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Issue 20, 2013
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Kinetics and mechanism of oxygen reduction in a protic ionic liquid

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Abstract

The oxygen reduction reaction (ORR) has been studied at Pt surfaces in the protic ionic liquid diethylmethylammonium trifluoromethanesulfonate. Water content measurements suggested that the ORR proceeded in the ionic liquid predominantly via a 4-electron reduction to water. A mechanistic analysis using rotating ring-disk electrode (RRDE) voltammetry confirmed that negligible amounts of hydrogen peroxide were formed during the ORR. A kinetic analysis of the ORR was performed using rotating disk electrode (RDE) voltammetry and the importance of correcting for ohmic (iR) drop prior to performing kinetic measurements in the ionic liquid is demonstrated. A Tafel analysis of the RDE voltammetry data revealed a change in the ORR Tafel slope from 70 mV per decade at low ORR overpotentials to 117 mV per decade at high overpotentials, and the reason for this change is discussed. The change in the Tafel slope for the ORR with increasing overpotential meant that the exchange current density for the ORR varied from 0.007 nA cm−2 to 10 nA cm−2, depending on the applied potential. Finally, the implications of these results for the development of protic ionic liquid fuel cells are discussed.

Graphical abstract: Kinetics and mechanism of oxygen reduction in a protic ionic liquid

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Publication details

The article was received on 24 Dec 2012, accepted on 03 Apr 2013 and first published on 05 Apr 2013


Article type: Paper
DOI: 10.1039/C3CP44669G
Citation: Phys. Chem. Chem. Phys., 2013,15, 7548-7554
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    Kinetics and mechanism of oxygen reduction in a protic ionic liquid

    D. A. Walsh, A. Ejigu, J. Smith and P. Licence, Phys. Chem. Chem. Phys., 2013, 15, 7548
    DOI: 10.1039/C3CP44669G

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