Nonadditivity of faradaic currents and modification of double layer capacitance in the voltammetry of mixtures of ferrocene and ferrocenium salts in ionic liquids

Shiddiky, Muhammad J. A., Torriero, Angel. A. J., Reyna-Gonzälez, Juan M. and Bond, Alan M. 2010, Nonadditivity of faradaic currents and modification of double layer capacitance in the voltammetry of mixtures of ferrocene and ferrocenium salts in ionic liquids, Analytical chemistry, vol. 82, no. 5, pp. 1680-1691, doi: 10.1021/ac9020159.

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Title Nonadditivity of faradaic currents and modification of double layer capacitance in the voltammetry of mixtures of ferrocene and ferrocenium salts in 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
Reyna-Gonzälez, Juan M.
Bond, Alan M.
Journal name Analytical chemistry
Volume number 82
Issue number 5
Start page 1680
End page 1691
Total pages 12
Publisher American Chemical Society
Place of publication Washington, D.C.
Publication date 2010-01-28
ISSN 0003-2700
1520-6882
Summary Electrochemical studies on the Fc + e− Fc+ (Fc = ferrocene) process have been undertaken via the oxidation of Fc and reduction of Fc+ as the hexafluorophosphate (PF6−) or tetrafluoroborate (BF4−) salts and their mixtures in three ionic liquids (ILs) (1-butyl-1-methylpyrrolidinium bis[(trifluoromethyl)sulfonyl]imide, 1-butyl-3-methylimidazolium tetrafluoroborate, and 1-butyl-3-methylimidazolium hexafluorophosphate). Data obtained at macro- and microdisk electrodes using conventional dc and Fourier-transformed large-amplitude ac (FT-ac) voltammetry reveal that diffusion coefficients for Fc and Fc+ differ significantly and are a function of the Fc and Fc+ concentration, in contrast to findings in molecular solvents with 0.1 M added supporting electrolyte media. Thus, the Faradaic currents associated with the oxidation of Fc (Fc0/+) and reduction of FcPF6 or FcBF4 (Fc+/0) when both Fc and Fc+ are simultaneously present in the ILs differ from values obtained when individual Fc and Fc+ solutions are used. The voltammetry for both the Fc0/+ and Fc+/0 processes exhibited near-Nernstian behavior at a glassy carbon macrodisk electrode and a platinum microdisk electrode, when each process was studied individually in the ILs. As expected, the reversible formal potentials (E°′) and diffusion coefficients (D) at 23 ± 1 °C were independent of the electrode material and concentration. However, when Fc and FcPF6 or FcBF4 were both present, alterations to the mass transport process occurred and apparent D values calculated for Fc and Fc+ were found to be about 25−39% and 32−42% larger, respectively, than those determined from individual solutions. The apparent value of the double layer capacitance determined by FT-ac voltammetry from individual and mixed Fc and Fc+ conditions at the GC electrode was also a function of concentration. Double layer capacitance values increased significantly with the concentration of Fc and FcPF6 or FcBF4 when species were studied individually or simultaneously, but had a larger magnitude under conditions where both species were present. Variation in the structure of the ILs and hence mobilities of the ionic species, when Fc and FcPF6 or FcBF4 are simultaneously present, is considered to be the origin of the nonadditivity of the Faradaic currents and variation in capacitance.
Language eng
DOI 10.1021/ac9020159
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 ©2010, American Chemical Society
Persistent URL http://hdl.handle.net/10536/DRO/DU:30038931

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