Electropolishing and Electroplating of Metals Using Ionic Liquids Based on Choline Chloride

Eutectic based ionic liquids containing choline chloride are shown to be useful for electrochemical applications that currently use aqueous solutions. It is shown that an ionic liquid composed of ethylene glycol (HOCH2CH2OH) and choline chloride (HOC2H4N(CH3)3+Cl-) offers the first practical alternative to the use of phosphoric and sulphuric acid mixtures for the electropolishing of type 316 stainless steel. The mechanism has been elucidated and it is shown to be significantly different in an ionic liquid from that observed in aqueous solutions. Results from large-scale testing show, that for several types of steel, surface finishes at least as good as aqueous solutions can be obtained. A recycling protocol has been developed for the ionic liquid, which allows full metal recovery. We also demonstrate that these mixtures and the corresponding analogue with urea can be used for the deposition of a wide range of metals and alloys. Judicious choice of ionic liquid can, not only affect the morphology of the deposit obtained but also the composition of metals in the alloy.