Wasted to electrodes in seconds: Ultrafast-carbonization of coffee powders for high performance zinc-ion hybrid supercapacitors

The conventional method for preparing porous carbon comprise carbonization and potassium hydroxide activation, with preparation times reaching up to 2 h. We present a method for synthesizing nanoscale porous carbon via ultrafast carbonization and activation of waste coffee grounds in just 30 s, achieving heating rates as high as 3000 degrees C center dot min-1. The activated coffee grounds (ACG) exhibit a specific surface area of 1977 m2 center dot g-1. Zinc-ion hybrid supercapacitors (ZHSCs) based on ACG cathodes offer high energy density of 85.6 Wh center dot kg-1, high power density of 11.7 kW center dot kg-1 respectively. Raman spectroscopy and electrolyte pH monitoring techniques analyze the charge storage process at the ACG cathode. The adsorption and desorption of Zn/H+ and SO2-4 ions on porous carbon was elucidated during the charging and discharging process of ZHSCs. This work not only establishes a pathway for manufacturing nanoscale porous carbon for ZHSCs but also enhances our knowledge of the energy storage processes.