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DOE OSTI2023

Polymer Architecture-Induced Trade-off between Conductivities and Transference Numbers in Salt-Doped Polymeric Ionic Liquids

Recent experiments have demonstrated that polymeric ionic liquids that share the same cation and anion but possess different architectures can exhibit markedly different conductivity and transference number characteristics when doped with lithium salt. In this study, we used atomistic molecular simulations on polymer chemistries inspired by the experiments to probe the mechanistic origins underlying the competition between conductivity and transference numbers. Our results indicate that the architecture of the polycationic ionic liquid plays a subtle but crucial role in modulating the anion–cation interactions, especially their dynamical coordination characteristics. Chemistries leading to longer-lived anion–cation coordinations relative to lithium–anion coordinations lead to lower conductivities and higher transference numbers. Furthermore, our results suggest that higher conductivities are accompanied by lower transference numbers and vice versa, revealing that alternative approaches may need to be considered to break this trade-off in salt-doped polyILs.

33 ADVANCED PROPULSION SYSTEMS↗

DOE OSTI2018

Dynamically Disordered Lattice in a Layered Pb-I-SCN Perovskite Thin Film Probed by Two-Dimensional Infrared Spectroscopy

The dynamically flexible lattices in lead-halide perovskites may play important roles in extending carrier recombination lifetime in 3D perovskite solar-cell absorbers and in exciton self-trapping in 2D perovskite white-light phosphors. Here, two-dimensional infrared (2D IR) spectroscopy was applied to study a recently reported Pb-I-SCN layered perovskite. The Pb-ISCN perovskite was spin-coated on a SiO 2 surface as a thin film, with a thickness of ~100 nm, where the S 12 CN – anions were isotopically diluted with the ratio of S 12 CN:S 13 CN=5:95 or 1:99 to avoid vibrational coupling and excitation transfer between adjacent SCN – anions. The minor S 12 CN – component was the principal vibrational probe that reported on the structural evolution through 2D IR spectroscopy. Spectral diffusion was observed with a time constant of 4.1 ± 0.3 ps. Spectral diffusion arises from small structural changes that result in sampling of frequencies within the distribution of frequencies that comprise the inhomogeneously broadened absorption spectrum of the in the Pb-I-SCN layered perovskite. These transitions among discrete local structures are distinct from oscillatory phonon motions of the lattice. To accurately evaluate the structural dynamics through measurement of spectral diffusion, the vibrational coupling between adjacent SCN – anions had to be carefully treated. Although the inorganic layers of typical 2D perovskites are structurally isolated from each other, the 2D IR data demonstrated that the layers of the Pb-I-SCN perovskite are vibrationally coupled. When both S 12 CN – and S 13 CN – were pumped simultaneously, cross-peaks between S 12 CN and S 13 CN vibrations and an oscillating 2D band shape of the S 12 CN – vibration were observed. Both observables demonstrate vibrational coupling between the closest SCN – anions, which reside in different inorganic layers. The thin films and the isotopic dilution produced exceedingly small vibrational echo signal fields; measurements were made possible using the near-Brewster’s angle reflection pump-probe geometry.

14 SOLAR ENERGY↗

DOE OSTI2018

Using Biomolecules to Separate Plutonium - 18393

Relying on the thermodynamics and the reaction kinetics of the metal-ligand bond is the traditional approach to selective separation of metals such as plutonium. An alternative is to use a biologically based separation that leverages multiple factors to sense, bind and transport metals in a series of steps. The protein serum transferrin (Tf) handles the regulation and transport of iron in the blood. Iron and a synergistic anion bind to Tf in one or both of Tf's two lobes (N-lobe and C-lobe). The conformation of Tf changes due to the lobes closing around the metals. The conformational change that occurs when a metal ion and synergistic anion bind to transferrin can trigger additional interactions with the transferrin receptor protein and the subsequent transport of the metal-transferrin complex into cells. Transferrin also is known to bind and transport plutonium into cells but this process is less efficient than iron transport because certain plutonium-transferrin complexes appear to be unable to trigger the same conformational change in transferrin as the iron-transferrin complex. We hypothesize that the synergistic anion is the cause of the different conformational changes that inhibit plutonium-transferrins from binding to the transferrin receptor protein. Using cerium as a non-radioactive surrogate for plutonium(IV), we have been able to synthesize cerium-transferrin complexes with only carbonate as the synergistic anion as a prelude to experiments with plutonium-transferrin complexes that can test our hypothesis. (authors)

07 ISOTOPE AND RADIATION SOURCES↗

DOE OSTI2022

Non‐Flammable Ester Electrolyte with Boosted Stability Against Li for High‐Performance Li Metal Batteries

Abstract In traditional non‐flammable electrolytes a trade‐off always exists between non‐flammability and battery performance. Previous research focused on reducing free solvents and forming anion‐derived solid‐electrolyte interphase. However, the contribution of solvated anions in boosting the stability of electrolyte has been overlooked. Here, we resolve this via introducing anions into Li + solvation sheaths using anions with similar Gutmann donor number (DN) to that of solvents. Taking trimethyl phosphate fire‐retardant (DN=23.0 kcal mol −1 ) and NO 3 − (DN=22.2 kcal mol −1 ) as an example, NO 3 − is readily involved in the Li + solvation sheath and reduces the polarity of solvent. This results in boosted stability of electrolyte against Li. The developed non‐flammable electrolyte has low viscosity, high ionic conductivity and is low cost. The reversibility of Li‐Cu cell was improved to 99.49 % and the lifespan of practical LMBs was extended by >100 %.

Wang, Zhijie↗

DOE OSTI2019

Transforming Porous Organic Cages into Porous Ionic Liquids via a Supramolecular Complexation Strategy

Porous liquids are a type of porous materials that engineer permanent porosity into unique flowing liquids, exhibiting promising functionalities for a variety of applications. In this study, a Type I porous liquid is synthesized by transforming porous organic cages into porous ionic liquids via a supramolecular complexation strategy. Simple physical mixing of 18-crown-6 with task-specific anionic porous organic cages affords a porous ionic liquid with anionic porous organic cages as the anionic parts and 18-crown-6/potassium ion complexes as the cationic parts. In contrast, mixing of 15-crown-5 and anionic porous organic cages in a 2:1 ratio gives only solids, while the addition of excess 15-crown-5 affords a Type II porous liquid. The permanent porosity in the cage-based porous liquids has been also confirmed by molecular simulation, positron (e + ) annihilation lifetime spectroscopy, and enhanced gas sorption capacity compared with pure crown ethers.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2022

Non‐Flammable Ester Electrolyte with Boosted Stability Against Li for High‐Performance Li Metal Batteries

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2023

Ambipolar Electrochemistry of Pre‐Intercalated Ti 3 C 2 T x MXene in Ionic Liquid Electrolyte

Abstract Cation intercalation with or without redox remains the dominant charge storage mechanism for two‐dimensional (2D) Ti 3 C 2 T x MXene. Anion‐based charge storage remains unexplored due to intrinsic negative surface charge of MXenes preventing spontaneous intercalation of anions and irreversible oxidation of Ti at anodic potentials in aqueous electrolytes. In this work, we report on the ambipolar electrochemical behavior of the Ti 3 C 2 T x in ionic liquid electrolyte over a 2.5 V electrochemically stable window. The experiments are conducted on a thin Ti 3 C 2 T x film current collector coated with an electroactive layer of small flakes (∼150 nm) of Ti 3 C 2 T x pre‐intercalated with 1‐ethyl‐3‐methylimidazolium bis‐(trifluoromethylsulfonyl)‐imide (EMIM‐TFSI) ionic liquid. Couples of redox peaks with a very small potential separation during the voltage sweep are observed at high negative (−0.75 V vs. Ag wire) and high positive (+0.75 V vs. Ag wire) potentials. Our experimental electrochemical data combined with density functional theory (DFT) calculations suggest feasibility of pseudo‐intercalation of TFSI anions between Ti 3 C 2 T x flakes. This study provides a pathway for elucidating anion intercalation for different MXene chemistries in solvent‐free electrolytes, which can lead to development of MXene based energy storage devices with improved performance.

Electrochemistry↗

DOE OSTI2018

Restricted Speciation and Supramolecular Assembly in the 5f Block

Hybrid materials bearing elements from the 5f block display a rich diversity of coordination geometries, connectivities, and assembly motifs. Exemplary in this regard have been the uranyl coordination polymers, which feature a wide range of secondary building units resulting from hydrolysis and oligomerization of the [UO2]2+ cation. An alternative approach to novel materials, however, suppresses hydrolysis and relies on non-covalent interactions (e.g. hydrogen or halogen bonding) to direct assembly of a more limited suite of species or building units. This may be achieved through the use of high-anion media to promote singular actinyl anions that are assembled with organic cations, or by way of functionalized chelating ligands that produce complexes suited for assembly through peripheral donor/acceptor sites. Presented in this Concept Article is therefore an overview of our efforts in this arena. We highlight examples of each approach, share our thoughts regarding delineation of assembly criteria and discuss the opportunities for exploring structure-property relationships in these systems.

Carter, Korey P.↗

DOE OSTI2024

High-throughput measurements of CO 2 permeance and solubility in ionic liquid reveal a synergistic role of ionic interactions and void fractions

The factors that govern CO 2 solubility in ionic liquids (ILs) are of great interest for the development of new materials for CO 2 capture and utilization. The cationic functional group (i.e., imidazolium, pyrrolidinium, pyridinium, etc.), alkyl chain length of cation, degree of fluorination of anion, anion size, and the void fraction in IL are known to influence CO 2 solubility. However, a comprehensive explanation of how these factors collectively affect CO 2 solubility has not been developed yet. This knowledge gap is largely attributed to the lack of CO 2 solubility data for IL structures other than imidazolium based ILs. We report here an automated high-throughput (HT) setup for the measurement of CO 2 solubility in room-temperature ILs (RTILs) combining six different anions and nine different cations for a total of 19 different specific ranges of RTILs. The HT setup first dispenses up to 200 µL of RTILs in a 96-well microtiter plate and then utilizes a robotic arm to measure cyclic voltammogram (CV) in each well using maneuverable Ag electrodes. The Cottrell analysis of the CO 2 reduction CV peak provides a direct measurement of CO 2 permeance in RTILs, which yields Henry’s constant from the estimated diffusion coefficient of CO 2 . Henry’s constants thus obtained are in very good agreement with those reported earlier. The measured CO 2 permeance and Henry’s constant of all RTILs seem to follow a first-order dependence on void fraction and a second-order dependence on electrostatic interaction between anion and cation of IL, with some synergistic dependence on the product of a void fraction and electrostatic interaction, making them two important descriptors for the design of novel ILs.

CO2 Solubility↗

DOE OSTI2020

Potassium iodide cluster based superhalogens and superalkalis: Theoretical calculations and experimental confirmation

We studied a series of potassium-iodide clusters with formulas of (KI)nI- and (KI)nK+ (n = 1-3) by quantum chemical calculations. The calculated vertical detachment energies (VDEs) of (KI)nI- clusters are all higher than those of halogen anions, and thus can be classified as superhalogen anions; while the calculated vertical electron affinities (VEAs) of (KI)nK+ clusters are all lower than those of alkali metal cations, and thus they can be recognized as superalkali cations. Our calculated VEA for (KI)K+, i.e., K2I+, agrees well with the previously measured value by thermal ionization mass spectrometry. We confirmed the theoretical predictions by measuring the negative ion photoelectron (NIPE) spectra of (KI)nI- anions, from which the measured VDEs are found to be in good agreement with the theoretically calculated values. In addition, we also explored the possibility of supersalts formed by these superhalogen anions and superalkali cations, for example, K3I3 can be regarded as a supersalt formed by K2I+ and KI2– subunits.

potassium-iodide clusters, superhalogen, superalka↗

DOE OSTI2020

Phosphate tolerance of nitrogen-coordinated-iron-carbon (FeNC) catalysts for oxygen reduction reaction: A size-related hindrance effect

The greatest challenges facing the large – scale commercialization of the intermediate temperature phosphoric acid fuel cell (PAFC) technology are: (i) the high cost of Pt catalyst that is required to overcome the slow kinetics of oxygen reduction reaction (ORR) on the PAFC cathode, and (ii) deactivation of the Pt catalyst by exposure to the phosphoric acid electrolyte. Inexpensive carbon-based materials, particularly iron- spectroscopy is used to explore the phenomenon of phosphate poisoning nitrogen-coordinated carbon supported catalysts (FeNC), are promising cathodes for PAFCs. The higher ORR activation energy and phosphate poisoning resistance of FeNC present a clear advantage over the Pt-based commercial catalysts that are easily susceptible to deactivation after exposure to phosphate anions. While the immunity of FeNC catalysts to phosphate anion poisoning has been reported previously, this work explores the counter-intuitive and conditional nature of this poisoning resistance based on the properties of the carbon support used in the preparation of the FeNC catalyst. Additionally, a combination of electrochemical measurements with characterization experiments performed using X-ray photoelectron spectroscopy, infrared spectroscopy and in-situ X-ray absorption on FeNC catalysts synthesized from two different carbon supports. Results from these studies reveal a “size-related hindrance effect” wherein the ORR active Fe centers in FeNC remain inaccessible to larger anions such as phosphate when the Fe sites are present deeper inside the pores of a carbon support with high porosity. However, FeNC catalyst is poisoned by phosphate anions when synthesized using a carbon support with low porosity. This work helps gain insights into the nature of active sites in FeNC catalysts that will be useful in designing precious-metal free ORR catalysts for intermediate temperature fuel cell technologies.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2018

What is the effect of lipophilic polymeric ionic liquids on friction and wear?

In this work, methacrylate-type ionic liquid (IL) monomers containing a quaternary ammonium cation and two different counter-anions were synthesized and used as co-monomers to obtain functional poly(alkyl methacrylates) (PAMAs) as friction and wear reducing additives for lubricants. The effect of molecular weight, polymer topology (random or diblock), and IL counter anion on friction and wear behavior of polymer PAO (poly-alpha olefin) solutions have been investigated. The results were compared to those of PAO solutions additized with a small molecule, non-polymeric ionic liquid, or non-ionic copolymers containing 2-(dimethylamino)ethyl methacrylate (DMAEMA) as the polar comonomer. No clear correlation between polymer molecular weight and friction or wear behavior was observed. Random ionic liquid copolymers led to lower wear volumes than their block counterparts. Polymers containing dicyanamide (DCA) counter anion showed lower wear volume compared to those containing bis((trifluoromethyl)sulfonyl)imide (TFSI) anion. Surprisingly, none of the IL copolymers studied outperformed the DMAEMA containing block copolymer in terms of wear volume reduction, suggesting the IL moiety had no beneficial effect on wear.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2023

Crystal structure of meglumine diatrizoate, (C 7 H 18 NO 5 )(C 11 H 8 I 3 N 2 O 4 )

The crystal structure of meglumine diatrizoate has been solved and refined using synchrotron X-ray powder diffraction data and optimized using density functional theory techniques. Meglumine diatrizoate crystallizes in space group P2 1 (#4) with a = 10.74697(4), b = 6.49364(2), c = 18.52774(7) Å, β = 90.2263(3), V = 1292.985(5) Å 3 , and Z = 2. Two different crystal structures, which yielded essentially identical refinement residuals and positions of the non-H atoms, were obtained. The differences were in the H atom positions and the hydrogen bonding. One structure was 123.0 kJ/mol/cell lower in energy than the other and was adopted for the final description. The crystal structure consists of alternating double layers of cations and anions along the c-axis. The hydrogen bonds link the cations and anions into a three-dimensional framework. Each of the hydrogen atoms on the ammonium nitrogen of the cation acts as a donor in a strong N–H∙∙∙O hydrogen bond. One of these is to a hydroxyl group of another cation, and the other is to the carboxylate group of the anion. Each of the amide nitrogen atoms of the anion forms a strong N–H∙∙∙O intermolecular hydrogen bond, one to a carbonyl and the other to a carboxylate group. The powder pattern has been submitted to ICDD for inclusion in the Powder Diffraction File™ (PDF®).

36 MATERIALS SCIENCE↗

DOE OSTI2021

Theory-Guided Inelastic Neutron Scattering of Crystalline Alkaline Aluminate Salts Bearing Principal Motifs of Solution-State Species

Aluminate salts precipitated from caustic alkaline solutions exhibit a correlation between the anionic speciation and the identity of the alkali cation in the precipitate, with the aluminate ions occurring either in monomeric (Al(OH) 4 – ) or dimeric (Al 2 O(OH) 6 2– ) forms. The origin of this correlation is poorly understood as are the roles that oligomeric aluminate species play in determining the solution structure, prenucleation clusters, and precipitation pathways. Characterization of aluminate solution speciation with vibrational spectroscopy results in spectra that are difficult to interpret because the ions access a diverse and dynamic configurational space. To investigate the Al(OH) 4 – and Al 2 O(OH) 6 2– anions within a well-defined crystal lattice, inelastic neutron scattering (INS) and Raman spectroscopic data were collected and simulated by density functional theory for K 2 [Al 2 O(OH) 6 ], Rb 2 [Al 2 O(OH) 6 ], and Cs[Al(OH) 4 ]·2H 2 O. These structures capture archetypal solution aluminate species: the first two salts contain dimeric Al 2 O(OH) 6 2– anions, while the third contains the monomeric Al(OH) 4 – anion. Here, comparisons were made to the INS and Raman spectra of sodium aluminate solutions frozen in a glassy state. In contrast to solution systems, the crystal lattice of the salts results in well-defined vibrations and associated resolved bands in the INS spectra. The use of a theory-guided analysis of the INS of this solid alkaline aluminate series revealed that differences were related to the nature of the hydrogen-bonding network and showed that INS is a sensitive probe of the degree of completeness and strength of the bond network in hydrogen-bonded materials. Results suggest that the ionic size may explain cation-specific differences in crystallization pathways in alkaline aluminate salts.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2019

Energetics of CO2– in Aqueous Solution

Gas-phase and aqueous solution properties of neutral and anionic clusters of CO2 with 3, 4, and 8 explicit H2O molecules are calculated at the coupled cluster (CCSD(T)) level plus a self-consistent reaction field. Anionic clusters with the radical electron density localized on the carbon of the CO2 molecule rather than localized on the H2O molecules are more favorable energetically by 10-20 kcal/mol in the gas phase (?Hgas(298 K)) and 20-30 kcal/mol in aqueous solution (?Gaq(298 K)). The most favorable structures are those with the largest number of strong hydrogen bonds between the CO2 - and the explicit H2O molecules. Adiabatic electron affinities were calculated in the gas phase and in aqueous solution for the microsolvated anion. The adiabatic electron affinity of aqueous CO2 - is predicted to be 2.35 ± 0.08 eV and is converged with as few as 3 explicit H2O molecules plus a self-consistent reaction field. The EA of aqueous CO2 is significantly greater than the aqueous solvation free energy of the electron. The vertical attachment energies to CO2 and the vertical detachment energies from CO2 - were calculated. The solvated CO2 - anion is substantially bent to 135°, which requires 1.52 eV. The large energy required for bending in combination with the vertical detachment and attachment energies shows that substantial local solvent reorganization occurs on detachment or attachment of an electron to solvated CO2. The formation of aqueous C2O4 2- from CO2 - was also explored, and dimerization is predicted to occur.

McNeill, Ashley↗

DOE OSTI2018

Methionine 170 is an Environmentally Sensitive Membrane Anchor in the Disordered HVR of K-Ras4B

Ras protein colocalization at the plasma membrane is implicated in the activation of signaling cascades that promote cell growth, survival, and motility. However, the mechanisms that underpin Ras self-association remain unclear. We use molecular dynamics simulations to show how basic and hydrophobic components of the disordered C-terminal membrane tether of K-Ras4B combine to regulate its membrane interactions. Specifically, anionic lipids attract lysine residues to the membrane surface, thereby splitting the peptide population into two states that exchange on the microsecond time scale. These states differ in the membrane insertion of a methionine residue, which is influenced by local membrane composition. As a result, these states may impose context-dependent biases on the disposition of Ras’ signaling domain, with possible implications for the accessibility of its effector binding surfaces. Furthermore, we investigate Ras’ ability to nanocluster by fly-casting for patches of anionic lipids and find that while anionic lipids promote the intermolecular association of K-Ras4B membrane tethers, at short range this appears to be a passive process in which anionic lipids electrostatically screen these cationic peptides to mitigate their natural repulsion. Together with the sub-microsecond stability of interpeptide contacts, this result suggests that experimentally observed K-Ras4B nanoclustering is not driven by direct intermolecular contact of its membrane tethers.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

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↗