LSVs, Tafel and EIS results collectively demonstrate the high ORR and OER catalytic activity of FeNi-NC@MWCNT. Furthermore, its robust stability was further proved by the negligible degradation on the chronoamperometric response after continuous 10 h polarization at 1.62 V (Figure ), which is further confirmed by the essentially identical LSV curves before and after CA (Insert figure in Figure ). The faradaic efficiency of FeNi-NC@MWCNT was also assessed with RRDE voltammetry. In this study, the ring potential was set as E=0.40 V to reductively detect the oxygen generated at the disk electrode. According to the monitored ring current, disk current and current collection efficiency (0.15), the OER faradaic efficiency of FeNi-NC@MWCNT was determined as 95.6%, which is higher than that of the reference catalysts (SI, Figure ). The electrochemically active surface area (ECSA) was further investigated to assess the number of accessible reactive sites, which is correlated with double-layer capacitance (Cdl). As shown in Figure and Figure (SI), the Cdl of FeNi-NC@MWCNT (18.81 mF cm -2 ) is considerably larger than that of FeNi-NC (12.35 mF cm -2 ) and Pt/C (6.14 mF cm -2 ).