Heteroatom self-doped graphitic carbon materials from Sargassum thunbergii with improved supercapacitance performance

It is well-known that high specific surface area and improved pore structure is significantly desired for the application of supercapacitor based on biomass-based activated carbon. Herein, Sargassum thunbergii was selected as carbon precursor. Then, a simple and environmentally friendly method was designed to synthesize heteroatom self-doped porous carbon materials via synchronous activation and graphitization by using K₂FeO₄. Our results demonstrated that activation temperature plays an important role in porous structure, morphology, and degree of graphitization, thus affecting the performance of supercapacitance. Sargassum thunbergii-based graphitized porous carbons STGPC-2 sample (calcination temperature at 700 °C) has a large specific surface area (1641.98 m² g⁻¹), pore volume (0.91 cm³ g⁻¹), high microporosity (V_micro = 0.62 cm³ g⁻¹, more than 68%), and a certain degree of graphitization. In three-electrode system, The STGPC-2 electrode exhibited a high specific capacitance of 325.5 F g⁻¹ at 0.5 A g⁻¹ and displays high rate capability (248 F g⁻¹ at 10 A g⁻¹ in 6 M KOH electrolyte). The symmetric STGPC-2 supercapacitor exhibits energy density as high as 21.3 Wh kg⁻¹ (at a power density of 450 W kg⁻¹) and excellent long-term cycling stability (97% capacitance retention after 3000 cycles) in 1 M Na₂SO₄ electrolyte.