Elevating Waste Biomass: Supercapacitor Electrode Materials Derived from Spent Coffee Grounds

Abstract

Waste biomass, such as spent coffee grounds (SCG), presents an abundant and sustainable source of carbon for energy storage and other applications. In this study, an ultrahigh surface area carbon was synthesized from spent coffee grounds and evaluated as an electrode material for supercapacitors. Using an alkali activation process with potassium hydroxide (KOH), the produced nanoporous carbon exhibited an ultrahigh BET area (∼3600 m²/g) and a large pore volume (1.80 cm³ g^–1), with 95% presence of micropores. These structural characteristics significantly enhanced the electrochemical performance of the material, making it suitable for use in energy storage devices. Electron spin resonance (ESR) measurements were conducted to quantify the number of radicals, aiming to shed light on the mechanism behind the formation of high surface area carbons. The activated carbon was tested in a two-electrode supercapacitor setup with an ionic liquid electrolyte, demonstrating excellent capacitive properties. It achieved high specific capacitances of 131 and 96 F g^–1 at 0.5 and 4 A g^–1, respectively. Furthermore, the material exhibited a gravimetric energy density of 52 W h kg^–1 and a power density of 871 W kg^–1 at 1 A g^–1, outperforming commercially available activated carbons with an S_BET of ∼2500 m²/g. The electrochemical testing showed stable performance across a wide voltage window of up to 3.5 V, with minimal pseudocapacitive behavior, confirming its suitability for use in supercapacitors with high power and energy density demands. This work underscores the potential of converting waste biomass into high-performance energy storage materials, offering an environmentally friendly and cost-effective solution. The results highlight the advantages of using spent coffee grounds-derived activated carbon in supercapacitors, opening pathways for further development of sustainable materials for energy applications.