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

Abstract

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.