Electrochemical and spectroscopic investigation of samarium in a neutral ligand based-ionic liquid

Abstract

• Electrochemistry of samarium(III) in neutral ligand is reported. • FT-IR and Raman spectroscopy confirm the interaction of Sm 3+ with TMP via P O. • Charge transfer coefficient, α ~ 0.44 & D Sm3+ ~2.10 × 10 −7 cm 2 /s at 303 K. • Uniform Sm deposit obtained on glassy carbon and copper substrates. • Low-cost, stable neutral ligands are potential electrolytes for depositing Rare Earths. In the past few decades, ionic liquids have emerged as potential replacements to conventional electrolytes in many academic and industrial applications owing to their remarkable properties. However, poor solubility towards different metal salts exhibited by majority of the ionic liquids limits their capacity to obtain solutions with higher metal ion concentrations. Combining neutral ligand with ionic liquid has been suggested as a promising route to solve this issue. In this regard, we report the electrochemical and spectroscopic study of samarium(III) in trimethyl phosphate (TMP) ligand. Infrared and Raman spectroscopy probing of samarium tris bis(trifluoromethylsulfonyl) imide / trimethyl phosphate reveals that Sm(III) is coordinated to TMP molecule via oxygen atom of the P O group. Cyclic voltammetry at glassy carbon working electrode indicates that the reduction of samarium(III) to metallic samarium in TMP proceeds via two-steps involving quasi-reversible Sm(III)/Sm(II) and irreversible Sm(II)/Sm(0) charge transfer. Diffusion coefficient of Sm(III) was determined to be 2.10 × 10 −7 cm 2 /s. Compact deposits of samarium were obtained on glassy carbon and copper electrodes under potentiostatic deposition. EDS and elemental mapping analyses confirm uniform deposition of samarium throughout the electrode surface. XPS analysis confirmed that the samarium deposit is composed of metallic samarium coexisting with substantial amount of oxide form likely due to high reactivity of samarium with atmospheric oxygen. In this work, we report the spectroscopic analyses and voltammetric behaviour, and the electrodeposition of samarium using trimethyl phosphate and this strategy can be conveniently extended to other rare earths using similar neutral ligand based ionic liquids