Behavior Of Electrolyte Solutions Research Articles

Nanoscale Transport during Liquid Film Thinning Inhibits Bubble Coalescing Behavior in Electrolyte Solutions.

The long-standing puzzle of why two colliding bubbles in an electrolyte solution do not coalesce immediately upon contact is resolved. The water film between the bubbles needs to be drained out first before its rupture, i.e., coalescence. Experiments reveal clearly that the film thinning exhibits a rather sudden slowdown (around 30-50nm), which is orders of magnitude smaller than similar experiments involving surfactants. A critical step in explaining this phenomenon is to realize that the solute concentration is different in bulk and at the surface. During thinning, this will generate an electrolyte concentration difference in film solution along the interacting region, which in turn causes a Marangoni stress to resist film thinning. We develop a film drainage model that explains the experimentally observed phenomena well. The underlying physical mechanism, that confused the scientific community for decades, is now finally revealed.

Effect of Aqueous Anions on Graphene Exfoliation.

Ion partitioning behavior in electrolyte solutions plays an important role in drug delivery and therapeutics, protein folding, materials science, filtration, and energy applications such as supercapacitors. Here, we show that the segregation of ions in solutions also plays an important role in the exfoliation of natural flake graphite to pristine graphene. Polarizable anions such as iodide and acetate segregate to the interfacial region of the aqueous phase during solvent interfacial trapping exfoliation of graphene. Ordered water layers and accumulated charges near the graphene surface aid in separating graphene sheets from bulk graphite, and, more importantly, reduce the reversibility of the exfoliation event. The observed phenomenon results not only in the improved stability of graphene-stabilized emulsions but also in a low-cost and environmentally friendly way of enhancing the production of graphene.

Unusual high-pressure intrusion-extrusion behavior of electrolyte solutions in Mu-26, a pure silica zeolite of topology STF

High pressure intrusion-extrusion of LiCl aqueous solutions in Mu-26 zeolite (STF-type zeosil) has been studied. “Mu-26 – LiCl aqueous solution” systems have demonstrated an unusual combination of bumper and shock absorber behavior with several features and a high absorbed energy of 40.2 J/g. Contrary to other zeosils, the increase of LiCl concentration does not lead to an increase of intrusion reversibility. This phenomenon could be explained by the creation of higher amount of silanol defects inside the pores under LiCl aqueous solution infiltration. A highest rise of intrusion pressure (~6.6 times) with LiCl concentration among all the zeosils with similar pore diameter is observed. The pressure increase is accompanied with a strong rise of the intruded volume.

In situ Raman spectroscopic analysis of solvent co-intercalation behavior into a solid electrolyte interphase-covered graphite electrode

Solid electrolyte interphase (SEI) on a graphite-negative electrode plays an important role in lithium-ion batteries. The roles of the SEI involve a passivation of a solvent co-intercalation reaction, but why the SEI can suppress the solvent co-intercalation reaction is not fully understood. In this study, the solvent co-intercalation behavior against various SEI-covered graphite electrodes was investigated using cyclic voltammetry and in situ Raman spectroscopy. Ethylene carbonate (EC)-treated, vinylene carbonate (VC)-treated, and untreated graphite electrodes were compared in a dimethoxyethane (DME)-based electrolyte solution. Whereas the DME co-intercalation constantly proceeded from 1.2 to 0.6 V versus Li/Li+ for the untreated graphite electrode, the co-intercalation was relatively suppressed above 0.8 V versus Li/Li+ for the EC-treated and VC-treated graphite electrodes. Below 0.7 V versus Li/Li+, the VC-treated electrode exhibited higher passivation ability than the EC-treated one. In addition, the co-intercalation behavior in electrolyte solutions containing an SEI-reagent in advance was also investigated. In this case, the passivation ability was further improved.

The first evaluation of the dynamic hydration number of hydrated ions confined in mesoporous silica MCM-41

Ion hydration in narrow pores is important in engineering, biology, and chemistry. The structures of hydrated ions confined in nanospaces have been studied by X-ray diffraction and X-ray absorption spectroscopy, and these confined hydrated ions have been found to have anomalous structures. On the other hand, the dynamic behavior has been studied only by molecular dynamics (MD) simulations, which have revealed the unique dynamics of hydration in nanospaces. However, no experimental studies of the dynamics of confined hydrated ions have been carried out. Here, we focus on the dynamic hydration number (nDHN) used in bulk solutions to evaluate the dynamic behavior of electrolyte solutions confined in nanospaces. To evaluate nDHN in nanospaces, we derived the molality dependence of the 2H spin–lattice relaxation time of D2O confined in nanospaces by considering the contribution of water bound to the pore surface. Next, we applied this to electrolyte solutions confined in mesoporous silica MCM-41 and evaluated nDHN. The absolute value of the dynamic hydration number in mesopores is significantly larger than that in the bulk solution; thus, the confinement effect drastically enhances the dynamic hydration properties (positive and negative hydration). This result supports the compressed hydration structure of ions with positive hydration character reported by previous structural and simulation studies. Our new approach for the evaluation of nDHN in nanospaces can be expected to give new insights in the investigation of electrolyte solutions confined in nanospaces from the viewpoint of the experimental verification of dynamic features of the hydration structure.

Tunable, concentration‐independent, sharp, hysteresis‐free UCST phase transition from poly(N‐acryloyl glycinamide‐acrylonitrile) system

ABSTRACTPoly(N‐acryloylglycinamide‐co‐acrylonitrile) (poly(NAGA‐AN)) copolymers were synthesized using reversible‐addition‐fragmentation transfer polymerization. In contrast to poly(NAGA) the thermoresponsive behavior of poly(NAGA‐AN) shows a narrow cooling/heating hysteresis in water with a tunable cloud point, depending on the acrylonitrile amount in polymer. Furthermore, we showed that there is no significant effect of the solution concentration on the cloud point and stable phase transition behavior in electrolyte solutions, which is presumable controlled by forming stable micellar like structures as a result of the block/graft‐copolymer structure. This is in contrast to poly(NAGA) which shows a strong concentration dependent cloud point in aqueous solution with a broad cooling/heating hysteresis. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017, 55, 274–279

Tuning the tetrahedrality of the hydrogen-bonded network of water: Comparison of the effects of pressure and added salts.

Experiments and simulations demonstrate some intriguing equivalences in the effect of pressure and electrolytes on the hydrogen-bonded network of water. Here, we examine the extent and nature of equivalence effects between pressure and salt concentration using relationships between structure, entropy, and transport properties based on two key ideas: first, the approximation of the excess entropy of the fluid by the contribution due to the atom-atom pair correlation functions and second, Rosenfeld-type excess entropy scaling relations for transport properties. We perform molecular dynamics simulations of LiCl-H2O and bulk SPC/E water spanning the concentration range 0.025-0.300 molefraction of LiCl at 1 atm and pressure range from 0 to 7 GPa, respectively. The temperature range considered was from 225 to 350 K for both the systems. To establish that the time-temperature-transformation behaviour of electrolyte solutions and water is equivalent, we use the additional observation based on our simulations that the pair entropy behaves as a near-linear function of pressure in bulk water and of composition in LiCl-H2O. This allows for the alignment of pair entropy isotherms and allows for a simple mapping of pressure onto composition. Rosenfeld-scaling implies that pair entropy is semiquantitatively related to the transport properties. At a given temperature, equivalent state points in bulk H2O and LiCl-H2O (at 1 atm) are defined as those for which the pair entropy, diffusivity, and viscosity are nearly identical. The microscopic basis for this equivalence lies in the ability of both pressure and ions to convert the liquid phase into a pair-dominated fluid, as demonstrated by the O-O-O angular distribution within the first coordination shell of a water molecule. There are, however, sharp differences in local order and mechanisms for the breakdown of tetrahedral order by pressure and electrolytes. Increasing pressure increases orientational disorder within the first neighbour shell while addition of ions shifts local orientational order from tetrahedral to close-packed as water molecules get incorporated in ionic hydration shells. The variations in local order within the first hydration shell may underlie ion-specific effects, such as the Hofmeister series.

Use of the Pitzer model for correlating thermodynamic phase behavior of salts in water–ethanol mixed solvent solutions

Hydrogen can be produced from Ethanol through many industrial processes which may involve electrolyte species in some cases. The thermodynamic phase behavior of electrolyte solutions is very important for the design of such processes.The Pitzer model, initially designed for aqueous electrolyte solutions, has been adapted to the case of electrolytes in mixed solvent solutions. This approach was applied for calculating activity coefficients of the electrolytes KCl, CsCl, NaCl and NaBr in water–ethanol mixtures at 25 °C. The Pitzer parameters have been evaluated for each salt in both aqueous and ethanol–water mixed solvent by minimizing the objective function using experimental data from literature.The values of the standard deviations show that the Pitzer model can be used successfully in modeling activity coefficients of the electrolytes studied in both aqueous and ethanol-water mixed solvent solutions.

Predicting the thermodynamic properties and dielectric behavior of electrolyte solutions using the SAFT‐VR+DE equation of state

We extend the SAFT‐VR+DE equation of state to describe 19 aqueous electrolyte solutions with both a fully dissociated and a partially dissociated model. The approach is found to predict thermodynamic properties such as the osmotic coefficient, water activity coefficient, and solution density, across different salt concentrations at room temperature and pressure in good agreement with experiment using only one or two fitted parameters. At higher temperatures and pressures, without any additional fitting, the theory is found to be in qualitative agreement with experimental mean ionic activities and osmotic coefficients. The behavior of the dielectric constant as a function of salt concentration is also reported for the first time using a statistical associating fluid theory (SAFT)‐based equation of state. At high salt concentrations, the stronger electrostatic interactions between the ionic species due to the dielectric decrement, is captured through the inclusion of ion association. © 2015 American Institute of Chemical Engineers AIChE J, 61: 3053–3072, 2015

PH Effect on Electrochemistry of Nitrogen-Doped Carbon Catalyst for Oxygen Reduction Reaction

In this work, the effect of pH on a nitrogen-doped ordered mesoporous carbon catalyst for the oxygen reduction reaction (ORR) is extensively investigated. Electrochemical methods, including cyclic voltammetry (CV), rotating ring-disk electrode (RRDE), and cathodic stripping voltammetry, are applied to investigate the electrochemical behavior in electrolyte solutions of different pHs (0–2, 7, 12–14). The CV result reveals that nitrogen-doped carbon has a variety of enriched reversible redox couples on the surface, and the pH has a significant effect. Whether these redox couples are electrochemically active or inactive to the ORR depends on the electrolyte used. In acid media, an oxygen molecule directly interacts with the redox couple, and its reduction proceeds by the surface-confined redox-mediation mechanism, yielding water as the product. Similarly, the first electron transfer in alkaline media is achieved by the surface-confined redox-mediation mechanism at the higher potentials. With decreasing poten...

A thermodynamic model of aqueous electrolyte solution behavior and solid-liquid equilibrium in the Li-H-Na-K-Cl-OH-H2O system to very high concentrations (40 molal) and from 0 to 250 C

This paper describes a chemical model that calculates solute and solvent activities and solid-liquid equilibria in the Li-H-Na-K-Cl-OH-H₂O system from dilute to high solution concentration within the 0 to 250 °C temperature range. The model coherently extends to Li the temperature-variable H-Na-K-OH-Cl-H₂O model of Christov and Møller (2004b, p. 1309). The solubility modeling approach based on Pitzer9s (1973, p. 268) specific interaction equations is used. All binary (LiCl-H₂O and LiOH-H₂O) and ternary (LiCl-HCl-H₂O, LiCl-NaCl-H₂O, LiCl-KCl-H₂O, LiOH-NaOH-H₂O, LiOH-KOH-H₂O, and LiOH-LiCl-H₂O) lithium subsystems are included in the model parameterization. The model for the LiCl-H₂O system is parameterized using two different approaches: (1) with 4 ion interaction binary parameters (β⁽⁰⁾, β⁽¹⁾, β⁽²⁾, and C^ϕ), and (2) with 3 ion interaction binary parameters (β⁽⁰⁾, β⁽¹⁾, and C^ϕ) and including neutral aqueous LiCl⁰(aq) species. Approach (2) provides a better fit of activity data in unsaturated binary solutions and accurately predicts solid solubilities up to 40 mol.kg⁻¹ and up to 250 °C. Therefore, this approach was used to parameterize lithium chloride mixed systems. Temperature functions for the thermodynamic solubility product (as log K^o_sp) of 5 simple lithium salts (LiCl.2H₂O(cr), LiCl. H₂O(cr), LiCl(cr), LiOH. H₂O(cr), and LiOH(cr)) are determined. The log K^o_sp values of 3 double lithium basic salts precipitating in the LiOH-LiCl-H₂O system at 50 °C (3LiOH.LiCl(cr), LiOH.LiCl(cr), and LiOH.3LiCl(cr)) are also estimated using solubility data.

Anomalously Enhanced Hydration of Aqueous Electrolyte Solution in Hydrophobic Carbon Nanotubes to Maintain Stability

An understanding of the structure and behavior of electrolyte solutions in nanoenvironements is crucial not only for a wide variety of applications, but also for the development of physical, chemical, and biological processes. We demonstrate the structure and stability of electrolyte in carbon nanotubes using hybrid reverse Monte Carlo simulations of X-ray diffraction patterns. Hydrogen bonds between water are adequately formed in carbon nanotubes, although some hydrogen bonds are restricted by the interfaces of carbon nanotubes. The hydrogen bonding network of water in electrolyte in the carbon nanotubes is further weakened. On the other hand, formation of the ion hydration shell is significantly enhanced in the electrolyte in the carbon nanotubes in comparison to ion hydration in bulk electrolyte. The significant hydrogen bond and hydration shell formation are a result of gaining stability in the hydrophobic nanoenvironment.

Drastic change of the intrusion-extrusion behavior of electrolyte solutions in pure silica *BEA-type zeolite.

High pressure water and electrolyte solutions intrusion-extrusion experiments in pure-silica *BEA-type zeolite (zeosil β) were performed in order to study the performances of these systems in energy absorption and storage. The "zeosil β-water" system displays a bumper behavior with an intrusion pressure of 53 MPa and an absorbed energy of 8.3 J g(-1). For the "zeosil β-LiCl aqueous solutions" systems the intrusion pressure increases with the LiCl concentration to 95, 111 and 115 MPa for 10, 15 and 20 M solution, respectively. However, for concentrations above 10 M, a transformation of the system behavior from bumper to shock-absorber is observed. The zeolite samples were characterized by several structural and physicochemical methods (XRD, TGA, solid-state NMR, N2 physisorption, ICP-OES) before and after intrusion-extrusion experiments in order to understand the influence of the LiCl concentration on the intrusion-extrusion behavior. It is shown that the intrusion of water and LiCl solutions with low concentration leads to the formation of Si-(OSi)3OH groups, whereas no defects are observed under intrusion of concentrated LiCl solutions. A possible mechanism of LiCl solution intrusion based on separate intrusion of H2O molecules and Li(H2O)x(+) ions is proposed.

Effects of nonaqueous electrolyte solutions mixed with carbonate-modified siloxane on charge–discharge performance of negative electrodes for secondary lithium batteries

Influence of mixing carbonate-modified siloxane into 1 M (M: mol L−1) LiPF6-ethylene carbonate (EC)/ethylmethyl carbonate (EMC) (mixing volume ratio = 3:7) mixed solvent electrolytes on charge–discharge cycling properties of lithium is examined. As siloxane, 4-(2-bis(trimethylsilyloxy)methylsilylethyl)-1,3-dioxolan-2-one is investigated. Charge–discharge cycling efficiencies of lithium metal anodes are improved and impedance of anode/electrolyte interface decreases by mixing siloxane, compared with those in 1 M LiPF6-EC/EMC alone. Mechanism of enhancement of lithium cycling efficiency is considered to be due to the suppression of excess reduction of LiPF6-EC/EMC by lithium and growth of surface film (SEI, solid electrolyte interphase) on lithium. Infrared study indicates that SEI formed in LiPF6-EC/EMC with siloxane contains more inorganic compounds than that in LiPF6-EC/EMC alone. Better cycling behavior of α-Fe2O3 and Si–SiO2–carbon composite anodes is obtained by mixing siloxane. Thermal behavior of electrolyte solutions toward graphite-lithium anodes is evaluated with a differential scanning calorimeter. Heat-output of graphite–lithium anodes with 1 M LiPF6-EC/EMC electrolyte solutions tends to decrease by mixing siloxane.

Asymmetric track membranes: Relationship between nanopore geometry and ionic conductivity

The revealing of the “diodelike” properties of electrolyte-filled asymmetric nanopores in track membranes has given significant impetus to a detailed study of the properties of “track” nanocapillaries. Studying the behavior of electrolyte solutions in nanovolumes of a given geometry is very important for many applications, such as nanofluid technology, the resistive pulse method for detecting colloidal particles and molecules, modeling of biological membranes, etc. An attempt to find a quantitative relationship between the geometric shape of asymmetric nanopores and asymmetry in electrical conductivity has been made in this paper. The method of chemical etching in the presence of a surfactant was used for the formation of nanopores with different profiles. The pore structure was studied by electron microscopy. It has been found that the rectification ratio increases with the membrane thickness and depends strongly on the curvature of the pore profile in the selective layer. The maximum of the rectification has been observed in a 0.05–0.1M KCl. Simulation of the ionic conductivity of asymmetric nanopores by the Poisson-Nernst-Planck equation qualitatively explains the observed behavior. The effect of the asymmetry of electrical conductivity is well expressed even in cases when the pore radius in the selective layer is substantially greater than the Debye length. The modification of the pore surface by grafting of aminopropyltriethoxysilane results in the sign inversion of electric charge and a sharp change in the current-voltage characteristics of the membranes.

Thermochemistry of electrolyte solutions

The results of calorimetric investigations of electrolyte solutions in the mixtures of water, methanol, N,N-dimethylformamide, and acetonitrile with numerous organic cosolvents are discussed with regard to the intermolecular interactions that occur in the solution. Particular attention is given to answer the questions how and to what extent the properties of the systems examined are modified by the cosolvent added and how much the properties of the cosolvent are revealed in the mixtures with the solvents mentioned above. To this goal, the analysis of the electrolyte dissolution enthalpies, single ionic transfer enthalpies, and enthalpic pair interaction coefficients as well as the preferential solvation (PS) model are applied. The analysis performed shows that in the case of the dissolution enthalpies of simple inorganic electrolytes in water–organic solvent mixtures, the shape of the dependence of the standard dissolution enthalpy on the mixed solvent composition reflects to a large extent the hydrophobic properties of the organic cosolvent. In the mixtures of methanol with organic cosolvents, the ions are preferentially solvated either by methanol molecules or by molecules of the cosolvent, depending on the properties of the mixed solvent components. The behavior of inorganic salts in the mixtures containing N,N-dimethylformamide is mostly influenced by the DMF which is a relatively strongly ion solvating solvent, whereas in acetonitrile mixtures, the thermochemical behavior of electrolyte solutions is influenced to a large extent by the properties of the cosolvent particularly due to the PS of cation by the cosolvent molecules.

Application of the Multisolute Osmotic Virial Equation to Solutions Containing Electrolytes

The prediction of multisolute solution behavior of solutions containing electrolytes is important in many areas of research, including cryopreservation. In this study, the use of a novel form of the osmotic virial equation for multisolute solutions containing an electrolyte is investigated and compared to a rigorous electrolyte solution theory, the Pitzer-Debye-Huckel equation. For aqueous solutions containing a small molecule (either dimethyl sulfoxide or glycerol) and sodium chloride, the multisolute osmotic virial equation, which utilizes only two parameters to capture the electrolyte solution behavior, is shown to be as accurate as the Pitzer-Debye-Huckel equation, which utilizes six empirical parameters and multiple functions to capture the electrolyte solution behavior. In addition, an approach based on the multisolute osmotic virial equation to investigate the effect of electrolyte concentration on macromolecule solution behavior is presented and applied to aqueous solutions of hydroxyethyl starch and sodium chloride. The multisolute osmotic virial equation is shown to be an accurate, straightforward predictive solution theory for important multisolute solutions containing electrolytes.

Rigorous Modeling and Simulation of an Absorption−Stripping Loop for the Removal of Acid Gases

In this work, a universal rate-based model is presented that enables the rigorous simulation of absorption and stripping units, as well as their combination as an absorption−stripping loop. The latter is realized by simultaneous treatment of the two units and their environment. The model is applied to the removal of acid gases by aqueous amine solutions. It is capable of describing the complex interplay of chemical reactions and heat and multicomponent mass transfer, as well as accounting for thermodynamic nonidealities including the specific behavior of electrolyte solutions. Furthermore, the influence of column internals and hydraulics is considered through relevant correlations. To simulate the total absorption−stripping loop, the model is supplemented by additional submodels for the column periphery (e.g., heat exchangers). All models are implemented in the simulation environment Aspen Custom Modeler and validated by comparison with experimental data of an industrial-scale acid gas removal process. In...

Activity behaviour of electrolyte solutions: Evaluation of temperature effects by means of the quasi-random lattice model

The paper presents some applications of the Moggia–Bianco (quasi-random lattice) model for the calculation of mean activity and osmotic coefficients of electrolyte solutions, with emphasis on temperature effects. Aqueous uni-univalent and uni-divalent electrolytes from 0 °C to 100 °C are considered. Results show that the model is in general applicable over wide ranges of concentrations and temperatures, despite its dependence on a unique fitting parameter (which is, sometimes, experimentally known). Some theoretical aspects of the model are investigated. Hydration diameters are evaluated for uni-univalent systems. Concerning uni-divalent systems, charge-asymmetry effects are accounted for more rigorously than in previous works, starting from a better assessment of the relationship between the behaviour of the electrolyte at very low concentrations and the behaviour occurring at high concentrations.

Carbonate-modified siloxanes as solvents of electrolyte solutions for rechargeable lithium cells

Influence of mixing carbonate-modified siloxanes into LiPF 6-ethylene carbonate (EC)/ethylmethyl carbonate (EMC) (mixing volume ratio = 3:7) mixed solvent electrolytes on charge–discharge cycling properties of lithium was examined. As the solute, 1 M (M: mol L −1) LiPF 6 was used. As siloxanes, 4-(2-trimethylsilyloxydimethylsilylethyl)-1,3-dioxolan-2-one and 4-(2-bis(trimethylsilyloxy)methylsilylethyl)-1,3-dioxolan-2-one were investigated. These siloxanes are derivatives of butylene cyclic carbonate or vinyl ethylene carbonate. Charge–discharge cycling efficiencies of lithium metal anodes improved and an impedance of anode/electrolyte interface decreased by mixing siloxanes, compared with those in 1 M LiPF 6-EC/MEC alone. Slightly better cycling behavior of natural graphite anode was obtained by adding siloxanes. Si–C/LiCoO 2 cells exhibited better anode utilization and good cycling performance by using 1 M LiPF 6-EC/MEC + siloxane electrolytes. Thermal behavior of electrolyte solutions toward graphite–lithium anodes was evaluated with a differential scanning calorimeter. By adding siloxanes, temperature starting the large heat-output of graphite–lithium anodes with 1 M LiPF 6-EC/MEC electrolyte solutions shifted to higher temperature about 100 °C. However, amount of heat-output did not decrease by adding siloxanes.