Solid-liquid redox reaction-assisted construction of hierarchical porous carbon derived from coal for zinc ion hybrid capacitors

Coal-based porous carbon shows tremendous potential for application in the energy storage field. However, traditional chemical activation ways cannot accurately adjust the formation of pores and the structure of the obtained carbon materials due to inhomogeneous mixing of precursor and activator. Herein, oxygen-enriched hierarchical porous carbon derived from coal was prepared by solid (coal powder) liquid (KMnO4 solution) redox reaction with the following high temperature pyrolysis. Under microwave heating conditions, the oxidation-reduction reaction between coal powder and potassium permanganate solution produces manganese dioxide and potassium salt, which cannot only be used as templates but also as activators, so as to achieve uniform mixing of activator and carbon precursor. Benefiting from the 3D interconnected hierarchical porous framework, high specific surface area and numerous oxygen functional groups, the optimized hierarchical porous carbon exhibits a superior specific capacitance of 342 F g- 1 at 0.5 A g-1 and good electrochemical stabilization (101.6 % capacitance retention after 10,000 cycles). Furthermore, the assembled Zn//ZnSO4//CPC-800 zinc ion hybrid capacitor shows a capacity of 149.4 mAh/g at 0.1 A/g, and an energy density of 119.5 Wh kg- 1 at a power density of 99.9 W kg- 1. Meanwhile, the device displays a capacity retention of 93.9 % after 10,000 cycles testing.