The electrochemical reduction of oxygen was investigated in some hydrophobic room-temperature molten salt systems (ionic liquids) consisting of bis(trifluoromethanesulfone)imide false(TFSI−false) anion with trimethyl-n-hexylammonium false(TMHA+false), 1-butyl-1-methylpyrrolidinium false(BMP+false), 1-ethyl-3-methylimidazolium false(EMI+false) or 1,2-dimethyl-3-propylimidazolium false(DMPI+false) cation. The oxygen dissolved in these melts was reduced to the superoxide ion on a gold electrode. The superoxide ion was stable against the aliphatic and alicyclic organic cations false(TMHA+ and BMP+false) but reacted with the aromatic ones false(EMI+ and DMPI+false), suggesting that nucleophilic reagents attack the melts consisting of imidazolium cations. The acceptor number of these TFSI− -based molten salt systems was estimated to be comparable to those of acetonitrile and dimethyl sulfoxide from the comparison of the redox potential of O2/O2−. The superoxide ion was further reduced, presumably to the peroxide, on a gold electrode in the melts consisting of the aliphatic or alicyclic organic cation. © 2003 The Electrochemical Society. All rights reserved.

The electrochemical behavior of oxygen ͑O 2 ͒/superoxide ion ͑O 2 − ͒ couple was investigated with the aid of the ultramicroelectrode technique in 1-butyl-1-methylpyrrolidinium bis͑trifluoromethylsulfonyl͒imide ͑BMPTFSI͒ room-temperature molten salt ͑ionic liquid͒. The diffusion coefficient of O 2 was ͑1.8 ± 0.2͒ ϫ 10 −6 cm 2 s −1 at 25°C. The activation energy of the diffusion process of O 2 was estimated to be 27 kJ mol −1 from the temperature dependence of the diffusion coefficient. The solubility of O 2 in BMPTFSI was 14 mmol dm −3 at 25°C and decreased with an increase in temperature. The diffusion coefficient of O 2 − was 0.86 ϫ 10 −6 cm 2 s −1 at 25°C. The formal potential of O 2 /O 2 − couple was 1.13 V vs ferrocene/ferrocenium.

The electrochemical behavior of samarium ͑Sm͒, europium ͑Eu͒, and ytterbium ͑Yb͒ was investigated in the hydrophobic roomtemperature molten salts based on bis͑trifluoromethylsulfonyl͒imide ͑TFSI − ͒ combined with either 1-ethyl-3-methylimidazolium ͑EMI + ͒ or 1-n-butyl-1-methylpyrrolidinium ͑BMP + ͒. The redox reactions of Sm͑III͒/Sm͑II͒, Eu͑III͒/Eu͑II͒, and Yb͑III͒/Yb͑II͒ were observed at −1.6, −0.3, and −1.0 V vs Ag/Ag͑I͒, respectively. In all cases, the electrode reactions were found to be quasior irreversible by the cyclic voltammetry. The diffusion coefficients of these lanthanides were estimated to be ϳ10 −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.

No abstract

No abstract