Micro-Mesoporous Carbon Materials Prepared from the Hogweed (Heracleum) Stalks as Electrode Materials for Supercapacitors

Abstract

The data on carbonization and surface activation of raw hogweed (Heracleum) are presented. The structural and electrochemical properties of thus synthesized carbon materials which can be used as the electrode materials in supercapacitors are studied. The hogweed samples are preliminarily carbonized at 400°C and then activated with potassium hydroxide (KOH) at temperatures of 700, 800, and 900°C in argon atmosphere. According to isotherms of nitrogen adsorption and the BET equation, the specific surface area of samples activated at 700, 800, and 900°C is 913 ± 22, 1215 ± 70, and 1929 ± 99 m²/g, respectively. As the activation temperature increases, the specific surface area and the mesopore volume of samples also increases, whereas the micropore fraction decreases. 1,1-Dimethylpyrrolidinium tetrafluoroborate in acetonitrile was used as an electrolyte. The specific capacitance of samples activated at 700, 800, and 900°C at the current density of 1 A/g is 51 ± 4, 114 ± 2, and 108 ± 3 F/g, respectively. The 40% increase in the specific surface area and the 35% increase in the volume of mesopores results in the increase in the specific capacitance. The further increase in the specific surface area and the volume of mesopores up to 70% does not increase the specific capacitance.