Ultrahigh-Surface-Area and N,O Co-Doping Porous Carbon Derived from Biomass Waste for High-Performance Symmetric Supercapacitors

Sustainable conversion of biomass waste into porous carbon with unique electronic, morphological, and chemical structures has attracted much attention in energy storage applications. Abutilon theophrasti is an annual subshrub herb of the mallow family, which grows along many country roads. Herein, N and O co-doping abutilon theophrasti stem-derived activated carbon (ATSAC) was synthesized by high-temperature carbonization and subsequent two-step activation processes, whose morphology, structure, and electrochemical performance were modulated by the KOH activation with different concentration. The optimized ATSAC-6 anode exhibits ultrahigh surface area (3783.1 m2 g–1) and micropore ratio (94%), which delivers superior specific capacitance (365.1 F g–1 at a current density of 1 A g–1), outstanding rate performance (64% retention at a high current density of 15 A g–1), and excellent cycling stability (97% retention after 6000 cycles). Furthermore, symmetric supercapacitors fabricated by two ATSAC-6 electrodes with different electrolytes (6 M KOH and [BMIM]BF4/AN) were investigated. The KOH device shows a high specific capacitance of 74.81 F g–1 at a current density of 0.25 A g–1, while the [BMIM]BF4/AN device achieves a remarkable energy density of 51.83 Wh kg–1 at a power density of 375 W kg–1.