Electrodeposition of nano- and microcrystalline aluminium in three different air and water stable ionic liquids

The present work shows, for the first time, a comparative experimental study on the electrodeposition of aluminium in three different water and air stable ionic liquids, namely 1-butyl-1-methylpyrrolidinium-bis(trifluoromethylsulfonyl)imide ([BMP]Tf2N), 1-ethyl-3-methylimidazolium-bis(trifluoromethylsulfonyl)imide ([EMIm] Tf2N), and trihexyl-tetradecyl-phosphoniumbis(trifluoromethylsulfonyl)imide (P(14,6,6,6) Tf2N). The ionic liquids [BMP]Tf2N and [EMIm]Tf2N show biphasic behaviour in the AlCl3 concentration range from 1.6 to 2.5 mol L(-1) and 2.5 to 5 mol L(-1), respectively. The biphasic mixtures become monophasic at temperatures >/=80 degrees C. It was found that nanocrystalline aluminium can be electrodeposited in the ionic liquid [BMP]Tf2N saturated with AlCl3. The deposits obtained are generally uniform, dense, shining, and adherent with very fine crystallites in the nanometer size regime. However, coarse cubic-shaped aluminium particles in the micrometer range are obtained in the ionic liquid [EMIm]Tf2N. In this liquid the particle size significantly increases as the temperature rises. A very thin, mirrorlike aluminium film containing very fine crystallites of about 20 nm is obtained in the ionic liquid [trihexyl-tetradecyl-phosphonium]Tf(2)N at room temperature. At 150 degrees C, the average grain size is found to be 35 nm.