Design and Synthesis of N‑Doped Carbon Skeleton Assembled by Carbon Nanotubes and Graphene as a High-Performance Electrode Material for Supercapacitors

Current, there is an urgent demand for electrode materials with superior electrochemical performances for the development of supercapacitors. A nitrogen-doped carbon skeleton (NCS) assembled by carbon nanotubes and graphene layers is designed and synthesized utilizing a layer-shaped humate-based zeolitic imidazolate framework (ZIF) (HA-CoFe-ZIF) as a template in this work. The synthesized NCS is mainly composed of graphitized carbon with a few hydroxyl groups on its surface, synchronously doped by 9.5 at % nitrogen in the state of pyridinic N and pyrrolic N. The rich mesoporous structure entitles it to a high Brunauer–Emmett–Teller (BET) specific surface area of 427 m² g^–1 and suitable BET average pore diameter of 3.14 nm. The NCS has a high capacity of 324 F g^–1 at 1 A g^–1, good rate capability (capacitance retention of 71% from 5 to 100 A g^–1), and excellent cycling stability (capacitance retention of 96 and 87% after 5000 and 10 000 cycles, respectively). The fabricated NCS//AC asymmetric supercapacitor also exhibits a high capacity of 93 F g^–1 at 1 A g^–1, large energy density of 10.3 Wh kg^–1 at 331 W kg^–1, and good cycling performance (capacitance retention of 88% after 5000 cycles). Our elaborately designed NCS materials exhibit multiple structural advantages including rich mesoporous structure, various graphitic carbon, and high-dosage nitrogen doping, resulting in high capacitance performances. This humate-based metal–organic framework (MOF)-derived strategy provides a good idea for the synthesis of high-performance carbon skeleton materials applied to energy storage.