Hierarchical Battery-Type MnFe₂O₄@Ni(OH)₂ Spinel Ferrite-Hydroxide Nanostructures for High-Performance Supercapacitors

Abstract

This study reports the synthesis and characterization of MnFe₂O₄, Ni(OH)₂, and MnFe₂O₄@Ni(OH)₂ electrodes grown on Ni foam through a facile hydrothermal approach. X-ray diffraction and Raman analyses confirm the coexistence of cubic spinel MnFe₂O₄ and mixed α/β-Ni(OH)₂ phases in the composite, while field-emission scanning electron microscopy reveals a hierarchical morphology, where Ni(OH)₂ nanosheets uniformly coat the MnFe₂O₄ nanoparticles, enhancing surface exposure and ion accessibility. X-ray photoelectron spectroscopy indicates the presence of mixed-valence Mn, Fe³⁺, and Ni²⁺ species, suggesting multiple redox-active centers for improved electrochemical activity. Electrochemical investigations demonstrate that all electrodes exhibit battery-type behavior, with well-defined redox peaks and plateau regions in cyclic voltammetry and galvanostatic charge–discharge curves. MnFe₂O₄@Ni(OH)₂ composite achieves significantly higher specific capacity (159.15 mA h g⁻¹ at 2 mA cm⁻²) and superior rate performance compared to the individual components, attributed to the synergistic interaction between the conductive MnFe₂O₄ core and electroactive Ni(OH)₂ shell. In symmetric supercapacitor devices, the MnFe₂O₄@Ni(OH)₂ electrode delivers excellent energy storage performance (20.16 Wh·kg⁻¹ at a power density of 395.4 W·kg⁻¹), with improved charge transfer and remarkable cycling stability (140.04% retention over 3000 cycles). The findings indicate that combining spinel ferrites with layered hydroxides in hierarchical architecture offers a promising strategy for designing high-performance, battery-type supercapacitors.