abstract
-
We report supercapacitors from hierarchical porous carbon nanostructures (HPCNs) by simple pyrolysis of corncob (CC), with urea doping providing performance comparable to the more common metal-doped electrodes. Via a systematic study of N doping, we establish for the first time that the types of nitrogen¿carbon species, which vary with the urea¿carbon ratio, affect electrode performance. The 1:3 ratio (CC
3 ) gave a higher specific capacitance of 335 F g¿1 at 1 mV s¿1 in a three-electrode system, and 287 F g¿1 at 0.2 A g¿1 in a symmetric device. We achieved solution and transfer resistances lower than reported for other materials: Rs = 0.20 ¿ and Rct = 0.78 ¿ respectively. We attribute the better performance of CC3 to its specific N-doping, dominated by graphitic-N plus oxidized nitrogen and C¿OH groups; showing also a larger carbon (002) interplanar distance (d(002) = 0.392) and high specific surface area (1149 m2 g¿1). The assembled prototype delivers a good energy density of 9.96 Wh kg¿1 at 403.22 W kg¿1 and retains ca. 76 % capacity after 10,000 cycles. This work shows that studying doping concentrations is essential to design and produce highly efficient biomass-based electrodes for energy storage applications, using simple synthesis methods and readily available reagents. © 2025 The Authors