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The Reduction of Oxygen in Various Room Temperature Ionic Liquids in the Temperature Range 293−318 K: Exploring the Applicability of the Stokes−Einstein Relationship in Room Temperature Ionic Liquids

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journal contribution
posted on 02.07.2009, 00:00 by Xing-Jiu Huang, Emma I. Rogers, Christopher Hardacre, Richard G. Compton
The voltammetry for the reduction of oxygen at a microdisk electrode is reported in six commonly used RTILs: [C4mim][NTf2], [C4mpyrr][NTf2], [C4dmim][NTf2], [C4mim][BF4], [C4mim][PF6], and [N6,2,2,2][NTf2], where [C4mim]+ is 1-butyl-3-methylimidazolium, [NTf2] is bis(trifluoromethanesulfonyl)imide, [C4mpyrr]+ is N-butyl-N-methylpyrrolidinium, [C4dmim]+ is 1-butyl-2,3-methylimidazolium, [BF4] is tetrafluoroborate, [PF6] is hexafluorophosphate, and [N6,2,2,2]+ is n-hexyltriethylammonium at varying scan rates (50−4000 mV s−1) and temperatures (293−318 K). Diffusion coefficients, D, of oxygen are deduced at each temperature from potential-step chronoamperometry, and diffusional activation energies are calculated. Oxygen solubilities are also reported as a function of temperature. In the six ionic liquids, the Stokes−Einstein relationship (D ∝ η−1) was found to apply only very approximately for oxygen. This is considered in relationship to the behavior of other diverse solutes in RTILs.