Abstract
The surface properties and the hierarchical pore structure of carbon materials are important for their actual application in supercapacitors. It is important to pursue an integrated approach that is both easy and cost-effective but also challenging. Herein, coal-based hierarchical porous carbon with nitrogen doping was prepared by a simple dual template strategy using coal as the carbon precursor. The hierarchical pores were controlled by incorporating different target templates. Thanks to high conductivity, large electrochemically active surface area (483 m(2) g(-1)), hierarchical porousness with appropriate micro-/mesoporous channels, and high surface nitrogen content (5.34%), the resulting porous carbon exhibits a high specific capacitance in a three-electrode system using KOH electrolytes, reaching 302 F g(-1) at 1 A g(-1) and 230 F g(-1) at 50 A g(-1) with a retention rate of 76%. At 250 W kg(-1), the symmetrical supercapacitor assembled at 6 M KOH shows a high energy density of 8.3 Wh kg(-1,) and the stability of the cycling is smooth. The energy density of the symmetric supercapacitor assembled under ionic liquids was further increased to 48.3 Wh kg(-1) with a power output of 750 W kg(-1) when the operating voltage was increased to 3 V. This work expands the application of coal-based carbon materials in capacitive energy storage.