Coffee-derived activated carbon from second biowaste for supercapacitor applications.

The electrochemical energy storage performance of activated carbons (ACs) obtained from coffee-derived biowastes was assessed. ACs were obtained from spent coffee ground second waste, after polyphenol extraction, by means of a hydrothermal process followed by physical or chemical activation. The resulting materials exhibited microporous structures with a total specific area between 585 and 2330 m2·g-1. Scanning electron microscopy (SEM) revealed a highly porous microstructure in the case of the chemically activated carbons, while physical activation led to a cracked micro-sized morphology. The electrochemical properties of the materials for supercapacitor applications were investigated in 1 M Na2SO4. After chemical activation, the coffee-derived material displayed a capacitance of 84 F·g-1 at 1 A·g-1 in a 1.9 V voltage window, with 70% capacitance retention at 10 A·g-1 and 85% retention after 5000 cycles of continuous charge-discharge. This work demonstrates how coffee secondary biowaste can be conveniently activated to perform as electrochemical energy storage material, contributing to its revalorization and reinsertion in a circular economy.