Design and structure optimization of coal-based hierarchical porous carbon by molten salt method for high-performance supercapacitors

Porous carbon is considered as one of the most ideal materials for supercapacitors due to its low cost, large specific area and high electrical conductivity. Here, we report a facile molten salt method to design and optimize the structure of porous carbon using coal as the precursor, and NaCl/ZnCl2 as the pore-forming agent and a strong polar solvent at high temperature. Through adjusting NaCl content in NaCl/ZnCl2 and the calcination temperature, the effects of preparation conditions on the morphologies and electrochemical properties of porous carbon are systematically explored. As a result, C-0.05N-700 exhibits a large specific surface area of 2548 m2 g−1, high yield of 42.9 wt% and specific capacitance of 344.3 F g−1 at 0.25 A g−1. The assembled symmetric supercapacitor displays a high energy density of 8.1 Wh kg−1 in 6 M KOH and 32 Wh kg−1 in 1 M Na2SO4, respectively. This work provides a referential strategy for the controllable preparation of hierarchical porous carbon with large specific surface area, and reveals the influence law of the preparation conditions on the properties of coal-based porous carbon nanomaterials, and the preparation route is cost-effective. Meanwhile, it can offer a new thought for the effective utilization of coal.