Efficient and Durable Bifunctional Oxygen Catalysts Based on NiFeO@MnO_x Core–Shell Structures for Rechargeable Zn–Air Batteries

Rechargeable Zn–air battery is limited by the sluggish kinetics and poor durability of the oxygen catalysts. In this Research Article, a new bifunctional oxygen catalyst has been developed through embedding the ultrafine NiFeO nanoparticles (NPs) in a porous amorphous MnO x layer, in which the NiFeO-core contributes to the high activity for the oxygen evolution reaction (OER) and the amorphous MnO x –shell functions as active phase for the oxygen reduction reaction (ORR), promoted by the synergistic effect between the NiFeO core and MnO x shell. The synergistic effect is related to the electron drawing of NiFeO core from MnO x shell, which decreases the affinity and adsorption energy of oxygen on MnO x shell and significantly increases the kinetics of ORR. The electrocatalytic activity and durability of NiFeO@MnO x depends strongly on the NiFeO:MnO x ratio. NiFeO@MnO x with NiFeO:MnO x weight ratio of 1:0.8 shows the best performance for reversible ORR and OER, with a potential gap (Δ E ) of 0.792 V to achieve a current density of 3 mA cm –2 for ORR ( E ORR=3 ) and 5 mA cm –2 for OER ( E OER=5 ) in 0.1 M KOH solution. The high activity of the NiFeO@MnO x (1:0.8) has been demonstrated in a Zn–air battery. Zn–air battery fabricated using the NiFeO@MnO x (1:0.8) oxygen electrode shows similar initial performance with that of Pt–Ir/C oxygen electrode but a much better durability under charge and discharge cycles as the result of the structure confinement effect of amorphous MnO x . The results demonstrate NiFeO@MnO x as an effective bifunctional oxygen catalysts for rechargeable metal–air batteries.