Controlled porous structures of soybean straw-based carbon via green liquefication and N/S in-situ doping facilitate supercapacitor performance at large current density

Abstract

It is important to maintain supercapacitor performance at high current density by regulating the micropore/mesopore balance and surface functional groups of biomass carbons. Here, the biomass porous carbon was successfully prepared from agroforestry waste of soybean straw by green activation was introduced on the basis of in-situ doping. Effective liquefaction and doping environment for non-metal N/S doping was achieved via green liquefaction using polyethylene glycol 400 (PEG400). The micropore/mesopore ratio, hydrophilic properties, and active sites of the carbon materials were regulated and enhanced by combing N in-situ doping and green activation with potassium citrate. The obtained soybean straw-based carbon with N doping (SSL-N1) showed higher surface area (1698.9 m2 g−1) and mesopore ratio (78.15%). The mesopore/micropore ratio shortened the ion adsorption distance and increased the ion surface accessibility. The specific capacitance of materials could reach 276.8 F g−1 at a current density of 0.5 A g−1. As the current density expand by 20 times, the specific capacitance could be preserved at 216 F g−1, the capacity retention rate is 78.0%. Notably, the SSL-N1//SSL-N1 symmetrical supercapacitor could generated an energy density of 10.14 W h kg−1. The specific porous and surface structures of carbon composite materials could effectively alleviate the capacity attenuation in supercapacitors at high current density.