Cobalt-and nitrogen-codoped porous carbon catalyst made from core-shell type hybrid metal-organic framework (ZIF-L@ZIF-67) and its efficient oxygen reduction reaction (ORR) activity

The development of carbon-based oxygen reduction reaction (ORR) catalysts to substitute the expensive and unstable platinum-based ORR catalysts is of great importance for their optimal utilization in energy conversion and storage. Herein, we report the production of highly active carbon-based ORR catalyst from well-designed core shell type hybrid metal-organic framework (MOF). Cobalt- and nitrogen-codoped porous carbon leaves (Co,N-PCLs) are prepared via a simple one-step pyrolysis of well-designed leaf-shaped core-shell type hybrid MOFs (ZIF-L@ZIF-67, ZIF (zeolitic imidazolate framework) is a subclass of MOF), which contain two different metal ions (Zn2+ in core and Co2+ in shell) and sufficient nitrogen source with a thin flat morphology. The structural and compositional features of resulting Co,N-PCIs are characterized using scanning electron microscopy, transmission electron microscopy, energy-dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy, Raman spectroscopy, and N-2 sorption isotherms, and the analyses reveal that they possess the ideal structural and compositional features for ORR, such as numerous carbon nanotubes (CNTs), substantial Co- and N-doping, large surface area, and high pore volume while maintaining the advantageous thin leaf-shape. Owing to such unique structural and compositional features, Co,N-PCLs display much better ORR activity than their counterparts prepared from the parent materials (ZIF-L or ZIF-67). In addition, Co,N-PCL even shows a better electrochemical stability and a better methanol tolerance compared to commercial Pt/C material.