Completely Eradicating Singlet Oxygen in Li-O₂ Battery via Cobalt(II)-Porphyrin Complex-Catalyzed LiOH Chemistry

Li-O₂ batteries have an extremely high theoretical specific energy; however, the large charge overpotential and highly reactive singlet oxygen (¹O₂) are two major obstacles. Porphyrin as a special kind of macrocyclic conjugated aromatic system exhibits excellent redox activity, which can be optimized by introducing a center metal atom. Herein, 5,10,15,20-tetrakis(4-aminophenyl)-porphyrin (TAPP) and 5,10,15,20-tetrakis(4-aminophenyl)-porphyrin-Co(II) (Co-TAP) are applied as effective redox mediators for Li-O₂ batteries. The synergistic effects of a center metal atom and organic ligand make Co-TAP more favorable for oxygen reduction and evolution. To understand the fundamental reaction mechanisms with or without TAPP or Co-TAP, the discharge/charge processes and the parasitic reactions have been comprehensively studied. The results reveal that TAPP affects the formation mechanism of Li₂O₂, while Co-TAP transforms the main discharge product into LiOH without adding extra water. Co-TAP-containing batteries operated via LiOH chemistry completely eradicate ¹O₂ and significantly alleviate the parasitic reactions associated with ¹O₂.