Electrochemically active species in aluminum electrodeposition baths of AlCl3/glyme solutions

Electrochemically active species in aluminum (Al) electrodeposition baths using AlCl3 and less volatile solvents i.e. glymes were investigated. Raman spectroscopy revealed that all the glyme baths contained AlCl4− anions and Al-Cl-glyme cations as ionic species. Room temperature conductivities were as high as the order of 10−3 S cm−1 for the diglyme (G2), triglyme (G3) and tetraglyme (G4) baths, whereas that for the butyl diglyme (butylG2) bath was only 10−4 S cm−1 due to a lower concentration of ionic species. Surprisingly, electrochemical measurements showed that, among the glyme baths, only the G2 bath enabled electrodeposition of Al. Consequently, despite the similar structures of Al-Cl-glyme complex cations, only the G2 complex cations are electrochemically active. This suggests that the desolvation of glymes from Al-Cl-glyme cations and their subsequent reduction is exceptionally easy for the G2 complexes.