Conductivity Of Electrolyte Solutions Research Articles

Influence of the Counterion and Co−Ion Diffusion Coefficient Values on Some Dielectric and Electrokinetic Properties of Colloidal Suspensions

The dependences of the conductivity increment, the electrophoretic mobility, and the permittivity increment on the counterion diffusion coefficient value were numerically determined. The use of the network simulation method made it possible to solve the governing equations for the whole range of counterion and co-ion diffusion coefficients and for very low frequencies, despite the far-reaching field-induced charge density outside the double layer. Calculations performed for different zeta potential and electrolyte concentration values show that increasing the counterion mobility, while keeping constant the electrolyte solution conductivity and the kappa a values, strongly increases the conductivity increment, barely affects the electrophoretic mobility, and strongly decreases the permittivity increment. The numerical results are discussed and compared to analytical predictions derived from the Shilov-Dukhin model, which generally leads to a good agreement, at least for high kappa a and moderate zeta.

New Family of Lithium Salts for Highly Conductive Nonaqueous Electrolytes

New lithium salts of weakly coordinating anions were prepared by treating lithium imidazolates or LiN(CH3)2 with 2 equiv of BF(3). They are LiIm(BF3)2, Li 2-MeIm(BF3)2, Li 4-MeIm(BF3)2, LiBenzIm(BF3)2, Li 2-iPrIm(BF3)2, and LiN(CH3)2(BF3)2 (Im=imidazolate, Me=methyl, iPr=isopropyl, BenzIm=benzoimidazolate). The salts were characterized by NMR spectroscopy and mass spectrometry. The structure of LiBenzIm(BF3)2 consists of a dimeric centrosymmetric unit with each lithium atom forming a bridge between the two anions through one fluorine contact to each anion. The structure of a hydrate of LiN(CH3)2(BF3)2 consists of an infinite chain in which each anion chelates two different lithium atoms through Li-F bonds. The conductivities of electrolyte solutions of these salts were measured and are discussed in terms of different ion-pairing modes determined from the solid-state structures, the anion's ability to distribute charge, and solution viscosity. Organic carbonate solutions of LiIm(BF3)2 partially disproportionate at 85 degrees C forming LiBF4, LiBF2[Im(BF3)]2, and Li[(BF3)ImBF2ImBF2Im(BF3)], reaching equilibrium by 3 months at 85 degrees C but not disproportionating at room temperature after 9 months. A mechanism for the formation of these disproportionation products is proposed. The lower conductivity of the 1 M LiIm(BF3)2 solution that has undergone disproportionation is attributed to the formation LiBF4, which is less conductive, and LiBF2[Im(BF3)]2 and Li[(BF3)ImBF2ImBF2Im(BF3)], which increase solution viscosity.

Effects of Pore Size and Conductivity of Electrolyte Solution on the Measurement of Streaming Potential and Zeta Potential of Microporous Membrane

In order to clarify the effect of electric double layer overlapping in the pore of microporous membrane on the measurements of streaming potential (SP) and the apparent zeta potential, ζobs, of the pore surface, the mixed cellulose ester microporous membranes having different pore sizes ranging from 0.025 to 0.8 μ m were used. The dependence of SP on KCl concentration was measured by the continuous measuring method of SP over the wide range of KCl concentration. Both the SP and the ζ obs estimated from the measured SP had the maximum negative value at a certain value of KCl concentration, which depended on the pore size. The ζ obs obtained from the different pore sizes did not coincide with each other even at the higher κγ, which is the ratio of pore radius, γ, to Debye length, κ-1, where the electric double layer overlapping was assumed to be negligible. However, it was demonstrated that the relationship between SP and KCl concentration could be evaluated from the theoretical calculation by using the fitting parameters of surface charge density and pore size. The calculated pore size of membrane tested was the same order of nominal one.

Conductivity dependence of the polarization impedance spectra of platinum black electrodes in contact with aqueous NaCl electrolyte solutions

Abstract The polarization resistance and capacitance of platinum black electrodes in contact with aqueous NaCl solutions was investigated. A series of measurements were made at 25±0.1 °C in the 10 Hz to 10 MHz range using a HP 4192A Impedance Analyzer. The measurement cell has flat parallel platinum electrodes 15 mm in diameter, with a continuously variable spacing from 0.5 to 9 mm. They were platinized prior to each measurement. The electrolyte solution conductivities were in the 0.004–0.6 S m−1 range. The data were analyzed using an equivalent circuit consisting in a constant phase element in series with a parallel connection of a resistance and another constant phase element. The characteristic parameters of the model are presented as a function of the electrolyte solution conductivity.

Investigations of van der Pauw method applied for measuring electrical conductivity of electrolyte solutions: Measurement of electrolytic conductivity

The four-point probe method, elaborated by van der Pauw, can be applied also in absolute measurements of electrical conductivity of electrolyte solutions. Conductance cells designed and used according to the method are more advantageous for this purpose than other calculable cells. Their cell constant depend on a single geometrical dimension only—the height. Three designs of such cells have been constructed and tested by the author. Absolute determinations of electrolytic conductivity of 0.01 and 0.1 kmol/m 3 NaCl solutions, with an overall uncertainty 0.28%, have been obtained. The analysis performed determinates that the consistency between theoretical and experimental results is limited rather by non-ideal properties of applied instrumentation than by the principle of the method. Considering available in practice uncertainty of determining the cell height and its uniformity all over the cell it is possible to produce the cell which constant could be determined with uncertainty lower than 0.01%.

Ionic dynamics in solutions: from models to experimental values

The relative influence of the electrophoretic and electrostatic relaxation effects on self-diffusion, mutual diffusion and electrical conductivity of electrolyte solutions is investigated with the aim of two kinds of theoretical calculations. All the theoretical results are compared with experimental data. Brownian dynamics simulation allows one to compute self-diffusion coefficients and the conductivity of KCl in water in good agreement with experimental data. It is shown that the self-diffusion is not only influenced by the electrostatic relaxation effect but also by the coupling between this effect and hydrodynamic interactions. The case of the mutual diffusion is also examined in the framework of an analytical transport theory. A good agreement between theoretical results and experimental data is obtained when a reference frame correction is taken into account.

Electronic structures and electrochemical properties of LiPF 6− n(CF 3) n

We evaluated (1) thermal and electrochemical stability and (2) ion-dissociation ability of PF 6− n (CF 3) n − anions by computational method. The thermal stability order by ΔΔ E (anion) is PF 4(CF 3) 2 −>PF 5(CF 3) −>PF 3(CF 3) 3 −>PF 6 −. The ion-dissociation ability order by ΔΔ E (Li salts) is LiPF 3(CF 3) 3>LiPF 4(CF 3) 2>LiPF 5(CF 3)>LiPF 6. The conductivity of electrolyte solution with LiPF 4(CF 3) 2 (3.9 mS/cm) was a little lower than that of LiPF 6 (4.4 mS/cm) in 0.1 mol/l Li salt/PC:DME electrolyte, while the oxidation potential of LiPF 4(CF 3) 2 in PC was higher than that of LiPF 6. The LiPF 4(CF 3) 2-cell showed better cycle characteristics than LiPF 6-cell.

Ion transport theory of nonaqueous electrolytes. LiClO 4 in γ-butyrolactone: the quasi lattice approach

As a part of a study on the optimisation of the electrolyte for high-density energy lithium batteries, transport properties of concentrated LiClO 4 solutions in γ-butyrolactone (BL) have been investigated. The effect of the salt concentration ( C) on the viscosity ( η) of BL solutions has been discussed in term of the Jones–Dole equation. At concentrations higher than 0.2 M, the molar conductivity ( Λ) of LiClO 4 solutions follow a C 1/3 cube root law which is predicted by the quasi lattice model first introduced by Gosh. In this model, the ions of the strong binary electrolyte are distributed in a lattice-like arrangement (fcc). The experimental value found for the slope of Λ vs. C 1/3 relation is in fair agreement with the calculated one. The effect of the temperature on the viscosity and the conductivity of electrolyte solutions have been examined. These two transport processes are well described by Arrhenius type laws from which the activation energies for the viscosity E a η and conductivity E a Λ are deduced. The variations of E a η and E a Λ with salt concentration are respectively dependent on C and C 4/3 as predicted by the quasi lattice model.

Quantitative assessment of ultrasound-induced resistance change in saline solution.

The purpose of the study was the experimental assessment of the interaction coefficient characterising the influence of pressure on the conductivity of electrolyte solutions. Pressure pulses were applied to samples of 9 gl-1 sodium chloride contained in cuboid measurement cells of identical cross-sectional dimensions but different thickness along the acoustic beam axis. The magnitude of the changes induced in cell resistance was recorded for three values of applied pressure increment (delta P = 0.94, 1.39 and 1.78 MPa) and three values of cell thickness (e = 0.58, 1.13 and 1.62 mm). A thick, focused transducer generated short (0.1 microsecond), unipolar pressure pulses. A model accounting for the characteristics of the pressure pulse and the geometry of the measurement cell was developed to predict the ultrasound-dependent changes in the measured electrical resistance. Despite some discrepancy between theoretical and experimental results, discussed in the paper, the results validated the order of magnitude of the interaction coefficient (10(-9) Pa-1). The predictions varied from about 50% (e = 1.62 mm, delta P = 0.94 MPa) to 77% (e = 0.58 mm, delta P = 1.78 MPa) of the experimental values.

Electrolytic characteristics of ethylene carbonate–diglyme-based electrolytes for lithium batteries

Dependencies of viscosity ( η) and conductivity ( κ) on temperature and solvent composition are examined for solutions of LiPF 6 and of LiClO 4 in ethylene carbonate (EC):diglyme (DG) binary mixtures to identify organic electrolyte systems with the highest conductivity as possible at room temperature. The energies of activation for viscous flow and for conductivity, determined as functions of the composition of the mixed solvent, show these two transport processes to be strongly related. Conductivities of electrolyte solutions prepared with LiPF 6 and LiClO 4 are comparable, but lower activation energy is required for LiClO 4. A flat maximum of conductivity at about 50% (v/v) in EC is observed when the composition of the mixed solvent is varied. A high value, independent of the considered temperature, has been found for the product κ η, meaning that free ions are the predominant ionic species in these media. As a consequence, the macroscopic viscosity of electrolytes under study mainly governs their conductivity. Cyclic voltammetry, performed on negative (Li x C) and positive (Li x NiO 2) intercalation electrodes in the optimized electrolyte (LiClO 4 or LiPF 6 (1 M)-50:50 EC:DG), gives evidence for the formation of passive layers during the first cycle and reversible electrochemical intercalation during the following cycles. DSC results show that this electrolyte system is a potential candidate for Li secondary batteries or electrochromic devices working at ambient or higher temperatures as it is safe and stable at least to 200°C.

Frequency dependence of ionic conductivity of electrolyte solutions

A theory for the frequency dependence of ionic conductivity of an electrolyte solution is presented. In this theory contributions to the conductivity from both the ion atmosphere relaxation and the electrophoretic effects are included in a self-consistent fashion. Mode coupling theory, combined with time-dependent density functional theory of ion atmosphere fluctuations, leads to expressions for these two contributions at finite frequencies. These expressions need to be solved self-consistently for the frequency dependence of the electrolyte friction and the ion conductivity at varying ion concentrations. In the limit of low concentration, the present theory reduces exactly to the well-known Debye–Falkenhagen (DF) expression of the frequency-dependent electrolyte friction when the non-Markovian effects in the ion atmosphere relaxation are ignored and in addition the ions are considered to be pointlike. The present theory also reproduces the expressions of the frequency-dependent conductivity derived by Chandra, Wei, and Patey when appropriate limiting situations are considered. We have carried out detailed numerical solutions of the self-consistent equations for concentrated solutions of a 1:1 electrolyte by using the expressions of pair correlation functions given by Attard. Numerical results reveal that the frequency dependence of the electrolyte friction at finite concentration can be quite different from that given by the DF expression. With the increase of ion concentration, the dispersion of the friction is found to occur at a higher frequency because of faster relaxation of the ion atmosphere. At low frequency, the real part of the conductivity shows a small increase with frequency which can be attributed to the well-known Debye–Falkenhagen effect. At high frequency, the conductivity decreases as expected. The extensions of the present theory to treat frequency-dependent diffusivities of charged colloid suspensions and conductivity of a dilute polyelectrolyte solution are discussed.

Electrochemical properties of polymer gel electrolytes based on poly(vinylidene fluoride) copolymer and homopolymer

Polymer gel electrolytes were prepared by soaking poly(vinylidene fluoride) (PVdF) membranes, obtained by casting solutions of PVdF copolymer or homopolymers in a solvent such as acetone, tetrahydrofuran (THF), methyl ethyl ketone (MEK) and N-methylpyrollidone (NMP), into an electrolyte solution of 1 M LiBF 4 in propylene carbonate (PC). During the casting process, phase separation occurred leading to non- or low-porous membranes when the phase separation remained in its early stage or to highly porous membranes when it was mostly achieved. The phase separation was enhanced with the increase in the polymer crystallinity and was more significant in the case of the homopolymers. The membranes cast from NMP solutions were non- or low-porous and showed very low uptakes of the electrolyte solution and low conductivity. In this case, the copolymer showed higher uptakes of the electrolyte solution than the homopolymers. It was also found that even for an equivalent uptake of the electrolyte solution the conductivity was higher for the copolymer than the homopolymer, attributable to the lowest crystallinity of the copolymer. On the contrary, the membranes obtained from MEK solutions with slow evaporation rates were highly porous for the homopolymers and absorb much more electrolyte solution than non- or low-porous membranes. The polymer electrolytes from the porous membranes exhibited conductivity of 10 −3 S/cm at 30°C. The phase separation process was very important since it allowed a higher uptake of the electrolyte solution and thus a higher conductivity. Nevertheless, increasing porosity affected the mechanical properties of the membranes when it exceeded 50% of the total volume. The principal limitation of the uptake of electrolyte was caused by the loss of mechanical strength. Concerning the potential window and the evolution of the interfacial resistance at the Li/polymer electrolyte interface, no significant difference could be pointed out between the copolymer and the homopolymers.

Conductance of symmetric electrolyte solutions: Formulation of the dressed-ion transport theory (DITT)

The concentration dependence of the electrical conductance of several symmetrical electrolytes is studied using the dressed-ion transport theory (DITT) formalism. This theoretical scheme is constructed from the Fuoss–Onsager theory using the equilibrium dressed-ion theory (DIT) distribution functions for electrolyte and colloid media. The conductance equation is constructed from previous results for the relaxation of the ionic atmosphere [Varela et al., J. Chem. Phys. 110, 4483 (1999)], now completed with the calculation of the concentration-dependent electrophoretic velocity of ions on the basis of a DIT in a hydrodynamic point of view. Onsager’s limiting law for the electrophoretic velocity based on the Debye–Hückel (DH) equilibrium distribution function is reformulated in terms of the DIT renormalized quantities, effective charges and effective screening length. The electrophoretic correction to the velocity calculated in the framework of this DITT is shown to exhibit a nontrivial dependence on the renormalized dielectric constant of the medium (ε*). The concentration dependence of both the deviations of the renormalized dielectric constant from the classical limit and the electrophoretic correction to the mobility is analyzed using the modified-mean spherical approximation (MMSA) value of the DIT linear response function α̂(k). The behavior of ε* and therefore of the electrophoretic correction to the ionic (or colloidal) mobilities is studied for both the random-phase approximation (RPA) and the MMSA and they are related to ionic association through the dimensionless coupling parameter, ζ, made up from the ratio between the Bjerrum length and the mean ionic radius. The expression for the conductance of the electrolyte solutions obtained in this new theoretical approach is cast in the form of a generalized Onsager’s limiting law with a concentration-dependent slope which is predicted in terms of the formation of DIT renormalized quasiparticles in the solution. Conductance predictions of several theoretical expressions for the renormalized magnitudes of electrolyte solutions are compared to direct experimental data of KCl, and are in very good agreement with the theoretical predictions of the mean-field DITT, which confirms the convenience of understanding transport processes in terms of effective dynamical entities with renormalized ionic charges interacting by means of a renormalized screened potential.

Velocity correlation function and frequency-dependent conductivity of electrolyte solutions in dipolar fluids

Abstract The velocity correlation function and frequency-dependent conductivity of a model electrolyte solution consisting of hard sphere ions in a Stockmayer fluid have been calculated by using a microscopic theoretical approach with self-consistent evaluation of diffusion constant and dielectric friction. The oscillating behaviour of the calculated quantities agrees quite well with available simulation results and through their dependence on various solvent and solute properties provide insight into the velocity correlation at intermediate time scale and ionic conductivity in the low frequency region.

Temperature dependence of conductivity in electrolyte solutions and ionic channels of biological membranes

Temperature is a key parameter in the description of any physical system. Experimental study of the temperature dependence of conductivity is very valuable in building and testing theoretical models. This fact does not appear to be fully appreciated and exploited in the study of ionic channels of biological membranes owing in part to the lack of an adequate theory for the temperature dependence of conductivity in electrolyte solutions. To redress this imbalance, and to encourage further temperature-dependence studies in ionic channels, we first give explicit expressions for the conductivity of ions in electrolyte solutions in terms of the microscopic parameters of the liquid. We then propose that the dynamics of ion transport in membrane channels are similar to that in bulk electrolyte solutions, except that ions permeating the pore need to surmount a potential barrier, the height of which can be deduced experimentally. Finally, we use our model to analyze the conductance-temperature relationships obtained in two types of single ionic channels.

The frequency dependent conductivity of electrolyte solutions

The frequency dependent conductivity, σ(ω), of model electrolyte solutions is investigated employing molecular dynamics simulations. Approximate analytical theories are also derived and evaluated. It is found that σ(ω) is generally not a simple function and that its detailed frequency dependence contains much useful information about the structure and dynamics of ionic solutions. By varying molecular and state parameters such as the dipole moment and moment of inertia of the solvent, the ionic charge, the solution density, etc., we are able to obtain a physical interpretation of the behavior of σ(ω). For example, very interesting dynamical solvation effects as well as features associated with ion pairs are identified and described.

Problem of in situ real-area determination in evaluation of performance of rough or porous, gas-evolving electrocatalysts. Part 2.—Unfolding of the electrochemically accessible surface of rough or porous electrodes: a case-study with an electrodeposited porous Pt electrode

The problem of evaluation of the electrochemically effective area of porous electrocatalyst materials is treated by examination of the kinetics of the hydrogen evolution reaction (HER) from aqueous KOH at a plated porous Pt electrode in relation to in situ real-area determination by means of scanning electron microscopy (SEM), cyclic voltammetry, potential relaxation and impedance measurements. With regard to its electrochemical accessibility, the rough or shallow-pore electrode surface can be ‘unfolded’ experimentally by increasing the electrolyte conductivity, i.e. simplifying the transmission-line model by diminishing the distributed electrolyte resistance. It was found in the impedance studies that, for the same porous plated Pt electrode, the constant phase element exponent, α, associated with double-layer capacitance varies from 0.56 to 1.0 for the HER in 0.5 and 2.0 mol dm–3 KOH solution, respectively. That is, α is not an intrinsic property of a given porous electrode, but depends strongly on the conductivity of electrolyte solution in the pores.

High ionic conductivity of new polymer electrolytes consisting of polypyridinium, pyridinium and aluminium chloride

Polymer complexes consisting of polypyridinium, pyridinium and aluminium chloride are found to be a new class of highly conductive polymer electrolytes, which exhibit a high ionic conductivity of 10–3 S cm–1 at room temperature within range of the conductivity of electrolyte solutions, in spite of film-forming properties.

高圧下における電解質溶液の電気伝導度

The electric conductivities of electrolyte solutions under high pressure are reviewed. First, the measurements of conductivity and transference number under high pressure are described briefly. Second, the interpretation of ionic conductivities in water in terms of the Walden product and the residual friction coefficient is presented. Finally, the pressure and isotope effects on the excess proton conductivity are discussed based on the Conway model.

Automatic measurement of the conductivity of an electrolyte solution by FFT electrochemical impedance spectroscopy

It is now possible to measure automatically the conductivity of an electrolyte solution by FFT electrochemical impedance spectroscopy using the measurement and modelling possibilities of the Hewlett Packard 3562A dynamic signal analyser (DSA) with a rational fraction in the Laplace variables. A new method has also been developed for synthesizing the equivalent electrical circuit of the conductivity cell. The electrolyte solution resistance can be readily measured by the DSA regardless of the form of the cell impedance graph. This measurement can be used to determine the electrolyte solution conductivity when the cell constant is known. It is thus possible to envisage automatic process control by conductivity measurements.