The electrochemical properties of a platinum electrode in functionalized room temperature imidazolium ionic liquids

Abstract

The electrochemical behavior of a platinum electrode in a set of 1-alkyl ether (and 1-alkyl)-3-methylimidazolium room-temperature ionic liquids (RTILs) 1–3 ([C_xO_yMim]⁺[Anion]⁻ or [C_xMim]⁺[Anion]⁻, where Mim = 3-methylimidazolium; C_xO_y = 1-alkyl ether; C₇O₃ = -(CH₂)₂O(CH₂)₂O(CH₂)₂OCH₃; C₃O₁ = -(CH₂)₂OCH₃; C_x = 1-alkyl; C₁₀ = C₁₀H₂₁; C₄ = C₄H₉; and ${\left[ {{\text{Anion}}} \right]}^{ - } = {\text{H}}_{3} {\text{CSO}}^{ - }_{3} ,{\text{ BF}}^{ - }_{4} {\text{, or PF}}^{ - }_{6}$) was studied by cyclic voltammetry and electrical conductivity. This complementary set of imidazolium RTILs allowed us to explore the effect of the imidazolium cation and the counter-ion, both of which affected the electrochemical window of these RTILs. Various electrochemical events with low current values were observed, which diminished the electrochemical windows. Interestingly, RTILs 2b [1-(2-methoxyethyl)-3-methylimidazolium tetrafluoroborate] and 2d [1-butyl-3-methylimidazolium tetrafluoroborate] showed quasireversible charge transfer processes. The length of the functional group attached to the imidazolium cation was shown to be of great influence as larger electrochemical windows, as well as lower electrical conductivities, were obtained with the longer C₇O₃ and C₁₀ functional groups. The largest electrochemical window of 2.0 V was achieved with RTIL 2c, 1-decyl-3-methylimidazolium tetrafluoroborate.