Ultrahigh surface area hierarchical porous carbon derived from biomass via a new KOH activation strategy for high-performance supercapacitor

The study presents a new two-step KOH activation strategy for the facile preparation of three-dimensionally (3D) O-doped interconnected hierarchical porous carbons with ultrahigh surface area (up to 4048.2 m2/g) derived from cost-effective biomass. The resulting porous carbon electrodes exhibited excellent electrochemical performances, with specific capacitances reaching up to 419 F/g at 0.5 A/g and energy densities up to 30.3 W h/kg at 250 W/kg. Meanwhile, the electrodes showed outstanding cycling stability (up to 91.2%) after 20,000 cycles. Compared to the conventional KOH activation method, the new strategy was found to be more effective in improving the porous structure, increasing the specific surface area, and enhancing O-doping of the obtained porous carbons. As a result, the electrochemical performances of the obtained carbon electrode materials were significantly enhanced. The positive effects of this new strategy were confirmed for four types of biomass, including lotus seedpods, rice husk, reed straw and corn cob. Overall, this work provides a simple and effective way to produce superb porous biomass-derived carbon materials for supercapacitor with high performance.