Aqueous Electrolyte Solutions Research Articles

Structural Study of Aqueous Electrolyte Solution by MeV Liquid Electron Scattering.

The impact of ions on water has long been a subject of great interest, as it is closely tied to the hydration structure, dynamics, and properties of electrolyte solutions. Over centuries of investigation, the influence of ions on water's structure remains highly debated. Prevailing techniques, such as neutron and X-ray scattering, primarily focus on the microscopic structure of salt solutions at very high concentrations, mostly above 1 mol/L. In this study, we measured the structure of aqueous potassium iodide (KI) and potassium chloride (KCl) solutions using MeV liquid electron scattering (MeV-LES) across a concentration range of 0.10 to 0.75 mol/L. The obtained results provide detailed insights into the variations in ion-oxygen and oxygen-oxygen correlations as a function of concentration. The observed structural differences between KI and KCl solutions are in line with the structure maker/breaker theory, which suggests that iodide ions exert a more pronounced effect than chloride ions on disrupting the water shell. This work demonstrates the potency of MeV-LES for investigating the atomic structure in liquids, augmenting the modern analytical toolbox.

X-ray Induced Cycling of Rare-Earth Elements between Bulk and Interfacial Liquid.

Reversible cycling of rare-earth elements between an aqueous electrolyte solution and its free surface is achieved by X-ray exposure. This exposure alters the competitive equilibrium between lanthanide ions bound to a chelating ligand, diethylenetriamine pentaacetic acid (DTPA), in the bulk solution and to insoluble monolayers of extractant di-hexadecyl phosphoric acid (DHDP) at its surface. Evidence for the exposure-induced temporal variations in the lanthanide surface density is provided by X-ray fluorescence near total reflection measurements. Comparison of results when X-rays are confined to the aqueous surface region to results when X-rays transmit into the bulk solution suggests the importance of aqueous radiolysis in the adsorption cycle. Amine binding sites in DTPA are identified as a likely target of radiolysis products. The molecules DTPA and DHDP are like those used in the separation of lanthanides from ores and in the reprocessing of nuclear fuel. These results suggest that an external source of X-rays can be used to drive rare-earth element separations. More generally, use of X-rays to controllably dose a liquid interface with lanthanides could trigger a range of interfacial processes, including enhanced metal ion extraction, catalysis, and materials synthesis.

Simulating the Competitive Ion Pairing of Hydrated Electrons with Chaotropic Cations.

Experiments show that the absorption spectrum of the hydrated electron (ehyd-) blue-shifts in electrolyte solutions compared with what is seen in pure water. This shift has been assigned to the ehyd-'s competitive ion-pairing interactions with the salt cation relative to the salt anion based on the ions' positions on the Hofmeister series. Remarkably, little work has been done investigating the ehyd-'s behavior when the salts have chaotropic cations, which should greatly change the ion-pairing interactions given that the ehyd- is a champion chaotrope. In this work, we remedy this by using mixed quantum/classical simulations to analyze the behavior of two different models of the ehyd- in aqueous RbF and RbI electrolyte solutions as a function of salt concentration. We find that the magnitude of the salt-induced spectral blue-shift is determined by a combination of the number of chaotropic Rb+ cations near the ehyd- and the number of salt anions near those cations so that the spectrum of the ehyd- directly reflects its local environment. We also find that the use of a soft-cavity ehyd- model predicts stronger competitive interactions with Rb+ relative to I- than a more traditional hard cavity model, leading to different predicted spectral shifts that should provide a way to distinguish between the two models experimentally. Our simulations predict that at the same concentration, salts with chaotropic cations should produce larger spectral blue-shifts than salts with kosmotropic cations. We also found that at high salt concentrations with chaotropic cations, the predicted blue-shift is greater when the salt anion is kosmotropic instead of chaotropic. Our goal is for this work to inspire experimentalists to make such measurements, which will help provide a spectroscopic means to distinguish between simulations models that predict different hydration structures for the ehyd-.

A flexible solid-state asymmetric supercapacitor device comprising cobalt hydroxide and biomass-derived porous carbon.

Development in the field of alternative and renewable energy sources is becoming necessary considering the current energy demands of the growing technologies. The main challenge associated with the produced energy is to store it for future use, such that it can be used when needed. Supercapacitors are among the electrochemical energy storage systems that provides higher power density, faster charging-discharging, high specific capacitance (C S), and long cycling life. Herein, the fabrication of a flexible solid-state asymmetric supercapacitor (ASC) device is reported, where Co(OH)2 hollow spheres and biomass-derived porous carbon (PC) are the cathode and anode, respectively. Co(OH)2 is a highly redox active material, whereas PC is an electric double-layer capacitive (EDLC) material. In this device, aqueous KOH solution (electrolyte) encapsulated in PVA gel (separator) was used to bind the electrodes. This Co(OH)2//PC ASC device exhibited a high C S of 260 F g-1 (at 2 A g-1). It retained ∼91% of the initial C S value (at 6 A g-1) till ∼5000 cycles. Electrochemical impedance spectroscopy (EIS) study confirmed low internal resistance (0.95 Ω) and charge transfer resistance (1.41 Ω) values of Co(OH)2//PC. These results indicate that the high electron transfer process in the electrode-electrolyte interface during the electrochemical reaction, which is responsible for the excellent performance of this ASC device. The high-performance Co(OH)2//PC ASC device exhibited an energy density of 76.7 W h kg-1 at a power density of 1416.9 W kg-1. To demonstrate its practical use, LED lights were illuminated using this Co(OH)2//PC ASC device.

New Mn Electrochemistry for Rechargeable Aqueous Batteries: Promising Directions Based on Preliminary Results

Aqueous batteries with metal anodes exhibit robust anodic capacities, but their energy densities are low because of the limited potential stabilities of aqueous electrolyte solutions. Current metal options, such as Zn and Al, pose a dilemma: Zn lacks a sufficiently low redox potential, whereas Al tends to be strongly oxidized in aqueous environments. Our investigation introduces a novel rechargeable aqueous battery system based on Mn as the anode. We examine the effects of anions, electrolyte concentration, and diverse cathode chemistries. Notably, the ClO4‐based electrolyte solution exhibits improved deposition and dissolution efficiencies. Although stainless steel (SS 316 L) and Ni are stable current collectors for cathodes, they display limitations as anodes. However, using Ti as the anode resulted in increased Mn deposition and dissolution efficiencies. Moreover, we evaluate this system using various cathode materials, including Mn‐intercalation‐based inorganic (Ag0.33V2O5) and organic (perylenetetracarboxylic dianhydride) cathodes and an anion‐intercalation‐chemistry (coronene)‐based cathode. These configurations yield markedly higher output potentials compared to those of Zn metal batteries, highlighting the potential for an augmented energy density when using an Mn anode. This study outlines a systematic approach for use in optimizing metal anodes in Mn metal batteries, unlocking novel prospects for Mn‐based batteries with diverse cathode chemistries.

A3B Zn(II)-Porphyrin-Coated Carbon Electrodes Obtained Using Different Procedures and Tested for Water Electrolysis

In the context of water electrolysis being highlighted as a promising technology for the large-scale sustainable production of hydrogen, the water-splitting electrocatalytic properties of an asymmetrically functionalized A3B zinc metalated porphyrin, namely, Zn(II) 5-(4-pyridyl)-10,15,20-tris(4-phenoxyphenyl)-porphyrin, were evaluated in a wide pH range. Two different electrode manufacturing procedures were employed to outline the porphyrin’s applicative potential for the O2 and H2 evolution reactions (OER and HER). The electrode, manufactured by coating the catalyst on a graphite support from a dimethylsulfoxide solution, displayed electrocatalytic activity for the OER in an acidic electrolyte. An overpotential value of 0.44 V (at i = 10 mA/cm2) and a Tafel slope of 0.135 V/dec were obtained. The modified electrode that resulted from applying a Zn(II)-porphyrin-containing catalyst ink onto the same substrate type was identified as a bifunctional water-splitting catalyst in a neutral medium. OER and HER overpotentials of 0.78 and 1.02 V and Tafel slopes of 0.39 and 0.249 V/dec were determined. This is the first Zn(II)-porphyrin to be reported as a heterogenous bifunctional water-splitting electrocatalyst in neutral aqueous electrolyte solution and is one of very few porphyrins behaving as such. The TEM analysis of the porphyrin’s self-assembly behavior revealed a wide variety of architectures.

Understanding the Electric Double Layer at the Electrode-Electrolyte Interface: Part I - No Ion Specific Adsorption.

We present a comprehensive mean-field model that takes into account the key components of modern electrical double layer theory at the interface between an electrode and an electrolyte solution. The model considers short-range specific interactions between different species, including electrode-ion repulsion, the hydration of ions, dielectric saturation of solvent (water), and excluded volume (steric) interactions between species. By solving a modified Poisson-Boltzmann equation and using the appropriate results of quantum chemistry calculations on the hydration of ions, we can accurately approximate the differential capacitance profiles of aqueous electrolyte solutions at the boundary with a silver electrode. The specific interactions between the ions and the electrodes in the systems under considerationare assumed to be significantly weaker than their Coulomb interactions. A novel aspect of our research is the investigation of the impact of short-range ion-water interactions on the differential capacitance, which provides new insights into the behavior of the electrical double layer. This model holds the potential to be useful for electrochemical engineers working on the development of supercapacitors and related electrochemical energy storage devices. It serves as a basis for future modeling of electrolyte systems on real electrodes, especially in scenarios where chemical ion-electrode interactions are significant.

Peculiar photoelectrochemical activity of zinc oxide and tin dioxide

Zinc oxide thin films made by pulsed reactive magnetron sputtering combined with RF ECWR plasma on FTO or ITO substrates exhibit high photoelectrochemical activity for water splitting under UV light, but are unstable against photocorrosion. It can be suppressed by a protective layer of SnO2 made by atomic layer deposition. The SnO2 layer is quasi-amorphous in the as-received state, but the thermal treatment causes partial crystallization to cassiterite, without significant change of the optical band gap. Ferrocene in acetonitrile electrolyte solution is a useful redox probe for the blocking-quality tests of thin films of n-semiconductors. Both ZnO and SnO2 are sensitive to irreversible electrochemical doping at potentials negative to the flatband potential. The flipping of electrochemical work functions of the Zn-terminated (0001) and O-terminated (000–1) faces of ZnO (wurtzite) takes place in acetonitrile vs. aqueous electrolyte solutions. The potentials for photocurrent onset are near the flatband potentials in an aqueous electrolyte solution for both ZnO and SnO2.

Water Transport Management in a Bipolar Membrane for CO2 Electrolysis Application

Bipolar membranes (BPMs) offer significant potential for electrochemical technologies, especially in CO2 electrolysis. Their unique ability to create pH gradients provides optimum chemical microenvironments at the cathode and anode for efficient, cheap and sustainable CO2 electrolysis. However, state-of-the-art BPMs are limited in their performance due to phenomena such as membrane degradation and membrane dehydration leading to low ionic conductivity, and hence their complete potential for various electrochemical technologies is yet to be realized. Previous studies have identified water transport as one of the main factors limiting the performance of BPM. A multi-physics model of BPM can serve as a useful tool to gain a comprehensive understanding of different performance limiting factors and thereafter propose solutions to overcome these limitations. The goal of the present study is to provide model based design guidelines for a BPM that facilitates efficient water transport, making it a suitable candidate for integration into a zero-gap CO2 reduction electrolyzer operating at industrial-grade performance levels.We have built a 1-D continuum model of a BPM kept in an aqueous (bi)carbonate electrolyte solution, incorporating physical phenomena such as water-dependent transport of ions and neutral species, field-enhanced homogeneous reactions (water-dissociation and acid-base reactions) along with CO2 phase transfer reaction at the BPM-aqueous electrolyte interfaces. The continuum model employs Poisson-Nernst-Planck equations to resolve local chemical species concentration. The effect of the electric field on the equilibrium dissociation constants of various charge-generating homogenous reactions is incorporated. This becomes important especially at interfaces within the domain where a sharp increase in electric field is observed. Unlike previous modeling studies, we also incorporate mass-conservation equation for water transport to resolve local water concentration inside the BPM. Local water concentration influences the transport of species in the BPM through their water-dependent activity and diffusivity. The electric potential distribution is resolved by incorporating water-dependent local permittivity of the BPM.Our model investigates both the reverse and forward bias operational modes of the BPM. In alignment with the experimental observation, in the reverse bias regime, the model identifies a distinct initial phase where current density is limited, with the majority of the current carried by protons and hydroxide ions at low overpotentials. As the potential increases, there's a rapid increase in current density, indicating a breakdown regime caused by an electric field-enhanced water dissociation reaction at the BPM interface. At even higher potentials, the polarization curve enters a third phase where the current density saturates characterized by water transport limitation. This aspect of the BPM polarization curve is uniquely captured by our model. Conversely, in the forward bias mode, as expected we do not observe any limitations due to mass transport, since water is generated at the bipolar junction. Here, the model forecasts a saturation of CO2 in the electrolyte, leading to gas bubbles forming at the BPM interface. To address the issue of water transport limitation, we conduct various parametric studies focusing on different membrane characteristics, such as individual layer thicknesses and their ion exchange capacities. The outcomes of these analyses provide crucial guidelines for optimizing these parameters and enhancing water management in BPM-based systems.

Effect of dissolved KOH and NaCl on the solubility of water in hydrogen: A Monte Carlo simulation study.

Vapor-Liquid Equilibria (VLE) of hydrogen (H2) and aqueous electrolyte (KOH and NaCl) solutions are central to numerous industrial applications such as alkaline electrolysis and underground hydrogen storage. Continuous fractional component Monte Carlo simulations are performed to compute the VLE of H2 and aqueous electrolyte solutions at 298-423K, 10-400bar, 0-8 molKOH/kg water, and 0-6 molNaCl/kg water. The densities and activities of water in aqueous KOH and NaCl solutions are accurately modeled (within 2% deviation from experiments) using the non-polarizable Madrid-2019 Na+/Cl- ion force fields for NaCl and the Madrid-Transport K+ and Delft Force Field of OH- for KOH, combined with the TIP4P/2005 water force field. A free energy correction (independent of pressure, salt type, and salt molality) is applied to the computed infinite dilution excess chemical potentials of H2 and water, resulting in accurate predictions (within 5% of experiments) for the solubilities of H2 in water and the saturated vapor pressures of water for a temperature range of 298-363K. The compositions of water and H2 are computed using an iterative scheme from the liquid phase excess chemical potentials and densities, in which the gas phase fugacities are computed using the GERG-2008 equation of state. For the first time, the VLE of H2 and aqueous KOH/NaCl systems are accurately captured with respect to experiments (i.e., for both the liquid and gas phase compositions) without compromising the liquid phase properties or performing any refitting of force fields.

A Method for Efficiently Predicting the Radial Distribution Function and Osmotic Coefficients of Aqueous Electrolyte Solutions.

The prediction of the structural and thermodynamic properties of electrolyte solutions is critical for a huge range of practical situations where these solutions play a vital role. Theoretical models, such as the continuum solvent model, attempt to explain the behavior of solutions using a coarse-grained description of the interactions of species in the solution, whereas molecular simulations aim to directly compute the behavior of the solution, including the interactions between all ions and molecules in the system. Both methods have limitations: theoretical models are generally less accurate because they rely on assumptions, while molecular simulations require significant computational resources, particularly if higher accuracy is desired. To address these issues, we propose an affordable and effective method that combines the advantages of the modified Poisson-Boltzmann equation (MPBE) with classical molecular dynamics (MD) simulations to predict the radial distribution functions and thermodynamic properties of electrolyte solutions. We demonstrate a method of using the MPBE to compute the short-range potential of mean force (PMF) from the radial distribution functions (RDFs) and vice versa. Furthermore, we provide insights into the relationship between the RDFs and the short-range PMF based on the MPBE. Our analysis reveals that the effective short-range PMFs can be approximately calculated using low concentration simulations but the short-range PMFs are slightly concentration-dependent in simulations at higher concentrations. Additionally, we demonstrate that for concentrated solutions, osmotic coefficients can be calculated in agreement with experiment using a virial approach. This is based on the effective short-range PMFs and RDFs obtained from the MPBE method. Our proposed MPBE can therefore accelerate the calculation of the structural and thermodynamic properties of electrolyte solutions.

Binary aqueous solutions of choline salts: Determination and modelling of liquid density (298.15 or 313.15 K) and Vapour Pressure Osmometry (313.15 K)

Salts composed of the cholinium cation (such as choline hydroxide and choline chloride) have become one of the main reactants for the synthesis of greener ionic liquids, but, for a proper description of the aqueous solutions of these strong electrolytes by thermodynamic modelling, reliable data on liquid density (ρ) and vapour pressure (p) are needed, which are often unavailable. So, in this work, the liquid density (ρ) of binary aqueous solutions of choline bicarbonate ([Ch][Bic]), choline (2R,3R)-bitartrate ([Ch][Bit]), choline chloride ([Ch]Cl), choline dihydrogen citrate ([Ch][H2Cit]) and choline hydroxide ([Ch]OH) were measured at 298.15 or 313.15 K and 0.1 MPa and correlated using second-degree polynomials with salt molality (m), obtaining determination coefficients (R2) higher than 0.9974. Furthermore, the osmotic coefficients (ϕ) of these binaries were determined using vapour pressure osmometry (VPO), at 313.15 K and 0.1 MPa, being satisfactorily described by the Extended Pitzer Model of Archer, which yielded low values of standard deviation (3.58<σϕ·103<12.86). Then, the mean molal activity coefficients (γ±) and excess Gibbs free energies (GE/RT) were calculated, following the order [Ch][H2Cit] > [Ch][Bit] > [Ch][Bic] > [Ch]OH > [Ch]Cl, which corresponds to the decreasing polarity of the choline salts and agrees with the empirical law of matching water affinities (LMWA).

Reflection coefficient of a natural sodium bentonite in aqueous mixed electrolyte solutions: positive and negative anomalous osmosis

Reflection coefficient of a natural sodium bentonite in aqueous mixed electrolyte solutions: positive and negative anomalous osmosis

Modeling hydrogeological conditions of noble gases in water and aqueous electrolyte solutions

Dissolved noble gases in water hold significant potential as tracers and precursors in various hydrogeological and geological applications, particularly in understanding surface water-groundwater interactions. These applications necessitate precise solubility predictions. Employing the fugacity-fugacity approach, our study models the solubilities of Neon, Argon, Krypton, Xenon, and Radon in both pure water and electrolyte solutions. Leveraging the Cubic-Plus-Association Equation of State, we achieve remarkable accuracy, with average deviations below 2.5 % for vapor pressure, liquid, and vapor-phase densities. Additionally, in water–gas binary systems, deviations in gas solubilities within pure water remain under 5.0 %. Extending our analysis to water–gas-salt ternary systems, our model demonstrates deviations smaller than 5.6 %. Alongside discussing the gas dissolution mechanism, this work emphasizes the adaptability of the model, informed by robust experimental and modeling data. The interpretations derived from modeling hydrogeological conditions are poised to enhance our understanding of hydrological processes, thereby assisting planners and water managers in achieving sustainable development and management of water resources.

Accelerating QM/MM simulations of electrochemical interfaces through machine learning of electronic charge densities.

A crucial aspect in the simulation of electrochemical interfaces consists in treating the distribution of electronic charge of electrode materials that are put in contact with an electrolyte solution. Recently, it has been shown how a machine-learning method that specifically targets the electronic charge density, also known as SALTED, can be used to predict the long-range response of metal electrodes in model electrochemical cells. In this work, we provide a full integration of SALTED with MetalWalls, a program for performing classical simulations of electrochemical systems. We do so by deriving a spherical harmonics extension of the Ewald summation method, which allows us to efficiently compute the electric field originated by the predicted electrode charge distribution. We show how to use this method to drive the molecular dynamics of an aqueous electrolyte solution under the quantum electric field of a gold electrode, which is matched to the accuracy of density-functional theory. Notably, we find that the resulting atomic forces present a small error of the order of 1 meV/Å, demonstrating the great effectiveness of adopting an electron-density path in predicting the electrostatics of the system. Upon running the data-driven dynamics over about 3ns, we observe qualitative differences in the interfacial distribution of the electrolyte with respect to the results of a classical simulation. By greatly accelerating quantum-mechanics/molecular-mechanics approaches applied to electrochemical systems, our method opens the door to nanosecond timescales in the accurate atomistic description of the electrical double layer.

Impact of electrolyte solutions on carbon dioxide fixation in single chamber Al–CO2 battery

Governments and research & development (R&D) organizations are actively initiating various programs and research strategies for CO2 capture, its utilization, and integration with long duration energy storage from renewable sources worldwide. In line with the carbon capture goals, here we report a novel electrochemical Al-CO2 battery cell, that can simultaneously capture CO2 and convert it into value-added products, in addition to long-duration energy generation and storage. This innovative approach employs cost-effective Al metal as an anode and an in-house synthesized Ni–Fe based bimetallic double hydroxide catalyst as the cathode, with meticulously optimized compositions and morphologies. We explore the impact of different aqueous electrolyte solutions compositions on the cell performance, demonstrating up to 10 h of stable long duration energy storage with a stable voltage profile. The cell exhibits low polarization even at high current densities of up to 12 mA cm−2 and maintains stable cycling over 500 h. Through Fourier-transform infrared spectroscopy (FTIR), Raman spectroscopy, X-ray Diffraction and X-ray photoelectron spectroscopy (XPS) analysis, we determined that the discharge product is either NaAlCO3(OH)2 or KAlCO3(OH)2, distinct from the Al2(CO3)3 typically reported in conventional Al–CO2 batteries.

Tuning the surface charge of rice straw-derived cellulose nanofibril membrane separator for electrochemical performance enhancement of supercapacitors

The electrochemical performance of supercapacitors has often overlooked the effect of surface charge on cellulose-based separators. Cellulose nanofibrils (CNFs) produced by 2,2,6,6-tetramethylpipridine-1-oxyl (TEMPO) oxidation possess a high anionic surface charge due to the presence of carboxylate groups, which could affect the transport of electrolyte ions. In this work, the surface of CNFs is modified with a cationic polyelectrolyte, namely polydiallydimethylammonium chloride (PDADMAC), to yield a nearly-zero surface charge CNF membrane derived from rice straw. The surface modification of CNFs using 20 wt% PDADMAC results in CNF-M2, with a surface charge of +5.3 mV, notable porosity (64 %), excellent electrolyte uptake (225 %), and improved ionic conductivity (5.0 mS cm−1). A symmetric supercapacitor assembled with CNF-M2 as a separator, exhibits enhanced specific capacitance (185.3 F g−1 at 0.1 A g−1), energy density (37.1 Wh kg−1 at a power density of 0.24 kW kg−1), and is able to maintain 100 % capacitance retention over 10,000 cycles in 1.0 M Na2SO4 aqueous electrolyte solution. This surface modification leads to 1.2–1.4 times increase in energy and power densities compared to the unmodified CNF membrane. Thus, the nearly-zero surface charge of the modified CNF membrane holds promise as a separator that elevates the performance of supercapacitors.

Bi2Se3/ZnSe heterojunction on flexible Mo metal foil for photo electrolysis water splitting application

Abstract The green hydrogen generation by photoelectrochemical (PEC) process emerged as a viable approach to replace non-renewable energy sources, which is done by using semiconducting materials. Recently ZnSe-based heterostructure/junction promise a suitable approach to enhance the PEC performance of photoelectrode. Here we have grown Bi2Se3/ZnSe heterojunction on flexible Mo metal foil by using magnetron sputtering technique toward PEC water splitting application. The crystallinity, structural, and surface morphology of the deposited films were investigated by X-ray diffraction, Raman spectroscopy, and field emission scanning electron microscopy, respectively. The PEC measurements were performed under 100 mW/cm2 (AM = 1.5 G) simulated solar radiation in 0.5 M Na2SO4 aqueous electrolyte solution. The PEC measurements show that Bi2Se3/ZnSe photoelectrode performs better as a photocatalyst, with a photocurrent density of ∼96.4 μA/cm2 (at 0.4 V vs Ag/AgCl), which was found to be three times higher than pristine ZnSe film (∼32.4 μA/cm2). This work suggests the importance of heterojunction towards efficient photoelectrodes for green hydrogen generation.

CuFe2O4 Nanofiber Incorporated with a Three-Dimensional Graphene Sheet Composite Electrode for Supercapacitor and Electrochemical Sensor Application

The demand for regenerative energy and electric automotive applications has grown in recent decades. Supercapacitors have multiple applications in consumer alternative electronic products due to their excellent energy density, rapid charge/discharge time, and safety. CuFe2O4-incorporated three-dimensional graphene sheet (3DGS) nanocomposites were studied by different characterization studies such as X-ray diffraction, transmission electron microscopy, and scanning electron microscopy. The electrochemical studies were based on cyclic voltammetry (CV), galvanostatic charge–discharge (GCD), and electrochemical impedance spectroscopy (EIS) measurements. As prepared, 3DGS/CuFe2O4 nanocomposites exhibited an excellent surface area, high energy storage with appreciable durability, and excellent electrocatalysis properties. A supercapacitor with 3DGS/CuFe2O4-coated nickel foam (NF) electrodes exhibited an excellent specific capacitance of 488.98 Fg−1, a higher current density, as well as a higher power density. After charge–discharge cycles in a 2.0 M KOH aqueous electrolyte solution, the 3DGS/CuFe2O4/NF electrodes exhibited an outstanding cyclic stability of roughly 95% at 10 Ag−1, indicating that the prepared nanocomposites could have the potential for energy storage applications. Moreover, the 3DGS/CuFe2O4 electrode exhibited an excellent electrochemical detection of chloramphenicol with a detection limit of 0.5 µM, linear range of 5–400 µM, and electrode sensitivity of 3.7478 µA µM−1 cm−2.

Novel promising aqueous electrolytes for manganese dioxide/stainless steel pseudocapacitor electrode

Manganese dioxide (MnO2) films are developed by potentiostatic electrodeposition on a stainless steel sheet as a current collector using manganese acetate tetrahydrate solution at a concentration of 0.25 mol L−1. The deposited sample layer is found to be amorphous as confirmed by the scanning electron microscope (SEM) and X-ray diffraction (XRD) analyses. The capacitive property of the prepared electrodes is characterized by charging/discharging, cyclic voltammetry, and electrochemical impedance spectroscopy techniques in four different aqueous solutions; sodium sulfate, magnesium acetate, nickel acetate, and a mixture of sodium chloride + sodium bicarbonate + borax. Charge–discharge curves reveal higher specific capacitance (Cs) of 1580 F g−1 at 0.5 mA cm−2 for the investigated MnO2 film which is characterized in Ni acetate aqueous solution. The structural, morphological, and electrochemical properties of the electrodeposited manganese oxide films are also studied. The results indicate that the specific capacitance of the deposited samples showed a strong dependency on the electrolyte aqueous solutions, resulting in developing new electrolytes which is a top priority effort in comparison to seeking new electrode materials. It is found that the matching between the pore size structure of the electrode and the ion size of the electrolyte is of great importance for the improved capacity of prepared capacitors.