Nitrogen self-doped activated carbon from neem seed waste as a high-efficiency supercapacitor electrode: An eco-friendly approach

The development of sustainable and high-performance electrode materials is critical to the advancement of next-generation supercapacitors. In this study, wild neem (Azadirachta indica) seed shells (WNS), an abundantagricultural waste, are utilizedas a renewable precursor for the preparation of porous activated carbon. A two-step synthesis procedure, comprising hydrothermal pre-carbonization followed by eco-friendly potassium carbonate (K₂CO₃) chemical activation was employed to create N self-doped porous activated carbon (WNS). The resultant carbon material has a high specific surface area of 1010.20 m²·g⁻¹, an interconnected micro/mesoporous structure, and enriched surface functionalities, as validated by Brunauer-Emmett-Teller analysis(BET), X-ray photoelectron spectrometry (XPS), and Fourier-transform infrared (FTIR)spectroscopy. Electrochemical evaluation demonstratesexcellent capacitive performance, delivering a high specific capacitance of 320 F·g⁻¹ at 0.5 A·g⁻¹ and capacitance retention of 101% over 5000 charge-dischargecycles in a three-electrode configuration. These results highlight the potential of WNS-derived activated carbon as a cost-effective and sustainable electrode material for supercapacitor applications, contributing to waste valorisation and the development of environmentally friendly energy storage technologies.