Template Synthesis of Nitrogen Self-Doped Hierarchical Porous Carbon with Supermicropores and Mesopores for Electrical Double-Layer Capacitors

Nitrogen self-doped hierarchical porous carbon for electrical double-layer capacitors was synthesized by direct carbonization of bean dregs-based tar with potassium acetate as the template agent. The pore structure parameters and chemical element composition were adjusted by varying the heating rate during the carbonization process. The electrochemical properties of the electrode materials were evaluated in a three electrode system with 6 M KOH as the electrolyte. The resultant bean dregs-based porous carbons (BDPCs) exhibited high specific surface area, unique hierarchical architecture (consisting of supermicro- and mesopores), and medium nitrogen content (0.66 to 0.78%). The BDPC-10 sample had the highest specific surface area of 1610 m2/g and reasonable pore size distribution, and consequently exhibited an excellent specific capacitance of 363.7 F/g at the current density of 1 A/g. Nevertheless, the capacitance was reduced to 280.5 F/g at 3 A/g, giving a capacitance retention ratio of 77.1%. This study suggests a facile and environmentally friendly template synthesis process for supercapacitor electrode materials preparation, but it also faces challenges to increase the rate capability.