Nucleation and morphologies in the process of electrocrystallization of aluminium on smooth gold and glassy-carbon substrates

Complementary to work reported in the preceding paper and elsewhere on the kinetics and mechanism of the elementary discharge steps involved in electrocrystallization of Al, studies are reported here on nucleation and growth of the Al phase electrodeposited from solutions of AlCl3 and LiAlH4 in tetrahydrofuran onto two inert smooth substrates, glassy carbon and gold. Two principal compositions of the plating baths are investigated, chloride-rich and hydride-rich, in which the speciations of dischargeable Al-complexes differ, as characterized in our earlier work by means of Al-27-NMR spectroscopy. Nucleation and growth transients are recorded in response to potential steps of various amplitudes applied in the two types of baths. The response currents are analyzed in terms of 'instantaneous' and 'progressive' nucleation mechanisms, together with examination of the role of diffusion. Owing to the chemical complexity of the species from which Al is deposited in these baths the two nucleation conditions cannot be distinguished clearly in the results obtained, although a large extent of replication of experimental results was made. The nucleation and growth results are related to microscopic morpholgies of the Al electrodeposits photographed by scanning electron microscopy. (C) 2000 Elsevier Science S.A. All rights reserved.