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

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 MnO2@NiO/NiMoO4 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 MnO2@NiO/NiMoO4 HPCSs without notable structural variation. Ultrathin NiO/NiMoO4 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, MnO2@NiO/NiMoO4 HPCSs, with an areal mass loading as high as 5mgcm(-2), deliver a specific capacitance of 918Fg(-1) at a current density of 1.0Ag(-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 MnO2@NiO/NiMoO4 HPCSs (still as high as 2mgcm(-2)) against activated carbon, and exhibits outstanding cycling stability with a high energy density of 26.5Whkg(-1) and a power density of 401Wkg(-1). These analytical and experimental results clearly confirm the advantages of distinctive 3D multicomponent hierarchical architectures for engineering high-performance electrochemical capacitors.