Electrodeposition of aluminium from hydrophobic perfluoro-3-oxa-4,5 dichloro-pentan-sulphonate based ionic liquids

Abstract

Aluminium electrodeposition from ionic liquids (ILs) prepared using a novel structure composed by perfluoro-3-oxa-4,5 dichloro-pentan-sulphonate [CF2ClCFClOCF2SO3-] and different cations is presented. The novel anion was designed by Solvay Specialty Polymers with the purpose to confer to the ionic liquids strong hydrophobic properties that facilitate the aluminium deposition in ambient conditions. Three cations, imidazolium, pyridinium and guanidinium are used to prepare the corresponding three liquids. In water, the resulting liquids prepared with imidazolium and pyridinium show very low miscibility and the liquid prepared with guanidinium is insoluble. Their electrochemical windows are dependent of both the cations and the substrate nature and are sufficiently wide to allow aluminium deposition. Even so, it was evidenced that the reduction of the new structure is not especially difficult. The AlCl3 was selected as useful source of Al(III) electroactive species to obtain coherent deposits. Using aluminium hydroxide, the coalescence of the aluminium deposits was not achieved. The viability of aluminium electrodeposition was, at first, tested on vitreous carbon, demonstrating it follows through a nucleation and growth process. As the practical interest carries to the use of metallic substrata, nickel was selected to analyse deposition process. The deposits prepared at constant current showed a better appearance, less stressed and smoother than the ones prepared at constant potential. The effect of temperature and concentration was studied in solutions prepared with tetramethyl guanidinium-perfluoro-3-oxa-4,5 dichloro-pentan-sulphonate, taking advantage of its immiscibility in water. Deposits prepared from the lower concentrations tested (AlCl3:IL 0.95:1 molar ratio) were continuous, fine grained and stress-free, provided that they were obtained at moderate applied current. From higher Al(III) concentration solutions it was only possible to allow stress-free deposits by applying low currents.