Electrodeposition from Ionic Liquids: Which Processes Have the Potential for Commercialization ?

Electrodeposition from aqueous solutions is well developped and widely used in the electroplating industry. One example among many other ones is the deposition of zinc on steel, in order to slow down or even prevent atmospheric corrosion, e.g. of cars. Such deposition processes are limited by the electrochemical window of water, which does not allow the deposition of reactive elements like Al, Ta, Nb, Si, Ge and other ones. Ionic liquids, that have gained a lot of interest in the recent years, have electrochemical windows that in some cases are as wide as ± 3 V vs. NHE. Thus, they allow the electrodeposition of reactive elements. From AlCl₃-based ionic liquids, often abbreviated as chloroaluminates, Aluminum can be deposited easily, and the main disadvantage might be that at least dry air is needed, as these liquids absorb moisture rapidly. Although low amounts of water are not a problem, continous absorption leads to a lower deposit quality, visible by black spots. Furthermore, the liquid has to be washed off carefully before the Al layers can be exposed to air. Neveretheless, such Al shows a good corrosion protection, for example of high and highest strength steels. Furthermore, nanostructured Al is of potential interest as host material for future Li ion batteries, and electrodeposition opens up an easy way to make macroporous materials for this purpose. A still rather rare possible application is the electrodeposition of semiconductors. Both Si and Ge can be electrodeposited as thin layers (and we have hints for GaN deposition), as nanowires/nanotubes and macroporous materials, and the deposits are amorphous. At the first glance this appears to be disadvantageous, however, at the second glance amorphous Si is of high interest as host material for Li ion batteries. Amorphous thin Ge is of considerable interest for ultrathin layers of future solar cells. The lecture intends to discuss that ionic liquids have their potential for future application in corrosion protection or in energy science, and maybe in other fields of electrochemistry.