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.

Functionality and design of Co-MOFs: unique opportunities in electrocatalysts for oxygen reduction reaction

“…The cyclic structure of UA suggests that N-doped carbon nanotubes with Co-N-C will be furnished upon carbonization. 133 Pure as-synthesized ZIF-67 was treated with UA via one-step programmed carbonization at 440 °C and 700 °C, as expressed in Fig. 19a.…”

“…(b) ORR LSV curves of Co 4 N@NCNTs, Co 4 N/NCNDs, ZIF/UA-440, and Pt/ C at 1600 rpm in O 2 -saturated 0.1 M KOH. Copyright 2020, WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim 133.…”

Preparation of “Co-Nx Carbon Net” Protected CoFe Alloy on Carbon Nanotubes as an Efficient Bifunctional Electrocatalyst in Zn-Air Batteries

“…Furthermore, the low content of transition metals in a composite catalyst is another limiting problem that impacts its performance . Nevertheless, it is difficult to significantly promote a catalyst activity via direct enhancement of metal loading with conventional approaches such as electrodeposition, hydrothermal methods, or simple pyrolysis. − This is because porous structures favorable for electrocatalysis are very difficult to form with these methods, which often produces carbon structures embedded with M-N x active sites, thereby impeding mass and charge transfer . Therefore, building high-density active sites in a porous nanostructure is an effective strategy to maximize the exposure of catalytic sites, which is crucial to the overall ORR/OER and ultimate performance improvement of ZABs …”

Design of cobalt nickel nitrides/carbon nitride composite catalysts for enhanced electrochemical water splitting

“…The unique electronic properties, the simplicity and convenience of tuning for the physical structure and electronic environment make metal nitrides a potential alternative candidate for low-cost efficient catalysts. At the same time, transition metal-based compounds are usually studied by compositing with other functional materials such as carbon-based nanomaterials due to their special properties [10][11][12].…”