Polysaccharide of agar based ultra-high specific surface area porous carbon for superior supercapacitor

Although extensive research has been focused on porous carbon in supercapacitor, the simple and non-template preparation of high specific surface area (SSA) carbon material with hierarchical porous structure is still a lingering issue. Herein, the cross-linked hierarchical porous carbon with ultra-high SSA of 3184 m² g^-1 is prepared via the sol-gel follows the freeze drying and followed activation process. Agar is used as carbon precursor, L-arginine is nitrogen sources, and the formed gel is activated by KHCO₃. The obtained N-doped porous carbon shows a superior specific capacitance of 443.0 F g^-1 at 0.5 A g^-1 in 6 M KOH, and exhibits an excellent rate capability (255 F g^-1 at 50 A g^-1). Furthermore, due to the combined synergistic effect of high SSA, hierarchical porous structure and N doping, the symmetric supercapacitor that assembled with the prepared gel electrolyte of Agar-Na₂SO₄ achieves a superior energy density of 35.5 Wh kg^-1 and a long cycle life with the capacitance retention of 99.7% after 20,000 cycles. This work provides an efficient and simple method to prepare ultra-high surface area, hierarchical porous structure carbon materials for high performance supercapacitor.