Hierarchical Fe₃O₄@Ni-MOF on Nickel Foam for Enhanced Electrochemical Water Splitting and Supercapacitor Performance

Abstract The hierarchical Fe₃O₄@Ni-MOF composite was successfully fabricated directly on nickel foam and systematically characterized to confirm its crystal structure, morphology, chemical composition, porosity, and thermal stability. X-ray diffraction (XRD) analysis was employed to identify the crystalline phases and verify the successful formation of the Fe₃O₄ and Ni-MOF components, while scanning electron microscopy (SEM) and transmission electron microscopy (TEM) revealed the hierarchical morphology, surface features, and nanoscale structural characteristics of the composite. Fourier-transform infrared (FTIR) spectroscopy was used to identify the characteristic functional groups and chemical bonding interactions within the composite. Furthermore, Brunauer–Emmett–Teller (BET) analysis was conducted to evaluate the specific surface area and pore characteristics, while thermogravimetric analysis (TGA) was performed to assess thermal stability and decomposition behavior. The resulting Fe₃O₄@Ni-MOF/NF electrode exhibited enhanced electrochemical performance for water splitting, achieving HER and OER overpotentials of 120 mV and 250 mV, respectively, at 10 mA cm⁻², together with Tafel slopes of 94 and 109 mV dec⁻¹. In supercapacitor measurements, the electrode delivered a specific capacitance of 531 F g⁻¹ at 0.5 A g ¹ and retained 77.6% of its initial capacitance after 8000 cycles. The improved electrochemical behavior is attributed to the synergistic interaction between Fe₃O₄ and Ni-MOF, the hierarchical porous architecture, and the highly conductive three-dimensional nickel foam substrate, which collectively promote efficient electron transport, electrolyte accessibility, and rapid ion diffusion. Furthermore, the electrode's practical water-splitting capability was demonstrated using a two-electrode electrolytic cell powered by a DC power supply. The assembled cell exhibited an overall cell voltage (E cell ) of only 1.73 V at a current density of 10 mA cm⁻², confirming the feasibility of the Fe₃O₄@Ni-MOF/NF electrode for real-time electrochemical water-splitting applications. These results highlight the potential of the hierarchical Fe₃O₄@Ni-MOF/NF architecture as a multifunctional platform for efficient hydrogen production and electrochemical energy storage.