Controllable synthesis of N-rich defective carbon materials for aqueous supercapacitors: Towards a trade-off between gravimetric and volumetric capacitance

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The conversion of biomass into porous carbon with high specific surface area (SSA) could be applied in the field of supercapacitors, which realised the resourceful use of biomass. However, the increase in SSA provided carbon materials with lower volumetric capacitance, thereby limiting the development of carbon-based supercapacitors (SCs). To trade off gravimetric and volumetric capacitance, the active nitrogen doping strategy was an effective route. Herein, nitrogen-rich micro-mesoporous composite carbon materials were synthesised from forestry waste (bamboo) as raw material, with guanidine carbonate as N-rich agent and KHCO3 as green activator. The N-rich agent exhibited multiple roles in the co-pyrolysis process, which were pore creation and heteroatom doping. In this paper, the correlation between the type of N-rich agent, the addition amount and the pre‑carbonization temperature and the electrochemical properties of carbon materials were investigated. Due to the multifunctionality of guanidine carbonate, the carbon material exhibited excellent SSA (1469.14 cm2/g), outstanding microporous structure, and abundant reactive N sites, which facilitated the efficient transport of electrolyte ions. Among them, the best carbon material (BC/CN-400-1) showed a high gravimetric capacitance of 376.25 F/g, demonstrating a volumetric capacitance of 355.54 F/cm3 at the same time. In addition, the aqueous symmetrical supercapacitor (BCN//BCN) displayed remarkable cycling stability (94.35 %). The BCN//BCN achieved an energy density of 15.64 Wh/kg at a power density of 75 W/kg. In summary, this study proposed a controllable N-atom doping technique, which offered a feasible route for the synthesis of N-doped hierarchical nanomaterials. Meanwhile, using forestry wastes as raw materials for the preparation of high-performance carbon-based supercapacitors facilitated resources utilization of biomass and sustainable development, providing a reference for the fabrication of N-rich biomass-derived carbon materials.