Biomass-derived 3D hierarchical porous carbon by two-step activation method for supercapacitor

3D hierarchical porous carbon is widely accepted as an ideal electrode material for supercapacitor. But template method is a complicated and expensive way to produce material with such a special structure. In this article, a two-step activation method is proposed. Two activating agents: H3PO4 and KOH, are involved in preparation process. By applying this method, the carbonization time can be reduced, the carbonization temperature can be decreased, and the amount of activating agent can be cut down. The specific capacitance of optimal product can reach 366 F g(-1) @ 1 A g(-1), and even 326 F g(-1) @ 10 A g(-1) in a two-electrode system using 6 M KOH as electrolyte. The excellent structure endows the product with excellent rate performance (the specific capacitance decreases 18% when the current density increases for 100 times) and cycle performance (95% retention after 5000 cycles). Rational process is benefit for reducing resistance and improving double layer characteristic. The maximum power density can reach 191.90 kW kg(-1), and energy density can reach 49.54 W h kg(-1). This paper also explores the mechanism of two-step activation and provided a new idea to build 3D hierarchical porous structure by a simple and environmentally friendly way.