Electrochemical behavior of Ni(II)/Ni in a hydrophobic amide-type room-temperature ionic liquid

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 ∼26 kJ mol^-1, which was close to that for the viscosity. The diffusion coefficient of Ni(II) was estimated to be 9.3 × 10^-8 cm² 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 °C were identified as metallic Ni by XRD.