The team from NUST MISIS in St Petersburg have investigated the possibilities of using the stems of hogweed, a poisonous plant that grows across Russia, for carbon electrodes in supercapacitors. They show that the treated dangerous plant can successfully replace traditional sources of energy without compromising the quality of the batteries.
Electrodes in supercapacitors use activated carbons with a highly developed surface with a large number of pores of different sizes, act as the electrode material. These pores provide an increase in the area of the electrodes, on which the maximum volume of the accumulated charge directly depends. Researchers are looking to develop the carbon materials from various plant raw materials, especially from agricultural waste — from the coconut, almond and walnut shells or the husk remaining after cereal processing.
The hogweed stems consist of a firm bark and a soft inner core, similar to a sponge, forming a diverse porous structure. This design is effective for using carbon material as the basis of electrodes for supercapacitors. In order to turn hogweed stalks into a material suitable for use as electrodes, it was necessary to find the optimal processing technology for them.
The dry stalks of the hogweed were cut into bars about a centimeter long. Then, to remove various inorganic compounds contained in the stems, they were treated with hydrochloric acid, washed and dried. To obtain a carbon material, crushed hogweed stems were saturated with carbon dioxide at a temperature of 400 °C and then mixed with potassium hydroxide and activated, that is, the appeared pores were opened in an argon atmosphere at various temperatures.
Processing the primary carbon material at a temperature of 900°C led to the formation of a surface with a large number of pores 2-4 nm in size.
“The main parameter of the supercapacitor is capacity, which means a measure of the ability to accumulate an electric charge,” said Oleg Levin, associate professor at the Department of Electrochemistry of St. Petersburg State University. “The capacity obtained from hogweed stems is at the same level as the one obtained from the other materials. Of course, when using, for example, graphene, it will be higher. However, the use of plant waste material for the production of active carbon is without a doubt a global trend. From this perspective, the work of scientists is promising and deserves attention”.