Self-activation of nitrogen and sulfur dual-doping hierarchical porous carbons for asymmetric supercapacitors with high energy densities

Porous carbon obtained by the conventional two-step method (chemical activation after carbonization) is confronted with the problems of complex preparation process, excess of strong corrosive chemical agents and poor ion-transport kinetics. Herein, we report a convenient way for the preparation of porous carbons by a self-activation process using potassium gluconate as the precursor, and then followed by effective nitrogen/sulfur dual-doping. The obtained carbon materials have hierarchical porous framework with moderate specific surface area, numerous mesopores and high content of heteroatoms doping. Benefitting from their synergistic effect, the nitrogen and sulfur dual-doped hierarchical porous carbons electrode displays a high specific capacitance of 320 F g−1 at 0.5 A g−1, superior rate characteristic and excellent electrochemical stabilization. More interestingly, an asymmetric supercapacitor using the nitrogen/sulfur dual-doped hierarchical porous carbons as negative electrode and the hierarchical porous carbons/manganese dioxide composite as positive electrode exhibits a high energy density of 42.5 Wh kg−1 and good electrochemical stabilization (90.3% capacitance retention after 5000 cycles). Contrast with the traditional preparation way for porous carbons, this method can be easily executed, avoiding complex process, hard/soft template and excess activation, and thus highlights a novel, convenient and efficient way to synthesize high performance porous carbons for supercapacitor.