Electrochemical behavior of samarium, europium, and ytterbium in hydrophobic room-temperature molten salt systems

The electrochemical behavior of samarium (Sm), europium (Eu), and ytterbium (Yb) was investigated in the hydrophobic room-temperature molten salts based on bis (trifluoromethylsulfonyl)imide (TFSI-) combined with either 1-ethyl-3-methylimidazolium (EMI+) or 1-n-butyl-1-methylpyrrolidinium (BMP+). The redox reactions of Sm(III)/Sm(II), Eu(III)/Eu(II), and Yb(III)/Yb(II) were observed at -1.6, -0.3, and -1.0 V vs Ag/Ag(I), respectively. In all cases, the electrode reactions were found to be quasi-or irreversible by the cyclic voltammetry. The diffusion coefficients of these lanthanides were estimated to be similar to 10(-8) cm(2) s(-1) by chronoamperometry and chronopotentiometry, indicating that their mobility is rather low, probably due to the complex formation or the strong coulombic interaction with TFSI-. The redox potentials of these divalent and trivalent lanthanide couples suggested that the donor property of TFSI--based room-temperature molten salts was lower than that of other conventional solvents. (c) 2005 The Electrochemical Society.