Synergistic Electric Double-Layer and Pseudocapacitance in NiMn₂O₄-Doped Chitosan-Derived Carbon for Energy Storage

This study presents a novel two-step simple hydrothermal synthesis of nitrogen-rich, porous carbon derived from chitosan, doped with nickel manganese oxide (NiMn₂O₄), for high-performance supercapacitor electrodes. The electrochemical evaluation was carried out in 6 M KOH aqueous electrolyte, where the material exhibited a specific capacitance of 1402 F g⁻¹ (cyclic voltammetry) and 837.7 F g⁻¹ (charge–discharge testing), along with excellent rate capability (508 F g⁻¹ at 12 A g⁻¹) and good cycling stability (over 70% capacitance retention after 5000 cycles). Structural and morphological analyses confirmed a highly porous carbon framework uniformly decorated with NiMn₂O₄ nanoparticles, which reduced the band gap from 2.6 to 1.6 eV, enhancing electrical conductivity and redox activity. Electrochemical evaluation in a two-electrode configuration which narrowly simulates the practical working conditions of real supercapacitor devices demonstrated a specific capacitance of 725 F g⁻¹ at 5 mV s⁻¹ and 501 F g⁻¹ at 1 A g⁻¹ indorsing its practicality. The synergistic effect of electric double-layer capacitance from the activated carbon and redox-based (pseudocapacitive) reactions from NiMn₂O₄ contributed to superior charge storage behaviour. Importantly, the simple and scalable synthesis process, based on renewable and low-cost chitosan, highlights the cost-effective and sustainable nature of this material, making it a promising electrode for next-generation energy storage devices.