Design and Preparation of Lotus Root Knot Hierarchical Porous Carbon by Highly Efficient Chemistry Activation for Electric Double Layer Capacitors

Abstract In this work, utilizing lotus root knot as raw material, nitrogen and oxygen co‐doped hierarchical porous carbon with appropriate heteroatom doping, multi‐connected 3D pore structure and suitable pore size distribution were produced by carbonization and chemical activation step. The maximum specific surface area the biochar material reached was 3659 m 2 g −1 . These physical properties exhibit ultrahigh specific capacitance of up to 454.3 F g −1 in a supercapacitor of the three‐electrode system under the current density of 1 A g −1 and a capacitance retention rate of 81.5 % within the range of 1∼10 A g −1 . Furthermore, the specific capacitance is maintained at 91.5 % of the initial value in a two‐electrode system after 10,000 cycles. In a two‐electrode system with tetraethylammonium tetrafluoroborate (TEABF 4 )/acetonitrile (ACN) solution as the electrolyte. The voltage window attained was 3 V with high energy density of 51.4 Wh kg −1 under the power density of 750 W kg −1 . These results show that the assembled supercapacitors provide excellent energy and power density at the same time.