Nitrogen-Enriched
Hierarchically Porous Carbons Prepared
from Polybenzoxazine for High-Performance Supercapacitors
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Abstract
Nitrogen-enriched hierarchically
porous carbons (HPCs) were synthesized
from a novel nitrile-functionalized benzoxazine based on benzoxazine
chemistry using a soft-templating method and a potassium hydroxide
(KOH) chemical activation method and used as electrode materials for
supercapacitors. The textural and chemical properties could be easily
tuned by adding a soft template and changing the activation temperature.
The introduction of the soft-templating agent (surfactant F127) resulted
in the formation of mesopores, which facilitated fast ionic diffusion
and reduced the internal resistance. The micropores of HPCs were extensively
developed by KOH activation to provide large electrochemical double-layer
capacitance. As the activation temperature increased from 600 to 800
°C, the specific surface area of nitrogen-enriched carbons increased
dramatically, micropores were enlarged, and more meso/macropores were
developed, but the nitrogen and oxygen content decreased, which affected
the electrochemical performance. The sample HPC-800 activated at 800
°C
possesses a high specific surface area (1555.4 m<sup>2</sup> g<sup>–1</sup>), high oxygen (10.61 wt %) and nitrogen (3.64 wt
%) contents, a hierarchical pore structure, a high graphitization
degree, and good electrical conductivity. It shows great pseudocapacitance
and the largest specific capacitance of 641.6 F g<sup>–1</sup> at a current density of 1 A g<sup>–1</sup> in a 6 mol L<sup>–1</sup> KOH aqueous electrolyte when measured in a three-electrode
system. Furthermore, the HPC-800 electrode exhibits excellent rate
capability (443.0 F g<sup>–1</sup> remained at 40 A g<sup>–1</sup>) and good cycling stability (94.3% capacitance retention over 5000
cycles)