Showing papers on "Ionic conductivity published in 1994"

Phase Diagrams and Conductivity Behavior of Poly(ethylene oxide)-Molten Salt Rubbery Electrolytes

Abstract: New alkali metal salts capable of forming ionic complexes with poly(ethylene oxide) (PEO) have been prepared from the amide CF 3 S0 2 NH(CH 2 ) 3 OCH 3 . Among these salts, the potassium salt KCF 3 -SO 2 N(CH 2 ) 3 OCH 3 (KMPSA), witch has both a low melting point (T m = 45°C) and a low T g (= -9°C), is miscible in all proportions with PEO at moderate temperatures. This allowed, for the first time, a study of the T g -composition and conductivity-composition relationships of PEO rubbery electrolytes from the semidilute regime to the molten salt

Physical Properties of Mixed Conductor Solid Oxide Fuel Cell Anodes of Doped CeO2

Abstract: Samples of CeO2 doped with oxides such as CaO and Gd203 were prepared. Their conductivities and expansions on reduction were measured at 1000~ and the thermal expansion coefficients in the range 50 to 1000~ were determined. The ionic and electronic conductivity were derived from curves of total conductivity vs. oxygen partial pressure. For both types of conductivity a dependence on dopant valency was observed. The electronic conductivity was independent of dopant radius in contrast to the ionic which was highly dependent. These measured physical properties are compared with the ideal requirements for solid oxide fuel cell anodes. Not all requirements are fulfilled. Measures to compensate for this are discussed.

A Polymer Electrolyte for Operation at Temperatures up to 200°C

Abstract: In developing advanced fuel cells and other electrochemical reactors, it is desirable to combine the advantages of solid polymer electrolytes with the enhanced catalytic activity associated with temperatures above 100 C. This will require polymer electrolytes which retain high ionic conductivity at temperatures above the boiling point of water. One possibility is to equilibrate standard perfluorosulfonic acid polymer electrolytes such as Nafion, with a high boiling point Bronsted base such as phosphoric acid. The Nafion/H[sub 3]PO[sub 4] electrolyte has been evaluated with respect to water content, ionic conductivity and transport of oxygen, and methanol vapor. The results show that at elevated temperatures reasonably high conductivity (>0.05 [Omega][sup [minus]1] cm[sup [minus]1]) can be obtained. Methanol permeability is shown to be proportional to the methanol vapor activity and thus decreases with increasing temperature for a given partial pressure. Comparisons and distinctions between this electrolyte and pure phosphoric acid are also considered.

High Li+ Conducting Ceramics

Abstract: In this Account, the authors describe one of the most suitable ways for preparing a high Li+ conducting polycrystalline material An excellent conductivity was realized by detailed studies of both the lattice size in the Li+ migrating bulk (intragrain) and the condition of the grain boundaries (integrain) 55 refs, 8 figs, 1 tab

Electric Double‐Layer Capacitor Composed of Activated Carbon Fiber Cloth Electrodes and Solid Polymer Electrolytes Containing Alkylammonium Salts

Abstract: Solid polymer electrolytes consisting of complexes of poly(ethylene oxide)‐grafted poly(methyl)‐methacrylate (PEO‐PMMA) and tetraalkylammonium salts [tetrabutylammonium perchlorate, tetraethylammonium perchlorate, and tetraethylammonium tetrafluoroborate (TEABF4)] have been investigated for electric double‐layer capacitors with activated carbon fiber cloth electrodes. The PEO‐PMMA and tetraalkylammonium composites obtained showed high ionic conductivity (>10−4 S cm−1 at 298 K). The ionic conductivity depended on both the concentration and the size of each ion. The composites had good stability over a wide potential range (ca. 5.0 V). When the PEO‐PMMA and TEABF4 composites were used in solid‐state electric double‐layer capacitors with activated carbon fiber cloths as polarizable electrodes, the capacitors showed charge/discharge behavior with large values of capacitance and high coulombic efficiency. The long voltage retention was observed in the self‐discharge test of the capacitor with TEABF4.

Investigation of Ion-Conducting Ormolytes: Structure-Property Relationships

Abstract: Hybrid organic-inorganic composites with ionic properties, so called ormolytes (organically modified electrolytes) have been prepared by the sol-gel process from mixtures of tetraethoxysilane, tetraethylene glycol, and lithium salt. They show ionic conductivity up to 5 x 10-5 Ω-1 cm-1, with activation energies around 0.6 eV. Their properties have been related to their structure using a multitechnique approach (IR, DSC, NMR, SAXS). These materials can be described as diphasic systems with silica clusters providing the mechanical properties and the organic phase allowing the dissolution of large quantities of salts. Optical transparency and mechanical stability can be explained by the interpenetration of these two phases at a molecular level.

Ionic conductivity of a polymer electrolyte with modified carbonate as a plasticizer for poly(ethylene oxide)

Abstract: A new type of plasticizer, a modified carbonate (MC3) made by attaching three ethylene oxide units to the 4-position of ethylene carbonate, has been synthesized. The ionic conductivity of a polymer electrolyte using this type of plasticizer in a poly(ethylene oxide) (PEO)-LiCF[sub 3]SO[sub 3] complex has been studied. Adding 50% of this plasticizer by weight of PEO to the PEO-LiCF[sub 3]SO[sub 3] complex, yielded an ionic conductivity of 5 [times] 10[sup [minus]5] S/cm at 25 C, which is two orders of magnitude higher than that found for a PEO-LiCF[sub 3]SO[sub 3] electrolyte without a plasticizer, and one order of magnitude higher than that found when using propylene carbonate (PC) as a plasticizer. The temperature dependence of the conductivity and thermal analysis results indicate that this new plasticizer increases the ionic conductivity throughout the entire complex system, whereas conventional plasticizers, like PC, simply create a high conductivity pathway through the plasticizer itself. The new plasticizer also enhances the ion pair dissociation which in turn improves the ionic conductivity.

The Development of a new plasticizer for poly(ethylene oxide) based polymer electrolyte and the investigation of their ion-pair dissociation effect

Abstract: One approach to increasing the ionic conductivity of polymer electrolyte is to add plasticizers to the polymer-salt complexes . Recently, we have synthesized a new plasticizer, modified carbonate (MC3), by attaching three ethylene oxide units to the 4-position of ethylene carbonate. AC impedance studies showed that an ionic conductivity of 5{times}10{sup {minus}5} S cm{sup {minus}1} could be achieved at room temperature, by adding 50 wt % of MC3 into PEO-LiCF{sub 3}SO{sub 3} complex. This is two orders of magnitude higher than that found in PEO-LiCF{sub 3}SO{sub 3} electrolyte without a plasticizer, and one order of magnitude higher than that found when using same amount of propylene carbonate (PC) as plasticizer. Temperature dependent conductivity measurement and thermal analysis show that this new plasticizer increased the ionic conductivity throughout the entire complex system, while the conventional plasticizers only create a high conductivity path way through the plasticizer itself. The samples are free standing films with good mechanical properties. When MC3 is used as a plasticizer, the ionic conductivity increase is much higher than using PC as a plasticizer at high temperature (65{degrees}C), implying an increase in the number of charge carriers. Therefore, we believe that MC3 has a stronger ion pair dissociationmore » effect than PC, when used as a plasticizer. The ion pair dissociation effect was studied by Raman, FTIR, and near edge x-ray absorption fine structure (NEXAFS) spectroscopy.« less

New polyelectrolyte materials based on smectite polyoxyethylene intercalation compounds

Abstract: The intercalation of poly(ethylene oxide), PEO, into homoionic phyllosilicates of the smectite group (montmorillonite and hectorite) gives composite materials able to act as solid polyelectrolytes. The synthesis and the structural characterization of new intercalation compounds belonging to this class of materials have been investigated. The resulting compounds exhibit good chemical and thermal stability, preserving their ion-exchange properties. PEO intercalation produces an enhancement of the electrical conductivity associated with the interlayer cations compared to the parent silicates. Ionic conductivity determined by impedance spectroscopy measurements of different polyoxyethylene compounds (PEO and crown-ethers) into homoionic 2:1 charged phyllosilicates reveals that the conductivity values can be correlated with the oxyethylene-cation strength interaction.

Ionic transport in ferroelectrics

Abstract: Ionic conductivity in ferroelectric oxides having the perovskite structure is reviewed. Depending on the compound, doping levels, and equilibration conditions, ionic transport numbers approaching unity have been observed under equilibium conditions. The ionic conductivity decreases with decreasing temperature with an activation energy of about 1 eV over the entire measured temperature range of 1000-60°C. This is attributed to the activation energy of the oxygen vacancy mobility. The p-type conductivity decreases somewhat less rapidly for both equilibrium and quenched conditions. Evidence is presented that suggests that the initial leakage current contains a substantial ionic component under device use conditions. Subsequent time-dependent behavior is critically dependent on whether or not the electrodes are blocking to oxygen.