Bernhard Gollas

Zinc Electrodeposition from a Deep Eutectic System Containing Choline Chloride and Ethylene Glycol

Deep eutectic electrolytes have recently been considered as alternatives to classical room-temperature ionic liquids. This work is an initial study of the zinc deposition process from a basic choline chloride/ethylene glycol deep eutectic solvent containing ZnCl 2 at 30°C. The system was examined by cyclic voltammetry at static and rotating glassy carbon disk electrodes and by potential step techniques. There was little deposition initially on sweeping or stepping the potential to ―0.5 to ―0.8 V vs Zn/Zn(II), but more rapid deposition was observed when the potential was subsequently raised to -0.4 to -0.2 V. The role of choline chloride was also studied by comparing with a choline-free electrolyte, which exhibited a more conventional voltammetric response. The formation of a dissolved, intermediate species Z on the cathodic sweep was proposed to account for the observed deposition behavior in the deep eutectic. Furthermore, an observation of the electrodeposition behavior with the addition of sodium ethoxide supports the suggestion that Z is a complex of Zn 2+ and deprotonated components of the solvent.

A Study of Zinc Electrodeposition From Zinc Chloride: Choline Chloride: Ethylene Glycol

This work is an initial study of the zinc deposition process from a Lewis-basic choline chloride/ ethylene glycol deep eutectic solvent containing ZnCl 2 at 30°C. The system was examined by cyclic voltammetry at static and rotating glassy carbon disc electrodes and by potential step techniques. Although there was little deposition initially on sweeping or stepping the potential to -0.5 to -0.8 V vs. Zn/Zn(II) more rapid deposition was observed when the potential was raised to -0.4 to -0.2 V. The role of choline chloride was also examined by comparison with a choline-free electrolyte, which exhibited a more conventional voltammetric response. A tentative suggestion has been proposed to account for the observed deposition behaviour.

Mesostructure and physical properties of aqueous mixtures of the ionic liquid 1-ethyl-3-methyl imidazolium octyl sulfate doped with divalent sulfate salts in the liquid and the mesomorphic states

This paper extends the study of the induced temperature change in the mesostructure and in the physical properties occurring in aqueous mixtures of the ionic liquid 1-ethyl-3-methyl imidazolium octyl-sulfate [EMIm][OSO4]. For some compositions, these mixtures undergo a phase transition between the liquid (isotropic in the mesoscale) and the mesomorphic state (lyotropic liquid crystalline) at about room temperature. The behavior of mixtures doped with a divalent metal sulfate was investigated in order to observe their applicability as electrolytes. Calcium sulfate salt is almost insoluble even in the 20 wt% water mixture. The magnesium salt, in contrast, can be dissolved up to concentrations of 730 ppm in the same mixture and it has a profound impact on its properties. Six aqueous mixtures (with water content from 10 wt% to 33 wt%) of [EMIm][OSO4] were saturated with magnesium sulfate salt, producing the ternary mixture [EMIm][OSO4] + H2O + MgSO4. Viscosity, density and ionic conductivity for these samples were measured from 10 °C to 90 °C. In addition, SAXS, FTIR, diffussion NMR and Raman spectroscopy of the most interesting samples have been performed, and structural data indicate a transition between a hexagonal lyotropic liquid crystalline phase below and an isotropic solution phase above room temperature. The octyl sulfate anions of the cylindrical micelles in the hexagonal phase are coordinated with water molecules through H-bonds (about four per sulfate anion), while the [EMIm] cations seem to be poorly coordinated and so free to move. Inorganic salt addition reinforces that network, increasing the phase transition temperature.

Tin, Bismuth, and Tin–Bismuth Alloy Electrodeposition from Chlorometalate Salts in Deep Eutectic Solvents

Abstract The electrodeposition of tin, bismuth, and tin–bismuth alloys from SnII and BiIII chlorometalate salts in the choline chloride/ethylene glycol (1:2 molar ratio) deep eutectic solvent was studied on glassy carbon and gold by cyclic voltammetry, rotating disc voltammetry, and chronoamperometry. The SnII‐containing electrolyte showed one voltammetric redox process corresponding to SnII/Sn0. The diffusion coefficient of [SnCl3]−, detected as the dominating species by Raman spectroscopy, was determined from Levich and Cottrell analyses. The BiIII‐containing electrolyte showed two voltammetric reduction processes, both attributed to BiIII/Bi0. Dimensionless current/time transients revealed that the electrodeposition of both Sn and Bi on glassy carbon proceeded by 3D‐progressive nucleation at a low overpotential and changed to instantaneous at higher overpotentials. The nucleation rate of Bi on glassy carbon was considerably smaller than that of Sn. Elemental Sn and Bi were electrodeposited on Au‐coated glass slides from their respective salt solutions, as were Sn–Bi alloys from a 2:1 SnII/BiIII solution. The biphasic Sn–Bi alloys changed from a Bi‐rich composition to a Sn‐rich composition by making the deposition potential more negative.

Separation of 1,3-substituted imidazoles for quality control of a Lewis acidic ionic liquid for aluminum electroplating

Ionic liquids (ILs) are already used or have great potential in many industrial applications. Knowledge about their unique physicochemical characteristics makes ILs suitable for the electrodeposition of metals with very low negative potentials. Aluminum with its good corrosion protection behavior has great capability to be electroplated from IL electrolytes on steel substrates. The stability of the chosen electrolyte is very important to ensure industrial applicability. In this study, temperature and electrochemical long‐term stability from electrolytes based on a Lewis acidic mixture of AlCl3 and 1‐ethyl‐3‐methylimidazolium chloride are investigated. A published method was modified to identify possible degradation products using mass spectrometric detection. The optimized method used an Agilent Zorbax SB‐Phenyl column (2.0 × 150 mm, 5 μm particles) with a 20 mmol TFA and 5% ACN mobile phase. This method allowed the quantification of several imidazoles from 0.1 to 100 mg/L. When analyzing the long‐term stressed electrolytes, no significant changes in electrolyte composition could be observed.

Stability of nicotinate and dodecyl sulfate in a Lewis acidic ionic liquid for aluminum electroplating and characterization of their degradation products

Plating bath additives are essential for optimization of the morphology of electroplated layers. The ionic liquid 1‐ethyl‐3‐methylimidazolium (EMIM) chloride plus 1.5 mol equivalents of AlCl3 has great potential for electroplating of aluminum. In this study, the chemical and electrochemical stability of the additives EMIM‐nicotinate and sodium dodecyl sulfate and their effect on the stability of EMIM was investigated and analyzed. Nicotinate and its electrochemical decomposition product β‐picoline could be detected and we show with a single HPLC‐UV‐MS method that EMIM is not affected by the decomposition of this additive. An adapted standard HPLC‐UV‐MS method together with GC‐MS and ion chromatography was used to analyze the decomposition products of SDS and possible realkylation products of EMIM. Several volatile medium and short chain‐length alkanes as well as sulfate ions have been found as decomposition products of SDS. Alkenium ions formed as intermediates during the decomposition of SDS realkylate EMIM to produce mono‐ up to pentasubstituted alkyl‐imidazoles. A reaction pathway involving Wagner–Meerwein rearrangements and Friedel–Crafts alkylations has been suggested to account for the formation of the detected products.

Virtual Issue: Advances in Electrochemistry

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