Heterogeneous Electron Transfer Kinetics at the Ionic Liquid/Metal Interface Studied Using Cyclic Voltammetry and Scanning Electrochemical Microscopy

Abstract

The electrochemical behavior of a redox-active, ferrocene-modified ionic liquid (1-ferrocenylmethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide) in acetonitrile and in an ionic liquid electrolyte (1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide) is reported. Reversible electrochemical behavior was observed in each electrolyte with responses typical of those for unmodified ferrocene observed in each medium. In the ionic liquid electrolyte, the diffusion coefficient of the redox-active ionic liquid increased by a factor of 5 upon increasing the temperature from 27 to 90°C. The kinetics of electron transfer across the ionic liquid/electrode interface were studied using cyclic voltammetry, and the standard heterogeneous electron transfer rate constant, k 0 was determined to be 4.25 × 10 -3 cm s -1 . Scanning electrochemical microscopy was then also used to probe the heterogeneous kinetics at the interface between the ionic liquid and the solid electrode and conventional kinetic SECM theory was used to determine k 0 . The k 0 value obtained using SECM was higher than that determined using cyclic voltammetry. These results indicate that SECM is a very useful technique for studying electron transfer dynamics in ionic liquids.

Mass transport and heterogeneous electron transfer of a ferrocene derivative in a room-temperature ionic liquid

“…Also, these results are in the same order of magnitude with those reported in literature [46]. One of the great advantages of EIS is that an independent check of the validity of impedance data is possible through the use of the Kramers-Kronig transforms [44].…”

“…Accordingly, care must be taken during the analysis of approach curves for a viscous medium such as an RTIL. Recently, it has been reported that SECM allows a better determination of the kinetic parameters in RTILs [46]. However, better control of the hydrodynamic regime is necessary in order to obtain stationary SECM approach curves.…”

Ultramicroelectrode Voltammetry and Scanning Electrochemical Microscopy in Room Temperature Ionic Liquids

“…For a simple quasi-reversible redox reaction at a disc-shaped SECM tip, coupled with the diffusion-controlled regeneration of the mediator at the substrate, the normalised tip current at potential E is given by [22]: [44]. In this case, the k 0 value obtained from fitting the experimental data to Eq.…”

Electrode–Electrolyte Interfacial Processes in Ionic Liquids and Sensor Applications

“…Our studies and others have shown that the capacitance of IL/electrode interface is potential dependent, and the adsorption of gas on the IL/electrode interface will decrease the double-layer capacitance under a specific DC bias potential [80]. In contrast to the EDL typically observed in dilute aqueous or nonaqueous electrolytes, the ions of ILs are strongly oriented near the electrode into an ordered layer structure with local ion density at maximum possible value [81,82]. Multiple ion pair layers form at the interface of IL and metal electrode.…”