Nitrogen-Doped Porous Carbon Nanospheres from Natural Sepia Ink: Easy Preparation and Extraordinary Capacitive Performance

Heteroatom-doped nanostructured porous carbons have attracted intensive attention for electrical-double layer capacitors (EDLCs) because of their large surface area and surface functionalization. Here we use biowaste sepia ink as a sustainable source to synthesize nitrogen-doped highly porous carbon nanospheres by a simple molten salt-based activation strategy. The introduction of molten salt is not only beneficial for repairing the carbon conjugate network, but can also further improve the activation effect of porogen. The as-obtained carbon nanospheres (MA-NCS) displayed a large surface area of 1760 m² g⁻¹, optimized pore architecture, and high nitrogen content (8.6 wt %). With this design, the MA-NCS as EDLCs electrode exhibited a remarkable specific capacitance of 320 F g⁻¹ at the current density of 0.5 A g⁻¹ and high rate capability in 6 m KOH electrolyte. Furthermore, the assembled EDLCs demonstrated a high specific capacitance of 130 F g⁻¹ at 0.5 A g⁻¹ in an organic electrolyte (1 m TEABF₄/AN), obtaining a maximum energy density of 28.2 Wh kg⁻¹ at a power density of 625 W kg⁻¹. This novel biowaste precursor-synthesis route presents great potential for facile large-scale production of high-performance porous carbons for green and long-term energy storage.