Designed Formation of MnO₂@NiO/NiMoO₄ Nanowires@Nanosheets Hierarchical Structures with Enhanced Pseudocapacitive Properties

Abstract

Abstract Although the preparation of hierarchical structures of transition‐metal oxides (TMOs) has been intensively studied in recent years, it is still a great challenge to synthesize hierarchical multicomponent TMOs. Herein, we report a versatile method to fabricate three‐component TMOs, namely MnO 2 @NiO/NiMoO 4 nanowires@nanosheets hierarchical porous composite structures (HPCSs). Through a combination of a chemical‐solution‐based route and subsequent calcination, the as‐prepared MnOOH@NiMo precursor is topotactically transformed to MnO 2 @NiO/NiMoO 4 HPCSs without notable structural variation. Ultrathin NiO/NiMoO 4 nanosheets become interconnected into a honeycomb analogue with plentiful mesopores. Comparative results demonstrate the vital role of hexamethylenetetramine (HMT), and the solvent system in the formation of the MnOOH@NiMo precursor. When examined as electrode materials for electrochemical capacitors, MnO 2 @NiO/NiMoO 4 HPCSs, with an areal mass loading as high as 5 mg cm −2 , deliver a specific capacitance of 918 F g −1 at a current density of 1.0 A g −1 and maintain good cycling stability, which displays better electrochemical performance than electrodes composed of a single component. Note that a high‐voltage asymmetric supercapacitor is configured with MnO 2 @NiO/NiMoO 4 HPCSs (still as high as 2 mg cm −2 ) against activated carbon, and exhibits outstanding cycling stability with a high energy density of 26.5 Wh kg −1 and a power density of 401 W kg −1 . These analytical and experimental results clearly confirm the advantages of distinctive 3D multicomponent hierarchical architectures for engineering high‐performance electrochemical capacitors.