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

Abstract 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.