Diffusion Of Ionic Species Research Articles

Mixtures of ethylammonium nitrate and ethylene carbonate: Bulk and interfacial analysis

The structure and dynamics of binary mixtures of a protic ionic liquid (ethylammonium nitrate) and ethylene carbonate are studied by means of atomistic molecular dynamics simulations and experimental measurements both in bulk and at the electrochemical interface. The solubility limit was experimentally found at 0.6 carbonate molar fraction. Likewise, density and conductivity experimental data are compared with computational results. Also, distribution and correlation functions obtained from bulk simulations are analyzed in the miscible range to clarify the role of the carbonate in the coordination and diffusion of ionic species. Understanding the evolution of the hydrogen bond network is of particular importance since its strength is detected as the most relevant feature in the structural organization of the mixture. Regarding the effects of the presence of an interface, the orientations of the molecules and the density and charge profiles are calculated both in the absence and in the presence of an electric field. This analysis reveals the tendency of the carbonate to displace the ionic liquid from the near-wall region when concentration is increased.

Tropaeline O‐oxalic acid‐benzalkonium chloride photogalvanic cells for solar energy conversion and storage

AbstractThe photogalvanic (PG) cells involve a change in the electrode potential by photochemical processes along with the diffusion of ionic species through the bulk electrolyte. The PG cells have used so far the complex H‐shaped cell design, heavy sensitizer molecules with low diffusivity, and low photo‐stability. All these factors are not conducive to the fabrication of cheap cells with good electrical output. To address all these concerns, the tropaeline‐O dye photosensitizer (a low molecular weight molecule with higher diffusion and higher photo‐stability) has been exploited with diffusion‐friendly low cost and a simple transparent cylindrical glass tube. The optimum values of the cell's electrical parameters are: potential 998 mV, current 3200 µA, and power 829.5 µW, and it is quite similar at all illumination window sizes.

Unraveling the Mechanism of Electrically Induced Adhesive Debonding: A Spectro‐Microscopic Study

AbstractThe design of new electrically debondable adhesives has been an area of enormous interest for the recycling, repair, and reuse of electrical components for the last decade. However, the complexity of analyzing the debonding process under real conditions is a major obstacle for elucidating the mechanism. Here, a general mechanism for the electrical debonding of ionic acrylic adhesives based on imidazolium ionic liquids is reported. Using synchrotron‐based characterization techniques, in situ experiments mimicking real debonding conditions allowed for the first time the recording of ionic diffusion and chemical reactions during the debonding process. Diffusion of ionic species toward the electrodes triggers the debonding via electrochemical reactions at the adhesive–substrate interfaces. The selection of ionic adhesive chemistry and electrodelamination conditions will eventually determine the type of adhesive failure. A detailed understanding of the mechanism allows the development of new electrically debondable adhesives, which is crucial to promote circular economy and a more sustainable environment.

The effect of chemical treatment on the adhesion strength and structural integrity of the epoxy coatings

This research aims to investigate the effect of chemical treatment on the integrity of the epoxy coating applied on mild steel substrates. Grit blasted steel samples were chemically treated in 10 vol.% NaOCl solution, 10 vol.% CrCl3 and 30 vol.% H3PO4–5 vol.% HNO3 solutions prior to coating application. Post-cleaning surface morphology and chemical composition revealed the formation of oxidation products on steel surface. Under optimized conditions, a dry film thickness of 135 ± 3 μm of epoxy coating was achieved. The CT2 sample (pre-treated with CrCl3) presented higher coating adhesion strength (∼4.12 MPa) and the lowest rust area of ∼0.03% compared to other chemically treated samples during 720 h of immersion in 5 wt.% NaCl solution. The coating degradation mechanism was evaluated by electrochemical impedance spectroscopy (EIS) after 24, 48, 72 and 120 h of immersion in 3.5 wt. % NaCl solution. EIS analysis of the coated samples pretreated with NaOCl and CrCl3 solutions exhibited low water uptake and limited corrosion due to hindrance in the diffusion of ionic species through the coating. However, coated steel samples pretreated in acidic solutions displayed appreciable corrosion damage as confirmed from salt spray and immersion tests. For instance, the delamination of the CT3 and CT4 (acid pre-treated) coatings was confirmed from the EIS analysis., which represented the formation of a double layer and occurrence of faradaic (corrosion) reactions as the coating-substrate interface, resulting in ∼15%–30% delamination in 120 h of exposure.

Corrosion behaviour of Al–20Cu intermetallic alloy in synthetic sea water

ABSTRACT In this work, Al–20Cu intermetallic alloy was subjected to corrosion evaluation in synthetic sea water at different pH values, and room temperature. The corrosion tests were made to study the alloy in potential applications in hydrogen generation. For this purpose, the electrochemical techniques of potentiodynamic polarisation, linear polarisation resistance, and electrochemical impedance spectroscopy were used. Experimental results showed that the alloy is not susceptible to passivation and exhibits the highest current density and corrosion rate at pH 14. In this condition, the governing corrosion mechanism was associated with activation, promoted by the continuous anodic dissolution of uncovered metallic zones, due to the detachment of previously formed corrosion products. However, the results at near-neutral pH presented higher corrosion resistance and a corrosion mechanism limited by main diffusion of ionic species. In general, the primary mechanism of corrosion in the solutions was associated to charge transfer.

Activated Carbon-Based Electrodes with Engineered Microstructure for Capacitive Deionization (CDI) of Aqueous Solutions

Capacitive Deionization (CDI) is a relatively novel technique which uses an external electric field to remove ionic species from water streams and adsorb them onto a highly porous material. In this system, the interplay between the transport phenomena taking place in the microstructure of the porous electrode and in the bulk flow is of paramount importance as it determines the concentration profile of the effluent. Microporosity and tortuosity of the electrodes dictate the motion of the species in the porous medium and set its adsorption capacity and resistivity. In this work, to achieve systems with better electrosorption and energetic performance, activated carbon electrodes with engineered microtopology are manufactured by employing magnetic field manipulation. By properly arranging the location of the macropores, the fabricated materials allow ions to freely diffuse within the electrode. Along with the electrochemical characterization methods, adsorption and energetic efficiency of the manufactured electrodes are evaluated using the proposed comprehensive figure-of-merits. The obtained results provide new insights into the effects of porous geometry on the microscale electro-sorption and diffusion of ionic species within the porous electrode and their correlation with the macroscale advection and diffusion in the bulk flow of CDI units. The adopted manufacturing process also leads towards development of large-scale production of carbon-based electrodes with controlled microstructures for different applications.

New insight on the lithium hydride–water vapor reaction system

The reaction of lithium hydride (LiH) powder with pure water vapor (H2O and D2O) was studied by thermogravimetry and in situ infrared spectroscopy at 298 K over a large pressure range. The mean particle size of LiH is around 27 μm. At very low pressure, the hydrolysis starts with the formation of lithium oxide (Li2O). Then, both Li2O and lithium hydroxide (LiOH) are formed on increasing pressure, thus, creating a Li2O/LiOH bilayer. The reaction takes place through the consumption of LiH and the formation of Li2O at the LiH/Li2O interface and through the consumption of Li2O and the formation of LiOH at the Li2O/LiOH interface. Above 10 hPa, only the monohydrate LiOH·H2O is formed. This hydration reaction of LiOH into LiOH·H2O occurs at a lower pressure (8 hPa) after the first hydration-dehydration cycle. The hydrolysis mechanism proposed in this paper suggests that the diffusion of ionic species across the intermediate Li2O layer is the rate limiting step of the reaction.

Effect of TiO2 Nanoparticle Layer and Dynamic Mechanisms on the Efficiency of Dye-Sensitized Solar Cells

This study deals with the analysis of the internal electrochemical characteristics of dye-sensitized solar cells (DSSC) using as semiconductor titanium dioxide (TiO2). The built DSSC was characterized by electrochemical impedance spectroscopy. This allowed to identify the mechanisms of degradation and extrapolation in function of efficiency improvement and factors of the cell such as current, voltage, capacitance, and lifetime electron. DSSC using different ways for the depositions of TiO2 nanostructures were manufactured, characterized, and the performance modeled. The influence of nanostructure (nanotubes or thin films), solvents (acetonitrile or ionic liquid), and the effect of additives (Tbp or lithium) were studied. The best results were obtained with the combination of nanotubes, acetonitrile, and lithium. Photocurrent density of 11.092 mA·cm2, open-circuit photovoltage of 0.707 V, fill factor of 71.9, and efficiency of 5.6 were obtained with the combination mentioned above, achieving the best resistance to the recombination, electron lifetime, and length of electrons diffusion. Low viscosity is the main advantage of organic solvents, which permits good diffusion of ionic species in the electrolyte, promoting dye regeneration, and acceptable reaction rate in the counter-electrode, consequently a better efficiency of the DSSC can be obtained.

Modelling and Simulation of Transport Mechanisms of Electro-Migration and Diffusion of Ionic Species in the Concrete through Meshless Methods

The transport of ions such as chloride ion through the concrete has been the subject of study, because the entrance of these, affects the useful life of the structure. The mechanism of ionic transport is described by the Nernst-Planck equation and to solve the problem numerical techniques such as the Finite Difference Method (MDF) or Finite Element (MEF) are used which require a meshing process and a higher cost Computational. In this work, relatively new methods such as the Radial Base Functions (FBR) method and the Fundamental Solution Method (MSF) were applied, which do not require a mesh to solve the ion transport problem.

The Carbonatation of Anhydrite: Kinetics and Reaction Pathways

A textural and kinetic investigation of the carbonatation of anhydrite in the presence of carbonate- and bicarbonate-bearing solutions under static conditions was conducted. The replacement occurs via a coupled dissolution–precipitation mechanism. Textural and kinetic evidence indicates that the rate-limiting step in the replacement reaction was the dissolution of anhydrite and that the dissolution rate was likely controlled by the diffusion of ionic species in the aqueous phase. Calcium carbonate polymorphism was sensitive to temperature and solution composition. Bicarbonate-bearing solutions up to 80 °C only produced calcite, but aragonite formed alongside calcite in carbonate-bearing solutions, occurring in trace amounts at 25 °C and becoming the dominant polymorph at temperatures ≥60 °C. Furthermore, within the carbonate-bearing solutions (high pH) at elevated temperature, kinetic and textural evidence indicates that competition between calcite and aragonite nucleation and growth plays a greater role ...

Trade-off between capacitance and cycling at elevated temperatures in redox additive aqueous electrolyte based high performance asymmetric supercapacitors

High surface area mesoporous MWCNTs/ZrO2 and MWCNTs/WO3 composites are used to fabricate asymmetric supercapacitors (ASCs) in 1M Li2SO4 aqueous electrolyte with and without addition of KI. The addition of redox electrolyte additive leads to simultaneous enhancement in specific energy and power. These ASCs, when operated upto temperatures ≤60°C, show reasonably stable specific capacitance and cycling stability. It is observed that the temperature predominantly affects the capacitance fade during galvanostatic charging-discharging whereas specific capacitance actually increases slightly at elevated temperatures. The Gouy-Chapman theory fails to explain such improvements in the specific capacitance. The improvement is strongly governed by the activation energy associated with the diffusion of ionic species and their chemical potential. Further, the capacitance fade at higher temperatures can be attributed to: (a) the total “time spent” at a given temperature during cycling and (b) reduced kinetic barrier for iodine/iodide redox pairs at the positive electrode/electrolyte interface, which facilitates H2 generation at the negative electrode and induce charge-imbalanced state.

Sputtering nickel-molybdenum nanorods as an excellent hydrogen evolution reaction catalyst

We report a novel fabrication of nickel-molybdenum alloy nanorods catalyst for hydrogen evolution reaction (HER), which is prepared by co-deposition of pure nickel and molybdenum in a multisource sputtering system on the surface of Ni foam substrate. The Ni–Mo alloy film exhibits favorable vertical nanorods structure and presents the most efficient activity for HER compared to the film only including one metal element. The remarkably enhanced catalytic activity is attributed to its ordered array geometry as well as the synergistic interaction between Ni and Mo. Meanwhile, the open space within nanorod arrays facilitates the electrolyte penetration and diffusion of ionic species, allowing high utilization efficiency of active species as well as rapidly release of evolved hydrogen gas from the electrode surface.

Study of Corrosion Behavior of Polyuretane/nanoHidroxiapatite Hybrid Coating in Hank Solution at 25 °C

ABSTRACTThe study of corrosion behavior of polyurethane/nanohydroxyapatite hybrid coating in aerated Hank solution at 25 °C by Potentiodinamic and Electrochemical Impedance techniques was realized. The nanohydroxyapatite (nHA) powders were synthesized by ultrasonic assisted co-precipitation wet chemical method and then mixed with pure polyurethane (PU) during the polymerization. Results were supported by SEM morphologic characterization. Results showed that good corrosion resistance of hybrid coating, showing small corrosion product layer formation. Corrosion mechanisms are affected by an increasing of polarization resistance, promoting decreasing in the corrosion rates. Diffusion of ionic species was the governing mechanism in the corrosion behavior of polyurethane/nanohydroxyapatite hybrid coating.

Influence of temperature on the gel electrophoresis of a pH-regulated, zwitterionic sphere

The gel electrophoresis of a pH-regulated, zwitterionic sphere is investigated based on a Brinkman model taking account of the steric effects coming from the presence of polymer structure. In particular, the influence of temperature on the mobility of a particle having dissociable/associable functional groups is assessed. The model proposed takes the temperature dependence of the permittivity and viscosity of the liquid medium, the diffusivity of ionic species, and the equilibrium constant of the surface reactions into account, and therefore, is more general and realistic than available models in the literature. A thorough numerical simulation is conducted for temperature and pH ranging from 283 K to 323 K and 5 to 8.5, respectively, to illustrate the electrophoretic behavior of the particle mobility in various conditions.

Non-equilibrium diffusive fluxes of ions and their impact on the refractory period of tightly packed neurons

Action potentials (APs) generated and sustained by ionic currents flowing through neural cell’s membrane constitute the main way these cells communicate with each other. The most common, although not the only possible mechanism of generating APs, involves sodium influx that ensures cell depolarization and potassium efflux that ensures cell repolaroization. A sodium-potassium exchanger and leakage currents eliminate the ionic disturbance created by an AP. In a closely packed bundle of neuronal cells with fast diffusion of ionic species in the extracellular space (ECS) an AP generated in one axon could impact the excitability of nearby neurons. The ECS is similar in composition to the cerebrospinal fluid that baths the outer surface of the brain and is present in large internal cavities or ventricles and in the spinal canal. The ionic composition of ECS is mostly made of sodium and chloride dissolved in water with much smaller amounts of other substances, including potassium and calcium. Previous studies have considered the role of potassium in seizures by employing a computational model of potassium diffusion between periodically firing neurons [1]. However, absent from most of these studies on diffusion coupling is the potential effect of sodium dynamics on this form of neuronal coupling [2]. Based on previously implemented models that include detailed balances of the main ionic species, we modeled a Hodgkin-Huxley cell able to generate periodic spiking or bursting APs. The model accounts for the dynamics of major (sodium and potassium) ionic species, as well as certain aspects of the extracellular environment (diffusion coefficients, the intracellular/extracellular pace ratio, etc.) The results from the full model were compared to reduced models, in which the dynamics of only one ionic species is considered, through analysis of refractory period induced by a simulated injected current into the neuron. Our results suggest that the refractory period and, therefore, the ability of a neuron to produce regenerative APs depends strongly on the firing rate of nearby neurons and the parameters of the extracellular space (diffusion coefficients and extracellular/intracellular space ratio).

Voltammetric determination of citric acid and quinine hydrochloride using polypyrrole–pentacyanonitrosylferrate/platinum electrode

Cyclic voltammetry was used to investigate the electrochemical behavior of citric acid (CA) and quinine hydrochloride (QH) at a polypyrrole-pentacyanoferrate/Platinum (PPY–PCNFe/Pt) electrode in aqueous medium. The analytical plots obtained were found to be linear in the concentration range between 1.0 and 9.0 mM for both the analyte solutions. The detection limits (3 δ) were found to be 1.17 × 10 −4 M and 1.08 × 10 −5 M for CA and QH analyte solutions, respectively. It was further observed that the diffusion of ionic species into and out of the polymeric film made the PPY–PCNFe/Pt electrode highly electroactive thereby enabling it to efficiently detect the analyte solutions having concentration as low as 1 mM.

Two layered silica protective film made by a spray-and-dip coating method on 304 stainless steel

The silica coating has attracted much attention because of its superior corrosion resistance with almost no harm to human health and to the environment. In this study, a two layered silica film was tried to get an enhanced corrosion resistance. The silica film was prepared on the hairline finish 304 stainless steel surfaces by-a-spray- and subsequent-dip-coating process. The spray coating solution was prepared by mixing sodium silicate solution, silica colloid, tetraethyl orthosilicate (TEOS), methyltriethoxysilane (MTES), ethanol, and distilled water. Then the solution was sprayed onto the stainless steel surface, and was dried and heat treated. The dip coating solution was prepared by a simple mixing of TEOS and acidic water into ethanol, and the prior spray coated sample was dipped into the solution. The outer dip coated layer was intended to cover spray coated rough and porous layer and hence to enhance the corrosion resistance. A homogeneous and crack free surface was successfully obtained after the dip coating. The prepared silica film was characterized using scanning electron microscopy, potentiodynamic polarization scan, and electrochemical impedance spectroscopy. The two layered film showed an enhanced corrosion resistance. The enhancement was attributed to a protecting effect of the dip coated layer where the diffusion of ionic species was successfully impeded.

Diffusiophoresis of a Soft Spherical Particle in a Spherical Cavity

The boundary effect on the diffusiophoresis of a colloidal particle is investigated theoretically by considering a soft spherical particle at an arbitrary position in a spherical cavity. The particle, which comprises a rigid core and an ion-penetrable layer, simulates biocolloids and particles covered by an artificial membrane layer. The diffusiophoretic behavior of the particle is governed by two types of DLP, the electrophoresis arising from the difference in the diffusivities of ionic species and diffusioosmotic flow. The influences of the thickness of the double layer, the size of the cavity, and the nature and the position of the particle on its diffusiophoretic behavior are discussed. We show that the presence of a boundary can have a profound influence on the behavior of a particle. The effect of electrophoresis can also lead to interesting diffusiophoretic behavior.

Hybrid sol–gel–conducting polymer synthesised by electrochemical insertion: tailoring the capacitance of polyaniline

The templated growth of polyaniline through porous sol–gel films on ITO substrates has been performed. The polyaniline–silica composites have been synthesized by electrochemical reactive insertion in potentiodynamic and potentiostatic conditions. When the polymer is synthesized by potential step experiments, the shape of the chronoamperograms indicates two regimes for the electrochemical polymerization of PANI. Electropolymerization happens faster within the silica pores than on bare ITO electrodes due to confinement effects of oligomeric species formed upon oxidation. The electrochemical capacitance of the silica–PANI hybrids is several time higher than the capacitance of ITO/PANI synthesized under the same conditions. The silica matrix avoids the electric collapse between vicinal conducting fibres in ITO/silica–PANI but allows the diffusion of ionic species that are in contact with the conjugated polymer, increasing therefore the conducting surface exposed to the electrolytic solution.

Chemical State and Ultra-Fine Structure Analysis of Biocompatible TiO2 Nanotube-Type Oxide Film Formed on Titanium Substrate

TiO2 nanotube-type oxide film on Ti substrate has been fabricated using an electrochemical method, and the chemical bonding state, ultra-fine structures, and surface characteristics of the TiO2 nanotube layer have been investigated. The formation and growth of a self-organized nanotube layer can be achieved directly by anodization in NH4-containing electrolytes. The diameter, length, and wall thickness of the nanotube are significantly affected by anodizing conditions such as applied voltage, current density, and anodizing time. The length limiting factor of nanotube growth was found to be the diffusion of ionic species in the electrolyte. XRD investigations revealed that annealed nanotubes have anatase and rutile structure, and some Ti-peaks from the Ti substrate were observed. From the compositional analysis of TiO2 nanotubes layer using Energy Dispersive Spectroscopy (EDS), Ti, O, and P elements were obtained in the wall nanotube layer. For incorporated P-containing in the TiO2 nanotube layer, various chemical states were presented, which were revealed mostly in the forms of H2PO4, HPO4 2-, and PO4 3-.