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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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In some examples, a method of forming alane (AlH3), the method comprising reacting one of: 1) a MAlH4, wherein M is an alkali metal; 2) alkali-metal hydride, MH; or 3) alkali-metal with one or more aluminum halides (AlX3, where X is a halogen), via a mechanochemical process, to form the alane, wherein the reaction is substantially solvent free and carried out in an environment with a temperature between approximately 250 K and approximately 330 K.
Intramolecular electron transfer between two biphenyl groups linked by an androstane spacer and excitation of the pyridinium-N-phenolate betaine dye B30 to the first excited singlet state are studied by quantum/classical molecular-dynamics simulations at temperatures between 150 and 300 K in solvents with a range of polarities. Temperature dependences of the solvent reorganization energies, free energies, entropies, and the inhomogeneous broadening of B30’s absorption band are examined. The variances of fluctuations of the energy gap between the reactant and product states do not have the direct proportionality to temperature that often is assumed to hold. An explanation for the observations is suggested.
One of the grand challenges that impedes practical applications of nanomaterials is the lack of robust manufacturing methods that are scalable, cheap, and environmentally friendly. In this work, we address this challenge by developing a microfluidic approach that produces surfactant-free Pd nanocrystals (NCs) uniformly loaded on N-doped porous carbon in a one-batch process. The deep eutectic solvent (DES) prepared from choline chloride and ethylene glycol was employed as a novel synthesis solvent, and its extended hydrogen networks and abundant ionic species effectively stabilize Pd facets and confine nanocrystal sizes without using surfactants. The microreactors provide faster heat exchange and more uniform mass transport, which in combination with DES produced Pd NCs with better-defined shape and predominately exposed Pd (100) facet. Furthermore, we describe that the N-doped functional groups in porous carbon direct dense and uniform heterogeneous growth of Pd NCs in a one-batch process, thereby eliminating a separate catalyst deposition step that is often involved in conventional synthesis. The Pd NCs in the one-batch-produced Pd/C catalysts exhibited a size distribution of similar to ~13 ± 3.5 nm and a high ESCA of 46.0 m 2 /g and delivered 362 mA/mg for formic acid electrochemical oxidation with improved stability, demonstrating the unique potentials of microfluidic reactors and DES for the controllable and scalable synthesis of electrocatalyst materials for practical applications.
The kinetics of CO 2 insertion into electronically different Re( R bpy)(CO) 3 H ( R bpy = 4,4'-R-2,2'- bipyridine; R = OMe, t Bu, Me, H, Br, COOMe, CF 3 ) complexes to form Re( R bpy)(CO) 3 {OC(H)O} compounds were determined in acetone, dimethylacetamide (DMAc), dimethylformamide (DMF), dimethylsulfoxide (DMSO), and 3-methoxypropionitrile (3-MPN) and compared with previous data in acetonitrile (MeCN). The rates of CO 2 insertion for any one complex of the type Re(Rbpy)(CO) 3 H in different solvents correlates with the Dimroth-Reichardt (E T (30)) solvent parameter. Hammett plots in each solvent indicate that insertion reactions are faster for bpy ligands with electron-donating groups. There is, however, no correlation between the slope of the Hammett plot in different solvents and any common solvent parameter. Similarly, the enthalpies and entropies of activation and kinetic isotope effects associated with CO 2 insertion into Re(bpy)(CO) 3 H in different solvents do not correlate with any common solvent parameters. Theoretical calculations were used to determine the relative thermodynamic hydricities of Re( R bpy)(CO) 3 H type complexes in MeCN, acetone, DMF, and DMSO and in each solvent complexes with more electron-donating substituents on the bpy ligand are stronger hydride donors. Linear Free Energy Relationships (LFERs) between calculated thermodynamic and experimental kinetic hydricity, as measured through CO 2 insertion reactions, were observed in MeCN, acetone, DMF, and DMSO. Furthermore, the slopes of the LFERs correlate with the dielectric constant of the solvent. Overall, this work provides fundamental information about the thermodynamics and kinetics of hydride transfer reactions in different solvents, which is valuable for catalyst design.
The conventional electrolyte of 1 m lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) in dimethyl sulfoxide (DMSO) is unstable against the Li metal anode and therefore cannot be used directly in practical Li–O 2 batteries. Here, we demonstrate that a highly concentrated electrolyte based on LiTFSI in DMSO (with a molar ratio of 1:3) can greatly improve the stability of the Li metal anode against DMSO and significantly improve the cycling stability of Li–O 2 batteries. This highly concentrated electrolyte contains no free DMSO solvent molecules, but only complexes of (TFSI − ) a Li + (DMSO) b (where a + b = 4), and thus enhances their stability with Li metal anodes. In addition, such salt–solvent complexes have higher Gibbs activation energy barriers than the free DMSO solvent molecules, indicating improved stability of the electrolyte against the attack of superoxide radical anions. Therefore, the stability of this highly concentrated electrolyte at both Li metal anodes and carbon‐based air electrodes has been greatly enhanced, resulting in improved cycling performance of Li–O 2 batteries. The fundamental stability of the electrolyte in the absence of free‐solvent against the chemical and electrochemical reactions can also be used to enhance the stability of other electrochemical systems.
The Recipient will study how flash Joule heating (FJH) from anthracite coal can afford high value graphene in gram scales in less than 1 second per conversion step. The graphene is termed flash graphene (FG). The process uses no furnace and no solvent or reactive gases, and the yields from anthracite coal are 85-95% with a purity >99%. The scaled electrical energy cost is projected at $100 per metric ton. FG can be among the lowest defect graphene ever reported (2D/G = 17:1) and turbostratic by powder X-ray diffraction (XRD) analysis, meaning that is has little order between the graphene layers, thereby facilitating its dispersion in composites. FG might provide the long-sought method to make graphene in bulk with industrially acceptable economics: inexpensive coal, furnace-free, solvent-free and chemical-free processing, and low-energy input to render it suitable for bulk plastic, metal and even concrete composites.
An optimized ether-based electrolyte is designed to suppress solvent co-intercalation and decomposition of graphite anodes, thereby enabling lithium–sulfur batteries with low N/P ratio.
CO 2 and H 2 solubilities, CO 2 /H 2 solubility selectivities, CO 2 diffusivities, and solvent viscosities in 27 commercially available physical solvents at 298 K were calculated from molecular simulations using the CHARMM36 all-atom force field for most solvents, and the simulation results were compared with available experimental data in this report. The van der Waals radius parameters for solvents were slightly tuned to reproduce the experimental solvent density. The simulated CO 2 solubilities are comparable with the experimental data, with an average absolute difference of 28%. For the homologous compounds containing the –(OCH 2 CH 2 )– repeat unit, both simulated and experimental data show that CO 2 solubility decreases when the number of repeat units is increased; CO 2 solubilities in these homologous compounds exhibit almost a perfect positive linear correlation with the solvent free-volume fractions. The simulated H 2 solubilities and CO 2 /H 2 solubility selectivities are also comparable with the experimental data, with differences of 22% and 17%, respectively. The H 2 solubilities in all solvents researched here correlate very well with the solvent free-volume fractions, exhibiting a positive linear correlation coefficient of 0.84. Additionally, simulations show that CO 2 solubility decreases when the temperature is increased. In contrast, H 2 solubility increases at elevated temperature, which is partly due to the increased solvent free-volume fraction at elevated temperature. Lastly, although the viscosity difference tends to be large (30%–246%) between simulation and experiment, both simulated and experimental data exhibit a similar solvent viscosity trend. Furthermore, simulations show that CO 2 diffusivities in solvents are very strongly correlated with the solvent viscosities and the relationship between them is given by D$_{CO_{2}}$ = (2.6 ± 0.3) × 10 –9 /η solvent 0.59 ± 0.03.
The instability of lithium (Li) metal anode due to the dendritic growth and low Coulombic efficiency hinders the practical application of the well-regarded high-energy-density Li metal batteries. Here we report the systematic studies of improving the stability of Li metal anode and the electrochemical performances of the related Li metal batteries through the addition of combinational additives and the optimization of solvent compositions in dual-salt/carbonate electrolytes. A dendrite-free and high Coulombic efficiency of 98.1% for Li metal anode is achieved. The well protection of the Li metal anode and the excellent cyclability and rate capability of the 4-V Li metal batteries have been obtained. This is attributed to the formation of a robust, denser, more polymeric and higher ionic conductive surface film on the Li metal anode via the electrochemical reductive decompositions of the electrolyte components and the ring-opening polymerization of additives and cyclic carbonate solvents. The key findings of this work emphasize that the optimization of solvent compositions and the manipulation of the additives are facile and effective to enhance the Li metal battery performances.
Implicit solvent models are important tools for calculating solvation free energies for chemical and biophysical studies since they require fewer computational resources but can achieve accuracy comparable to that of explicit-solvent models. In past papers, geometric flow-based solvation models have been established for solvation analysis of small and large compounds. In the present work, the use of realistic experiment-based parameter choices for the geometric flow models is studied. We find that the experimental parameters of solvent internal pressure p = 172 MPa and surface tension γ = 72 mN/m produce solvation free energies within 1 RT of the global minimum root-mean-squared deviation from experimental data over the expanded set. Our results demonstrate that experimental values can be used for geometric flow solvent model parameters, thus eliminating the need for additional parameterization. We also examine the correlations between optimal values of p and γ which are strongly anti-correlated. Geometric analysis of the small molecule test set shows that these results are inter-connected with an approximately linear relationship between area and volume in the range of molecular sizes spanned by the data set. In spite of this considerable degeneracy between the surface tension and pressure terms in the model, both terms are important for the broader applicability of the model.
The failure of hemicellulose valorization in a deep eutectic solvent (DES) pretreatment has become a bottleneck that challenges its further development. Here, to address this issue, this study developed a DES/GVL (γ-valerolactone) biphasic system for effective hemicellulose-furfural conversion, enhanced cellulose saccharification and lignin isolation. The results indicated that the biphasic system could significantly improve the lignin removal (as high as 89.1%), 86.0% higher than the monophasic DES, accompanied by ~100% hemicellulose degradation. Notably, the GVL in the biphasic solvent restricted the condensation of hemicellulose degradation products, which as a result generated large amount of furfural in the pretreatment liquid with a yield of 68.6%. With the removal of hemicellulose and lignin, cellulose enzymatic hydrolysis yield was boosted and reached near 100%. This study highlighted that the novel DES/GVL is capable of fractionating the biomass and benefiting their individual utilization, which could provide a new biorefinery configuration for a DES pretreatment.
Alkali metal monohydrides, AH (A = Li–Cs) have been synthesized in quantitative yields at room temperature by reactive milling of alkali metals in the presence of hydrogen gas at 200 bar or less. The mechanochemical approach reported here eliminates problems associated with the malleability of alkali metals — especially Li, Na, and K — and promotes effective solid–gas reactions, ensuring their completion. This is achieved by incorporating a certain volume fraction of the corresponding hydride powder as a process control agent, which allows continuous and efficient milling primarily by coating the surface of metal particles, effectively blocking cold welding. Formation of high-purity crystalline monohydrides has been confirmed by powder X-ray diffraction, solid-state NMR spectroscopy, and volumetric analyses of reactively desorbed H 2 from as-milled samples. The proposed synthesis method is scalable and particularly effective for extremely air-sensitive materials, such as alkali and alkaline earth metal hydrides. Furthermore, the technique may also be favorable for production in continuous reactors operating at room temperature, thereby reducing the total processing time, energy consumption and, hence, the cost of production of these hydrides or their derivatives and composites.
Using rapidly acquired spectral diffusion, a recently developed variation of heterodyne detected infrared photon echo spectroscopy, we observe ∼3 ps solvent independent spectral diffusion of benzene chromium tricarbonyl (C{sub 6}H{sub 6}Cr(CO){sub 3}, BCT) in a series of nonpolar linear alkane solvents. The spectral dynamics is attributed to low-barrier internal torsional motion. This tripod complex has two stable minima corresponding to staggered and eclipsed conformations, which differ in energy by roughly half of k{sub B}T. The solvent independence is due to the relative size of the rotor compared with the solvent molecules, which create a solvent cage in which torsional motion occurs largely free from solvent damping. Since the one-dimensional transition state is computed to be only 0.03 k{sub B}T above the higher energy eclipsed conformation, this model system offers an unusual, nearly barrierless reaction, which nevertheless is characterized by torsional coordinate dependent vibrational frequencies. Hence, by studying the spectral diffusion of the tripod carbonyls, it is possible to gain insight into the fundamental dynamics of internal rotational motion, and we find some evidence for the importance of non-diffusive ballistic motion even in the room-temperature liquid environment. Using several different approaches to describe equilibrium kinetics, as well as the influence of reactive dynamics on spectroscopic observables, we provide evidence that the low-barrier torsional motion of BCT provides an excellent test case for detailed studies of the links between chemical exchange and linear and nonlinear vibrational spectroscopy.
Here, in this work, a newly benzodithiophene-free D-A polymer donor, named PDTP-BDD, was developed for realizing green-solvent processed high-performance OSCs. By bridging two electron-rich unit of dithieno[3,2-b:2',3'-d]pyridin-5(4H)-one (DTP) and electron-deficient benzo[1,2-c:4,5c']dithiophene-4,8-dione (BDD) with thiophene units, PDTP-BDD possesses high absorption in the short wavelength range and a deep HOMO energy level. The rigid building blocks also make PDTP-BDD has strong aggregation and poor solubility in common halogen-free solvents (such as o-xylene) at room temperature, but it is readily dissolved and disaggregated at high temperature (120 °C). After cooling down to a lower temperature (60 °C), PDTP-BDD self-assembled and pre-aggregated slowly in the solution at a long time. By employing a delayed processing strategy in the layer-by-layer processed OSCs (LbL-OSCs), an optimized fibril network of the underling layer was realized, enabling the permeation of acceptor into the donor network. The optimized PDTP-BDD/L8-BO-based LbL-OSCs realized a high PCE of 18.42 %. By adding a small amount of D18 to further optimize the PDTP-BDD fibril network, an impressive PCE of 19.36 % was achieved finally in the resulting ternary LbL-OSCs, which is the highest value for OSCs processed by halogen-free solvents.
Highlights: • The binder-free sulfur electrode with high sulfur contents of 75 wt.% was fabricated. • The binder-free sulfur electrode using NMP solvents showed 784 mAh g{sup −1} after 40 cycles. • The solvent affect the electrochemical properties of binder-free sulfur electrode films. - Abstract: The effects of solvents on the preparation of sulfur cathodes were investigated by fabricating binder-free sulfur electrode films using three different solvents: 1-methyl-2-pyrrolidinone (NMP), acetonitrile, and deionized water. These solvents are commonly employed to dissolve binders used to prepare sulfur cathodes for lithium–sulfur batteries. The sulfur electrode fabricated with NMP had a higher discharge capacity and longer cycle life than the ones fabricated with acetonitrile and deionized water. Better adhesion between the current collector and the sulfur electrode accounted for the improved capacity and cycle life of the battery. In addition, the stability of the electrode in the electrolyte was a result of the solubility of sulfur in the solvent. We thus concluded that the solvents used in the fabrication of sulfur electrodes had a positive influence on the electrochemical properties of Li–S batteries.
High-quality perovskite films are predominantly prepared by anti-solvent assisted spin-coating method. How- ever, small device size and narrow operation window limit their applications in practical and scalable production. Here, a spontaneously supersaturated nucleation strategy is developed to fabricate high-quality perovskite films without any antisolvents. The rapid precipitation behavior of the precursor solutions could be triggered by the volatilization of methylamine ethanol at the initial film formation stage, forming uniform and compact intermediate phase films. Mirror-like large area (10 cm × 10 cm) methylammonium lead triiodide (MAPbI 3 ) perovskite films with micrometer-sized grains can be achieved by phase transition via annealing. The average power conversion efficiency (PCE) of 19.4% is achieved for 0.1 cm 2 perovskite solar cells (PSCs). The 1 cm 2 device shows a PCE of 17.57% and retains 96.8% after aging for 39 days in the air with a relative humidity of 5–30%. The perovskite module based on the perovskite films prepared by our strategy exhibits a PCE of 13.13%. Here, the perovskite film fabrication method developed in this work shows high reproducibility of the fabrication process due to the spontaneous nucleation process. Meanwhile, it also exhibits significant potential in the application of scalable solution processing deposition techniques toward the commercialization of PSCs.
Accelerated bearing life tests were conducted to evaluate the effects of ODC-free bearing cleaning solvents as a replacement to CFC-113. Three chemically different, ODC-free cleaning solvents were tested against the CFC-113 baseline. Test bearings were representative of the type that would be used for a space scanner bearing application. The bearings were lubricated with two space flight oils. Lives with the replacement solvents exceeded those obtained with CFC-113 baseline. Pennzane-lubricated bearings enjoy a 2 to 6X life advantage over those lubricated with Bray 815Z oil.
Formation of soluble polysulfide (PS), which is a key feature of lithium sulfur (Li–S) batteries, provides a fast redox kinetic based on a liquid–solid mechanism; however, it imposes the critical problem of PS shuttle. Here, we address the dilemma by exploiting a solvent-swollen polymeric single-ion conductor (SPSIC) as the electrolyte medium of the Li–S battery. The SPSIC consisting of a polymeric single-ion conductor and lithium salt-free organic solvents provides Li ion hopping by forming a nanoscale conducting channel and suppresses PS shuttle according to the Donnan exclusion principle when being employed for Li–S batteries. The organic solvents at the interface of the sulfur/carbon composite and SPSIC eliminate the poor interfacial contact and function as a soluble PS reservoir for maintaining the liquid–solid mechanism. Furthermore, the quasi-solid-state SPSIC allows the fabrication of a bipolar-type stack, which promises the realization of a high-voltage and energy-dense Li–S battery.