Nonadditivity of Faradaic currents and modification of capacitance currents in the voltammetry of mixtures of ferrocene and the cobaltocenium cation in protic and aprotic ionic liquids

Shiddiky, Muhammad J. A., Torriero, Angel A. J., Zhao, Chuan, Burgar, Iko, Kennedy, Gareth and Bond, Alan M. 2009, Nonadditivity of Faradaic currents and modification of capacitance currents in the voltammetry of mixtures of ferrocene and the cobaltocenium cation in protic and aprotic ionic liquids, Journal of the American chemical society, vol. 131, no. 23, pp. 7976-7989, doi: 10.1021/ja8092295.

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Title Nonadditivity of Faradaic currents and modification of capacitance currents in the voltammetry of mixtures of ferrocene and the cobaltocenium cation in protic and aprotic ionic liquids
Author(s) Shiddiky, Muhammad J. A.
Torriero, Angel A. J.ORCID iD for Torriero, Angel A. J. orcid.org/0000-0001-8616-365X
Zhao, Chuan
Burgar, Iko
Kennedy, Gareth
Bond, Alan M.
Journal name Journal of the American chemical society
Volume number 131
Issue number 23
Start page 7976
End page 7989
Total pages 14
Publisher American Chemical Society
Place of publication Washington, D.C.
Publication date 2009
ISSN 0002-7863
1520-5126
Summary Unexpected nonadditivity of currents encountered in the electrochemistry of mixtures of ferrocene (Fc) and cobaltocenium cation (Cc+) as the PF6 - salt has been investigated by direct current (dc) and Fourier-transformed alternating current (ac) cyclic voltammetry in two aprotic (1-butyl-3-methylimidazolium tetrafluoroborate and 1-butyl-3-methylimidazolium hexafluorophosphate) and three protic (triethylammonium formate, bis(2-hydroxyethyl)ammonium acetate, and triethylammonium acetate) ionic liquids (ILs). The voltammetry of the individual Fc0/+ and Cc+/0 couples always exhibits near-Nernstian behavior at glassy carbon and gold electrodes. As expected for an ideal process, the reversible formal potentials and diffusion coefficients at 23 ( 1 °C in each IL determined from measurement on individual Fc and Cc+ solutions were found to be independent of electrode material, concentration, and technique used for the measurement. However, when Fc and Cc+ were simultaneously present, the dc and ac peak currents per unit concentration for the Fc0/+ and Cc+/0 processes were found to be significantly enhanced in both aprotic and protic ILs. Thus, the apparent diffusion coefficient values calculated for Fc and Cc+ were respectively found to be about 25 and 35% larger than those determined individually in the aprotic ILs. A similar change in the Fc0/+ mass transport characteristics was observed upon addition of tetrabutylammonium hexafluorophosphate (Bu4NPF6), and the double layer capacitance also varied in distinctly different ways when Fc and Cc+ were present individually or in mixtures. Importantly, the nonadditivity of Faradaic current is not associated with a change in viscosity or from electron exchange as found when some solutes are added to ILs. The observation that the 1H NMR T1 relaxation times for the proton resonance in Cc+ also are modified in mixed systems implies that specific interaction with aggregates of the constituent IL ionic species giving rise to subtle structural changes plays an important role in modifying the mass transport, double layer characteristics, and dynamics when solutes of interest in this study are added to ILs. Analogous voltammetric changes were not observed in studies in organic solvent media containing 0.1 M added supporting electrolyte. Implications of the nonadditivity of Faradaic and capacitance terms in ILs are considered.
Language eng
DOI 10.1021/ja8092295
Field of Research 030604 Electrochemistry
030699 Physical Chemistry not elsewhere classified
Socio Economic Objective 970103 Expanding Knowledge in the Chemical Sciences
HERDC Research category C1.1 Refereed article in a scholarly journal
Copyright notice ©2009, American Chemical Society
Persistent URL http://hdl.handle.net/10536/DRO/DU:30038933

Document type: Journal Article
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