Hierarchical structure N, O-co-doped porous carbon/carbon nanotube composite derived from coal for supercapacitors...

The energy and environmental crises have forced us to search for a new green energy source and develop energy storage and environmental restoration technologies. Fabrication of carbon functional materials derived from coal has attracted increasing attention in the energy storage and gas adsorption fields. In this study, an N, O-co-doped porous carbon/carbon nanotube composite was prepared by functionalizing coal-based porous carbon with carbon nanotubes (CNTs) and ionic liquid via annealing. The resulting material not only inherited the morphology of CNTs and porous carbon, but also developed a three dimensional (3D) hierarchical porous structure with numerous heteroatom groups. The N, O co-doped porous carbon/CNT composite (N, O-PC-CNTs) showed a surface area of 2164 m² g^-1, and a high level of N/O dopants (8.0 and 3.0 at%, respectively). Benefiting from such merits, N, O-PC-CNTs exhibited a rather high specific capacitance of 287 F g^-1 at a current density of 0.2 A g^-1 and a high rate capability (70% and 64% capacitance retention at 10 and 50 A g^-1, respectively) in a three electrode system. Furthermore, an N, O-PC-CNT symmetrical supercapacitor showed a high cycling stability with 95% capacitance retention after 20 000 cycles at 20 A g^-1 and an energy density of 4.5 W h kg^-1 at a power density of 12.5 kW kg^-1 in 6 mol L^-1 KOH electrolyte. As a CO₂ adsorbent, N, O-PC-CNTs exhibited a high CO₂ uptake of 5.7 and 3.7 mmol g^-1 at 1 bar at 273 and 298 K, respectively. Moreover, N, O-PC-CNTs showed cycling stability with 94% retention of the initial CO₂ adsorption capacity at 298 K over 10 cycles. This report introduces a strategy to design a coal based porous carbon composite for use in efficient supercapacitor electrodes and CO₂ adsorbents.