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

Abstract

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-PCLs are characterized using scanning electron microscopy, transmission electron microscopy, energy-dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy, Raman spectroscopy, and N2 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.