Agricultural and industrial wastes applied on the high performance energy storage devices

Driven by population growth, the destruction of the environment and the energy demand continue to increase dramatically. This study uses garlic skin and carbon fiber from agricultural and industrial wastes to prepare energy storage devices. Carbon quantum dots (CQDs) were obtained from garlic skin using high-temperature pyrolysis. The specific capacitance of the gel electrolyte could be effectively increased with a small number of CQDs doping. A methylcellulose-based carbon fiber-electrode was prepared by grinding and depositing the industrial recycled carbon fiber onto a biodegradable methylcellulose substrate. The methylcellulose-based recycled carbon fiber-electrode has the highest specific capacitance, energy density, and power density, which are 155 F/g, 10 Wh/kg, and 4047 W/kg, respectively, at a scan rate of 0.02 V/s, and demonstrates excellent performance, such like high specific capacitance, low internal resistance as well as rapid charge and discharge characteristics, which may have potential to replace the expensive carbon nanotubes and graphenes. The electrodes were made from recycled carbon fiber, the gel electrolyte with garlic CQDs, and a separator assembled into a sandwich structure to form supercapacitors. The capacity retention rate of the supercapacitor still retained 96 % of its initial value after 2000 cycles of charge and discharge testing at a constant current of 0.20 mA. This demonstrates the supercapacitor prepared in this study with competitive power density, energy density, high rate capability, and excellent life cycle stability by combining the garlic skin and carbon fiber from agricultural and industrial wastes, highlighting the enormous potential of agricultural and industrial wastes for energy storage applications. •Agricultural and industrial wastes are applied to the supercapacitor preparation.•CQDs and conductive electrodes were successfully prepared from garlic skin and recycled C-fibers.•The specific capacitance of the gel electrolyte is enhanced after 0.1 % CQDs adding.•Supercapacitor with C-fibers-based electrodes and CQDs-doped gel electrolyte exhibits good electrochemical performance.