Coal tar pitch-based hierarchical porous carbons prepared in molten salt for supercapacitors

As electrode materials for supercapacitors (SCs), hierarchical porous carbons (HPCs) have attracted tremendous attention due to their high specific surface area (SSA) and hierarchical pore structure. However, the complex template preparation process for HCPs usually brings high cost. Here, by combining the pre-carbonizing process of coal tar pitch (CTP) in eutectic salt (ZnCl2–NaCl, denoted as MZS, Sm260 °C) with the KOH activating process, HPCs with high capacitive performance have been prepared. The pre-carbonizing process is carried out under atmosphere to obtain the primitive carbon (PC), during which the MZS will not only provide a liquid environment for catalytic cross-linking of CTP but also act as the porogen agent. The effects of temperatures, heating rates, the mass ratio of KOH to PC (mKOH/mC) and the activating temperatures on the structure and capacitive properties of HPCs are explored. The results show that the HPCs prepared by activating the optimal PC (prepared at 560 °C in the MZS with a heating rate of 2.5 °C min−1) at temperature of 800 °C (heating rate of 10.0 °C min−1 and mKOH/mC ratio of 5) exhibit high specific surface area (2984 m2 g−1), large total pore volume (2.2 cm3 g−1) and wide pore size distribution. Based on the two-electrode test system, the optimal HCP shows a specific capacitance of 320 F g−1, the symmetric cells exhibit an energy density of 10.6 Wh kg−1 at power density of 50.1 W kg−1. Furthermore, the cell displays a good cyclic stability (the capacitance retention of 94.0% after 10,000 cycles). This strategy may be developed as a promising method for preparing high-performance HPC from CTP.