Iodide/triiodide electrochemistry in ionic liquids: Effect of viscosity on mass transport, voltammetry and scanning electrochemical microscopy

The electrochemistry of I−/I3− was studied in ionic liquids using a combination of cyclic voltammetry, chronoamperometry and scanning electrochemical microscopy (SECM). The electrolytes were 1-alkyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide [CnC1Im][Tf2N], ionic liquids (where n = 2, 4 and 8) and I− was typically added at a concentration of approximately 11 mM. During cyclic voltammetry, two sets of peaks were observed in each ionic liquid due to oxidation and reduction of the I−/I3− redox couple and oxidation/reduction of the I3−/I2 redox couple. The diffusion coefficients of I− and I3−, as determined using chronoamperometry, increased with increasing temperature and decreased with increasing ionic liquid viscosity. The effect of ionic liquid viscosity on ultramicroelectrode (UME) voltammetry was also determined using the I−/I3− redox couple. Steady-state behaviour was observed at 1.3 μm UMEs at slow voltammetric scan rates and steady-state SECM feedback approach curves were also obtained at a 1.3 μm Pt SECM tips, provided that the tip approach speed was sufficiently low.

► Electrochemical behavior of I−/I3− was studied in ionic liquids using a range of electrochemical techniques.
► The ionic liquid viscosity has a drastic effect on the electrochemical behavior of the system.
► Mass transport properties of the ionic liquid electrolytes depend on viscosity.
► Steady-state electrochemical responses can be obtained in ionic liquids if the experimental parameters are carefully controlled.