Electrochemical reaction of Ni(II)/Ni was investigated in a hydrophobic room-temperature ionic liquid, 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)amide (BMPTFSA) containing Ni(TFSA)(2) as a Ni source. The UV-vis spectra showed that Ni(II) in BMPTFSA is octahedrally coordinated with TFSA- anions. The average activation energy for the diffusion coefficients of this Ni(II) complex was similar to 26 kJ mol(-1), which was close to that for the viscosity. The diffusion coefficient of Ni(II)was estimated to be 9.3 x 10(-8) cm(2) s(-1). Chronoamperometric measurements showed that the electrodeposition of Ni on a platinum substrate involved three-dimensional instantaneous nucleation under diffusion control at room-temperature. The electrodeposits obtained by galvanostatic electrolysis with the current density of -0.046 mA cm(-2) at 70 and 100 degrees C were identified as metallic Ni by XRD. (C) 2009 Elsevier Ltd. All rights reserved.