The bifunctional ORR/OER performance of the native FeNi-NC@MWCNT catalyst were investigated with a half-cell setup based on a typical three-electrode configuration (see SI for details). All potentials reported were referenced to reversible hydrogen electrode potentials (RHE). The performance of the reference materials Fe-NC@MWCNTs, Ni-NC@MWCNTs, FeNi-NC and commercial Pt/C, IrO2 were also evaluated for comparison. The ORR tests were conducted in an O2-saturated 0.1 M aqueous KOH solution using a rotating disk electrode (RDE) as working electrode. Compared with the negligible background currents in Ar-saturated solution, the cyclic voltammetry (CV) of FeNi-NC@MWCNT in O2-saturated solution shows a major cathodic oxygen reduction peak at 0.77 V (SI, Figure ). As shown in the linear sweep voltammetry (LSV) curves, (Figure ), FeNi-NC@MWCNT exhibits superior ORR catalytic activity in term of high onset potential (0.98 V), high half-wave potential (E1/2) (0.9 V) and large limiting current density (4.5 mA cm -2 ), which surpass these values of the references Fe-NC@MWCNTs (0.91 V, 0.88 V, 3.47 mA cm -2 ), Ni-NC@MWCNTs (0.89 V, 0.83 V, 3.95 mA cm -2 ), FeNi-NC (0.93 V, 0.87 V, 3.93 mA cm -2 ), and even outperforms that of commercial Pt/C (0.95 V, 0.88V, 3.74 mA cm -2 ). In fact, the performance of FeNi-NC@MWCNT is superior to most currently reported SAC or DAC materials based on non-precious metals (SI, Table ). Comparison of the title compound with the single-metal species Fe-NC@MWCNTs and Ni-NC@MWCNTs as well as the MWCNT-free sample FeNi-NC demonstrates the impact of the dual metal sites and the carbon nanotube linkage. Figure (SI) shows that FeNi-NC@MWCNT also exhibits a smaller Tafel slope (59.2 mV dec -1 ) than FeNi-NC (73.6 mV dec -1 ) and Pt/C (69.6 mV dec -1 ), indicating a faster ORR electrocatalytic kinetics. Furthermore, the electron transfer number (n) and selectivity of FeNi-NC@MWCNT as well as its counterparts were evaluated by rotating ring disk electrode (RRDE) measurements. In Figure , the peroxide yield of FeNi-NC@MWCNT is below 3.14% and the monitored n is above 3.9 over the potential range of 0.2 V -0.8 V, verifying the high ORR selectivity and dominant 4 e -transfer mechanism. In contrast, the FeNi-NC shows a much higher peroxide yield (20%) and lower n value of 3.6 at 0.48 V vs. RHE, suggesting an enhanced activity retention of FeNi-NC@MWCNT. The average n value of FeNi-NC@MWCNT was also calculated to be around 3.98 (SI, Figure ) using Koutecky-Levich (K-L) analysis of polarization curves obtained at different electrode rotation rates, further confirming a 4e -transfer pathway. Moreover, the K-L plots for FeNi-NC@MWCNT at different potentials exhibit parallel linear correlation (SI, Figure ), indicating its potentialindependent electron transfer rate and the first-order reaction kinetics with O2 concentration.