The effects of addition of acetonitrile (ACN) on electrodeposition of nickel were investigated in a hydrophobic room-temperature ionic liquid 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)amide (BMPTFSA) containing Ni(TFSA)(2) Addition of ACN resulted in the change of the color of the ionic liquid The UV-vis and Ff-IR spectra of the electrolyte showed the coordination environment of Ni(II) changed gradually fiorn [Ni(TFSA)(3)](-) to [Ni(ACN)(6)](2+) with an increase in the concentration of ACN The diffusion coefficient of Ni(II) in BMPTFSA was increased and the reduction potential of Ni(II) shifted to the more positive side in the presence of ACN The nucleation/growth process of Ni was not affected by the change in the coordination environment of NI(II) nom the chronoamperometric results although the more nuclei formed on the electrode surface SEM showed smoother deposit was obtained in Ni(TFSA)(2)/BMPTFSA with ACN (C) 2010 Elsevier Ltd All rights reserved