replacing oxygen anions with hydrides in the perovskite support (Cu/BaTiO 2.8 H 0.2 yields ~146 mg/h/gCu vs. Cu/BaTiO 3 yields ~50 mg/h/gCu). The contrast suggests that significant roles are played by the support hydrides in the reaction. Temperature programmed reaction and isotopic labelling studies indicate that BaTiO 2.8 H 0.2 surface hydride species follow a Mars van Krevelen mechanism in CO 2 hydrogenation, promoting methanol production. High‐pressure steady‐state isotopic transient kinetic analysis (SSITKA) studies suggest that Cu/BaTiO 2.8 H 0.2 possesses both a higher density and more active and selective sites for methanol production compared to Cu/BaTiO 3 . An operando high‐pressure diffuse reflectance infrared spectroscopy (DRIFTS)‐SSITKA study shows that formate species are the major surface intermediates over both catalysts, and the subsequent hydrogenation steps of formate are likely rate‐limiting. However, the catalytic reactivity of Cu/BaTiO 2.8 H 0.2 towards the formate species is much higher than Cu/BaTiO 3 , likely due to the altered electronic structure of interface Cu sites by the hydrides in the support as validated by density functional theory (DFT) calculations.

He, Yang↗
DOE OSTI2020

Ligand Protonation Triggers H 2 Release from a Dinickel Dihydride Complex to Give a Doubly “T”-Shaped Dinickel(I) Metallodiradical

The dinickel(II) dihydride complex (1 K ) ofapyrazolate-based compartmental ligand with b-diketiminato (nacnac) chelate arms (L - ), providing two pincer-type {N 3 } binding pockets, has been reported to readily eliminate H 2 and to serve as a masked dinickel(I) species. Discrete dinickel(I) complexes (2 Na , 2 K ) of L - are now synthesized via a direct reduction route. They feature two adjacent T-shaped metalloradicals that are antiferromagnetically coupled, giving an S = 0 ground state. The two singly occupied local d x 2 -y 2 type magnetic orbitals are oriented into the bimetallic cleft, enabling metal–metal cooperative 2 e - substrate reductions as shown by the rapid reaction with H 2 or O 2 . X-ray crystallography reveals distinctly different positions of the K + in 1 K and 2 K , suggesting a stabilizing interaction of K + with the dihydride unit in 1 K . H 2 release from 1 K is triggered by peripheral g-C protonation at the nacnac subunits, which DFT calculations show lowers the barrier for reductive H 2 elimination from the bimetallic cleft.

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

Multiple Roles of Alkanethiolate‐Ligands in Direct Formation of H 2 O 2 over Pd Nanoparticles

Abstract Coadsorbed organic species including thiolates can promote direct synthesis of hydrogen peroxide from H 2 and O 2 over Pd particles. Here, density functional theory based kinetic modeling, augmented with activity measurements and vibrational spectroscopy are used to provide atomistic understanding of direct H 2 O 2 formation over alkylthiolate(RS) Pd. We find that the RS species are oxidized during reaction conditions yielding RSO 2 as the effective ligand. The RSO 2 ligand shows superior ability for proton transfer to the intermediate surface species OOH, which accelerates the formation of H 2 O 2 . The ligands promote the selectivity also by blocking sites for unselective water formation and by modifying the electronic structure of Pd. The work rationalizes observations of enhanced selectivity of direct H 2 O 2 formation over ligand‐funtionalized Pd nanoparticles and shows that engineering of organic surface modifiers can be used to promote desired hydrogen transfer routes.

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

Computational Discovery of Active and Selective Metal‐Nitrogen‐Graphene Catalysts for Electrooxidation of Water to H 2 O 2

A direct electrosynthesis of H 2 O 2 from either O 2 or H 2 O is an attractive strategy to replace the energy-intensive industrial anthraquinone process. Two-electron water oxidation reaction (2e-WOR) offers several advantages over the oxygen reduction reaction such as better mass transfer due to the absence of gas-phase reactants. However, 2e-WOR is a more challenging and less studied process with only a handful of metal oxides exhibiting reasonable activity/selectivity properties. Herein, we employ density-functional-theory calculations to screen a variety of metal-nitrogen-graphene structures for 2e-WOR. As a consequence of scaling between the adsorption energies of reaction intermediates, we determine a linear relation between selectivities for the first and second reaction steps of 2e-WOR, viz. that if selectivity toward adsorbed OH is improved, then selectivity toward H 2 O 2 at the subsequent step is decreased. We also find that selectivity and activity are linearly scaled in such a way that a higher activity (i.e., a lower overpotential) leads to a lower selectivity for the H 2 O 2 formation step. Based on the obtained results several chemistries, e.g., containing NiN x -C moieties, are predicted to rival the best-performing metal oxides such as ZnO and CaSnO 3 in terms of combination of their activity/selectivity characteristics for 2e-WOR.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗