The Equilibrium Structure of Lithium Salt Solutions in Ether-Functionalized Ammonium Ionic Liquids

Molecular dynamics simulations have been performed for ionic liquids based on a ternary mixture of lithium and ammonium cations and a common anion, bis(trifluoromethylsulfonyl)imide, [Tf2N](-). We address structural changes resulting from adding Li+ in ionic liquids with increasing length of an ether-functionalized chain in the ammonium cation. The calculation of static structure factors reveals the lithium effect on charge ordering and intermediate range order in comparison with the neat ionic liquids. The charge ordering is modified in the lithium solution because the coordination of [Tf2N](-) toward Li+ is much stronger than ammonium cations. Intermediate range order is observed in neat ionic liquids based on ammonium cations with a long chain, but in the lithium solutions, there is also a nonhomogenous distribution of Li+ cations. The presence of Li+ enhances interactions between the ammonium cations due to correlations between the oxygen atom of the ether chain and the nitrogen atom of another ammonium cation.

Molecular dynamics of poly(Ethylene Glycol) intercalated in clay, studied using 13C solid-state NMR

In this study, Cross-Polarization Magic-angle Spinning CP/MAS, 2D Exchange, Centerband-Only Detection of Exchange (CODEX), and Separated-Local-Field (SLF) NMR experiments were used to study the molecular dynamics of poly(ethylene glycol) (PEG) inside Hectorite/PEG intercalation compounds in both single- and double-layer configurations. The results revealed that the overall amplitude of the motions of the PEG chain in the single-layer configuration is considerably smaller than that observed for the double-layer intercalation compound. This result indicates that the effect of having the polymer chain interacting with both clay platelets is to produce a substantial decrease in the motional amplitudes of those chains. The presence of these dynamically restricted segments might be explained by the presence of anchoring points between the clay platelets and the PEG oxygen atoms, which was induced by the Na+ cations. By comparing the PEG motional amplitudes of the double-layered nanocomposites composed of polymers with different molecular weights, a decrease in the motional amplitude for the smaller PEG chain was observed, which might also be understood using the presence of anchoring points.

Investigation of the lithium ion mobility in cyclic model compounds and their ion conducting properties

Efficient energy storage and conversion is playing a key role in overcoming the present and future challenges in energy supply. Batteries provide portable, electrochemical storage of green energy sources and potentially allow for a reduction of the dependence on fossil fuels, which is of great importance with respect to the issue of global warming. In view of both, energy density and energy drain, rechargeable lithium ion batteries outperform other present accumulator systems. However, despite great efforts over the last decades, the ideal electrolyte in terms of key characteristics such as capacity, cycle life, and most important reliable safety, has not yet been identified. rnrnSteps ahead in lithium ion battery technology require a fundamental understanding of lithium ion transport, salt association, and ion solvation within the electrolyte. Indeed, well-defined model compounds allow for systematic studies of molecular ion transport. Thus, in the present work, based on the concept of ‘immobilizing’ ion solvents, three main series with a cyclotriphosphazene (CTP), hexaphenylbenzene (HBP), and tetramethylcyclotetrasiloxane (TMS) scaffold were prepared. Lithium ion solvents, among others ethylene carbonate (EC), which has proven to fulfill together with pro-pylene carbonate safety and market concerns in commercial lithium ion batteries, were attached to the different cores via alkyl spacers of variable length.rnrnAll model compounds were fully characterized, pure and thermally stable up to at least 235 °C, covering the requested broad range of glass transition temperatures from -78.1 °C up to +6.2 °C. While the CTP models tend to rearrange at elevated temperatures over time, which questions the general stability of alkoxide related (poly)phosphazenes, both, the HPB and CTP based models show no evidence of core stacking. In particular the CTP derivatives represent good solvents for various lithium salts, exhibiting no significant differences in the ionic conductivity σ_dc and thus indicating comparable salt dissociation and rather independent motion of cations and ions.rnrnIn general, temperature-dependent bulk ionic conductivities investigated via impedance spectroscopy follow a William-Landel-Ferry (WLF) type behavior. Modifications of the alkyl spacer length were shown to influence ionic conductivities only in combination to changes in glass transition temperatures. Though the glass transition temperatures of the blends are low, their conductivities are only in the range of typical polymer electrolytes. The highest σ_dc obtained at ambient temperatures was 6.0 x 10-6 S•cm-1, strongly suggesting a rather tight coordination of the lithium ions to the solvating 2-oxo-1,3-dioxolane moieties, supported by the increased σ_dc values for the oligo(ethylene oxide) based analogues.rnrnFurther insights into the mechanism of lithium ion dynamics were derived from 7Li and 13C Solid- State NMR investigations. While localized ion motion was probed by i.e. 7Li spin-lattice relaxation measurements with apparent activation energies E_a of 20 to 40 kJ/mol, long-range macroscopic transport was monitored by Pulsed-Field Gradient (PFG) NMR, providing an E_a of 61 kJ/mol. The latter is in good agreement with the values determined from bulk conductivity data, indicating the major contribution of ion transport was only detected by PFG NMR. However, the μm-diffusion is rather slow, emphasizing the strong lithium coordination to the carbonyl oxygens, which hampers sufficient ion conductivities and suggests exploring ‘softer’ solvating moieties in future electrolytes.rn

Analysis of estrogens in environmental waters using polymer monolith in-polyether ether ketone tube solid-phase microextraction combined with high-performance liquid chromatography

A simple, rapid and sensitive on-line method for simultaneous determination of four endocrine disruptors (17 beta-estradiol, estriol, bisphenol A and 17 alpha-ethinylestradiol) in environmental waters was developed by coupling in-tube solid-phase microextraction (SPME) to high-performance liquid chromatography (HPLC) with fluorescence detection (FLD). A poly(acrylamide-vinylpyridine-NAP-methylene bisacrylamide) monolith, synthesized inside a polyether ether ketone (PEEK) tube, was selected as the extraction medium. To achieve optimum extraction performance, several parameters were investigated, including extraction flow-rate, extraction time, and pH value, inorganic salt and organic solvent content of the sample matrix. By simply filtered with nylon membrane filter and adjusting the pH of samples to 6.0 with phosphoric acid, the sample solution then could be directly injected into the device for extraction. Low detection limits (S/N = 3) and quantification limits (S/N = 10) of the proposed method were achieved in the range of 0.006-0.10 ng/mL and 0.02-0.35 ng/mL from spiked lake waters, respectively. The calibration curves of four endocrine disruptors showed good linearity ranging from quantification limits to 50 ng/mL with a linear coefficient R-2 value above 0.9913. Good method reproducibility was also found by intra- and inter-day precisions, yielding the RSDs less than 12 and 9.8%, respectively. Finally, the proposed method was successfully applied to the determination of these compounds in several environmental waters. (c) 2006 Elsevier B.V. All rights reserved.

Ionic conductivity of polymer gel electrolytes based on poly(polyethylene glycol dimethacrylate)

Gel electrolytes have been prepared by thermal polymerization of poly(polyethylene glycol dimethacrylate) (P(PEGD)) in the presence of propylene carbonate (PC) and alkali metal salts, such as LiClO4, LICF(3)SO(3) and LiBF4. The conductivity was studied by means of impedance spectroscopy, and it is found that the temperature dependence of conductivities follow a Arrhenius relationship when the molar percentage of PC is higher than 75% or LiClO4 concentration is lower than 0.9 mol/l. However, when LiCF3SO3 or LiBF4 is used instead of LiClO4 as the salt, the situation is different. For LICF(3)SO(3), the Arrhenius relationship almost holds true for all the salt concentrations studied; while for LiBF4, the Arrhenius equation hardly fits for any salt concentration. The dependence of activation energy on salt concentration is also examined, both for LiClO4 and LiCF3SO3, the values of E(a) tend to reach a minimum value with increasing salt concentration. Copyright (C) 1996 Elsevier Science Ltd.

Ion transport in small-molecule electrolytes based on LiI/3-hydroxypropionitrile with high salt contents

Abnormal “polymer-in-salt” conduction behavior is observed in a solid electrolyte composed of lithium iodide (LiI) and 3-hydroxypropionitrile (HPN). Based on comprehensive investigations by X-ray diffraction (XRD) and Raman and infrared spectroscopy, this abnormal conduction behavior is attributed to the formation of new ionic associates [Lim +In−]· · ·N C (m> n) and the reinforced hydrogen bonding of I· · ·HO in the electrolyte at high LiI concentrations.

Mordenite-incorporated PVA-PSSA membranes as electrolytes for DMFCs

Composite membranes with mordenite (MOR) incorporated in poly vinyl alcohol (PVA)–polystyrene sulfonic acid (PSSA) blend tailored with varying degree of sulfonation are reported. Such a membrane comprises a dispersed phase of mordenite and a continuous phase of the polymer that help tuning the flow of methanol and water across it. The membranes on prolonged testing in a direct methanol fuel cell (DMFC) exhibit mitigated methanol cross-over from anode to the cathode. The membranes have been tested for their sorption behaviour, ion-exchange capacity, electrochemical selectivity and mechanical strength as also characterized by Fourier transform infrared spectroscopy and thermogravimetric analysis. Water release kinetics has been measured by magnetic resonance imaging (NMR imaging) and is found to be in agreement with the sorption data. Similarly, methanol release kinetics studied by volume-localized NMR spectroscopy (point resolved spectroscopy, PRESS) clearly demonstrates that the dispersion of mordenite in PVA–PSSA retards the methanol release kinetics considerably. A peak power-density of 74 mW/cm2 is achieved for the DMFC using a PVA–PSSA membrane electrolyte with 50% degree of sulfonation and 10 wt.% dispersed mordenite phase. A methanol cross-over current as low as 7.5 mA/cm2 with 2 M methanol feed at the DMFC anode is observed while using the optimized composite membrane as electrolyte in the DMFC, which is about 60% and 46% lower than Nafion-117 and PVA–PSSA membranes, respectively, when tested under identical conditions.

Novel organic-inorganic composite polymer-electrolyte membranes for DMFCs

Organic-inorganic composite membranes comprising Nation with inorganic materials such as silica, mesoporous zirconium phosphate (MZP) and mesoporous titanium phosphate (MTP) are fabricated and evaluated as proton-exchange-membrane electrolytes for direct methanol fuel cells (DMFCs). For Nation-silica composite membrane, silica is impregnated into Nation matrix as a sol by a novel water hydrolysis process precluding the external use of an acid. Instead, the acidic nature of Nation facilitates in situ polymerization reaction with Nation leading to a uniform composite membrane. The rapid hydrolysis and polymerization reaction while preparing zirconia and titania sols leads to uncontrolled thickness and volume reduction in the composite membranes, and hence is not conducive for casting membranes. Nafion-MZP and Nafion-MTP composite membranes are prepared by mixing pre-formed porous MZP and MTP with Nation matrix. MZP and MTP are synthesised by co-assembly of a tri-block co-polymer, namely pluronic-F127, as a structure-directing agent, and a mixture of zirconium butoxide/titanium isopropoxide and phosphorous trichloride as inorganic precursors. Methanol release kinetics is studied by volume-localized NMR spectroscopy (employing ``point resolved spectroscopy'', PRESS), the results clearly demonstrating that the incorporation of inorganic fillers in Nation retards the methanol release kinetics under osmotic drag. Appreciable proton conductivity with reduced methanol permeability across the composite membranes leads to improved performance of DMFCs in relation to commercially available Nafion-117 membrane.

Nafion and modified-Nafion membranes for polymer electrolyte fuel cells: An overview

Polymer electrolyte fuel cells (PEFCs) employ membrane electrolytes for proton transport during the cell reaction. The membrane forms a key component of the PEFC and its performance is controlled by several physical parameters, viz. water up-take, ion-exchange capacity, proton conductivity and humidity. The article presents an overview on Nafion membranes highlighting their merits and demerits with efforts on modified-Nafion membranes.

Ion Transport in a Polymer-Plastic Solid Soft Matter Electrolyte in the Light of Solvent Dynamics and Ion Association

Ion transport in a recently demonstrated promising soft matter solid plastic-polymer electrolyte is discussed here in the context of solvent dynamics and ion association. The plastic-polymer composite electrolytes display liquid-like ionic conductivity in the solid state,compliable mechanical strength (similar to 1 MPa), and wide electrochemical voltage stability (>= 5 V). Polyacrylonitrile (PAN) dispersed in lithium perchlorate (LiClO4)-succinonitrile (SN) was chosen as the model system for the study (abbreviated LiClO4-SN:PAN). Systematic observation of various mid-infrared isomer and ion association bands as a function of temperature and polyme concentration shows an effective increase in trans conformer concentration along with free Li+ ion concentration. This strongly supports the view that enhancement in LiClO4-SN:PAN ionic conductivity over the neat plastic electrolyte (LiClO4-SN) is due to both increase in charge mobility and concentration. The ionic conductivity and infrared spectroscopy studies are supported by Brillouin light scattering. For the LiClO4-SN:PAN composites, a peak at 17 GHz was observed in addition to the normal trans-gauche isomerism (as in neat SN) at 12 GHz. The fast process is attributed to increased dynamics of those SN molecules whose energy barrier of transition from gauche to trans has reduced under influences induced by the changes in temperature and polymer concentration. The observations from ionic conductivity, spectroscopy, and light scattering studies were further supplemented by temperature dependent nuclear magnetic resonance H-1 and Li-7 line width measurements.

Increasing ionic conductivity of polymer-sodium salt complex by addition of a non-ionic plastic crystal

Ionic conductivity and other physico-chemical properties of a soft matter composite electrolyte comprising of a polymer-sodium salt complex and a non-ionic plastic crystal are discussed here. The electrolyte under discussion comprises of polyethyleneoxide (PEO)-sodium triflate (NaCF3SO3) and succinonitrile (SN). Addition of SN to PEO-NaCF3SO3 resulted in significant enhancement in ionic conductivity. At 50% SN concentration (with respect to weight of polymer), the polymer-plastic composite electrolyte room temperature (= 25 degrees C) ionic conductivity was similar to 1.1 x 10(-4) Omega(-1) cm(-1), approximately 45 times higher than PEO-NaCF3SO3. Observations from ac-impedance spectroscopy along with X-ray diffraction, differential scanning calorimetry and Fourier transform inrared spectroscopy strongly suggest the enhancement in the composite is ionicconductivity due to enhanced ion mobility via decrease in crystallinity of PEO. The free standing composite polymer-plastic electrolytes were more compliable than PEO-NaCF3SO3 thus exhibiting no detrimental effects of succinonitrile addition on the mechanical stability of PEO-NaCF3SO3. We propose that the exploratory PEO-NaCF3SO3-SN system.discussed here will eventually be developed as a prototype electrolyte.for sodium-sulfur batteries capable of operating at ambient and.sub-ambient conditions. (C) 2010 Elsevier B.V. All rights reserved.

Soft matter electrolytes based on polymethylmetacrylate dispersions in lithium bis(trifluoromethanesulfonyl)imide/1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide ionic liquids

Ion transport in a polymer-ionic liquid (IL) soft matter composite electrolyte is discussed here in detail in the context of polymer-ionic liquid interaction and glass transition temperature The dispersion of polymethylmetacrylate (PMMA) in 1-butyl-3-methylimidazolium hexafluorophosphate (BMIPF6) and 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide (BMITFSI) resulted in transparent composite electrolytes with a jelly-like consistency The composite ionic conductivity measured over the range -30 C to 60 C was always lower than that of the neat BMITFSI/BMIPF6 and LiTFSI-BMITFSI/LiTFSI-BMIPF6 electrolytes but still very high (>1 mS/cm at 25 degrees C up to 50 wt% PMMA) While addition of LiTFSI to IL does not influence the glass T-g and T-m melting temperature significantly dispersion of PMMA (especially at higher contents) resulted in increase in T-g and disappearance of T-m In general the profile of temperature-dependent ionic conductivity could be fitted to Vogel-Tamman-Fulcher (VTF) suggesting a solvent assisted ion transport However for higher PMMA concentration sharp demarcation of temperature regimes between thermally activated and solvent assisted ion transport were observed with the glass transition temperature acting as the reference point for transformation from one form of transport mechanism to the other Because of the beneficial physico-chemical properties and interesting ion transport mechanism we envisage the present soft matter electrolytes to be promising for application in electrochromic devices (C) 2010 Elsevier Ltd All rights reserved

Electrochemical studies of polyaniline in a gel polymer electrolyte - High energy and high power characteristics of a solid-state redox supercapacitor

Studies on redox supercapacitors employing electronically conducting polymers are of great importance for hybrid power sources and pulse power applications. In the present study, polyaniline (PANI) has been potentiodynamically deposited on stainless steel substrate and characterized in a gel polymer electrolyte (GPE). Use of the GPE facilitates a voltage limit of the capacitor to 1 V, instead of 0.75 V in aqueous electrolytes. From charge-discharge studies of the solid-state PANI capacitors, a specific capacitance of 250 F g(-1) has been obtained at a specific power of 7.5 kW kg(-1) of PANI. The values of specific capacitance and specific power are considerably higher than those reported in the literature. High energy and high power characteristics of the PANI are presented. (C) 2002 The Electrochemical Society.

SEC-MALDI-TOF mass spectral characterization of a hyperbranched polyether prepared via melt transetherification

An AB(2) monomer, 1-(2-hydroxyethoxy)-3,5-bis-(methoxymethyl)-2,4,6-trimethylbenzene, was synthesized from mesitol and melt-polycondensed in the presence of an acid catalyst via a transetherification process at 145-150 degreesC to yield a soluble, moderately high molecular weight hyperbranched polyether. The degree of branching in the polymer was calculated to be 0.78 by a comparison of its NMR spectrum with that of an appropriately designed model compound. The weight-average molecular weight of the hyperbranched polymer was determined to be 64,600 (weight-average molecular weight/number-average molecular weight = 5.2) by size exclusion chromatography (SEC) in CHCl3, with polystyrene standards. The origin of the broad molecular weight distribution, which could either be intrinsic to such hyperbranched structures or be due to structural heterogeneity, was further probed by the fractionation of the samples by SEC and by the subjection of each fraction to matrix-assisted laser desorption/ionization time-of-flight mass spectral analysis. The mass spectral analysis suggested the presence of two primary types of species: one corresponding to the simple branched structure and the other to macrocyclics. Interestingly, from the relative intensities of the two peaks, it was apparent that cyclization became favorable at higher conversions in the melt transetherification process. (C) 2002 Wiley Periodicals, Inc.