Aqueous Electrolyte Solutions Research Articles

A manganese dioxide nanoparticle-bimetallic metal organic framework composite for selective and sensitive detection of vitamin D3 in human plasma.

For the first time a metal organic framework nanomaterial has been developedcomprising manganese dioxide nanoparticle and iron and zinc metal ions interlinked with each other via terephthalic acid. The framework shape was identified as an elongated hexagonal nanorod (TEM) with varying functional groups (FT-IR) and diffraction patterns (XRD). The framework nanocomposite as such in aqueous acidic electrolyte solution has displayed an excellent conductivity (redox behavior) and surface excess (3.08 × 10-8 cm-2). Under the optimized conditions (0.1 M H2SO4 as electrolyte, 50 mV/s scan rate, +1.26 V (vs Ag/AgCl)), the metal organic framework coated electrode has selectively identified vitamin D3 (VD3) in the presence of various other interfering molecules and displayed excellent limit of detection (1.9 ng mL-1). The developed sensor has been applied to the determination of VD3 in extracted human plasma samples (RSD of 0.3-2.6 % and recovery of 96-102 %), and the obtained VD3 values are similar to HPLC-UV method.

Novel Phosphate Conversion Coating with Superior Corrosion Resistance on the Mg-Al-RE Alloy Based on the Introduction of Silane.

A novel chemical conversion method based on an aqueous electrolyte solution containing hydrolyzed silane as a crucial film-forming agent has been developed successfully. An organic/inorganic composite coating with superior corrosion protection was fabricated on the Mg-Al-RE alloy. The micro-morphology and chemical composition of the coating were examined using scanning electron microscopy, X-ray diffraction, and energy-dispersive X-ray spectroscopy. The prepared conversion coating possesses a double-layer structure, with a dense bottom layer and a loose outer layer containing microcracks. In addition, the anti-corrosion capacity of various samples was evaluated using salt spray, hydrogen evolution, and electrochemical tests. The analysis revealed that the samples converted by 3-aminopropyl triethoxysilane (APTES)-phosphate solution possessed a higher corrosion resistance. Compared to the blank sample, a 2 orders of magnitude reduction in icorr (6.678 × 10-7 A/cm2) and a 1.360 V improvement in Ecorr were observed. The MPCC-Si sample exhibited the lowest hydrogen evolution rate, indicating the best corrosion protection. Also, the rust grade could still reach 7 after 72 h of the neutral salt spray test.

Atomic insights into the heterogeneity and the interface interactions of nanoconfined aqueous electrolyte solution

The structure and properties of nanoconfined electrolyte (nano electrolyte) solutions are important subjects in biochemistry, electrochemistry, separation science, etc. In the present work, neutron scattering and data driven reverse Monte Carlo were employed to quantitatively reveal the microstructure of aqueous CaCl2 solution in mesoporous silica MCM-41 at the atomic level. The electrolyte solution distributes in-homogeneously in the pores of mesoporous silica along the radial direction, which can be divided into the core, the transition, and the interface regions. The hydrogen bond structure of water in nano electrolytes is strengthened in the core region, analogous to that of nano water confined in nanochannels, and the ion association was enhanced in the transition region. The structure of the solution in the interface region was analogous to the bulk electrolyte solution under high pressure because of the confinement and interface effects. When the package ratio of nano electrolyte solution is insufficient, small amount of solution quasi-monolayer adsorb on the internal surface of mesoporous silica, the majority solution preferentially forms clusters with different sizes to adhere to the wetted interface. The anomalous hydrogen-bonding structure and ion association found in the present work improve our understanding of nanoconfined electrolyte solutions.

Extraction of Copper Ions with Composite Sorbents Based on Chitosan from Aqueous Solutions of Electrolytes in the Presence of a Surfactant

Extraction of Copper Ions with Composite Sorbents Based on Chitosan from Aqueous Solutions of Electrolytes in the Presence of a Surfactant

Facile hydrothermal synthesis of monoclinic VO2/graphene nanowhisker composite for enhanced performance electrode material for energy storage applications

Vanadium dioxide/reduced graphene oxide (VO2/G) nanowhisker composites are synthesized under hydrothermal conditions by a simple method. VO2 nanowhisker and 2D flexible graphene sheets are formed during the formation of VO2/G architecture to build interconnected porous microstructure via hydrogen bonding which allows charging and ion transport in the electrode. The composite electrode shows outstanding electrochemical performances due to the hierarchical network structure and pseudo-capacity contribution from VO2 nanowhiskers. The composite electrode used for electrochemical investigations in the aqueous electrolyte solution of 1 M Na2SO4. Noteworthy is the galvanostatic charge-discharge test which shows that, with a current density of 1 Ag−1, the specific capacitance value of the composite attained a high value of 294.5 Fg−1, which is significantly better than pure vanadium dioxide (VO2), and retains its capacitance at 203 Fg−1 at 10 Ag−1. The specific capacitance remained 96.3 % after 5000 continuous discharge cycles at 0.6 Ag−1 and shows an excellent cycle life for the material. It has also a high power density with a reasonably high-energy density. (i.e) energy density reached 48.07 Wh kg−1 at a power density of 213.6 Wkg−1. The results of the composite electrode were due to synergistic effects of VO2 and graphene, and excellent VO2 redox activity coupled with high electronic graphene sheet conductivity.

Computation of Electrical Conductivities of Aqueous Electrolyte Solutions: Two Surfaces, One Property.

In this work, we computed electrical conductivities under ambient conditions of aqueous NaCl and KCl solutions by using the Einstein-Helfand equation. Common force fields (charge q = ±1 e) do not reproduce the experimental values of electrical conductivities, viscosities, and diffusion coefficients. Recently, we proposed the idea of using different charges to describe the potential energy surface (PES) and the dipole moment surface (DMS). In this work, we implement this concept. The equilibrium trajectories required to evaluate electrical conductivities (within linear response theory) were obtained by using scaled charges (with the value q = ±0.75 e) to describe the PES. The potential parameters were those of the Madrid-Transport force field, which accurately describe viscosities and diffusion coefficients of these ionic solutions. However, integer charges were used to compute the conductivities (thus describing the DMS). The basic idea is that although the scaled charge describes the ion-water interaction better, the integer charge reflects the value of the charge that is transported due to the electric field. The agreement obtained with experiments is excellent, as for the first time electrical conductivities (and the other transport properties) of NaCl and KCl electrolyte solutions are described with high accuracy for the whole concentration range up to their solubility limit. Finally, we propose an easy way to obtain a rough estimate of the actual electrical conductivity of the potential model under consideration using the approximate Nernst-Einstein equation, which neglects correlations between different ions.

Effective Interactions between Double-Stranded DNA Molecules in Aqueous Electrolyte Solutions: Effects of Molecular Architecture and Counterion Valency.

A computational investigation of the effects of molecular topology, namely, linear and circular, as well as counterion valency, on the ensuing pairwise effective interactions between DNA molecules in an unlinked state is presented. Umbrella sampling simulations have been performed through the introduction of bias potential along a reaction coordinate defined as the distance between the centers-of-mass of pairs of DNA molecules, and effective pair interaction potentials have been computed by employing the weighted histogram analysis method. An interesting comparison can be drawn between the different DNA topologies studied here, especially with regard to the contrasting effects of divalent counterions on the effective pair potentials: while DNA-DNA repulsion in short center-of-mass distances decreases significantly in the presence of divalent counterion-ions (as compared to monovalent ions) for linear DNA, the opposite effect occurs for the DNA minicircles. This can be attributed to the fact that linear DNA fragments can easily adopt relative orientations that minimize electrostatic and steric repulsions by rotating relative to one another and by exhibiting more pronounced bending due to the presence of free ends.

Self-Consistent Implementation of a Solvation Free Energy Framework to Predict the Salt Solubilities of Six Alkali Halides.

To assess the salt solubilities of six alkali halides in aqueous systems, we proposed a thermodynamic cycle and an efficient molecular modeling methodology. The Gibbs free energy changes for vaporization, dissociation, and dissolution were calculated using the experimental data of ionic thermodynamic properties obtained from the NBS tables. Additionally, the Marcus' and Tissandier's solvation free energy data for Li+, Na+, K+, Cl-, and Br- ions were compared with the conventional solvation free energies by substituting into our self-consistent thermodynamic cycle. Furthermore, Tissandier's absolute solvation free energy data were used as the training set to refit the Lennard-Jones parameters of OPLS-AA force field for ions. To predict salt solubilities, an assumption of a pseudo-solvent was proposed to characterize the coupling work of a solute with its environment from infinitely diluted to saturated solutions, indicating that the Gibbs energy change of solvation process is a function of ionic strength. Following the self-consistency of the cycle, the newly derived formulas were used to determine the salt solubilities by interpolating the intersection of Gibbs free energy of dissolution and the zero free energy line. The refined ion parameters can also predict the structure and thermodynamic properties of aqueous electrolyte solutions, such as densities, pair correlation functions, hydration numbers, mean activity coefficients, vapor pressures, and the radial dependences of the net charge at 298.15 K and 1 bar. Our method can be used to characterize the solid-liquid equilibria of ions or charged particles in aqueous systems. Furthermore, for highly concentrated strong electrolyte systems, it is essential to introduce accurate water models and polarizable force fields.

Exploring nucleation modeling of the voltammetry of solid-to-solid-state redox processes with phase changes

An operational description of the linear potential scan voltammetry of solids experiencing a solid-state redox transformation with phase changes is described. The modeling is based on the application of nucleation equations of solid-state reaction kinetics to express the transferred charge/applied potential relationships. The flexible use of Prout-Tompkins and Avrami-Erofe’ev kinetics permits a satisfactory description of the voltammetry of solid-to-solid redox transformations with phase segregation. The model satisfactorily applies to reproduce linear potential scan curves recorded for graphite electrodes modified with several lead compounds in contact with aqueous electrolyte solutions.

Ultrasonic investigation of L- leucine in aqueous electrolyte solutions

This paper reports the densities as well as thespeed of soundL-leucine (0.02 –0.20 mol /kg) in (0.1 mol /kg) aqueous medium of the electrolytes: KCl and NaClat various temperatures (283.15–293.15 K) under atmospheric pressure. Acoustic impedance (Z), free length, isobaric thermal expansion coefficient (α), adiabatic compressibility (β), isothermal compressibility (KT), and specific heat (ϒ), surface tension (σ) using experimental density and speed of sound data, hasbeen computed. The outcomes are illustrated in terms of several electrostatic and hydrophobic interactions associated withthe ternary system of electrolyte, water,and amino acid. A great number of interactions between the electrolyte and L-leucine have been confirmed by electrolyte and temperature. Positive transfer quantities indicate that ion-hydrophilic and hydrophilic-hydrophilic interactions between leucine, sodium chloride, as well as potassium chloride in anaqueous medium, predominate. Overall findings are now explained in terms of solute–solvent as well as solute–solute interactions.

Plasma Electrolytic Oxidation for Dental Implant Surface Treatment.

50 IRIS dental implants (Scientific Production Company LICOSTOM, Russia), 10-mm long and 4 mm in diameter, were manufactured from the VT1-0 alloy. The implant surface was treated by two PEO methods: 1) in the aqueous solution of alkaline electrolyte without any additional modifiers (PEO-Ti); 2) in the aqueous solution of orthophosphoric acid-based electrolyte containing calcium carbonate (PEO-Ca). Implants made of VT1-0 alloy after milling and without additional treatment served as control samples. The implant surfaces were studied by electron microscopy and energy dispersive X-ray spectrometry. Some of the implants were installed in sheep, samples were obtained at 2, 4, and 8 weeks and studied by microcomputer tomography. Regardless of the electrolyte composition, a highly developed porous surface was formed in the samples with PEO-modified surfaces. The surface of the PEO-Ti samples in a simple unmodified electrolyte was characterized by a large number of open pores with a wide range of size distribution from 200 nm to 3 μm. The pore size distribution was of a monomodal character, with a maximum near 0.23 μm. The PEO samples in the Ca-containing electrolyte had pores also in a wide range from ~80 nm to ~7 μm. The pore distribution, in contrast to PEO-Ti, was bimodal in nature, with the main maximum in the region of 1.05 μm and the concomitant maximum near 2.45 μm.The obtained surfaces of both types (PEO with Ca and Ti) possessed high purity and optimal microroughness for osseointegration. Both types of PEO treatment (PEO with Ca and Ti) have demonstrated a similar osseointegrative potential, nevertheless, the surface of the PEO-Ca showed a better contact with the implant surface (49.8%) than PEO-Ti (42.4%) obviously due to the presence of calcium in its composition. The PEO-formed implant surfaces demonstrate high osseointegrative properties after any variants of treatment and show the potential for application in osteoporosis.

Hydrogel Polymer Electrolytes: Synthesis, Physicochemical Characterization and Application in Electrochemical Capacitors.

Electrochemical capacitors operating in an aqueous electrolyte solution have become ever-more popular in recent years, mainly because they are cheap and ecofriendly. Additionally, aqueous electrolytes have a higher ionic conductivity than organic electrolytes and ionic liquids. These materials can exist in the form of a liquid or a solid (hydrogel). The latter form is a very promising alternative to liquid electrolytes because it is solid, which prevents electrolyte leakage. In our work, hydrogel polymer electrolytes (HPEs) were obtained via photopolymerization of a mixture of acrylic oligomer Exothane 108 with methacrylic acid (MAA) in ethanol, which was later replaced by electrolytes (1 M Na2SO4). Through the conducted research, the effects of the monomers ratio and the organic solvent concentration (ethanol) on the mechanical properties (tensile test), electrolyte sorption, and ionic conductivity were examined. Finally, hydrogel polymer electrolytes with high ionic conductivity (σ = 26.5 mS∙cm-1) and sufficient mechanical stability (σmax = 0.25 MPa, εmax = 20%) were tested using an AC/AC electrochemical double layer capacitor (EDLC). The electrochemical properties of the devices were investigated via cyclic voltammetry, galvanostatic charge/discharge, and impedance spectroscopy. The obtained results show the application potential of the obtained HPE in EDLC.

Use of the Photoelectrolysis of Ordinary Water Powered by the Light Energy for the Non-Stop Operation of the Electric Car Engine

Today, the non-stop operation of an electric vehicle engine requires continuous charging of the engine's fuel cell with pure hydrogen and oxygen. Pure hydrogen is obtained by various industrial methods, including: steam reforming of methane and natural gas; coal gasification; biotechnology; electrolysis of water, etc. The most effective method for obtaining pure hydrogen and oxygen is the use of photoelectrolysis of an aqueous electrolyte solution in a photoelectrochemical cell. In this method, hydrogen and oxygen are produced in a photoelectrochemical cell from light energy. However, the photoelectrochemical cells used today lose most of the light energy due to the high resistance of the conductive medium between the electrodes, are expensive, have material limitations that significantly reduce their efficiency. The article presents the use of photoelectrolysis of ordinary water, powered by light energy for the non-stop operation of an electric vehicle engine by continuously charging the fuel cell of the engine with hydrogen and oxygen, continuously produced in a specially designed photoelectrolyzer, powered by light energy, at a price below the market and participating in a continuously operating closed cycle: ordinary water tank + photoelectrolyzer: formation of gas bubbles of hydrogen and oxygen in the process of photoelectrolysis of ordinary water + fuel cell charging and electric car engine operation + steam water + ordinary water tank. The developed photoelectrolyzer, in contrast to existing photoelectrochemical cells, has a specially designed electrolysis base, located in the lower part of the photoelectrolyzer, includes a fire hose material membrane, located between a silicon semiconductor with an attached mesh; a burnt graphite cathode and a mechanism for adjusting the gap between the electrodes.

Influence of strong bromine binding complexing agent in electrolytes on the performance of hydrogen/bromine redox flow batteries

1-n-Hexylpyridin-1-ium bromide [C6Py]Br is investigated in this work as bromine complexing agent (BCA) in aqueous bromine electrolytes on its influence on hydrogen bromine redox flow battery (H2/Br2-RFB) performance. [C6Py]+-cations bind bromine of aqueous polybromide solutions safely in an additional fused salt phase limiting the vapor pressure of Br2. Dissolved in aqueous electrolyte solutions, however, [BCA]+ cations drastically lower PFSA membranes' conductivity in the H2/Br2-RFB. In this work the combination of the very strong bromine-binding [C6Py]+cation and an excess of bromine in the electrolyte lead to an almost complete absorption of 99.6 mol% [C6Py]+ into the fused salt within the electrolyte's operation range. In comparison to similar application of short side chain 1-ethylpyridinium bromide, adverse effects are stronger compensated by use of [C6Py]Br. Increases in membrane resistance of the membrane in contact with [C6Py]+ cations are reversible in contrast for contact with [C2Py]+ cations. Electrolytes are cycled for at least 12 cycles and offer a stable useable capacity of 176.7 Ah L−1 and reach and stable discharge energy densities of 138.91 Wh L−1. Strong bromine binding properties between [C6Py]+ cations and polybromides are confirmed by DFT studies. In contrast to [C2Py]+ electrolytes, the long-chain [C6Py]+ cation in electrolytes has a higher cycling stability or a low decrease in capacity and energy density.

Synergetic effect on enhanced electrochemical properties of MnO2 nanorods on g-C3N4/rGO nanosheet ternary composites for pouch-type flexible asymmetric supercapattery device

In this work, one-dimensional MnO2 nanorods are distributed evenly over two-dimensional g-C3N4/rGO nanosheets using a simple hydrothermal approach. The structure, functional group, morphologies, elemental analyses and surface area of prepared samples have been investigated. Moreover, the electrochemical performance of MnO2/g-C3N4/rGO in 1 M Na2SO4 aqueous electrolyte solution was tested using cyclic voltammetry (CV), galvanostatic charge and discharge (GCD), electrochemical impedance spectroscopy (EIS) and capacitance retention. The MnO2/g-C3N4/rGO material has superior electrochemical performance than pure and binary electrode materials due to the high surface area of ternary composite (469.26 m2/g) compared to pure (38.083 m2/g). The ternary MnO2/g-C3N4/rGO electrode obtained the high specific capacitance of 716.6 Fg−1 at 1 Ag−1 and kept 97 % capacitance retention after 10,000 cycles at a current density of 10 Ag−1. Since the synergistic effects of MnO2 and g-C3N4/rGO improve electrochemical performance, the ternary composite is an excellent option for high-performance supercapacitors. Moreover, the pouch-type supercapattery device was assembled using MnO2/g-C3N4/rGO and activated carbon electrodes. The supercapattery device exhibits a maximum specific capacitance of 108.5 Fg−1 with 91.5 % capacitance retention after 10,000 cycles at a high current density of 10 Ag−1. The device achieved a high energy density of 48.6 Wh kg−1 at a power density of 899.9 W kg−1 in the operating potential value of 0–1.8 V. The fabricated supercapattery device was tested for real practical application by charging 30 s and attained a self-discharging time of 5 min.

In Situ Polymerization Synthesis of Graphdiyne Nanosheets as Electrode Material and Its Application in NMR Spectroelectrochemistry.

In situ NMR spectroelectrochemistry is extremely powerful in studying redox reactions in real time and identifying unstable reaction intermediates. In this paper, in situ polymerization synthesis of ultrathin graphdiyne (GDY) nanosheets was realized on the surface of copper nanoflower/copper foam (nano-Cu/Cuf)-based electrode with hexakisbenzene monomers and pyridine. Palladium (Pd) nanoparticles were further deposited onto the GDY nanosheets by the constant potential method. By using this GDY composite as electrode material, a new NMR-electrochemical cell was designed for in situ NMR spectroelectrochemistry measurement. The three-electrode electrochemical system consists of a Pd/GDY/nano-Cu/Cuf electrode as the working electrode, a platinum wire as the counter electrode, and a silver/silver chloride (Ag/AgCl) wire as a quasi-reference electrode, which can be dipped into a specially constructed sample tube and adapted for convenient operation in any commercial high-field, variable-temperature FT NMR spectrometer. The application of this NMR-electrochemical cell is illustrated by monitoring the progressive oxidation of hydroquinone to benzoquinone by controlled-potential electrolysis in aqueous solution.

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.

Elucidation of Molecular‐level Mechanisms of Oxygen Atom Reactions with Chlorine Ion in NaCl Solutions using Molecular Dynamics Simulations Combined with Density Functional Theory

AbstractMolecular dynamics simulations combined with density functional theory were performed to investigate the reaction mechanisms for oxygen atom and chlorine ion in NaCl solutions. Considering the ground and first excited states of the oxygen atom, four bulk systems, O(3P)‐NaCl‐63H2O, O(1D)‐NaCl‐63H2O, O(3P)‐4NaCl‐63H2O, and O(1D)‐4NaCl‐63H2O were studied. The main reaction pathway depended on the concentration of the aqueous electrolyte solution. For a dilute solution with a 1 : 64 ratio of NaCl to H2O, the singlet oxygen atom first attached a water molecule to produce a neutral OH radical, and then the OH radical and chlorine ion approach each other to form an intermediate structure [Cl…OH]−. Synchronously, the intermediate transferred charge to the solvated OH radical by accessing the hydrogen bond network. Finally, neutral HOCl and OH− ions were formed. For a dense solution with a 4 : 64 ratio of NaCl to H2O, a singlet oxygen atom was directly combined with Cl− to produce ClO− via an oxygen transfer reaction. The subsequent ab‐initio energy computations indicated the most probable mechanism, where the O atom directly combines with Cl− ion to OCl−. This study provides insights into the fundamental mechanisms of the behavior of dissolved oxygen radicals in aqueous electrolyte solutions.

Structural and electrochemical properties of Cu doped NiCo2O4 prepared by microwave hydrothermal method

A series of NiCuxCo2-xO4 with x = 0, 0.02, 0.04, 0.06, 0.08 and 0.10 samples were synthesized using microwave hydrothermal method (MH). The structural, microstructural, and spectroscopic characterizations were carried out using X-ray diffraction (XRD), scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). All the samples are in Cubic phase with space group Fd3m. The samples x ≥ 0.08 shows some impurity phases. The average grain size for all the samples is in the range of 30–55 nm. The specific capacitance (Csp) 250.66 Fg−1, energy density (E) 22.22 Whkg−1 and power density (P) 757.80 Wkg−1 was observed for x = 0.06 with a mass loading of 7 mgcm−2 and in 2 M aqueous KOH electrolyte solution at a current density of 1 Ag−1. Therefore, the Cu doping with x = 0.06 shows good redox activities and hence can be used in electric batteries and supercapacitors.

Use of Pitzer’s model to calculate thermodynamic properties of aqueous electrolyte solutions of sulfuric acid

Over this study we calculated the coefficients of activity of different species and the concentration in the presence of H+ ion when H2SO4 is alone in solution. The coefficient of average activity was calculated using the model of Pitzer. The constants of dissociation of these reactions were calculated from the values of the free standard energies. The reaction reaches a balance while producing H+, HSO4- and SO42-. The research reported here concentrated on the effect of some important operational parameters on dissolution process. The parameters were investigated and their ranges are as follows: initial molality ranging from 0.001 to 5 mol.kg-1 and temperatures between 25 and 200°C. Fortran 90 (Mathematical formula translating system) was used to perform all mathematical calculations. The numerical code can be used to calculate the molarity of ion H+ of an aqueous solution of sulfuric acid. The objective of the present work is to optimize the parameters of leaching such as activity of sulfuric acid on the dissociation phenomena.