Tailoring in-situ N, O, P, S-doped soybean-derived porous carbon with ultrahigh capacitance in both acidic and alkaline media

In order to improve electrochemical capacitance properties of biomass-derived porous carbon materials, this work develops a low temperature pre-carbonization, hydrothermal stabilization and KOH activation method to derive N, O, P, S co-doped porous carbon materials from protein-rich soybeans and effectively enhances specific capacitances in both acidic and alkaline aqueous electrolytes. Specially, the derived porous carbon demonstrates an ultra-high specific capacitance of 685.1 F g−1 at 0.5 A g−1 in 2 M KOH and 439.5 F g−1 at 1 A g−1 in 1 M H2SO4, respectively. Moreover, a superior cycling stability is achieved with a capacitance retention of 80% after 13,000 cycles at a current density of 20 A g−1 in 2 M KOH. An asymmetric supercapacitor consisting of soybean-derived carbon and NiCo-sulfide delivers a high energy density of 41.8 Wh kg−1 at a power density of 750 W kg−1. The findings above indicate hydrothermal process can effectively stabilize heteroatoms (N and P), improve graphitization and thereby enhance capacitive properties of biomass-derived carbon materials.