Enhancing supercapacitor performance through rapid charge transport induced by magnetic field-driven spin polarization

Abstract

Magnetic supercapacitors have garnered significant attention, with notable progress in recent years. However, the underlying mechanisms remain unclear and require further investigation for future energy storage applications. In this study, we designed and fabricated Mn-Fe₂O₃/reduced graphene oxide (Mn-Fe₂O₃/rGO) nanostructures by employing heteroatom doping and interface engineering. Theoretical calculations showed that incorporating Mn²⁺ into Fe₂O₃ modulates electron localization around Fe atoms, leading to spin polarization in Fe 3d orbital electrons. Our experiments demonstrated that the optimized Mn-Fe₂O₃/rGO nanostructure processes ferromagnetic properties with a negative magnetoresistance effect at room temperature, suggesting that substantial spin-polarized charges rapidly participate in surface charge–discharge reactions under an applied magnetic field. This phenomenon resulted in a remarkable specific capacitance of 2956.4 F g⁻¹ at 1 A g⁻¹, along with superior cyclic stability. Additionally, the asymmetric supercapacitor device achieved an energy density of 220.19 W h kg⁻¹ at a power density of 3.93 kW kg⁻¹, with excellent capacitance retention of 98.5 % after 5000 cycles. This work paves the way for improving the performance of magnetic supercapacitors based on metal oxide electrode materials.