Superior magnetocapacitance in ferro/ferrimagnetic Fe3O4/Fe/Fe3C integrated N-doped carbon hybrid nanostructures under mild magnetic fields

Abstract

To address the low energy density challenges of supercapacitors, two key strategies were implemented. The first involved designing Fe₃O₄/Fe/Fe₃C wrapped by N-doped carbon onto N-doped carbon nanosheets (Fe@NCNS) using a template free, scalable, simple pyrolysis process. The second strategy focused on enhancing energy storage capacitance using external magnetic fields (MFs). The optimized Fe@NCNS hybrid nanostructure demonstrated a specific capacitance of 1327.3 F g⁻¹ at 1.5 A g⁻¹ with an excellent rate capability of 88.3% at 45 A g⁻¹ in a three-electrode system. Under a mild MF strength of 6 mT, the specific capacitance significantly increased to 2057.3 F g⁻¹, attributed to the reduced electrode and electrolyte resistance based on magnetoresistance and magnetohydrodynamics. The constructed asymmetric supercapacitor (ASC) demonstrated a significant energy density of 181.9 W h kg⁻¹. Furthermore, a remarkable enhancement in energy density was recorded, reaching 263.7 W h kg⁻¹, representing a 1.45-fold increase when subjected to a 6 mT MF. This ASC device exhibits exceptional cycle stability after 10 000 cycles. It is worth highlighting that the specific capacitance and energy and power densities achieved under varying MFs surpass those of most metal oxide-based hybrid structures reported to date. These findings indicate significant potential for the advancement of efficient energy storage devices, including memory devices.