Redox‐Mediated Two‐Electron Oxygen Reduction Reaction with Ultrafast Kinetics for Zn–Air Flow Battery

Abstract Rechargeable Zn–air batteries (ZABs) as high‐energy density and cost‐effective power sources for next generation energy storage have attracted considerable attention. However, the sluggish oxygen electrochemistry leads to high polarization of the air electrode during charge/discharge and consequently a low round‐trip energy efficiency of the cell. Here it is shown that the two‐electron oxygen redox chemistry enabled by a redox mediator, anthraquinone‐2,7‐disulfonic acid disodium salt (AQDS), can effectively boost the performance of ZABs. The kinetics and underlying mechanism of the AQDS‐mediated oxygen reduction reaction at different pH are scrutinized both computationally and experimentally to delineate the reaction pathways and rate‐limiting step. An ultrafast catalytic rate constant of 2.53 × 10⁶ s^–1 is achieved at a pH of 13.13 and based on a flow cell configuration, the AQDS‐mediated Zn–air flow battery demonstrates considerably enhanced energy efficiency of 85% at 10 mA cm⁻².