Morphological evolution process of δ-MnO2 from 2-D to 1-D without phase transition

In this work, the evolution process of delta-MnO2 from 2-D nanosheets to 1-D nanofibers has been systematically investigated by regulating the concentration of reactants, reaction time and temperature. The morphological evolution and growth process could be described by a dissolution-recrystallization mechanism. In detail, the partial nanosheets dissolve in the solution and serve as sources supplied for the growth of nanofibers, while other portions grow directly to form larger and irregular nanosheets and then re-dissolve due to the limited solubility. The conversion of delta-MnO2 from nanoflakes to nanofibers mainly depends on the concentrated NaOH solution, adequate reaction period and suitable reaction temperature in the hydrothermal reaction. Importantly, sufficient Na+ ions in solution play an important role to keep the delta phase structure. In addition, the 1-D delta-MnO2 nanofibers can be a promising candidate as supercapacitor electrode.