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 α‐MnO₂ nanowires@Ni_1‐xMn_xO_y nanoflakes core–shell nanostructures. Ultralong α‐MnO₂ nanowires were synthesized by a hydrothermal method in the first step. Subsequently, Ni_1‐xMn_xO_y nanoflakes were grown on α‐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) α‐MnO₂ nanowires in hierarchical core–shell nanostructures offer a stable and efficient backbone for charge transport; while the two‐dimensional (2D) Ni_1‐xMn_xO_y nanoflakes on α‐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 α‐MnO₂@Ni_1‐xMn_xO_y 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.