Enhancing the performance of supercapacitor electrodes from corncob-derived 3D hierarchical porous carbon: Effects of N concentration

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 (CC₃) 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: R_s = 0.20 Ω and R_ct = 0.78 Ω 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.