LAUSR

The thermodynamic stability and relatively low free energy of formation (ΔG0 = −239.4 kJ mol–1) of KO2 offer the possibility of K–O2 cells as a catalyst-free, low overpotential energy storage system. Having identified dimethyl sulfoxide (DMSO) as a solvent that promotes KO2 production due to its high donor number, the present study elucidates the oxygen reduction reaction mechanism of the K–O2 cell with a DMSO electrolyte. The use of DMSO-based electrolytes led to distinct first and second electron-transfer peaks, suggesting the possibility of facile voltage-based control of the cathode reaction to selectively produce KO2 as the product. However, the observed low overpotential i–E behavior on a rotating ring-disk electrode could only be accounted for by postulating further chemical reactions (disproportionation on the electrode surface and in the electrolyte) of KO2 to form K2O2. The rate of the surface disproportionation reaction to produce K2O2 was found to be competitive with the KO2 desorption step, w...