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

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 Cu-0 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+/Cu-0 reaction from potentiometric measurements. In the basic IL (< 50 mol % AlCl3), potentiometric measurements showed that the oxidation of Cu-0 resulted in the formation of [CuCl2](-). In this case, the formal potential of the [CuCl2](-)/Cu-0 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.

Automated summary

The anodic dissolution of copper in chloroaluminate ionic liquids was studied, revealing different reaction mechanisms in Lewis acidic and basic compositions. In Lewis acidic IL, the reaction is under mixed kinetic-mass transport control, while in basic IL, the reaction transitions to mass transport control with the formation of [CuCl2](-).