S. Zein El Abedin

Ionic liquids as green electrolytes for the electrodeposition of nanomaterials

Ionic liquids, especially air and water stable ones, experience much attention, since they have attractive physical properties. We exemplify in this paper the potential of ionic liquids in the electrodeposition of nanocrystalline metals without additives. The results show that nanocrystalline copper and aluminium can be electrodeposited in the air and water stable ionic liquids 1-butyl-1-methylpyrrolidinium trifluoromethanesulfonate ([BMP]TFO) and 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)amide ([BMP]Tf2N), respectively, on conventional solid electrodes with sufficient electronic conductivity. Generally, the obtained Al or Cu deposits are shiny, dense and adherent with very fine crystallites with average sizes of about 30 and 40 nm, respectively. The [BMP]+ cation might act as a grain refiner, leading to nanosized deposits. The results of first attempts to use plasmas as mechanically contact-free electrodes for the cathodic deposition of nanoscaled metals (glow discharge electrodeposition) are also presented. The relevance of our results for the development of a green process to make nanomaterials as catalysts for fuel processing is briefly discussed.

Electrodeposition of Ge, Si and SixGe1−x from an air- and water-stable ionic liquid

The electrodeposition of Ge, Si and, for the first time, of Si(x)Ge(1-x) from the air- and water-stable ionic liquid 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)amide ([Py(1,4)]Tf(2)N) containing GeCl(4) and/or SiCl(4) as precursors is investigated by cyclic voltammetry and high-resolution scanning electron microscopy. GeCl(2) in [Py(1,4)]Tf(2)N is electrochemically prepared in a two-compartment cell to be used as Ge precursor instead of GeCl(4) in order to avoid the chemical attack of Ge(iv) on deposited Ge. Silicon, germanium and Si(x)Ge(1-x) can be deposited reproducibly and easily in this ionic liquid. Interestingly, the Si(x)Ge(1-x) deposit showed a strong colour change (from red to blue) at room temperature during electrodeposition, which is likely to be due to a quantum size effect. The observed colours are indicative of band gaps between at least 1.5 and 3.2 eV. The potential of ionic liquids in Si(x)Ge(1-x) electrodeposition is demonstrated.

Electroreduction of tantalum fluoride in a room temperature ionic liquid at variable temperatures

The present paper deals with the electroreduction of TaF5 in the room temperature ionic liquid 1-buty-1-methyl-pyrrolidinium bis(tri-fluoromethylsulfonyl)imide ([BMP]Tf2N) at different temperatures for the sake of electrodeposition of tantalum. The study was carried out using cyclic voltammetry and chronoamperometry measurements complemented by SEM-EDAX and XRD investigations. In situ scanning tunneling microscopy and I-U tunneling spectroscopy were also utilized for characterization of the electrodeposits. The results show that, in addition to the formation of insoluble compounds, Ta can be electrodeposited in the ionic liquid ([BMP]Tf2N) containing 0.5 M TaF5 at 200 degrees C on polycrystalline Pt and Au(111) electrodes. By addition of LiF to the electrolyte, the quality and the adherence of the electrodeposit were found to be improved. An in situ I-U tunneling spectrum with about 300 nm thickness of the electrodeposit shows metallic behaviour indicating the formation of elemental tantalum. Moreover, the XRD patterns of the electrodeposit, obtained potentiostatically at -1.8 V (vs. Pt) in ([BMP]Tf2N) containing 0.25 M TaF5 and 0.25 M LiF on Pt electrode at 200 degrees C, show the characteristic patterns of crystalline tantalum.

Electrodeposition of Nanocrystalline Aluminum: Breakdown of Imidazolium Cations Modifies the Crystal Size

In this paper we describe the aluminum electrodeposition in 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)amide [EMIm]Tf 2 N/AlCl 3 and 1-ethyl-3-methylimidazolium chloride [EMIm]Cl/AlCl 3 , respectively. It is found that, besides microcrystalline aluminum, nanocrystalline aluminum can also be obtained by electrodeposition from both ionic liquids at room temperature without additives. The crystal refinement is due to a cathodic decomposition of the imidazolium ions to a certain extent giving rise to nanocrystalline aluminum. The electrochemical behavior was studied by cyclic voltammetry, galvanostatic, and potentiostatic polarization experiments complemented by scanning electron microscopy/energy-dispersive X-ray analysis. The upper phase of the biphasic ionic liquid [EMIm]Tf 2 N/AlCl 3 and the Lewis acidic [EMIm]Cl/AlCl 3 ionic liquid are both subject to some decomposition at low electrode potentials: the color of the ionic liquids instantly changes from colorless to purple, starting near the working electrode. The subsequent electrodeposition performed on various substrates no longer leads to microcrystalline but rather to nanocrystalline aluminum, presumably because cation breakdown products act as a crystal refiner during the electrodeposition.

Electrosynthesis of Poly(para)phenylene in an Ionic Liquid: Cyclic Voltammetry and in Situ STM/Tunnelling Spectroscopy Studies

The electropolymerization of benzene in the air and water-stable ionic liquid 1-hexyl-3-methylimidazolium tris(pentafluoroethyl)trifluorophosphate (HMIm)FAP is investigated. The study comprises cyclic voltammetry, IR and in situ STM/tunnelling spectroscopy measurements. The IR results indicate that poly(para)phenylene is the end product of the electropolymerization of benzene in the employed ionic liquid. The resulting conjugation lengths of the product fall between 19 and 21. A polymer reference electrode is used successfully for the electrochemical polymerization of benzene. The first in situ STM results show that the electropolymerization of benzene in the ionic liquid can be probed on the nanoscale and the band gap of the prepared polymer can be determined. The electrodeposited polymer film obtained at a constant potential of 1.0 V vs PPP (polyparaphenylene) exhibits a band gap of 2.9+/-0.2 eV.

Electrodeposition of iron and iron–aluminium alloys in an ionic liquid and their magnetic properties

In this work we show that nanocrystalline iron and iron-aluminium alloys can be electrodeposited from the ionic liquid 1-butyl-1-methylpyrrolidinium trifluoromethylsulfonate, [Py1,4]TfO, at 100 °C. The study comprises CV, SEM, XRD, and magnetic measurements. Two different sources of iron(ii) species, Fe(TfO)2 and FeCl2, were used for the electrodeposition of iron in [Py1,4]TfO. Cyclic voltammetry was employed to evaluate the electrochemical behavior of FeCl2, Fe(TfO)2, and (FeCl2 + AlCl3) in the employed ionic liquid. Thick iron deposits were obtained from FeCl2/[Py1,4]TfO at 100 °C. Electrodeposition of iron-aluminium alloys was successful in the same ionic liquid at 100 °C. The morphology and crystallinity of the obtained deposits were investigated using SEM and XRD, respectively. XRD measurements reveal the formation of iron-aluminium alloys. First magnetic measurements of some deposits gave relatively high coercive forces and power losses in comparison to commercial iron-silicon samples due to the small grain size in the nanometer regime. The present study shows the feasibility of preparing magnetic alloys from ionic liquids.

Template-assisted electrodeposition of highly ordered macroporous zinc structures from an ionic liquid

The present paper shows the template-assisted electrodeposition of highly ordered macroporous zinc films in the ionic liquid 1-butyl-1-methylpyrrolidinium trifluoromethylsulfonate ([Py1,4]TfO). Polystyrene (PS) spheres were employed as templates, and zinc films were electrodeposited within the interstitial voids of the template. The results show that well-ordered two- or three-dimensional macroporous zinc films can easily be made. The obtained macroporous films showed diffractive light when illuminated with white light. The contact angle measurements revealed that the wettability of the employed ionic liquid on PS templates is much better than the one of aqueous solutions, leading to better infiltration into the interstitial voids of the PS spheres. Macroporous zinc is potentially interesting as host material for lithium ion batteries.

Electrochemical Deposition of Nanostructured Metals and Alloys from Ionic Liquids

Metals like aluminium, magnesium, tungsten or their alloys cannot be electrodeposited from aqueous electrolytes. We have developed a procedure using AlCl3-based ionic liquids for the deposition of nanostructured metals and alloys. The ionic liquids (IL) employed for these studies consist of mixtures of an inorganic (e.g., AlCl3) and an organic component (e.g., 1-butyl-3-methyl-imidazoliumchloride or [BMIm]Cl). In our contribution we describe the electrochemical deposition of less noble metals like Al or Fe and alloys like AlxMn1−x with a controlled nanostructure. The variation of physical and chemical process parameters allows the deposition of samples with crystallite sizes from 10 up to several hundred nm. Deposits prepared from ILs show remarkable properties. Based on nanoindentation measurements we observe crystallite size dependent microhardness for nanostructured aluminium (from 1.44 GPa (100 nm) to 3.40 GPa (14 nm)). The thermal stability of the deposits was measured by high temperature X-ray diffraction. The deposits show a thermal stability up to 350 °C resulting from oxide impurities in the grain boundaries. An activiation energy of 41 kJ/mol can be determined for the crystallite growth process. The magnetization curves of nanostructurd iron exhibit soft magnetic behavior; the coercivity is inverse proportional to the crystallite size.

Electrodeposition and stripping behavior of a zinc/polystyrene composite electrode in an ionic liquid

The cycling behavior of a zinc/polystyrene composite electrode in the ionic liquid 1-butyl-1-methylpyrrolidinium trifluoromethylsulfonate ([Py1,4]TfO) was studied at room temperature. A brass substrate covered by polystyrene spheres was used to produce a zinc composite electrode. The obtained electrode was investigated using various techniques like potentiostatic and galvanostatic deposition/stripping cycles, scanning electron microscopy (SEM), and energy dispersive x-ray spectroscopy (EDX). The effect of a uniaxial mechanical pressure on adhesion and cycling behavior was also investigated. The results show that zinc grows uniformly within the voids of the polystyrene structures with no hints of dendritic growth. Such a composite material is interesting as electrode material for zinc-based batteries.

Coating of mild steel by aluminium in the ionic liquid [EMIm]Tf2N and its corrosion performance

The present paper shows for the first time that dense, adherent aluminium layers can be electrodeposited on mild steel in the water and air stable ionic liquid 1-ethyl-3methylimidazolium bis(trifluoromethylsulfonyl) amide [EMIm]Tf 2N containing AlCl3 as a source of aluminium. The study was carried out using electrochemical techniques such as, cyclic voltammetry, chronopotentiometry, chronoamperometry, potentiodynamic polarization and electrochemical impedance spectroscopy, as well as surface analytical techniques such as SEM-EDX analysis and i situ STM. It was found that well adherent aluminium layers can be obtained after anodic oxidation of the substrate in the employed electrolyte prior to bulk deposition of aluminium. The corrosion behaviour of mild steel without and with coating by an aluminium layer with thickness of about 10 μm was investigated in 3.5% NaCl solutions. Compared to the uncoated sample, the Al-coated mild steel shows lower corrosion current and higher polarization resistance indicating the improvement of the corrosion resistance by Al coating.