A hierarchical nanostructure consisting of amorphous MnO2, Mn3O4 nanocrystallites, and single-crystalline MnOOH nanowires for supercapacitors

In this communication, a porous hierarchical nanostructure consisting of amorphous MnO₂ (a-MnO₂), Mn₃O₄ nanocrystals, and single-crystalline MnOOH nanowires is designed for the supercapacitor application, which is prepared by a simple two-step electrochemical deposition process. Because of the gradual co-transformation of Mn₃O₄ nanocrystals and a-MnO₂ nanorods into an amorphous manganese oxide, the cycle stability of a-MnO₂ is obviously enhanced by adding Mn₃O₄. This unique ternary oxide nanocomposite with 100-cycle CV activation exhibits excellent capacitive performances, i.e., excellent reversibility, high specific capacitances (470 F g⁻¹ in CaCl₂), high power property, and outstanding cycle stability. The highly porous microstructures of this composite before and after the 10,000-cycle CV test are examined by means of scanning electron microscopy (SEM) and transmission electron microscopy (TEM).