Electrode Reactions of Platinum Bromide Complexes in an Amide-Type Ionic Liquid

Abstract

The electrode reactions of platinum bromide complexes were investigated in an amide-type room-temperature ionic liquid, 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)amide (BMPTFSA). Platinum bromides were dissolved in BMPTFSA with addition of BMPBr. Ultraviolet and visible absorption spectra of the electrolytes revealed that Pt(II) and Pt(IV) species were dissolved as [PtIIBr4]2− and [PtIVBr6]2−, respectively. The cyclic voltammogram in BMPTFSA containing 10 mM [PtIVBr6]2− showed two reduction peaks at −1.2 and −2.6 V, which can be assigned to reduction of [PtIVBr6]2− and [PtIIBr4]2−, respectively. The diffusion coefficients of the [PtIIBr4]2− and [PtIVBr6]2− at 25°C were determined to be 1.5 × 10−7 and 0.49 × 10−7 cm2 s−1 in BMPTFSA, respectively, by chronoamperometry. Electrodeposition of metallic platinum was possible by galvanostatic cathodic reduction on a glassy carbon electrode in BMPTFSA containing 10 mM [PtIIBr4]2−. In addition, platinum nano-particles (2–3 nm in diameter) formed and dispersed in the ionic liquid after potentiostatic cathodic reduction at −2.6 V. Platinum nano-particles could be collected by heating the ionic liquid containing the nano-particles with carbon black at 200°C.