Anodic Dissolution of Copper in the Acidic and Basic Aluminum Chloride 1-Ethyl-3-methylimidazolium Chloride Ionic Liquid

Abstract

The anodic dissolution of copper was investigated at a copper RDE in the Lewis acidic and basic composition regions of the room-temperature AlCl3-EtMeImCl ionic liquid (IL) to assess the utility of chloroaluminate liquids as solvents for the electrochemical machining and electropolishing of copper. In the Lewis acidic IL (60 mol % AlCl3), the dissolution of Cu0 proceeds under mixed kinetic-mass transport control with an exchange current density of 7.00 mA cm−2 at 306 K and an apparent activation free energy of 19.7 kJ mol−1. A formal potential of 0.843 V was obtained for the Cu+/Cu0 reaction from potentiometric measurements. In the basic IL (< 50 mol % AlCl3), potentiometric measurements showed that the oxidation of Cu0 resulted in the formation of [CuCl2]−. In this case, the formal potential of the [CuCl2]−/Cu0 reaction is −0.412 V. At small positive overpotentials, the reaction exhibited mixed control and was first order in the chloride concentration, indicating that only a single Cl− is involved in the RDS. However, at more positive overpotentials, the reaction transitions to mass transport control, and a well-defined limiting current is observed for the anodization process. This limiting current scales linearly with the free chloride concentration in the IL.