Three‐Dimensional Co₃O₄@MnO₂ Hierarchical Nanoneedle Arrays: Morphology Control and Electrochemical Energy Storage

In this paper, a highly ordered three‐dimensional Co 3 O 4 @MnO 2 hierarchical porous nanoneedle array on nickel foam is fabricated by a facile, stepwise hydrothermal approach. The morphologies evolution of Co 3 O 4 and Co 3 O 4 @MnO 2 nanostructures upon reaction times and growth temperature are investigated in detail. Moreover, the as‐prepared Co 3 O 4 @MnO 2 hierarchical structures are investigated as anodes for both supercapacitors and Li‐ion batteries. When used for supercapacitors, excellent electrochemical performances such as high specific capacitances of 932.8 F g −1 at a scan rate of 10 mV s −1 and 1693.2 F g −1 at a current density of 1 A g −1 as well as long‐term cycling stability and high energy density (66.2 W h kg −1 at a power density of 0.25 kW kg −1 ), which are better than that of the individual component of Co 3 O 4 nanoneedles and MnO 2 nanosheets, are obtained. The Co 3 O 4 @MnO 2 NAs are also tested as anode material for LIBs for the first time, which presents an improved performance with high reversible capacity of 1060 mA h g −1 at a rate of 120 mA g −1 , good cycling stability, and rate capability.