High-yield green synthesis of carbon-nanohair/carbon quantum dots/activated carbon composite from agricultural or textile wastes for enhanced supercapacitor performance

A novel approach is demonstrated to fabricate decorated carbon nanohair/carbon quantum dots (CQDs)/activated carbon (ACs) composites from diverse waste sources via thermal activation, omitting the need for inert gas or nitrogen sources, enhancing sustainability, cost-efficiency, decreasing carbon footprint and gaining carbon credit which aligning with Sustainable Development Goals (SDGs). The synthesized composites undergo thermal and chemical treatment with potassium hydroxide, resulting in high yield and increasing both the porosity and surface area with values ranged from 1160 m²/g to 1620 m²/g. Notably, Jeans-carbon-composite (J_AC) demonstrates outstanding cell-specific capacitance of 988.8 F/g at 0.5 A/g and 0.9 V, with a capacitance retention increasing up to ∼ 260 % over 1200 cycle. Furthermore, at 1.2 V and 0.5 A/g, cell-specific capacitances for other wastes are: Wood-dust-carbon (W_AC) = 983.3 F/g, Olive-leaves-carbon (O_AC) = 750 F/g, Bagasse-carbon (B_AC) = 476.6 F/g, Peanut-shell-carbon (P_AC) = 220 F/g and Garlic-leaves-carbon (G_AC) = 163.3 F/g. G_AC has a negative capacitance-to-potential window relationship, characterized by a high cell-specific capacitance value of 6296 F/g at a low potential of 0.5 V, which declines to 780 F/g at 0.8 V and drops to 163.3 F/g at 1.2 V, demonstrating high energy and power densities simultaneously. The synthesized composites demonstrate compelling electrochemical performance, making them promising supercapacitor electrode materials, owing to their unique hierarchical porous structure.