Peeling to power: integrating laser-induced carbon nanospheres from onion peel/electrochemical pani, sodium alginate gel for sustainable supercapacitor application

Abstract The growing demand for eco-friendly energy storage technologies has accelerated research into sustainable supercapacitor materials. This study presents an innovative, green and economical method for producing high-performance electrodes using a novel combination of laser-induced carbon nanospheres (CNS) derived from onion peels, electrochemically synthesised polyaniline (PANI) and a sodium alginate (SA)-based gel electrolyte. Onion peel, an abundant agricultural waste, was converted to highly conductive carbon nanospheres using a laser beam supporting SDG 12 (Responsible Consumption and Production) by converting biomass waste into functional materials. PANI was electrochemically deposited onto the CNS framework, significantly boosting the electrode’s pseudocapacitive properties and electrical conductivity. The SA-based electrolyte, which is crosslinked by calcium ions, provided biodegradability, mechanical flexibility, and excellent electrode–electrolyte interfacial contact. Electrochemical tests showed that the CNS/PANI electrode had a remarkable specific capacitance of 291 F/g at 0.4 A/g, with a huge 82.06% retention of its capacity after 8000 cycles, and a coulombic efficiency of 91%. The assembled device exceeded the performance of many traditional supercapacitors in terms of energy density, at 49.44 Wh/kg and power density, at 6.6 kW/kg. These results highlight the strong synergistic effects between biomass-derived carbon nanostructures, conducting polymers, and biopolymer-based gel electrolytes, demonstrating a viable pathway toward sustainable, high-performance, and flexible energy storage systems suitable for future green electronics directly supporting SDG 7 (Affordable and Clean Energy) and SDG 9 (Industry, Innovation, and Infrastructure). Graphical abstract