| Summary: | The reduction of oxygen was studied over a range of temperatures (298-318 K) in n -hexyltrietliylammonium bis(trifluorometlianesulfonyl)imide, [N 6,2,2,2] [NTf2], and 1-butyl-2,3-methylimidazorium bis(trifluoromethanesulfonyl)imide, [Qdmim] [NTf2] on both gold and platinum microdisk electrodes, and the mechanism and electrode kinetics of the reaction investigated. Three different models were used to simulate the CVs, based on a simple electron transfer ('E'), an electron transfer coupled with a reversible homogeneous chemical, step ('ECrev') and an electron transfer followed by adsorption of the reduction product ('EC(ads)'), and where appropriate, best fit parameters deduced, including the heterogeneous rate constant, formal electrode potential., transfer coefficient, and homogeneous rate constants for the ECrev mechanism, and adsorption/desorption rate constants for the EC(ads) mechanism. It was concluded from the good simulation fits on gold that a simple E process operates for the reduction of oxygen in [N6,2,2,2][NTf2], and an ECrev process for [Qdmim J[NTf2], with the chemical, step involving the reversible formation of the O2-⋯ [C4dmim] - ion-pair. The E mechanism was found to loosely describe the reduction of oxygen in [N6,2,2,2] [NTf2] on platinum as the simulation fits were reasonable although not perfect, especially for the reverse wave. The electrochemical kinetics are slower on Pt, and observed broadening of the oxidation peak is likely due to the adsorption of superoxide on the electrode surface in a process more complex than simple Langmuirian. In [C 4dmim] [NTf2] the O2- ⋯ predominantly ion-pairs with the solvent rather than adsorbs on the surface, and an EC16V quantitatively describes the reduction of oxygen on Pt also. © 2009 American Chemical Society.
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