Efficient and Durable Bifunctional Oxygen Catalysts Based on NiFeO@MnO 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 layer, in which the NiFeO-core contributes to the high activity for the oxygen evolution reaction (OER) and the amorphous MnO-shell functions as active phase for the oxygen reduction reaction (ORR), promoted by the synergistic effect between the NiFeO core and MnO shell. The synergistic effect is related to the electron drawing of NiFeO core from MnO shell, which decreases the affinity and adsorption energy of oxygen on MnO shell and significantly increases the kinetics of ORR. The electrocatalytic activity and durability of NiFeO@MnO depends strongly on the NiFeO:MnO ratio. NiFeO@MnO with NiFeO:MnO weight ratio of 1:0.8 shows the best performance for reversible ORR and OER, with a potential gap (ΔE) of 0.792 V to achieve a current density of 3 mA cm for ORR (E) and 5 mA cm for OER (E) in 0.1 M KOH solution. The high activity of the NiFeO@MnO(1:0.8) has been demonstrated in a Zn-air battery. Zn-air battery fabricated using the NiFeO@MnO(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. The results demonstrate NiFeO@MnO as an effective bifunctional oxygen catalysts for rechargeable metal-air batteries.