Dissolved Argon Changes the Rate of Diffusion in Room Temperature Ionic Liquids: Effect of the Presence and Absence of Argon and Nitrogen on the Voltammetry of Ferrocene

This work explores the effects of argon and nitrogen, two electrochemically and chemically inert gases frequently used in sample preparation of room temperature ionic liquid (RTIL) solutions, on the eelectrochemical characterization of ferrocene (Fc) dissolved in the RTIL 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide ([C(2)mim][NTf2]). Remarkably, chronoamperometrically determined diffusion coefficients of Fc in [C(2)mim][NTf2] are found to increase from 4.8 (+/- 0.2) x 10(-11) m(2) s(-1) under vacuum conditions to 6.6 (+/- 0.5) x 10(-11) m(2) s(-1) in an atmosphere of 1 atm Ar. In contrast, exposing a vacuum-purified sample to an atmosphere of 1 atm N-2 resulted in no significant change in the measured diffusion coefficient of Fc. The effect of dissolved argon on diffusion transport is unexpected and has implications in electrochemistry and elsewhere. Fc was found to volatilize under vacuum conditions. We propose, however, that evacuation of the cell by vacuum prior to electrochemical measurements being carried out is the only way to ensure that no contamination of the sample occurs, and use of an in situ method of determining the diffusion coefficient and concentration of Fc dispells,any ambiguity associated with Fc depletion by vacuum.

Relevance of heterometallic binding energy for metal underpotential deposition

We present first-principles calculations for a number of metals adsorbed on several different metallic substrates. Some of these systems are very relevant in electrochemistry, especially in the field of underpotential deposition phenomena. The present studies reveal the existence of a relationship between the excess binding energy and the surface energy difference between substrate and adsorbate. Comparisons with experimental underpotential shifts show that excess binding energies are systematically underestimated. By analyzing experimental information on different systems, we conclude that this discrepancy between our vacuum calculations and experiments carried out in an electrolytic solution is likely to be due to anion adsorption and/or solvent effects.

Electrochemistry of phenol in bis{(trifluoromethyl)sulfonyl}amide ([NTf2](-)) based ionic liquids

The electrochemistry of phenol and 4-tert-butyl-phenol is described in [C(2)mim][NTf2] and [C(4)mpyrr][NTf2] ionic liquids. Oxidation of phenol and phenolate is observed at E-p(a) = +1.64 and +0.24 V vs. Ag in both ionic liquids. On the cathodic sweep at a potential of -2.05 P 02 V vs. Ag under an oxygen atmosphere, the production of O-2(2-) dianions triggers the formation of phenolate anions which undergo chemical oxidation to the phenoxyl radical. The phenoxyl radical then reacts with the [NTf2](-) anion of the ionic liquid to form the corresponding phenyl triflate molecule. (c) 2005 Elsevier B.V. All rights reserved.

Electrochemistry in Room-Temperature Ionic Liquids: Potential Windows at Mercury Electrodes

The cathodic and anodic: potential limit of eleven different ionic liquids were determined at a mercury hemisphere electrode. Ionic liquids containing the phosphonium cation (tri(n-hexyl)tetradecylphosphonium, [P-14.6,P-6.6](+)) give the largest potential window, especially When Coupled to a trifluorotris(pentafluoroethyl)- [FAP](-). or bis(trifluoromethanesulfonyl)imide, [NTf2](-), anion.

Solubilization of an ionic liquid, 1-butyl-3-methylimidazolium hexafluorophosphate, in a surfactant-water system

The amphiphilic association structures were determined in the system; water, Laureth 4 (approximately C-12(EO)(4)), and the ionic liquid 1-butyl-3-methylimidazolium hexafluorophosphate ([bmim][PF6]), using visual observation and small angle x-ray diffraction. The system showed a lamellar liquid crystal solubilizing the ionic liquid ([bmim][PF6]) to a maximum of 15%, an isotropic surfactant solution dissolving the ionic liquid to a maximum of 39%, an isotropic ionic liquid solution with less than 0.5% of water and surfactant and finally, an aqueous solution with only traces of surfactant and ionic liquid. The small angle x-ray diffraction results showed the ionic liquid to be solubilized into the lamellar liquid crystal without changing the dimensions of the amphiphile layer or the interlayer spacing dependence on the water content.

Electrochemistry of Hg(II) Salts in Room-Temperature Ionic Liquids

The electrochemistry of HgCl(2) and [Hg(NTf(2))(2)] ([NTf(2)](-) = bis-{(trifluoromethyl)sulfonyl}imide) has been studied in room temperature ionic liquids. It has been found that the cyclic voltammetry of Hg(II) is strongly dependent on a number of factors (e.g., concentration, anions present in the mixture, and nature of the working electrode) and differs from that found in other media. Depending on conditions, the cyclic voltammetry of Hg(II) can give rise to one, two, or four reduction peaks, whereas the reverse oxidative scans show two to four peaks. Diffuse reflectance UV-vis spectroscopy and X-ray powder diffraction have been used to aid the assignment of the voltammetric waves.

Electrochemistry of Sulfur and Polysulfides in Ionic Liquids

The electrochemistry of elemental sulfur (S-8) and the polysulfides Na2S4 and Na2S6 has been studied for the first time in nonchloroaluminate ionic liquids. The cyclic voltammetry of S-8 in the ionic liquids is different to the behavior reported in some organic solvents, with two reductions and one oxidation peak observed. Supported by in situ UV-vis spectro-electrochemical experiments, the main reduction products of S-8 in [C(4)mim][DCA] ([C(4)mim] = 1-butyl-3-methylimidazolium; DCA = dicyanamide) have been identified as s(6)(2-) and S-4(2-), and plausible pathways for the formation of these species are proposed. Dissociation and/or disproportionation of the polyanions S-6(2-) and S-4(2-) appears to be slow in the ionic liquid, with only small amounts of the blue radical species S3(center dot-) formed in the solutions at r.t., in contrast with that observed in most molecular solvents.

Seedless synthesis of octahedral gold nanoparticles in condensed surfactant phase

We report a seedless synthetic method of gold octahedral nanoparticles in an aqueous phase. Eight facets with {111} crystalline structures of octahedral nanoparticles could be formed in an aqueous medium when the gold salt was reduced by ascorbic acid at room temperature in the presence of cetyltrimethylammonium bromide as a shape-inducing agent, and hydrogen peroxide as a reaction promoter. The growth kinetics and surface crystalline structures were characterized by UV–vis spectroscopy, transmission electron microscopy (TEM), scanning electron microscopy (SEM), and X-ray photoelectron spectroscopy.

Observation of an optical phonon band in situ in TiO electrochemistry:A possible indicator of strongly trapped intermediates in the O evolution reaction

This Letter reports in situ Fourier transform infrared (FTIR) spectroscopic data on thermal TiO films fabricated by heating titanium plates in air at 475, 700 and 800 °C. The films were studied in the dark and under UV-irradiation in aqueous 0.1MNaClO in the presence and absence of 0.1 M Na(OOC) and at 10, 25 and 50 °C. The film fabricated at 800 °C showed a broad feature near 1580cm under UV-irradiation that was not observed in the dark, whilst the films fabricated at lower temperatures, 475 and 700 °C, showed no such feature. This feature appears to be associated with the accumulation of surface-mobile holes at the complex, porous film-electrolyte interface and the capacity of such holes to enhance the absorption cross-section of optical phonons characteristic of the rutile crystal form at and near the surface of the TiO/electrolyte interface. © 2001 Elsevier Science B.V.

The Role of Water and Adsorbed Hydroxyls on Ethanol Electrochemistry on Pd: New Mechanism, Active Centers and Energetics for Direct Ethanol Fuel Cell Running in Alkaline Medium

First principles calculations with molecular dynamics are
utilized to simulate a simplified electrical double layer formed in the
active electric potential region during the electrocatalytic oxidation of
ethanol on Pd electrodes running in an alkaline electrolyte. Our
simulations provide an atomic level insight into how ethanol oxidation
occurs in fuel cells: New mechanisms in the presence of the simplified
electrical double layer are found to be different from the traditional
ones; through concerted-like dehydrogenation paths, both acetaldehyde
and acetate are produced in such a way as to avoid a variety of
intermediates, which is consistent with the experimental data obtained
from in situ FTIR spectroscopy. Our work shows that adsorbed OH on
the Pd electrode rather than Pd atoms is the active center for the
reactions; the dissociation of the C−H bond is facilitated by the
adsorption of an OH− anion on the surface, resulting in the formation
of water. Our calculations demonstrate that water dissociation rather than H desorption is the main channel through which
electrical current is generated on the Pd electrode. The effects of the inner Helmholtz layer and the outer Helmholtz layer are
decoupled, with only the inner Helmholtz layer being found to have a significant impact on the mechanistics of the reaction. Our
results provide atomic level insight into the significance of the simplified electrical double layer in electrocatalysis, which may be
of general importance.