Bourbon Whiskey Waste-Derived Carbons for Electric Double Layer and Lithium-Ion Supercapacitors

Bourbon is an American whiskey almost entirely crafted (95%) in Kentucky (KY). Distilleries have increased by 250% over the past 15 years in KY, leading to significant new challenges. One of the industry’s biggest challenges is the spent grain (stillage). For every barrel of bourbon produced, it is estimated that six to ten barrels of stillage remain. Here, bourbon stillage is transformed into carbon materials for conventional (electric-double-layer) and hybrid (lithium-metal-ion) supercapacitor electrodes. The bourbon stillage transformation involves hydrothermal carbonization, hydrochar pyrolysis, and multiple activations. Electric Double-Layer supercapacitors (EDLCs) demonstrate excellent cyclability (96% capacitance retention after 15,000 cycles), and similar to current commercially available devices, specific energy (14-34 Wh/kg) and power (1,660-3,997 W/kg) densities at variable specific current (0.1-10 A/g). Experiments show that hybrid Lithium-ion Capacitors (LiC) assembled perform better than commercially available devices. LiC displayed energy densities of 66-93 Wh/kg and power densities of 4412-4531 W/kg at current densities from 0.1-10 A/g. This research presents an innovative, potentially scalable, and sustainable strategy for repurposing bourbon stillage into efficient, green, and high-performance materials for energy storage applications, with the potential to be adopted by the entire whiskey and ethanol production industry.