Heterogeneous Bimetallic Organic Coordination Polymer-Derived Co/Fe@NC Bifunctional Catalysts for Rechargeable Li-O₂ Batteries

The Li-O₂ battery has attracted substantial attention due to its high theoretical energy density. In particular, high-efficiency oxygen catalysts are very important for the design of practical Li-O₂ batteries. Herein, we have synthesized heterogeneous crystalline-coated partially crystalline bimetallic organic coordination polymers (PC@C-BMOCPs), which are further pyrolyzed to obtain Co- and Fe-based nanoparticles embedded within rodlike N-doped carbon (Co/Fe@NC) as a bifunctional oxygen reduction reaction/oxygen evolution reaction (ORR/OER) catalyst used in the Li-O₂ battery. Owing to excellent ORR/OER catalytic ability, the Co/Fe@NC bifunctional catalyst exhibits an efficient reversible reaction between O₂ and Li₂O₂. Additionally, a large number of mesoporous channels are present in the core-shell Co/Fe@NC nanoparticles. These channels not only promote the diffusion of Li⁺ and O₂, but also create ample room to store insoluble discharge product Li₂O₂. The Li-O₂ batteries utilizing the bifunctional Co/Fe@NC oxygen electrode exhibit a large capacity of 17,326 mAh g^-1, a long cycling life of more than 250 cycles, and excellent reversibility. This work provides a universally applicable strategy for designing nonnoble metal ORR/OER catalysts with excellent electrochemical performance for metal-air batteries.