Special Features of Ionic Liquids as Electrolytes

The electrochemistry of ionic liquids is different in some essential features from the electrochemistry of aqueous electrolytes. Particularly for electrodeposition, which involves charge transfer from the electrolyte to the electrode, the double layer on the electrode is of great importance. In general the cathode is negatively charged for the electrodeposition of metals and therefore coated with a (Helmholtz-) layer of cations at least 0.5 nm thick but the metal species in most ionic liquids is anionic (for instance AlCh ). This makes the metal deposition process complicated, for more details we refer to Chapter 2. 

In ionic liquids the coordination chemistry and concentration of metal complexes are also substantially different from those in aqueous electrolytes, with consequent effects on both the thermodynamics, i.e., the redox potential, and the kinetics of the deposition process. For details we again refer to Chapter 2. 

Since the viscosity of ionic liquids is large in some cases and concomitantly the diffusion is slow, ionic liquids generally exhibit a lower conductivity than aqueous electrolytes. To improve the mass transport it has been suggested to add diluents like benzene, toluene or acetonitrile. Water may also be a suitable diluent in some cases, acting as both a ligand and a viscosity improver. 

Nanocrystalline Metals and Alloys from Chlorometallate-based Ionic Liquids 

Nanostructured aluminum [74—78], iron [74] and aluminum-manganese alloys [74] have been prepared from a Lewis acid A1Q3/[BMIM]Q mixture (65 mol% AICI3, 35 mol% [BMIMJC1) whereas palladium alloys have been deposited from a Lewis basic system (45 mol% Aid , 55 mol% [BMIMJC1). The electrochemical cell and all parts which are in contact with the electrolyte have to be built from inert materials. As cathode material glassy carbon can be used. A constant ion concentration in the electrolyte can be realized by the use of a sacrificial anode consisting of the 

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