In situ hydrothermal preparation of mesoporous Fe₃O₄ film for high-performance negative electrodes of supercapacitors

A mesoporous Fe₃O₄ film was prepared as binder-free electrode material for supercapacitors through a facile process that included the hydrothermal electroplating of an Fe/Zn alloy, in situ electrolytic dealloying to remove the Zn template, and oxidation in a water vapor environment. The Fe₃O₄ film showed a cubic structure and mesoporosity with a specific surface area of 247 m² g⁻¹. As a negative electrode material, the mesoporous Fe₃O₄ film delivered a high gravimetric capacity of 221 C g⁻¹ at 1 A g⁻¹, and the gravimetric capacity was maintained at 154 C g⁻¹ even at a high current density of 50 A g⁻¹. In addition, the mesoporous Fe₃O₄ electrode exhibited very high cycling stability (only 4.7% capacity loss after 10,000 galvanostatic charge–discharge cycles). Electrochemical impedance spectroscopy revealed that the mesoporous Fe₃O₄ film had excellent conductivity, implying its promising application as a supercapacitor electrode.