An AlCl₃ based ionic liquid with a neutral substituted pyridine ligand for electrochemical deposition of aluminum

A new ionic liquid (IL) based on a "neutral" ligand, 4-propylpyridine, is obtained via complexation with AlCl₃. It is found that the asymmetric cleavage of AlCl₃ generates AlCl₂⁺ and AlCl₄^-, and the former is coordinated by 4-propylpyridine to produce the Al-containing cations ([AlCl₂(4-Pr-Py)₂]⁺). The AlCl₃/4-propylpyridine IL with a molar ratio of 1.3/1 is highly fluidic with a viscosity of 42.8 mPa s and an ionic conductivity of 5.0 × 10^-4 S/cm at room temperature. In contrast to conventional ILs for electroplating aluminum in which the electrochemically active species are Al-containing anions (for example Al₂Cl₇^-), this new IL has an Al-containing cation as the electroactive species, which is beneficial to electrodeposition of aluminum.