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

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-O 2 ) batteries. Recently, the iron phthalocyanine (FePc) complex has been considered a promising candidate for bifunctional (ORR/OER) O 2 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 Li 2 O 2 is structurally less order than the solution-grown toroidal Li 2 O 2 .