Concentrated Electrolyte Solutions Research Articles

Improved electrode reversibility of anionic redox with highly concentrated electrolyte solution and aramid-coated polyolefin separator

High-capacity electrode materials made of abundant elements are necessary to develop cost-effective energy storage applications.

Dielectric-free electrowetting on graphene.

Electrowetting is a simple way to induce the spreading and retraction of electrolyte droplets. This method is widely used in "device" applications, where a dielectric layer is applied between the electrolyte and the conducting substrate. Recent work, including contributions from our own laboratory, have shown that reversible electrowetting can be achieved directly on conductors. We have shown that graphite surfaces, in particular when combined with highly concentrated electrolyte solutions, show a strong wetting effect. The process is driven by the interactions between the electrolyte ions and the surface, hence models of double-layer capacitance are able to explain changes in the equilibrium contact angles. Herein, we extend the approach to the investigation of electrowetting on graphene samples of varying thickness, prepared by chemical vapor deposition. We show that the use of highly concentrated aqueous electrolytes induces a clear yet subtle electrowetting response due to the adsorption of ions and the suppression of the negative effect introduced by the surface impurities accumulating during the transfer process. The latter have been previously reported to fully hinder electrowetting at lower electrolyte concentrations. An amplified wetting response is recorded in the presence of strongly adsorbed/intercalated anions in both aqueous and non-aqueous electrolytes. The phenomenon is interpreted based on the anion-graphene interactions and their influence on the energetics of the interface. By monitoring the dynamics of wetting, an irreversible behaviour is identified in all cases as a consequence of the irreversibility of anion adsorption and/or intercalation. Finally, the effect of the underlying reactions on the timescales of wetting is also examined.

Vibrational Raman Spectroscopy of the Hydration Shell of Ions

Ionic perturbation of water has important implications in various chemical, biological and environmental processes. Previous studies revealed the structural and dynamical perturbation of water in the presence of ions, mainly with concentrated electrolyte solutions having significant interionic interactions. These investigations highlighted the need of selective extraction of the hydration shell water from a dilute electrolyte solution that is largely free from interionic interactions. Double-difference infrared (DDIR) and Raman multivariate curve resolution (Raman-MCR), as well as MD simulation, provided valuable insight in this direction, suggesting that the perturbed water mainly resides in the immediate vicinity of the ion, called the hydration shell. Recently, we have introduced Raman difference spectroscopy with simultaneous curve fitting (Raman-DS-SCF) analysis that can quantitatively extract the vibrational response of the perturbed water pertaining to the hydration shell of fully hydrated ions/solute. The DS-SCF analysis revealed novel hydrogen-bond (H-bond) structural features of hydration water, such as the existence of extremely weakly interacting water–OH (νmax ~ 3600 cm−1) in the hydration shell of high-charge-density metal ions (Mg2+, Dy3+). In addition, Raman-DS-SCF retrieves the vibrational response of the shared water in the water–shared-ion pair (WSIP), which is different from the hydration shell water of either the interacting cation and anion. Herein, we discuss the perturbation of water H-bonding in the immediate vicinity of cation, anion, zwitterion and hydrophobes and also the inter-ionic interactions, with a focus on the recent results from our laboratory using Raman-DS-SCF spectroscopy.

Effective Formation of Superior Surface Films on Si Negative Electrodes in a Highly Concentrated Fluorinated Carbonate Ester Solvent/Diluent Electrolyte Solution System

Highly concentrated electrolyte solutions that used methyl 2,2,2-trifluoroethyl carbonate (MFEC) as a single solvent were studied for Si nano-flake powder negative electrodes. The nearly saturated 3.68 mol/L LiN(SO2F)2 (LiFSI)/MFEC electrolyte solution improved the charge/discharge cycle performance of the Si electrode. This electrolyte solution was moderately diluted with bis(2,2,2-trifluoroethyl) carbonate (TFEC), which did not dissolve LiFSI, to such an extent that the solvation structure was not disturbed. The solvates containing FSI– anions and MFEC molecules in the diluted electrolyte solution effectively decomposed to form a LiF-rich thin surface film on a Si electrode. As a result, the swelling of a Si electrode upon charge/discharge cycling was further suppressed, and the charge/discharge cycle performance greatly improved.

Ion Dynamics in Concentrated Electrolyte Solutions: Relating Equilibrium Fluctuations of the Ions to Transport Properties in Battery Cells

In recent years, the interest in the development of highly concentrated electrolyte solutions for battery applications has increased enormously. Such electrolyte solutions are typically characterized by a low flammability, a high thermal and electrochemical stability and by the formation of a stable solid electrolyte interphase (SEI) in contact to electrode materials. However, the classification of concentrated electrolyte solutions in terms of the classical scheme “strong” or “weak” has been controversially discussed in the literature. In this paper, a comprehensive theoretical framework is presented for a more general classification, which is based on a comparison of charge transport and mass transport. By combining the Onsager transport formalism with linear response theory, center‐of‐mass fluctuations and collective translational dipole fluctuations of the ions in equilibrium are related to transport properties in a lithium‐ion battery cell, namely mass transport, charge transport and Li+ transport under anion‐blocking conditions. The relevance of the classification approach is substantiated by showing that i) it is straightforward to classify highly concentrated electrolytes and that ii) both fast charge transport and fast mass transport are indispensable for achieving fast Li+ transport under anion‐blocking conditions.

THE CONCENTRATION EFFECT OF K2SO4 ELECTROLITE SOLUTION ON GLOW DISCHARGE PLASMA ELECTROLYSIS

Plasma electrolysis is currently an environmentally friendly technology that is used as an alternative to nitrogen fixation, clean water treatment, batik waste degradation and the synthesis of other compounds. The success indicator of plasma electrolysis technology is seen from the formation of glow discharge. One of the factors that influence the formation of plasma in this method is the electrolyte solution. The electrolyte solution used in this study is K2SO4 because its conductivity causes electron jumps. This study aims to determine the effect of various concentrations of K2SO4 electrolyte solution on glow discharge plasma at the anode.In the plasma electrolysis reactor with stainless steel cathode and tungsten anode and 0.01 M electrolyte solution; 0.02 M; and 0.03 M K2SO4. The formation of glow discharge plasma occurs at the anode. Changes in concentration affect the critical voltage (VD) where the higher the concentration (0.03 M), glow discharge occurs at a lower voltage (600 V). This is due to the presence of high dielectric strength in the solution causing lower discharge strength to occur in solutions with lower electrolyte concentrations.Keywords: anode, plasma electrolysis, K2SO4 electrolyte, glow discharge

The impact of electrolyte solution concentrations on the optical characteristics of CdS nanoparticles

The aim of this work is to examine the influence of the type and concentration of an electrolyte solution on the optical characteristics of CdS nanoparticles produced by the sonochemical approach. The optical characteristics of the samples were examined using an Ultraviolet–Visible (UV–Vis) spectrophotometer in order to calculate the bandgap value. Acquired samples were examined on how to change the bandgap at various concentrations within various electrolyte solutions in order to ascertain the effects of various ambiences. Cadmium nitrate tetrahydrate (Cd (NO[Formula: see text]4H2O), cadmium acetate dihydrate (Cd(CH3COO)[Formula: see text]2H2O) and sodium chloride (NaCl) water solutions were utilized as electrolytes in three different environments. When the sample was exposed to a different environment, its energy spectrum changed. Measurements show that raising the concentration of various electrolyte solutions decreased the bandgap values of the samples.

Carbonaceous-Material-Induced Gelation of Concentrated Electrolyte Solutions for Application in Lithium-Sulfur Battery Cathodes.

Lithium-sulfur (Li-S) batteries can theoretically deliver high energy densities exceeding 2500 Wh kg-1. However, high sulfur loading and lean electrolyte conditions are two major requirements to enhance the actual energy density of the Li-S batteries. Herein, the use of carbon-dispersed highly concentrated electrolyte (HCE) gels with sparingly solvating characteristics as sulfur hosts in Li-S batteries is proposed as a unique approach to construct continuous electron-transport and ion-conduction paths in sulfur cathodes as well as achieve high energy density under lean-electrolyte conditions. The sol-gel behavior of carbon-dispersed sulfolane-based HCEs was investigated using phase diagrams. The sol-to-gel transition was mainly dependent on the amount of the carbonaceous material and the Li salt content. The gelation was caused by the carbonaceous-material-induced formation of an integrated network. Density functional theory (DFT) calculations revealed that the strong cation-π interactions between Li+ and the induced dipole of graphitic carbon were responsible for facilitating the dispersion of the carbonaceous material into the HCEs, thereby permitting gel formation at high Li-salt concentrations. The as-prepared carbon-dispersed sulfolane-based composite gels were employed as efficient sulfur hosts in Li-S batteries. The use of gel-type sulfur hosts eliminates the requirement for excess electrolytes and thus facilitates the practical realization of Li-S batteries under lean-electrolyte conditions. A Li-S pouch cell that achieved a high cell-energy density (up to 253 Wh kg-1) at a high sulfur loading (4.1 mg cm-2) and low electrolyte/sulfur ratio (4.2 μL mg-1) was developed. Furthermore, a Li-S polymer battery was fabricated by combining the composite gel cathode and a polymer gel electrolyte.

Preparation and Characterization of Cu2O Thin Films by Electrodeposition in Acidic Media

Cu2O is a p-type semiconductor with a band gap of about 2.17 eV. It has an octahedral cubic structure, and has a broad prospect in photocatalysis, battery, and superconductor. The Cu2O thin films prepared by electrochemical deposition method can effectively control the morphology of the sample with low cost and easy operation. Traditionally, the preparation methods of Cu2O thin films mostly use alkaline systems. In this paper, Cu2O thin films were successfully prepared by the electrodeposition method in an acidic system, using copper acetate (Cu(CH3COO)2·H2O) and sodium acetate (CH3COONa) as raw materials. The cyclic voltammetry curve of the solution was tested on an electrochemical workstation. The phase composition of the thin films were characterized using X-ray diffraction (XRD). The surface morphology of the thin films were analyzed by using scanning electron microscope(SEM). The influence of process conditions such as deposition potential, deposition time and electrolyte solution concentration on the preparation of thin films was studied. The results shows that the moderate extension of the deposition time and the increase of the electrolyte solution concentration are beneficial to the preparation of Cu2O thin films. When the deposition potential is −0.1 V, the deposition time is 30 min, and the electrolyte solution concentration is 0.06 mol/L, the continuous and dense Cu2O thin films can be obtained. The XRD peaks of Cu2O thin films correspond to the (110), (111), and (200) crystal planes respectively

Effect of Concentration of Electrolyte Solution on the Electrochemical Stability of Ionogel

Ionogel is an emerging hybrid material where the ionic liquid is immobilized within polymer matrix. Interesting combination of properties has permitted wide applications of ionogel. In this study, a well-known method, sol-gel is used to synthesize ionogel. However, it is intended to identify the optimum concentration of ionic liquid within ionogel which endows the ionogel with the best electrochemical performance. By varying the concentration of ionic liquid, the appearance of ionogel is compared. FTIR is performed to understand the structural changes that occur in ionogel. Linear Sweep Voltammetry is performed to study the electrochemical stability of ionogel.

Numerical analysis of thermophoresis of charged colloidal particles in non-Newtonian concentrated electrolyte solutions.

Thermophoresis of colloidal particles in aqueous media is more frequently applied in biomedical analysis with processed fluids as biofluids. In this work, a numerical analysis of the thermophoresis of charged colloidal particles in non-Newtonian concentrated electrolyte solutions is presented. In a particle-fixed reference frame, the flow field of non-Newtonian fluids has been governed by the Cauchy momentum equation and the continuity equation, with the dynamic viscosity following the power-law fluid model. The numerical simulations reveal that the shear-thinning effect of pseudoplastic fluids is advantageous to the thermophoresis, and the shear-thickening effect of dilatant fluids slows down the thermophoresis. Both the shear-thinning and shear-thickening effects of non-Newtonian fluids on a thermodiffusion coefficient are pronounced for the case when the thickness of electric double layer (EDL) surrounding a particle is moderate or thin. Finally, the reciprocal of the dynamic velocity at the particle surface is calculated to approximately estimate the thermophoretic behavior of a charged particle with moderate or thin EDL thickness.

Effect of AZ31 PEO Coating Layer Formation According to Alginic Acid Concentration in Electrolyte Solution

Effect of AZ31 PEO Coating Layer Formation According to Alginic Acid Concentration in Electrolyte Solution

Colloidal Systems in Concentrated Electrolyte Solutions Exhibit Re-entrant Long-Range Electrostatic Interactions due to Underscreening.

Surface force measurements have revealed that at very high electrolyte concentrations as well as in neat and diluted ionic liquids and deep eutectic solvents, the range of electrostatic interactions is far greater than the Debye length. Here, we explore the consequences of this underscreening for soft-matter and colloidal systems by investigating the stability of nanoparticle dispersions, the self-assembly of ionic surfactants, and the thickness of soap films. In each case, we find clear evidence of re-entrant properties due to underscreening at high salt concentrations. Our results show that underscreening in concentrated electrolytes is a general phenomenon and is not dependent on confinement by macroscopic surfaces. The stability of systems at very high salinity due to underscreening may be beneficially applied to processes that currently use low-salinity water.

Absence of anomalous underscreening in highly concentrated aqueous electrolytes confined between smooth silica surfaces

Recent surface forces apparatus experiments that measured the forces between two mica surfaces and a series of subsequent theoretical studies suggest the occurrence of universal underscreening in highly concentrated electrolyte solutions. We performed a set of systematic Atomic Force Spectroscopy measurements for aqueous salt solutions in a concentration range from 1 mM to 5 M using chloride salts of various alkali metals as well as mixed concentrated salt solutions (involving both mono- and divalent cations and anions), that mimic concentrated brines typically encountered in geological formations. Experiments were carried out using flat substrates and submicrometer-sized colloidal probes made of smooth oxidized silicon immersed in salt solutions at pH values of 6 and 9 and temperatures of 25 °C and 45 °C. While strong repulsive forces were observed for the smallest tip-sample separations, none of the conditions explored displayed any indication of anomalous long range electrostatic forces as reported for mica surfaces. Instead, forces are universally dominated by attractive van der Waals interactions at tip-sample separations of ≈2 nm and beyond for salt concentrations of 1 M and higher. Complementary calculations based on classical density functional theory for the primitive model support these experimental observations and display a consistent decrease in screening length with increasing ion concentration.

Hanging meniscus configuration for characterizing oxygen-reduction electrocatalysts in highly concentrated electrolytes

• Hanging meniscus configuration method was newly developed for porous catalysts. • This method evaluates oxygen reduction activity in highly concentrated electrolyte. • This method complements conventional rotating disk electrode (RDE) method. Oxygen reduction reaction (ORR) in metal-air batteries or fuel cells often require highly concentrated electrolyte for higher conductivity and electrochemical stability. However, conventional rotating disk electrode (RDE) method is ineffective to evaluate ORR activity in the real systems, because the scarce dissolved oxygen in highly concentrated electrolyte fails to provide significant ORR on RDE. Herein, we report a hanging meniscus configuration method for evaluating the electrocatalytic activity in highly concentrated electrolyte solutions, utilizing atmospheric oxygen through the triple-phase boundary. The newly developed method evaluated the ORR activity of silver and platinum catalysts in highly concentrated KOH electrolyte for zinc-air batteries, enabling the characterization in more realistic experimental condition.

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+.

Kinetic and mechanistic investigation of geosmin and 2-methylisoborneol degradation using UV-assisted photoelectrochemical

The taste and odor (T&O) problem represented by 2-methylisoborneol (2-MIB) and geosmin (GSM) in water is the multiple undesirable substances in the drinking water and the aquatic industry. In this study, the UV-assisted photoelectrochemical, a prospective advanced oxidation process (AOP), was evaluated for the degradation of 2-MIB and GSM. In contrast to UV photochemical and electrochemical, the degradation ratio of GSM (2-MIB) increase to 96% (95%) in 25 min. The removal ratio and rate depended on reaction time, electrolyte concentration, current density, and water quality parameters (e.g. pH, HCO3−, natural organic matter, and tap water). Among these parameters, a high concentration of electrolyte and acidic solutions could accelerate the rate and increase the ratio, while alkaline conditions and the impurity content had negative effects. Furthermore, the significant role of various reactive species (e.g. HO∙, Cl, ClO, etc) were highlighted by scavenging experiments. Complex free radicals exist was further verified by electron paramagnetic resonance spectroscopy (EPR) experiments. The intermediates were identified and the possible degradation pathways during the UV-assisted photoelectrochemical reactions of both compounds were proposed. Overall, the UV-assisted photoelectrochemical is beneficial to the removal of GSM and 2-MIB in water.

The effect of high-molecular compounds nature on the electroflotation removal of the metal compounds from electrolyte solutions

• Removal of heavy metal ions (Fe (III), Ni (II), Cu (II), Pb (II) and Zn (II)) as part of the multi-component system from electrolyte solutions by means of electroflotation and filtration with presence of the high-molecular compounds (HMC) of different nature. • Effect of solution pH, metal and electrolyte concentration on the dispersed properties and electrokinetic potential of the dispersed low-soluble metal compounds and efficiency of their electroflotation removal. • Effect of HMC (flocculants and surfactants) with the anionic, cationic, non-ionic and amphoteric nature upon the dispersed properties, electrokinetic potential and efficiency of electroflotation and electroflotation with subsequent filtration removal of the low-soluble metal compounds particles in electrolyte solutions. • The efficiency of electroflotation removal of heavy metals from concentrated electrolyte solutions with the anionic HMS runs to 98–99% for all components. The process of removal of heavy metal ions as part of the multi-component system from electrolyte solutions by means of electroflotation and filtration with presence of the high-molecular compounds (HMC) of different nature has been studied. Studies were performed in solutions with ions of iron (III), nickel (II), copper (II), lead (II) and zinc(II), as well as NaCl and Na 2 SO 4 (pH 9.5–10.5). It has been shown that addition of the sulphate and sodium chloride mixture in 50 g/L concentration to solutions containing metal ions with total 0.1 g/L concentration reduced the absolute value of dispersed phase ζ-potential from −2.5 mV to −6 mV. The dispersed phase size is getting smaller, two particle types appear in the solution − 54 µm (72% of the total particle quantity) and 5.0 µm (28%). Rise of the total metal ion concentration up to 0.2 g/L results in reduction of the dispersed phase size: 1.5 µm (63%) and 46 µm (37%) particles prevail, the ζ-potential is reduced slightly (-7.1 mV). In this case, the rate of removal of the studied metals by mean of electroflotation is not more than 32–46%. Addition of the anionic HMS (flocculants and surfactants) to the solutions with the total concentration of metal ions of 0.2 g/L and salts of 50 g/L results in rise of dispersed phase ζ-potential and tends its value to the isoelectric point (±0 mV). When the cationic surfactants are added, the particle surface is recharged, the ζ-potential acquires the + values (5.3–7.8 mV). It has been concluded, that the rate of electroflotation removal of heavy metals from concentrated electrolyte solutions with the anionic HMS runs to 98–99% for all components. Subsequent solution filtration with the anionic flocculant allows for reduction of the residual concentration to the following values: 0.5∙10 -4 g/L for Fe (III), Cu (II) and Pb (II) ions and. 0.1∙10 -4 g/L for for Ni (II), 0.14∙10 -3 g/L for Zn (II). Addition of the cationic, non-ionic and amphoteric surfactants does not result in increase of electroflotation process efficiency.

Electrochemical method of obtaining copper (II) oxide powders in alkaline electrolyte

Within the framework of these studies, an electrochemical method for the synthesis of highly dispersed powders of copper compounds in aqueous solutions of alkalis is presented. The factors influencing the rate of production of nanoscale copper (II) oxide particles are determined. It is shown that during the anodic oxidation of copper by direct current, the speed of highly dispersed powders formation depends on current density, the nature of alkali cation, and the concentration of electrolyte solution. The mass loss of copper electrodes in NaOH solution is higher than in solutions of potassium hydroxide and lithium hydroxide by 10% and 12%, respectively. This experiment suggests that the studied alkalis act similarly on the anodic behavior of copper and the nature of cation does not significantly affect the speed of anodes destruction. The change in the concentration of alkali solution practically does not affect the mass loss of copper electrodes. The speed of copper oxidation remains almost constant over time, but noticeable weight loss and, accordingly, the speed of copper dissolution is achieved within 15 minutes. The speed of copper oxidation does not depend on current density. It is determined by the amount of electricity that has passed. The current density of 1 A/cm2 can be considered optimal.

Optically Transportable Optofluidic Microlasers with Liquid Crystal Cavities Tuned by the Electric Field.

Liquid crystal microdroplets with readily adjustable optical properties have attracted considerable attention for building reconfigurable optofluidic microsystems for sensing, imaging, and light routing applications. In this quest, development of active optical microcavities serving as versatile integrated sources of coherent light and ultra-sensitive environmental sensors has played a prominent role. Here, we study transportable optofluidic microlasers reversibly tunable by an external electric field, which are based on fluorophore-doped emulsion droplets of radial nematic liquid crystals manipulated by optical tweezers in microfluidic chips with embedded liquid electrodes. Full transparency of the electrodes formed by a concentrated electrolyte solution allows for applying an electric field to the optically trapped droplets without undesired heating caused by light absorption. Taking advantage of independent, precise control over the electric and thermal stimulation of the lasing liquid crystal droplets, we characterize their spectral tuning response at various optical trapping powers and study their relaxation upon a sudden decrease in the trapping power. Finally, we demonstrate that sufficiently strong applied electric fields can induce fully reversible phase transitions in the trapped droplets even below the bulk melting temperature of the used liquid crystal. Our observations indicate viability of creating electrically tunable, optically transported microlasers that can be prepared on-demand and operated within microfluidic chips to implement integrated microphotonic or sensing systems.