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.

Porous carbon is the commonly used electrode material for supercapacitor, and its electrochemical performance is affected by the factors such as specific surface area (SSA), pore structure, heteroatomic content, and resistivity. In this paper, bean dregs-based porous carbon (BDPC) was synthesized with bean dregs as the carbon and nitrogen sources and magnesium citrate as template.The electrochemical properties of BDPC were investigated in 6 M KOH electrolyte. It is found that BDPC presents a well-developed mesoporous structure and BDPC-20 owns the highest SSA of 1637 m 2 /g. The nitrogen content decreases significantly with the heating rate, debilitating the hydrophilicity of BDPC. High heating rate can increase the relative content of graphitic-N and the degree of graphitization and consequently reduces the resistivity of BDPC enormously. The BDPC-20 shows the lowest resistivity of 97.2 μΩÁm. The cyclic voltammetry curves of BDPC electrodes exhibit the quasi-rectangular shape, demonstrating a typical electrical double-layer capacitor nature of energy storage. According to the galvanostatic charge-discharge measurement, BDPC-10 possesses the largest specific capacitance of 184.0 F/g.

Hierarchical porous carbons (HPCs) with tailored pore structure were fabricated via direct carbonization of a precursor consisting of agar and acetates in an inert atmosphere. The agar served as the carbon source and curing agent, while potassium acetate and calcium acetate were used to create micropores and mesopores, respectively. The morphology and structural features of the HPCs were characterized, and the electrochemical properties were estimated in a three‐electrode system with 6 M KOH as the electrolyte. The resulting HPCs possess a developed pore structure and concentrated pore size distribution (focused at 0.4 and 4 nm), and exhibit typical electrical double‐layer capacitive behaviour. Specially, the HCP‐2 owns a large specific surface area of 1441.65 m2/g and excellent electrochemical properties, including a favourable specific capacitance (235 F/g at 1 A/g), good rate capability (capacitance retention rate of 88.1% at 20 A/g), and impressive long‐term cycling stability (90.6% retention of initial capacitance after 3000 cycles).