To explore the feasibility of bifunctional oxygen electrocatalysis for rechargeable Zn-air batteries, the OER performance of as-synthesized catalysts and other comparison catalysts were investigated in 0.1 M aqueous KOH. As shown in Figure , for FeNi-NC@MWCNT shows a low OER overpotential (380 mV) at j = 10 mA cm -2 . This is significantly lower Fe-NC@MWCNT (483 mV), Ni-NC@MWCNT (464 mV), FeNi-NC (427 mV) and even commercial IrO2 (400 mV). Also, low Tafel slopes are observed for FeNi-NC@MWCNT (87.3 mV dec -1 , Figure , SI). The composite outperforms many other recently reported OER catalysts (SI, Table ). Electrochemical impedance spectroscopy (EIS) was performed at a potential of 1.56 V to further evaluate the OER kinetics. As shown in Figure (SI), the diameter of the semicircle of EIS spectrum for FeNi-NC@MWCNT is much smaller than that of the reference catalysts, revealing more efficient charge transfer and lower overall impedance, leading to faster OER kinetics. The potential gap ∆E (the difference between the half-wave potential (E1/2) of ORR and the OER potential at 10 mA cm -2 (Ej=10)) is used as indicator to evaluate the bifunctional activity of the studied oxygen catalysts. Note that smaller ∆E values imply high bifunctional OER/ORR performance. Figure shows that FeNi-NC@MWCNT has a ∆E value of 0.71 V, which is lower than that of FeNi-NC (0.8 V) and Pt/C+IrO2 (0.75V). Durability is another key performance indicator for practical applicability of bifunctional oxygen catalysts, e.g., in rechargeable ZABs. Thus, the stability of the catalysts was assessed by chronoamperometry (CA). As shown in Figure (SI), after 24 h of CA at a constant potential of 0.8 V in O2-saturated electrolyte, FeNi-NC@MWCNT retained 93.5% of the initial current density, while significantly higher current density drops were observed for the references FeNi-NC (81.5%) and Pt/C (52.6%). The superior durability of FeNi-NC@MWCNT is further corroborated by virtually identical LSV curves before and after the CA analysis (Figure , SI).