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[Display omitted] • Co/Co 3 Fe 7 heterostructure is constructed by using an in-situ growth strategy. • NCNTs mitigates the corrosion of active sites to stabilize bifunctional activity. • Interfacial interactions activate electron transfer/redistribution to boost activity. • A small potential difference (0.62 V) obtains a superior charge/discharge capacity. • Zn-air battery shows high power density (165 mW cm−2) and cycling stability (300 h). In oxygen electrocatalysis, how to rationally design low-cost catalysts with reasonable structure and long-term stability is a crucial issue. Here, an in-situ growth strategy is used to construct a shaped structure encapsulating a uniformly-dispersed Co/Co 3 Fe 7 heterojunction in nitrogen-doped carbon nanotubes (Co/Co 3 Fe 7 @NCNTs). Hollow CoFe layered-double-hydroxide prisms act as sacrifices for in-situ growth of Co/Co 3 Fe 7 nanoparticles, which also catalyze the growth of bamboo-like NCNTs. Tubular structure not only accelerates the charge transfer through the interactions between Co and Co 3 Fe 7 , but also limits the aggregation of the particles, thereby promoting the 4e- oxygen reduction/evolution reactions (ORR/OER) kinetics and stabilizing the bifunctional activity. Co/Co 3 Fe 7 @NCNTs-800 (pyrolyzed at 800 °C) shows exceptional ORR activity (half-wave potential of 0.89 V) and methanol tolerance. Meanwhile, Co/Co 3 Fe 7 @NCNTs-800 shows a small OER overpotential of 280 mV, which increases by only 9 mV after 1000 cyclic voltammetry (CV) cycles. The outstanding bifunctionality (potential gap of 0.62 V) is ascribed to the electronic structure modulation at the Co/Co 3 Fe 7 heterointerface. Notably, it also has a high performance as an air–cathode for rechargeable zinc-air battery, showing high power density (165 mW cm−2) and specific capacity (770.5 m Ah kg−1). This work provides a new reference for promoting the development of alloy catalysts with heterogeneous interfaces. [ABSTRACT FROM AUTHOR]

To overcome slow kinetics of oxygen reduction/evolution reactions (ORR/OER), the development of bifunctional electrocatalysts remains a huge challenge. FeCo alloy as an active-species usually suffers from its poor catalytic stability by easy corrosion. Here, we synthesize a core (FeCo)-shell (carbon) alloy anchored on nitrogen-doped porous carbon-nanosheets (FeCo/NUCSs) via a self-growth strategy. FeCo/NUCSs (140 m2 g−1) exhibits promising half-wave potential (E 1/2 =0.89 V) and methanol tolerance for ORR. Prussian blue analog-derived carbon shell protects binary active-sites (Fe-N x /Co-N x) on FeCo core to stabilize ORR activity. FeCo/NUCSs also displays a higher OER activity (overpotential of 300 mV) than RuO 2 , due to generation of highly-active FeOOH/CoOOH species on FeCo alloys as indicated by in situ X-ray diffraction. Assembled Zn-air battery (ZAB) exhibits promising open-circuit voltage of 1.51 V, specific capacity of 791.86 mA h g−1, and durability (102 h). This novel bimetallic alloy-based catalyst provides an interesting option for design of durable oxygen-electrocatalysts for ZAB. [Display omitted] • A bifunctional FeCo alloy catalyst is obtained by using in-situ self-growth strategy. • Carbon shell protects the Fe-N x /Co-N x sites on FeCo core to stabilize ORR activity. • β-FeOOH/γ-CoOOH intermediates detected by in situ XRD can promote the OER kinetics. • The potential difference from ORR to OER (ΔE) is as excellent as 0.64 V. • The assembled Zn-air battery exhibits good rechargeability and durability (102 h). [ABSTRACT FROM AUTHOR]