Controlled Synthesis of Fe₃O₄ Nanospheres Coated with Nitrogen-Doped Carbon for High Performance Supercapacitors

Hybrid nanospheres made of carbon-coated iron oxides (Fe3O4) have attracted attention as high-performance electrode materials for supercapacitors. Herein, we report a simple yet effective method to fabricate Fe3O4 particles coated with nitrogen-doped carbon (Fe3O4–NC) by a strategy combining polymerization and carbonization. The materials are characterized using scanning electron microscopy-energy dispersive X-ray (SEM-EDX), transmission electron microscopy (TEM), high resolution transmission electron microscopy (HRTEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and electrochemical techniques including cyclic voltammetry (CV), galvanostatic charge/discharge (GCD), and electrochemical impedance spectroscopy (EIS). The results show that the Fe3O4 nanoparticles are completely encapsulated by the nitrogen-doped carbon materials, and the nanosized sphere-like Fe3O4–NC materials can deliver a capacitance of 346 F g–1 at 5 mV s–1, with 97% of the initial specific capacitance after 5000 cycles. The outstanding capacitive performance is due to the unique and uniform structure of the Fe3O4–NC nanocomposites, where the synergistic effect between coated-carbon layers with high conductivity and Fe3O4 nanoparticles with good pseudocapacitance.