Solid-Liquid Redox Reaction-Assisted Construction of Hierarchical Porous Carbon Derived from Coal for Zinc Ion Hybrid Capacitors

Abstract

Coal-based porous carbon shows tremendous potentiality for application in 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 materials derived from coal were prepared by solid (coal powder) liquid (KMnO4 solution) redox reaction with the followed 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 can not 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 frameworks, high specific surface area and abundant oxygen functional groups, the optimized hierarchical porous carbon delivers a specific capacitance of 342 F g-1 at 0.5 A g-1 and superior electrochemical stabilization (101.6% capacitance retention after 10,000 cycles). Furthermore, the assembled Zn//ZnSO4//CPC-800 zinc ion hybrid shows a capacity of 149.4 mAh g-1 at 0.1 A g-1, 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 93.91% after 10,000 cycles testing.

Keywords: Coal, Hierarchical porous carbon, Supercapacitor, Zinc ion hybrid capacitors