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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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All sourcesNASA NTRSDOE OSTI
DOE OSTI2025

Ultrahigh-pressure crystallographic passage towards metallic hydrogen

The structural evolution of molecular hydrogen H 2 under multi-megabar compression and its relation to atomic metallic hydrogen is a key unsolved problem in condensed-matter physics. Although dozens of crystal structures have been proposed by theory, only one, the simple hexagonal-close-packed (hcp) structure of only spherical disordered H 2 , has been previously confirmed in experiments. Through advancing nano-focused synchrotron X-ray probes, here we report the observation of the transition from hcp H 2 to a post-hcp structure with a six-fold larger supercell at pressures above 212 GPa, indicating the change of spherical H 2 to various ordered configurations. Theoretical calculations based on our XRD results found a time-averaged structure model in the space group $P\bar{6}2c$ with alternating layers of spherically disordered H 2 and new graphene-like layers consisting of H 2 trimers (H 6 ) formed by the association of three H 2 molecules. Here, this supercell has not been reported by any previous theoretical study for the post-hcp phase, but is close to a number of theoretical models with mixed-layer structures. The evidence of a structural transition beyond hcp establishes the trend of H 2 molecular association towards polymerization at extreme pressures, giving clues about the nature of the molecular-to-atomic transition of metallic hydrogen. Considering the spectroscopic behaviours that show strong vibrational and bending peaks of H 2 up to 400 GPa, it would be prudent to speculate the continuation of hydrogen molecular polymerization up to its metallization.

Ji, Cheng [Center for High Pressure Science and Te↗
DOE OSTI2022

Radiolytic Gas Production from Aluminum Coupons (Alloy 1100 and 6061) in Helium Environments—Assessing the Extended Storage of Aluminum Clad Spent Nuclear Fuel

Corrosion of aluminium alloy clad nuclear fuel, during reactor operation and under subsequent wet storage conditions, promotes the formation of aluminium hydroxide and oxyhydroxide layers. These hydrated mineral phases and the chemisorbed and physisorbed waters on their surfaces are susceptible to radiation-induced processes that yield molecular hydrogen gas (H 2 ), which has the potential to complicate the long-term storage and disposal of aluminium clad nuclear fuel through flammable and explosive gas mixture formation, alloy embrittlement, and pressurization. Here, we present a systematic study of the radiolytic formation of H 2 from aluminium alloy 1100 (AA1100) and 6061 (AA6061) coupons in “dry” (~0% relative humidity) and “wet” (50% relative humidity) helium environments. Cobalt-60 gamma irradiation of both aluminium alloy types promoted the formation of H 2 , which increased linearly up to ~2 MGy, and afforded G-values of 1.1 ± 0.1 and 2.9 ± 0.1 for “dry” and “wet” AA1100, and 2.7 ± 0.1 and 1.7 ± 0.1 for “dry” and “wet” AA6061. The negative correlation of H 2 production with relative humidity for AA6061 is in stark contrast to AA1100 and is attributed to differences in the extent of corrosion and varying amounts of adsorbed water in the two alloys, as characterized using optical profilometry, scanning electron microscopy, Raman spectroscopy, and X-ray diffraction techniques.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2024

Constraining dark matter-proton scattering from molecular cloud ionization

Optically dense clouds in the interstellar medium composed predominantly of molecular hydrogen, known as molecular clouds, are sensitive to energy injection in the form of photon absorption, cosmic-ray scattering, and dark matter (DM) scattering. The ionization rates in dense molecular clouds are heavily constrained by observations of abundances of various molecular tracers. Recent studies have set constraints on the DM-electron scattering cross section using measurements of ionization rates in dense molecular clouds. Here we calculate the analogous bounds on the DM-proton cross section using the molecular Migdal effect, recently adapted from the neutron scattering literature to the DM context. These bounds may be the strongest limits on a strongly coupled DM subfraction, and represent the first application of the Migdal effect to astrophysical systems. Published by the American Physical Society 2024

Astronomy & Astrophysics↗
DOE OSTI2020

Materials Data on MgH20C4Br2(N4O3)2 by Materials Project

MgC4H4(N2O3)2(NH2)4(H2)2(H2Br)2 crystallizes in the monoclinic P2_1/c space group. The structure is zero-dimensional and consists of eight ammonia molecules, four hydrogen molecules, four molecular hydrogen;hydrobromide molecules, and two MgC4H4(N2O3)2 clusters. In each MgC4H4(N2O3)2 cluster, Mg2+ is bonded in an octahedral geometry to six O2- atoms. There are a spread of Mg–O bond distances ranging from 1.97–2.23 Å. There are two inequivalent C4+ sites. In the first C4+ site, C4+ is bonded in a 1-coordinate geometry to two N3- and one O2- atom. Both C–N bond lengths are 1.33 Å. The C–O bond length is 1.26 Å. In the second C4+ site, C4+ is bonded in a single-bond geometry to one O2- atom. The C–O bond length is 1.17 Å. There are two inequivalent N3- sites. In the first N3- site, N3- is bonded in a distorted single-bond geometry to one C4+ atom. In the second N3- site, N3- is bonded in a distorted single-bond geometry to one C4+ atom. There are two inequivalent H1+ sites. In the first H1+ site, H1+ is bonded in a single-bond geometry to one O2- atom. The H–O bond length is 0.98 Å. In the second H1+ site, H1+ is bonded in a single-bond geometry to one O2- atom. The H–O bond length is 0.98 Å. There are three inequivalent O2- sites. In the first O2- site, O2- is bonded in a bent 120 degrees geometry to one Mg2+ and one C4+ atom. In the second O2- site, O2- is bonded in a bent 150 degrees geometry to one Mg2+ and one C4+ atom. In the third O2- site, O2- is bonded in a distorted trigonal planar geometry to one Mg2+ and two H1+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on NaCaB5(H7O4)3 by Materials Project

NaCaB5H13O12(H2)4 crystallizes in the triclinic P-1 space group. The structure is three-dimensional and consists of two hydrogen molecules, four molecular hydrogen molecules, and one NaCaB5H13O12 framework. In the NaCaB5H13O12 framework, Na is bonded in a 7-coordinate geometry to five H and two equivalent O atoms. There are a spread of Na–H bond distances ranging from 2.33–2.52 Å. There are one shorter (2.39 Å) and one longer (2.57 Å) Na–O bond lengths. Ca is bonded in a 6-coordinate geometry to one H and five O atoms. The Ca–H bond length is 2.45 Å. There are a spread of Ca–O bond distances ranging from 2.30–2.54 Å. There are five inequivalent B sites. In the first B site, B is bonded in a trigonal planar geometry to three O atoms. There are a spread of B–O bond distances ranging from 1.36–1.43 Å. In the second B site, B is bonded to four O atoms to form corner-sharing BO4 tetrahedra. There are a spread of B–O bond distances ranging from 1.47–1.50 Å. In the third B site, B is bonded in a trigonal planar geometry to three O atoms. There is two shorter (1.37 Å) and one longer (1.40 Å) B–O bond length. In the fourth B site, B is bonded to four O atoms to form corner-sharing BO4 tetrahedra. There are a spread of B–O bond distances ranging from 1.46–1.52 Å. In the fifth B site, B is bonded to four O atoms to form corner-sharing BO4 tetrahedra. There are a spread of B–O bond distances ranging from 1.48–1.50 Å. There are thirteen inequivalent H sites. In the first H site, H is bonded in a distorted L-shaped geometry to one Na and one H atom. The H–H bond length is 0.77 Å. In the second H site, H is bonded in a single-bond geometry to one O atom. The H–O bond length is 0.98 Å. In the third H site, H is bonded in an L-shaped geometry to one Ca and one H atom. The H–H bond length is 0.76 Å. In the fourth H site, H is bonded in a single-bond geometry to one O atom. The H–O bond length is 0.98 Å. In the fifth H site, H is bonded in a single-bond geometry to one Na and one H atom. In the sixth H site, H is bonded in a single-bond geometry to one O atom. The H–O bond length is 1.00 Å. In the seventh H site, H is bonded in a distorted single-bond geometry to two O atoms. There is one shorter (1.00 Å) and one longer (1.67 Å) H–O bond length. In the eighth H site, H is bonded in a distorted single-bond geometry to one Na atom. In the ninth H site, H is bonded in a distorted linear geometry to two O atoms. There is one shorter (1.02 Å) and one longer (1.62 Å) H–O bond length. In the tenth H site, H is bonded in a distorted L-shaped geometry to one Na and one H atom. The H–H bond length is 0.75 Å. In the eleventh H site, H is bonded in a single-bond geometry to one O atom. The H–O bond length is 0.97 Å. In the twelfth H site, H is bonded in a distorted single-bond geometry to one Na and one H atom. In the thirteenth H site, H is bonded in a single-bond geometry to one H atom. There are twelve inequivalent O sites. In the first O site, O is bonded in a 2-coordinate geometry to two equivalent Na, one B, and one H atom. In the second O site, O is bonded in a 2-coordinate geometry to one B and two H atoms. In the third O site, O is bonded in a 3-coordinate geometry to one B and two H atoms. In the fourth O site, O is bonded in a bent 120 degrees geometry to two B atoms. In the fifth O site, O is bonded in a bent 120 degrees geometry to two B atoms. In the sixth O site, O is bonded in a bent 120 degrees geometry to two B atoms. In the seventh O site, O is bonded in a distorted trigonal planar geometry to one Ca and two B atoms. In the eighth O site, O is bonded in a distorted bent 120 degrees geometry to two equivalent Ca and two B atoms. In the ninth O site, O is bonded in a 2-coordinate geometry to one Ca, one B, and one H atom. In the tenth O site, O is bonded in a distorted water-like geometry to one B and one H atom. In the eleventh O site, O is bonded in a 2-coordinate geometry to one Ca, one B, and one H atom. In the twelfth O site, O is bonded in a bent 120 degrees geometry to two B atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on ZnH12(NO3)2 by Materials Project

ZnNHO3(H2)5HNO3 crystallizes in the monoclinic P2_1/c space group. The structure is zero-dimensional and consists of sixteen hydrogen molecules, four molecular hydrogen molecules, four nitric acid molecules, and four ZnNHO3 clusters. In each ZnNHO3 cluster, Zn2+ is bonded in a distorted linear geometry to one H1+ and one O2- atom. The Zn–H bond length is 1.51 Å. The Zn–O bond length is 1.89 Å. N1- is bonded in a trigonal planar geometry to three O2- atoms. There are a spread of N–O bond distances ranging from 1.23–1.37 Å. H1+ is bonded in a single-bond geometry to one Zn2+ atom. There are three inequivalent O2- sites. In the first O2- site, O2- is bonded in a bent 120 degrees geometry to one Zn2+ and one N1- atom. In the second O2- site, O2- is bonded in a single-bond geometry to one N1- atom. In the third O2- site, O2- is bonded in a single-bond geometry to one N1- atom.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on UH14(SeO5)2 by Materials Project

(UH3(SeO5)2)2(H2)11 crystallizes in the monoclinic P2_1/c space group. The structure is two-dimensional and consists of sixteen hydrogen molecules; four molecular hydrogen molecules; and one UH3(SeO5)2 sheet oriented in the (1, 0, 0) direction. In the UH3(SeO5)2 sheet, U4+ is bonded to seven O2- atoms to form distorted UO7 pentagonal bipyramids that share corners with three equivalent SeO4 tetrahedra and corners with two equivalent SeO4 trigonal pyramids. There are a spread of U–O bond distances ranging from 1.80–2.49 Å. There are three inequivalent H1+ sites. In the first H1+ site, H1+ is bonded in a single-bond geometry to one O2- atom. The H–O bond length is 1.00 Å. In the second H1+ site, H1+ is bonded in a single-bond geometry to one O2- atom. The H–O bond length is 1.01 Å. In the third H1+ site, H1+ is bonded in a single-bond geometry to one O2- atom. The H–O bond length is 0.98 Å. There are two inequivalent Se1+ sites. In the first Se1+ site, Se1+ is bonded to four O2- atoms to form SeO4 tetrahedra that share corners with three equivalent UO7 pentagonal bipyramids. There are a spread of Se–O bond distances ranging from 1.65–1.76 Å. In the second Se1+ site, Se1+ is bonded to four O2- atoms to form distorted SeO4 trigonal pyramids that share corners with two equivalent UO7 pentagonal bipyramids. There are a spread of Se–O bond distances ranging from 1.69–1.97 Å. There are ten inequivalent O2- sites. In the first O2- site, O2- is bonded in a distorted bent 150 degrees geometry to one U4+ and one Se1+ atom. In the second O2- site, O2- is bonded in a distorted single-bond geometry to one H1+ and one Se1+ atom. In the third O2- site, O2- is bonded in a water-like geometry to one H1+ and one Se1+ atom. In the fourth O2- site, O2- is bonded in a 2-coordinate geometry to one U4+ and one Se1+ atom. In the fifth O2- site, O2- is bonded in a bent 150 degrees geometry to one U4+ and one Se1+ atom. In the sixth O2- site, O2- is bonded in a single-bond geometry to one U4+ atom. In the seventh O2- site, O2- is bonded in a distorted water-like geometry to one H1+ and one Se1+ atom. In the eighth O2- site, O2- is bonded in a distorted bent 120 degrees geometry to one U4+ and one Se1+ atom. In the ninth O2- site, O2- is bonded in a distorted bent 150 degrees geometry to one U4+ and one Se1+ atom. In the tenth O2- site, O2- is bonded in a distorted single-bond geometry to one U4+ atom.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Fe6P4H23O21 by Materials Project

Fe6P4(H3O7)3(H2)7 crystallizes in the monoclinic C2/c space group. The structure is three-dimensional and consists of sixteen hydrogen molecules, eight molecular hydrogen molecules, and one Fe6P4(H3O7)3 framework. In the Fe6P4(H3O7)3 framework, there are four inequivalent Fe+2.50+ sites. In the first Fe+2.50+ site, Fe+2.50+ is bonded to four O2- atoms to form distorted FeO4 tetrahedra that share corners with two FeO6 octahedra, a cornercorner with one FeO4 tetrahedra, a cornercorner with one PO4 tetrahedra, and a cornercorner with one PO4 trigonal pyramid. The corner-sharing octahedra tilt angles range from 54–63°. There are a spread of Fe–O bond distances ranging from 1.97–2.09 Å. In the second Fe+2.50+ site, Fe+2.50+ is bonded to six O2- atoms to form distorted FeO6 octahedra that share a cornercorner with one FeO4 tetrahedra, corners with two equivalent PO4 tetrahedra, corners with two equivalent PO4 trigonal pyramids, and a faceface with one FeO6 octahedra. There are a spread of Fe–O bond distances ranging from 2.00–2.29 Å. In the third Fe+2.50+ site, Fe+2.50+ is bonded to six O2- atoms to form FeO6 octahedra that share corners with two equivalent FeO4 tetrahedra, corners with four equivalent PO4 tetrahedra, and faces with two equivalent FeO6 octahedra. There are a spread of Fe–O bond distances ranging from 2.02–2.11 Å. In the fourth Fe+2.50+ site, Fe+2.50+ is bonded in a square co-planar geometry to four O2- atoms. There are two shorter (1.98 Å) and two longer (2.14 Å) Fe–O bond lengths. There are two inequivalent P1+ sites. In the first P1+ site, P1+ is bonded to four O2- atoms to form PO4 tetrahedra that share corners with four FeO6 octahedra and a cornercorner with one FeO4 tetrahedra. The corner-sharing octahedra tilt angles range from 28–57°. There are a spread of P–O bond distances ranging from 1.54–1.57 Å. In the second P1+ site, P1+ is bonded to four O2- atoms to form PO4 trigonal pyramids that share corners with two equivalent FeO6 octahedra and a cornercorner with one FeO4 tetrahedra. The corner-sharing octahedra tilt angles range from 32–61°. There are a spread of P–O bond distances ranging from 1.49–1.91 Å. There are five inequivalent H1+ sites. In the first H1+ site, H1+ is bonded in a single-bond geometry to one O2- atom. The H–O bond length is 0.98 Å. In the second H1+ site, H1+ is bonded in a single-bond geometry to one O2- atom. The H–O bond length is 0.99 Å. In the third H1+ site, H1+ is bonded in a single-bond geometry to one O2- atom. The H–O bond length is 0.97 Å. In the fourth H1+ site, H1+ is bonded in a single-bond geometry to one O2- atom. The H–O bond length is 0.98 Å. In the fifth H1+ site, H1+ is bonded in a single-bond geometry to one O2- atom. The H–O bond length is 0.99 Å. There are eleven inequivalent O2- sites. In the first O2- site, O2- is bonded in a distorted single-bond geometry to two Fe+2.50+ and one H1+ atom. In the second O2- site, O2- is bonded in a bent 120 degrees geometry to one Fe+2.50+ and one P1+ atom. In the third O2- site, O2- is bonded in a distorted single-bond geometry to three Fe+2.50+ and one H1+ atom. In the fourth O2- site, O2- is bonded in a bent 150 degrees geometry to one Fe+2.50+ and one P1+ atom. In the fifth O2- site, O2- is bonded in a distorted trigonal non-coplanar geometry to one P1+ and two H1+ atoms. In the sixth O2- site, O2- is bonded in a 3-coordinate geometry to two Fe+2.50+ and one P1+ atom. In the seventh O2- site, O2- is bonded in a distorted trigonal planar geometry to two equivalent Fe+2.50+ and one H1+ atom. In the eighth O2- site, O2- is bonded in a 3-coordinate geometry to two Fe+2.50+ and one P1+ atom. In the ninth O2- site, O2- is bonded in a bent 120 degrees geometry to one Fe+2.50+ and one P1+ atom. In the tenth O2- site, O2- is bonded in a distorted bent 150 degrees geometry to one Fe+2.50+ and one P1+ atom. In the eleventh O2- site, O2- is bonded in a bent 150 degrees geometry to one Fe+2.50+ and one P1+ atom.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Basic Energy Sciences Roundtable: Foundational Science for Carbon-Neutral Hydrogen Technologies

The amount of molecular hydrogen used worldwide is enormous; about 70 million metric tons are produced globally every year, with approximately 10 million metric tons produced within the U.S. alone. 1 Hydrogen is used primarily by the industrial sector for oil refining; chemical production, especially for ammonia; steel manufacturing; and transportation fuels. With the recent announcement of the Hydrogen Shot, the first U.S. Department of Energy (DOE) Energy Earthshot, the DOE declared a near-term focus on “accelerating breakthroughs of more abundant, affordable, and reliable clean energy solutions within the decade.” Consequently, there is a compelling need for novel approaches to enable hydrogen processes and technologies that do not emit carbon dioxide (i.e., are carbon-neutral). Innovative hydrogen research and development is required to impact how hydrogen is produced, stored, transported, converted, and used. Although progress has been made over the previous two decades, fundamental research can play a critical role in overcoming the technical hurdles that continue to limit implementation of economically viable systems and processes for carbon-neutral hydrogen technologies.

08 HYDROGEN↗
DOE OSTI2023

Materials Design Directions for Solar Thermochemical Water Splitting

The sustainable, economical production of molecular hydrogen is a crucial component of a net zero-greenhouse-gas-emissions future. Solar thermochemical water splitting (STWS) offers a renewable route to hydrogen with the potential to help decarbonize several industries, including transportation, manufacturing, mining, metals processing, and electricity generation, as well as provide sustainable hydrogen as a chemical feedstock. STWS uses high temperatures generated from concentrated sunlight or other sustainable means for high-temperature heat to produce hydrogen and oxygen from steam. For example, in its simplest form of a two-step thermochemical cycle, a redox-active metal oxide is heated to ≈1700-2000 K, driving off molecular oxygen while producing oxygen vacancies in the material. The reduced metal oxide then cools (ideally with the extracted heat recuperated for re-use) and, in a separate step, comes into contact with steam, which reacts with oxygen vacancies to produce molecular hydrogen while recovering the original state of the metal oxide. Despite its promising use of the entire solar spectrum to split water thermochemically, the current estimated cost of hydrogen produced via STWS is ≈4-6× the U.S. Department of Energy (DOE) Hydrogen Shot target value of $1/kg. One contributing approach to bridging this cost gap is the design of new materials with improved thermodynamic properties to enable higher efficiencies. The state-of-the-art (SOA) redox-active metal oxide for STWS is ceria (CeO 2 ), due to its close to optimal, although too high, oxygen vacancy formation enthalpy and large configurational and electronic entropy of reduction. However, ceria requires high operating temperatures and its efficiency is insufficient. Therefore, efforts to increase the efficiency of STWS cycles have focused on further optimizing oxygen vacancy formation enthalpies and augmenting the reduction entropy via substitution or doping and materials discovery schemes. Examples of the latter include the perovskites BaCe 0.25 Mn 0.75 O 3 and (Ca,Ce)(Ti,Mn)O 3 . These efforts and others have revealed intuitive chemical principles for the efficient and systematic design of more effective materials, such as the strong correlation between the enthalpies of crystal bond dissociation and solid-state cation reduction with the enthalpy of oxygen vacancy formation, as well as configurational entropy augmentation via the coexistence of two or more redox-active cation sublattices. The purpose of this chapter is to prepare the reader with an up-to-date account of STWS redox-active materials, both the SOA and promising newcomers, as well as to provide chemically intuitive strategies for improving their cycle efficiencies through materials design – in conjunction with ongoing efforts in reactor engineering and gas separations – to reach the cost points for commercial viability. First, we will introduce the thermodynamics of STWS using a two-step, metal-oxide, thermochemical cycle with economics in mind. We also will compare the pros and cons of processes that do or do not involve phase changes. Second, we will describe the qualities that make ceria the SOA STWS redox-active material, as well as its limitations. Third, we will survey some of the most promising candidates to date in the search for materials to supplant ceria, emphasizing the post-ternary, metal-oxide-perovskite alloys. Lastly, we will enumerate and discuss the following materials design directions for STWS redox-active materials: crystal reduction potentials as a proxy for oxygen vacancy formation enthalpies, engineering the electronic and configurational entropy of reduction via f-shells and simultaneous redox, and vetting materials stability via temperature-dependent phase diagrams and melting-point prediction.

08 HYDROGEN↗
DOE OSTI2022

A Molecular Gas Ring Hidden in the Sombrero Galaxy

We present Herschel, ALMA, and MUSE observations of the molecular ring of Messier 104, also known as the Sombrero galaxy. These previously unpublished archival data shed new light on the content of the interstellar medium of M104. In particular, molecular hydrogen measured by CO emission and dust measured by far-infrared light are uniformly distributed along the ring. The ionized gas revealed by Hα and [C II] emission is distributed in knots along the ring. Despite being classified as an SAa galaxy, M104 displays features typical of early-type galaxies. We therefore compared its [C II] and dust emission to a sample of early-type galaxies observed with Herschel and SOFIA. The [C II]/FIR ratio of M104 is much lower than that of typical star-forming galaxies and is instead much more similar to that of early-type galaxies. By classifying regions using optical emission line diagnostics, we also find that regions classified as H II lie closer to star-forming galaxies in the [C II]/FIR diagram than those classified as low-ionization emission regions. The good match between [C II] and Hα emission, in conjunction with the lack of correlation between CO emission and star formation, suggests that there is very limited active star formation along the ring and that most of the [C II] emission is from ionized and neutral atomic gas rather than molecular gas. From the total intensity of the CO line, we estimate a molecular hydrogen mass of 0.9 × 10 9 M ⊙ , a value intermediate between those of early-type galaxies and the content of the molecular ring of our galaxy.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2025

Introducing metal–sulfur active sites in metal–organic frameworks via post-synthetic modification for hydrogenation catalysis

Metal–sulfur active sites play a central role in catalytic processes such as hydrogenation and dehydrogenation, yet the majority of active sites in these compounds reside on the surfaces and edges of catalyst particles, limiting overall efficiency. Here we present a strategy to embed metal–sulfur active sites into metal–organic frameworks (MOFs) by converting bridging or terminal chloride ligands into hydroxide and subsequently into sulfide groups through post-synthetic modification. We apply this method to two representative MOF families: one featuring one-dimensional metal–chloride chains and another containing discrete multinuclear metal clusters. Crystallographic and spectroscopic analyses confirm structural integrity and sulfide incorporation, and the transformation is monitored by in situ total scattering methods. The sulfided MOFs display enhanced catalytic activity in the selective hydrogenation of nitroarenes using molecular hydrogen. Density functional theory calculations indicate that sulfur incorporation promotes homolytic metal–ligand bond cleavage and facilitates H 2 activation. This work establishes an approach to construct MOFs featuring accessible metal–sulfide sites.

Catalyst synthesis↗
DOE OSTI2020

Materials Data on H4NF2 by Materials Project

N2(H2)3(HF2)2 crystallizes in the trigonal R-3m space group. The structure is zero-dimensional and consists of six hydrogen fluoride hydrogen fluoride molecules, six molecular hydrogen molecules, and three nitrogen molecules.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on H2 by Materials Project

H2 is Cyanogen Chloride-derived structured and crystallizes in the triclinic P-1 space group. The structure is zero-dimensional and consists of four hydrogen molecules and four molecular hydrogen molecules.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Role of Metal Cocatalysts in the Photocatalytic Production of Hydrogen from Water Revisited

The use of photocatalysts to promote the production of molecular hydrogen from water, following the so-called water splitting reaction, continues to be a promising route for the green production of fuels. The molecular basis of this photocatalysis is the photoexcitation of electrons from the valence band of semiconductors to their conduction band, from which they can be transferred to chemical reactants, protons in the case of water, to promote a reduction reaction. The mechanism by which such a process takes place has been studied extensively using titanium oxide, a simple material that fulfills most requirements for water splitting. However, photocatalysis with TiO 2 tends to be highly inefficient; a cocatalyst, commonly a late transition metal (Au, Pt) in nanoparticle form, needs to be added to facilitate the production of H 2 . The metal is widely believed to help with the scavenging of the excited electrons from the conduction band of the semiconductor in order to prevent their recombination with the accompanying hole formed in the valence band, a step that cancels the initial photon absorption and competes with the photolytic chemical reduction. Here we review and analyze the molecular basis for that mechanism and argue for an alternative explanation, that the role of the metal is to help with the recombination of the atomic hydrogen atoms produced by proton reduction on the semiconductor surface instead. First, we summarize what is known about the electronic structure of these photocatalysts and how the electronic levels need to line up for the reduction of protons in water to be feasible. Next, we review the current understanding of the dynamics of the steps associated with the absorption of photons, the de-excitation via electron–hole pair recombination and fluorescence decay, and the electronic transitions that lead to proton reduction, and contrast those with the rates of the chemical steps required to produce molecular hydrogen. The following section addresses the changes introduced by the addition of the metal cocatalyst, comparatively evaluating its role as either an electron scavenger or a promoter of the recombination of hydrogen atoms. A discussion of the viable chemical mechanisms for the latter pathway is included. Finally, we briefly mention other associated aspects of this photocatalysis, including the possible promotion of H 2 production with visible light via resonant excitation of the surface plasmon of Au nanoparticles, the use of single-metal (Au, Pt) atom catalysts and of yolk–shell nanostructures, and the reduction of organic molecules. We end with a brief personal perspective on the possible generality of the concepts introduced in this Critical Review.

08 HYDROGEN↗
DOE OSTI2022

Anisotropic angular scattering models of elastic electron-neutral collisions for Monte Carlo plasma simulations

Many laboratory and industrial plasma applications require accurate modeling techniques to understand the interplay between microscopic and macroscopic processes. A prime example of this interplay is how particle and Monte Carlo (MC) simulation codes describe angular scattering of electrons following elastic scattering events. The forward peaked nature of high energy electron elastic scattering is relatively trivial to accurately describe in plasma simulations. However, for lower energy collisions, which produce near isotropic or backward peaked differential cross sections, there is not a strong consensus among the plasma modeling community on how to best describe these angular scattering trends. Here, in this study, we propose a systematic method to approximate the aforementioned non-trivial angular scattering behavior with a formula that can be readily implemented in particle-in-cell (PIC) and/or MC plasma simulation codes. The present approach is specifically applied to fusion relevant atomic hydrogen and helium, as well as for molecular hydrogen, and results are also applicable to the atomic isotopes and homonuclear molecular isotopologues of these species. Comparisons between the present angular distribution function and benchmark scattering data were used to validate the proposed models. In addition, two-term Boltzmann calculations and PIC direct simulation MC simulations revealed that the proposed angular distribution function is accurate, agreeing very well with benchmark convergent close-coupling scattering calculations, and electron transport measurements. These studies confirmed that the present angular distribution function model can be utilized without the need of renormalization to the momentum transfer cross section (as opposed to using the elastic scattering integrated cross section), which has been suggested by several studies in order to correct for deficient angular scattering models, and to agree with transport measurements. Hence, the present anisotropic angular scattering model can be utilized to accurately model the momentum transfer as well as the electron trajectories of elastic collisions.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2021

Milestone 1.2.9: Radiolytic Gas Generation Measurements from Helium Backfilled Samples of AA1100 and AA6061 Coupons

Nearly 18 metric tons of aluminum-clad spent nuclear fuel (ASNF) is safely managed by the U.S. Department of Energy (DOE). These assemblies are currently in interim storage, with the intention of extended storage (>50 years) until final disposal. Strategies for the continued safe storage of this material are under evaluation, of which a key criterion is the extent of molecular hydrogen gas (H2) formation from the radiolysis of hydrated (oxy)hydroxide aluminum corrosion layers arising from in-reactor and wet storage conditions. Radiation-induced H2 formation has the potential to compromise cladding and storage canister integrity, in addition to promoting the formation of unfavorable gaseous environments. Consequently, understanding this radiation-induced phenomenon is essential for the development of predictive modeling capabilities to support technical considerations and the identification of radiation related challenges for the extended storage of ASNF. Here, we report radiolytic H2 yields (G-values, G(H2)) from the gamma irradiation of ‘pristine’ and pre-corroded aluminum coupons in helium (He) environments as a function of alloy composition (AA1100 and AA6061), relative humidity, and absorbed gamma dose. Measured yields were lower than corresponding values reported for argon environments, a positive result for proposed extended dry storage strategies that would employ helium as a backfill gas. Interestingly, the presented G(H2)He values are comparable to those previously measured in nitrogen environments, suggesting a He mediated H2 inhibition process, attributed here to Penning ionization.

38 RADIATION CHEMISTRY, RADIOCHEMISTRY, AND NUCLEA↗