Electrodeposition synthesis and electrochemical properties of nanostructured γ-MnO2 films

The thin films of carambola-like γ-MnO2 nanoflakes with about 20 nm in thickness and at least 200 nm in width were prepared on nickel sheets by combination of potentiostatic and cyclic voltammetric electrodeposition techniques. The as-prepared MnO2 nanomaterials, which were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS), were used as the active material of the positive electrode for primary alkaline Zn/MnO2 batteries and electrochemical supercapacitors. Electrochemical measurements showed that the MnO2 nanoflake films displayed high potential plateau (around 1.0 V versus Zn) in primary Zn/MnO2 batteries at the discharge current density of 500 mA g−1 and high specific capacitance of 240 F g−1 at the current density of 1 mA cm−2. This indicated the potential application of carambola-like γ-MnO2 nanoflakes in high-power batteries and electrochemical supercapacitors. The growth process for the one- and three-dimensional nanostructured MnO2 was discussed on the basis of potentiostatic and cyclic voltammetric techniques. The present synthesis method can be extended to the preparation of other nanostructured metal-oxide films.