Promoting Surface-Mediated Oxygen Reduction Reaction of Solid Catalysts in Metal–O2 Batteries by Capturing Superoxide Species

The oxygen reduction reaction (ORR) in aprotic electrolyte is the essential reaction in metal–oxygen batteries. Capturing and shifting the absorbed metal superoxide intermediates/products from a cathode surface is a long-standing challenge to clarify the ORR mechanism, accelerate the ORR, and improve the stability and energy density of metal–oxygen batteries. Herein, a bioinspired pathway in which cathode solid catalysts and soluble anthraquinone (AQ) molecules initiate an "enzyme–coenzyme" cooperative catalysis mechanism is developed to greatly boost the ORR activity of solid catalysts over 10-fold, in which AQ acts as a scavenger to capture and shift the absorbed superoxide species from the cathode surface to the aprotic electrolyte. Taking the lithium–oxygen (Li–O2) battery as a model system, the cell discharge ORR mechanism is well illustrated and capacities are significantly improved over 3 times in the presence of AQ molecules. This concept represents the first demonstration of stabilizing and solvating superoxide species to substantially accelerate ORR catalysis of solid catalysts and enhance the performance of metal–O2 batteries through biomimicking coenzyme-assisted reactions.