Heteroatoms self-doped porous carbon from cottonseed meal using K2CO3 as activator and DES electrolyte for supercapacitor with high energy density

Biomass had been extensively explored and applied in many fields due to their abundance, attractive structure, low cost, renewability, and environmental friendliness. Cottonseed meal (CM), one of the by-products of cotton, consisted of much crude protein, fiber, and inorganic ions, was a potential carbon precursor. In this work, CM was used to prepare N, S, and O self-doped carbon materials by two steps (hydrothermal pre-carbonization and K2CO3 carbonization–activation) processes. The optimized material displayed high capacitive performance, which benefited from the large surface area (2361 m2/g), hierarchical porous structure and rich multi-heteroatoms doping of the prepared porous carbon. What's more, we prepared a new-type K2CO3-based deep eutectic solvent (DES) electrolyte. The assembled symmetric device using DES electrolyte displayed a superior energy density (34.4 Wh/kg) at room temperature. Furthermore, the energy density could reach 36.5 Wh/kg when the temperature rose to 50 °C. Even under extreme conditions, the device delivered a not particularly bad energy density (11.8 Wh/kg at −25 °C and 8.6 Wh/kg at 105 °C). This study provided an efficient and simple method to prepare CM-based heteroatoms self-doped porous carbon materials and uncovered a new possibility for the exploitation of carbon-based supercapacitors with high energy density.