Electroreduction of oxygen in a series of room temperature ionic liquids composed of group 15-centered cations and anions

R.G. Evans, O.V. Klymenko, S.A. Saddoughi, Christopher Hardacre, R.G. Compton

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Abstract

The electrochemical reduction of oxygen is reported in four room temperature ionic liquids (RTILs) based on quaternary alkyl -onium cations and heavily fluorinated anions in which the central atom is either nitrogen or phosphorus. Data were collected using cyclic voltammetry and potential step chronoamperometry at gold, platinum, and glassy carbon disk electrodes of micrometer dimension under water-free conditions at a controlled temperature. Analysis via fitting, to appropriate theoretical equations was then carried out to obtain kinetic and thermodynamic information pertaining to the electrochemical processes observed. In the quaternary ammonium electrolytes, reduction of oxygen was found to occur reversibly to give stable superoxide, in an analogous manner to that seen in conventional aprotic solvents such as dimethyl sufoxide and acetonitrile. The most significant difference is in the relative rate of diffusion; the diffusion coefficients of oxygen in the RTILs are an order of magnitude lower than in common organic solvents, and for superoxide these values are reduced by a further factor of 10. In the quaternary phosphonium ionic liquids, however, more complex voltammetry is observed, akin to that expected for the reduction of oxygen in acidified organic media. This is shown to be consistent with the occurrence of a proton abstraction reaction between the electrogenerated superoxide and quaternary alkyl phosphonium cations following the initial electron transfer.
Original languageEnglish
Pages (from-to)7878-7886
Number of pages9
JournalJournal of Physical Chemistry B
Volume108
Issue number23
Publication statusPublished - 10 Jun 2004

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Ionic Liquids
Ionic liquids
Anions
Cations
inorganic peroxides
Negative ions
Positive ions
Superoxides
Oxygen
anions
cations
room temperature
oxygen
liquids
Temperature
Chronoamperometry
carbon
glassy carbon
Glassy carbon
Voltammetry

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Evans, R. G., Klymenko, O. V., Saddoughi, S. A., Hardacre, C., & Compton, R. G. (2004). Electroreduction of oxygen in a series of room temperature ionic liquids composed of group 15-centered cations and anions. Journal of Physical Chemistry B, 108(23), 7878-7886.
Evans, R.G. ; Klymenko, O.V. ; Saddoughi, S.A. ; Hardacre, Christopher ; Compton, R.G. / Electroreduction of oxygen in a series of room temperature ionic liquids composed of group 15-centered cations and anions. In: Journal of Physical Chemistry B. 2004 ; Vol. 108, No. 23. pp. 7878-7886.
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Evans, RG, Klymenko, OV, Saddoughi, SA, Hardacre, C & Compton, RG 2004, 'Electroreduction of oxygen in a series of room temperature ionic liquids composed of group 15-centered cations and anions', Journal of Physical Chemistry B, vol. 108, no. 23, pp. 7878-7886.

Electroreduction of oxygen in a series of room temperature ionic liquids composed of group 15-centered cations and anions. / Evans, R.G.; Klymenko, O.V.; Saddoughi, S.A.; Hardacre, Christopher; Compton, R.G.

In: Journal of Physical Chemistry B, Vol. 108, No. 23, 10.06.2004, p. 7878-7886.

Research output: Contribution to journalArticle

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N2 - The electrochemical reduction of oxygen is reported in four room temperature ionic liquids (RTILs) based on quaternary alkyl -onium cations and heavily fluorinated anions in which the central atom is either nitrogen or phosphorus. Data were collected using cyclic voltammetry and potential step chronoamperometry at gold, platinum, and glassy carbon disk electrodes of micrometer dimension under water-free conditions at a controlled temperature. Analysis via fitting, to appropriate theoretical equations was then carried out to obtain kinetic and thermodynamic information pertaining to the electrochemical processes observed. In the quaternary ammonium electrolytes, reduction of oxygen was found to occur reversibly to give stable superoxide, in an analogous manner to that seen in conventional aprotic solvents such as dimethyl sufoxide and acetonitrile. The most significant difference is in the relative rate of diffusion; the diffusion coefficients of oxygen in the RTILs are an order of magnitude lower than in common organic solvents, and for superoxide these values are reduced by a further factor of 10. In the quaternary phosphonium ionic liquids, however, more complex voltammetry is observed, akin to that expected for the reduction of oxygen in acidified organic media. This is shown to be consistent with the occurrence of a proton abstraction reaction between the electrogenerated superoxide and quaternary alkyl phosphonium cations following the initial electron transfer.

AB - The electrochemical reduction of oxygen is reported in four room temperature ionic liquids (RTILs) based on quaternary alkyl -onium cations and heavily fluorinated anions in which the central atom is either nitrogen or phosphorus. Data were collected using cyclic voltammetry and potential step chronoamperometry at gold, platinum, and glassy carbon disk electrodes of micrometer dimension under water-free conditions at a controlled temperature. Analysis via fitting, to appropriate theoretical equations was then carried out to obtain kinetic and thermodynamic information pertaining to the electrochemical processes observed. In the quaternary ammonium electrolytes, reduction of oxygen was found to occur reversibly to give stable superoxide, in an analogous manner to that seen in conventional aprotic solvents such as dimethyl sufoxide and acetonitrile. The most significant difference is in the relative rate of diffusion; the diffusion coefficients of oxygen in the RTILs are an order of magnitude lower than in common organic solvents, and for superoxide these values are reduced by a further factor of 10. In the quaternary phosphonium ionic liquids, however, more complex voltammetry is observed, akin to that expected for the reduction of oxygen in acidified organic media. This is shown to be consistent with the occurrence of a proton abstraction reaction between the electrogenerated superoxide and quaternary alkyl phosphonium cations following the initial electron transfer.

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