Rational Design And Properties Of High-Surface-Area Carbon Nanotube/Microporous Carbon Core-Shell Nanocomposites

All-carbon-based carbon nanotube (CNT)/microporous carbon core-shell nanocomposites, in which the CNT as the core and high surface-area microporous carbon as the shell, have been prepared by in situ resorcinol-formaldehyde resin or resorcinol-melamine-formaldehyde resin coating of CNTs, followed by carbonization and activation. By controlling the porosity and the length of the pore in the shell and the nitrogen doped surface chemistry, the rule of structure and the relation between structures and properties have been investigated. The main conclusions are summarized as follows:The CNT/microporpos carbon core-shell nanocomposites were prepared by in situ polymerization of the RF precursors and CNT, followed by CO2 activation or KOH activation, which exhibit great potentials as the electrode material for supercapacitors. The thickness of the microporous carbon shell can be easily tuned from 20 to 215 nm by changing the carbon precursor/CNT mass ratio under the optimal reaction time. After KOH activation, the nanocomposites with core shell structure have high Brunauer-Emmett-Teller (BET) surface areas (up to 1700 m2/g) and 1D tubular structure within a 3D entangled network. As the thickness of the shell improved, the ratio of the microporous shell and the surface area improved. As a result, the capacitance was as high as 237 F/g. The obtained nanocomposites delivered the high cyclability with 99% maintenance after 20000 cycles, which suffered a little decreased with the thicker shell. The thicker the carbon shell, the longer the diffusion path and the lower the electron conductivity, as a result of higher ESR value.The nitrogen doping nanocomposites with the core-shell nanostructure were prepared by uniform coating RMF on the surface on CNT after introducing M into the system, which were applied as the adsorbent of the Cr(VI) ions and the electrode material for the supercapacitors. As the precursor/CNT mass ration increased, the BET surface areas of the nanocomposites increased to 1267 m2/g. The nitrogen content increased with the increasing content of the melamine, while the BET surface areas could achieve 1714 m2/g at M/R of 1. The adsorption capacity increased with the surface area and the nitrogen content, and reached as high as 517 mg/g at 35℃ and pH=1. For the supercapacitors, the results clearly suggested that the capability depended both on the nitrogen content and the porosity, which could achieve as high as 243 F/g.