Imidazole linker-induced covalent triazine framework-ZIF hybrids for confined hollow carbon super-heterostructures toward a long-life supercapacitor

Abstract

Carbon super-heterostructures with high nitrogen contents from the covalent hybrid precursors of covalent triazine frameworks (CTFs) and zeolitic imidazolic frameworks (ZIFs) are scarcely explored because of CTF's ordered structure and toxic superacid that dissolves or destabilizes the metal nodes. To solve this problem, herein, we report a straightforward two-step pathway for the covalent hybridization of disordered CTF (d？CTF)？ZIF composites via preincorporation of an imidazole (IM) linker into ordered CTFs, followed by the imidazole-site-specific covalent growth of ZIFs. Direct carbonization of these synthesized d？CTF？IM？ZIF hybrids results in unique hollow carbon super-heterostructures with ultrahigh nitrogen content (>18.6%), high specific surface area (1663？m2？g？1), and beneficial trace metal (Co/Zn NPs) contents for promoting the redox pseudocapacitance. As proof of concept, the obtained carbon super-heterostructure (Co？Zn？NCSNH？800) is used as a positive electrode in an asymmetric supercapacitor, demonstrating a remarkable energy density of 61？Wh？kg？1 and extraordinary cyclic stability of 97% retention after 30,000 cycles at the cell level. Our presynthetic modifications of CTF and their covalent hybridization with ZIF crystals pave the way toward new design strategies for synthesizing functional porous carbon materials for promising energy applications.