Ultrafast-Freezing-Assisted Mild Preparation of Biomass-Derived, Hierarchically Porous, Activated Carbon Aerogels for High-Performance Supercapacitors

Lignin-derived carbon aerogels (CAs) with hierarchically porous morphologies are facially prepared via ultrafast freezing of droplets of lignin/KOH solutions followed by freeze-drying and in situ activation during carbonization. The CAs exhibit a high specific surface area of 1681.6 m² g⁻¹ and abundant mesopores and macropores, which facilitate electrolyte absorption into the carbon framework, ion diffusion, and charge transport. Moreover, the CAs also possess abundant oxygenated groups, which provide additional Faradaic redox reactions. Thus, this mild process, which involves much less KOH, is effective in boosting the electrochemical performance of the CAs as supercapacitor electrodes. The optimized CA exhibits a high specific capacitance of 189 F g⁻¹ at 1 A g⁻¹, a high energy density of 26.25 Wh kg⁻¹ at a power density of 1000 W kg⁻¹, and capacitance retention of 97.4% after 10000 cycles.