Cation Transport Number Research Articles

Polyethylene oxide and ionic liquid-based solid polymer electrolyte for rechargeable magnesium batteries

Solid polymer electrolytes (SPEs) based on polyethylene oxide (PEO) complexed with magnesium triflate Mg(Tf)2 or Mg(CF3SO3)2) and incorporating the ionic liquid (IL) (1-butyl-1-methylpyrrolidinium bis(trifluoromethanesulfonyl)imide (PYR14TFSI)) were prepared by solution cast technique. The electrolyte was optimized and characterized using electrical conductivity, cationic transport number measurements, and cyclic voltammetry. The highest conductivity of the PEO/Mg(Tf)2, 15:1 (molar ratio), electrolyte at room temperature was 1.19 × 10−4 S cm−1 and this was increased to 3.66 × 10−4 S cm−1 with the addition of 10 wt.% ionic liquid. A significant increase in the Mg2+ ion transport number was observed with increasing content of the ionic liquid in the PEO-Mg(Tf)2 electrolyte. The maximum Mg2+ ion transport number obtained was 0.40 at the optimized electrolyte composition. A battery of the configuration Mg/ and [(PEO)15:Mg(Tf)2+10%IL]/TiO2-C was assembled and characterized. Preliminary studies showed that the discharge capacity of the battery was 45 mA h g−1.

The permselectivity and water transference number of ion exchange membranes in reverse electrodialysis

Reverse electrodialysis of saline solutions (RED) is a renewable energy technology with large potential. Key components in the system are the ion exchange membranes. This work evaluates the efficiency of commercially available anion and cation selective membranes for RED. Their efficiency is often described with the apparent transport number for the ion in question, and this number depends on the salt concentration. It is known since long that the water transference coefficient contributes to the apparent transport number, but much of the recent literature on RED takes the permselectivity as defined by the apparent transport number as a direct measure of the membrane selectivity. The purpose of this paper is to clarify that situation with new data on Fumasep membranes. Concentration cell potentials were measured for anion- and cation exchange membranes from Fumasep (FAD and FKS, respectively, Fumatech, Germany) in the temperature range 12−45°C in salt solutions relevant for reverse electrodialysis. The results show that the anion exchange membrane is a perfectly selective ion exchange membrane, and has a water transference coefficient of −6±1. The cation selective membrane has a cation transport number of 0.93 and a water transference coefficient of 8± 7. We suggest that the developers of membranes should pay more attention to the water transference coefficient. To enhance the performance of ion selective membranes and RED, it is beneficial to have water transference coefficients as close to zero as possible.

Ionic conductivity, ionic transport and electrochemical characterizations of plastic crystal polymer electrolytes

In this work, the plastic crystal polymer electrolytes (PCPEs), composed of polyacrylonitrile (PAN), succinonitrile (SN) and lithium bis(trifluoromethane)sulfonimide (LiTFSI) were prepared. The concentrations of lithium salt were varied by weight percentage from 10 wt% to 50 wt%. The ionic conductivity of the PCPE films increases with the increase of lithium salt, where the highest value recorded is in the order of ~10−2 S cm−1. The temperature-dependence conductivity analysis shows that the PCPE films exhibit Arrhenius behaviour when subjected to the temperature range from 303 K to 343 K. The decrease in crystallinity was confirmed by X-ray diffraction (XRD) and Differential Scanning Calorimetry (DSC) analyses. The cationic transport number also increases with the increase of salt which corresponds well to their conductivity values. It is found that the films are electrochemically stable up to ~3.6 V as revealed by the linear sweep voltammetry (LSV) analysis. The cyclic voltammetry (CV) plots of the films shown no substantial change in the redox peaks which mean that the charge transfer reaction is reversible.

Characteristics of novel plastic crystal gel polymer electrolytes based on PVdC-co-AN

A new gel polymer electrolytes composed of poly(vinylidene chloride-co-acrylonitrile) (PVdC-co-AN) co-polymer and plastic crystal succinonitrile (SN) were prepared to form plastic crystal gel polymer electrolytes (PGPEs) with the variation of magnesium triflate (MgTf2) salt from 5 to 30 wt.%. The room temperature and temperature dependence studies of the PGPE films were determined by using AC impedance spectroscopy. The conductivity versus reciprocal temperature plot has shown a nonlinear behavior. The ionic and cationic transport numbers were evaluated by DC polarization method and the combination of DC polarization and AC impedance methods, respectively to determine the charge carrier species in the PGPE films. To study the interactions among the constituents in the PGPEs as well as to confirm the complexation between them, Fourier transform infrared spectroscopy (FTIR) was carried out. The analysis of FTIR spectra was further investigated by deconvolution of the FTIR spectra to prove the dependability of ionic conductivity and transport number with the presence of free ions, ion pairs, and ion aggregates in the PGPEs.

New approach to characterization of hybrid nanocomposites

This paper presents a novel approach to the characterization of hybrid cation-exchange membranes by applying the “fine porous membrane” model. We verify this approach using samples of cation-exchange membranes synthesized on the base of the perfluorinated MF-4SC membrane and halloysite nanotubes and prepared by the casting method. For characterization we use the initial pure MF-4SC membrane and two hybrid membranes MF-4SC spatially modified with halloysite nanotubes encapsulated by Pt nanoparticles or intercalated by Fe nanoparticles. Based on our own experimental data for the diffusion permeability and specific conductivity in dependence on electrolyte concentration (HCl), we calculate the main physico-chemical parameters of these membrane systems, i.e. the ambipolar diffusion and equilibrium distribution coefficients of the electrolyte inside the membrane. Comparing the theoretically calculated parameters to the experimentally measured current-voltage curves, selectivity, transport numbers of cations and water for all the three samples we conclude that the hybrid membrane with platinum nanoparticles is superior to the other two membranes as far as fuel cells are concerned.

A Study of the Transport Properties of [Bmim]BF4 and PEG Mixtures Using Diffusion-Ordered NMR and UV–Visible Spectroscopy Techniques

Proton nuclear magnetic resonance (1H NMR), diffusion-ordered NMR spectroscopy (DOSY-NMR), and ultraviolet–visible (UV–vis) spectroscopy techniques were used to study the specific intermolecular interactions within the binary mixtures of 1-butyl-3-methylimidazolium tetrafluoroburate, [bmim]BF4, and poly(ethylene glycol), PEG, with different average molecular weights (i.e., 200, 400, 600, and 1000) in the whole composition range. Also, the electrical conductivity and the viscosity of these four mixtures were measured at different compositions and temperatures. The results of 1H NMR spectra show that the change in proton chemical shifts of ionic liquid (IL) and PEG molecules in the mixtures is more than that of the pure ones. DOSY-NMR was used to measure the diffusion coefficients of the ionic species in the mixtures. Also, the other parameters such as hydrodynamic radii, transport numbers of anions and cations, and dissociation and association degrees of IL molecules were calculated from the diffusion coef...

New cation-exchange membranes based on cross-linked sulfonated polystyrene and polyethylene for power generation systems

The present paper is devoted to the properties of sulfonated cation-exchange membranes obtained by radiation chemical grafting polymerization of styrene with divinylbenzene on a polyethylene film. The mechanical and transport properties (conductivity, diffusion permeability, and transport numbers) of the membranes obtained with various amounts of a cross-linking agent (0–3.5%) and degrees of polystyrene grafting (23–32%) were investigated in comparison with commercially available membranes, i.e. Nafion® 117 and Neosepta® CMX. Tensile strength values around 15–20MPa were obtained, and they increased with increasing cross-linker amounts. The conductivity of membranes containing no cross-linking agent reached 8.4·10−2Ω−1cm−1 at 25°C and high relative humidity. As the amount of the cross-linking agent increased, the water uptake in membranes and their conductivity at high relative humidity decreased, whereas the activation energy of conductivity increased. At low humidity (RH=30%), the water uptake and conductivity increased with increasing amounts of the cross-linking agent. The membranes based on cross-linked polystyrene had low diffusion permeability, while the associated cation transport numbers were higher than those with commercial Nafion® 117 membrane. The calculated theoretical power of reverse electrodialysis batteries based on the best membranes was 10% higher than that of the battery based on the Neosepta® CMX membrane.

Size and Charge Dependence of Ion Transport in Human Nail Plate

The electrical properties of human nail plate are poorly characterized yet are a key determinate of the potential to treat nail diseases, such as onychomycosis, using iontophoresis. To address this deficiency, molar conductivities of 17 electrolytes comprising 12 ionic species were determined in hydrated human nail plate in vitro. Cation transport numbers across the nail for 11 of these electrolytes were determined by the electromotive force method. Effective ionic mobilities and diffusivities at infinite dilution for all ionic species were determined by regression analysis. The ratios of diffusivities in nail to those in solution were found to correlate inversely with the hydrodynamic radii of the ions according to a power law relationship having an exponent of −1.75 ± 0.27, a substantially steeper size dependence than observed for similar experiments in skin. Effective diffusivities of cations in nail were 3-fold higher than those of comparably sized anions. These results reflect the strong size and charge selectivity of the nail plate for ionic conduction and diffusion. The analysis implies that efficient transungual iontophoretic delivery of ionized drugs having radii upward of 5 Å (molecular weight, ca. ≥340 Da) will require chemical or mechanical alteration of the nail plate.

All-Solid-State Lithium-Sulfur Battery Based on a Nanoconfined LiBH4 Electrolyte

In this work we characterize all-solid-state lithium-sulfur batteries based on nano-confined LiBH4 in mesoporous silica as solid electrolytes. The nano-confined LiBH4 has fast ionic lithium conductivity at room temperature, 0.1 mScm−1, negligible electronic conductivity and its cationic transport number (t+ = 0.96), close to unity, demonstrates a purely cationic conductor. The electrolyte has an excellent stability against lithium metal. The behavior of the batteries is studied by cyclic voltammetry and repeated charge/discharge cycles in galvanostatic conditions. The batteries show very good performance, delivering high capacities versus sulfur mass, typically 1220 mAhg−1 after 40 cycles at moderate temperature (55°C), 0.03 C rates and working voltage of 2 V.

Synthesis, estimation of stability in different media, electrochemical properties and potentiometric studies of PVC-based NP ion-exchange composite membrane for desalination and waste water treatment applications

The chemical stability of PVC-based Neodymium phosphate (NP) ion-exchange membrane shows better results with strong oxidizing agent KMnO4 as compared to the acidic and alkaline medium and it was synthesized by sol–gel and die casting method. The characterization of the ion-exchange composite membrane was carried out by employing Fourier transform infrared spectroscopy, thermogravimetry analysis and scanning electron microscopy. The membrane with 25% PVC and 75% NP shows excellent mechanical and thermal stability as well as good ion-exchange capacity. The observed membrane potential data were used to determine the transport number of cation and anion and other electrochemical parameters of the composite membrane. The prepared membrane can be considered as an excellent material for desalination and wastewater treatment applications.

Sharp decline in counter-ion transport number of electrodialysis ion exchange membrane on moderate increase in temperature

The counter-ion transport-number of membrane affects columbic efficiency of electrochemical cells, many of which encounter varying salt concentration or temperature at different times of operation. Effect of NaCl concentration and temperature on the counter-ion transport number of commercial cation (Selemion CMV and Neosepta CMX) and anion (Selemion AMV and Neosepta AMX) exchange membranes was determined using chronopotentiometry. The transport number of the membranes didn't change with increasing NaCl concentration from 0.017M to 0.1M. Variation of transport number with temperature was determined from chronopotentiometric data using the Sand equation as well as a novel procedure. Values obtained from the Sand equation showed an anomalous trend, but the values obtained from the second procedure followed a consistent trend. The counter-ion transport number decreased significantly on increasing temperature by 20°C and the decline was higher for the cation exchange membranes.

Effect of current density and behaviour of second phases in anodizing of a Mg-Zn-RE alloy in a fluoride/glycerol/water electrolyte

Anodizing of a Mg-Zn-RE alloy was carried out at constant current densities from 0.1 to 10 mA cm−2 in a fluoride/glycerol/water electrolyte. Rutherford backscattering spectroscopy, nuclear reaction analysis and analytical transmission electron microscopy revealed barrier-type films composed of oxide and fluoride species. The films were formed by outward migration of cations and inward migration of anions. The transport number of cations in the film above the matrix was in the range ∼0.5 to 0.6, and ∼0.1 in the film above the grain boundary Mg-Zn-RE phase. From the oxidation behaviour of the Zn-Zr phases, it is suggested that anions and cations migrate through short-circuit paths in the film.

Growth of barrier-type anodic films on magnesium in ethylene glycol electrolytes containing fluoride and water

This study demonstrates the formation of uniform barrier-type anodic films on magnetron-sputtered magnesium films at high current efficiency in ethylene glycol electrolytes containing 0.1moldm−3 NH4F and various concentrations (0.1–28moldm−3) of H2O. The anodic films containing a crystalline MgF2 phase develop both at the metal/film and film/electrolyte interfaces due to simultaneous migrations of anions inwards and cations outwards, respectively. When a Mg −1.2at% Au/Mg bilayer film is anodized, initial prior oxidation of magnesium proceeds with gold atoms accumulating in a thin layer beneath the anodic film. The accumulated gold atoms are incorporated into the anodic film as a band when the alloy layer is completely anodized. Fluoride-containing gold species are formed by the incorporation and the gold species migrate outwards at a rate of 0.4 times the rate of Mg2+ ions. The addition of phosphate in the electrolyte results in the formation of an amorphous anodic film, and the phosphate incorporated into the anodic film is distributed throughout the film thickness. The transport number of cations is also influenced by the phosphate incorporation.

Ion Transport in Separator Membranes of Lithium Secondary Batteries

The migration properties of cations and anions in lithium electrolyte solutions through separator membranes were evaluated on the basis of diffusion coefficients. The observed diffusion coefficients for the cationic (DLi), anionic (DF), and solvent species (DH) of the electrolyte solution in the membrane are lower than those of the free electrolyte solution. Two main effects are responsible for the reduction in D. One is the physical barrier effect of the membrane substrate. The magnitude of this effect depends on the size, configuration, and the total volume of the pore spaces which hold the solution. The other is a chemical interaction effect, which is associated with polar groups or sites in the membrane substrate. For example, DF values are anomalously lower than DLi values for solutions in polyvinylidene difluoride- (PVDF-) based membranes, leading to an increase in the apparent cation transport number. This would indicate that the anions selectively interact with the membrane substrate through a Cou...

Characterization of the Mass-Transport Phenomena in a Superconcentrated LiTFSI:Acetonitrile Electrolyte

Superconcentration of aprotic electrolytes has recently emerged as a way to stabilize solvents that otherwise would be impossible to use, in e.g. lithium-ion batteries (LIBs). As demanding applications, such as hybrid electric vehicles and fast charging, become increasingly important, battery manufacturers are struggling to find a suitable electrolyte able to deliver high power with low polarization. Electrolyte characterizations able to accurately predict the high-power performance of such electrolytes are also of utmost importance. This study reports a full characterization of the mass-transport phenomena for a superconcentrated LiTFSI:acetonitrile electrolyte in concentrations ranging from 2.7 M to 4.2 M. The method obtains the ionic conductivity, cationic transport number, diffusion coefficient, and the thermodynamic enhancement factor, by combining mathematical modeling and three electrochemical experiments. Furthermore, the density and the viscosity were measured. The transport number with respect to the room is found to be very high compared to other liquid LIB electrolytes, but a low diffusion coefficient lowers overall performance. The ionic conductivity decreases quickly with concentration, dropping from 12.7 mS/cm at 2.7 M to 0.76 mS/cm at 4.2 M. Considering all the effects in terms of the mass-transport of the electrolyte, the lower end of the studied concentration range is favorable.

Heterogeneous Membranes Modified with Nanoparticles of Inorganic Ion-Exchangers for Whey Demineralization

Composite materials were obtained by modification of polymer ion exchange membranes with nanoparticles of zirconium hydrophosphate and hydrated zirconium dioxide. Empirical parameters related to porosity of the membranes and ion transport were proposed. Nanoparticles (4-20nm) in clusters and channels of ion exchange polymer improve transport of counter-ions: transport number of cations increases from 0.46 to 0.78 under limiting current. The aggregates in non-transport pores are a barrier against organic matters. The composites were applied to whey electrodialysis. Current efficiency reaches 97% for K+, Na+, Ca2+, Mg2+ cations and 11-22% for HPO42− and H2PO4− anions.

A model problem concerning ionic transport in microstructured solid electrolytes

We consider ionic transport by diffusion and migration through microstructured solid electrolytes. The assumed constitutive relations for the constituent phases follow from convex energy and dissipation potentials which guarantee thermodynamic consistency. The effective response is determined by homogenizing the relevant field equations via the notion ofmulti-scale convergence. The resulting homogenized response involves several effective tensors, but they all require the solution of just one standard conductivity problem over the representative volume element. A multi-scale model for semicrystalline polymer electrolytes with spherulitic morphologies is derived by applying the theory to a specific class of two-dimensional microgeometries for which the effective response can be computed exactly. An enriched model accounting for a random dispersion of filler particles with interphases is also derived. In both cases, explicit expressions for the effective material parameters are provided. The models are used to explore the effect of crystallinity and filler content on the overall response. Predictions support recent experimental observations on doped poly-ethylene-oxide systems which suggest that the anisotropic crystalline phase can actually support faster ion transport than the amorphous phase along certain directions dictated by the morphology of the polymeric chains. Predictions also support the viewpoint that ceramic fillers improve ionic conductivity and cation transport number via interphasial effects.

Effect of acid/basic solutions contact on ion transport numbers and conductivity for an anion-exchange membrane

Electrical parameters for a commercial positively charged membrane and after submerged for 1 month in 0.1 M acidic solution (HCl) or 0.1 M basic solution (NaOH) were determined by measuring membrane potential and electrical resistance using NaCl solutions. Changes in the values of the cation transport number in the membranes and in the conductivity as a result of chemical treatments were determined, while membrane surface modification was obtained from contact angle measurements. Moreover, the effect of pilot plant wastewaters on both membrane transport number and conductivity have also been determined and compared with those obtained for the model solutions. According to these results, membrane immersion in the HCl solution hardly affects to transport parameters and membrane surface, while the NaOH treatment significantly modified all the studied parameters and its effect is even more important than that caused by plant wastewaters.

On the Evaluation of Ionic Transport and Pair Formation in Polymer Electrolytes from Conductivity and Diffusion Measurements

Salt-in-polymer electrolytes have interesting properties for practical use in batteries, smart windows, and electrochemical solar cells. However, a technological breakthrough is hampered by the relatively low mobility of the cations and a pronounced tendency to pair formation. Ionic transport in these electrolytes can be effectively studied by combining conductivity measurements using electrochemical impedance spectroscopy with self-diffusion experiments of both cations and anions employing nuclear magnetic resonance or radiotracer methods. Comparisons of conductivity and diffusivity are based on the Nernst-Einstein equation which allows for calculating the charge diffusivity Dσ . However, the mass and charge transport data so obtained can be analyzed at different levels of sophistication, as outlined below.Level #1 denotes the common, basic analysis which only uses ratios between the three measured diffusion coefficients for the global characterization of the transport properties. These include the cation transport number t * cat, the Haven ratio H R, and the Nernst-Einstein deviation parameter Δ. The latter quantities characterize the degree of ion association, however, with limited explanatory power.Level #2 analysis utilizes the fact that in polymer electrolytes of low or moderate salt concentration neutral ion pairs dominate over higher-order aggregates. By evaluating this case in detail more specific information can be extracted from the same body of experimental data that is used for the calculation of Δ, H R and t * cat. This concerns the individual contributions of pairs and free ions (or `effective diffusivities´) to the measured self-diffusion coefficients. Also the cation transference number – based on charged species only – can be deduced.Level #3 evaluations make it feasible to split up each `effective diffusivity´ in a `true diffusivity´ and the relative abundance of the corresponding species. Such an extended approach requires assumptions about the temperature dependence of the true diffusivities and the reaction constant of ion pairing, involving the well-known Vogel-Tammann-Fulcher parameters as well as the enthalpy and entropy of pair formation. Within such a specific model, containing reasonable assumptions to reduce the number of free parameters, all experimental data of each electrolyte can be simultaneously fitted using a least-squares routine.Level #4 signifies an even more elaborate approach in which different compositions of an electrolyte system are jointly evaluated in order to further reduce the number of fitting parameters. Assuming a monotonic dependence of the model parameters on salt-concentration, this scenario enables us to better identify compositional trends in passing from the dilute to the concentrated electrolyte regime.We present the theoretical framework and some pertinent examples dealing with systems based on poly(ethylene oxide) dissolving inorganic salts or ionic liquids [1,2].[1] N.A. Stolwijk, J. Kösters, M. Wiencierz, M. Schönhoff, Electrochimica Acta 102, 451-458 (2013)[2] M. Wiencierz, N.A. Stolwijk, Solid State Ionics 212, 88-99 (2012); SSI Best Paper Award 2012

Preparation of Cellulose acetate membrane by phase inversion technique and modification of surface by Copper Ferro cyanide multilayers

Cellulose acetate (CA) membranes were prepared by wet phase inversion technique from acetone/formamide (2/1 wt/wt). The casting solution using a 20 weight-percentage polymer concentration was used for phase inversion. The solution of Potassium Ferro cyanide and Copper sulphate having molar concentration 0.1m, 0.01m, 0.001m, 0.2m, 0.02m, 0.002m were used for deposition on the surface of Cellulose acetate (CA) membrane by alternate changing the two solutions in a special cell. Values of membrane potential were measured and the transport number, fixed charged density and the permselectivity values were calculated for the electrolytes NaCl and KCl. Scanning electron micrographs (SEM) were taken for simple Cellulose acetate (CA) membrane and surface modified multilayers Cellulose acetate (CA) membrane which showed the fine deposition of multilayers of Copper Ferro Cyanide which reduced the pore size ofCellulose acetate(CA) membrane up to nano order. The values of membrane potential (with and without deposition of inorganic multilayers) slightly decreased with time reaching to a constant value, which showed initial accumulation of solution fluid within transmembrane region and saturation thereafter. The values of membrane potential increased with the deposition of multilayers showing decrease in pore size of membrane which has become of the order of nanosize. The values of transport number of cations of (K+ and Na+) were calculated using membrane potential data, which was foundin good resemblance of the ionic size of trace metal ions.