Heterogeneous electron transfer kinetics at the ionic liquid/metal interface studied using cyclic voltammetry and scanning electrochemical microscopy

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 degrees 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 x 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.