In Situ Growth of Co4N Nanoparticles–Embedded Nitrogen‐Doped Carbon Nanotubes on Metal–Organic Framework–Derived Carbon Composite as Highly Efficient Electrocatalyst for Oxygen Reduction and Evolution Reactions.

Highly efficient and low‐cost bifunctional electrocatalysts for oxygen reduction and evolution reactions (ORR/OER) are central to new generation rechargeable metal–air batteries. Herein, hierarchical microspheres assembled by in situ generated Co4N nanoparticles (Co4N Nps)‐embedded nitrogen‐doped carbon nanotubes (Co4N@NCNTs) are constructed by a facile urea acid (UA)‐assisted pyrolysis of zeolitic imidazole framework (ZIF)‐67. In this strategy, the UA sharply decomposes at 440 °C to carbonaceous gases, which facilitate the nucleation of Co4N Nps for the catalytic growth of the NCNT microspheres structure from the intermediate ZIF‐67 polyhedrons. The as‐prepared Co4N@NCNTs exhibit high N content, abundant Co4N active species, high electron conductivity, and large specific area on a hierarchical micro‐mesoporous structure. Therefore, the Co4N@NCNTs not only exceed Pt/C in terms of ORR half wave potential (0.85 vs 0.83 V) and limiting current density (5.50 vs 5.20 mA cm−2), but also manifest comparable OER activity with Ru/C. In the rechargeable zinc–air battery test, the bifunctional Co4N@NCNTs show excellent performance with high discharge and low charge potentials and relatively stable voltage gap as long as 500 cycles, which greatly outperform those of commercial Pt–Ru/C. [ABSTRACT FROM AUTHOR]