Ferrocene as a Reference Redox Couple for Aprotic Ionic Liquids

The electrochemical behavior of ferrocene has been studied in a number of room temperature ionic liquids. Diffusion‐controlled, well‐defined anodic and cathodic peaks were found for the Fc/Fc+ (ferrocene/ferrocenium) oxidation/reduction on the gold electrode. Ohmic resistance R between working and auxiliary electrodes was deduced from impedance measurements. Cyclic voltammograms were corrected for the base line current as well as for the ohmic drop (IR). The formal potential 1/2(Epa+Epc) for ferrocene reduction/oxidation in aprotic ionic liquids tested is within a relatively narrow range and may be approximated by the value of 0.527±0.018 V (against the cryptate Ag/Ag+222 in acetonitrile reference). Ferrocene diffusion coefficients, calculated from the peak current dependence on the sweep rate, were of the order of 10−7 cm2 s−1.