Electrochemical Reduction of Oxygen in Some Hydrophobic Room-Temperature Molten Salt Systems

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Abstract
The electrochemical reduction of oxygen was investigated in some hydrophobic room-temperature molten salt systems (ionic liquids) consisting of bis(trifluoromethanesulfone)imide (TFSI−)(TFSI−) anion with trimethyl-n-hexylammonium (TMHA+),(TMHA+), 1-butyl-1-methylpyrrolidinium (BMP+),(BMP+), 1-ethyl-3-methylimidazolium (EMI+)(EMI+) or 1,2-dimethyl-3-propylimidazolium (DMPI+)(DMPI+) 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 (TMHA+(TMHA+ and BMP+)BMP+) but reacted with the aromatic ones (EMI+(EMI+ and DMPI+),DMPI+), suggesting that nucleophilic reagents attack the melts consisting of imidazolium cations. The acceptor number of these TFSI−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−.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.