Elementary steps and mechanism of electrodeposition of Al from complex hydride ions in tetrahydrofuran baths

Electrocrystallization of Al cannot be achieved from aqueous media, but is possible from low melting-point organic salts, and from aromatic and etheric solutions. In the present paper studies are reported on the kinetics and mechanisms of electrodeposition of Al from plating baths of varying ratios of AlCl3 and LiAlH4 dissolved in tetrahydrofuran (THF). A complementary paper, which follows, deals with the topic of nucleation and growth processes involved in Al phase electrocrystallization and provides experimental results on that process. Steady-state cathodic and anodic Tafel polarization relations are determined, complemented by ac impedance studies. Back-reaction corrected Tafel plots enable anodic and cathodic transfer coefficients (α) to be evaluated together with corresponding stoichiometric numbers (ν). Critical evaluation both of the present α and ν results, and previous α values in the literature, enables a mechanism of elementary steps in Al deposition from the hydrido-chloride baths to be proposed.