Greatly promoted oxygen reduction reaction activity of solid catalysts by regulating the stability of superoxide in metal-O2 batteries

Abstract

Oxygen reduction reactions (ORRs) with one- or two-electron-transfer pathways are the essential process for aprotic metal-oxygen batteries, in which the stability of superoxide intermediates/products (O2−, LiO2, NaO2, etc.) mainly dominates the ORR activity/stability and battery performance. However, little success in regulating the stability of the superoxides has been achieved due to their highly reactive characteristics. Herein, we identified and modulated the stability of superoxides by introducing anthraquinone derivatives as cocatalysts which functioned as superoxide trapper adsorbing the superoxides generated via surface-mediated ORR and then transferring them from the solid catalyst surface into electrolyte. Among the studied trappers, 1,4-difluoroanthraquinone (DFAQ) with electron-withdrawing groups showed the highest adsorption towards superoxides and could efficiently stabilize LiO2 in electrolyte, which greatly promoted the surface-mediated ORR rate and stability. This highlighted the magnitude of adsorption between the trapper and LiO2 on the ORR activity/stability. Using an aprotic Li-O2 battery as a model metal-O2 battery, the overall performance of the cell with DFAQ was substantially improved in terms of cell capacity, rate capability and cyclic stability. These results represent a significant advance in the understanding of ORR mechanisms and promoting the performance of metal-O2 batteries.