Studies of oxygen reduction in 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide by microdisk voltammetry

The electrochemical behavior of oxygen reduction in the room temperature ionic liquid 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl) imide (BMPTFSI) was examined using staircase cyclic voltammetry on a 50 μm diameter platinum microdisk electrode. The diffusion coefficients for oxygen and superoxide, and the heterogeneous rate constants were obtained with a fit to experimental voltammograms. A modified transport equation in 1D spherical symmetry and Tsallis’ q-exponential function were utilized in the fit procedure, and its applicability was compared to 2D simulations made with Comsol Multiphysics. In addition, the formal standard potential of oxygen reduction was referenced to the cobaltocene/cobaltocenium (Co(cp)2+/0) redox couple. It was found that oxygen reacts with homogeneously with Co(cp)2+, making the quantitative determination of oxygen reaction kinetics rather difficult. Also, small amounts of water in the liquid cause complex reaction mechanisms. Finally, proton reduction was also measured, and its formal potential resides at ca. 1.45 V vs. Co(cp)2+/0 reference, which more than 1 V positive to those of water or oxygen reduction.