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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 1,405 records · Page 78
All sourcesNASA NTRSDOE OSTI
DOE OSTI2024

Synthesis and Characterization of Isostructural Th(IV) and U(IV) Pyridine Dipyrrolide Complexes

A series of pyridine dipyrrolide actinide(IV) complexes, ( Mes PDP Ph )AnCl 2 (THF) and An( Mes PDP Ph ) 2 (An = U, Th, where ( Mes PDP Ph ) is the doubly deprotonated form of 2,6-bis(5-(2,4,6-trimethylphenyl)-3-phenyl-1H-pyrrol-2-yl)pyridine), have been prepared. Characterization of all four complexes has been performed through a combination of solid- and solution-state methods, including elemental analysis, single crystal X-ray diffraction, and electronic absorption and nuclear magnetic resonance spectroscopies. Collectively, these data confirm the formation of the mono- and bis-ligated species. Time-dependent density functional theory has been performed on all four An(IV) complexes, providing insight into the nature of electronic transitions that are observed in the electronic absorption spectra of these compounds. Room temperature, solution-state luminescence of the actinide complexes is presented. Both Th(IV) derivatives exhibit strong photoluminescence; in contrast, the U(IV) species are nonemissive.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2025

Bis( tert -butoxydiphenylsilyl)amide Divalent Lanthanide Complexes

The development of new ligand systems to stabilize “nontraditional/ non-classical” divalent lanthanides is key to tuning the chemical and physical properties of their mixed principal quantum number 4f n 5d 1 ground states. The design and study of novel ligand systems which stabilize occupation of differing orbitals within the 5d manifold for these ions constitutes an area ripe for exploration. Our efforts toward the development of redox-innocent bulky silylamide ligands to stabilize pseudo-octahedral coordination geometries for divalent lanthanides have resulted in the synthesis of the bis( tert -butoxydiphenylsilyl) amide ligand, whose coordination complexes with Sm 2+ , Eu 2+ , and Yb 2+ are reported herein. These systems have been fully characterized by single-crystal X-ray diffraction, elemental analysis, cyclic voltammetry, direct-current magnetometry, and infrared, nuclear magnetic resonance, and electronic absorption spectroscopies. Attempts to extend this system to the more reducing Tm 2+ ion resulted in an inseparable mixture of products from which crystals of the analogous Tm 2+ species and a reduced dinitrogen, bimetallic Tm 3+ -Tm 3+ complex bridged by a η 2 -N 2 3− radical could be identified. Though progress toward six-coordinate complexes of reducing “traditional/ classical” divalent ions is noted for these systems, further work is needed to improve the synthetic utility of this ligand framework for the study of “non-traditional/non-classical” divalent lanthanides with a mixed-principal quantum number 4f n 5d 1 ground state.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2025

Trans-Influence in Dinuclear Pt(III) Complexes: Electronic Structure, σ-Donation, and Pt–Pt Spin–Spin Coupling

This study investigates the trans influence in dinuclear platinum(III) complexes using a combined approach of ab initio molecular dynamics and natural localized molecular orbital (NLMO) analysis. Focusing on pivalamidate-bridged Pt III complexes with axial ligands of varying σ-donation strength, it is quantified how ligand−metal interactions propagate through the Pt−Pt bond, and how they affect bond polarization, axial water coordination, and 1 J PtPt spin−spin coupling constants. NLMO analysis reveals quantitatively that strong σ-donating ligands polarize the Pt−Pt bond, shifting the electron density toward the opposite platinum center. The polarization mechanism is identified as the primary reason for the observed reduction of 1 J PtPt , because the bond polarization diminishes the transmission of the nuclear magnetic spin-induced electron spin density through the Pt−Pt bond. Additionally, the destabilization of axial water coordination at the opposite Pt site can be rationalized through a polarizationinduced Pt IV − Pt II -like mixed-valence character.

Ab initio molecular dynamics↗
DOE OSTI2016

Cooperative Electronic and Structural Regulation in a Bioinspired Allosteric Photoredox Catalyst

Here in this article, we report the first allosteric photoredox catalyst regulated via constructively coupled structural and electronic control. While often synergistically exploited in nature, these two types of control mechanisms have only been applied independently in the vast majority of allosteric enzyme mimics and receptors in the literature. By embedding a model of photosystem II in a supramolecular coordination complex that responds to chloride as an allosteric effector, we show that distance and electronic control of light harvesting can be married to maximize allosteric regulation of catalytic activity. This biomimetic system is composed of a Bodipy photoantenna, which is capable of transferring excited-state energy to a photoredox pair, wherein the excitation energy is used to generate a catalytically active charge-separated state. The structural aspect of allosteric regulation is achieved by toggling the coordination chemistry of an antenna-functionalized hemilabile ligand via partial displacement from a Rh I structual node using chloride. In doing so, the distance between the antenna and the central photoredox catalyst is increased, lowering the inherent efficiency of through-space energy transfer. At the same time, coordination of chloride lowers both the charge of the Rh I node and the reduction potential of the Rh II/I couple, to the extent that electronic quenching of the antenna excited state is possible via photoinduced electron transfer from the metal center. Compared to a previously developed system that operates solely via electronic regulation, the present system demonstrates that coupling electronic and structural approaches to allosteric regulation gives rise to improved switching ratios between catalytically active and inactive states. Contributions from both structural and electronic control mechanisms are probed via nuclear magnetic resonance, X-ray diffraction, electrochemical, spectroelectrochemical, and transient absorption studies. Overall, this work establishes that intertwined electronic and structural regulatory mechanisms can be borrowed from nature to build stimuli-responsive inorganic materials with potential applications in sensing, catalysis, and photonic devices.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2016

Octafluorodirhenate(III) Revisited: Solid-State Preparation, Characterization, and Multiconfigurational Quantum Chemical Calculations

A simple method for the high-yield preparation of (NH 4 ) 2 [Re 2 F 8 ]· 2H 2 O has been developed that involves the reaction of (n-Bu 4 N)2[Re 2 Cl 8 ] with molten ammonium bifluoride (NH 4 HF 2 ). Using this method, the new salt [NH 4 ] 2 [Re 2 F 8 ]·2H 2 O was prepared in ~90% yield. The product was characterized in solution by ultraviolet-visible light (UV-vis) and 19 F nuclear magnetic resonance (19F NMR) spectroscopies and in the solid-state by elemental analysis, powder X-ray diffraction (XRD), and infrared (IR) spectroscopy. Multiconfigurational CASSCF/CASPT2 quantum chemical calculations were performed to investigate the molecular and electronic structure, as well as the electronic absorption spectrum of the [Re 2 F 8 ] 2- anion. The metal-metal bonding in the Re 2 6+ unit was quantified in terms of effective bond order (EBO) and compared to that of its [Re 2 Cl 8 ] 2- and [Re 2 Br 8 ] 2- analogues.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2017

Topological Transformation of a Metal–Organic Framework Triggered by Ligand Exchange

Metal-organic frameworks (MOFs) have shown to be unsuspectedly dynamic. Here we describe the topological interconversion of a new framework in the bio-MOF-100 family (dia-c) into the known isomer (lcs) by doubling the pore volume, which occurs during post-synthesis modifications. During this transformation, re-assembling of the MOF building blocks into a completely different framework occurs, involving breaking/forming of metal-ligand bonds. MOF crystallinity and local structure are retained, as determined by powder X-ray diffraction (PXRD) and pair distribution function (PDF) analyses, respectively. We have exploited the inherent dynamism of bio-MOF-100 by coupling chemical decorations of the framework using solvent-assisted ligand exchange (SALE) to the topological change. Following this method and starting from the pristine dense dia-c phase, open lcs-bio-MOF-100 was prepared and functionalized in-situ with an iridium complex (IrL). Alternatively, the dia-c MOF could be modified with wide-ranging amounts of IrL up to ca. 50 mol%, as determined by solution 1 H Nuclear Magnetic Resonance (NMR) spectroscopy, by tuning the concentration of the solutions used and with no evidence for isomer interconversion. The single-site nature of the iridium complexes within the MOFs was assessed by X-ray absorption spectroscopy (XAS) and PDF analyses. As a result, ligand exchanges occurred quantitatively at room temperature, with no need of excess of the iridium metallolinker.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2017

The Role of Structural and Compositional Heterogeneities in the Insulator-to-Metal Transition in Hole-Doped APd 3 O 4 (A = Ca, Sr)

The cubic semiconducting compounds APd 3 O 4 (A = Ca, Sr) can be hole-doped by Na substitution on the A site and driven toward more conducting states. This process has been followed here by a number of experimental techniques to understand the evolution of electronic properties. While an insulator-to-metal transition is observed in Ca 1–x Na x Pd 3 O 4 for x ≥ 0.15, bulk metallic behavior is not observed for Sr 1–x Na x Pd 3 O 4 up to x = 0.20. Given the very similar crystal and (calculated) electronic structures of the two materials, the distinct behavior is a matter of interest. We present evidence of local disorder in the A = Sr materials through the analysis of the neutron pair distribution function, which is potentially at the heart of the distinct behavior. Solid-state 23 Na nuclear magnetic resonance studies additionally suggest a percolative insulator-to-metal transition mechanism, wherein presumably small regions with a signal resembling metallic NaPd 3 O 4 form almost immediately upon Na substitution, and this signal grows monotonically with substitution. Here, some signatures of increased local disorder and a propensity for Na clustering are seen in the A = Sr compounds.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2018

Diastereomerically Differentiated Excited State Behavior in Ruthenium(II) Hexafluoroacetylacetonate Complexes of Diphenyl Thioindigo Diimine

Mono- and diruthenium hexafluoroacetylacetonate (hfac) complexes of the thioindigo- N , N '-diphenyldiimine chelating ligand 3 have been prepared. The thioindigo diimine ligand binds to ruthenium in a bidentate fashion in the mononuclear compound 2 and serves as a bidentate chelating bridging ligand in the diruthenium complexes 1a and 1b . Compound 2 was isolated as a racemic mixture while the diruthenium complexes were isolated as the meso (ΔΛ) 1a and rac (ΔΔ and ΛΛ) 1b diastereomers. In-depth structural characterization of the compounds was performed, including X-ray crystallography, 1 H, 13 C, and 19 F nuclear magnetic resonance (NMR) spectroscopy, and 2D NMR correlation experiments. Electrochemical properties were evaluated utilizing cyclic voltammetry. Ground state optical properties of the complexes were examined using UV–visible spectroscopy and spectroelectrochemistry. The excited state dynamics of the series were explored by ultrafast transient absorption spectroscopy. Variable temperature NMR experiments demonstrated that the rac diruthenium compound 1b undergoes conformational exchange with a rate constant of 8700 s –1 at 298 K, a behavior that is not observed in the meso diastereomer 1a . The series of complexes possess metal-to-ligand charge transfer (MLCT) absorption bands in the near-infrared (λ max 689–783 nm). The compounds do not display photoluminescence in room temperature solution-phase experiments or in experiments at 77 K. Transient absorption spectroscopy measurements revealed excited states with picosecond lifetimes for 1a , 1b , and 2 , and spectroelectrochemical experiments confirmed assignment of the transient species as arising from MLCT transitions. Surprisingly, the transient absorption measurements revealed disparate time constants for the excited state decay of diastereomers 1a and 1b .

14 SOLAR ENERGY↗
DOE OSTI2019

Unraveling Gibbsite Transformation Pathways into LiAl-LDH in Concentrated Lithium Hydroxide

The intercalation of lithium (Li+) ions into metallic hydroxides (e.g. gibbsite, Al(OH)3) facilitates the synthesis of layered double hydroxides. Caustic environments, such as in lithium hydroxide (LiOH) solutions, present additional pathways beyond the intercalation of ions, specifically dissolution/precipitation processes. Herein, the phase transformation Al(OH)3 to lithium aluminum hydroxide dihydrate, Li[Al(OH)3)]2OH•2H2O in partially deuterated LiOH solutions is tracked through multinuclear, magic angle spinning, high-field nuclear magnetic resonance spectroscopy (27Al and 6Li MAS-NMR) , X-ray diffraction, and scanning electron microscopy of harvested solids. At high magnetic fields (19.975 T), 27Al MAS-NMR enabled detection and quantification of the reactive interface between Al(OH)3 and Li[Al(OH)3)]2OH•2H2O. 6Li MAS-NMR spectra collected on the harvested solids exhibited exchange mediated narrowing as the reaction time progressed, consistent with transport of Li+ ions between the interface and the bulk Li[Al(OH)3)]2OH•2H2O. Complimentary in-situ 27Al MAS-NMR at lower magnetic fields (7.046 T) utilized unique rotors capable of simultaneous resolution of solution and solid state Al-species in caustic environments. The reaction between Al(OH)3 (0.5 M) and LiOH (3 M) initially exhibited greater dissolution and formation of Al(OH)4- than the precipitation. Over several hours, the supersaturated Al(OH)4- solution precipitated Li[Al(OH)3)]2OH•2H2O. Simultaneous, in-situ observations of the solid component tracked the formation of Li[Al(OH)3)]2OH•2H2O evident by an increase in signal and narrowing of the Oh resonance. These results provides insight into Al precipitation in alkaline media with applications ranging from the reduction of Al content in Hanford site, high-level radioactive waste (HLRW) to the precipitation of LDH materials for application as catalyst materials, drug delivery devices, and ion-ion exchangers.

Graham, Trenton R.↗
DOE OSTI2019

Complexation of Light Trivalent Lanthanides with N-(2-Hydroxyethyl)ethylenediamine-N,N',N'-triacetic Acid in Aqueous Solutions: Thermodynamic Analysis and Coordination Modes

N-(2-hydroxyethyl)ethylenediamine-N,N',N'-triacetic acid (HEDTA, denoted as H 3 L) is a strong chelating ligand that is widely used in separation of f-elements as relevant to the nuclear fuel cycle. There is much to be known about the structure and composition of the coordination sphere of the complexes of HEDTA with lanthanides. The complexation of HEDTA with light lanthanides (La 3+ , Nd 3+ and Eu 3+ ) was investigated thermodynamically and structurally in aqueous solutions. Potentiometry and microcalorimetry were performed to acquire the complexation constants (25-70°C) and enthalpies (25°C), respectively, at I = 1.0mol·L -1 NaClO 4 . Coordination modes of the complexes were analyzed by luminescence spectroscopy and nuclear magnetic resonance spectroscopy. The results indicate that there are two successive Ln 3+ /HEDTA complexes, LnL(aq) and Ln 2 (H -1 L) 2 2- (Ln 3+ referred to La 3+ , Nd 3+ and Eu 3+ ; H -1 L 4- referred to the deprotonation of the hydroxyl group) during the titration. The hydroxyl group of HEDTA is coordinated in Ln 3+ /HEDTA complex. The dinuclear Ln 2 (H -1 L) 2 2- complex is present as a carboxyl-bridged centrosymmetric dimer, and two carboxyl groups in bridging positions are coordinated to two adjacent Ln 3+ cations. Complexation of the NdL(aq) is exothermic, while formation of the hydrolytic complex Nd 2 (H -1 L) 2 2- is endothermic. Both NdL aq and Nd 2 (H -1 L) 2 2- complexes are driven by entropic force. These data will help to predict the behavior of lanthanides in the separation process where HEDTA is used as the aqueous complexant.

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

Butyltin Keggin Ion with a Rare Four-Coordinate Ca Center

Alkyltin clusters are exploited in nanolithography for the fabrication of microelectronics. The alkyltin Keggin family is unique among Keggin clusters across the periodic table; its members appear to favor the lower-symmetry β and γ isomers rather than the highly symmetrical α and ε isomers. Therefore, the alkyltin Keggin family may provide important fundamental information about the formation and isomerization of Keggin clusters. In this study, we have synthesized and structurally characterized a new butyltin Keggin cluster with a tetrahedral Ca 2+ center, fully formulated [(BuSn) 12 (CaO 4 )(OCH 3 ) 12 (O) 4 (OH) 8 ] 2+ (β-CaSn 12 ). The synthesis is a simple one-step process. Extensive solution characterization including electrospray ionization mass spectrometry, small-angle X-ray scattering, and multinuclear ( 1 H, 13 C, and 119 Sn) nuclear magnetic resonance shows β-CaSn 12 is essentially phase-pure and stable. This differs from the previously reported Na-centered analogues that always form a mixture of β and γ isomers, with facile interconversion. Therefore, this study has clarified prior confusion over complex spectroscopic and crystallographic characterization of the Na-centered analogues. Density functional theory calculations showed the following stability order: γ-CaSn 12 < γ-NaSn 12 < β-CaSn 12 < β-NaSn 12 . The β analogue is always more stable than the γ analogue, consistent with experiment. Notable outcomes of this study include a rare tetrahedral Ca coordination, a Na-free alkyltin cluster (important for microelectronics manufacturing), and a better understanding of Keggin families built of different metal cations.

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

Lithium Solvation and Mobility in Ionic Liquid Electrolytes with Asymmetric Sulfonyl-Cyano Anion

The solvation structure and transport properties of Li + in ionic liquid (IL) electrolytes based on n-methyl-n-butylpyrrolidinium cyano(trifluoromethanesulfonyl)imide [PYR 14 ][CTFSI] and [Li][CTFSI] (0 ≤ x Li ≤ 0.7) were studied by Raman and Nuclear Magnetic Resonance (NMR) diffusometry, and molecular dynamics (MD) simulations. At x Li < 0.3, Li + coordination is dominated by the cyano group. As x Li is increased, free cyano-sites become limited, resulting in increased coordination via the sulfonyl group. Here, the 1:1 mixture of the symmetric anions bis(trifluoromethanesulfonyl)imide ([TFSI]) and dicyanamide ([DCA]) results in similar physical properties as the IL with [CTFSI]. However, anion asymmetry is shown to increase Li-salt solubility and promote Li+ transference. The lifetimes of Li + -cyano coordination for [CTFSI] are calculated to be shorter than those for [DCA], indicating that the competition from the sulfonyl group weakens its solvation with Li + . This resulted in higher Li + transference for the electrolyte with [CTFSI]. In relation to the utility of these electrolytes in energy storage, the Li–LiFePO 4 half cells assembled with IL electrolyte (x Li = 0.3, 0.5, and 0.7) demonstrated a nominal capacity of 140 mAh/g at 0.1C rate and 90 °C where the cell with x Li = 0.7 IL electrolyte demonstrated 61% capacity retention after 100 cycles and superior rate capability owing to increased electrochemical stability.

25 ENERGY STORAGE↗
DOE OSTI2023

Machine Learning Full NMR Chemical Shift Tensors of Silicon Oxides with Equivariant Graph Neural Networks

The nuclear magnetic resonance (NMR) chemical shift tensor is a highly sensitive probe of the electronic structure of an atom and furthermore its local structure. Recently, machine learning has been applied to NMR in the prediction of isotropic chemical shifts from a structure. Current machine learning models, however, often ignore the full chemical shift tensor for the easier-to-predict isotropic chemical shift, effectively ignoring a multitude of structural information available in the NMR chemical shift tensor. Here we use an equivariant graph neural network (GNN) to predict full 29 Si chemical shift tensors in silicate materials. The equivariant GNN model predicts full tensors to a mean absolute error of 1.05 ppm and is able to accurately determine the magnitude, anisotropy, and tensor orientation in a diverse set of silicon oxide local structures. When compared with other models, the equivariant GNN model outperforms the state-of-the-art machine learning models by 53%. The equivariant GNN model also outperforms historic analytical models by 57% for isotropic chemical shift and 91% for anisotropy. The software is available as a simple-to-use open-source repository, allowing similar models to be created and trained with ease.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

Quantifying Species Populations in Multivalent Borohydride Electrolytes

Multivalent batteries represent an important beyond Li-ion energy storage concept. The prospect of calcium batteries, in particular, has emerged recently due to novel electrolyte demonstrations, especially that of a ground-breaking combination of the borohydride salt Ca(BH 4 ) 2 dissolved in tetrahydrofuran. Recent analysis of magnesium and calcium versions of this electrolyte led to the identification of divergent speciation pathways for Mg 2+ and Ca 2+ despite identical anions and solvents, owing to differences in cation size and attendant flexibility of coordination. To test these proposed speciation equilibria and develop a more quantitative understanding thereof, we have applied pulsed-field-gradient nuclear magnetic resonance and dielectric relaxation spectroscopy to study these electrolytes. Additionally, concentration-dependent variation in anion diffusivities and solution dipole relaxations, interpreted with the aid of molecular dynamics simulations, confirms these divergent Mg 2+ and Ca 2+ speciation pathways. These results provide a more quantitative description of the electroactive species populations. We find that these species are present in relatively small quantities, even in the highly active Ca(BH 4 ) 2 /tetrahydrofuran electrolyte. This finding helps interpret previous characterizations of metal deposition efficiency and morphology control and thus provides important fundamental insight into the dynamic properties of multivalent electrolytes for next-generation batteries.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

Solvation Dynamics of Wet Ethaline: Water is the Magic Component

The past two decades witnessed the development of a new type of solvent system, named deep eutectic solvents, which have become increasingly investigated because they offer new and potentially favorable properties, such as wide tunability in electrochemical, mechanical, and transport properties. Deep eutectic solvent (DES) systems are composed of at least one main solvent and an additional component that is meant to interrupt the original solvent/solvent interactions, thereby introducing lower melting points relative to each individual component. Ethaline (a 1:2 mole% mixture of choline chloride and ethylene glycol) is one of the most promising DES systems. However, it is also known to be very hygroscopic, which is a constant concern because water absorption during the use of ethaline alters its properties. Within this work, we demonstrate that modest amounts of water addition (1-10%) to ethaline are of little concern for practical use and can even lead to performance improvements, such as accelerated relaxation and solvation. In contrast, very small amounts of <1% of water lead to additional slowing of the solvent response. Thus, we suggest that the attempt to dry ethaline below 1% moisture is rather counter-productive if one attempts to achieve effective solvation and charge transport properties from DESs. This study investigates the effect of water content on the diffusional relaxation dynamics of ethaline. A set of independent spectroscopic experiments and computational simulations are aimed to provide insight into the solvent response of the DES system using femtosecond time-resolved absorption spectroscopy (fs-TA), broadband dielectric spectroscopy (BDS), nuclear magnetic resonance (NMR) diffusometry and broadband relaxometry, and molecular dynamics simulations (MDS) on ethaline with 0, 0.1, 1, 10, and 28.5wt% added water. For dry ethaline, we identify choline chloride as the rate-limiting solvation component in ethaline. However, the role of the solvent components changes gradually as water is added. Further, we provide quantitative solvent relaxation rates using the different presented time-resolved spectroscopic techniques and find remarkable agreement between them. Based on the solvent relaxation rates and combined with MDS, we develop a molecular understanding of the individual solvent components and their interactions in dry and wet ethaline with varying amounts of water content.

25 ENERGY STORAGE↗
DOE OSTI2022

NMR and Theoretical Study of In-Pore Diffusivity of Ionic Liquid–Solvent Mixtures

We report despite having a lower energy density than common batteries, electric double-layer capacitors (EDLCs) offer several advantages for high-power applications, including high power density, quick charge and discharge time, and long cycle life. Room-temperature ionic liquids (RTILs) have been intensely studied as promising electrolytes for applications in ELDCs because of their wide potential window, low volatility, as well as thermal and chemical stability. The main deficiency of neat RTILs in such applications is the sluggish diffusivity, which restricts the EDLCs’ power density. To alleviate the slow diffusivity, RTILs can be used in a mixture with organic solvents. In this study, we applied two-dimensional exchange nuclear magnetic resonance spectroscopy (2D EXSY NMR) and molecular dynamics (MD) simulations to investigate the diffusivity of anions of an RTIL, namely, 1-butyl-3-methyl-imidazolium bis(trifluoromethylsulfonyl)imide (BMIM + –TFSI – ), dissolved in five different organic solvents, in the micropores of activated carbon. We determined that the relative concentrations of ions in solutions in the micropores were higher than those in the bulk solutions and were also solvent-dependent. The ion diffusivities in the pores were found to be almost 2 orders of magnitude slower than in the bulk solutions, with methanol showing the largest relative disparity. These results suggested that the interactions of solvents with the activated carbon are critical not only to the power density of EDLCs but also to the energy density. The comparisons of ion diffusivities between the experiments and the MD simulations suggest the need to consider also the surface functionalities of activated carbon for the simulation of ion diffusion in the micropores of activated carbon.

electric double layer capacitors↗
DOE OSTI2024

Selective Detection of Intermediate-Amplitude Motion by Solid-State NMR

The coexistence of rigid and mobile molecules or molecular segments abounds in biomolecular assemblies. Examples include the carbohydrate-rich cell walls of plants and intrinsically disordered proteins that contain rigid β-sheet cores. In solid-state nuclear magnetic resonance (NMR) spectroscopy, dipolar polarization transfer experiments are well suited for detecting rigid components, whereas scalar-coupling experiments are well suited for detecting highly mobile components. However, few NMR methods are available to detect the segments that undergo intermediate-amplitude fast motion. Here, we introduce two NMR experiments, a two-dimensional T 2H -filtered CP-hCH correlation and a three-dimensional J-INADEQUATE CCH correlation, to observe this intermediate-amplitude motion. Both experiments involve 1 H detection under fast magic-angle spinning (MAS). By combining 1 H transverse relaxation (T 2H ) filters with dipolar polarization transfer, we suppress the signals of both highly rigid and highly mobile species, thus revealing the signals of intermediate mobile species. 1 H detection under fast MAS is crucial for distinguishing the different motional amplitudes. Here, we demonstrate these techniques on several plant cell wall samples and show that they allow the selective detection and resolution of certain hemicellulose and pectin signals, which are usually masked by the signals of the rigid cellulose and the highly dynamic pectins in purely dipolar and scalar NMR spectra.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2024

Proton Diffusion in Liquid 1,2,3-Triazole Studied by Incoherent Quasi-Elastic Neutron Scattering

Improving the proton transport in polymer electrolytes impacts the performance of next-generation solid-state batteries. However, little is known about proton conductivity in nonaqueous systems due to the lack of an appropriate level of fundamental understanding. Here, we studied the proton transport in small molecules with dynamic hydrogen bonding, 1,2,3-triazole, as a model system of proton hopping in a nonaqueous environment using incoherent quasi-elastic neutron scattering. By using the jump-diffusion model, we identified the elementary jump-diffusion motion of protons at a much shorter length scale than those by nuclear magnetic resonance and impedance spectroscopy for the estimated long-range diffusion. In addition, a spatially restricted diffusive motion was observed, indicating that proton motion in 1,2,3-triazole is complex with various local correlated dynamics. In conclusion, these correlated dynamics will be important in elucidating the nature of the proton dynamics in nonaqueous systems.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗