Electrochemical Behavior of Cobaltocene in Ionic Liquids

Abstract

The electrochemical behavior of cobaltocenium has been studied in a number of room temperature aprotic ionic liquids. Well defined, diffusion controlled, anodic and cathodic peaks were found for the Cc+/Cc (cobaltocenium/cobaltocene) reduction/oxidation on gold, platinum and glassy carbon electrodes. Values of the peak separation parameters suggest quasireversibility or even irreversibility for the redox process. The difference between the ferrocene/ferrocenium and cobaltocenium/cobaltocene couples has been evaluated as equal to (1.350 ± 0.020) V. Values of the cobaltocenium (Cc+) diffusion coefficients D have been calculated on the basis of the Randles–Sevcik equation.

Analysis of water in room temperature ionic liquids by linear sweep, differential pulse and square wave cathodic stripping voltammetries

“…Each reference electrode was filled with an internal solution of [C 2 mim][Cl] in the corresponding RTIL and all of them were stored five days before use [28]. The stability of their electrode potential values through time was determined by cyclic voltammetry (CV) of the cobaltocenium ion, [Co(Cp) 2 ] + , at gold electrodes, since the cobaltocenium/cobaltocene redox couple, [Co(Cp) 2 ] +/0 , is a reliable internal standard for calibration of the RE potential in different nonaqueous media, as well as in RTILs [15,29] 2 ] +/0 couple. All electrochemical measurements were performed under dry N 2 in an AtmosBag 1 (Aldrich), using an electrochemical cell with a maximum volume of 1 mL.…”

“…In RTILs, when the size of the diffusing species is similar to the size of the RTIL ions, the Stokes-Einstein equation seems to work properly [14], thus one of the major factors influencing the diffusion coefficient, D, of electroactive species is the viscosity of the medium, h [15]. Therefore, the water content of the RTILs should be reported in order to prevent systematic errors and incorrect comparisons when calculating data such as the Walden product, Dh.…”

Voltammetric and spectroscopic study of ferrocene and hexacyanoferrate and the suitability of their redox couples as internal standards in ionic liquids

“…[19][20][21] Commonly used redox standards for comparing potentials between different IL media include the IUPAC-recommended ferrocene, [22][23][24][25][26] bis(biphenyl)chromium, 27 and cobaltocene. 7,8,[28][29][30] Yet, the use of ferrocene as internal standard can be problematic and there is, mostly anecdotal, evidence of the following issues: (I) the solubility of ferrocene in some ionic liquids is not high enough to enable electrochemical measurements, especially in cases where high viscosity (i.e. slow mass transport) will slow down the electrode reaction;…”

Catalysis by electrons and holes: formal potential scales and preparative organic electrochemistry

“…Ferrocene has also been measured in a series of ionic liquids 123,124 as well as cobaltocene. 124 Errors in reported potentials may be caused by re-referencing against already unreliable reference points. We recommend providing multiple reference scales if a conversion is necessary.…”