Electrodeposition of palladium in a hydrophobic 1-n-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide room-temperature ionic liquid

The electrochemical reduction of palladium halide complexes such as PdBr42− and PdCl42− was investigated in a hydrophobic room-temperature ionic liquid (RTIL), 1-n-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide (BMPTFSI). The irreversible electrode reaction between Pd(II) and Pd(0) was observed in BMPTFSI containing PdBr42− or PdCl42− by cyclic voltammetry. The diffusion coefficient of PdBr42− was estimated to be (1–2) × 10−7 cm2 s−1 by choronopotentiometry and chronoamperometry. The deposition of crystalline Pd metal was confirmed by X-ray diffraction and X-ray photoelectron spectroscopy. It was suggested by the chronoamperometric measurements on PdBr42− in BMPTFSI that the initial stage of the electrodeposition of Pd on the polycrystalline Pt electrode surface involves three-dimensional progressive nucleation under diffusion control. The reduction potential of PdCl42− was more negative than that of PdBr42−, reflecting the difference in the donor property between chloride and bromide.