Enhanced performance of phosphonium based ionic liquids towards 4 electrons oxygen reduction reaction upon addition of a weak proton source

•Study of different proton donor additives towards oxygen reduction reaction (ORR).•4-Electron are transferred in ethylene glycol/[P66614]Cl mixtures during ORR.•Ethylene glycol/[P66614]Cl mixtures exhibited superior proton activity.•Corroboration of this superior proton activity via Kamlet–Taft parameters

The oxygen reduction reaction (ORR) in the presence of proton donors of similar proton activities (water, methanol and ethylene glycol), as well as weak and strong acids has been studied in a phosphonium-based IL, [P66614][Cl].[P66614][Cl]/ethylene glycol mixtures showed better ORR performance than mixtures containing water or methanol in terms of onset potential and current density. This enhancement in performance similar to that produced by weak acids, is attributed to the self-stabilization of ethylene glycol after proton removal; this has been corroborated by calculation of the hydrogen-bond donating ability. Interestingly under these conditions, the oxygen reduction reaction on a glassy carbon electrode follows an overall 4-electron pathway (i.e., two 2-electron processes) which is of importance in the performance of air cathodes in electrochemical devices.

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