Necklace-like Nitrogen-Doped Tubular Carbon 3D Frameworks for Electrochemical Energy Storage

The design and synthesis of a necklace-like nitrogen-doped tubular carbon (NTC) are presented by growing microporous polyhedral ZIF-8 particles and a uniform layer of ZIF-8 on sacrificial ZnO tetrapods (ZTPs). Oxygen vacancies together with defect regions on the surface of the ZTPs result in the formation of ZIF-8 polyhedra in conjunction with a very thin shell. This necklace-like NTC structure has a high N content, very large surface area, ultrahigh microporosity, and quite high electrical conductivity. NTC-based symmetrical supercapacitor and zinc-ion capacitor (ZIC) devices are fabricated and their electrochemical performance is measured. The NTC supercapacitor shows an ultrahigh rate capability (up to 2000 mV s(-1)) and promising cycle life, retaining 91.5% of its initial performance after 50 000 galvanostatic charge-discharge cycles. An aqueous ZIC, constructed using the NTC, has a specific capacitance of 341.2 F g(-1) at a current density of 0.1 A g(-1) and an energy density of 189.6 Wh kg(-1) with a 2.0-V voltage window, respectively. The outstanding performance is attributed to the NTC high N-doping content, a continuous "polyhedral 3D hollow" architecture and the highly porous microtubular arms exhibiting very high surface area.