Medicinal cannabis industry waste for energy storage in symmetric solid-state supercapacitors

Abstract

The exploitation of the Cannabis sativa L plant in Argentina is limited to its medicinal, therapeutic, or pain relief purposes. These formulations are produced by extracting active compounds from their flowers, which generates leaves and stems as discarded. A considerable number of countries have approved laws for Cannabis medicinal use around the world, encouraging challenging research to find ways to use this residue generated by this new industry. This study proposes valorizing cannabis waste (stems and leaves) by producing and evaluating activated biocarbons as electrode materials for supercapacitors. Cannabis waste were pyrolyzed at 500 °C; then activation conditions were varied from 60 to 180 min; the impregnation ratio was from 1.5 to 4.5 g KOH/g pyrolyzed waste and fixed temperature at 850 °C. Textural properties were evaluated through scanning electron microscopy, infrared spectroscopy, and N2 adsorption/desorption isotherms. The electrochemical characterization was done using an alkaline electrolyte in a three and two-electrode configuration. Cyclic voltammetry, galvanostatic charge and discharge measurements, and electrochemical impedance spectroscopy were performed. Activated biocarbon reached high surface areas over 2500 m2g−1 and adequate porosity development. The best electrochemical performance was obtained at 0.1 Ag−1 achieving 195.83 Fg−1 as specific capacitance, 23.3 KWKg−1, and 54.40 WhKg−1 as power and energy density in the electrode cells. A symmetric solid-state supercapacitor of 2.78 F maximum capacitance at 7.5 mA and 1.2 V potential was developed. These results position activated biocarbon derived from cannabis residues as potential electrode materials in supercapacitors.