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.