N, O-Codoped Porous Carbon Derived from Longan Shells for High-Performance Supercapacitor Electrodes

Biomass-derived porous carbon offers an eco-friendly solution for energy storage, but challenges persist in optimizing the pore structure and electrochemical stability. In this study, we present a novel approach for fabricating nitrogen–oxygen-codoped porous carbon (NOPC) electrodes derived from sustainable longan shells, designed for electrical double-layer capacitors (EDLCs). The N3OPC-3 electrode, optimized through high-temperature activation and surface doping with urea and nitric acid, exhibits outstanding electrochemical properties, achieving a specific capacitance of 463 F·g–1 at a current density of 0.5 A·g–1 in a 6 M KOH electrolyte during a three-electrode test. Furthermore, the symmetric supercapacitor based on N3OPC-3 exhibits a high energy density of 31.9 W h·kg–1 at a power density of 700 W·kg–1, as well as an exceptional cycling stability, retaining 89% of its initial capacitance after 10,000 cycles. These superior performance characteristics can be attributed to the well-developed 3D hierarchical porous structure, which enhances ion diffusion, and the synergistic effects of nitrogen and oxygen doping, which promote pseudocapacitive behavior and improve electronic conductivity. The results highlight the potential of biomass-derived materials as sustainable, high-performance electrode materials for energy storage applications, offering an eco-friendly alternative to traditional carbon sources while addressing the growing need for efficient and scalable energy storage systems.