Combining Solid FePc Immobilized on Py-Functionalized Carbon Matrix with Soluble Redox Mediator FePc As an Efficient Cathode Catalyst for Non-Aqueous Li-O2 Batteries

Abstract

It is important to develop bifunctional catalysts with high activity and stability for reversible oxygen reduction reactions (ORRs) and oxygen evolution reactions (OERs) in lithium-oxygen (Li-O2) batteries. Recently, the iron phthalocyanine (FePc) complex has been considered a promising candidate for bifunctional (ORR/OER) O2 catalysts due to its low cost, high catalytic properties, and ease of preparation. In this work, two different structural types of FePc-based solution-phase catalysts as soluble redox mediators (SRMs) and solid FePc immobilized on pyridine-functional carbon supports (multi-walled carbon nanotube, MWCNT and graphene, GR) are investigated to evaluate the influence of FePc structural design on their catalytic activity and kinetics.Our work demonstrated that FePc(solid)/Py/MWCNT exhibited better bifunctional catalytic activity than FePc(solid)/Py/GR in the same electrolyte because of the stronger axial bonding between FePc(solid) and Py/MWCNT. The combination of FePc(solid)/Py/MWCNT and FePc(sol) displays the best cyclability, which can be attributed to the highly efficient solid-liquid interface. Moreover, FePc(solid)/Py/MWCNT without FePc(sol) shows the lowest overpotential owing to the surface-grown thin film Li2O2 is structurally less order than the solution-grown toroidal Li2O2.