K-O₂ electrochemistry at the Au/DMSO interface probed by in situ spectroscopy and theoretical calculations

The reaction mechanism underpinning the operation of K-O-2 batteries, particularly the O-2 reactions at the positive electrode, is still not completely understood. In this work, by combining in situ Raman spectroelectrochemistry and density functional theory calculations, we report on a fundamental study of K-O-2 electrochemistry at a model interface of Au electrode/DMSO electrolyte. The key products and intermediates (O-2(-), KO2 and K2O2) are identified and their dependency on the electrode potential is revealed. At high potentials, the first reduction intermediate of O-2(-)* radical anions (* denotes the adsorbed state) can desorb from the Au electrode surface and combine with K+ cations in the electrolyte producing KO(2)via a solution-mediated pathway. At low potentials, O-2 can be directly reduced to on the Au electrode surface, which can be further reduced to at extremely low potentials. The fact that K2O2 has only been detected in the very high overpotential regime indicates a lack of KO2 disproportionation reaction both on the Au electrode surface and in the electrolyte solution. This work addresses the fundamental mechanism and origin of the high reversibility of the aprotic K-O-2 batteries.