Hierarchical α-MnO2 Nanowires@Ni1-xMnxOy Nanoflakes Core-Shell Nanostructures for Supercapacitors

A facile two-step solution-phase method has been developed for the preparation of hierarchical alpha-MnO2 nanowires@Ni1-xMnxOy nanoflakes core-shell nanostructures. Ultralong alpha-MnO2 nanowires were synthesized by a hydrothermal method in the first step. Subsequently, Ni1-xMnxOy nanoflakes were grown on alpha-MnO2 nanowires to form core-shell nanostructures using chemical bath deposition followed by thermal annealing. Both solution-phase methods can be easily scaled up for mass production. We have evaluated their application in supercapacitors. The ultralong one-dimensional (1D) alpha-MnO2 nanowires in hierarchical core-shell nanostructures offer a stable and efficient backbone for charge transport; while the two-dimensional (2D) Ni1-xMnxOy nanoflakes on alpha-MnO2 nanowires provide high accessible surface to ions in the electrolyte. These beneficial features enable the electrode with high capacitance and reliable stability. The capacitance of the core-shell alpha-MnO2@Ni1-xMnxOy nanostructures (x = 0.75) is as high as 657 F g(-1) at a current density of 250 mA g(-1), and stable charging-discharging cycling over 1000 times at a current density of 2000 mA g(-1) has been realized.