Unusual voltammetry of the reduction of O₂ in [C₄dmim][N(Tf)₂] reveals a strong interaction of O₂^•− with the [C₄dmim]⁺ cation

Voltammetric studies of the reduction of oxygen in the room temperature ionic liquid [C₄dmim][N(Tf)₂] have revealed a significant positive shift in the back peak potential, relative to that expected for a simple electron transfer. This shift is thought to be due to the strong association of the electrogenerated superoxide anion with the solvent cation. In this work we quantitatively simulate the microdisc electrode voltammetry using a model based upon a one-electron reduction followed by a reversible chemical step, involving the formation of the [C₄dmim]⁺···O₂^•- ion-pair, and in doing so we extract a set of parameters completely describing the system. We have simulated the voltammetry in the absence of a following chemical step and have shown that it is impossible to simultaneously fit both the forward and reverse peaks. To further support the parameters extracted from fitting the experimental voltammetry, we have used these parameters to independently simulate the double step chronoamperometric response and found excellent agreement. The parameters used to describe the association of the O₂^•- with the [C₄dmim]⁺ were k_f = 1.4 × 10³ s^-1 for the first-order rate constant and K_eq = 25 for the equilibrium constant.