Unusual Voltammetry of the Reduction of O2 in [C4dmim][N(Tf)2] Reveals a Strong Interaction of O_2~( ·-) with the [C4dmim]~+ Cation

摘要

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]~+ · · ·O_2~( ·-)on-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 O_2~( ·-) with the [C4dmim]~+ were k_f = 1.4 x 10~3 s~(-1) for the first-order rate constant and K_(eq) = 25 for the equilibrium constant.