Sodium-Ion-Assisted Hydrothermal Synthesis of γ-MnO[sub 2] and Its Electrochemical Performance

Abstract

A γ-Mn O2 nanomaterial was synthesized by hydrothermally treating an amorphous manganese oxide, which was obtained by the reaction between NaMn O4 and MnS O4 at ambient conditions. It is only in a narrow range of adding an amount of NaOH (e.g. 0.08-0.09 M in our case) that γ-Mn O2 can be obtained. The addition of NaOH may affect the radii of hydrated Na+ and, consequently, the formation of γ-Mn O2; the related mechanism was discussed. γ-Mn O2 was characterized by X-ray diffraction (XRD), scanning electron microscope, transmission electron microscope, and temperature-programmed XRD. γ-Mn O2 was also characterized by the combined thermogravimetric/ differential thermal analysis-mass spectrometry; accordingly, the annealed forms of γ-Mn O2 were prepared and characterized electrochemically. The results show that the γ-Mn O2 calcined at 275°C for 10 h showed excellent capacity (296 mAh g-1) with a good rate capability. © 2009 The Electrochemical Society.