Chloroaluminate liquid

Palladium and gold Palladium electrodeposition is of special interest for catalysis and for nanotechnology. It has been reported [49] that it can be deposited from basic chloroaluminate liquids, while in the acidic regime the low solubility of PdCl2 and passivation phenomena complicate the deposition. In our experience, however, thick Pd layers are difficult to obtain from basic chloroaluminates. With different melt compositions and special electrochemical techniques at temperatures up to 100 °C we succeeded in depositing mirror-bright and thick nanocrystalline palladium coatings [10]. 

Zinc and tin The electrodeposition of Zn [52] has been investigated in acidic chloroaluminate liquids on gold, platinum, tungsten, and glassy carbon. On glassy carbon only three-dimensional bulk deposition was observed, due to the metal s underpotential deposition behavior. At higher overvoltages, codeposition with A1... 

The Lewis acid-base properties of these ionic liquids are determined by the chloroaluminate species. The equilibrium of the chloroaluminate liquid is primarily described by two equilibria at x AICI3 below 0.67 ... 

The authors reported that they obtained Nb contents of up to 29 wt-% in the deposits, at temperatures between 90 and 140 °C. In [22], chloroaluminate liquids were employed at room temperature and AlNb films could only be obtained if NbCl5 was prereduced in a chemical reaction. The authors reported that Nb powder is the most effective reducing agent for this purpose. Similar preliminary results have been obtained for Ta electrodeposition. Although it seems to be difficult to deposit pure Nb and Ta in low-melting ionic liquids, the alloys with A1 could have quite interesting properties. 

Tin has been electrodeposited from basic and acidic chloroaluminate liquids on platinum, gold, and glassy carbon [53]. On Au the deposition starts in the UPD regime and, from the electrochemical data, one monolayer was reported. Furthermore there seems to be some evidence for alloying between Sn and Au. On glassy carbon three-dimensional growth of Sn occurs. 

In order to obtain colorless chloroaluminate liquids it is recommended to sublime the AICI3 several times prior to use after the addition of sodium chloride and aluminum wire [8],... 

Elemental gallium has been electrodeposited from chlorogallate ionic liquids formed between [EMIM]Q and GaClj [112], The direct electrodeposition of GaAs from ionic liquids was studied mainly by two groups. Wicelinski et al. [113] used an acidic chloroaluminate liquid to co-deposit Ga and As. However, it was reported... 

The absorption of species from the atmosphere is common to all electrolyte solutions and clearly the absorption of water is the biggest issue. This is not solely confined to ionic liquids, however, as all electroplaters who deal with aqueous solutions of acids know, if the solution is not heated then the tank will overflow from absorption of atmospheric moisture after some time. In the aqueous acid the inclusion of water is not a major issue as it does not significantly affect the current efficiency or potential window of the solution. Water absorption is also not such a serious issue with eutectic-based ionic liquids and the strong Lewis acids and bases strongly coordinate the water molecules in solution. The presence of up to 1 wt.% water can be tolerated by most eutectic-based systems. Far from having a deleterious effect, water is often beneficial to eutectic-based liquids as it decreases the viscosity, increases the conductivity and can improve the rate of the anodic reaction allowing better surface finishes. Water can even be tolerated in the chloroaluminate liquids to a certain extent [139] and it was recently shown that the presence of trace HQ, that results from hydrolysis of the liquid, is beneficial for the removal of oxide from the aluminum anode [140]. 

Method 1 is known as the method of incipient wetness, because the ionic liquid is added to the support until the mixture starts to lose the appearance of an dry powder. This is the most simple of the presented methods, allowing the immobilisation of high amounts of chloroaluminate liquids on any given silica support. Unfortunately, during the immobilisation step HC1 is created which leads to a decomposition of zeolites and MCM 41 type supports. This problem could be overcome by a modification of the immobilisation method. The supported ILs synthesised this way show a high catalytic activity in Friedel-Crafts reactions. 

Sodium and lithium Both sodium [15] and lithium [16] electrodeposition was successful in neutral chloroaluminate ionic liquids that contained protons. These elements are interesting for Na- or Li-based secondary batteries, where the metals would serve directly as the anode material. The electrodeposition is not possible in basic or acidic chloroaluminates, only proton-rich NaQ or LiQ buffered neutral chloroaluminate liquids were feasible. The protons enlarged the electrochemical window towards the cathodic regime so that the alkali metal electrodeposition became possible. For Na the proton source was dissolved HQ that was introduced via the gas phase or via 1-ethyl-3-methylimidazolium hydrogen dichloride. Triethanolamine hydrogen dichloride was employed as the proton source for Li electrodeposition. For both alkali metals, reversible deposition and stripping were reported on tungsten and stainless steel substrates, respectively. 

Lairthanum and aluminum-lanthanum alloys It was reported, that La can be elec-trodeposited from chloroaluminate liquids [28]. Whereas firom the pure liquid only AlLa alloys can be obtained, the addition of excess liQ and small quantities of thionylchloride (SOCI2) to a LaQs-saturated melt allows the deposition of elemental La. However, the electrodissolution seems to be somewhat kinetically hindered. 

Cd electrodeposition has been reported by Noel et al. and by Chen et al. [38,39]. CdCb was used to buffer neutral chloroaluminate liquids and the element could be deposited [38]. Chen et al. used a basic l-ethyl-3-methylimidazolium chloride/tetrafluoroborate ionic liquid to deposit Cd successfiiUy [39]. It is formed on platinum, tungsten and glassy carbon from CdCU in a quasi-reversible two-electron reduction process. This result is promising as Te could perhaps also be deposited from such an ionic liquid thus giving a system for direct CdTe electrodeposition. 

Sectrodeposition of nickel and cobalt has been investigated intensively in aqueous solutions. Both metals are interesting for nanotechnology as magnetic nanostructures can be formed in aqueous solutions [47]. Hovrever, the bulk electrodeposition is accompanied by a massive hydrogen evolution. Both elements can also be deposited from acidic chloroaluminate liquids [48,49]. Cobalt and zinc-cobalt alloys... 

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