Conductivity Isotherms Research Articles

Effect of Sodium-mixed Anion Doping in PEO-based Polymer Electrolytes

Three poly(ethylene oxide) based sodium ion-conducting mixed anion systems, namely . PEO: (1 - x )NaI + xNaSCN, PEO:(1 - x )NaI + xNaCH3COO, PEO:(1 - x) NaSCN + xNaCH 3COO have been studied. The characteristic dip in conductivity isotherm for all the three systems was observed below and above the melting of the complex. The isolated cation transference number has also been reported by the combined a.c.—d.c. technique for all three systems. The value of tNa+ was found to be modified due to mixed anion doping. The detailed analysis of the systems under optical microscopy, differential scanning calorimetry, complex impedance spectroscopy and dielectric constant is discussed in the paper. It is shown that the mixed anion doping in polar-non polar combination of the anions is more effective in terms of changes in σ and tNa+ The percentage crystallinity and dielectric constant of the medium are also correlated with the observed effect. The electrolyte dissociation model has been applied to explain the composition-dependent behavior.

Measurements of Electrical Conductivity and Oxygen Nonstoichiometry of La0.5Sr0.5Ga0.2Fe0.8O3 − δ Using Gastight Electrochemical Cells

The effect of on the electrical conductivity of was investigated at and . At , a discontinuity, i.e., a plateau and a steep slope, was observed in the intermediate region, indicating that a phase separation occurred, most likely forming a mixture of a perovskite and an oxygen vacancy ordered phase. Above , a smooth isotherm without the discontinuity was obtained. The slopes in the plot of the logarithm of the conductivity vs were ≈1/4 in the p-type region. The dependence of the oxygen nonstoichiometry was studied using the solid-state coulometric titration technique. The phase separation was also observed in the form of the δ isotherm hysteresis at the condition where the discontinuity appeared in the conductivity isotherms. Based on the nonstoichiometry data, a point defect model was derived and the partial molar quantities (, , and ) of oxygen in were calculated.

AC conductivity in Li2O and Li2O-K2O doped vanado-tellurite glasses

In the present study, two sets of vanado-tellurite glasses doped with Li2O and Li2O-K2O have been prepared by the melt quenching method. AX conductivity was measured using in the frequency range 50Hz to 5MHz and temperature from 300 to 525K. By non-linear regressional analysis of the measured total conductivity, dc and ac components and frequency exponent, s, were determined. In both the series of glasses, the conductivity increased with increasing frequency and decreased with increasing alkali content. The temperature dependence of conductivity has been analyzed using Mott's small polaron hopping model and the high temperature activation energies were determined. The activation energy decreased with increasing Li2O content in single alkali glasses and with increase in K2O content in mixed alkali glasses. The frequency exponent, s, was observed to be nonlinearly varying with temperature and it has been looked at in terms of Correlated Barrier Hopping and Quantum Mechanical Tunneling models. By scaling the conductivity isotherms and drawing master curves, the time-temperature superposition principle has been verified in both the series of glasses. It is for the first time that the alkali doped vanado-tellurite glasses are reported for ac conductivity in the frequency range 50Hz-5MHz, and the data has been subjected to thorough analysis.

Effect of thermal history and characterization of plasticized, composite polymer electrolyte based on PEO and tetrapropylammonium iodide salt (Pr 4N +I -)

The search for anionic conductors based on solid polymer electrolytes is important for the development of photo-electrochemical (PEC) solar cells due to their many favourable chemical and physical properties. Although solid polymer electrolytes have been extensively studied as cation, mainly lithium ion, conductors for applications in secondary batteries, their use as anionic conductors have not been studied in greater detail. In a previous paper we reported the application of a PEO based iodide ion conducting electrolyte in a PEC solar cell. This electrolyte had the composition PEO: Pr 4N +I − = 9:1 with 50 wt.% ethylene carbonate (EC). In this work we have studied the effect of incorporating alumina filler on the properties of this electrolyte. The investigation was extended to electrical and dielectric measurements including high frequency impedance spectroscopy and thermal analysis. In the DSC themograms two endothermic peaks have been observed on heating, one of these peaks is attributed with the melting of the PEO crystallites, while the other peak with a melting temperature ~ 30 °C is attributed to the melting of the EC rich phase. The melting temperature of both these peaks shows a marked variation with alumina content in the electrolyte. The temperature dependence of the conductivity shows that there is an abrupt conductivity increase in the first heating run evidently due to the melting of the EC rich phase. High conductivity values are retained at lower temperatures in the second heating. Conductivity isotherms show the existence of two maxima, one at ~ 5% Al 2O 3 content and the other at ~ 15%. The occurrence of these two maxima has been explained in terms of the interactions caused by alumina grains, the crystallinity and melting of the PEO rich phase. As seen from latent heat of melting, the crystallinity of the electrolyte has reduced considerably during the first heating run. In contrast to the conductivity enhancement caused by ceramic fillers in PEO-based cation containing electrolytes, no conductivity enhancement has been observed in the present PEO based anionic conducting materials by adding alumina except at low temperatures.

Electrical conductivity of aqueous acids in binary and ternary water-electrolyte systems

We analyze electrical conductivity data for aqueous solutions of strong and weak acids over a wide range of concentrations at various temperatures. Electrical conductivity isotherms in these solutions are characterized by peaks, whose parameters correlate with the molecular structure of solutions. On the basis of the concentration dependence of the activation energy of electrical conductivity, the acid solutions are divided into two groups. One includes HIO3, H2SO4, and H3PO4; the other includes HCl, HBr, HI, HClO4, HNO3, and carboxylic acids. We show that anomalous proton migration is operative only in low-concentration solutions until their concentration reaches the peak on conductivity isotherms. The effect of extrinsic ions on proton mobility and on conductivity in acid-salt-water systems is considered.

A novel intrinsically proton conducting star-shaped imidazole terminated oligomers

In this paper, intrinsically proton conducting imidazole-terminated oligomers were synthesized by tethering imidazole units via flexible ethylene oxides (EO) chain onto 1,3,5-benzenetricarbonyl chloride (TMA). The structure of the resulting material was confirmed by FT-IR; 1H-NMR spectrometer and compositions were obtained by elemental analysis. Thermogravimetry results showed that the materials are thermally stable up to approximately 160 °C. Differential scanning calorimeter studies were performed to study the influence of the length of EO units on the glass transition temperatures of the materials. The conductivity isotherms exhibit Vogel–Tamman–Fulcher behavior with a maximum proton conductivity of \(\sigma = 2 \times 10^{ - 2} \;{\operatorname{S} \mathord{\left/ {\vphantom {\operatorname{S} {\operatorname{cm} }}} \right. \kern-\nulldelimiterspace} {\operatorname{cm} }}\) at 110 °C for TMA-(Peg600-Imi)3.

Ac conductivity and dielectric relaxation in ionically conducting soda–lime–silicate glasses

The frequency dependent conductivity and dielectric relaxation of alkali ions in some soda–lime–silicate (Na 2O–CaO–SiO 2) glasses are investigated over a frequency range from 50 Hz to 1 MHz and in a temperature range from room temperature to 603 K by using alternating current impedance spectroscopy. The conductivity isotherms show a transition from frequency independent dc region to dispersive region where the conductivity continuously increases with increasing frequency. The electric modulus representation has been used to provide comparative analysis of the ion transport properties in these glasses. The scaling behavior of imaginary part of electric modulus indicates that all dynamical processes occurring at different frequencies give the same activation energy.

Fabrication and characteristics of planar-type methane reformer using ceria-based oxygen permeable membrane

This paper describes the fabrication of a planar-type methane reformer based on a composite-type oxygen permeable membrane and its reforming properties. The membrane reformer module comprising of (Ce 0.85Sm 0.15)O 2–15 vol.%MnFe 2O 4 and a ferric stainless steel separator with a same thermal expansion coefficient was successfully developed. For the reformer module, high CH 4 conversion, CO and H 2 selectivity of 96%, 84%, and 89% were achieved, respectively. Based on an electrical conductivity isotherm, joule heat caused by oxygen permeation in the module was estimated to be approximately 8.4 W. In addition, the effect of ZrO 2-doping on the mechanical properties and oxygen permeability of the composite material was investigated. The highest Zr-content sample, (Ce 0.85Sm 0.15) 0.2Zr 0.8O 2–15 vol.% MnFe 2O 4, showed a tetragonal structure. As a result of the crystal structural change, superior mechanical properties of Young's modulus of 337 GPa and fracture toughness of 2.8 MPa m 1/2 were obtained.

Electrical conductivity and oxygen nonstoichiometry of acceptor (Ga)-doped titania

Electrical conductivity and oxygen nonstoichiometry (delta) have been measured, respectively, by a dc 4-probe technique and coulometric titrometry on the system of polycrystalline Ti0.99Ga0.01O1.995-delta against oxygen activity in the range of -20 < log aO2 < or = 0 at different temperatures in the range of 1073 < or =T/K < or = 1373. It is found that isothermal conductivity varies as sigma alpha aO2m with m approximately -1/4, -1/5, -1/4, +1/4, in order of increasing aO2, finally exhibiting an n-type (m = -1/4) to p-type (m = +1/4) transition crossing the stoichiometric composition (delta = 0), in perfect agreement with the oxygen nonstoichiometry variation. The electrical conductivity and oxygen nonstoichiometry isotherms are combined to evaluate the ionic partial conductivity and transference number, the intrinsic electronic excitation equilibrium constant, and eventually both mobilities of electrons and holes without employing any assumption at all. The partial molar enthalpy and entropy of the component oxygen are also evaluated as functions of nonstoichiometry.

Electrical Conductivity of Melts Containing Rare-Earth Halides. I. MCl-NdCl3 (M = Li, Na, K, Rb, Cs)

The electrical conductivity of molten MCl-NdCl3 (M = Li, Na, Rb and Cs) has been measured from the liquidus temperature up to ~ 1180 K. The measurements were performed in usual U-shaped capillary quartz cells with platinum electrodes. The molar conductivity (Λ) has been computed by using literature data on the densities of the binary systems. In all cases, when the temperature range exceeds about 100 K, the plot lnΛ vs. 1/T is not a straight line. The activation energy of the conductivity does not remain constant but reduces with increasing temperature. In the specific and molar conductivity isotherms strong deviations from additivity are noted. The results are discussed in terms of octahedral local coordination of Nd3+ over the entire concentration range.

High temperature electrical conductivity in ZnSe:In and in CdSe:In under selenium vapor pressure

AbstractHigh temperature electrical conductivity (HTEC) isotherms and isobars of ZnSe:In and of CdSe:In are compared. There are differencies in In‐doping mechanisms of II–VI compounds. When HTEC isotherms and isobars of ZnSe:In and of CdSe:In, measured under metal component vapour pressure give both n‐type conductivity then differences appear in the results of measurements under the selenium vapor pressure (p). ZnSe:In isotherms in the last case are characterized by the conductivity type conversion but no such drastic change of HTEC type is observed on CdSe:In isotherms. Under the conditions of p, the activation energy of HTEC isobars for ZnSe:In is ΔE ≈ 1.3–1.6 eV and for CdSe:In is ΔE ≈ 1.2 eV. The onefold ionized substitutional In at Zn place is proposed to be compensated by native defects in ZnS:In and in CdSe:In under high p. This native defect may be onefold ionized zinc vacancy for ZnSe:In and twofold ionized cadmium vacancy for CdSe:In. Association of defects occur at lower temperatures. (© 2007 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

Interaction in the Li2Mo3O10-CO(NH2)2-H2O system at 25°C

The solubilities and solid phases in the Li2Mo3O10-CO(NH2)2-H2O system at 25°C are studied. A compound of composition Li2Mo3O10 · 6CO(NH2)2 · 4H2O and lithium trimolybdate decahydrate Li2Mo3O10 · 10H2O are found to exist. The Li2Mo3O10 · 6CO(NH2)2 · 4H2O ray crosses the solubility isotherm, which indicates the congruent solubility of the double compound in water. The density, refractive index, dynamic viscosity, surface tension, electrical conductivity, and pH of saturated solutions of the system are determined. The molar volume, equivalent electrical conductivity, reduced conductivity, and solution ionic strength isotherms are calculated. A strong correlation between all the property isotherms and the solubility is observed.

Electrical conductivity of solutions of the LiIO3-HIO3-H2O system

The electrical conductivity of aqueous LiIO3 solutions and solutions of the LiIO3-HIO3-H2O system is measured over a wide range of compositions at 25, 50, and 75°C. Isothermal surfaces of electrical conductivity are mapped, and the activation energies of conductivity are calculated. The conductivity isotherms in the LiIO3-H2O and HIO3-H2O boundary binary systems and in mixed solutions along sections with fixed electrolyte ratios each have a maximum as a function of electrolyte concentration. It is assumed that structure reorganization occurs in solutions in the concentration range corresponding to the peak conductivity. Proton migration features in the solutions in question are considered.

Temperature dependence of electric conductivity of molten binary mixtures of alkali and rare-earth metals chlorides

The temperature dependences of the specific and molar electric conductances of CeCl3-MCl and LnCl3-KCl (M=Li, Na, K, and Cs; Ln=Er and Yb) molten binary mixtures of various compositions were studied. The size of the cations of alkali and rare-earth metals was demonstrated to affect the intensity of the interactions of the components of the systems. Deviations of the molar conductance isotherms from additivity and dependence of the isotherms on the ratio between the mixture components were explained by the formation of complexes in the melts.

Counterion effect on the solution and thermodynamic properties of lithium perfluoroalkanoates

The isotherms of conductivity of lithium perfluorooctanoate and perfluoroundecanoate were measured and the critical micelle concentration, cmc, degree of ionization of the micelles, β, determined in a range of temperatures above the Krafft point. The thermodynamic parameters, Gibbs free energy,, enthalpy, and entropy of micelle formation, were determined from a proposed thermodynamic model. Apparent molar volume and the apparent molar adiabatic compressibility for both surfactants have been calculated over a wide concentration range from density and ultrasound velocity measurements. Positive deviations of the apparent molar volume from the Debye–Hückel limiting law in dilute solutions indicate the existence of premicellar aggregation. Changes in the slope of adiabatic compressibility of lihium perfluoroundecanoate from positive to negative have been interpreted in terms of solute solvent interactions. Dynamic surface tension measurements allow us to calculated diffusion coefficients, areas and aggregation numbers. These values are discussed comparing the corresponding sodium compounds.

Transport Phenomena in Polymer Electrolyte Membranes: I. Modeling Framework

This paper presents a critical examination and analysis of classical and recently proposed models for transport phenomena in polymer electrolyte membranes. Key experimental observations related to membrane conductivity, membrane hydration, and sorption isotherms are first reviewed. Proton transport mechanisms in bulk water, and the influence of the membrane phase on these mechanisms, are examined. Finally, various formulations and underlying assumptions to account for macroscopic transport are reviewed, and an analysis of the binary friction model (BFM) and dusty fluid model (DFM) is performed to resolve an outstanding formulation issue. It is shown that the BFM provides a physically consistent modeling framework and implicitly accounts for viscous transport (i.e., Schloegl equation), whereas the dusty fluid model erroneously accounts twice for viscous transport. In Part II we apply the BFM framework to develop a general transport model for perfluorosulfonic acid membranes.

Dependences on the Composition and a Comparison of Electrolytic Properties of Some Germanium-Containing Quasi-binary Salt Systems

Germanium-containing quasi-binary salt systems GeSe-GeI2 and NaI-GeI2 (GeI2 is a dopant) are studied by methods of electroconductance and x-ray diffraction analysis (XRDA). The conductivity isotherms combined with the XRDA data show that the domain of restricted solid solutions in these systems comes to 3 and 1 mol % GeI2, respectively. The maximal electrolytic admittance is observed at 2 and 0.25 mol % GeI2 in GeSe-GeI2 and NaI-GeI2 systems. The GeSe system has better ceramic properties, is less susceptible to water traces, and has higher conductivity and lower activation energy for conduction.

Two‐Fold Diffusion Kinetics of Oxygen Re‐Equilibration in Donor‐Doped BaTiO3

Oxygen (nonstoichiometry) re‐equilibration kinetics was examined, via a conductivity relaxation method, on 1 m/o donor (La)‐doped BaTiO3 (nominal composition, Ba0.99La0.01Ti0.9975O3) against oxygen partial pressure in the range of −16&lt;log (PO2/ atm)≤ 0 at 1200°C. The kinetics has been found to be onefold with a single relaxation time or twofold with two different relaxation times depending on oxygen activity. It is attributed to the relative contributions depending on oxygen activity of fast relaxation of the oxygen sublattice and sluggish relaxation of the cation sublattices: their revelations are determined by the ratio of oxygen vacancy to cation vacancy (say, ) concentrations and their relaxation times. Their chemical diffusion coefficients have been extracted from the relaxation times asanddepending on oxygen activity, which are in good agreement with the reported values. Defect diffusivities are subsequently determined by using the thermodynamic factors of component O and Ti, which have been evaluated from the equilibrium conductivity isotherm, asand.

Ionic conductivity of glasses with two and three types of alkali ions

We report, for the first time, frequency-dependent conductivity spectra of glassy 0.1Li 2O·0.1Na 2O·0.1K 2O·0.7B 2O 3 over a wide temperature range. The conductivity isotherms of the studied glasses show a transition from their dc plateaus into a dispersive regime where the conductivity continuously increases with frequency tending towards a linear frequency dependence at sufficiently low temperatures. At a given temperature, the dc conductivity values of glassy 0.1Li 2O·0.1Na 2O·0.1K 2O·0.7B 2O 3 are much lower than those of 0.3[ xM 2O·(1− x)Me 2O]·0.7B 2O 3 (M–Me=Li–Na, Li–K, and Na–K) and 0.2[ xLi 2O·(1− x)Na 2O]·0.8B 2O 3 glass systems, and the dc conductivity activation energy of glassy 0.1Li 2O·0.1Na 2O·0.1K 2O·0.7B 2O 3 is higher than those of 0.3[ xM 2O·(1− x)Me 2O]·0.7B 2O 3 and 0.2[ xLi 2O·(1− x)Na 2O]·0.8B 2O 3 glasses with x=0, 0.2, 0.4, 0.6, 0.8, and 1, respectively. The experimental results are interpreted in terms of the Dynamic Structure Model (DSM) developed by Bunde, Ingram, and Maass. On the basis of our results, we predict that mixed alkali glasses with three types of cations will show a stronger mixed alkali effect in physical quantities related to the ion transport than glasses with only two types of cations.

Structural micellar transition for fluorinated and hydrogenated sodium carboxylates induced by solubilization of benzyl alcohol.

The solubility of benzyl alcohol in micellar solutions of sodium octanoate and sodium perfluorooctanoate was studied. From the isotherms of specific conductivity versus molality at different alcohol concentrations, the critical micelle concentration and the degree of ionization of the micelles were determined. The cmc linearly decreases upon increasing the amount of benzyl alcohol present in aqueous solutions with two distinct slopes. This phenomenon was interpreted as a clustering of alcohol molecules above a critical point, around 0.1 mol kg(-1). Attending to the equivalent conductivity versus square root of molality, the presence of a second micellar structure for the fluorinated compound was assumed. The thermodynamic parameters associated with the process of micellization were estimated by applying Motomura's model for binary surfactant mixtures, modified by Pérez-Villar et al. (Colloid Polym. Sci 1990, 268, 965) for the case of alcohol-surfactant solutions. A comparison of the hydrogenated and fluorinated compounds was carried out and discussed.