Metal water-stable ionic liquid

In the 1990s John Wilkes and coworkers introduced air- and water-stable ionic liquids (see Chapter 2.2) which have attractive electrochemical windows (up to 3 V vs. NHE) and extremely low vapor pressures. Furthermore, they are free from any aluminum species per se. Nevertheless, it took a while until the first electrodeposition experiments were published. The main reason might have been that purity was a concern in the beginning, making reproducible results a challenge. Water and halide were prominent impurities interfering with the dissolved metal salts and/or the deposits. Today about 300 different ionic liquids with different qualities are commercially available from several companies. Section 4.2 summarizes the state-of-the-art of electrodeposition in air- and water-stable ionic liquids. These liquids are for example well suited to the electrodeposition of reactive elements such as Ge, Si, Ta, Nb, Li and others. 

Electrodeposition of Metals in Air- and Water-stable Ionic Liquids... 

In this section we will show that air- and water-stable ionic liquids can be used for the electrodeposition of highly reactive elements which cannot be obtained from aqueous solutions, such as aluminum, magnesium and lithium, and also refractory metals such as tantalum and titanium. Although these liquids are no longer air-and water-stable when AICI3, TaFs, TiCU and others are dissolved, quite interesting results can be obtained in these liquids. 

In this chapter we have briefly discussed the high potential of air- and water-stable ionic liquids as electrolytes for metal deposition. Their extraordinary physical properties, superior to those of water or organic solvents, and their stability, open the door to the electrodeposition of many metals. Some advantages of air- and water-stable ionic liquids in electrodeposition are that they are quite easy to purify and handle and in most cases they do not decompose under environmental conditions. They can have pretty wide electrochemical windows of up to 6 V, and hence they... 

Over the past two decades, ionic liquids (ILs) have attracted considerable interest as media for a wide range of applications. For electrochemical applications they exhibit several advantages over the conventional molecular solvents and high temperature molten salts they show good electrical conductivity, wide electrochemical windows of up to 6 V, low vapor pressure, non-flammability in most cases, and thermal windows of 300-400 °C (see Chapter 4). Moreover, ionic liquids are, in most cases, aprotic so that the complications associated with hydrogen evolution that occur in aqueous baths are eliminated. Thus ILs are suitable for the electrodeposition of metals and alloys, especially those that are difficult to prepare in an aqueous bath. Several reviews on the electrodeposition of metals and alloys in ILs have already been published [1-4], A selection of published examples of the electrodeposition of alloys from ionic liquids is listed in Table 5.1 [5-40]. Ionic liquids can be classified into water/air sensitive and water/air stable ones (see Chapter 3). 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... 

For the electrodeposition of metals or alloys from air- and water-stable ionic liquids, it is necessary first to dissolve the corresponding metal ions in the ionic liquid. Such a dissolution process is made possible by introducing excess amounts of halide ions (such as Cl ) to form soluble metal-halide complex anions. Alternatively, the metal is dectrochemically oxidized in the ionic liquid to form the soluble salt such as Sn(Tf2N) in the trimethyl-n-hexylammonium [bis(trifluoromethyl)sulfonyl]amide ([TMHAj TfiN ) ionic liquid. 

The electrodeposition of Zn-Mn was investigated at 80 °C in the hydrophobic tri-1-butylmethylammonium bis((trifluoromethyl)sulfonyl)amide ([TBMA]+Tf2N ) [46] ionic liquid containing Zn(II) and Mn(II) species that were introduced into the ionic liquid by anodic dissolution of the respective metal electrodes. Cyclic voltam-mograms indicated that the reduction of Zn(II) occurs at a potential less negative than that of the Mn(II). Due to some kinetic limitations, which is a common phenomenon in air- and water-stable ionic liquids, incomplete oxidation of Mn electrodeposits was observed in this system. The current efficiency of Mn electrodeposition in this ionic liquid approaches 100%, which is a great improvement compared to the results obtained in aqueous solution (20-70%). Electrodeposition of Zn-Mn alloy coatings has never been carried out in chloroaluminate ionic liquid because of the unavoidable codeposition of Mn and Al. 

In this chapter some results on the electrodeposition of alloys from ionic liquids are summarized. Many fundamental studies have been performed in chloroaluminate first generation ionic liquids but the number of studies employing air- and water-stable ionic liquids rather than the chloroaluminates is increasing. Currently, new ionic liquids with better electrochemical properties are being developed. For example, Abbott et al. [47] have prepared a series of ionic liquids by mixing commercially available low-cost choline chloride and MCI2 (M = Zn, Sn) or urea and demonstrated that these ILs are good media for electrodeposition for pure metals (see Chapter 4.3). It can be expected that in the near future, the electrodeposition of alloys from ILs may become available for industrial applications. Furthermore, due to their variety, their wide electrochemical and thermal windows air- and water-stable ionic liquids have unprecedented prospects for electrodeposition. 

In this chapter we present a few selected results on the nanoscale electrodeposition of some important metals and semiconductors, namely, Al, Ta and Si, in air- and water-stable ionic liquids. Here we focus on the investigation of the electrode/electrolyte interface during electrodeposition with the in situ scanning tunneling microscope and we would like to draw attention to the fascinating... 

Tantalum Tantalum has unique properties that make it useful for many applications, from electronics to mechanical and chemical systems. Many efforts have been made to develop an electroplating process for the electrodeposition of Ta. High-temperature molten salts were found to be efficient baths for the dectrodepo-sition of refractory metals. To the best of our knowledge, imtil now no successful attempts have been made for Ta electrodeposition at room temperature or even at low temperature in ionic liquids. We present here the first results of tantalum dec-trodeposition in the air and water stable ionic liquid 1-butyl-l-methyl-pyrrolidinium bis(tri-fiuoromethylsulfonyl)amide ([BMP][Tf2N]). 

Water-stable ionic liquids were later used for Friedel-Crafts acylations, using a metal triflate catalyst. Cu(0Tf)2 proved to be the most efficient catalyst for this transformation, and acylation of anisole by benzoyl chloride in [bmim][BF4] gave almost exclusively the para adduct 68 (Scheme 24). This reaction can also be performed in organic solvents, but an accelerated rate is observed in ionic liquids.Catalyst loading can be decreased (up to 1 mol%) using bismuth(m) salts as catalysts. ... 

Zein El Abedin S, Endres F (2006) Electrodeposition of metals and semiconductors in air- and water-stable ionic liquids. Chem Phys Chem 7 58 Endres F (2002) Ionic liquids solvents for the electrodeposition of metals and semiconductors. Chem Phys Chem 3 144... 

Similarly, Kou et al. published the synthesis of PVP-stabilized noble-metal nanoparticles in ionic liquids BMI PF6 at room temperature [76]. The metal nanoparticles (Pt, Pd, Rh) were produced by reduction of the corresponding metal halide salts in the presence of PVP into a refluxing ethanol-water solution. After evaporation to dryness the residue was redissolved in methanol and the solution added to the ionic liquid. The methanol was then removed by evaporation to give the ionic liquid-immobilized nanoparticles. These nanoparticles were very stable. TEM ob-... 

Additive free electrodeposition of nanocrystalline aluminium in a water and air stable ionic liquid. Electrochem. Commun., 7,1111-1116 Zhong, C. Sasaki, T. Jimbo-Kobayashi, A. Fujiwara, E. Kobayashi, A. Tada, M. Iwasawa, Y. (2007). Syntheses, structures, and properties of a series of metal ion-containing dialkylimidazolium ionic liquids. Bull. Chem. Soc. fpn., 80, 2365-2374... 

Antimony is a brittle silvery-white metal. Although the unalloyed form of antimony is not often used in industry, alloys of antimony have found wide commercial applications. The integration of antimony gives certain desirable properties, such as increased corrosion resistance and hardness. Moreover, antimony is also the component of some semiconductors such as InSb and InAsi %Sb%. Sb electrodeposits with good adherence were obtained in a water-stable l-ethyl-3-methylimidazolium chloride-tetrafluoroborate ([EMIM]C1-BF4) room-temperature ionicliquid [53]. Furthermore, it was stated that a crystalline InSb compound can be obtained through direct electrodeposition in the ionic liquid [EMIM]C1-BF4 containing In(III) and Sb(III) at 120 °C [54]. It is just a question of time until antimony electrodeposition is reported in the third generation of ionic liquids. 

Abbott et al. [98-103] reported the synthesis and characterization of new moisture-stable, Lewis acidic ionic liquids made from metal chlorides and commercially available quaternary ammonium salts (see Chapter 2.3). They showed that mixtures of choline chloride (2-hydroxyethyltrimethylammonium chloride, [Me3NC2H40H]Cl and MCU (M=Zn, Sn) give conducting and viscous liquids at or around room temperature. These deep eutectic solvents/ionic liquids are easy to prepare, are water-and air-stable, and their low cost enables their use in large-scale applications. Furthermore, they reported [104] that a dark green, viscous liquid can be formed by mixing choline chloride with chromium(III) chloride hexahydrate and that the... 

It is of course essential that the ionic liquid is stable in the presence of the oxidant, which excludes ionic liquids with metallic anions such as chlorocuprates. In many oxidation reactions water is present as co-solvent, reagent or it is produced in the course of the reaction, which further eliminates the use of chloroaluminates. However, less care has to be taken with respect to drying the ionic liquid compared to other catalytic reactions when aqueous oxidants are used. Common imidazolium and ammonium based ionic liquids are neither water-nor oxygen sensitive and thus well suited and may even act as co-catalyst in the oxidation reaction. Some anions like [BF4] and [PF6] are, however, susceptible towards hydrolysis. Where the ionic liquid is highly viscous, a co-solvent such as dichloromethane might be necessary to afford acceptable reaction rates, especially when molecular oxygen is used as reagent. 

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