Electrochemical Behavior of Sm(III) and Electrodeposition of Samarium from 1-Butyl-1-Methylpyrrolidinium Dicyanamide Ionic Liquid

Abstract

Electrodeposition of rare-earth metals using ionic liquid is considered as a potential alternative to conventional high-temperature molten salt electrolysis. Herein, the electrochemical reduction of samarium(III) at near ambient conditions is investigated using different samarium precursors, namely, triflate (Sm(OTf) 3 ), nitrate (Sm(NO 3 ) 3 .6H 2 O) and chloride (SmCl 3 ), in 1-butyl-1-methylpyrrolidinium dicyanamide ([BMP][DCA]) ionic liquid. FT-infrared and Raman spectroscopy analyses of Sm 3+ /[BMP][DCA] solutions confirm the coordination of Sm 3+ species with D CA − ion through nitrogen atom. Cyclic voltammetry of Sm 3+ at glassy carbon electrode provides evidence of a two-step reduction process in all the systems via Sm 3+ to Sm 2+ and Sm 2+ to Sm 0 with peaks observed at similar reduction potentials owing to indifference in samarium(III) chemistries in each medium which is supported by a plausible mechanism. The diffusion coefficient of Sm 3+ in [BMP][DCA] was determined to be 3.00 × 10 −7 , 3.64 × 10 −8 and 1.90 × 10 −7 cm 2 .s −1 for Sm(OTf) 3 , Sm(NO 3 ) 3 .6H 2 O and SmCl 3 systems, respectively. The electrodeposition of samarium was achieved on nickel and glassy carbon substrates under two different potentials and temperatures. X-ray photoelectron spectroscopy confirms that the samarium electrodeposits are a mixture of metallic and oxide forms.