Hierarchical structure N, O co-doped porous carbon/carbon nanotubes composite derived from coal for supercapacitors and CO2 capture
The energy and environmental crisis forces us to search for new green energy and develop energy storage and environmental restoration technology. Fabrication of carbon functional materials derived from coal has attracted increasing attention among the energy storage and gas adsorption fields. In this work, N, O co-doped porous carbon/carbon nanotubes composite was prepared by functionalizing coal based porous carbon with carbon nanotubes (CNTs) and ionic liquid annealing. The resulting materials not only inherited the morphology of CNTs and porous carbon, but also developed the three dimension (3D) hierarchical porous structure with numerous heteroatom groups. N, O co-doped porous carbon/CNTs composite (N, O-PC-CNTs) showed a phrase surface area of 2164 m2 g-1, and high level N/O dopants (8.0 and 3 at%). Benefiting from such merits, the N, O-PC-CNTs exhibited a rather high specific capacitance of 287 F g-1 at current densities 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, N, O-PC-CNTs 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 Wh kg-1 at a power density of 12.5 kW kg−1 in 6 mol L-1 KOH electrolyte. As CO2 adsorbents, 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 cycle stability with 94% retention of the initial CO2 adsorption capacity at 298 K over 10 cycles. This report introduces a strategy to design coal based porous carbon for efficient supercapacitor electrodes and CO2 adsorbents.