Polymer gel electrolytes based on oligomeric polyether/cross-linked PMMA blends prepared via in situ polymerization

Very-low-vapor-pressure oligomeric polyether electrolytes blended with and dimensionally stabilized by cross-linked poly(methyl methacrylate) (PMMA) are prepared via in situ polymerization. The synthesized polymer gel electrolytes (PGEs) are freestanding films with excellent dimensional stability, mechanical integrity and strength. They exhibit high ionic conductivity at room temperature reaching 4.3 × 10⁻⁴ S/cm for the highest conducting sample and exceptional thermal stability. The oligomeric polyether and PMMA appear to have molecular level interaction in the blends and the PGEs remain a single phase from at least −50 to 200 °C, potentially enabling their application in advanced batteries in wide temperature ranges. The novel in situ polymerization process allows precise control of the composition of the PGEs and can enable in situ fabrication of advanced cells.     

Electrochemical synthesis and study of polydiphenylamine

The electrochemical oxidation of diphenylamine in acetonitrile produces an adherent conducting polymer film at the electrode. Conductivity measurements on pressed pellets of this polymer give a room temperature conductivity of 10 S cm⁻¹. The polymer can be cycled between 25 and 200°C without deterioration in the conductivity. Preliminary SEM/EDS studies suggest that there is one BF⁻₄ counter ion for every four monomer units in the oxidised polymer film.     

Novel composite polymer electrolytes based on poly(ether-urethane) network polymer and modified montmorillonite

Novel composite solid polymer electrolytes (CSPEs) and composite gel polymer electrolytes (CGPEs) have been prepared. CSPE consists of poly(ether-urethane) network polymer, which is superior to poly(ethylene oxide) in mechanical stability due to its cross-linked structure, modified montmorillonite (MMMT) and LiClO₄, and CGPE with good mechanical strength comprises of the CSPE and LiClO₄–PC (propylene carbonate) solution. The ionic conductivity can be enhanced after the addition of MMMT, and CGPE exhibits ionic conductivity in the order of 10⁻³ S/cm at room temperature. The temperature dependence of the ionic conductivity of the CSPE follows the Vogel–Tamman–Fulcher (VTF) equation. The effects of MMMT on the interactions in these systems and the possible conduction mechanisms are also discussed.     

Novel composite polymer electrolytes based on poly(ether-urethane) network polymer and fumed silicas

Novel composite solid polymer electrolytes (CSPEs) and composite gel polymer electrolytes (CGPEs) have been prepared. CSPE consists of poly(ether-urethane) network polymer (PUN), fumed silicas and LiClO₄. The ionic conductivity of CSPEs can be enhanced nearly 20 times in comparison with the plain system without the addition of fumed silicas and can be above 1×10⁻⁵ S/cm at room temperature. The effects of both kinds of fumed silicas, viz. uSiO₂ with hydrophilic groups at the surface and mSiO₂ with hydrophobic groups at the surface on ionic conductivity were investigated. CGPE comprising of the CSPE and LiClO₄–PC solution with good mechanical strength exhibits ionic conductivity in the order of 10⁻³ S/cm at room temperature and above 3×10⁻⁴ S/cm at low temperature −40 °C.     

Novel method for the preparation of ionically crosslinked sulfonated poly(arylene ether sulfone)/polybenzimidazole composite membranes via in situ polymerization

A series of ionically crosslinked composite membranes were prepared from sulfonated poly(arylene ether sulfone) (SPAES) and polybenzimidazole (PBI) via in situ polymerization method. The structure of the pristine polymer and the composite membranes were characterized by FT-IR. The performance of the composite membranes was characterized. The study showed that the introduction of PBI led to the reduction of methanol swelling ratio and the increase of mechanical properties due to the acid–base interaction between the sulfonic acid groups and benzimidazole groups. Moreover, the oxidative stability and thermal stability of the composite membranes were improved greatly. With the increase of PBI content, the methanol permeability coefficient of the composite membranes gradually decreased from 1.59 × 10⁻⁶ cm²/s to 1.28 × 10⁻⁸ cm²/s at 30 °C. Despite the fact that the proton conductivity decreased to some extent as a result of the addition of PBI, the composite membrane with PBI content of 5 wt.% still showed a proton conductivity of 0.201 S/cm at 80 °C which could actually meet the requirement of proton exchange fuel cell application. Furthermore, the composite membranes with PBI content of 2.5–7.5 wt.% showed better selectivity than Nafion117 taking into consideration the methanol swelling ratio and proton conductivity comprehensively.     

Gelation and ionic conductivity of fluoroalkyl end-capped 2-acrylamido-2-methylpropanesulfonic acid oligomers in ionic liquids

Fluoroalkyl end-capped 2-acrylamido-2-methylpropanesulfonic acid oligomer could cause a gelation in an ionic liquid (1-methylpyrazolium tetrafluoroborate) under non-crosslinked conditions. This new fluorinated oligomer gel formed in the ionic liquid was found to exhibit a high ionic (proton) conductivity of 10⁻² S/cm level at room temperature.     

Glass–ceramic Li2S–P2S5 electrolytes prepared by a single step ball billing process and their application for all-solid-state lithium–ion batteries

We report that glass–ceramic Li₂S–P₂S₅ electrolytes can be prepared by a single step ball milling (SSBM) process. Mechanical ball milling of the xLi₂S·(100 − x)P₂S₅ system at 55 °C produced crystalline glass–ceramic materials exhibiting high Li-ion conductivity over 10⁻³ S cm⁻¹ at room temperature with a wide electrochemical stability window of 5 V. Silicon nanoparticles were evaluated as anode material in a solid-state Li battery employing the glass–ceramic electrolyte produced by the SSBM process and showed outstanding cycling stability.     

Ionic liquids to the rescue? Overcoming the ionic conductivity limitations of polymer electrolytes

Polymer electrolytes – solid polymeric membranes with dissolved salts – are being intensively studied for use in all-solid-state lithium-metal-polymer (LMP) batteries to power consumer electronic devices. The low ionic conductivity at room temperature of existing polymer electrolytes, however, has seriously hindered the development of such batteries for many applications. The incorporation of salts molten at room temperature (room temperature ionic liquids or RTILs) into polymer electrolytes may be the necessary solution to overcoming the inherent ionic conductivity limitations of ‘dry’ polymer electrolytes.     

Study of the effect of the membrane composition on ion transfer across a supported liquid membrane

The rate of ion transfer across the supported liquid membrane (SLM) is studied in the rotating diffusion cell (RDC), varying the chemical composition of the SLM from net-cloth supported gel membranes to radiation-grafted polymer membranes. Steady-state current–voltage curves are measured as a function of the rotation rate, and values for the standard rate constant, k⁰, are determined for a series of tetraalkylammonium cations from the analysis of the initial slopes and the diffusion limiting currents. The analysis gives values for k⁰ of the order of 10⁻²–10⁻⁴ cm s⁻¹, which is in rather good agreement with the values found in the literature for this type of the system. As controlled delivery of ionic drugs can be achieved by control of the electric current, whereby the SLM acts as a drug reservoir, the study is extended to the release of the anti-Alzheimer drug Tacrine, where ion-exchange fibers are embedded in the membrane as the drug carrier. Our previous transient experiments are also discussed, and it is suggested that their interpretation is seriously hampered by the non-uniform potential distribution, which brings about high capacitive currents.     

Characterization of PVdF(HFP) gel electrolytes based on 1-(2-Hydroxyethyl)-3-methyl imidazolium ionic liquids

Poly(vinylidenefluoride)-hexafluoropropylene (PVdF(HFP))-ionic liquid gel electrolytes were prepared using ionic liquids based on 1-(2-hydroxyethyl)-3-methyl imidazolium tetrafluoroborate and 1-(2-hydroxyethyl)-3-methyl imidazolium hexafluorophosphate. A conventional metathesis reaction was used to prepare these ionic liquids, which have high purity and exhibit a liquid state at room temperature. The prepared polymer-ionic liquid gel proved to be a free-standing and rubbery film in which the degree of transparency differed according to the ratio and type of ionic liquid used. TGA and FTIR analyses confirmed that the solvent, N,N-Dimethylacetamide (DMAC), used for mixing PVdF(HFP) polymer with ionic liquid was almost totally removed during the gelling and drying processes. SEM photographs were taken of the surface structure of the PVdF(HFP)-ionic liquid gel in order to evaluate the morphology of the film's surface according to the mixing ratio and the nature of the ionic liquid. The thermal behaviors of PVdF(HFP)-ionic liquid gels were observed to be similar to those of neat ionic liquids through DSC analysis, and the compatibility between the polymer and ionic liquid was investigated by XRD analysis. The ionic conductivities of all the gels were 10(-3)-10(-5) S cm(-1) in a temperature range of 20-70 degrees C.     

Low glass transition temperature polymer electrolyte prepared from ionic liquid grafted polyethylene oxide

In this contribution, we report a new type of poly (ionic liquids) prepared by imidazolium ionic liquids directly grafting onto polyethylene oxide backbone. Different molecular weights of poly (ionic liquids) are obtained with a low glass transition temperature up to ?14 °C. The materials as polymer electrolyte achieve a high conductivity around 10^?5 S cm^?1 at 30 °C and close to 10^?3 S cm^?1 at 90 °C. High viscosity up to 4000 Pa s at room temperature would minimize the electrolytes leaking in electrochemical devices. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 2104–2110     

A novel polymer gel electrolyte: Direct polymerization of ionic liquid from surface of silica nanoparticles

A novel polymer electrolyte is synthesized by directly grafting poly ionic liquids onto silica nanoparticles. The kinetic study of this surface‐initiated polymerization has also been included. A gel‐state electrolyte is formed by mixing this type of polymer/silica nanocomposite with ionic liquids under 60 °C, which exhibits an excellent conductivity of 0.8 mS/cm at room temperature and 14.7 mS/cm at 90 °C. In addition, the mechanism of gel formation has also been discussed in this article. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 121–127     

Proton Conducting Organic/Inorganic Sol–Gel Membranes Produced from Phenyltriethoxysilane and 3-Methacryloxypropyl Trimethoxysilane

The increase of the operation temperature in Proton Exchange Membrane Fuel Cells (PEMFC) above 100^∘C would be an important breakthrough for the application of this type of fuel cell in electric vehicles. Hybrid organic-inorganic membranes with nano-sized interfaces can combine all the properties to meet this objective. Membranes using phenyltriethoxysilane and 3-methacryloxypropyl trimethoxysilane have been synthesised by polymerisation of methacrylate groups and inorganic condensation of silanol groups. Sulfonation process to provide proton conductivity affects both proton conductivity and chemical stability of hybrid membranes. Liquid sulfonation during the sol preparation and chlorosulfonic acid as sulfonating agent leads to chain cleavage while trimethylsilyl chlorosulfonate does not affect the polymer backbone. The increase of temperature (up to 120–130^∘C) and relative humidity leads to an increase of proton conductivity close to 10^{− 3} S/cm.     

Preparation and characterization of spherical V2O3 nanopowder

V₂O₃ nanopowder with spherical particles was prepared by reducing pyrolysis of the precursor, (NH₄)₅[(VO)₆(CO₃)₄(OH)₉]·10H₂O, in H₂ atmosphere. The thermolysis process of the precursor in a H₂ flow was investigated by thermogravimetric analysis and differential thermal analysis. The results indicate that pure V₂O₃ forms at 620°C and crystallizes at 730°C. The effects of various reductive pyrolysis conditions on compositions of V₂O₃ products were studied. Scanning electron micrographs show that the particles of the V₂O₃ powder obtained at 650°C for 1 h are spherical about 30 nm in size with more homogeneous distribution. Experiments show that nanopowder has larger adsorption capacity to gases and is more easily reoxidized by air at room temperature than micropowder. Differential scanning calorimetry experiment indicates that the temperature of phase transition of nano-V₂O₃ powder is −119.5°C on cooling or −99.2°C on heating. The transition heats are −12.55 J g⁻¹ on cooling and 11.42 J g⁻¹ on heating, respectively.     

Ionic transport in P(VDF-HFP)-PMMA-LiCF3SO3-(PC + DEC)-SiO2 composite gel polymer electrolyte

Composite gel polymer electrolytes composed of poly(vinylidene fluoride-co-hexafluoropropylene) P(VDF-HFP) and polymethylmethacrylate PMMA polymers, PC + DEC as plasticizer and LiCF₃SO₃ as salt and fumed silica as filler have been synthesized by solvent casting technique with varying plasticizer-filler ratio systematically. Films of thickness in the range of 40-70 μm were characterized by a.c. impedance measurements in the temperature range 303 K to 373 K. Addition of filler to the polymer electrolyte was found to result in an enhancement of the ionic conductivity. A maximum electrical conductivity of ∼1 × 10⁻³ S/cm at 303 K and ∼2.1 × 10⁻³ S/cm at 373 K has been achieved with the dispersion of the SiO₂. FTIR spectral studies confirmed the polymer-salt interaction. XRD patterns exhibit the increased amorphicity in the blended composite gel polymer electrolytes. Scanning electron micrograph shows the dispersion of SiO₂ particle in the polymer electrolyte.     

Flow-injection hydride generation atomic absorption spectrometric study of the automated on-line pre-reduction of arsenate, methylarsonate and dimethylarsinate and high-performance liquid chromatographic separation of their -cysteine complexes

An automated on-line pre-reduction of arsenate, monomethylarsonate (MMA) and dimethylarsinate (DMA) using flow injection hydride generation atomic absorption spectrometry (FI-HGAAS) is feasible. The kinetics of pre-reduction and complexation depend strongly on the concentration of -cysteine and on the temperature in the following increasing order: inorganic As(V)<DMA<MMA. Arsenate is pre-reduced/complexed within less than 50 s at 70–100°C compared to 1 h at room temperature, while MMA and DMA require 1.5–2 min at 70–100°C and up to 1–2 h at room temperature. The characteristic masses and concentrations for 100 μl injections are 0.01 ng and 0.1 μg l⁻¹ in integrated absorbance and 0.2 ng and 2 μg l⁻¹ in peak height measurements, and the limits of detection are ca. 0.5 ng and 5 μg l⁻¹, respectively. In a high-performance liquid chromatography (HPLC)–HGAAS system, the -cysteine complexes of inorganic As(III), MMA and DMA are best separated within 7 min by HPLC on a strongly acidic cation exchange column such as Spherisorb S SCX 120×4 mm (5 μm) with a mobile phase containing 12 mmol l⁻¹ phosphate buffer (KH₂PO₄/H₃PO₄)–2.5 mmol l⁻¹ -cysteine, pH 3.3–3.5. Upon dilution to -cysteine levels below 10 mmol l⁻¹, which are compatible with HPLC separations, the DMA–cysteine complex is unstable on storage. No baseline separations are possible with anion exchange and reverse phase C₁₈ HPLC columns. The limits of detection with 50 μl injections in peak area mode are ca. 0.5 ng and 10 μg l⁻¹, respectively.     

Voltammetric studies on the α-tocopherol anion and α-tocopheroxyl (Vitamin E) radical in acetonitrile

The α-tocopheroxyl radical was generated voltammetrically by one-electron oxidation of the α-tocopherol anion (E ^r_1/2=−0.73 V versus Ag|Ag⁺) that was prepared by reacting α-tocopherol with Et₄NOH in acetonitrile (with Bu₄NPF₆ as the supporting electrolyte). Cyclic voltammograms recorded at variable scan rates (0.05–10 V s⁻¹), temperatures (−20 to 20°C) and concentrations (0.5–10 mM) were modelled using digital simulation techniques to determine the rate of bimolecular self-reaction of α-tocopheroxyl radicals. The k values were calculated to be 3×10³ l mol⁻¹ s⁻¹ at 20°C, 2×10³ l mol⁻¹ s⁻¹ at 0°C and 1.2×10³ l mol⁻¹ s⁻¹ at −20°C. In situ electrochemical-EPR experiments performed at a channel electrode confirmed the existence of the α-tocopheroxyl radical.     

Inorganic–organic hybrid polymers with pendent sulfonated cyclic phosphazene side groups as potential proton conductive materials for direct methanol fuel cells

A synthetic method is described to produce a proton conductive polymer membrane with a polynorbornane backbone and inorganic–organic cyclic phosphazene pendent groups that bear sulfonic acid units. This hybrid polymer combines the inherent hydrophobicity and flexibility of the organic polymer with the tuning advantages of the cyclic phosphazene to produce a membrane with high proton conductivity and low methanol crossover at room temperature. The ion exchange capacity (IEC), the water swelling behavior of the polymer, and the effect of gamma radiation crosslinking were studied, together with the proton conductivity and methanol permeability of these materials. A typical membrane had an IEC of 0.329 mmol g⁻¹ and had water swelling of 50 wt%. The maximum proton conductivity of 1.13 × 10⁻⁴ S cm⁻¹ at room temperature is less than values reported for some commercially available materials such as Nafion. However the average methanol permeability was around 10⁻⁹ cm s⁻¹, which is one hundred times smaller than the value for Nafion. Thus, the new polymers are candidates for low-temperature direct methanol fuel cell membranes.     

Preparation and performance characterization of polymer Li-ion batteries using gel poly(diacrylate) electrolyte prepared by in situ thermal polymerization

A gel polymer electrolyte (GPE) was prepared by in-situ thermal polymerization of 1,3-butanediol diacrylate (BDDA) in a EC/EMC/DMC electrolyte solution at 100 °C. The GPE with 15 wt.% polymer content appears as apparently dry polymer with sufficient mechanical strength and shows a high ionic conductivity of 3.2×10^–3 S cm^–1 at 20 °C. The MCMB–LiCoO₂ type polymer Li-ion batteries (PLIB) prepared using this in-situ internal polymerization method exhibit a very high initial charge–discharge efficiency of 92.1%, and can deliver 94.4% of its nominal capacity at 1.0 C rate and 70.7% of its room temperature capacity at –20 °C. Also, the PLIB cells show very good cycling ability with >85% capacity retention after 300 cycles. The excellent charge–discharge properties of the PLIB cells are attributed to the integrated structure in which the polymer matrix spreads over entire region of the cell acting as a strong binder and electrolyte carrier to produce a stabilized electrode–electrolyte interface. In addition, the fabricating process of the polymer cell is quite simple and convenient for practical applications.     

Proton and methanol transport behavior of SPEEK/TPA/MCM-41 composite membranes for fuel cell application

This paper reports proton and methanol transport behavior of composite membranes prepared for use in the direct methanol fuel cell (DMFC). The composite membranes were prepared by embedding various proportions (10–30 wt.%) of inorganic proton conducting material (tungstophosphoric acid (TPA)/MCM-41) into sulfonated poly(ether ether ketone) (SPEEK) polymer matrix. The results indicate that the proton conductivity of the membranes increases with increasing loading of solid proton conducting material. The highest conductivity value of 2.75 mS/cm was obtained for the SPEEK composite membrane containing 30 wt.% solid proton conducting material (50 wt.% TPA in MCM-41). The methanol permeability and crossover flux were also found to increase with increasing loading of the solid proton conducting material. Lowest permeability value of 5.7 × 10⁻⁹ cm² s⁻¹ was obtained for composite membrane with 10 wt.% of the solid proton conducting material (40 wt.% TPA in MCM-41). However, all the composite membranes showed higher selectivity (ratio between the proton conductivity and the methanol permeability) compared to the pure SPEEK membrane. In addition, the membranes are thermally stable up to 160 °C. Thus, these membranes have potential to be considered for use in direct methanol fuel cell.