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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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Preparation of metals and compounds by radiation induced chemical reactions involves irradiation of metal salt solutions with high energy electrons. This technique offers a method for the preparation of high purity metals with minimum contamination from the container material or the cover gas.
Zintl phases containing rare-earth metals have gained attention due to their magnetic, electronic, and thermoelectric properties. Eu 5.08 Al 3 Sb 6 is a new structure type (monoclinic space group C2/m) that can be described as a pseudorock-salt EuSb motif with the Eu-centered Sb octahedra at the origin of the unit cell, and on the C-face center, containing either Eu (8%) or an Al 4 tetrahedron modeled as a dual tetrahedron (37.5%). The complete solid solution of Eu 5.08–x Sr x Al 3 Sb 6 can be prepared; however, the cation totals vacillate from 5 to 5.24 depending on the Al content. Al K-edge XANES shows a shift to higher energy relative to the Al metal but at slightly lower energy relative to AlSb, indicating an intermediate oxidation state closer to +3 than 0. The lack of an Al K-edge shift with the incorporation of Sr suggests that changes in Sr content do not have a meaningful impact on the electronics of the Al tetrahedra. Investigation of the solid solution structures provides evidence for classifying this structure type as a polar intermetallic phase with variable composition. Magnetization measurements were collected for the solid solution and show complex magnetic ordering with competing ferromagnetic and antiferromagnetic interactions as the Sr content increases.
The absolute band-edge potentials of semiconductors, i.e., the conduction-band minimum, valence-band maximum, and their relative positions to solution redox potentials, are often invoked as design principles for photoelectrochemical (PEC) devices, especially for particulate photocatalysts. Here we show that reliance on these criteria is not necessary and limits the exploration of materials that will advance the fields of photoelectrochemistry, photochemistry, and photocatalysis. We discuss how i) band-edge energies are not singular parameters and instead shift with pH, electrolyte type, and surface chemistry; ii) the free energy of electrons and holes in comparison to that of solution redox couples dictates overall reaction spontaneity and thus reactivity; and iii) favorable charge-transfer kinetics can occur even when the relevant electrolyte redox potential(s) appear ‘outside’ the bandgap, enabled by the inversion or accumulation of electronic charge at the semiconductor surface. As a result, this discussion informs design principles for photocatalyst systems engineering for both one-electron redox reactions as well as for more complex multi-electron transfer reactions (e.g, H 2 evolution, H 2 O oxidation, CO 2 reduction).
Magnesium batteries have long been pursued as potentially low-cost, high-energy and safe alternatives to Li-ion batteries. However, Mg 2+ interacts strongly with electrolyte solutions and cathode materials, leading to sluggish ion dissociation and diffusion, and consequently low power output. Here we report a heterogeneous enolization chemistry involving carbonyl reduction (C=O ↔ C–O-), which bypasses the dissociation and diffusion difficulties, enabling fast and reversible redox processes. This kinetically favoured cathode is coupled with a tailored, weakly coordinating boron cluster-based electrolyte that allows for dendrite-free Mg plating/stripping at a current density of 20 mA cm -2 . The combination affords a Mg battery that delivers a specific power of up to 30.4 kW kg -1 , nearly two orders of magnitude higher than that of state-of-the-art Mg batteries. Here, the cathode and electrolyte chemistries elucidated here propel the development of magnesium batteries and would accelerate the adoption of this low-cost and safe battery technology.
Electrolytes in many lithium ion batteries decompose at the low potentials near the anode. The decomposition products form a layer termed the solid electrolyte interphase (SEI). The composition and growth of the SEI layer significantly affect both the capacity fade and safety of lithium ion batteries. However, SEI formation and growth kinetics are not well understood. In this work, we present an extension of the Reaction Mechanism Generator (RMG) software to automatically generate mechanisms for SEI formation. We extend RMG’s solvation correction framework to account for kinetic solvent effects and demonstrate the accuracy of our technique. We calculate thermochemical parameters for 252 species and rate coefficients for 69 reactions, most with associated solvation corrections. This and additional quantum chemistry data are used to extend RMG’s thermodynamic group additivity and solute parameter estimation schemes to handle lithiated species and add 14 new reaction families to RMG. RMG is additionally extended to simulate electrocatalytic systems. Lastly, we demonstrate RMG on the decomposition of acetonitrile and ethylene carbonate near a battery anode. Furthermore, while this framework does not yet resolve individual ions, as appropriate thermochemistry estimators are not available, and thus, cannot yet resolve more complex electrochemical pathways, RMG is able to generate reasonable pathways for SEI formation that match literature pathways and products. In particular, RMG identifies a new important reaction pathway that is not present in literature.
The exploitation of singlet fission (SF) in photovoltaic devices is restricted by the limited number of SF materials available and the conflicting requirement of intermolecular interactions to satisfy both efficient SF and subsequent triplet extraction. Intramolecular SF (iSF) represents an emerging alternative and may prove simpler to implement in devices. Here, on account of the excellent chemical structure tunability and solution processability, conjugated polymers have emerged as promising candidates for iSF materials despite being largely underexplored. It remains a significant challenge to develop SF-capable conjugated polymers and achieve efficient dissociation of the formed triplet pairs simultaneously. In this contribution, we present a new iSF material in a para-azaquinodimethane-based quinoidal conjugated polymer. Using transient optical techniques, we show that an ultrafast iSF process dominates the deactivation of the excited state in such polymer, featuring ultrafast population (<1 ps) and stepwise dissociation of triplet pairs. Notably, these multiexciton states could further diffuse apart to produce long-lived free triplets (tens of μs) in strongly coupled aggregates in solid thin film. Such findings not only introduce a new iSF-active conjugated polymer to the rare SF material family but also shed unique insight into interchain interaction-promoted triplet pair dissociation in aggregates of conjugated polymers, thus openning new avenues for developing next-generation SF-based photovoltaic materials.
The transition to new energy resources is driving the need for efficient energy storage. Redox flow batteries (RFBs) are a promising solution due to their flexible design and safer materials, particularly for long-duration storage applications. Despite these advantages, RFB technologies still have considerable room for growth in terms of utilizing all of their available energy storage density. Herein, we assess RFB energy storage density utilization trends for multiple chemistries by accounting for their unique thermodynamic limits, energy efficiencies, and charge capacity constraints. Of the RFBs chemistries analyzed, most still use less than 60% of their theoretical energy storage capacity. The conventional all-vanadium RFB was the closest to its thermodynamic limit available. Moreover, the volumetric footprint and electrolyte cost analyses demonstrate the real-world implications of these inefficiencies. This analysis further indicates that future studies would benefit from clearer reporting of two key quantities: discharge efficiency, which is more directly tied to practically recoverable energy density than round-trip energy efficiency, and state-of-charge or capacity-utilization limits, which govern access to theoretical storage capacity. More consistent reporting of these factors would improve the accuracy and comparability of energy storage utilization analyses across RFB chemistries.
The diffusive isothermal partitioning of solute in a layered two-phase material has been analyzed to help elucidate the phenomenon of solute partitioning in multiphase lunar and terrestrial materials and to estimate the cooling history of samples. After reviewing the physical chemistry of partitioning and the case of an infinite one-dimensional diffusion couple, we solve in analytic form the case of a finite one-dimensional couple. The solution can be used to estimate cooling histories or to interpret laboratory experiments on partitioning. A sample calculation is included.
With the advent of supercomputers, modern computational chemistry algorithms and codes, a powerful tool was created to help fill NASA's continuing need for information on the properties of matter in hostile or unusual environments. Computational resources provided under the National Aerodynamics Simulator (NAS) program were a cornerstone for recent advancements in this field. Properties of gases, materials, and their interactions can be determined from solutions of the governing equations. In the case of gases, for example, radiative transition probabilites per particle, bond-dissociation energies, and rates of simple chemical reactions can be determined computationally as reliably as from experiment. The data are proving to be quite valuable in providing inputs to real-gas flow simulation codes used to compute aerothermodynamic loads on NASA's aeroassist orbital transfer vehicles and a host of problems related to the National Aerospace Plane Program. Although more approximate, similar solutions can be obtained for ensembles of atoms simulating small particles of materials with and without the presence of gases. Computational chemistry has application in studying catalysis, properties of polymers, all of interest to various NASA missions, including those previously mentioned. In addition to discussing these applications of computational chemistry within NASA, the governing equations and the need for supercomputers for their solution is outlined.
The effective removal of radioactive 99 TcO 4 – anion from nuclear wastewater remains a very difficult unsolved problem. Functional adsorbent materials with high stability, anion-exchange capacity, excellent selectivity, and recyclability are much needed to solve this problem. In this work, we designed two stable cationic metal–organic frameworks (MOFs)—Zr-tcbp-Me and Zr-tcpp-Me—for possible use as adsorbent materials to remove 99 TcO 4 – . Both compounds were synthesized by solvothermal reactions of the tetracarboxylate ligand with zirconium salt, followed by postsynthetic modification (N-methylation). Here, the crystallinity of both zirconium-based MOFs can be well retained under harsh conditions, and they exhibit high adsorption capacity and selectivity toward ReO 4 – anion, a nonradioactive analogue of 99 TcO 4 – . Zr-tcbp-Me and Zr-tcpp-Me demonstrate the highest framework stability toward acidity among all previously reported cationic MOFs that have been tested for perrhenate removal from wastewater.
In this work, bulk turbostratic graphitic carbon of varying levels of disorder and chemical compositions has been synthesized by a direct synthesis method in the temperature range of 750–1100 °C, with a focus on boron incorporation within the graphitic lattice. The atomistic and electronic/vibrational structures were characterized by X-ray diffraction, energy-dispersive X-ray spectroscopy, Auger electron spectroscopy, X-ray absorption spectroscopy, and Raman spectroscopy. The phonon dispersion relation of graphitic carbon was found to be uniquely sensitive to substitutional boron doping, which perturbs the phonon structure while leaving the lattice structure unchanged. The dispersion relation of the D peak measured by Raman spectroscopy can be used to uniquely identify bulk graphitic materials containing a large content of ordered trigonal planar g-BC 3 units, which are of high interest in applications ranging from hydrogen storage to lithium-ion batteries.
The reaction of AnCl 4 (DME) x (An = Th, x = 2; An = U, x = 0) with 4 equiv of NaNR 2 (R = SiMe 3 ) in THF at 65 °C results in the formation of [An{N(R)(SiMe 2 CH 2 )}(NR 2 ) 2 ] (An = U, 1; An = Th, 2), and not the reported monomeric actinide hydrides, [AnH(NR 2 ) 3 ], as expected. Furthermore, both complexes 1 and 2 were characterized by X-ray crystallography. Surprisingly, their unit cell parameters are remarkably close to those reported for [AnH(NR 2 ) 3 ], suggesting that the original crystals of [AnH(NR 2 ) 3 ] were, in fact, [An{N(R)(SiMe 2 CH 2 )}(NR 2 ) 2 ], but were misidentified. Reduction of 1 with 1.1 equiv of KC 8 in THF, in the presence of 1 equiv of 2.2.2-cryptand, results in the formation of [K(2.2.2-cryptand)][U{N(R)(SiMe 2 CH 2 )}(NR 2 ) 2 ] (3) in good yield. Likewise, the reaction of 1 with 1 equiv of bis(diisopropylamino)cyclopropenylidene (BAC) results in the formation of the BAC adduct, [(BAC)U{N(R)(SiMe 2 CH 2 )}(NR 2 ) 2 ] (4), in moderate yield. Finally, the addition of H 2 (10 bar) to 2 in C 6 D 6 at room temperature results in the formation of the targeted monomeric hydride, [ThH(NR 2 ) 3 ], in 32% yield, according to integrations against an internal standard. However, removal of the H 2 atmosphere results in rapid reformation of 2. In contrast, the addition of H 2 (10 bar) to 1 in C 6 D 6 at room temperature results in no apparent reaction.
Phosphinodiboranates (H 3 BPR 2 BH 3 – ) are a class of borohydrides that have merited a reputation as weakly coordinating anions, which is attributed in part to the dearth of coordination complexes known with transition metals, lanthanides, and actinides. We recently reported how K(H 3 BP t Bu 2 BH 3 ) exhibits sluggish salt elimination reactivity with f-metal halides in organic solvents such as Et 2 O and THF. Here we report how this reactivity appears to be further attenuated in solution when the t Bu groups attached to phosphorus are exchanged for R = Ph or H, and we describe how mechanochemistry was used to overcome limited solution reactivity with K(H 3 BPPh 2 BH 3 ). Grinding three equivalents of K(H 3 BPPh 2 BH 3 ) with UI 3 (THF) 4 or LnI 3 (Ln = Ce, Pr, Nd) allowed homoleptic complexes with the empirical formulas U(H 3 BPPh 2 BH 3 ) 3 (1), Ce(H 3 BPPh 2 BH 3 ) 3 (2), Pr(H 3 BPPh 2 BH 3 ) 3 (3), and Nd(H 3 BPPh 2 BH 3 ) 3 (4) to be prepared and subsequently crystallized in good yields (50–80%). Single-crystal XRD studies revealed that all four complexes exist as dimers or coordination polymers in the solid-state, whereas 1 H and 11 B NMR spectra showed that they exist as a mixture of monomers and dimers in solution. Treating 4 with THF breaks up the dimer to yield the monomeric complex Nd(H 3 BPPh 2 BH 3 ) 3 (THF) 3 (4-THF). XRD studies revealed that 4-THF has one chelating and two dangling H 3 BPPh 2 BH 3 – ligands bound to the metal to accommodate binding of THF. In contrast to the results with K(H 3 BPPh 2 BH 3 ), attempting the same mechanochemical reactions with Na(H 3 BPH 2 BH 3 ) containing the simplest phosphinodiboranate were unsuccessful; only the partial metathesis product U(H 3 BPH 2 BH 3 )I 2 (THF) 3 (5) was isolated in poor yields. Here, despite these limitations, our results offer new examples showing how mechanochemistry can be used to rapidly synthesize molecular coordination complexes that are otherwise difficult to prepare using more traditional solution methods.
In-situ Raman spectroscopy has the potential to be a powerful technique for monitoring geochemical reactions at a solid–liquid interface in real time. In this article, we present the development and testing of an in-situ Raman spectroscopic cell, which can be used for reaction systems at moderate temperatures and pressure [<1000 psi (6.89 MPa), <100 °C, relevant to subsurface geologic systems] and can hold samples large enough for chemical mapping of heterogeneous rock surfaces. The system is validated by measuring the temperature-dependent conversion of gypsum to calcite over time. Near total conversion of gypsum to calcite on the mineral surface took 29 hours at room temperature and 150 minutes at 100 °C, corresponding to an 11.6-fold increase in the conversion rate. Further, we anticipate that this cell can be an important tool in quantifying the rates of carbon mineralization relevant to geologic carbon sequestration, particularly for the elevated rates recently observed in mafic/ultramafic rocks.
Raman spectroscopy is a widely utilized method for determining information about the solvate species present in electrolyte solutions. Difficulties arise, however, when interpreting the Raman data in terms of correlating the spectroscopic vibrational bands with specific solvate species. Examples are provided to demonstrate how erroneous conclusions may be drawn with regard to the identity and population (distribution) of the solvent-separated ion pair (SSIP), contact ion pair (CIP) and aggregate (AGG) solvate species frequently mentioned in the scientific literature.
Accurately modeling large biomolecules such as DNA from first principles is fundamentally challenging due to the steep computational scaling of ab initio quantum chemistry methods. This limitation becomes even more prominent when modeling biomolecules in solution due to the need to include large numbers of solvent molecules. We present a machine-learned electron density model based on a Euclidean neural network framework that includes a built-in understanding of equivariance to model explicitly solvated double-stranded DNA. By training the machine learning model using molecular fragments that sample the key DNA and solvent interactions, we show that the model predicts electron densities of arbitrary systems of solvated DNA accurately, resolves polarization effects that are neglected by classical force fields, and captures the physics of the DNA-solvent interaction at the ab initio level.
CRA (Compliance Recertification Application)-2024 will update the oxidation state specific model used to calculate actinide solubility in the WIPP (Waste Isolation Pilot Plant). The pentavalent Np(V) ion is the most stable ion in solution within the An(V) series. This valence stability of Np(V) in aqueous solution makes Np a useful representative element for studying the aqueous complex chemistry of all An(V), but in the predicted WIPP scenario, this is the only TRU component that increases in the inventory with time as it is the main daughter product of 241 Am decay (alpha, n) so its relative importance increases throughout the 10,000-year performance period of the WIPP, it is only used to represent itself. This work is focused on confirming organic, borate and carbonate effects on solubility of Np(V) in WIPP simulated brines and 5 M NaCl and reassessing the predicted model speciation to strengthen the overall WIPP An(V) model.