Nano-flower-like porous carbon derived from soybean straw for efficient N-S co-doped supercapacitors by coupling in-situ heteroatom doping with green activation method

The interlayer nanoflower porous carbon was prepared in this paper by coupling green and sustainable liquefied with in-situ doping using soybean straw as a biomass precursor. The pore structures of the obtained samples were reasonably controlled with non-toxic potassium citrate. The specific surface area of SSL-N/S-K-800 reaches 1756.74 m2 g−1, and the microporosity is 75.38%. In the three-electrode system test, SSL-N/S-K-700 exhibits a specific capacitance of 220 F g−1 at a current density of 0.5 A g−1. Moreover, in the two-electrode system test, the SSL-N/S-K-700 assembled symmetric supercapacitor exhibits an energy density of 11.24 W h kg−1 at a power density of 400 W kg−1. Notably, excellent cycling stability (capacitance retention > 99.2%) is presented after 10,000 cycles. The superior electrochemical properties are attributed to the ion diffusion channels provided by the macropores and mesopores, and the abundant micropores can provide ion adsorption and desorption sites. Additionally, the synchronizing N S doping effectively enhances the pseudo-capacitance of the material. This work explores a green, efficient and sustainable approach for achieving high value-added utilization of waste biomass and enhancing the energy density of supercapacitors for electrochemical energy storage.