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All sourcesNASA NTRSDOE OSTI
DOE OSTI2021

Ab-initio investigation of the effect of adsorbed salts on segregation of Cr at the Ni (100) surface

The dissolution and depletion of chromium (Cr) in salt facing nickel (Ni) alloy surfaces is one of the predominant degradation mechanisms of structural components in molten salt technology. Here, we use density functional theory to investigate the role of electronic level interactions that may underlie the depletion phenomenon of Cr in a Ni (100) surface exposed to various adsorbed salt species. Our results show that, under vacuum, Ni preferentially segregates to the surface layer. Conversely, in the presence of adsorbed anionic salt species (e.g., chlorine (Cl), fluorine (F) or the impurity oxygen (O)) Cr segregation becomes more favorable. In these cases, Cl has the weakest effect on segregation, while O has the strongest effect. Our analysis reveals the strong correlation between Cr segregation and the amount of valence charge transferred between the Cr atom and surface adsorbate: the greater the charge transfer, the lower the segregation energy. We also show that, when considered, secondary cations screen Cr-anion interactions, which in turn reduce the magnitude of the anions effect on segregation. These results shed light on the role of salt impurities likely play in the overall corrosion phenomena in molten salt environments. This work provides insights into the atomic level interactions fundamental to molten salt corrosion and on the importance of maintaining salt purity.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2014

Heterologous expression and solution structure of defensin from lentil Lens culinaris

Highlights: • Lentil defensin Lc-def and its {sup 15}N-labeled analog were overexpressed in E. coli. • Lc-def is active against fungi, but does not inhibit growth of G+ and G− bacteria. • Lc-def spatial structure involves triple-stranded β-sheet and α-helix (CSαβ motif). • Lc-def is able to bind to anionic lipid vesicles under low-salt conditions. • NMR data revealed significant μs–ms mobility in the loops 1 and 3 of Lc-def. - Abstract: A new defensin Lc-def, isolated from germinated seeds of the lentil Lens culinaris, has molecular mass 5440.4 Da and consists of 47 amino acid residues. Lc-def and its {sup 15}N-labeled analog were overexpressed in Escherichia coli. Antimicrobial activity of the recombinant protein was examined, and its spatial structure, dynamics, and interaction with lipid vesicles were studied by NMR spectroscopy. It was shown that Lc-def is active against fungi, but does not inhibit the growth of Gram-positive and Gram-negative bacteria. The peptide is monomeric in aqueous solution and contains one α-helix and triple-stranded β-sheet, which form cysteine-stabilized αβ motif (CSαβ) previously found in other plant defensins. The sterically neighboring loop1 and loop3 protrude from the defensin core and demonstrate significant mobility on the μs–ms timescale. Lc-def does not bind to the zwitterionic lipid (POPC) vesicles but interacts with the partially anionic (POPC/DOPG, 7:3) membranes under low-salt conditions. The Lc-def antifungal activity might be mediated through electrostatic interaction with anionic lipid components of fungal membranes.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2023

Elucidating the speciation of extracted lanthanides by diglycolamides

Many studies over the past few decades have been devoted to addressing the application of diglycolamides (DGAs) for hydrometallurgical-based, f-element separations. Work to date has shown the molecular structure of a DGA derivative can have a significant impact on intra-lanthanide partitioning patterns. More recent studies have pushed towards probing the structure function relationship of the lanthanide-DGA complex to enable the design of more efficient lanthanide separation systems. Spectroscopic techniques, such as UV–Visible, Fourier Transformed Infrared Spectroscopy (FT-IR), Nuclear Magnetic Resonance (NMR), and Extended X-ray Absorption Fine Structure (EXAFS), provide information regarding the inner-sphere coordination of a given lanthanide-DGA complex. Scattering techniques, such as Dynamic Light Scattering (DLS), Small-Angle X-ray Scattering (SAXS), and Small-Angle Neutron Scattering (SANS), address nanoscale structures including aggregate sizes and morphology. Here, this review assesses the current state-of-knowledge regarding lanthanide-DGA hydrometallurgical (i.e., solvent extraction systems) interrogated using spectroscopic and scattering techniques to characterize the extracted Ln 3+ DGA species. Of particular interest to this review is the impact of varied diluents, inclusion and variation of phase modifiers, and DGA derivatization on system characteristics. While there has been extensive literature on the application of DGAs for f-element separations, the literature lacks a collective assessment of the speciation of Ln 3+ in the organic phase. This review provides new insights into the field of DGA separations, explicitly with an application to intra-lanthanide separations. Specifically, this review illustrates the importance of both the co-extraction anion (Cl - , NO 3 - , or ClO 4 - ) as it pertains to both the aggregate size and Ln 3+ distribution coefficient. It is evident the ability of the anion to disrupt the hydrogen bonding network limits both aggregate size and distribution coefficients according to the Hoffmeister series. This suggests the importance of the large, softer anions with a low charge-to-surface area ratio on encouraging hydrogen bond interactions. In addition, the co-extracted cation (H + vs Na + ) is important for mitigating transfer of Ln 3+ from the aqueous to the organic phase through extensive hydrogen bonding networks. These networks are responsible for forming supramolecular aggregates where a change in morphology is observed with increasing concentrations of H + and/or Ln 3+ in the organic phase.

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

How mixing tetraglyme with the ionic liquid 1- n -hexyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide changes volumetric and transport properties: An experimental and computational study

The viscosity and density of the ionic liquid (IL) 1-n-hexyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([C 6 mim][NTf 2 ]), the molecular solvent tetraethylene glycol dimethyl ether (tetraglyme or G4) and their binary mixtures were measured experimentally as a function of temperature. The same systems were also studied using classical molecular dynamics (MD) simulations. The viscosities of the [C 6 mim][NTf 2 ]/G4 mixtures decrease with increasing G4 concentration, though not as much as an ideal mixing model would predict. Detailed analysis of the MD results reveals that G4 preferentially solvates cations, leading to a reduction in the interaction energy between cations and anions and a subsequent enhancement in anion mobility. A similar effect has been reported when glymes are mixed with salts containing alkali metal cations, with the resulting mixtures being called “solvate” ionic liquids. The simulations predict that the ionic conductivity will be maximized when the G4 mole fraction is around 10–20%. The ability of G4 to effectively solvate the cations stems from localized charges on the oxygen. In conclusion, the simulations predict that solvents having large localized positive charges would preferentially solvate anions, leading to enhanced cation mobility.

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

Thermodynamic modeling of aqueous lithium salt solutions with association electrolyte nonrandom two-liquid activity coefficient model

The high charge density of lithium ion and the resulting strong association phenomena make thermodynamic modeling of aqueous lithium electrolyte solutions extremely challenging. In this study, the association electrolyte nonrandom two-liquid activity coefficient model of Lin et al. (AIChE J. 2022, 68(2), e17422) is utilized to correlate and predict thermodynamic properties and solubility behavior of aqueous single electrolyte solutions of LiCl, LiBr, LiI, and LiNO 3 , and their mixed electrolyte solutions. Capturing self-association of water, cross-association of ion and water for hydration, and cross-association of cation and anion for ion-pairing, the association model accurately represents the literature experimental data up to saturation concentrations and at the temperature ranging from 263 K to 523 K. Here, this study further investigated the effect of anions of the lithium salts, and re-confirmed that the order of solution non-ideality as LiI > LiBr > LiCl > LiNO 3 because the anions with stronger association strengths are more likely to form ion pairs and thus lower the mean ionic activity coefficients.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2023

Methane foam performance in oil-wet unconsolidated porous media: A systematic experimental investigation at reservoir conditions

Methane foam performance was systematically evaluated using high-pressure and high-temperature experiments performed on oil-wet proppant packs. The sensitivities of foam performance to various key factors, including surfactant concentration, foam quality, total injection rate, salinity, operating pressure, and initial oil saturation were examined. The results showed that even though the foamability and foam strength in oil-wet proppant packs were adversely affected by wettability and presence of oil, the steady-state pressure drops across the proppant packs were insensitive to the quantity of oil initially present. The presence of oil above the critical oil saturation impeded the onset of foam generation. This suggested that the foamability of surfactants depends on the synergetic effects of surfactant’s ionic nature and foam parameters, such as foam quality and total injection rate, on their ability to reduce the oil saturation to a threshold value below which favorable bubble generation sites could be created. It was observed that, for low injection rate, anionic surfactant was ineffective at low salinity conditions, while amphoteric agent performed well at all salinities. Additionally, an increase in salinity resulted in enhanced pressure drop across the proppant packs for both anionic and amphoteric surfactants. Further, the results also established that too high operating pressures are somewhat detrimental to the foam strength and stability, irrespective of the ionic nature of foaming agents and the wettability of the porous medium. For the anionic surfactant, the increase in the total flow rate was found to mitigate the adverse effects of low salt concentration and operating pressure. Results from quality-sensitivity foam tests identified two regions for the foam behavior, named low-quality and high-quality regimes, separated by the transition foam quality. Finally, we discuss the implications of the results for the design and effective implementation of enhanced oil recovery (EOR) schemes that deploy hydrocarbon-based foams.

02 PETROLEUM↗
DOE OSTI2020

Characterization of Spent Purolite A530E Resin with Implications for Long-Term Radioactive Contaminant Removal

Direct removal of pertechnetate anion (TcO4-) from the subsurface contaminated plumes at legacy nuclear weapons production sites, is effective remediation strategy to prevent their spread to adjacent aquifers but is also challenging because TcO4- is a trace component of the contaminated groundwater typically containing large access of other anionic constituents, such nitrate, sulfate, chloride and others. It can be achieved through ion exchange treatment using Purolite A530E resin which to date however has only been evaluated under laboratory conditions and many questions regarding its long-term operational performance remain. To address this need, here we report comprehensive characterization of the spent Purolite A530E resin which processed over 5.38x109 L of contaminated groundwater and successfully removed about 3.78 Ci of Tc-99 during four years of operation at the 200 West Pump & Treat facility at the US DOE Hanford site. This Tc-99 loading constitutes however only about 0.034% of the theoretical capacity of the resin which retained significant amounts of sulfate. Among other radioactive contaminants, small quantities of U-238, Co-60, and I-129 were retained by the resin. The total loading of iodine (combined 1-127 and I-129) on the spent resin exceeded that of Tc-99. To elucidate the mechanism of iodine retention, ion exchange behavior of iodide and iodate was investigated. Purolite A530E resin exhibited highly efficient uptake of iodide and only moderate affinity for iodate in accord with their Gibbs energy of hydration. Sorption isotherms for both anions obeyed Freundlich model.

Levitskaia, Tatiana G.↗
DOE OSTI2021

Structural and spectral studies of hydrated hexaamminecobalt(III)–hexafluororhenate(IV)

The crystal structure of the [Co(NH 3 ) 6 ] 2 [ReF 6 ] 3 ·3H 2 O (I) salt is reported. The salt crystallizes in the trigonal space group P31m with the following unit cell dimensions: a = 15.8714(4) Å, b = 15.8714(4) Å, and c = 9.8657(4) Å. Here, the structure of (I) consists of [Co(NH 3 ) 6 ] 3+ cations, [ReF 6 ] 2– anions, and co-crystallized water molecules which are linked by hydrogen bonding. In (I), independent [ReF 6 ] 2– anions and [Co(NH 3 ) 6 ] 3+ cations octahedron are slightly distorted. Characteristic vibration bands of the [Co(NH 3 ) 6 ] 3+ cation, [ReF 6 ] 2– anion as well as the co-crystallized H 2 O molecules are observed in the infrared spectra of (I). UV-Visible analyses in water showed that the absorption of the [Co(NH 3 ) 6 ] 3+ cation predominate the spectra of (I).

99 GENERAL AND MISCELLANEOUS↗
DOE OSTI2019

Structural underpinnings of cathode protection by in situ generated lithium oxyfluorophosphates

The in situ strategy of cathode protection opportunistically uses PF$_6^-$ anions in electrolyte as chemical reagents to convert inactive precursor molecules to active electrolyte additives. With our approach, a bifunctional x(SiMe 3 ) 2 precursor replaces fluoride in the hexafluorophosphate, forming either a bidentate monoanion P(x)F$^-_4$ or a linear x(PF$_5^-$) 2 dianion, depending on the bridge $x$ (e.g., oxalato, malonato, succinato, and catecholato). While the efficiency of these species as cathode protective agents has been demonstrated, the mechanism for their beneficial action remains unknown. In this study, several molecular precursors have been synthesized, and the topology and energetics of secondary anions were correlated with their cycling performance. Regardless of their structural motif, all such additives demonstrated improved electrochemical performance by reducing initial cathode impedance and lowering the rate of capacity fade compared to the baseline electrolyte. However, we note bidentate monoanions with a malonato bridge showed significant advantage over other molecular designs for mitigating the impedance rise, suggesting that structural strain in the anion is important for easing surface modification of the cathode.

25 ENERGY STORAGE↗
DOE OSTI2020

A highly stable Cu(OH) 2 -Poly(vinyl alcohol) nanocomposite membrane for dramatically enhanced direct borohydride fuel cell performance

Nano-additive aggregation, limited performance, and unclear modification mechanisms are the main obstacles in developing nanocomposite anion exchange membranes (AEMs). In this work, for the first time, an effective and highly stable Poly(vinyl alcohol) (PVA)-based AEMs with dispersive Cu(OH)$_2$ nanoclusters (Cu-AEMs) are prepared by a simple and eco-friendly three-step method: ‘CuCl$_2$ doping-casting-KOH immersing’. The doped Cu$^{2+}$ ions chemically combine with OH- ions to form anionic conductive Cu(OH)2 nanoclusters intermediated by attaching resins. The PVA skeletons wrap around Cu(OH)$_2$ while the hydroxyl groups expose to bulk water, forming Cu(OH)$_2$-PVA complex, which avoids nano-additive aggregation, increases anionic channels, and strengthens additive-matrix connection. A direct borohydride fuel cell using Cu-AEM with 0.56 wt % CuCl$_2$ possess the highest power density of 403.3 mW cm$^{-2}$ at 60 °C and a life span of over 200 h. The high-performance and durability come from the unique structure of Cu(OH)$_2$ nanoclusters-PVA complex. ‘Vehicle’ theory is considered to be the dominant mechanism for enhancing such nanocomposite Cu-AEMs. This work demonstrates a new concept for preparing the stable AEMs toward high-performance fuel cells. The synthetic chemistry involved can be broadly extended for fabricating versatile AEMs.

25 ENERGY STORAGE↗
DOE OSTI2015

Temperature-dependent polymorphism and magnetic properties of three-dimensional copper pyromellitate coordination polymers containing 4,4′-dipyridylamine

A pair of three-dimensional divalent copper pyromellitate (1,2,4,5-benzene-tetracarboxylate, pyro) coordination polymers containing 4,4′-dipyridylamine (dpa) was hydrothermally prepared and structurally characterized by single-crystal X-ray diffraction. The higher-temperature phase ([H{sub 2}dpa][Cu{sub 3}(pyro){sub 2}(H{sub 2}O){sub 3}]·2.5H{sub 2}O){sub n} (1) displays an acentric 3-D 4,4,6-connected anionic network with (4{sup 4}5.6)(5{sup 4}8{sup 2})(4{sup 4}5{sup 4}6{sup 3}7{sup 4}) topology, featuring (Cu{sub 2}(OCO){sub 4}) paddlewheel dimers and isolated copper ions. Charge-balancing H{sub 2}dpa cations are embedded in incipient voids. Prepared at lower temperature, ([Cu{sub 3}(pyro){sub 2}(dpa){sub 2}(dpaH){sub 2}]·3H{sub 2}O){sub n} (2) manifests a 3-D 4,4,4-connected neutral network with uncommon (4{sup 2}6{sup 4}){sub 4}(6{sup 4}8{sup 2}) frl topology based on (Cu{sub 3}(OCO){sub 2}) linear trimers. Antiferromagnetic coupling (J=–82(5) cm{sup –1}) was observed within the (Cu{sub 2}(OCO){sub 4}) dimeric units in 1, while weak ferromagnetic coupling (J=1.0(4) cm{sup –1}) was evident for the (Cu{sub 3}(OCO){sub 2}) linear trimers in 2. Thermal degradation behavior of these new materials is also presented. - Graphical abstract: Two copper pyromellitate coordination polymers containing 4,4′-dipyridylamine were prepared. The higher-temperature phase ([H{sub 2}dpa][Cu{sub 3}(pyro){sub 2}(H{sub 2}O){sub 3}]∙2.5H{sub 2}O){sub n} displays an acentric 3-D trinodal anionic network with (4{sup 4}5.6)(5{sup 4}8{sup 2})(4{sup 4}5{sup 4}6{sup 3}7{sup 4}) topology, featuring antiferromagnetically coupled (Cu{sub 2}(OCO){sub 4}) paddlewheel dimers and isolated copper ions. - Highlights: • Copper pyromellitate (pyro) coordination polymers with 4,4′-dipyridylamine (dpa). • Higher-temperature phase 1 has 3-D anionic trinodal network with H{sub 2}dpa cations. • Lower-temperature phase 2 has rare 3-D frl network. • Dimers and chains in 1 show antiferromagnetism, trimers in 2 show ferromagnetism.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2015

Hydrothermal synthesis and photocatalytic performance of hierarchical Bi{sub 2}MoO{sub 6} microspheres using BiOI microspheres as self-sacrificing templates

Bi{sub 2}MoO{sub 6} hierarchical microspheres were successfully prepared through phase transformation from BiOI microspheres with the assistance of sodium citrate under hydrothermal condition. The possible formation mechanism for the conversion of BiOI to Bi{sub 2}MoO{sub 6} is discussed here. After being annealed at 300 °C for 2 h, the obtained Bi{sub 2}MoO{sub 6} microspheres exhibited remarkably enhanced photocatalytic activity towards the degradation of rhodamine B and phenol. The superior catalytic performance can be attributed to its larger surface area and higher crystallinity. In addition, Bi{sub 2}MoO{sub 6} microspheres are stable during the degradation reaction and can be used repeatedly. - Graphical abstract: Bi{sub 2}MoO{sub 6} hierarchical microspheres were successfully prepared through a facile partial anion exchange strategy using BiOI microspheres as self-sacrificing templates. The Bi{sub 2}MoO{sub 6} microspheres show high visible light photocatalytic activity. - Highlights: • Bi{sub 2}MoO{sub 6} microspheres were prepared via self-sacrificing template anion exchange. • Sodium citrate-assisted anion exchange for preparation of Bi{sub 2}MoO{sub 6} photocatalyst. • Bi{sub 2}MoO{sub 6} catalysts show high visible light photocatalytic activity.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2015

Facile formation of Ag{sub 2}WO{sub 4}/AgX (X = Cl, Br, I) hybrid nanorods with enhanced visible-light-driven photoelectrochemical properties

Highlights: • Ag{sub 2}WO{sub 4}/AgX hybrid nanorods were prepared by a facile in-situ anion exchange reaction. • Ag{sub 2}WO{sub 4} nanorods and different X{sup −} ions were reacted in water at room temperature. • The hybrids possess significantly enhanced photoelectrochemical properties. • Ag{sub 2}WO{sub 4}/AgBr hybrids exhibit the highest photocatalytic activity among three samples. • The active species tests were also investigated to confirm photocatalytic mechanism. - Abstract: In this work, we demonstrated a general strategy for the preparation of a series of uniform Ag{sub 2}WO{sub 4}/AgX (X = Cl, Br, I) hybrid nanorods by a facile in-situ anion exchange reaction occurring at room temperature between pregrown Ag{sub 2}WO{sub 4} nanorods and different X{sup −} ions in water. Compared with Ag{sub 2}WO{sub 4} nanorods, further investigation has revealed that the as-prepared hybrid nanorods possess significantly enhanced photocurrent response and photocatalytic activity in degrading methyl orange (MO) under visible-light irradiation. In particular, the Ag{sub 2}WO{sub 4}/AgBr hybrid nanorods exhibit the highest photocatalytic activity among the three kinds of samples. The active species tests indicate that superoxide anion radicals and photogenerated holes are responsible for the enhanced photocatalytic performance.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Activation behavior for ion permeation in ion-exchange membranes: Role of ion dehydration in selective transport

Here we explored the mechanisms governing the selectivity of anion- and cation-exchange membranes for the transport of four monovalent anions (i.e., fluoride, chloride, bromide, and nitrate) and four monovalent cations (i.e., sodium, potassium, cesium, and ammonium), respectively. Our ion adsorption and transport tests with mixed ion solutions reveal that an ion with larger ionic radius and lower hydration energy is more favorably adsorbed onto the ion-exchange membrane but diffuses more slowly through the polymer matrix compared to an ion with smaller ionic radius and higher hydration energy. Individual anion (as sodium salt) or cation (as chloride salt) permeation tests at different temperatures were performed to evaluate the activation behavior of ion transport through the ion-exchange membranes by calculating the energy barrier and pre-exponential factor (i.e., the ion flux when the energy barrier is negligible) for ion transport from an Arrhenius-type equation. Our results show that an ion with smaller ionic radius and higher hydration energy experiences higher energy barrier (e.g., fluoride, 10.3 kcal mol -1 ) and possesses higher pre-exponential factor compared to an ion with larger ionic radius and lower hydration energy (e.g., bromide, 4.6 kcal mol -1 ). This correlation corroborates our main hypothesis that the activation behavior observed for ion transport is a result of ion dehydration at the water-membrane interface. Our proposed ion selectivity mechanism elucidates how ion dehydration governs the extent of ion permeation into the membrane and the subsequent transport through the charged polymer matrix. Future membrane design that promotes dehydration of target ions is challenging but can result in unprecedented ion selectivity.

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

Parametric study and speciation analysis of rare earth precipitation using oxalic acid in a chloride solution system

Oxalic acid precipitation is a common step in the purification of rare earth elements (REE) from a concentrated pregnant leach solution (PLS). However, the presence of contaminants such as Al, Fe, and Ca in given amounts decreases the REE precipitation efficiency and product purity while also increasing the amount of oxalic acid needed to maximize recovery. As such, a statistically designed test program was performed to identify the optimal conditions necessary for a relatively low REE content PLS containing elevated concentrations of contaminant ions. The performance objective was maximization of REE precipitation efficiency while minimizing the oxalic acid dosage. A central composite design was utilized to quantify performance impacts and identify the ultimate set of parameter values for oxalic acid dosage, Fe(III) contamination concentration, solution pH, and reaction temperature. The resultant model suggested that oxalic acid dosage and reaction pH are the most significant factors for the REE precipitation efficiency, followed by the interaction of oxalic dosage and Fe concentration. Test results indicate that increasing the oxalic acid concentration from 0 g/L to 80 g/L improved the REE precipitation efficiency from approximately 4.2% to 95.0%. Furthermore, raising the solution pH from 0.5 to 2.5 considerably enhanced the precipitation efficiency from 0.0% to 98.9%. A solution temperature elevation decreased REE recovery, which indicated an exothermic reaction between REEs and oxalate anions. Finally, a high level of Fe contamination adversely impacted REE precipitation efficiency. Here, to further the understanding of the REE-oxalate system, a fundamental solution chemistry study was performed using the equilibrium constants of the reactions. The study resulted in the development of oxalate speciation diagrams and provided an analysis of the REE precipitation characteristics at various oxalate anion concentrations and Fe(III) contamination levels using MINTEQ software. The dominant Fe(III) species in the solution system were found to be Fe-(C 2 O 4 ) 3 3- , Fe-(C 2 O 4 ) 2- , and Fe-(C 2 O 4 ) + , which consume the majority of the oxalate anions. The simulated model was found to be in agreement with the experimental findings and helped to explain the adverse impact of increased iron concentrations on REE precipitation efficiency.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2023

Choline Fluoride-Ethylene glycol deep eutectic solvent mixture – Synthesis and physicochemical properties

A critical factor in achieving tunability in DESs is varying the type of hydrogen bond acceptors (HBAs) and donors (HBDs). Choline halides (ChX), such as ChCl and ChBr, have been studied to investigate the effect of the choline anion on DESs. However, ChF-based DESs have been underrepresented in scientific research. ChF has excellent potential, such as high electron affinity, ionization potential, and strong hydrogen bond interactions. Moreover, ChF-based DES can lead to a deeper understanding of DESs due to the NMR-active 19F nuclear spin nature. We report the first synthesis and characterization of choline fluoride-EG (1:2, ChF:EG) DES, which we named “EthalineF.” We studied this mixture using various spectroscopic techniques, including NMR, FT-IR, Raman, and UV–vis spectroscopies. Polarity, density, viscosity, and conductivity measurements were collected as well. Transient absorption spectroscopy (TAS) was used to study the solvation dynamics of EthalineF. 19F NMR indicated that some fluoride anions (~15%) are coordinated to the choline cation. In EthalineF, the new type of observed fluoride anions is proposed to be a tight-binding choline-fluoride ion pair. Further, EthalineF has a larger solvodynamic radius than Ethaline. This can explain the lower conductivity for EthalineF compared to Ethaline despite the higher fluidity and solvation dynamics for EthalineF.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2023

Poly(diallylmethylammonium) proton conducting membranes with high ionic conductivity at intermediate temperatures

High temperature proton exchange membrane fuel cells are being lately investigated because of their high energy efficiency, their superior heat/water management, CO tolerance, and electrode reaction kinetics. To further advance this technology, the polymer membrane portfolio and performance should be improved for intermediate or high temperature operation (>100 °C). In this work we present new poly(diallylmethylammonium) proton conducting membranes with high ionic conductivity at 120 °C. First, new protic ionic liquids, hereafter called DAMAH + X - , were synthesized leading to diallylmethylammonium monomers with different counter-anions. By radical cyclopolymerization through thermal and photoinitiation mechanisms, self-standing protic polymeric membranes of poly(diallylmethylammonium X - ) were obtained. Membranes showed good thermal stability (>250 °C) and mechanical properties without the need of additives such as (protic) ionic liquids, solvents or inorganic charges. Great attention was paid to understand the effect of the different counter-anions on the membrane properties. As a general trend, fluorinated anions coming from strong acids confer high ionic conductivity and allow to reduce the hygroscopic properties on the protic polymeric membranes. Proton structural and dynamical stability at different temperatures and humidification conditions were investigated by Neutron Scattering (QENS and NR). The optimized poly(diallylmethylammonium X - ) shows similar ionic conductivity values than Nafion 212 under varying relative humidity conditions at 80 °C. Furthermore, it shows a high ionic conductivity value of 1.9 × 10 -3 Scm -1 at 120 °C under dry conditions.

08 HYDROGEN↗