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 etheri c 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 pay er, which follows, deals with the topic of nucleation and growth processes involved in Al phase electrocrystallization and provides experimental resul ts on that process. Steady-state cathodic and anodic Tafel polarization rel ations are determined, complemented by ac impedance studies. Back-reaction corrected Tafel plots enable anodic and cathodic transfer coefficients (alp ha) to be evaluated together with corresponding stoichiometric numbers (v). Critical evaluation both of the present alpha and v results, and previous alpha values in the literature, enables a mechanism of elementary steps in Al deposition from the hydride-chloride baths to be proposed. (C) 2000 Else vier Science S.A. All rights reserved.