Concentrated Aqueous Electrolyte Solutions Research Articles

Giant Thermoelectric Response of Confined Electrolytes with Thermally Activated Charge Carrier Generation.

The thermoelectric response of thermally activated electrolytes (TAEs) in a slit channel is studied theoretically and by numerical simulations. The term TAE refers to electrolytes whose charge carrier concentration is a function of temperature, as recently suggested for ionic liquids and highly concentrated aqueous electrolyte solutions. Two competing mechanisms driving charge transport by temperature gradients are identified. For suitable values of the activation energy that governs the generation of charge carriers, a giant thermoelectric response is found, which could help explain recent experimental results for nanoporous media infiltrated with TAEs.

Enabling long-cycling aqueous sodium-ion batteries via Mn dissolution inhibition using sodium ferrocyanide electrolyte additive

Aqueous sodium-ion batteries (AIBs) are promising candidates for large-scale energy storage due to their safe operational properties and low cost. However, AIBs have low specific energy (i.e., <80 Wh kg−1) and limited lifespans (e.g., hundreds of cycles). Mn-Fe Prussian blue analogues are considered ideal positive electrode materials for AIBs, but they show rapid capacity decay due to Jahn-Teller distortions. To circumvent these issues, here, we propose a cation-trapping method that involves the introduction of sodium ferrocyanide (Na4Fe(CN)6) as a supporting salt in a highly concentrated NaClO4-based aqueous electrolyte solution to fill the surface Mn vacancies formed in Fe-substituted Prussian blue Na1.58Fe0.07Mn0.97Fe(CN)6 · 2.65H2O (NaFeMnF) positive electrode materials during cycling. When the engineered aqueous electrolyte solution and the NaFeMnF-based positive electrode are tested in combination with a 3, 4, 9, 10-perylenetetracarboxylic diimide-based negative electrode in a coin cell configuration, a specific energy of 94 Wh kg–1 at 0.5 A g−1 (specific energy based on the active material mass of both electrodes) and a specific discharge capacity retention of 73.4% after 15000 cycles at 2 A g−1 are achieved.

Molecular simulations of alkali metal halide hydrates

It has been known that classical molecular simulations of concentrated aqueous electrolyte solutions are limited by the ability of microscopic models (force fields) to predict the correct values of salt solubility, which also requires their ability to faithfully model crystalline salts. Previous simulation studies have often focused on the solubility of anhydrous crystalline salts, but virtually never on crystalline hydrates, except for hydrohalite, NaCl⋅2H2O, despite there are at least 23 experimentally known different hydrates that can precipitate from alkali-halide solutions. This work attempts to fill this gap in hydrate simulation studies by systematically investigating the ability of the best force fields selected to qualitatively capture the stability of the individual phases of various alkali-halide hydrates and to quantitatively predict their lattice parameters. First, we show that the nonpolarizable force fields studied often fail to model hydrates containing the Li+ cations, whereas the polarizable force fields recently refined by us are able to model all the hydrates except for LiCl⋅H2O. Second, we further refine our FFs for Li+ to yield stable LiCl⋅H2O. Third, our simulations clarify the positions of the Li+ cations in the β phases of LiBr⋅H2O and LiI⋅H2O, whose distributions were previously described only as stochastic. As a byproduct, a simple and reliable simulation methodology suitable also for complex polarizable models and nonorthorhombic crystal lattices is proposed and tested, based on simulations of finite crystals floating in vacuum.

Mass transport limitations in concentrated aqueous electrolyte solutions: Theoretical and experimental study of the hydrogen–bromine flow battery electrolyte

Modelling and simulation is a powerful tool to support the development of novel flow cells such as electrolysers and flow batteries. Electrolytes employed in such cells often consist of aqueous solutions of highly concentrated solutes at elevated temperatures. Such conditions pose numerous challenges in conventional model parametrisation because of non-ideal behaviour of the electrolytes. The aim of this work is to study mass transport of electroactive species in highly-concentrated media.We selected the hydrogen–bromine flow battery posolyte, HBr (aq) and Br2, as an exemplary flow battery electrolyte and we leveraged chronoamperometric techniques involving ultramicroelectrodes to study diffusion and migration of bromide and bromine at high concentration and temperature. We successfully simulated the current densities of HBr/Br2 redox reactions in solutions up to 8 mol L–1 using advanced mass transport theory which agreed well with the results obtained with ultramicroelectrodes.While uncharged species transport (Br2) can be credibly modelled using conventional theories such as Fick’s law, charged species (Br–) require special treatment as the diffusion coefficient vary with concentration up to 50 % with respect to the limiting value at infinite dilution. The transport of charged species without added supporting electrolyte occurs via both migration and diffusion and the contribution of migration current may be up to 50 % of the total current. At HBr concentration > 0.6 mol L–1 migration appears to be suppressed due to the “self-screening” effect of the electrolyte.Proper experimental electrolyte characterisation under operating conditions similar to the actual flow cell applications is indispensable to establish predictive models and digital twins of electrochemical devices. Straightforward transfer of concepts known in electro-analytical chemistry to flow cells modelling may lead to erroneous simulations or model overfitting.

Development of rechargeable high-energy hybrid zinc-iodine aqueous batteries exploiting reversible chlorine-based redox reaction

The chlorine-based redox reaction (ClRR) could be exploited to produce secondary high-energy aqueous batteries. However, efficient and reversible ClRR is challenging, and it is affected by parasitic reactions such as Cl2 gas evolution and electrolyte decomposition. Here, to circumvent these issues, we use iodine as positive electrode active material in a battery system comprising a Zn metal negative electrode and a concentrated (e.g., 30 molal) ZnCl2 aqueous electrolyte solution. During cell discharge, the iodine at the positive electrode interacts with the chloride ions from the electrolyte to enable interhalogen coordinating chemistry and forming ICl3-. In this way, the redox-active halogen atoms allow a reversible three-electrons transfer reaction which, at the lab-scale cell level, translates into an initial specific discharge capacity of 612.5 mAh gI2−1 at 0.5 A gI2−1 and 25 °C (corresponding to a calculated specific energy of 905 Wh kgI2−1). We also report the assembly and testing of a Zn | |Cl-I pouch cell prototype demonstrating a discharge capacity retention of about 74% after 300 cycles at 200 mA and 25 °C (final discharge capacity of about 92 mAh).

Experimental verification of increased electronic excitation energy of water in hydrate-melt water by attenuated total reflection-far-ultraviolet spectroscopy.

The demand for Li secondary batteries is increasing, with the need for batteries with a higher level of performance and improved safety features. The use of a highly concentrated aqueous electrolyte solution is an effective way to increase the safety of batteries because it is possible to use "water-in-salt" (WIS) and "hydrate-melt" (HM) electrolytes for practical applications. These electrolytes exhibit a potential window of >3.0V, which is attributed to the difference between the HOMO and the LUMO energies of the n orbital of the pure water molecules and that of the water molecules in the hydration shells of a metal ion, according to theoretical predictions. Thus, in the present study, the attenuated total reflectance (ATR)-far-ultraviolet (FUV) spectra of water and super-concentrated aqueous solutions, such as WIS and HM using a Li salt, were experimentally investigated. The effects of anions, cations, and deuteriums on the ATR-FUV spectra were examined. The ATR-FUV method is an excellent means of studying highly concentrated aqueous salt solutions. The results suggest that the transition energy of water molecules in an ultrahighly concentrated aqueous electrolyte containing HM and WIS increased by nearly 0.4eV (corresponding to an energy shift of over 10nm) compared to an aqueous electrolyte with a typical water concentration. It was also revealed that the transition energy of water changes depending on the environment of the non-bonding electron, which is directly connected with or affected by hydrogen bonding with other water molecules or directly connected with Li+.

Can Anions Be Inserted into MXene?

Despite the continuous progress in the research and development of Ti3C2Tx (MXene) electrodes for high-power batteries and supercapacitor applications, the role of the anions in the electrochemical energy storage and their ability to intercalate between the MXene sheets upon application of positive voltage have not been clarified. A decade after the discovery of MXenes, the information about the possibility of anion insertion into the restacked MXene electrode is still being questioned. Since the positive potential stability range in diluted aqueous electrolytes is severely limited by anodic oxidation of the Ti, the possibility of anion insertion was evaluated in concentrated aqueous electrolyte solutions and aprotic electrolytes as well. To address this issue, we have conducted in situ gravimetric electrochemical quartz crystal microbalance with dissipation monitoring (EQCM-D) measurements in highly concentrated LiCl and LiBr electrolytes, which enable a significant extension of the operation range of the MXene electrodes toward positive potentials. Also, halogens are among the smallest anions and should be easier to intercalate between MXene layers, in comparison to multiatomic anions. On the basis of mass change variations in the positive voltage range and complementary density functional theory calculations, it was demonstrated that insertion of anionic species into MXene, within the range of potentials of interest for capacitive energy storage, is not likely to occur. This can be explained by the strong negative charge on Ti3C2Tx sheets terminated by functional groups.

Densely Grafted Polyelectrolyte Brushes Trigger “Water-in-Salt”-like Scenarios and Ultraconfinement Effect

Summary This paper presents an all-atom molecular dynamics (MD) simulation of highly charged and densely grafted polyelectrolyte (PE) brushes on a flat surface. Simulation findings for the variation of brush height with polymer size and grafting density are explained by the scaling laws for brushes in the non-linear osmotic regime. More importantly, this study establishes the triggering of an ultraconfinement effect by the densely grafted brushes. This effect leads to significant changes in the distribution, structure, and properties as well as a massive mobility reduction of both the counterions and water. Furthermore, the interplay of the ultraconfinement effect and the large counterion-PE electrostatic interactions trigger a “water-in-salt”-like scenario (witnessed in highly concentrated aqueous electrolyte solutions), which is characterized by the counterion-PE-functional group serving as the “salt” with the “salt” overwhelming the water in both mass and volume and affecting the solvation structure of the counterions by replacing the solvation water with the PE-functional group.

ON ORIGIN OF SMALL-ANGLE MAXIMA ON X-RAY SCATTERING INTENSITY CURVES OF AQUEOUS ELECTROLYTE SOLUTIONS

At the X-ray diffraction analysis of high concentrated aqueous electrolyte solutions with multiply charged cations small angle maxima or pre-peaks are arising on scattering intensity curves (IC) (at about 1 Å). Their existence is connected with structural appearance so called “intermediate-range order”. Previously for explanation of this phenomenon some not completely correct hypotheses were suggested. On the example of raw X-ray diffraction data of some aqueous electrolyte solutions in wide concentration range collected by using MoKα-radiation the dynamic of small angle maxima shape change has been studied. It has been noted that pre-peaks absence on IC of cesium iodide and chloride solutions is not supporting the hypothesis about pure small angle contribution from “heavy” ions [1, 2]. In the case of Al3+, Sc3+, Fe3+ chloride solutions relative similarity of IC shapes has been noted for solutions with similar concentrations. The common tendency of pre-peaks position and intensity change has also been followed up. At the same time at comparing of saturated neodymium and ytterbium chloride and bromide solutions IC unexpectable pre-peaks position relative shift for bromide solutions to the long range distance comparing with chloride solutions has also been noted. These observations do not find complete agreement with hypothesis on realization in the structure mainly inter cationic distances [3, 4] and on existence in solutions “liquid type quasi-close-packing for cations” [5, 6]. On the basis of mainly realistic explanation of the pre-peak appearance reason from [7] the authors of this paper propose their own version. Noted shift of pre-peak position with concentration decreasing has been made in accordance with consideration described earlier for lanthanide solutions [8, 9]. The conclusion about pre-peaks on IC arising nature is conditioned by ordered interionic distribution which depends not only on ionic nature but also on solution concentration. For high concentrated solutions with considerable solvent deficit the quasi-periodic inter complex distribution has been supposed. The composition of structure determined cationic complexes has also been discussed. The diluted aqueous electrolyte solutions structure is determined by simple cationic and anionic complexes equidistant distribution.

Solubility of Sodium Oxalate in Concentrated Electrolyte Solutions

The solubility of solid sodium oxalate (Na2Ox) has been measured in a variety of concentrated aqueous electrolyte solutions at T = 298.15, 323.15, and 343.15 K by titration of dissolved oxalate with permanganate. The electrolyte solutions studied (not necessarily at all temperatures) were NaCl, NaClO4, NaOH, LiCl, KCl, Me4NCl, and KOH at concentrations ranging from approximately 0.5 mol·kg–1 to at least 5 mol·kg–1. Where comparisons were possible, the present results were in excellent agreement with literature data. The solubility of Na2Ox(s) decreased markedly with increasing concentrations of Na+(aq), due to the common ion effect. This decrease was almost independent of the electrolyte anion. A number of ternary mixtures of these electrolytes were also investigated at constant ionic strength. Consistent with the binary mixtures, the solubility of Na2Ox(s) showed almost no dependence on solution composition at constant Na+(aq) concentrations. Solubilities in non-Na+ media, with the exception of Me4NCl, showed small but regular increases with increasing concentration of added electrolyte, probably reflecting activity coefficient variations. The solubility data in certain Na+-containing media could be correlated accurately at all temperatures and concentrations using a relatively simple Pitzer model with interaction parameters for Na2Ox(aq) assumed to be identical to those available in the literature for Na2SO4(aq).

Dielectric Characteristics of Water and Electric Conductivity of Aqueous Electrolytes

The specific electric conductivities (ECs) of concentrated aqueous solutions of electrolytes were shown to be comparable to the limiting high-frequency (HF) EC of water. The limiting HF EC of water is determined by the ratio of the absolute dielectric constant to the dipole dielectric relaxation time. It was assumed that the specific EC of an aqueous solution cannot exceed the limiting HF EC of water. The specific ECs of the 1.0 М aqueous solutions of lithium, sodium, and potassium chlorides were calculated from the limiting HF EC of water. At elevated temperatures, the specific ECs of aqueous salts were shown to increase in direct proportion to the limiting HF EC of water.

A Molecular Dynamics Study of Concentrated Aqueous Solutions of Lithium Salts at Charged Electrodes

Li-ion batteries (LiBs) are widely used in very diverse set of applications from portable electronics, to electric vehicle transportation. Hence, improving LiBs’ power and energy while not compromising safety, remains a hot research topic. Organic solvents permit higher operating voltages; however, they have the disadvantage of being volatile and flammable. Aqueous solvents, on the other hand, are inexpensive and non-flammable but they are typically stable only at low voltages (<1V) resulting in relatively low energy density (<100Wh/kg). Recently, an intriguing paradigm shift regarding the extending electrochemical stability window of aqueous electrolytes was reported for the aqueous electrolytes.(1-4) Specifically, highly concentrated aqueous solutions of electrolytes (i.e. “water in salt”) were shown to have electrochemical stability window above 3V, despite the presence of water in the system. In this presentation we explore an intriguing supposition that the electrochemical stability of these systems can be correlated with the electrolyte structure near surface. Using classical molecular dynamics simulations we investigate the electrolyte partition near the electrode, as a function of the applied potential. The studied system consisted of a highly concentrated solution of two salts LiTFSI and LiCF3SO3in water that was recently shown to have one wide electrochemical stability.(2) The electrolyte structuring near the electrode was found to be strongly dependent on the applied potential. Specifically, at the positively charged electrode water is displaced from the surface by the voluminous anions, while at the negatively charged electrode a large accumulation of water is observed in the interfacial layer. Interestingly, the water is displaced rapidly from the negative surface as the potential increases from -2V to 0V, and surprisingly elevated densities of F groups were found next to surface at -1V. In such concentrated electrolytes, the Li ions are only partly coordinated with water (2-2.6 water molecules per Li). The partly desolvated Li+ can drag the TFSI anion near the negative electrode. In agreement with this observation, our simulations confirmed the presence of F groups in the proximity of the interfacial Li+ at the negative electrode. The presence of Li+and F next to the negative charged surface can trigger electrochemical reactions that kinetically passivate the negative electrode surface.

Gibbsite Solubility in Hanford Nuclear Waste Approached from above and below Saturation

Liquid Hanford nuclear wastes are highly concentrated caustic aqueous electrolyte solutions. They contain elevated dissolved aluminum concentrations compared to simple NaOH(aq) solutions in equilibrium with gibbsite [γ-Al(OH)3]. The reason for this elevated solubility has been debated for years, with slow gibbsite precipitation kinetics or various unverified thermodynamic factors being historically offered as explanations. The present study determines whether there is a kinetic or thermodynamic explanation. Here, dissolved aluminum in real tank waste was equilibrated with excess gibbsite, approached from both above and below saturation at 40 °C. In both cases, the samples equilibrated to an aluminum concentration up to four times higher than in pure NaOH(aq) solutions of the same hydroxide concentration. However, in one case, when all of the gibbsite dissolved during heating, no measurable precipitation was observed from the supersaturation direction when gibbsite seed was unavailable for nucleation. Thes...

Enhancing Cycle Stability of Lithium Iron Phosphate in Aqueous Electrolytes by Increasing Electrolyte Molarity

Aqueous lithium ion batteries (ALIBs) exhibit great potential to reduce the cost and improve the safety of rechargeable energy storage technologies. Lithium iron phosphate (LFP) cathodes have become a material of choice for many conventional, high power LIBs. However, experimental studies on LFP in aqueous lithium (Li) ion electrolytes are limited. Here, results of systematic studies are shown where it is demonstrated that the Li salt concentration of the aqueous electrolyte can significantly improve discharge capacity retention while minimally impacting rate capability, for electrodes made with a typical commercial sub‐micron sized LFP powder. Based on the postmortem analysis and the results of electrochemical characterization it is proposed that undesirable side reactions of aqueous electrolytes with LFP induce electrochemical separation of individual particles within the electrode, leading to the observed capacity fading. Increasing the salt concentration in aqueous solutions effectively reduces the concentration of water molecules in the electrolyte, which are mostly responsible for these undesirable side reactions. Similar trends observed with other cathode materials suggest that the use of concentrated aqueous electrolyte solutions offers an effective route to improve stability of aqueous Li ion batteries.

Numerical values of individual activity coefficients of single-ion species in concentrated aqueous electrolyte solutions and the attempt of a qualitative interpretation on a model of electrostatic interaction

Individual activity coefficients of single-ion species can be achieved by the factorizing of a new concentration function for the mean activity coefficient to the required power applying a purely mathematical method. These single-ion activity coefficients, calculated in this manner, are listed for some aqueous strong electrolytes. The reasons for the magnitude and variation of the activity coefficients as a function of the concentration are, without a doubt, of complex nature. Activity coefficients have their meaning as practical values. In relation to the analytical concentration, the individual activity coefficients represent the macroscopic effectiveness of the single-ion species in solution an easy manner. However, with increasing deviations from Debye–Huckel conditions of an infinitely diluted electrolyte solution, a physically correct interpretation of the macroscopically visible activity coefficient is becoming more and more difficult, if not impossible to find. On the basis of a model of electrostatic interaction, an attempt has been made to create a qualitative interpretation of the individual ion activity coefficients in concentrated aqueous electrolyte solutions which were calculated applying the purely mathematical method by Ferse.

GEM-SELEKTOR GEOCHEMICAL MODELING PACKAGE: TSolMod LIBRARY AND DATA INTERFACE FOR MULTICOMPONENT PHASE MODELS

The development of highly accurate and computationally efficient modeling software based on Gibbs energy minimization (GEM) makes it possible to thermodynamically simulate geochemically realistic subsurface fluid-rock interaction processes. This involves consideration of non-ideal multicomponent-multiphase systems that include dilute to concentrated aqueous electrolyte solutions, mineral solid solutions, supercritical fluids, silicate and metal melts, and sorption and ion exchange phases. Predicting the stability and thermodynamic properties of non-ideal solution phases over wide ranges of pressures and temperatures requires that theoretically sound and sufficiently accurate equation of state and activity models are used within the GEM framework. The variety of such models calls for a novel, flexible, and computationally efficient code architecture that supports a wide range of models of non-ideal mixing with different mathematical structures and input data. Here, we introduce the TSolMod C++ class library for equation of state and activity models, implemented within the GEMS3K solver of geochemical equilibria as part of the GEM-Selektor code package (http://gems.web.psi.ch). Essential features of the TSolMod library include a generic and flexible model parameter setup, computationally efficient data exchange with the GEM algorithm, and a straightforward extensibility with any new models of mixing. The current version of TSolMod features a comprehensive selection of fluid, gas, liquid, and solid solution models of interest for geochemical, petrological, material science, and chemical engineering applications.

A New, Highly Conductive, Lithium Salt/Nonionic Surfactant, Lyotropic Liquid‐Crystalline Mesophase and Its Application

Highly conductive electrolyte materials are an essential part of many electrochemical systems, such as fuel cells, solar cells, batteries, electrochromic devices, and next-generation renewable-energy sources. The growing diversity in batteries and electrochemical cells increases the demand for novel electrolyte materials. For instance, in solar-cell applications, an electrolyte material with high viscosity and low volatility is desirable, together with high ionic conductivity. Electrolytes can be solids, gels, or liquids depending on the application. Gel electrolytes are advantageous when the conductivity in the solid form is not sufficient or the leakage or vaporization of the liquid electrolyte is a problem. Gel electrolytes can be aqueous or non-aqueous depending on the application type. While in some battery systems aqueous gel electrolytes have no use—for example, in Li ion batteries—they can be used in many rechargeable batteries, electrochemical capacitors, solar cells, and so on. Liquid-crystal gel electrolytes have also been investigated and are considered to be an important class of ordered materials for the above applications. A lyotropic liquid-crystalline (LLC) mesophase is formed by two main constituents: an amphiphile and a solvent. Common solvents are water, organic liquids, or ionic liquids. LLC-based electrolytes offer many advantages, like rigidity and high ionic mobility and can be an alternative to polymer electrolytes. Solvent-free LC systems (thermotropic LC) usually have low ionic conductivities at room temperature, typically around 10 6 Scm , whereas solvent-containing LLC systems have room-temperature ionic conductivities around 10 3 Scm . Usually high ionic conductivity in solvent-free LC electrolyte systems is achieved at high temperatures, that is, 150 8C and above. Recently we have shown that transition-metal aqua complex salts ([M ACHTUNGTRENNUNG(H2O)6]X2; in which M is a transition-metal cation and X is a suitable counterion), which have melting points close to room temperature, can also be used as solvents in the self-assembly process of some surfactants. The LLC mesophases of molten transition-metal-salt aqua complexes have important physical properties, such as high thermal stability (between 83 and 383 K), high ionic conductivity (room-temperature conductivities close to 2.0 10 4 Scm ), and nonvolatility. A highly concentrated aqueous electrolyte solution of an alkali metal salt can also act as a solvent in the assembly process of oligo(ethylene oxide) type surfactants, in which the highly concentrated electrolyte solution can be considered as an analogue of a molten salt. Their similarities arise due to strong ion–dipole (salt–water) interactions at high salt concentrations (highly concentrated refers to water/salt mole ratios of less than 8 in the case of lithium salts) and as a consequence, the heat of vaporization of water sharply increases. In this contribution, we have investigated the phase behavior and ionic conductivity of a new class of hydrated-salt/ surfactant mesophase, namely; LiNO3–H2O–C12EO10, LiCl– H2O–C12EO10, and LiClO4–H2O–C12EO10 systems, in which C12EO10 is C12H25 ACHTUNGTRENNUNG(OCH2CH2)10OH. The mesophase is a collaborative assembly of a hydrated salt species in the liquid phase and surfactant molecules. Earlier studies on salt– water–surfactant mesophases focus on the effect of salts on the phase behavior of surfactants in dilute aqueous solutions (18–1, water/salt mole ratio). Here, we demonstrate that as little as two water molecules per molecule of lithium salt is sufficient to form a LLC mesophase. At such a low water and high salt concentrations, the bulk properties of water are altered by the salt–water interactions and the salt– water couple collaboratively acts as the solvent in the LLC mesophase. An important outcome of the salt–water interaction is that the LLC mesophase is stable under ambient atmospheric conditions for years (see Supporting Information) and displays high ionic conductivity over a broad temperature range. The LLC samples were prepared by adding each ingredient: salt (LiNO3, LiCl, or LiClO4), surfactant (C12EO10), and water in the required amounts and the resulting mixture was then homogenized by constant shaking in a shaking water bath at 60–110 8C for 24 h. Under ambient conditions, the amount of water in the samples depends on the temperature, relative humidity, and the amount of salt in the mesophase, but always enough water remains in the samples to [a] C. Albayrak, Prof. . Dag Department of Chemistry, Bilkent University 06800, Ankara (Turkey) Fax: (+90)312-266-4068 E-mail : dag@fen.bilkent.edu.tr [b] Prof. A. Cihaner Department of Chemical Engineering and Applied Chemistry Atilim University 06836, Ankara (Turkey) Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/chem.201103705.

Molecular dynamics simulations of concentrated aqueous electrolyte solutions

Transport properties of concentrated electrolytes have been analysed using classical molecular dynamics simulations with the algorithms and parameters typical of simulations describing complex electrokinetic phenomena. The electrical conductivity and transport numbers of electrolytes containing monovalent (KCl), divalent (MgCl2), a mixture of both (KCl+MgCl2) and trivalent (LaCl3) cations have been obtained from simulations of the electrolytes in electric fields of different magnitude. The results obtained for different simulation parameters have been discussed and compared with experimental measurements of our own and from the literature. The electroosmotic flow of water molecules induced by the ionic current in different cases has been calculated and interpreted with the help of the hydration properties extracted from the simulations.

The Nature of Aqueous Solutions: Insights into Multiple Facets of Chemistry and Biochemistry from Freezing‐Point Depressions

Contrary to current widely held beliefs, many concentrated aqueous solutions of electrolytes and nonelectrolytes behave ideally. For both, the same simple equation yields mole fractions of water that are equal to the theoretical activities of water. No empirical activity coefficients or ad hoc parameters are needed. Thermodynamic hydration numbers and the number of particles produced per mole of solute are found by searching freezing-point depression measurements, as if asking the water, "How much available water solvent is left and how many solute particles are there?" The results answer questions currently under debate: Do solutes alter the nature of water outside their immediate surroundings? What is the number of ion pairs formed by various electrolytes and what affects extents of their formation? What are some factors that cause precipitation of proteins, latexes, and so forth from aqueous solutions upon addition of other solutes (Hofmeister series)? Which nonelectrolytes form aggregates in water and what are the implications? Why do different solutes affect viscosity differently? How do ion-selective channels in cell membranes function at the molecular level?

Ideal Behavior of Water Solutions of Strong Electrolytes and Non-electrolytes at High Concentrations

Contrary to widely held beliefs, many concentrated aqueous solutions of strong electrolytes and nonelectrolytes are shown to behave ideally by calculating the activity of water (a w) from vapor pressure data. The mole fraction of water (x w) is equal to the water activity a w(Raoult’s Law) when the mole fraction of water is calculated by accounting for water strongly bound to the solute, which is then not available to act as solvent. In this case x w=(55.51−mH T)/(55.51−mH T+im), where m is the molality of the solute particles, i is the stoichiometric number of solute particles produced per mole of dissolved solute, and H T is the thermodynamic hydration number H T. Published reservations about previous work of this type are addressed. The values of H T vary little over wide ranges of concentration and correlate with the Hofmeister series, the B coefficient of the Jones-Dole viscosity equation, and other properties of water. Activity coefficients of the bulk or “free” water remain at unity even at high concentrations.