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

Abstract

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-O-2 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-O-2 cells employing the diverse MPc-RMs are compared. The MPc-containing Li-O-2 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.