The effects of additives, acetone (AC) and thiourea (TU), 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). The UV-vis spectra showed the coordination environment of Ni(II) species was affected by the presence of AC. The diffusion coefficient of Ni(II) in BMPTFSA was increased slightly and the reduction potential of Ni(II) shifted to the more positive side in the presence of AC. The nucleation/growth process of Ni was not affected by the change in the coordination environment of Ni(II) from the chronoamperometric results. Addition of TU also changed the color of the electrolyte from yellow to yellow-green, while the coordination environment of Ni(II) was not changed with the existence of TU. The overpotential for Ni(II)/Ni with TU was slightly larger than that without the additive. The effects of the additives on the morphology of the Ni deposits were also characterized by SEM, XPS and EDX. (C) 2012 Elsevier Ltd. All rights reserved.