High-Surface-Area Porous Carbon Flakes Derived from Boat-Fruited Sterculia Seeds for High-Energy-Density Aqueous Symmetric Supercapacitors

A new kind of N-doped porous carbon flake with a super high surface area of 3243.92 m² g^–1 was derived from a common biomass waste (boat-fruited sterculia seeds) by a facile low-cost pyrolysis and activation method. This particular biomass has a natural netlike structure consisting of interconnected polysaccharide chains rich in hydrophilic groups. We used the spongelike biomass gel as carbon precursor directly without a drying process and added some NaCl as the structure template, and were surprised to find that it is crucial for high surface area and the formation of two-dimensional materials. It is noted that the obtained materials possess a high specific capacitance (411.5 F g^–1 at 1 A g^–1) and excellent cycling stability in aqueous electrolytes. Moreover, the assembled symmetric cell with has a wide voltage range of 2.0 V in 1 M Na₂SO₄ aqueous electrolyte, delivering a high energy density of 22.4 W h kg^–1 at 500 W kg^–1. Therefore, the outstanding electrochemical performance of the developed materials makes them promising candidates for high-performance supercapacitors