Hydrophobic Electrolyte Research Articles

Chemical manipulations of nanoscale electron transfers

The recent progress in nanoscale electron transfers is reviewed. Here, we focus on quantized capacitance charging of monolayer-protected nanoparticle molecules. For gold nanoparticles larger than 1.6 nm in diameter, this novel charge transfer phenomenon is represented by a series of voltammetric peaks that are evenly separated around 0 V; whereas for smaller-sized particles, uneven spacings of the discrete charging peaks are observed. Additionally a sizeable bandgap starts to evolve with decreasing particle core size, due to the quantum size effect. This bandgap can be further manipulated by the interactions between the particle core and surface ligands. When nanoparticles are immobilized onto electrode surfaces by bifunctional chemical linkages, one system that is of particular interest is the observation of ion-induced rectification of nanoparticle quantized charging in aqueous media in the presence of hydrophobic electrolyte ions. This is interpreted on the basis of the ion-pair formation between “soft” electrolyte ions and particle molecules which leads to the variation of the electrode interfacial double-layer capacitance (Randles equivalent circuit). Further control of nanoscale electron transfers can be accomplished by magnetic and photochemical interactions. Fundamentally, these studies offer a rare glimpse of the molecular origin and mechanistic regulation of electron transfers at nanoscale interfaces.

Au/PVC composite—a new material for solid-state gas sensors: Detection of nitrogen dioxide in the air

A new composite material for indicator electrodes of solid-state electrochemical gas sensors was prepared by dispersion of a fine gold powder in a highly plasticized PVC matrix containing a hydrophobic electrolyte (Au/PVC electrode). The material consists of clusters of gold particles partially protruding from the polymer matrix into the gaseous phase. The composite, functioning both as a solid polymer electrolyte and as an indicator electrode, was tested in a planar amperometric NO 2 sensor in the air. The Au/PVC electrode behaves as an array of microelectrodes and exhibits a high catalytic activity. The response at −500 mV versus Pt/air reference electrode was linearly dependent on the concentration over the whole tested range of 0.6–2.6 ppm (v/v) NO 2. The sensitivity of determination amounted to 400 nA/ppm, the detection limit was 50 ppb, and the response time t 90 was 50 s. The relative standard deviation of the sensitivity, calculated from 18 NO 2 determinations performed within 1 month, was 12%. The Au/PVC electrode is applicable to continuously operating sensors monitoring the gaseous environment under conditions of slow variation in NO 2 content.

Electrocatalytic Reactions Mediated by N,N,N‘,N‘-Tetraalkyl-1,4-phenylenediamine Redox Liquid Microdroplet-Modified Electrodes: Chemical and Photochemical Reactions In, and At the Surface of, Femtoliter Droplets

The electro-oxidation of electrolytically unsupported ensembles of N,N-diethyl-N',N'-dialkyl-para-phenylenediamine (DEDRPD, R = n-butyl, n-hexyl, and n-heptyl) redox liquid femtoliter volume droplets immobilized on a basal plane pyrolytic graphite electrode is reported in the presence of aqueous electrolytes. Electron transfer at these redox liquid modified electrodes is initiated at the microdroplet-electrode-electrolyte three-phase boundary. Dependent on both the lipophilicity of the redox oil and that of the aqueous electrolyte, ion uptake into or expulsion from the organic deposits is induced electrolytically. In the case of hydrophobic electrolytes, redox-active ionic liquids are synthesized, which are shown to catalyze the oxidation of l-ascorbic acid over the surface of the droplets. In contrast, the photoelectrochemical reduction of the anaesthetic reagent halothane proceeds within the droplet deposits and is mediated by the ionic liquid precursor (the DEDRPD oil).

Rectifying Nanoscale Electron Transfer by Viologen Moieties and Hydrophobic Electrolyte Ions

The rectifying effects of electrolyte ions on interfacial electron transfers were investigated with a gold nanoparticle monolayer anchored by bifunctional chemical bridges with viologen moieties. Gold nanoparticle monolayers were fabricated by using a sequential anchoring mechanism with viologen dithiols as the chemical linkers. For viologen monolayers, the voltammetric currents were found to be sensitive to electrolyte ions. Due to the ion-pair formation between the bipyridinium moieties and hydrophobic anions, the electron-transfer kinetics of the viologen functional groups seems impeded by the increasing concentration of “soft” ions, leading to the diminishment of the faradaic currents. This response to electrolyte ions is in great contrast to that of gold nanoparticle monolayers, where the quantized charging currents become better-defined with increasing concentration of hydrophobic ions. By hybridizing these conventional and nanoscale redox-active entities into the interfacial organized structure, one can manipulate interfacial charge transfer, where the voltammetric responses behave analogously to Coulomb blockade with the currents rectified at either negative or positive electrode potentials, depending on the nature of the electrolyte ions.

Charge transfer across the water/nitrobenzene interface by three-electrode system

A droplet of aqueous solution containing a certain molar ratio of redox couple is first attached onto a platinum electrode surface, then the resulting drop electrode is immersed into the organic solution containing very hydrophobic electrolyte. Combined with reference and counter electrodes, a classical three-electrode system has been constructed. Ion transfer (IT) and electron transfer (ET) are investigated systematically using three-electrode voltammetry. Potassium ion transfer and electron transfer between potassium ferricyanide in the aqueous phase and ferrocene in nitrobenzene are observed with potassium ferricyanide/potassium ferrocyanide as the redox couple. Meanwhile, the transfer reactions of lithium, sodium, potassium, proton and ammonium ions are obtained with ferric sulfate/ferrous sulfate as the redox couple. The formal transfer potentials and the standard Gibbs transfer energy of these ions are evaluated and consistent with the results obtained by a four-electrode system and other methods.

Study of facilitated potassium ion transfer across a water ∣ 1,2-dichloroethane interface using different phase volume ratio systems

A study of potassium ion transfer across a water ∣ 1,2-dichloroethane (W ∣ DCE) interface facilitated by dibenzo-18-crown-6 (DB18C6) with various phase volume ratio systems is presented. The key point was that a droplet of aqueous solution containing a redox couple, Fe(CN) 6 3−/Fe(CN) 6 4−, with equal molar ratio, was first attached to a platinum electrode surface, and the resulting droplet electrode was then immersed into the organic solution containing a hydrophobic electrolyte to construct a platinum electrode/aqueous phase/organic phase system. The interfacial potential of the W ∣ DCE within the series could be externally controlled because the specific compositions in the aqueous droplet make the Pt electrode function like a reference electrode as long as the concentration ratio of Fe(CN) 6 3−/Fe(CN) 6 4− remains constant. In this way, a conventional three-electrode potentiostat can be used to study the ion transfer process at a liquid ∣ liquid (L ∣ L) interface facilitated by an ionophore with variable phase volume ratio ( r= V o/ V w). The effect of r on ion transfer and facilitated ion transfer was studied in detail experimentally. We also demonstrated that as low as 5×10 −8 M DB18C6 could be determined using this method due to the effect of the high phase volume ratio.

Electrochemical Preparation and Characterization of Meisenheimer Complexes of Trinitrofluorenone with Pyrrole, Indole, and Carbazole

The mechanism of Meisenheimer complex formation by a novel electrochemical route was investigated. The synthetic route utilizes a CH3CN solution consisting of trinitrofluorenone (TNF), electron-donative molecules (EDM = pyrrole, indole, and carbazole), and a supporting electrolyte. Electroreduction of the solution causes a complexation of TNF with the EDMs to yield a green anionic σ complex. To understand this electrode reaction, the effects of electrolysis and solution conditions (solvent, supporting electrolyte, the role of O2, etc.) on the complex formation were investigated. As a result, it was revealed that the σ-complex formation proceeds in the following successive steps: (1) charge-transfer (CT) complex formation between TNF and the EDMs, (2) two-electron reduction of the CT complex to yield double-anionic radical species, (3) attack of O2 on the radical species to induce complexation of TNF with the EDMs, and (4) stabilization of the resulting σ complex by hydrophobic electrolyte cations. In add...

Charge transfer resistance and differential capacity of the plasticized PVC membrane | water interface

Impedance measurements were used to evaluate the differential capacity and the charge transfer resistance of the o-nitrophenyl octyl ether ( o-NPOE) plasticized PVC membrane | water interface over the range of potential differences from −280 to 180 mV and the range of temperatures from 290 to 305 K. The equilibrium potential difference at the membrane | water interface was controlled by the partition of tetramethyl-, tetraethyl-, tetrapropyl- or tetrabutylammonium ion. Soaking of the PVC membrane in water for up to 8 h does not have an effect on the impedance parameters, which points to an absence of water sorption into the membrane in the presence of hydrophobic electrolytes. The differential capacity of the membrane | water interface is comparable with that of the o-NPOE | water interface, and its dependence on temperature throws some light on the role of the surface dipole. Lower apparent rate constants of ion transfer across the membrane | water interface ( k a 0≈10 −2 cm s −1) can be linked to the activation barrier associated with a modification of surface layer at the o-NPOE | water interface by PVC molecules.

Effect of gas humidity on the potential of pseudoreference Pt/air electrode in amperometric solid-state gas sensors

The effect of air relative humidity (RH) on the potential of two different Pt/air electrodes was examined. One electrode was platinum in contact with a hydrophilic Nafion (Pt-Nafion/air), the other was platinum in contact with a plasticized polyvinyl chloride containing a hydrophobic electrolyte (Pt-PVC/air). Over the RH range, from 11 to 72%, the potential of the Pt-Nafion/air electrode decreases non-linearly with increasing RH from 880 to 710 mV versus Ag/AgCl electrode. The potential decrease at the steepest part of the dependence (for RH from 30 to 70%) amounts to about −4 mV/%RH. The potential of the Pt-PVC/air electrode increases linearly with increasing RH from 324 to 337 mV versus Ag/AgCl electrode, with a slope of 0.21 mV/%RH. The change of the reference electrode potential with changing RH might influence the properties of the sensors where the current is measured on the increasing or descending part of the current–potential curve (e.g. the sensors with an indicator electrode exposed to test gas without a diffusion barrier).

A dynamic method of measuring surface potential change due to binding of bitter substance at monolayer-coated liquid membrane surface

A dynamic method of determining the membrane surface potential change due to a binding of a hydrophobic ion has been presented. The surface potential was determined from the time course of membrane potential under zero electric current during a transition between two steady states in a membrane filter impregnated with a phospholipid and 1-octanol. One of the alkaloids, quinine hydrochloride, was used as a hydrophobic electrolyte. Surface charge density and equilibrium constant for binding of quinine ions with ionizable groups of the phospholipids at the membrane surface were determined from the surface potential according to the Poisson–Boltzmann equation.

Ion-induced rectification of nanoparticle quantized capacitance charging in aqueous solutions.

Ion-induced rectification of nanoparticle quantized capacitance charging was studied using nanoparticle self-assembled monolayers in aqueous solutions in the presence of some unique electrolyte ions. The rectified charging features were interpreted on the basis of a Randles equivalent circuit where the binding of hydrophobic electrolyte ions to surface-confined particle molecules led to the manipulation of the electrode interfacial capacitance. It was found that the rectification effects were directly related to the ion hydrophobicity, manifested by the cathodic (anodic) shift of the onset potential with anions (cations) of increasing hydrophobicity Additionally, the voltammetric responses evolved from those similar to conventional molecular diodes to those of quantized charging rectifiers with increasing anion hydrophobicity. Electron-transfer kinetics evaluated by using various electrochemical methods yielded a rate constant within the range of 10-100 s(-1) which decreased with increasing length of the alkyl spacers with a coupling coefficient (beta) within the range of 0.8-0.9. Comparisons with conventional electroactive functional moieties were also discussed.

Polyelectrolytes of High Charge Density in Organic Solvents. Synthesis and Viscosimetric Behavior

An easy anion exchange between electrolyte monomers of the quaternary ammonium halide type such as [(2-methacryloyloxy)ethyl]trimethylammonium chloride or 1-vinyl-3-methylimidazolium iodide and various cyanocarbon salts such as 1,2,2-tricyanoethenolate, 1,1,2,3,3-pentacyanopropenide, α,α-dicyano-p-toluoylcyanide, or p-(tricyanovinyl)phenyldicyanomethide readily leads to a series of new hydrophobic electrolyte monomers with yields generally over 70%. [(2-Methacryloyloxy)ethyl]trimethylammonium 1,1,2,3,3-pentacyanopropenide is a most representative example. Its free radical polymerization in homogeneous solution (DMF, 60 °C) currently yields atactic chains (Bernoulli stereopropagation process, probability of meso placement Pm = 0.31) of fairly high degree of polymerization (DPw ∼ 1600) which show an unique spectrum of solubility in dipolar organic solvents (dipole moment μ > 2.6 D) covering a very broad range of dielectric constants (e ∼ 10−180). Viscosity measurements performed in 13 solvents allow us to a...

Development of Electrochromic Devices Working with Hydrophobic Lithium Electrolyte

This manuscript report on a new lithium electrolyte, allowing the manufacturing of electrochemical systems, such as electrochromic devices, in ambient atmosphere. It is based on lithiumbis-trifluoromethane sulfonimide dissolved in the following hydrophobic salt, which was first prepared by M. Grätzelet al.: 1-ethyl. 3-methyllimidazoliumbis-trifluoromethane sulfonimide. We have also successfully tested the compatibility of this electrolyte with WO3and TiO2-CeO2films acting respectively as efficient electrochromic electrode and counter electrode for smart-window working with Li+ions.

Comparison of the thermodynamic and transport properties of lithium bis(trifluoromethylsulfonyl)imide (LiTFSI) with LiClO4 and Bu4NBr in water at 25 °C

Lithium bis(trifluoromethylsulfonyl)imide (LiTFSI) is a promising electrolyte for lithium batteries. While it presents many interesting features in aprotic solvents (high solubility and conductivity, electrochemical stability, etc.), little is known about its properties in water. The solid–liquid phase diagram, surface tension, volume, heat capacity, and conductivity were therefore measured at 25 °C and compared with the same properties of typical hydrophilic (LiClO4) and hydrophobic (Bu4NBr) electrolytes. To help in the comparison, some of the literature data for LiClO4 and Bu4NBr were extended. The standard Λ0, [Formula: see text] and [Formula: see text] are respectively 71.12 S cm2 mol−1, 139.7 cm3 mol−1 and 543 J K−1 mol−1at 25 °C. LiTFSI s quite soluble, and shows surface activity and a small tendency for self-association in water. The aggregation number estimated from a mass-action model is of the order of 4. Keywords: lithium bis(trifluoromethylsulfonyl)imide, lithium perchlorate, tetrabutylammonium bromide, volume, heat capacity, phase diagram, thermal analysis, surface tension, conductance.

Amperometric solid-state NO 2 sensor based on plasticized PVC matrix containing a hydrophobic electrolyte

An amperometric solid-state sensor for the detection of nitrogen oxide in air has been constructed using a gold minigrid indicator electrode, Pt/air reference and platinum counter electrodes in contact with a solid polymer electrolyte containing 9.6% PVC, 87.0% 2-nitrophenyl octyl ether and 3.4% tetrabutylammonium hexafluorophosphate. The stationary electric current corresponding to the NO 2 reduction at the indicator electrode at − 0.3 V versus Pt/air electrode exhibited a linear dependence on the NO 2 concentration in the range 0.2 to 5.0 ppm, with a sensitivity of 21.7 nA ppm −1 (at 54% relative humidity), a standard deviation of 3.3 nA at 1.06 ppm NO 2, and a detection limit of 75 ppb. The time constant or time required to attain 90% of the steady-state response is 3.3 s or 14 s, respectively. The response decreases linearly with increasing relative humidity (RH) with a slope of 0.14 nA ppm −1 per 1% RH. The sensor shows an excellent stability over one month.

Electrochemical investigations in supercritical carbon dioxide

It has been shown that hydrophobic electrolytes can be dissolved in supercritical carbon dioxide (scCO2) to give conducting media. The conductivity is comparable with that of similar electrolytes in cyclohexane under ambient conditions. The solubility of the electrolyte in supercritical media is related to the density of the medium. Electron-transfer processes are demonstrated for the first time in both cyclohexane and unmodified scCO2 at a macroscopic electrode.

Enthalpy of interaction of some electrolytes with 2-methyl-2-butanol in wate at 25�C

Enthalpies of mixing in water of 2-methyl-2-butanol with several electrolytes (alkali-metal halides, tetra-n-alkylammonium bromides, Ph4PCl, Ph4AsCl and NaPh4B) have been determined by flow microcalorimetry at 25°C. Enthalpic pair interaction coefficients, hNE, of the virial expansion of the excess enthalpy were calculated. All coefficients are positive and increase as the anionic size increases in anionic series of alkali-metal halides. A linear correlation between hNE and the number of carbon atoms in the apolar group of R4NBr is observed. For alkali-metal halides coefficients hNE depend mainly on the partial desolvation of halides, and for hydrophobic electrolytes both the partial desolvation of halide ions and hydrophobic interaction are the leading factors in the value of hNE.

New charged microheterogeneous system ? A microemulsion with droplets of variable electrostatic potential

A method has been proposed for varying the electrostatic potential of droplets in emulsions of the oil/water type by introducing nonsurface-active hydrophilic—hydrophobic electrolytes into the aqueous phase. Consideration has been given to the simplest two-phase model using standard Galvani potentials for interphase transfer of the individual ions to describe the properties of the electrolyte. From calculations based on this model relationships have been obtained between the electrostatic potential of the microphase and the electrolyte properties: concentration, droplet dimensions of the dispersed phase, and its mole fraction. Limiting conditions have been discovered in terms of the droplet dimensions and mole fraction of the dispersed phase. Calculations have demonstrated the possibility of controlling the electrostatic potential of the emulsion droplets in the range ± 300 mV.

Anion Effect on Single Ionic Salting-out Coefficients of Hydrophobic Electrolytes.

Anion Effect on Single Ionic Salting-out Coefficients of Hydrophobic Electrolytes.

311 - A new model of membrane transport: electrolysis at the interface of two immiscible electrolyte solutions

A simple membrane model is the interface between water and an organic liquid immiscible with water, with a strongly hydrophilic electrolyte dissolved in the aqueous phase and a strongly hydrophobic electrolyte in the organic phase. This interface can be electrochemically polarized in the same way as the interface electrode |electrolyte solution using various modes of voltammetry or the galvanostatic method. A four-electrode potentiostatic system is required for such studies. An electrolyte dropping electrode, analogous to Heyrovsky's DME, was also constructed. The voltammograms fully resemble those obtained with metallic electrodes. The faradaic proceses studied so far are mainly connected with the transfer of hydrophobic ions across the interface. These processes are quite rapid and the half-wave potential of a particular ion is related to its standard Gibbs transfer energy. Observed electron-transfer effects model redox processes at membranes. Macrocyclic ionophores facilitate transfer of alkali metal ions across this interface. Very fast ion transfer as well as complex formation was observed in the systems under investigation so that, generally, the diffusion of the ionophore toward the interface and of the complex into the organic phase is the rate-controlling step, no surface reaction retarding the overall process. Apart from the investigation of membrane processes, this approach can be used for elucidation of processes in ion-selective electrodes and in phase-transfer catalysis.