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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 1,351 records · Page 75
All sourcesNASA NTRSDOE OSTI
DOE OSTI2017

Molecular Dynamics Simulations of the Interfacial Region between Boehmite and Gibbsite Basal Surfaces and High Ionic Strength Aqueous Solutions

Classical molecular dynamics (MD) simulations were used to study the interactions of up to 2 M NaCl and NaNO3 aqueous solutions with the presumed inert boehmite (010) and gibbsite (001) surfaces. The force field parameters used in these simulations were validated against density functional theory calculations of Na+ and Cl- hydrated complexes adsorbed at the boehmite (010) surface. In all the classical MD simulations and regardless of the ionic strength or the nature of the anion, Na+ ions were found to preferably form inner-sphere complexes over outer-sphere complexes at the aluminum (oxy)hydroxide surfaces, adsorbing closer to the surface than both water molecules and anions. In contrast, Cl- ions were distributed almost equally between inner- and outer-sphere positions. The resulting asymmetry in adsorption strengths offers molecular-scale evidence for the observed isoelectric point (IEP) shift to higher pH at high ionic strength for aluminum (oxy)hydroxides. As such, the MD simulations also provided clear evidence against the assumption that the basal surfaces of boehmite and gibbsite are inert to background electrolytes. Finally, the MD simulations indicated that, although the adsorption behavior of Na+ in NaNO3 and NaCl solutions was similar, the different affinities of NO3- and Cl- for the aluminum (oxy)hydroxide surfaces might have macroscopic consequences, such as difference in the sensitivity of the IEP to the electrolyte concentration.

Shen, Zhizhang↗
DOE OSTI2018

Molecular Structure and Dynamics of Interfacial Polymerized Ionic Liquids

Polymerized ionic liquids (polyILs) hold great promise for applications in energy conversion and storage. Many of these applications are underpinned by the structures and processes at the interface between polyILs and solid surfaces; however, the interfacial behavior of polyILs remains largely unexplored. Here, we report the molecular simulation results of poly(1-butyl-3-vinylimidazolium hexafluorophosphate) supported on neutral and charged quartz substrates. It is found that the structure of interfacial polyILs deviates greatly from that of bulk polyILs, affected by the distance from the substrate and the surface charge on the substrate. Particularly, the coordination of interfacial anions by the cations differs from that in the bulk since their coordination environment, e.g., conformation and clustering of polymer chains and their pendant cations, is greatly modified by the confinement at the substrate and the electrostatic polyIL-substrate interactions. Similar to the bulk anions, the interfacial anions diffuse mainly by intra-chain hopping, but at a rate much slower than in the bulk due to the slow decay of the association between interfacial anions and their neighboring cations, which can be traced to the unique structure of polymer chains and cations near the quartz surfaces.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Thiocyanate Ions Form Antiparallel Populations at the Concentrated Electrolyte/Charged Surfactant Interface

Anions play significant roles in the separation of lanthanides and actinides. The molecular-scale details of how these anions behave at aqueous interfaces are not well understood, especially at high ionic strengths. Here, we describe the interfacial structure of thiocyanate anions at a soft charged interface up to 5 M bulk concentration with combined classical and phase-sensitive and molecular dynamics (MD) simulations. At low concentrations thiocyanate ions are mostly oriented with their sulfur end pointing toward the charged surfactants. In this work, the VSFG signal reaches a plateau at around 100 mM bulk concentration, followed by significant changes above 1 M. At high concentrations a new thiocyanate population emerges with their sulfur end pointing toward the bulk liquid. The –CN stretch frequency is different for up and down oriented SCN – ions, indicating different coordination environments. These results provide key molecular-level insights for the interfacial behavior of complex anions in highly concentrated solutions.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2024

Adsorption, Orientation, and Speciation of Amino Acids at Air–Aqueous Interfaces for the Direct Air Capture of CO 2

Amino acids make up a promising family of molecules capable of direct air capture (DAC) of CO 2 from the atmosphere. Under alkaline conditions, CO 2 reacts with the anionic form of an amino acid to produce carbamates and deactivated zwitterionic amino acids. The presence of the various species of amino acids and reactive intermediates can have a significant effect on DAC chemistry, the role of which is poorly understood. In this study, all-atom molecular dynamics (MD) based computational simulations and vibrational sum frequency generation (vSFG) spectroscopy studies were conducted to understand the role of competitive interactions at the air–aqueous interface in the context of DAC. We find that the presence of potassium bicarbonate ions, in combination with the anionic and zwitterionic forms of amino acids, induces concentration and charge gradients at the interface, generating a layered molecular arrangement that changes under pre- and post-DAC conditions. In parallel, an enhancement in the surface activity of both anionic and zwitterionic forms of amino acids is observed, which is attributed to enhanced interfacial stability and favorable intermolecular interactions between the adsorbed amino acids in their anionic and zwitterionic forms. The collective influence of these competitive interactions, along with the resulting interfacial heterogeneity, may in turn affect subsequent capture reactions and associated rates. Finally, these effects underscore the need to consider dynamic changes in interfacial chemical makeup to enhance DAC efficiency and to develop successful negative emission and storage technologies.

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

Combinatorial Discovery of Lanthanum–Tantalum Oxynitride Solar Light Absorbers with Dilute Nitrogen for Solar Fuel Applications

© 2017 American Chemical Society. Oxynitrides with the photoelectrochemical stability of oxides and desirable band energetics of nitrides comprise a promising class of materials for solar photochemistry. Challenges in synthesizing a wide variety of oxynitride materials has limited exploration of this class of functional materials, which we address using a reactive cosputtering combined with rapid thermal processing method to synthesize multi-cation-multi-anion libraries. We demonstrate the synthesis of a LaxTa1-xOyNzthin film composition spread library and its characterization by both traditional thin film materials characterization and custom combinatorial optical spectroscopy and X-ray absorption near edge spectroscopy (XANES) techniques, ultimately establishing structure-chemistry-property relationships. We observe that over a substantial La-Ta composition range the thin films crystallize in the same perovskite LaTaON2structure with significant variation of anion chemistry. The relative invariance in optical band gap demonstrates a remarkable decoupling of composition and band energetics so that the composition can be optimized while retaining the desirable 2 eV band gap energy. We also demonstrate the intercalation of diatomic nitrogen into the La3TaO7structure, which gives rise to a direct-allowed optical transition at 2.2 eV, less than half the value of the oxide's band gap. These findings motivate further exploration of the visible light response of this material that is predicted to be stable over a wide range of electrochemical potential.

Suram, Santosh K.↗
DOE OSTI2022

Impact of Ion–Ion Correlated Motion on Salt Transport in Solvated Ion Exchange Membranes

The influence of dynamical ion-ion correlations and ion pairing on salt transport in ion exchange membranes remain poorly understood. In this study, we use the framework of Onsager transport coefficients within atomistic molecular dynamics sim- ulations to study the impact of ion-ion correlated motion on salt transport in hydrated polystyrene sulfonate membranes and compare with the results from aqueous salt so- lutions. At sufficiently high salt concentrations, cation-anion dynamical correlations exert a significant influence on both salt diffusivities and conductivities. Anion-anion distinct correlations, arising from the imbalance between the concentration of free (mo- bile) cations and anions, and the retarding effect of the fixed charge groups on cations, proves to be an additional important feature for polymer membranes. Furthermore, our results demonstrate that dynamical correlations should become an important consideration in experimental measurements of salt diffusivities and conductivities for non-dilute salt solutions in polymer membranes.

36 MATERIALS SCIENCE↗
DOE OSTI2020

P-Type Electrochemical Doping Can Occur by Cation Expulsion in a High Performing Polymer for Organic Electrochemical Transistors

We investigate the mechanism of ion-dependent charge compensation during electrochemical oxidation (doping) of the model mixed ionic/electronic transporting polythiophene derivative poly(3-{[2-(2-methoxyethoxy)ethoxy]methyl}thiophene-2,5-diyl) (P3MEEMT). Using a combination of electrochemical quartz microbalance gravimetry and glow discharge optical emission spectroscopy, we show that charge compensation during polymer redox processes proceeds via a cation-dependent mechanism. For p-type polymer oxidation in certain electrolytes, charge compensation is achieved by both eventual injection of anions into the film, as well as initial expulsion of cations from the film. We compare doping mechanisms for a variety of electrolyte salts including potassium chloride, tetrabutylammonium chloride, potassium hexafluorophosphate (KPF6), and tetrabutylammonium hexafluorophosphate. For the electrolyte KPF6, both the cations and anions coexist in the water-swelled polymer even prior to application of electrical bias. Our data indicate that electrochemical doping (hole injection into the polymer and ionic charge compensation) proceeds via the following mechanism: (1) hydration of the neutral film by electrolyte (water, cations, anions), (2) cation (K+) expulsion from the film upon initial application of an oxidative bias, and (3) anion injection into the film at higher oxidation/doping levels (>~2 × 1020/cm3). Understanding the mechanism of charge compensation during the doping process should allow for the design of improved mixed ionic/electronic conductors for use in applications ranging from organic supercapacitors and redox flow batteries to bioelectronic sensors, thermoelectrics, and devices for neuromorphic computing.

Flagg, Lucas Q.↗
DOE OSTI2024

Solvation Structure of Methanol-in-Salt Electrolyte Revealed by Small-Angle X-ray Scattering and Simulations

The solvation structure of water-in-salt electrolytes was thoroughly studied, and two competing structures—anion solvated structure and anion network—were well-defined in recent publications. To further reveal the solvation structure in those highly concentrated electrolytes, particularly the influence of solvent, methanol was chosen as the solvent for this proposed study. In this work, small-angle X-ray scattering, small-angle neutron scattering, Fourier-transform infrared spectroscopy, and Raman spectroscopy were utilized to obtain the global and local structural information. With the concentration increment, the anion network formed by TFSI - became the dominant structure. Meanwhile, the hydrogen bonds among methanol were interrupted by the TFSI - anion and formed a new connection with them. Further, molecular dynamic simulations with two different force fields (GAFF and OPLS-AA) are tested, and GAFF agreed with synchrotron small-angle X-ray scattering/wide-angle X-ray scattering (SAXS/WAXS) results well and provided insightful information about molecular/ion scale solvation structure. This article not only deepens the understanding of the solvation structure in highly concentrated solutions, but more importantly, it provides additional strong evidence for utilizing SAXS/WAXS to validate molecular dynamics simulations.

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

Controlling the Activity and Stability of Electrochemical Interfaces Using Atom-by-Atom Metal Substitution of Redox Species

Understanding the molecular-level properties of electrochemically active ions at operating electrode–electrolyte interfaces (EEI) is key to the rational development of high-performance nanostructured surfaces for applications in energy technology. An electrochemical cell coupled with ion soft landing is employed to examine the effect of “atom-by-atom” metal substitution on the activity and stability of well-defined redox-active anions, PMo x W 12–x O 40 3– (x = 0, 1, 2, 3, 6, 9, or 12) at nanostructured ionic liquid EEI. A striking observation made by in situ electrochemical measurements and further supported by theoretical calculations is that the substitution of only one to three tungsten atoms by molybdenum atoms in the PW 12 O 40 3– anions results in a substantial spike in their first reduction potential. Specifically, PMo 3 W 9 O 40 3– showed the highest redox activity in both in situ electrochemical measurements and as part of a functional redox supercapacitor device, making it a “super-active redox anion” compared with all other PMo x W 12–x O 40 3– species. Electronic structure calculations showed that metal substitution in PMo x W 12–x O 40 3– causes the lowest unoccupied molecular orbital (LUMO) to protrude locally, making it the “active site” for reduction of the anion. Several critical factors contribute to the observed trend in redox activity including (i) multiple isomeric structures populated at room temperature, which affect the experimentally determined reduction potential; (ii) substantial decrease of the LUMO energy upon replacement of W atoms with more-electronegative Mo atoms; and (iii) structural relaxation of the reduced species produced after the first reduction step. Our results illustrate a path to achieving superior performance of technologically relevant EEIs in functional nanoscale devices through understanding of the molecular-level electronic properties of specific electroactive species with “atom-by-atom” precision.

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

Inverted Region in Bimolecular Electron Transfer in Solution Enabled by Delocalization

Rate constants for bimolecular electron transfer (ET) increased with driving force, -ΔG°, reached a plateau, and then decreased in an inverted region. This rate data was described well by electron transfer theory subject to a diffusion-controlled limit. These were for ET from radical anions of polydecylthiophene (P3DT) to a series of acceptors in THF solution. When the donor was the smaller anion of quaterthiophene (T4 •- ) the inverted region was much less prominent, and still less so for when the donor was the anion of bithiophene (T2 •- ). Description of the data using ET theory identifies smaller electronic couplings for the highly-delocalized P3DT anions as enabling the inverted behavior: The presence of a Marcus inverted region is a consequence of delocalized electronic states. The results of this study further imply that electronic couplings smaller than usually found for molecules in contact could boost efficiency of energy storage by electron transfer, and identifies size-mismatch as an important concept in control of electronic couplings.

14 SOLAR ENERGY↗
DOE OSTI2017

Influence of Countercation Hydration Enthalpies on the Formation of Molecular Complexes: A Thorium–Nitrate Example

The influence of countercations (A(n+)) in directing the composition of monomeric metalligand (ML) complexes that precipitate from solution are often overlooked despite the wide usage of A(n+) in materials synthesis. Herein, we describe a correlation between the composition of ML complexes and A(+) hydration enthalpies found for two related series of thorium (Th)-nitrate molecular compounds obtained by evaporating acidic aqueous Th-nitrate solutions in the presence of A(+) counterions. Analyses of their chemical composition and solid-state structures demonstrate that A(+) not only affects the overall solid-state packing of the Th-nitrato complexes but also influences the composition of the Th-nitrato monomeric anions themselves. Trends in composition and structure are found to correlate with A(+) hydration enthalpies, such that the A(+) with smaller hydration enthalpies associate with less hydrated and more anionic Th-nitrato complexes. This perspective, broader than the general assumption of size and charge as the dominant influence of A(n+), opens a new avenue for the design and synthesis of targeted metal-ligand complexes.

Jin, Geng Bang↗
DOE OSTI2018

Deconvoluting the Role of Charge in a Supramolecular Catalyst

In this paper, we have demonstrated that the microenvironment of a highly anionic supramolecular catalyst can mimic the active sites of enzymes and impart rate accelerations of a million-fold or more. However, these microenvironments can be challenging to study, especially in the context of understanding which specific features of the catalyst are responsible for its high performance. We report here the development of an experimental mechanistic probe consisting of two isostructural catalysts. When examined in parallel transformations, the behavior of these catalysts provides insight relevant to the importance of anionic host charge on reactivity. These two catalysts exhibit similar host-substrate interactions, but feature a significant difference in overall anionic charge (12 – and 8 – ). Within these systems, we compare the effect of constrictive binding in a net neutral aza-Cope rearrangement. Finally, we then demonstrate how the magnitude of anionic host charge has an exceptional influence on the reaction rates for a Nazarov cyclization, evidenced by an impressive 680-fold change in reaction rate as a consequence of a 33% reduction in catalyst charge.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2019

Reverse Dual-Ion Battery via a ZnCl 2 Water-in-Salt Electrolyte

Dual-ion batteries are known for anion storage in the cathode coupled to cation incorporation in the anode. We flip the sequence of the anion/cation-storage chemistries of the anode and the cathode in dual-ion batteries (DIBs) by allowing the anode to take in anions and a cation-deficient cathode to host cations, thus operating as a reverse dual-ion battery (RDIB). The anion-insertion anode is a nano-composite having ferrocene encapsulated inside a micro-porous carbon, and the cathode is a Zn-insertion Prussian blue, Zn-3[Fe(CN)(6)](2). This unique battery configuration benefits from the usage of a 30 m ZnCl2 "water-in-salt" electrolyte. This electrolyte minimizes the dissolution of ferrocene; it raises the cation-insertion potential in the cathode, and it depresses the anion-insertion potential in the anode, thus widening the full cell's voltage by 0.35 V compared with a dilute ZnCl2 electrolyte. RDIBs provide a configuration-based solution to exploit the practicality of cation-deficient cathode materials in aqueous electrolytes.

25 ENERGY STORAGE↗
DOE OSTI2021

Strengthening of Calcite Assemblages Through Chemical Complexation Reactions

Abstract Utilization of subsurface reservoirs, including fluid extraction/injection, can induce stress changes and modify in‐situ chemical equilibrium causing subcritical fracturing and deformation. Here, we show that chemical complexation reactions at the newly created fracture surfaces within the crack tip limit fracturing during consolidation of granular calcite assemblages. Previously, we showed that analogous chemical complexation reactions can increase in‐situ fracture toughness in pre‐fractured single crystal calcite. To test the chemical complexation effect under subsurface conditions, we consolidated samples under increasing hydrostatic pressure to induce widespread intergranular fracturing in the presence of fluid containing common anions. Measured consolidation, acoustic emissions, and microfracturing demonstrate that deformation correlates with complexation affinity for calcium in calcite and aqueous anions. We observed that deformation is lowest in the presence of strongly complexing anions (e.g., sulphate), provided sufficient anion diffusion rates. This understanding is important for predicting reservoir effective strength in the presence of complex aqueous fluids.

Choens, R. C.↗
DOE OSTI2019

Injection of oxygen vacancies in the bulk lattice of layered cathodes

Surfaces, interfaces, and grain boundaries are, classically, known to be sinks at which defects generated within bulk lattice will preferentially migrate to and get annihilated, therefore rejuvenating a crystalline lattice to restore the intended functionalities.1, 2, 3 Here we report an inverse case by which the defects generated at the particle surface are continuously pumped into the bulk lattice and consequentially compromising the intended functionalities. We discovered that during the operation of a rechargeable battery, oxygen vacancies generated at cathode particle surfaces migrate toward inside of a perfect lattice in lithium-rich layered cathodes, featuring electrochemical driven surface vacancy creation, injection and condensation phenomenon and revealing an unrecognized surface process induced bulk lattice degradation featured with void formation and lattice reorganization. This process is associated with a high-cutoff voltage at which the anionic redox is activated. Coupling with calculations, we substantiate that triggering of anionic redox leads to sharply lowering of both formation energy of oxygen vacancy and migration barrier of oxidized oxide ions, therefore enabling migration of oxygen vacancy via oxidized oxide ion and leading to the injection of oxygen vacancy generated at the particle surface into the bulk lattice. This work unveils unpredicted behavior of oxidized oxide ion, leading to essential insight for designing of high capacity cathode for better batteries through coupled cationic and anionic redox dynamics in layered cathodes. In a broad term, this work provides insight on the intimate coupling between interfacial process and bulk lattice behavior for governing electrode functionality.

Yan, Pengfei↗
DOE OSTI2020

Synthesis and structural characterization of Ca 12 Ga 14 O 33

Ca 12 Ga 14 O 33 was successfully synthesized using a wet chemistry technique to promote the homogenous mixing of the Ca and Ga cations. Rietveld refinements on X-ray and neutron powder diffraction data confirm that the compound is isostructural to Ca 12 Al 14 O 33 , however, with a significantly larger lattice parameter allowing for the cages that result from the framework arrangement to expand. In naturally occurring Ca 12 Al 14 O 33 , the mineral mayenite, these cages are occupied by O 2- anions, however, experimental studies exchanging the O 2- anions with other anions has led to a host of applications, depending on the caged anion. The functional nature of the structure, where framework distortions coupled with cage occupants, are correlated to electronic band structure and modifications to the framework could lead to interesting physical properties. The phase evolution was tracked using thermogravimetric analysis and high temperature X-ray diffraction and showed a lower formation temperature for the Ca 12 Ga 14 O 33 analogue compared to Ca 12 Al 14 O 33 synthesized using the same wet chemistry technique. Analyzing both X-ray and neutron powder diffraction using the Rietveld method with two different starting models results in one structural model, with one Ca position and the caged O on a 24d special position, being preferred.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Electrophilicity of oxalic acid monomer is enhanced in the dimer by intermolecular proton transfer

We have analyzed the effect of excess electron attachment on the network of hydrogen bonds in the oxalic acid dimer (OA) 2 . The most stable anionic structures may be viewed as complexes of a neutral hydrogenated moiety HOA˙ coordinated to an anionic deprotonated moiety (OA–H) - . HOA˙ acts as a double proton donor and (OA–H) - as a double proton acceptor. Thus the excess electron attachment drives intermolecular proton transfer. We have identified several cyclic hydrogen bonded structures of (OA) 2 - . Their stability has been analyzed in terms of the stability of the involved conformers, the energetic penalty for deformation of these conformers to the geometry of the dimer, and the two-body interaction energy between the deformed HOA˙ and (OA–H) - . There are at least seven isomers of (OA) 2 - with stabilization energies in the range of 1.26–1.39 eV. These energies are dominated by attractive two-body interaction energies. The anions are vertically bound electronically by 3.0–3.4 eV and adiabatically bound by at least 1.6 eV. The computational predictions are consistent with the anion photoelectron spectrum of (OA) 2 - . The spectrum consists of a broad feature, with an onset of 2.5 eV and spanning to 4.3 eV. The electron vertical detachment energy (VDE) is assigned to be 3.3 eV.

Keolopile, Zibo G.↗