Biomass Nanoarchitectonics: Nitrogen-doped Hierarchical Porous Carbons as Electrode Materials for High-Performance Supercapacitors

This paper reports on the fabrication of self-nitrogen-doped nanoporous carbon materials via Zinc chloride (ZnCl2) activation of Macrotyloma uniflorum seeds at different carbonization temperatures (600-900 °C) and impregnation ratios (0.5 to 3), and on their supercapacitance performance in an aqueous electrolyte (1 M H2SO4). The sample carbonized at 800 °C with a 3:1 impregnation ratio (HGC_Z3_800) demonstrated an optimum surface area of 1518 m2 g-1 and a large pore volume of 1.14 cm3 g-1 due to the presence of hierarchical micro- and mesoporous structures along with a 4.4 at% nitrogen doping, suggesting that ZnCl2 facilitated the formation of nanoporous structures and effectively prevented nitrogen loss during carbonization. The optimal sample exhibited outstanding supercapacitance performance, achieving a high specific capacitance of 441 F g-1 at a current density of 1 A g-1 in a three-electrode system. The assembled symmetric cell delivered an energy density of 8.4 Wh kg-1 at a power density of 600 W kg-1 and retained 87.2% capacitance after 10,000 charging/discharging cycles. These results highlight the potential of self-nitrogen-doped nanoporous carbons with a tailored pore structure as a sustainable, high-performance electrode material for next-generation energy storage devices.