Grishika AroraNuur Syahidah Sabran0000-0002-1945-9052Chai Yan Ng0000-0003-2551-7623Foo Wah LowH. K. Jun2025-09-242025-09-2420259789819638130978981963814710.1007/978-981-96-3814-7_4https://dspace-cris.utar.edu.my/handle/123456789/11359Electric double-layer capacitors (EDLCs) often suffer from limited energy storage and surface area. This study addresses these limitations by repurposing spent coffee grounds to produce carbon quantum dots (CQDs). These CQDs are integrated into EDLCs to the device surface area, energy density, biocompatibility, and electrical properties. Various characterization techniques, including X-ray diffraction, transmission electron microscopy, linear sweep voltammetry, cyclic voltammetry, and galvanostatic charge–discharge, are performed. The hydrothermal synthesis of CQDs, incorporated into a carbon slurry, results in electrodes for EDLCs with optimized polyvinyl alcohol gel electrolyte, achieving a specific capacitance of 125 F/g, and energy and power density of 4.3 Wh/kg and 130.6 W/kg, respectively. © The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2025.enCarbon quantum dotsPolymer electrolyteSpecific capacitanceSpent coffee groundSupercapacitorCapacitor storageCarbon Quantum DotsHigh resolution transmission electron microscopyHydrothermal synthesisCoffee groundsDouble-layer capacitorsEnergy densityLimited energiesSpent coffee groundsStorage areaSurface areaCyclic voltammetrytext::conference output::conference proceedings::conference paper