Ionic liquids are solvents that consist entirely of ions. They have unique properties such as a negligible vapor pressure, good electrochemical stability, and an intrinsic electric conductivity. These solvents have a great potential as safe non-aqueous electrolytes for the electrodeposition of metals. For high-rate electrodeposition, the electrolyte needs to have a large metal concentration. Unfortunately, many metal salts are poorly soluble in ionic liquids.
The groups of Koen Binnemans and Jan Fransaer, Katholieke Universiteit Leuven, Belgium, have developed silver-containing ionic liquids that allow high-rate electrodeposition of silver coatings, which could be used as electric contacts on electronic circuit boards. The solubility problem was solved by incorporation of a silver ion in the ionic liquid cation. The silver center is coordinated by two or more alkylamine ligands, such as 2-ethylhexylamine (2-EtHexAm) or ethylenediamine (en), and a bis(trifluoromethylsulfonyl)imide (Tf2N) anion.
Such ionic liquids are electrolytes with the highest possible metal concentration, because the metal is an integral part of the ionic liquid. As such, the electrodeposition behaviour of two of the ionic liquids, [Ag(2-EtHexAm)2][Tf2N] and [Ag(en)2][Tf2N], was investigated both at room temperature and at 90 °C. It was possible to achieve very high current densities in unstirred solutions and to electrodeposit closed, crack-free, silver coatings.
- Silver-Containing Ionic Liquids with Alkylamine Ligands,
Daphne Depuydt, Neil R. Brooks, Stijn Schaltin, Luc Van Meervelt, Jan Fransaer, Koen Binnemans,