Rational Design of Highly Conductive Nitrogen-Doped Hollow Carbon Microtubes Derived from Willow Catkin for Supercapacitor Applications

The rational design of carbon materials with high electrical conductivity, low tortuosity, large specific surface area, and sufficient heteroatom doping for high-performance supercapacitor application is highly desired but remains as a major challenge. Herein, by templating the natural microtubular and thin-walled structure of willow catkin, a highly conductive nitrogen-doped hollow carbon microtube material was synthesized through an integrated procedure including polymerization, pyrolysis, and activation. Robust N-doped crosslinked graphene was grafted on the internal and external walls of carbonized hollow catkin to form a sandwich structure of the derived carbon. The obtained carbon microtubes exhibit a large specific surface area (2608 m(2) g(-1)), short and unimpeded ion-diffusion paths, high-level heteroatom doping (O: 12.5 at %, N: 3.4 at %), and excellent electrical conductivity (128 S m(-1)). Benefitting from its desirable textural properties and favorable elemental composition, the derived electrode, without the addition of conductive additives, delivers impressive capacitance values of 408 F g(-1) (0.5 A g(-1)) in 6 M KOH electrolyte and 420.8 F g(-1) (1 A g(-1)) in 1 M H2SO4, as well as an outstanding rate capability and excellent cycling stability. In addition, the assembled symmetric supercapacitor displays an ultrahigh energy density of 27.3 Wh kg(-1) at 182 W kg(-1) in 1 M Na2SO4 electrolyte. These advanced characteristics ensure the carbon microtubes hold great promise for energy storage/conversion applications.