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

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 [N _6,2,2,2][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 [N_6,2,2,2]⁺ 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.