Template-activated bifunctional soluble salt ZnCl2 assisted synthesis of coal-based hierarchical porous carbon for high-performance supercapacitors

A series of coal-based hierarchical porous carbons with adjustable pores were successfully prepared with the assistance of the soluble salt Zinc chloride (ZnCl 2 ). During the carbonization process , ZnCl 2 , with a low melting point (238 °C), “in situ occupied” and “occupied” within the coal solids to generate interconnected pores, which acted as a template. Simultaneously, the activation of ZnCl 2 reduced the oxygen content of products and further improves their electrical conductivity . Optimization of the mass of the salt and the carbonization temperature resulted in targeted product with a suitable specific surface area (1581 m 2  g −1 ) and unique pores (V meso /V total  = 45%), which exhibited a high specific capacitance (470.7 F g −1  at 0.5 A g −1 ) in 6 M KOH electrolyte. The symmetrical supercapacitor of targeted product has favorable rate performance (256.7 F g −1  at 0.5 A g −1 , 84.8% capacity retention at 30 A g −1 ) and excellent cycling performance (after 10000 cycles, the specific capacitance increases to 115% of the initial capacity at 10 A g −1 ). In the EMIMBF 4 electrolyte system, the energy density is 95.31 Wh kg −1  at 213.13 W kg −1 . Therefore, this work provides an effective method to improve the green and efficient use of coal.