Hydrothermally controlled synthesis of a-MnO^sub 2^, ?-MnOOH, and Mn^sub 3^O^sub 4^ nanomaterials with enhanced electrochemical properties

In this work, a facile hydrothermal method was used to obtain various manganese oxides nanomaterials including α-MnO2, γ-MnOOH, and Mn3O4 with different morphology based on the direct reaction between Mn(CH3COO)2·4H2O and NaOH. Gelatin and cetyltrimethylammonium bromide were adopted as dispersants to decrease the size and inhibit agglomeration of nanomaterials in the synthesis process. It is significant that the chemical composition and morphology of as-prepared materials can be controlled by solely tuning the hydrothermal time. All the findings of morphological and structural studies on α-MnO2, γ-MnOOH, and Mn3O4 nanomaterials show the regular shapes, pure crystal phases, and high specific surface areas (51.6–67.2 m2 g−1). Furthermore, those nanomaterials were applied as electrode materials in the presence of Na2SO4 electrolyte that exhibited the satisfactory electrochemical performances such as excellent redox reversibility, high mass specific capacitance, and eminent capacitance retention with minor loss after long-term cycles, which confirms that these manganese oxides nanomaterials are outstanding candidates of supercapacitors electrode materials.