Oxygen Reduction Reaction in Ionic Liquids: The Addition of Protic Species

The effect of proton donors on the mechanism of the electrochemical oxygen reduction reaction (ORR) is examined in the supporting ionic liquid 1-butyl-2,3-dimethylimidazolium trifluoromethanesulfonate (C4dMImTf). ORR in aqueous media is contrasted with that in aprotic media and in aprotic ionic liquid (IL) systems with the addition of protic species. This study elucidates the effect of proton activity encompassing almost thirty orders of magnitude for both platinum (Pt) and glassy carbon (GC) electrodes. In neat aprotic C4dMImTf for both platinum and glassy carbon electrodes, ORR proceeds entirely through a one electron process as expected. In ILs with protic additives, ORR approaches a four-electron pathway regardless of the identity of the protic additive on Pt, whereas ORR on GC is limited to a two-electron process due to a lack of Hads and Oads species.