Electroplating of Pure Aluminum from [HMIm][TFSI]–AlCl3 Room-Temperature Ionic Liquid

Abstract

Electrodeposition of aluminum and its alloys is of great interest in the aerospace, automobile, microelectronics, energy, recycle, and other industrial sectors, as well as for defense and, potentially, electrochemical printing applications. Here, for the first time, we report room-temperature electroplating of pure aluminum on copper and nickel substrates from an ionic liquid (IL) consisting of 1-Hexyl-3-methylimidazolium (HMIm) cation and bis(trifluoromethylsulfonyl)imide (TFSI) anion, with a high concentration of 8 mol/L AlCl3 aluminum precursor. The aluminum deposits are shown to have a homogeneous and dense nanocrystalline structure. A quasi-reversible reaction is monitored, where the current is affected by both charge transfer and mass transport. The electrocrystallization of Al on Ni is characterized by instantaneous nucleation. The deposited Al layers are dense, homogeneous, and of good surface coverage. They have a nanocrystalline, single-phase Al (FCC) structure, with a dislocation density typical of Al metal. An increase in the applied cathodic potential from −1.3 to −1.5 V vs. Pt resulted in more than one order of magnitude increase in the deposition rate (to ca. 44 μm per hour), as well as in ca. one order of magnitude finer grain size. The deposition rate is in accordance with typical industrial coating systems.