Porous carbon derived from herbal plant waste for supercapacitor electrodes with ultrahigh specific capacitance and excellent energy density

Here in this work, porous carbon is prepared from waste of a traditional Chinese medicine Salvia miltiorrhiza flowers. Structures of the porous carbons are regulated by simply regulating of activation temperatures and dosages of activator. The optimized porous carbon owns a high specific surface area of 1715.3 m2 g−1 and total pore volume of 0.6392 cm3 g−1, together with a unique hierarchical architecture and ultrahigh content of 45.97 at% self-doped O and 0.49 at% of N. When used as electrode materials for supercapacitors, the prepared porous carbon exhibited excellent specific capacitance and energy density as well as fantastic cycle stability. Under a current density of 0.5 A/g, the electrode based on this material showed high specific capacitance of 530 F/g, with fantastic rate performance of 258 F/g at 20 A/g and excellent cycle stability of 91% capacitance retention for 10,000 cycles at 10 A/g in a three-electrode system in 6 M KOH. In assembled supercapacitors, the SF-PC700-3 based electrode worked under potential of 1 V and exhibited 222 F/g of specific capacitance at a current density of 0.5 A/g, and even when the current density was increased up to 30 A/g, the specific capacitance can still as high as 168 F/g, verified the excellent performance of SF-PC700-3. Symmetric supercapacitors in Na2SO4 and TEABF4/AN electrolyte showed voltage ranges of 1.8 V and 3 V respectively, and high energy density of 22.2 Wh Kg−1 at 448. W Kg−1 and 40.6 Wh Kg−1 at 755.8 W Kg−1 are obtained.