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) x 10(-7) cm(2) 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. (C) 2007 Elsevier Ltd. All rights reserved.