Electrochemical Behavior of Samarium Species in an Amide-Type Ionic Liquid at Different Temperatures

Abstract

Electrochemical reaction of samarium (Sm) species was explored in an amide-type ionic liquid, 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)amide (BMPTFSA), at 25 and 100°C. The cathodic and anodic current peaks corresponding to the reduction of Sm(III) and the oxidation of Sm(II), respectively, were observed in BMPTFSA containing Sm(TFSA)3 by cyclic voltammetry at 25°C. However, the anodic current peak corresponding to the oxidation of Sm(II) diminished significantly at lower scan rates when the temperature was elevated to 100°C, suggesting the disproportionation of Sm(II) at higher temperatures. Deposits were obtained on a glassy carbon electrode by potentiostatic cathodic reduction at –1.6 and –2.5 V in BMPTFSA containing Sm(TFSA)3 at 100°C. The deposits were found to contain Sm by energy dispersive X-ray spectroscopy (EDX), although no diffraction peak was observed by X-ray diffraction. The formation and dispersion of nanoparticles in the ionic liquid were also confirmed by transmission electron microscopy with and without exposure of the samples to air. The nanoparticles were considered to be metallic Sm, which was identified by electron diffraction and EDX. Sm nanoparticles were anticipated to be formed by the disproportionation reaction of Sm(II) to Sm(III) and Sm in the ionic liquid.