Auto‐Oxygenated Porphyrin‐Derived Redox Mediators for High‐Performance Lithium Air‐Breathing Batteries

Because of their distinct energy potentials, Li air‐breathing batteries have been highlighted as promising energy storage systems; however, the sluggish oxygen reduction and evolution reactions (ORR and OER) disturb the reversible cell operation during cycling. Therefore, catalyst materials should be tailored to mitigate the low efficiencies of air‐breathing batteries. A porphyrin‐derived catalyst is optimized by introducing different metal‐centered organometallic phthalocyanine (MPc) complexes and their potential application as redox mediators (RMs) for fabricating efficient Li–O2 cells is investigated. The feasibility of each MPc is determined as a potential RM by calculating its orbital levels. The electrochemical properties of the Li–O2 cells employing the diverse MPc‐RMs are compared. The MPc‐containing Li–O2 cells exhibit improved cell performance, reduced polarization, and stable cyclability with auto‐oxygenated properties as revealed by directly injecting superoxide species into the MPc‐containing electrolytes. The synergistic effects of blended MPcs—a mixture consisting of the two most effective MPcs—in both the OER and ORR regions in ambient air atmosphere are also elucidated. The reaction mechanism of the MPc‐containing cells is proposed based on first‐principles calculations and experimental results. The introduction of natural functional catalysts provides a basis for developing effective eco‐friendly catalysts for application to sustainable air‐breathing batteries. Along with its role as redox mediators, metal‐centered organometallic phthalocyanine's auto‐oxygen‐binding properties facilitates reversible cell reactions for oxygen reduction and evolution in Li air‐breathing cells. By stabilizing highly reactive oxygen radicals, metal‐centered organometallic phthalocyanine‐containing Li air‐breathing cells exhibit improved capacity, stable cycling performance, and lower charge overpotentials compared to pristine Li air‐breathing cells.