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 (Vmicro=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.