Ethyl Viologen as a Superoxide Quencher to Enhance the Oxygen Reduction Reaction in Li-O₂ Batteries

LiO₂ is a critical intermediate of oxygen reduction reaction in nonaqueous Li-O₂ batteries that largely determines the discharge capacity and cycling stability. Currently, functional redox mediators that can promote the solution reaction route by enhancing the solvation of LiO₂ have attracted tremendous interest to increase the attainable capacity. Conversely, redox mediators that quench LiO₂ and facilitate the surface reaction route receive little attention. Here, we provide an in-depth exploration of the catalytic pathway and effect of a superoxide quencher that modulates the surface growth of Li₂O₂. Surprisingly, the predomination of the surface reaction route by ethyl viologen helps deliver a capacity as much as that promoted by the solution reaction route. The findings of this work provide a new direction of screening and evaluating functioning redox mediators for Li-O₂ batteries.