Voltammetric Behaviour and Electrodeposition of Samarium in 1-Butyl-1-methylpyrrolidinium Bis(trifluoromethylsulfonyl)imide Ionic Liquid

Abstract

Low-temperature electrodeposition strategies to obtain lanthanides in metallic form using ionic liquids are explored as sustainable substitutes to high-temperature molten salt electrolytes. Herein, we report the electrochemical behaviour of samarium(III) and the electrodeposition of samarium in 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide, ionic liquid. Raman spectroscopic analysis indicated the existence of complex in as-prepared electrolyte. Trivalent samarium species undergoes two-step reduction via Sm(III)↔Sm(II) at –1.0 V and Sm(II)→Sm(0) at –2.1 V with the corresponding oxidation peaks observed at potentials ∼+1.0 V and +1.9 V vs Ag/Ag+, respectively, and attributed to the stripping of zero-valent samarium to Sm(II) which subsequently undergoes re-oxidation to Sm(III) species, respectively. Diffusion coefficient of Sm(III) species increases from 1.75 × 10−7 at 343 K to 6.27 × 10−7 cm2 s−1 at 373 K due to decrease in the electrolyte viscosity and activation energy (Ea) was determined to be 42 kJ mol−1. Samarium electrodeposited at −2.5 V vs Ag/Ag+ was ∼3-micron thick coating with visible crack. XPS analysis provided qualitative proof for elemental samarium in the deposit co-existing with its oxide film likely due to exposure to atmosphere during analysis. The present study demonstrates the possibility to electrodeposit samarium using [BMP][Tf2N] ionic liquid at near ambient conditions.