Electrodeposition room-temperature ionic liquids

Recently, a eutectic mixture of choline chloride and urea (commercially known as Reline) was used as a medium from which CdS, as well as CdSe and ZnS, thin films were electrodeposited for the first time [53]. Reline is a conductive room-temperature ionic liquid (RTIL) with a wide electrochemical window. The voltammetric behavior of the Reline-Cd(II)-sulfur system was investigated, while CdS thin films were deposited at constant potential and characterized by photocurrent and electrolyte electroabsorbance spectroscopies. 

In technical processes, several high-temperature molten salts are employed for electrocoating, and the morphology of the deposit is strongly influenced by the composition of the baths. Some attempts have been made to deposit Nb and Ta from ionic liquids [21, 22]. In [21] the authors focused on the electrodeposition of AlNb alloys from room-temperature ionic liquids containing both AICI3 and chlorides of Nb. 

Ghen, R. Y., Hussey, G. L., Electrodeposition of cesium at mercury electrodes in the tri-l-butylmethylammonium bis((trifluoromethyl)sulfonyl)imide room-temperature ionic liquid, Electrochim. Acta, 49, 5125-5138, 2004. 

The electrodeposition of silver from chloroaluminate ionic liquids has been studied by several authors [45-47], Katayama et al. [48] reported that the room-temperature ionic liquid l-ethyl-3-methylimidazolium tetrafluoroborate ([EMIM]BF4) is applicable as an alternative electroplating bath for silver. The ionic liquid [EMIM]BF4 is superior to the chloroaluminate systems since the electrodeposition of silver can be performed without contamination of aluminum. Electrodeposition of silver in the ionic liquids 1-butyl-3-methylimidazolium tetrafluoroborate ([BMIM]BF4) and l-butyl-3-methylimidazoliumhexafluorophosphate was also reported [49], Recently we showed that isolated silver nanoparticles can be deposited on the surface of the ionic liquid Tbutyl-3-methylimidazolium trifluoromethylsulfonate ([BMIMJTfO) by electrochemical reduction with free electrons from low-temperature plasma [50] (see Chapter 10). This unusual reaction represents a novel electrochemical process, leading to the reproducible growth of nanoscale materials. In our experience silver is quite easy to deposit in many air- and water-stable ionic liquids. 

Because of its high reactivity (—1.67 V vs. NHE), the electrodeposition of aluminum from aqueous solutions is not possible. Therefore, electrolytes for A1 deposition must be aprotic, such as ionic liquids or organic solvents. The electrodeposition of aluminum in organic solutions is commercially available (SIGAL-process [56, 57]) but due to volatility and flammability there are some safety issues. Therefore, the development of room-temperature ionic liquids in recent years has resulted in another potential approach for aluminum electrodeposition. Many papers have been published on the electrodeposition of aluminum from chloroaluminate (first... 

Voltammetric, electrodeposition, electrosynthetic and electroanalytical studies are carried out in room-temperature ionic liquids (RTILs) by a significant and increasing number of both industrial and academic laboratories [23-25], Such studies, when carried out at anything other than a very empirical level, require the use of a reference electrode . The purpose of this chapter is to address the special problems this poses and their solutions. First, however, we start by considering the essential features of a reference electrode in general. 

Room-temperature ionic liquids (denoted RTILs) have been studied as novel electrolytes for a half-century since the discovery of the chloroaluminate systems. Recently another system consisting of fluoroanions such as BF4 and PFg , which have good stability in air, has also been extensively investigated. In both systems the nonvolatile, noncombustible, and heat resistance nature of RTILs, which cannot be obtained with conventional solvents, is observed for possible applications in lithium batteries, capacitors, solar cells, and fuel cells. The nonvolatility should contribute to the long-term durability of these devices. The noncombustibility of a safe electrolyte is especially desired for the lithium battery [1]. RTILs have been also studied as an electrodeposition bath [2]. 

Room-temperature ionic liquids are the promising electrolytes for the electrodeposition of various metals because they have the merits of both organic electrolytes and high-temperature molten salts. Ionic liquids can be used in a wide temperature range, so temperatures can be elevated to accelerate such phenomena as nucleation, surface diffusion and crystallization associated with the electrodeposition of metals. In addition the process can be safely constracted because ionic liquids are neither flammable nor volatile if they are kept below the thermal decomposition temperature of the organic cations. 

Mukhopadhyay et al. [98] studied the titanium electrodeposition on a Au(lll) substrate in the l-methyl-3-butyl-imidazolium bis(trifluoromethylsulfone) imide ([BmimJBTA) ionic liquids with 0.24 M TiCl at room temperature. It was found that TiCl is converted to TiCl in a first step, which is subsequently reduced to metallic Ti. Two-dimensional (2D) clusters form preferentially on the terraces in underpotential deposition range. At a potential of -1.8 V, a dense layer of three-dimensional (3D) clusters of titanium of 1-2 nm thickness is formed. The electrochemical reduction of tetravalent titanium species in hydrophobic 1-n-butyl-l-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide ([BMP]TFSI) room-temperature ionic liquid was studied by Kayayana et al. [182]. It was found that the stepwise reduction from Ti(IV) to Ti(III) and probably Ti(II) in [BMP]TFSI containing TiBr without [BMP] Br. The potentiostatic cathodic reduction gave some deposits at 180°C. The reduction of Ti(rV) species at -2.3 V led to the deposition of some Ti compounds containing... 

Abedin SZE, Borissenko N, Endres F (2004) Electrodeposition of nanoscale silicon in a room temperature ionic liquid. Electrochem Commun 6 510-518... 

Borissenko N, Abedin SZE, Endres F (2006) In situ STM investigation of gold reconstruction and of silicon electrodeposition on Au(lll) in the room temperature ionic liquid 1-butyl-l-methylpyrroUdinium his(trifluoromethylsulfonyl)imide. J Phys Chem B 110 6250-6256... 

Endres F (2001) Electrodeposition of a thin germanium film on gold from a room temperature ionic liquid. Phys Chem Chem Phys 3 3165-3170... 

Yang MH, Sun IW (2003) Electrodeposition of antimony in a water-stable l-ethyl-3-meth-ylimidazolium chloride tetrafluoroborate room temperature ionic liquid. J Appl Electrochem 33 1077-1082... 

Oyama, T, Okajima, T, and Ohsaka, T. [2007]. Electrodeposition of gold at glassy carbon electrodes in room-temperature ionic liquids. / Electrochem. Soc, 154, pp. D322-D327. 

A wide variety of metals can be electrodeposited from room-temperature ionic liquids. The electrodeposition mechanisms of transition metals, lanthanides and Group 13 metals have been investigated as have cobalt,iron, manganese," tin," gold, " " silver, " palladium, " mercury, cerium, and lead, and the actinides. In addition, ionic liquids have been used extensively to study the electrochemistry and spectrochemistry of metal-chloride complexes. ... 

This is of course not the case when working with room temperature ionic liquid systems. Electrochemical and spectroscopic studies of cobalt, copper, and nickel, have been carried out in the AlClj-butylpyridinium chloride molten salt system. The direct current and pulsed current electrodeposition of Ni-Al alloys has also been shown in acidic AlCls-butylpyridinium chloride ionic liquids. This particular alloy has also been shown to be successful in AlCl3-[C2-mim]Cl ashave Co-Al andCu-Al. Electrochemical techniques can also be used to calculate the diffusion coefficients of metal ions. Table 21.2.6 shows the calculated diffusion coefficients and stokes-Einstein products of cobalt(II), copper(I), nickel(II) and zinc(II) in the 40-60 mol% [Cj-mimlCl-AlClj ionic liquid. 

Tsuda T, Hussey CL (2008) Electrodeposition of photocatalytic AllnSb semiconductor alloys in the lewis acidic aluminum chloride-l-ethyl-3-methylimidazolium chloride room-temperature ionic liquid. Thin Solid Eifrns 516(18) 6220-6225. doi 10.1016/J.tsf.2007.11.114... 

Zhang D, Chang W, Okajima T, Ohsaka T (2011) Electrodeposition of platimun nanoparticles in a room-temperature ionic liquid. Langmuir 27 14662-14668... 

The first room temperature ionic liquid (RTIL), [EtNHs][N03] (mp 12°C), was reported in 1914 (1), and since then a great deal of research effort has been exerted to exploit possible applications of these compounds. Initially, RTILs were used mainly as electrolytes in batteries or for metal electrodeposition however, nowadays they are finding an ever increasing range of applications. 

Silvester DS, Ward KR, Aldous L, Hardacre C, Compton RG (2008a) The electrochemical oxidation of hydrogen at activated platinum electrodes in room temperature ionic liquids as solvents. J Electroanal Chem 618 53-60 Silvester DS, Rogers El, Compton RG, McKenzie KJ, Ryder KS, Endres F, MacFarlane D, Abbott AP (2008b) Reference electrodes for use in room-temperature ionic liquids. In Endres F, MacFarlane DR, Abbot A (eds) Electrodeposition from ionic liquids. Wiley, Weinheim, pp 296-309... 

The electrodeposition of InSb from a 1-ethyl-3-methyhmidazolium chloride/tetrafluoroborate room-temperature ionic liquid (molten salt) was investigated by Yang et al. [191] using SbCls and InCla as precursors. The composition of the In-Sb codeposits can be varied by the deposition potential and bath concentrations. At a potential at which the deposition of Sb and In is mass-transport limited, InSb compound can be obtained from solutions containing equal moles of Sb(lll) and In(ni). The electrodeposited InSb was a p-type semiconductor which exhibited a direct optical transition with an optical bandgap of 0.20 eV. 

Abbott, A.P., Eardley, C.A., Farley, N.R.S. et al. (2001) Electrodeposition of aluminium and aluminium/platinum alloys from AlClj/benzyltrimethylammonium chloride room temperature ionic liquids. J. Appl. Electrochem, 31(12), 1345-1350. 

Legeai S, Diliberto S, Stein N, Boulanger C, Estager J, Papaiconomou N, Draye M (2008) Room-temperature ionic liquid for lanthanum electrodeposition. Electrochem Commun 10 1661-1664... 

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