Performance of Activated Carbon from Salvia miltiorrhiza Roots as the Electrode Material for Supercapacitors

Activated carbons (ACs) were obtained from roots of Salvia miltiorrhiza Bunge (Danshen) followed by chemical activation with potassium hydroxide (KOH). The ACs were characterized by nitrogen adsorption, X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), and electrochemical testing. Results showed that ACs from cultivation sites in Pingyi (ASPY), possessed many micropores, a dominant amount of mesopores, and few macropores. They achieved a value of 1615 m(2)/g of specific surface area calculated by the Brunauer-Emmett-Teller (BET) method with numerous oxygen-containing functional groups. Electrodes fabricated with ASPY particles exhibited excellent double-layer specific capacitance (245 F/g), while the other two marked as ASFC (ACs from Fangcheng) and ASZJ (ACs from Zhongjiang) reached values of 163 F/g and 81 F/g, respectively, at a current density of 1 A/g in 6 mol/L KOH electrolytes. Electrodes made by ASPY had a good cyclic stability for 1000 cycles at a potential range from -1 V to 0 V and lower equivalent series resistance (ESR). Meanwhile, the authors found that roots of Danshen that grew in different cultivation sites were remarkably different while they were activated, which was the same with electrochemical properties of the electrodes fabricated by ACs.