Electrodeposition of metals that can also be obtained from water

4 Electrodeposition of metals that can also be obtained from water 

Indium and antimony The electrodeposition of In on glassy carbon, tungsten, and nickel has been reported [26]. In basic chloroaluminates, elemental indium is 

InSb is a direct semiconductor, and quantum dots of InSb, made under ultra-high vacuum conditions, have already been successfully studied for laser appHcations [32]. Quantum dots are widely under investigation nowadays and this is a rapidly growing research field. Definite electrodeposition from ionic Hquids would be an important contribution. 

Tellurium and cadmium Electrodeposition of Te has been reported [33] in basic chloroaluminates the element is formed from the [TeClg] complex in one four-electron reduction step, furthermore, metallic Te can be reduced to Te species. Electrodeposition of the element on glassy carbon involves three-dimensional nucleation. A systematic study of the electrodeposition in different ionic liquids would be of interest because - as with InSb - a defined codeposition with cadmium could produce the direct semiconductor CdTe. Although this semiconductor can be deposited from aqueous solutions in a layer-by-layer process [34], variation of the temperature over a wide range would be interesting since the grain sizes and the kinetics of the reaction would be influenced. 

Electrodeposition of Cd has also been reported [35, 36]. In [35], CdCl2 was used to buffer neutral chloroaluminate Hquids from which the element could be deposited. 

The electrodeposition of Ag has also been intensively investigated [41 3]. In the chloroaluminates - as in the case of Cu - it is only deposited from acidic solutions. The deposition occurs in one step from Ag(I). On glassy carbon and tungsten, three-dimensional nucleation was reported [41]. Quite recently it was reported that Ag can also be deposited in a one-electron step from tetrafluoroborate ionic liquids [43]. However, the charge-transfer reaction seems to play an important role in this medium and the deposition is not as reversible as in the chloroaluminate systems. 

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]. 

4 Electrodeposition of Metals That Can Also Be Obtained From Water 

Te electrodeposition has been reported in basic chloroaluminates [36] where the element is formed from the [TeCle] complex in a four-electron reduction step. 

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. 

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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. 

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