Free-standing and binder-free electrochemical capacitor electrode based on hierarchical microfibrous carbon–graphene–Mn₃O₄ nanocomposites materials

Hierarchical microfibers carbon–graphene–Mn₃O₄ (MFC–G–Mn₃O₄) nanocomposites have been successfully prepared via a simple, effective, and scalable chemical deposition method. It was applied as a free-standing and binder-free electrodes for an electrochemical capacitor. The graphene was first synthesized by electrochemical exfoliation of graphite rods and deposited on the microfibers carbon using gradually drop of the temperature until 150 °C to form MFC–G electrode. Then the Mn₃O₄ was prepared by direct redox depositions on MFC–G substrate at the temperature of 150 °C to form MFC–G–Mn₃O₄. For comparison purposes, the Mn₃O₄ was deposited directly on MFC to form MFC–Mn₃O₄ electrode under similar conditions. The synthesized materials were characterized by using scanning electronic microscopy, X-ray diffraction, Raman spectroscopy, cyclic voltammetry, galvanostatic charge–discharge (GCD) and electrochemical impedance spectroscopy techniques. The results from different characterization techniques indicate that the graphene and Mn₃O₄ were successfully synthesized and deposited on substrates. The specific capacitance of the electrode MFC–G–Mn₃O₄ reached 414 F g⁻¹, this is five times greater than that obtained capacitance from the electrode MFC–Mn₃O₄ which is 83 F g⁻¹. In addition, the introduction of graphene in the matrix of Mn₃O₄ allows an improvement of contact resistance between the active material and the current collector, electronic conductivity of the electrode, and stability over GCD cycling. The specific capacitance of the MFC–G–Mn₃O₄ is one of the highest values recorded in the literature of Mn₃O₄ based materials. Combination of the graphene and Mn₃O₄ using the direct deposition resulted in efficient synergetic effect between the two materials. The facile synthesis techniques and the good capacitive performances indicate that the developed nanocomposite electrode would be promising as electrode materials for the high-performance electrochemical capacitor.