Microporous MOFs Engaged in the Formation of Nitrogen-Doped Mesoporous Carbon Nanosheets for High-Rate Supercapacitors

Nitrogen-doped mesoporous carbon nanosheets (NMCS) have been fabricated from zinc-based microporous metal-organic frameworks (ZIF-8) by pyrolysis in a molten salt medium. The as-prepared NMCS exhibit significantly improved specific capacitance (NMCS-8: 232Fg(-1) at 0.5Ag(-1)) and capacitance retention ratio (75.9% at 50Ag(-1)) compared with the micropore-dominant nitrogen-doped porous carbon polyhedrons (NPCP-5: 178Fg(-1) at 0.5Ag(-1), 15.9% at 20Ag(-1)) obtained by direct pyrolysis of nanocrystalline ZIF-8. The excellent capacitive performance and high rate performance of the NMCS can be attributed to their unique combination of structure and composition, that is, the two-dimensional and hierarchically porous structure provides a short ion-transport pathway and facilitates the supply of electrolyte ions, and the nitrogen-doped polar surface improves the interface wettability when used as an electrode.