Sustainable nitrogen-rich hierarchical porous carbon nest for supercapacitor application

Chitosan has high synthetic flexibility, making it a promising nitrogenous bioresource for industrial applications. Nitrogen-rich hierarchically porous carbon (NHPC) was successfully synthesized by hydrothermal carbonization and self-activation of a chitosan-transition metal ion (Zn²⁺) complex. The N₂ adsorption-desorption isotherm revealed that the as-made NHPC had large specific surface area (1067 m² g^-1) and a unique hierarchical pore structure (0.6-6.4 nm). Scanning electron microscopy (SEM) indicated a 3D finely interconnected nest architecture for NHPC. X-ray photoelectron spectroscopy (XPS) analysis demonstrated that the nitrogen atoms in the chitosan were protected by coordination with zinc ions, and most of them were still retained in the carbon matrix (6.36 at%) after high temperature activation. Electrochemical measurements exhibited that NHPC delivers a high specific capacitance (228.7 Fg^-1 at 1 A g^-1), impressive rate capability (the specific capacitance at 20 A g^-1 was 174 Fg^-1, maintaining 74.6% of the initial capacitance at 0.5 A g^-1), and outstanding long-term cycling stability (98.3% retention after 5000 cycles), together with excellent energy density of 25.7 Wh kg^-1 at the power density of 500 W kg^-1. This study offers a novel strategy for synthesizing NHPC as one of the desirable electrode material candidates for energy storage.