Electrolyte Solution Research Articles

CoFe Hydroxide Nanopheres for Enhanced Alkaline Splitting and Seawater Oxidation:Anion Doping Effects of Fluorine and Carbonate

Green hydrogen production can be achieved through electrolysis of fresh water or the use of renewable energy to electrolyze seawater. However, due to the low activity and poor stability of oxygen evolution reaction catalysts, direct electrolysis of alkaline seawater faces significant challenges. Herein, The catalyst F‐CoFe(OH)‐CO3/NF with three‐dimensional nanosphere structure was prepared, The introduction of CO32‐ into the intermediate layer of CoFe Hydroxide improves the corrosion resistance of alkaline electrolyte and the doping of F‐ is to design three‐dimensional layered nanostructures, increase the active site, and accelerate the diffusion of the electrolyte. By in situ Raman analysis, partial oxidation of CoFe hydroxide to CoFe (oxy)hydroxide as the active center can accelerating the adsorption of oxygen‐related intermediates. In 1M KOH, it requires overpotentials of 210 mV and 251mV to drive current densities of 10 and 100 mA cm‐2, respectively. And it remained stable at the current density of 100 mA cm‐2 for 120 h in 1M KOH. F‐CoFe(OH)‐CO3/NF can also catalyzes the decomposition of electrolytic seawater. Compared with hydroxide, anion‐doped carbonate hydroxide is more efficient and stable in electrolyte solution, which is of great importance for the development of a new stable electrocatalyst for water decomposition.

Electrochemical Reactions Affected by Electric Double Layer Overlap in Conducting Nanopores.

When a potential is applied to an electrode immersed in an electrolyte solution, ions with opposite charges accumulate around the electrode, forming an electrical double layer (EDL). Unlike flat electrodes, nanoporous electrodes with pore sizes comparable to the EDL thickness experience overlapping EDLs, altering the electrochemically effective surface area. Although previous research has primarily examined the ion charging dynamics and EDL formation in nanoporous electrodes, the impact of EDL overlap on Faraday reactions remains underexplored. In this study, we examined the influence of EDL overlap on electrochemical reactions within nanoporous electrodes using chronoamperometry and DC and AC voltammetry. We used the electrolyte concentration, measurement duration, overpotential, and electrode material as variables to determine the relationship between the extent of EDL overlap and the electrochemical reaction. The electrolyte concentration-dependent electrochemical reaction due to the EDL overlap was more pronounced for electrodes with faster potential changes, shorter measurement times, lower overpotentials, and slower catalytic activity. This is a unique nanoporous electrochemical phenomenon that is not observed on flat electrodes. These findings provide insight into the utilization of nanoporous electrodes in catalytic and sensor applications.

Interfacial [S─Cu─C] Bonds Induced π-d Electron Coupling Toward Modulating Charge Transfer for Efficient Solar Water Oxidation.

Regulating the interfacial electric field to achieve rapid charge transfer is crucial for superior photoelectrochemical water splitting. Herein, the ultra-thin hydrogen-substituted graphdiyne (HsGDY) is precisely assembled on the surface of CdS nanorod array (Cu-CdS-HsGDY) by an in situ polymerization strategy. The strong π-d electron coupling is aroused by the delocalized π electrons of HsGDY and the delocalized d electrons of CdS through the interfacial [S─Cu─C] bonds. The strong interfacial electric field can effectively promote the charge localization distribution and reduce the charge transfer resistance. The optimized Cu-CdS-HsGDY photoanode obtain a photocurrent density as high as 4.83 mA cm-2 at 1.23 V versus reversible hydrogen electrode in neutral electrolyte solution under AM 1.5G illumination, which is 6.8 times that of the pristine CdS. Moreover, the photoanode maintains an initial photocurrent density of 84% within 4 h without any assistance of sacrificial agents, which is a rather competitive performance of similar sulfide photoanodes. The mechanism of strong π-d electron coupling on interfacial charge transfer and surface reaction kinetics is investigated by transient spectroscopy measurements, density functional theory calculation, and finite element simulation analysis. This work provides new insights into designing a reasonable interface structure to regulate charge transfer for achieve efficient PEC water splitting.

Intramolecular Polarization Contributions to the pKa's of Carboxylic Acids Through the Chain Length Dependence of Vibrational Tag-Shifts in Cryogenically Cooled Pyridinium-(CH2)n-COOH (n = 1-7) Cations.

The pKa's of acids are known to depend on the ionic strength of an electrolyte solution, an effect that qualitatively results from electrostatic interactions of the acid and conjugate base with proximal ions. Here, we explore an intramolecular variation on this theme in which a carboxylic acid group is tethered to a pyridinium cationic charge center with increasingly long alkyl linkages in the series Py+-(CH2)n-COOH, with n = 1-7. The effective acidities of the carboxylic acid group in the isolated cations are determined by recording the red-shifts in the frequencies of the acid OH stretches upon attachment to D2 and N2 molecules, measured by using cryogenic ion spectroscopy. The short chains indeed lead to substantial increases in acidity, with the effect falling off in the range of n = 4-5. The response of the CO stretch on the acid head group is surprisingly strong and, in contrast to the expected red shift of the OH, displays a blue shift as the chain length is reduced. Electronic structure calculations recover these trends and indicate that the proximal cationic charge center acts to draw electron density away from the acid C═O bond. This acts to blue-shift the CO stretch while weakening the C-C bond that attaches the head group to the chain.

Polymer Electrolytes for Supercapacitors

Because of safety concerns associated with the use of liquid electrolytes and electrolyte solutions, options for non-liquid materials like gels and polymers to be used as ion-conducting electrolytes have been explored intensely, and they attract steadily growing interest from researchers. The low ionic conductivity of most hard and soft solid materials was initially too low for practical applications in supercapacitors, which require low internal resistance of a device and, consequently, highly conducting materials. Even if an additional separator may not be needed when the solid electrolyte already ensures reliable separation of the electrodes, the electrolytes prepared as films or membranes as thin as practically acceptable, resistance may still be too high even today. Recent developments with gel electrolytes sometimes approach or even surpass liquid electrolyte solutions, in terms of effective conductance. This includes materials based on biopolymers, renewable raw materials, materials with biodegradability, and better environmental compatibility. In addition, numerous approaches to improving the electrolyte/electrode interaction have yielded improvements in effective internal device resistance. Reported studies are reviewed, material combinations are sorted out, and trends are identified.

Fundamentals and Implication of Point of Zero Charge (PZC) Determination for Activated Carbons in Aqueous Electrolytes.

The point of zero charge (PZC) is a crucial parameter for investigating the charge storage mechanisms in energy storage systems at the molecular level. This paper presents findings from three different electrochemical techniques, compared for the first time: cyclic voltammetry (CV), staircase potentio electrochemical impedance spectroscopy (SPEIS), and step potential electrochemical spectroscopy (SPECS), for two activated carbons (ACs) with 0.1molL-1 aqueous solution of LiNO3, Li2SO4, and KI. The charging process of AC operating in aqueous electrolytes appears as a complex phenomenon - all ionic species take an active part in electric double-layer formation and the ion-mixing zone covers a wide potential region. Therefore, the so-called PZC should not be considered as an absolute one-point potential value, but rather as a range of zero charge (RZC). SPECS technique is found to be a universal and fast method for determining RZC, as applied here together with the EQCM. In most cases, the RZC covers a potential range from ≈100 to ≈200mV and the correlation of the range with the carbon microtexture is clear, highlighting the role of the ion-sieving effect. It is postulated that PZC for porous materials in aqueous electrolytic solutions should be considered instead as RZC.

Sorption-desorption of rare earth metal cations by ferromanganese crusts of Govorov’s guyote of the Magellanic Mountains of the Pacific Ocean

The article presents the results of experimental studies on the sorption and desorption of rare earth metal (REM) cations by cobalt-rich ferromanganese crusts (CMC) of Govorov’s guyot. It has been established that the sorption of REM cations occurs on the ore minerals KMK – Fe-vernadite, vernadite, Mn-feroxygite, goethite. The crusts are characterized by a high exchange capacity – 1.78–3.57 mg-eq/g, which increases in a series: (Dy Gd Lu Sm Nd Y, La Eu) Ce. The sorption of REM cations proceeds by an ion exchange equivalent irreversible mechanism. The exchange complex of ore minerals consists of Na+, K+, Ca2+, Mg2+ cations, which contribute 97‒98% to their total capacity. The crusts are characterized by the group sorption of REM cations from multicomponent aqueous solutions of metal salts. The selectivity of ore manganese and ferruginous minerals of crusts to REM cations is significantly higher than to the main cations of ocean water. From experimental data on the desorption of sorbed REM cations with NaCl solution, their irreversible absorption by ore minerals follows, and the strengthening of the chemical bond of sorbed REM cations with the main structural elements of these minerals over time. An important property of ore minerals, primarily manganese minerals, is their chemical and structural stability in aqueous solutions of electrolytes. This suggests the repeated use of ferromanganese crusts as sorbents of REM cations.

Physicochemical and electrical properties of DPPC bilayer membranes in the presence of oleanolic or asiatic acid

This study aimed to investigate the effect of selected compounds from the group of triterpene sapogenins on model phosphatidylcholine membranes. Two types of biological membrane model systems were used in the work, i.e., liposomes (microelectrophoresis method) and spherical bilayers (interfacial tension method). Each model was modified with the tested sapogenin compounds, and the change in their physicochemical and electrical parameters was analyzed. Parameters characterizing the equilibrium in the membrane of 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC)-oleanolic acid (OA) and DPPC-asiatic acid (AA) were determined). Based on the Young-Laplace equation, the interfacial tensions of spherical lipid bilayers were measured. The formation of 1:1 complexes was assumed in the DPPC-OA and DPPC-AA membrane systems, and the parameters characterizing the interactions in the formed complexes were calculated. Microelectrophoresis was used to study the surface charge density of lipid membranes. These values were obtained from electrophoretic mobility data using Smoluchowsky’s equation. The influence of pH on the electrolyte solution and the composition of the membranes was investigated. The results indicate that modifying DPPC membranes with selected triterpene sapogenins, both OA and AA, causes changes in the surface charge density and shifts of the isoelectric point. Data presented in this work, obtained through mathematical derivation and confirmed experimentally, are of great importance for interpreting phenomena occurring in lipid membranes. A quantitative description of equilibria between phosphatidylcholine and sapogenins lets us understand the processes on the membrane surface. The equilibria are particularly significant from the standpoint of cell functioning. Phosphatidylcholine-sapogenin interactions modulate a range of physicochemical properties of membranes, and they are important in the course of the multiple processes involving membranes in the living cell (e.g., transport mechanism).

Grain-Boundary-Rich Interphases for Rechargeable Batteries.

The formation of stable interphases on the electrodes is crucial for rechargeable lithium (Li) batteries. However, next-generation high-energy batteries face challenges in controlling interphase formation due to the high reactivity and structural changes of electrodes, leading to reduced stability and slow ion transport, which accelerate battery degradation. Here, we report an approach to address these issues by introducing multicomponent grain-boundary-rich interphase that boosts the rapid transport of ions and enhances passivation toward prolonged lifespan. This is guided by fundamental principles of solid-state ionics and geological crystallization differentiation theory, achieved through improved solvation chemistry. Demonstrations showcase how the introduction of the interphase substantially impacts the Li-ion transport across the interphase and the electrode-electrolyte compatibility in cost-effective electrolyte solutions optimized with multiple Li salts. The resulting interphases feature microstructures rich in inorganic grain boundaries with a diverse array of nanosized grains, presenting enhanced Li-ion transport. Comprehensive analyses revealed that this realizes remarkable electrochemical stability over extended cycling periods by inhibiting electrode corrosion, thus holding promise for high-capacity thin-Li-metal, Si-based anodes, and even Li-free anodes when paired with high-capacity oxide cathodes. This work opens new avenues to customize protective interphases on high-capacity electrodes, promoting the development of batteries with the highest energy density using cost-effective electrolytes.

Ion-Specific Surface Tension of Aqueous Electrolyte Solutions: Analytical Insights from a Restricted Primitive Model.

The ion-specific surface tension of aqueous electrolyte solutions is of fundamental importance in physical chemistry, solution chemistry, electrochemistry, and biochemistry, yet it remains a challenge to be qualitatively predicted. In this work, an analytical theory of ion-specific surface tension is developed. By modeling the solution to a restricted primitive model (RPM), the surface tension increment of the electrolyte solution reduces to the surface tension of the RPM, which is further determined analytically by using the integral equation theory and the morphological thermodynamics theory. According to our formula, the surface tension increment of the electrolyte solution consists of a dominant and positive hard sphere contribution, which depends on the salt concentration, and a secondary electrostatic contribution, which depends on the inverse Debye length and the salt concentration. Our theory is applied to 1:1, 2:2, 1:2, 2:1, 3:1, and 3:2 electrolyte solutions with typical salt concentrations up to several mol/L and compared with experimental data. Without introducing any adjustable parameters, our theory leads to a good prediction of the surface tension increment of more than 50 kinds of aqueous solutions. Such a good agreement demonstrates the great potential of our theory for a fundamental understanding of specific ion effects in a variety of electrolyte solutions.

Modified Debye-Hückel-Onsager theory for electrical conductivity in aqueous electrolyte solutions: Account of ionic charge nonlocality.

This paper presents a mean field theory of electrolyte solutions, extending the classical Debye-Hückel-Onsager theory to provide a detailed description of the electrical conductivity in strong electrolyte solutions. The theory systematically incorporates the effects of ion specificity, such as steric interactions, hydration of ions, and their spatial charge distributions, into the mean-field framework. This allows for the calculation of ion mobility and electrical conductivity, while accounting for relaxation and hydrodynamic phenomena. At low concentrations, the model reproduces the well-known Kohlrausch's limiting law. Using the exponential (Slater-type) charge distribution function for solvated ions, we demonstrate that experimental data on the electrical conductivity of aqueous 1:1, 2:1, and 3:1 electrolyte solutions can be approximated over a broad concentration range by adjusting a single free parameter representing the spatial scale of the nonlocal ion charge distribution. Using the fitted value of this parameter at 298.15K, we obtain good agreement with the available experimental data when calculating electrical conductivity across different temperatures. We also analyze the effects of temperature and electrolyte concentration on the relaxation and electrophoretic contributions to total electrical conductivity, explaining the underlying physical mechanisms responsible for the observed behavior.

Achieving Excellent H2 Evolution Activity of Silver Nanocatalyst by a Simple Electrochemical Treatment Process.

Silver nanoparticles (AgNPs) were synthesized in an aqueous solution via the reduction of AgNO3 employing citrate reducing agent. The resultant AgNPs were first assayed for the catalytic H2 evolution in an acidic electrolyte, namely pH 0.3 H2SO4 solution, showing negligible activity. The AgNPs were then conditioned in the same electrolyte solution while repeating the cyclic potential polarization between -0.25 V and 0.95 V (or 1.8 V) versus RHE. Effects of the electrochemical treatment to the morphology, crystalline, surface chemistry and H2 evolution catalytic activity of AgNPs were examined. It was found that the electrochemical treatment remarkably boosted the H2 evolution catalytic activity of AgNPs. The electrochemically activated AgNPs represents an attractive Pt-free catalyst for the H2 evolution in acidic medium.

Study on the Mechanism of Temperature Effect on SO2 Electrochemical Gas Sensor

Abstract Temperature can affect the measurement values of electrochemical gas sensors, increasing measurement errors. The influence mechanism of temperature on electrochemical gas sensors was studied based on Fick's first law and the limit diffusion current formula. Temperature affects the sensitive characteristics of sensor by changing the diffusion coefficient Dl1 of SO2 in air, the Henry's coefficient KH of SO2 dissolved in water and the water content of the electrolyte solution. When the temperature increases, the degree of influence of Henry's coefficient KH and the reduction of water content is greater than the degree of influence on the increase in diffusion coefficient, which decreases the sensor measurement value. The results of the temperature experiments show that the optimal temperature range for the sensor is -25 °C to 50 °C, and the average measurement error in this temperature range is less than 20%. When the temperature exceeds 50 ℃, it will cause a reduction in the evaporation of water in the electrolyte solution, leading to a rapid increase in the measurement error. The structure of the sensor can be improved by adding a water retention layer inside the sensor to supplement the electrolyte solution with water, so as to reduce the measurement error.

Electrochemical Characteristics of Ambarella Peel Waste as Liquid Electrolyte for Zn-Cu Biobattery

This study focuses on the electrochemical characterization of Zn-Cu bio-battery cells utilizing electrolytes derived from ambarella peel waste. The primary objectives are to determine the half-cell and full-cell characteristics of these bio-batteries at various concentration ratios and to identify the optimal concentration ratio for maximum performance. Cyclic voltammetry analysis of the half-cells revealed an oxidation peak at 0.5 V vs Ag/AgCl, corresponding to the conversion of uronic acid to aldaric acid. Additionally, two reduction peaks were observed: hydrogen ion reduction to H2 at 0 V vs Ag/AgCl and water reduction at –0.42 V vs Ag/AgCl. The rate-determining step analysis indicated that the redox reactions in the ambarella peel electrolyte solution were surface reactions. The highest rate constant (ks) of 0.722 ± 0.05 s–1 was observed at a 1:2 concentration ratio. This ratio also resulted in the highest battery capacity of 0.0816 mAh and the maximum power density of 16.13 mW/m2. The study concluded that the 1:2 concentration ratio of ambarella peel waste electrolyte solution is optimal, outperforming the 1:1 and 1:3 ratios in terms of battery capacity and power density.

Selective ion transport through hydrated micropores in polymer membranes.

Ion-conducting polymer membranes are essential in manyseparation processes and electrochemical devices, including electrodialysis1, redox flow batteries2, fuel cells3 and electrolysers4,5. Controlling ion transport and selectivity in these membranes largely hinges on the manipulation of pore size. Although membrane pore structures can be designed in the dry state6, they are redefined upon hydration owing to swelling in electrolyte solutions. Strategies to control pore hydration and a deeper understanding of pore structure evolution are vital for accurate pore size tuning. Here we report polymer membranes containing pendant groups of varying hydrophobicity, strategically positioned near charged groups to regulate theirhydration capacity and pore swelling. Modulation of thehydrated micropore size (less thantwo nanometres) enables direct control over water and ion transport across broad length scales, as quantified by spectroscopic and computational methods. Ion selectivity improves in hydration-restrained pores created by more hydrophobic pendant groups. These highly interconnected ion transport channels, with tuned pore gate sizes, show higher ionic conductivity and orders-of-magnitude lower permeation rates of redox-active species compared with conventional membranes, enabling stable cycling of energy-dense aqueous organic redox flow batteries. This pore size tailoringapproach provides a promising avenue to membranes with precisely controlled ionic and molecular transportfunctions.

Comparison of Au Nanoparticle/Poly(9-vinylcarbazole) Thin-Film Electrogeneration at 3 Distinct Liquid/Liquid Interfaces: Water/1,2-Dichloroethane, /α,α,α-Trifluorotoluene, Or/Ionic Liquid.

Metal nanoparticle (NP) incorporated conductive polymer films are attractive for their mechanical stability for biomedical applications and as heterogeneous electrocatalysis materials. Novel approaches to generate these materials with tunable properties are still being sought. Herein, the interface between two immiscible electrolyte solutions (ITIES) has been employed as a molecularly sharp and reproducible platform for simultaneous Au NP and poly(9-vinylcarbazole) generation. Three interfaces have been compared, including between water|1,2-dichloroethane (w|DCE), water|α,α,α-trifluorotoluene (w|TFT), and water|ionic liquid (w|IL). In this case the IL was P8888TB (tetraoctylphosphonium tetrakis(pentafluorophenyl)borate). 9-Vinylcarbazole (VC) can polymerize via two routes, either propagating through the vinyl substituent or the aryl rings. The former gives rise to a white semiconducting polymer with a wide bandgap, while the latter produces a green, conducting polymer. External potential control through voltammetric cycling was found to generate the film more rapidly favoring heterogeneous electron transfer with formation of the green poly(VC) variant at the ITIES. This was a free-standing film that could be easily removed from the interface. In the absence of external control, white polymer crystals formed within the oil phase spontaneously likely via AuCl4- w → o transfer followed by a homogeneous electron transfer reaction mechanism. Scanning electrochemical microscopy probe approach curve experiments were used to quantify the electroactivity of the film and are complemented by direct conductivity measurements.

Intercalation Behavior of a Spiro-bipyrrolidinium Cation into a Graphite Electrode from Dimethyl/Propylene Carbonates.

Quaternary ammonium-graphite intercalation compounds (QA+-GICs) are promising negative electrode materials in dual-carbon batteries by virtue of safety, low cost, and environmental friendliness. However, the intercalation behavior of QA+ into graphite electrodes in mixed solvents has never been reported. Herein, spiro-(1,1')-bipyrrolidinium tetrafluoroborate dissolved in a dimethyl/propylene carbonate (DMC/PC) binary solvent system was employed in graphite/activated carbon (AC) capacitors. The storage behavior of the spiro-(1,1')-bipyrrolidinium cation into graphite is very related to the solvent composition of the electrolyte solutions. In situ X-ray diffraction tests revealed that the graphite electrodes can form different QA+-GICs during cycling, which is a key factor influencing the electrochemical performance of graphite/AC capacitors. Besides, the reversible thickness change of graphite in graphite/AC capacitors with different electrolytes during the charge-discharge process was also addressed. These findings provide sound evidence for the co-intercalation of the solvent with the cation.

Derivation of the General Equation of State for a Doped Semiconductor. The Equation is Solved Concerning the Electron Concentration in the Conduction Band for Different Concentrations and Properties of Doping Substances

The paper examines the state of a system consisting of a crystalline semiconductor doped with donor and acceptor impurities. The General Equation of State of the system is derived. Methods are proposed to solve the general equation for the concentration of electrons or holes in a semiconductor. The identity of the General Equations of State of semiconductors and aqueous solutions of electrolytes is discussed. An assumption is made about the practical application of the found relationships.

High-energy Mn2V2O7//C asymmetric supercapacitors in aqueous/organic hybrid electrolytes

The demand for advanced energy storage devices, such as high-energy density supercapacitors, has spurred efforts to develop new environmentally friendly and efficient electrode materials and electrolyte solutions for sustainable development. A prominent strategy is the fabrication of high-voltage and energy-density asymmetric supercapacitors (AS). In this study, dimanganese divanadate (Mn2V2O7, MVO) particles were synthesized via a hydrothermal process and used as pseudocapacitive electrodes for AS. The pseudocapacitive MVO electrode offered synergistic advantages of reversible surface or near-surface Faradaic reactions for charge storage. Another approach to address the challenges of limited energy density in supercapacitors was modifying the electrolyte solution to widen the operating voltage window and increase energy density. A hybrid electrolyte solution of 5 M sodium perchlorate (NaClO4) in a mixture of (2:1) volume ratio of acetonitrile (AN) and water (H2O) was introduced to expand the voltage window in the AS. The fabricated AS with MVO as a pseudocapacitive electrode and activated carbon as a double-layer capacitive electrode operated in a voltage window > 2.0 V with the hybrid electrolyte. The AS device exhibited a capacitance of 156.9 F g−1 at 0.1 A g−1 and a high energy density of 87.2 Wh kg−1, surpassing the carbon-based symmetric supercapacitor (58.9 Wh kg−1). Furthermore, the pseudocapacitive supercapacitor showed exceptional long-term stability over 50,000 cycles. Structural and surface characterization of the MVO electrode after CV testing validated that the charge storage mechanism in Mn2V2O7//C was a surface-controlled process. The performance of the AS pouch cell revealed the great promise of the pseudocapacitive electrode in practical applications.

Performance of Single Nanopore and Multi-Pore Membranes for Blue Energy.

The salinity gradient power extracted from the mixing of electrolyte solutions at different concentrations through selective nanoporous membranes is a promising route to renewable energy. However, several challenges need to be addressed to make this technology profitable, one of the most relevant being the increase of the extractable power per membrane area. Here, the performance of asymmetric conical and bullet-shaped nanopores in a 50 nm thick membrane are studied via electrohydrodynamic simulations, varying the pore radius, curvature, and surface charge. The output power reaches ~60 pW per pore for positively charged membranes (surface charge σw=160 mC/m2) and ~30 pW for negatively charges ones, σw=-160 mC/m2 and it is robust to minor variations of nanopore shape and radius. A theoretical argument that takes into account the interaction among neighbour pores allows to extrapolate the single-pore performance to multi-pore membranes showing that power densities from tens to hundreds of W/m2 can be reached by proper tuning of the nanopore number density and the boundary layer thickness. Our model for scaling single-pore performance to multi-pore membrane can be applied also to experimental data providing a simple tool to effectively compare different nanopore membranes in blue energy applications.