Mechanism of biomass activation and ammonia modification for nitrogen-doped porous carbon materials

The effect of chemical activation and NH₃ modification on activated carbons (ACs) was explored via two contrasting bamboo pyrolysis strategies involving either two steps (activation followed by nitrogen doping in NH₃ atmosphere) or one step (activation in NH₃ atmosphere) with several chemical activating reagents (KOH, K₂CO₃, and KOH + K₂CO₃). The ACs produced by the two-step method showed relatively smaller specific surface areas (∼90% micropores) and lower nitrogen contents. From the one-step method, the ACs had larger pore diameters with about 90% small mesopores (2-3.5 nm). Due to a promotion effect with the KOH + K₂CO₃ combination, the AC attained the greatest surface area (2417 m² g^-1) and highest nitrogen content (3.89 wt%), endowing the highest capacitance (175 F g^-1). The balance between surface area and nitrogen content recommends KOH + K₂CO₃ activation via the one-step method as the best choice for achieving both greener production process and better pore structure.