Electrodeposition eutectic-based ionic liquid

Abbott, A.P. Ttaib, KEl Ryder, KS. Smith, E.L. (2008), Electrodeposition of nickel using eutectic based ionic liquids, Trans.Inst Met. Finish., Vol.86, July 2008, pp. 234-240, ISSN 0020-2967... 

Section 4.3 is devoted to electrodeposition in a special class of deep eutectic solvents/ionic liquids which are based on well-priced educts such as e.g. choline chloride. The impressive aspect of these liquids is their easy operation, even under air, as well as their large-scale commercial availability. One disadvantage has to be mentioned the choline chloride-based liquids especially are currently not yet... 

Since 1980s, a large number of studies on the electrodeposition of metals have been reported. Historically, the water-sensitive chloroaluminate first-generation ILs are the most intensively studied. However, in future, the focus will rather be on air-and water-stable ionic liquids due to their variety and the less strict conditions under which they can be handled. Several review articles, books, and book chapters on the electrodeposition of metals and alloys from ILs have already been published [27-183], Ionic liquids can be classified as water/air sensitive (first-generation ionic liquids based on AIX3 (X=C1, Br)) and water/air stable (discrete anions based and eutectic solvents/ionic liquids such as ZnCl, urea, ethylene glycol, and choline chloride). A selection of published examples of the electrodeposition of metals and alloys from ionic liquids is listed in Table 5.3 the original work for each metal can be found in Refs. [23, 29-183], In this section, we mainly focus on the electrodeposition of active metals such as Al, Mg, and Ti in ionic liquids. 

In the case of Type 1 and 11 eutectics the potential window is limited at high potentials by chlorine gas evolution and at low potentials by the metal ion reduction with metal deposition from the melt. Type I eutectics have been prepared using Zn, Sn, Fe, Al, Ge and Cu chlorides. Their reduction potential is shifted towards more electronegative values as the metal halide is closer by Lewis acid. Because the reduction potential is associated with Lewis acidity, the corresponding proportions of metal and quaternary ammonium salts affect the potential window. Type 11 eutectics have been developed in order to extend the range of metals able to be electrodeposited from ionic liquids and Cr electrodeposition with good characteristics has been reported (Abbott et al., 2004 Abbott et al., 2004 Benaben Sottil, 2006). Hydration water plays a significant role on the stability and fluidity of choline chloride based ionic liquids. In this case water behaviour is different compared to the case of aqueous electrolytes and the potential window is limited rather by the metallic species... 

The electrodeposition of chromium in a mixture of choline chloride and chromium(III) chloride hexahydrate has been reported recently [39]. A dark green, viscous liquid is obtained by mixing choline chloride with chromium(III) chloride hexahydrate and the physical properties of this deep eutectic solvent are characteristic of an ionic liquid. The eutectic composition is found to be 1 2 choline chloride/chromium chloride. From this ionic liquid chromium can be electrode-posited efficiently to yield a crack-free deposit [39]. Addition of LiCl to the choline chloride-CrCl3-6H20 liquid was found to allow the deposition of nanocrystalline black chromium films [40], The use of this ionic liquid might offer an environmentally friendly process for electrodeposition of chromium instead of the current chromic acid-based baths. However, some efforts are still necessary to get shining... 

Recently a novel class of deep eutectic solvents based on choline chloride have been developed. These can be handled easily under environmental conditions and circumvent many problems that occur in aqueous solutions. They also offer the first economically viable liquids that can be used on an industrial scale. As the interest of electrochemists and classical electroplaters in ionic liquids has risen strongly in the last few years we decided, in 2006, to collect the key aspects of the electrodeposition from ionic liquids in the present book. The book has been written by a panel of expert authors during late 2006 and the first half of 2007 and thus describes the state of the art as of that point in time. 

Although many ionic liquids and deep eutectic mixtures based on choline have the advantages to be cheap and no-toxic, they are all hydrophilic and miscible with aqueous solvents. This may be a problem for applications such as the extraction of metal ions from an aqueous phase or the electrodeposition of reactive metals (aluminium, magnesium, tantalum..). 

Mele C, Catalano M, Taurino A, Bozzini B (2013) Electrochemical fabrication of ntmoporous gold-supported manganese oxide nanowires based on electrodeposition from eutectic urea/cho-line chloride ionic liquid. Electrochim Acta 87 918-924. doi 10.1016/j.electacta.2012.09.038... 

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