Abstract
Hierarchical nanotubes@mesoporous carbon composite materials were controllably synthesized by an innovative method based on plant waste corncob and nitrogen source melamine via thermal treatment. The corncob provides both a carbon source and a small amount of Fe as the catalyst, while melamine offers a nitrogen source. Corncobs were firstly pretreated with concentrated sulfuric acid and then mixed with melamine. After calcination at 800 degrees C for 2 hours, a new composite carbon material with a unique structure with a large amount of thin walled nitrogen-doped carbon nanotubes orderly and vertically growing on the mesoporous carbon frame was obtained. The diameter of nanotubes is similar to 50 nm while their length varies from 0.1-20 mu m, which could be controlled by adjusting the ratio of pretreated corncob to melamine. Meanwhile, the composite material possesses stable interconnected pores and channels with a high surface area of 1100 m(2) g(-1), which significantly accelerated the transfer rates of ions and electrons. The electrochemical test results demonstrated that this composite material exhibits a superior capacitance of 538 F g(-1) in an aqueous electrolyte and 320 F g(-1) in an organic electrolyte at a current density of 1 A g(-1). The specific capacitance of the composite material remained up to 90% of the initial value after 10 000 cycles, showing excellent long-term cycling stability. For lithium sulfur battery application, the composite material as a sulfur host delivered an initial capacity of 1047 mA h g(-1), and exhibited a relatively stable cycling performance, maintained a capacity of 682 mA h g(-1) for 300 charge/discharge cycles at 0.5C. The structure, morphology and growth mechanism of the composite material were also analyzed and discussed in detail.