Electrochemical quartz crystal microbalance study on the oxygen reduction reaction in Li+ containing DMSO solution

Electrochemical quartz crystal microbalance (EQCM), which can detect surface mass change in ng scale, was employed to investigate the deposition of Li–O2 species on a gold electrode upon reduction of oxygen in a DMSO solution containing Li+ cation. In relatively positive potential region, the mass per mol-electron (mpe) calculated from the slope of the relation between mass change and accumulated charge was 37 g/mol-e, indicating the deposition of lithium superoxide (LiO2) with the reaction of O2 + e− + Li+ → LiO2. As the potential became more negative, where superoxide (O2-) was formed in Li+ free solution, the mpe became much smaller (ca. 7 g/mol-e), suggesting the formation of O2-, some of which were diffused away.