Enhanced energy storage in electric double-layer capacitors using boron-doped graphene and upcycled carbon quantum dots derived from spent coffee grounds as electrode materials

In the pursuit of high-efficiency and sustainable energy storage solutions, we investigate a novel electrode material: boron-doped graphene (BG) combined with carbon quantum dots (CQDs) derived from upcycled, medium-roasted local Liberica spent coffee grounds. Boron doping of graphene is effective in imparting p-type characteristics that significantly enhance electrical conductivity and create abundant active sites for ion adsorption. This modification establishes graphene as an ideal complement to CQDs, whose integration further increases surface area and improves electron mobility. The resulting BG-CQDs composite exhibited strong synergistic properties, yielding good electrochemical properties in electric double-layer capacitors (EDLCs), as demonstrated by cyclic voltammetry and galvanostatic charge-discharge tests. At a scan rate of 5 mV/s, the BG-CQD EDLC device achieved a specific capacitance of 43.5 F/g, higher than the 3.61 F/g observed in EDLC with electrode material consists of boron-doped graphene alone. Under constant current density, the BG-CQD EDLC attained a specific capacitance of 150 F/g, an energy density of 5.2 Wh/kg, and a power density of 156.8 W/kg, showcasing the impact of boron doping on charge storage capabilities through enhanced conductivity and ion adsorption. This study underscores the pivotal role of boron-doped graphene in enhancing CQDs performance, presenting a promising composite for next-generation supercapacitors in sustainable energy storage applications.