Aqueous Electrolyte Solutions Research Articles

Effect of aqueous solutions of KCl, MgCl2, Dextrose and Urea on solvation behavior of aqueous myo-Inositol

Owing to the indispensable role of myo-Inositol (MI), a cyclic polyol, in biological, pharmaceutical and food industries, in this investigation, we herewith report the systematic data of densities (ρ) and speed of sound (u) of MI in water, aqueous electrolytic (0.06 mol∙kg−1 KCl/MgCl2) and non-electrolytic (0.06 mol∙kg−1 Dextrose/Urea) solutions at seven different temperatures T/K (=288.15–318.15) and ambient pressure over the dilute concentration range of (0.03–0.2) mol∙kg−1. The experimental data of density (ρ) and speed of sound (u) were further processed to obtain respective derived parameters, such as apparent molar volume of solute Vϕ, isentropic compressibility of solution κs and apparent molar isentropic compression of the solute Ks,ϕ. The limiting values of apparent molar volume Vϕ0, apparent molar isentropic compression Ksϕ0 and apparent molar expansibility Eϕ0 of solute have been computed. Further, the coefficient of thermal expansion α∗, second order derivative of limiting apparent molal volume ∂2Vϕ0/∂T2, hydration number (nH) and transfer properties (ΔtrVϕ0andΔtrKs,ϕ0) of MI have also been obtained. An attempt has been made to analyse the molecular interactions through the coulomb attenuated hybrid exchange–correlation density functional theory (DFT) by gaussian tool. The effect of temperature and the studied electrolytic and non-electrolytic moieties (i.e., KCl, MgCl2, Dextrose and Urea) have been discussed in the light of prevailing interactions between solute-co-solute and solvent molecules on the basis of co-sphere overlap model.

Gel combustion synthesized NiMoO4 anchored polymer nanocomposites as a flexible electrode material for solid state asymmetric supercapacitors

Recent research has focused on the search for new electrode materials to improve the specific capacitance of supercapacitors. Conductive polymers and metal oxides have been extensively tested as electrode materials for supercapacitors. Incorporating both conductive polymers and metal oxides into a composite provides excellent results for the electrochemical performance of supercapacitors. In this present work, we have fabricated the nanoscale α-NiMoO4 particles that enwrapped on electronically conducting polymer nanocomposites (PNCs) based on Polyvinyl alcohol (PVA)/Poly(vinyl) pyrrolidone (PVP) for supercapacitor applications. The different concentrations of PVA/PVP with α-NiMoO4 loaded polymer nanocomposites were developed by using a solution casting method. All the polymer nanocomposites have been subjected to Scanning Electron Microscopy (SEM), Fourier Transforms Infrared (FTIR), X-ray diffraction (XRD), and electrochemical studies. The prepared PNCs surface morphology has been acquired as a non-uniform rod-like structure. The electrochemical performances of the prepared PNCs have been investigated and the resultant value of the maximum specific capacitance is 15.56 F g−1 for 1 wt % of α-NiMoO4 nanoparticles(NPs) loaded polymer blended electrode at a scan rate of 5 mVs−1. The prepared PNCs exhibit 97.12% of columbic efficiency studied by using two electrode systems at room temperature in an aqueous electrolyte solution of 3 M KOH. From these investigation, it has been revealed that the PVA/PVP/α-NiMoO4 composites could be portable and flexible electrodes for energy storage applications.

Sponge-Supported Low-Temperature Chemical Synthesis of the Hybrid Bi2O3@Ppy Electrode Material for Energy-Storage Devices

Most of the electrode materials used in energy-storage devices are either framed or deposited onto a conductive substrate. In the present work, the stretchable, foldable, and flexible commercial sponge, envisaged for cleaning in daily life, has been converted to a conducting material with the help of polypyrrole (PPy). The bismuth oxide (Bi2O3) electrode material of wool ball-like morphology is synthesized over pre-deposited PPy as a hybrid Bi2O3@PPy electrode using successive ionic layer adsorption and reaction method. Due to the special wool ball-like morphology of Bi2O3 and the porous structure of the PPy@sponge, more active sites with the shortest diffusion pathways for easy and fast electron-ion transportation are dominant. At a current density of 2 A g–1, the hybrid Bi2O3@PPy electrochemical supercapacitor (SC) exhibits a specific capacitance of 471.2 F g–1, and, even at a high current density of 10 A g–1, nearly 88% of the original capacitance has been retained over 5 K redox cycles. A pencil-type asymmetric supercapacitor designed using Bi2O3@PPy//graphite rod electrodes has delivered energy densities of 12 Wh kg–1 and 1363.6 W kg–1 of power density by consuming a 1.2 V voltage window in 3.0 M KOH aqueous electrolyte solution, and an excellent 70% cycling stability at a higher current density of 10 A g–1 is maintained. Two asymmetric supercapacitor devices connected in series can shine a red light-emitting diode with full brightness for 2 min, suggesting the energy storage efficacy of Bi2O3@PPy on the nonconductive substrate.

Building a Hofmeister-like series for the maximum in density temperature of aqueous electrolyte solutions

The temperature of the maximum in density (TMD) at room pressure is experimentally evaluated for aqueous solutions of a set of halides containing F−, Cl−, Br−, I−, Li+, Na+, K+, Rb+, Cs+ and Mg2+ at a 1 m concentration. The measurements were performed by monitoring the density-temperature profiles and tracking the temperature-dependent position of the meniscus, in a capillary glass tube. Adding salts diminishes the TMD of the solutions with respect to pure water, being the magnitude of the change dependent on the nature of the electrolyte. The experimental values of the shift in the TMD can be split into individual ion contributions. From this information we were able to establish a rank of ions (i.e., a Hofmeister-like series) according to their efficiency in shifting down the TMD. The experimental results are also compared to simulation values obtained via Molecular Dynamics using the Madrid-2019 force field that assigns non-integer charges for the ions and is parametrized for the TIP4P/2005 water model. Finally, since the TMD is a fingerprint property of water, we will discuss the impact of ions on this maximum in relation with the way different ions modify the structure of water.

Hydrated Ionic Liquids: Perspective for Bioscience.

Hydrated ionic liquid (IL) is a simple mixture of IL and water. Unique aqueous electrolyte solution can be designed by mixing IL with limited amount of water. In most hydrated ILs, there are no free water and all are strongly interacted with ions. The properties of hydrated ILs, such as polarity, viscosity, ion mobility, and hydrogen bonding ability, can therefore be controlled simply by water content. This mixture is expected to provide similar environment to that of living cell, and is desired to be effective solvents for biomolecules. In this account, we would like to survey the basic properties, recent results, and future aspects of the hydrated ILs.

High Resolution Electrochemical Imaging for Sulfur Vacancies on 2D Molybdenum Disulfide.

Molybdenum disulfide (MoS2 ) is considered as one of the most promising non-noble-metal catalysts for hydrogen evolution reaction (HER). To achieve practical application, introducing sulfur (S) vacancies on the inert basal plane of MoS2 is a widely accepted strategy to improve its HER activity. However, probing active sites at the nanoscale and quantitatively analyzing the related electrocatalytic activity in electrolyte aqueous solution are still great challenges. In this work, utilizing high-resolution scanning electrochemical microscopy, optimized electrodes and newly designed thermal drift calibration software, the HER activity of the S vacancies on an MoS2 inert surface is in situ imaged with less than 20-nm-radius sensitivity and the HER kinetic data for S vacancies, including Tafel plot and onset potential, are quantitatively measured. Additionally, the stability of S vacancies over the wide range of pH 0-13 is investigated. This study provides a viable strategy for obtaining the catalytic kinetics of nanoscale active sites on structurally complex electrocatalysts and evaluating the stability of defects in different environments for 2D material-based catalysts.

Ethanol Solvent Used in Constructing Ultra-Low-Temperature Zinc-Ion Capacitors with a Long Cycling Life.

Zinc-ion capacitors (ZICs) gain enormous attraction for their high power density, low cost, and long life, but their poor low-temperature performance is still a challenge due to the dissatisfactory freezing point of aqueous electrolyte solution. It is difficult for them to meet the requirements in cold environments as well as the extreme low temperature and severe temperature fluctuations in aerospace environments. Herein, ethanol (EtOH) solvent with ZnCl2 is used as an electrolyte to address these issues. Benefiting from the low freezing point (-114 °C) of EtOH, the ZIC with the ZnCl2/EtOH electrolyte can be operated at an ultralow temperature of -78 °C. It also demonstrates long cycling stability over 30,000 cycles. Such an enhancement is attributed to the unique properties of [ZnCl(EtOH)5]+ that can stabilize the coordination environment of Zn2+, slow the diffusivity, and raise the nucleation overpotential, leading to uniform Zn plating/stripping and subsequently suppressing dendrite growth. Meanwhile, the lower activation energy in ZnCl2/EtOH than that in ZnSO4/H2O electrolytes endows the ZIC excellent charge transfer properties. This work provides a fascinating electrolyte and a feasible pathway for ultra-low-temperature ZICs with a long cycling life.

Alchemical Osmostat for Monte Carlo Simulation: Sampling Aqueous Electrolyte Solution in Open Systems.

Molecular simulations involving electrolytes are usually performed at a fixed amount of salt ions in the simulation box, reproducing macroscopic concentration. Although this statement is valid in the bulk, the concentration of an electrolyte confined in nanoporous materials such as MOFs or zeolites is greatly affected and remains a priori unknown. The nanoporous material in equilibrium with the bulk electrolyte exchange water and ions at a given chemical potential Δμ in the semi-grand-canonical ensemble, that must be calibrated in order to determine the concentration in the nanoporous material. In this work, we propose an algorithm based on nonequilibrium candidate Monte Carlo (NCMC) moves to ultimately perform MC simulations in contact with a saline reservoir. First, we adapt the Widom insertion technique to calibrate the chemical potential by alchemically transmuting water molecules into ions by using NCMC moves. The chemical potential defines a Monte Carlo osmostat in the semi-grand-constant volume and temperature ensemble (Δμ, N, V, T) to be added in a Monte Carlo simulation where the number of ions fluctuates. In order to validate the method, we adapted the NCMC move to determine the free energy of water solvation and subsequently explore thermodynamics of electrolyte solvation at infinite dilution in water. Finally, we implemented the osmostat in MC simulations initialized with bulk water that are driven toward electrolyte solutions of similar concentration as the saline reservoir. Our results demonstrate that alchemical osmostat for MC simulation is a promising tool for use to sample electrolyte insertion in nanoporous materials.

Dynamics of Aqueous Electrolyte Solutions: Challenges for Simulations

This Perspective article focuses on recent simulation work on the dynamics of aqueous electrolytes. It is well-established that full-charge, nonpolarizable models for water and ions generally predict solution dynamics that are too slow in comparison to experiments. Models with reduced (scaled) charges do better for solution diffusivities and viscosities but encounter issues describing other dynamic phenomena such as nucleation rates of crystals from solution. Polarizable models show promise, especially when appropriately parametrized, but may still miss important physical effects such as charge transfer. First-principles calculations are starting to emerge for these properties that are in principle able to capture polarization, charge transfer, and chemical transformations in solution. While direct ab initio simulations are still too slow for simulations of large systems over long time scales, machine-learning models trained on appropriate first-principles data show significant promise for accurate and transferable modeling of electrolyte solution dynamics.

Quadrupolar 23Na+ NMR relaxation as a probe of subpicosecond collective dynamics in aqueous electrolyte solutions

Nuclear magnetic resonance relaxometry represents a powerful tool for extracting dynamic information. Yet, obtaining links to molecular motion is challenging for many ions that relax through the quadrupolar mechanism, which is mediated by electric field gradient fluctuations and lacks a detailed microscopic description. For sodium ions in aqueous electrolytes, we combine ab initio calculations to account for electron cloud effects with classical molecular dynamics to sample long-time fluctuations, and obtain relaxation rates in good agreement with experiments over broad concentration and temperature ranges. We demonstrate that quadrupolar nuclear relaxation is sensitive to subpicosecond dynamics not captured by previous models based on water reorientation or cluster rotation. While ions affect the overall water retardation, experimental trends are mainly explained by dynamics in the first two solvation shells of sodium, which contain mostly water. This work thus paves the way to the quantitative understanding of quadrupolar relaxation in electrolyte and bioelectrolyte systems.

Thermoacoustic, Electrochemical, Solvation and Antimicrobial Analysis of Ternary Potassium Salts Solutions at 308.15K

Introduction: Amino acids join with each other by peptide bonds and build polymers referred to peptides and proteins. Peptides are recognized for being very therapeutic, selective and comparably safe. As a result, peptides are receiving more attention in pharmaceutical research and development. The scientific progress of ultrasonics has been employed extensively in past decades for both industrial and medical applications. Aim/Objectives: Ultrasonic investigation in non- aqueous solutions of electrolytes with peptides provide information that is helpful in understanding the behaviour of liquids/solutions system. In the present work, the ultrasonic velocity of a peptide with electrolyte in formamide has been measured at various concentrations at 308.15K. Methods: Utilizing the measured data the thermoacoustical, electrochemical and solvation analysis are carried out. The interionic and intermolecular interactions existing in the present system are studied in detail. Conclusion: The results arrived from ultrasonic methods have been corroborated with antimicrobial activity of the samples.

Dicarboxylate-containing and fully substituted ferrocene with rapid dissolvability, high solubility, good stability, and moderate formal potential for mediated electrochemical detection.

An electron mediator with rapid dissolvability and high solubility in aqueous electrolyte solutions is essential for point-of-care testing based on mediated electrochemical detection. However, most ferrocenyl (Fc) compounds have slow dissolvability and poor solubility owing to high hydrophobicity of the Fc backbone. Moreover, many Fc compounds have poor stability and nonoptimal formal potential (). Herein, we present an Fc compound, Fc8m2c, which exhibits rapid dissolvability, high solubility, good stability, and moderate along with its high electron-mediation rate. The of Fc8m2c (0.17 V vs. Ag/AgCl) is tuned by two electron-withdrawing acyl substituents and eight electron-donating methyl substituents. Two pendant carboxylate groups of Fc8m2c allow for rapid dissolvability and high solubility (0.63 M in water), whereas full substitution in its two cyclopentadienyl ligands facilitates good chemical stability against decomposition in the presence of dissolved O2 and ambient light. A moderate enables the application of a potential of 0.07 V at which electrochemical background currents are low and also contributes toward resisting the decomposition of both Fc8m2c and Fc8m2c+. Fc8m2c provides a high electron-mediation rate constant (2.4 × 106 M-1 s-1) in glucose detection using glucose dehydrogenase. When Fc8m2c is applied to a glucose sensor, the calculated detection limit is ∼0.1 mM with a measurement period of 5 s. Considering that the normal concentration of glucose in serum is between 3.9 and 6.6 mM, the detection limit is sufficiently low. These results show that Fc8m2c is an excellent electron-mediator candidate for sensitive and rapid glucose detection.

Karl Heinzinger and computer modelling of water and aqueous solutions

This brief essay commemorates Karl Heinzinger, one of the pioneers in the field of computer modelling of fluid systems, particularly of water and aqueous electrolyte solutions in the bulk phase and near interfaces. Karl Heinzinger died peacefully on January 14, 2023, after a short illness. We express our deepest condolences to his family, colleagues, and friends.

Structure and self-diffusivity of alkali-halide electrolytes in neutral and charged graphene nanochannels.

Understanding the microscopic behaviour of aqueous electrolyte solutions in graphene-based ultrathin nanochannels is important in nanofluidic applications such as water purification, fuel cells, and molecular sensing. Under extreme confinement (<2 nm), the properties of water and ions differ drastically from those in the bulk phase. We studied the structural and diffusion behaviour of prototypical aqueous solutions of electrolytes (LiCl, NaCl, and KCl) confined in both neutral and positively-, and negatively-charged graphene nanochannels. We performed molecular dynamics simulations of the solutions in the nanochannels with either one, two- or three-layer water structures using the effectively polarisable force field for graphene. We analysed the structure and intermolecular bond network of the confined solutions along with their relation to the self-diffusivity of water and ions. The simulations show that Na and K cations can more easily rearrange their solvation shells under the graphene nanoconfinement and adsorb on the graphene surfaces or dissolve in the confinement-induced layered water than the Li cation. The negative surface charge together with the presence of ions orient water molecules with hydrogens towards the graphene surfaces, which in turn weakens the intermolecular bond network. The one-layer nanochannels have the biggest effect on the water structure and intermolecular bonding as well as on the adsorption of ions with only co-ions entering these nanochannels. The self-diffusivity of confined water is strongly reduced with respect to the bulk water and decreases with diminishing nanochannel heights except for the negatively-charged one-layer nanochannel. The self-diffusivity of ions also decreases with the reducing the nanochannel heights except for the self-diffusivity of cations in the negatively-charged one-layer nanochannel, evidencing cooperative diffusion of confined water and ions. Due to the significant break-up of the intermolecular bond network in the negatively-charged one-layer nanochannel, self-diffusion coefficients of water and cations exceed those for the two- and three-layer nanochannels and become comparable to the bulk values.

Surface tension models for binary aqueous solutions: a review and intercomparison.

The liquid-air surface tension of aqueous solutions is a fundamental quantity in multi-phase thermodynamics and fluid dynamics and thus relevant in many scientific and engineering fields. Various models have been proposed for its quantitative description. This Perspective gives an overview of the most popular models and their ability to reproduce experimental data of ten binary aqueous solutions of electrolytes and organic molecules chosen to be representative of different solute types. In addition, we propose a new model which reproduces sigmoidal curve shapes (Sigmoid model) to empirically fit experimental surface tension data. The surface tension of weakly surface-active substances is well reproduced by all models. In contrast, only few models successfully model the surface tension of aqueous solutions with strongly surface-active substances. For substances with a solubility limit, usually no experimental data is available for the surface tension of supersaturated solutions and the pure liquid solute. We discuss ways in which these can be estimated and emphasize the need for further research. The newly developed Sigmoid model best reproduces the surface tension of all tested solutions and can be recommended as a model for a broad range of binary mixtures and over the entire concentration range.

Unlimiting ionic conduction: manipulating hydration dynamics through vibrational strong coupling of water.

The energy states of molecules and the vacuum electromagnetic field can be hybridized to form a strong coupling state. In particular, it has been demonstrated that vibrational strong coupling can be used to modify the chemical dynamics of molecules. Here, we propose that ion dynamics can be altered through modifications of the dynamic hydration structure in a cavity vacuum field. We investigated the effect of different electrolyte species on ionic conductivity. Infrared spectroscopy of aqueous electrolyte solutions within the cavity confirmed the formation of vibrational ultrastrong coupling of water molecules, even in the presence of electrolytes. Interestingly, we observed significant enhancements in ionic conductivity, for specific alkali cations, particularly those classified as structure-breaking cations. These enhancements cannot be explained within the current theoretical framework for liquid electrolytes. Our analysis suggests that the vibrational strong coupling modifies the local dielectric friction experienced by hydrated ions. In addition, we propose the enthalpic and entropic modification of ionic conductivity through the systematic investigation of the hydration properties of different electrolytes. This study unveils the potential role of polaritons for exploring uncharted spaces in the design of materials with enhanced ionic conduction. Harnessing the unique properties of strong coupling and its influence on hydration dynamics could lead to the development of novel electrolytes and advancements in the field of ionic conduction.

Активация угольного электрода соединениями цинка

The process of cathodic polarization of a carbon electrode in an aqueous solution of zinc chloride with a concentration of 0,5 mmol/l in the potential range from equilibrium to –1,6 V was studied. It was found that staged reduction of zinc ions occurs in this region. At the initial moment after the completion of polarization, the potential of the carbon electrode was –1,2 V, later it increased to 0,8 V under the condition of stabilization in the electrolyte solution, and up to 1 V when the electrode was exposed to air for 15 min after polarization (then it was returned to aqueous electrolyte solution, where the potential increase occurred). To explain the potential shift phenomenon, a reaction scheme was proposed, where one of the stages is the formation of zinc peroxide on the surface of the working electrode. The carbon electrode modified with zinc in the course of further studies showed good reproducibility of electrochemical properties, which are proved by the cyclic current-voltage characteristics of cathodic and anode processes.

Synthesis and modification of corncob-based carbon as high performance negative material for supercapacitor

Porous carbons derived from agricultural waste biomass are ideal active materials for eco-friendly and low-cost supercapacitors electrode materials. However, the challenge remains to further functional modification of biomass-based carbon to achieve high specific capacitance. Herein, PPD-modified porous carbon (MPC) was synthesized by KOH soaking coupled with facile carbonization method of natural corncob and covalently graft of p-phenylenediamine. The MPC exhibits a high specific capacitance of 393 F·g-1 at a scan rate of 5mV·s-1 in a three electrode system in a 1 M KOH aqueous electrolyte solution. MPC was expected to become promising active materials for high performance negative electrode materials.

Перспективные слоистые гибкие радиопоглощающие материалы на основе порошкообразного угля

The article presents the technique for obtaining advanced layered radio-absorbing materials based on powdered charcoal. The technique includes the following technologies: incorporation of the electrolyte aqueous solution into the material particles pores; adhesive pressing. The developed technique is more manufacturable compared to the analogs. Materials obtained in accordance with this technique are characterized by the flexibility, as well as lower cost compared to other carbon-containing radio-absorbing materials. The experimental characteristics of electromagnetic radiation reflection and transmission coefficients in the frequency range 2.0 – 17.0 GHz of the materials obtained in accordance with the developed technique are described. The results of the comparative analysis of these characteristics are provided. Based on these results, it’s determined that the average values of electromagnetic radiation reflection coefficient in the specified frequency range of the materials based on powdered non-activated wood charcoal, powdered activated wood charcoal and powdered activated coconut charcoal are –4.5 dB, –8,5 dB and –9.0 dB (when these materials fixed on metal reflectors). The average values of their electromagnetic radiation transmission coefficient are –11.5 dB, –20.0 dB and –15.5 dB respectively. The investigated materials seem to be promising for use in order to protect electronic equipment from external electromagnetic interference.

Ionization Difference between Weak and Strong Electrolytes as Perturbed by Conductivity Spectra Analysis

While the static structure of aqueous electrolytes has been studied for decades, their dynamic microscopic structure remains unresolved yet critical in many areas. We report a comparative study of dc and ac (1 Hz to 20 GHz) conductivity data of weak and strong electrolytes, highlighting previously missing differences and similarities. Based on these results, we introduce into consideration the intrinsic short-lived ions of water, namely, excess protons (H3O+) and proton holes (OH-). We show that the model accounting for the neutralization of these ions by the species of electrolyte explains the conductivity of aqueous solutions in the concentration range 10-7-10 M. Based on independent experimental data, we hypothesize that the aggregation of the species in weak electrolytes may determine the main difference between the conductivity of weak and strong electrolytes. Our results push forward the understanding of the dynamic structure of aqueous electrolyte solutions and are important to nanofluidic, biological, and electrochemical systems.