Core@Shell Fe ₃ O ₄ @Metal–Organic Frameworks as Electrode Materials for Supercapacitors

Ensnaring an active guest molecule within a metal–organic framework (MOF) is a promising method for enhancing the functionality of pristine MOFs. Unlike typical guest encapsulation in MOF cavities, core@shell nanoarchitectures offer superior pore accessibility, which ensures optimal ion diffusion pathways on the nanoscale. Additionally, this nanoscale arrangement prevents active guest agglomeration and leaching while promoting enhanced interactions between the core and shell, resulting in synergistic effects. By utilizing a sequential growth strategy, we synthesized a core@shell nanohybrid MOF, Fe 3 O 4 @Mn-MOF-NH 2 . This hybrid combines a Mn-based MOF with a metal oxide to achieve both redox hopping and a through-layer mechanism of charge transport in a single system. The nanoscale core@shell architecture integrates a redox-active metal oxide nanocore with a porous MOF nanoshell, enabling the simultaneous operation of redox hopping and through-layer charge transport mechanisms within a single nanoengineered system, a feature unattainable in either pristine component alone. The synthesized nanohybrid was used as an electrode material for the supercapacitors. The Fe 3 O 4 @Mn-MOF-NH 2 nanohybrid showed a specific capacitance of 300 F/g, nearly 200% higher than that of the individual components, due to the synergistic effect of the nanoengineered core@shell interface. It also retained 87% capacitance with 100% Coulombic efficiency after 1000 cycles, underscoring the structural robustness and electrochemical stability of the nanoarchitecture. Moreover, an asymmetric device Fe 3 O 4 @Mn-MOF-NH 2 //activated carbon with a PVA-H 2 SO 4 gel electrolyte delivered an energy density of 25.8 Wh/kg at a power density of 600 W/kg and showed stable performance over 10,000 cycles. These results showcase the untapped potential of core@shell nanoarchitectures as promising electrode materials for supercapacitors and their potential to open avenues for futuristic energy storage applications.