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

The electrochemistry of I(-)/I(3)(-) 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 [C(n)C(1)Im][Tf(2)N], 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(-)/I(3)(-) redox couple and oxidation/reduction of the I(3)(-)/I(2) redox couple. The diffusion coefficients of I(-) and I(3)(-), 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(-)/I(3)(-) redox couple. Steady-state behaviour was observed at 1.3 mu m UMEs at slow voltammetric scan rates and steady-state SECM feedback approach curves were also obtained at a 1.3 mu m Pt SECM tips, provided that the tip approach speed was sufficiently low. (C) 2011 Elsevier Ltd. All rights reserved.