Metal–Organic Framework-Induced Synthesis of Ultrasmall Encased NiFe Nanoparticles Coupling with Graphene as an Efficient Oxygen Electrode for a Rechargeable Zn–Air Battery

Rational design of electrocatalysts to replace the noble-metal-based materials for oxygen reactions is highly desirable but challenging for rechargeable metal–air batteries. Herein, we demonstrate a unique two stage encapsulation strategy to regulate the structure and performance of catalysts featured with thin graphene nanosheets coupling with full encapsulated ultrafine and high-loaded (∼25 wt %) transition metal nanoparticles (TMs@NC X ) for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). By optimizing the electronic modulation effect from suitable metal cores, the best NiFe@NC X catalyst exhibits high stability and activity with an onset potential of 1.03 V for ORR and an overpotential of only 0.23 V at 10 mA cm –2 for OER, which is superior to commercial Pt/C and IrO 2 catalysts. Rechargeable Zn–air battery using NiFe@NC X catalyst exhibited an unprecedented small charge–discharge overpotential of 0.78 V at 50 mA cm –2, high reversibility, and stability, holding great promise for the practical implementation of rechargeable metal–air batteries.