Three-Dimensional NiCo₂O₄@MnMoO₄ Core–Shell Nanoarrays for High-Performance Asymmetric\nSupercapacitors

Abstract

Design\nof new materials with sophisticated nanostructure has been proven\nto be an efficient strategy to improve their properties in many applications.\nHerein, we demonstrate the successful combination of high electron\nconductive materials of NiCo₂O₄ with high capacitance\nmaterials of MnMoO₄ by forming a core–shell nanostructure.\nThe NiCo₂O₄@MnMoO₄ core–shell\nnanoarrays (CSNAs) electrode possesses high capacitance of 1169 F\ng^–1 (4.24 F cm^–2) at a current\ndensity of 2.5 mA cm^–2, obviously larger than the\npristine NiCo₂O₄ electrode. The asymmetric supercapacitors\n(ASCs), assembled with NiCo₂O₄@MnMoO₄ CSNAs as binder-free cathode and active carbon (AC) as anode, exhibit\nhigh energy density of 15 Wh kg^–1 and high power\ndensity of 6734 W kg^–1. Cycle performance of NiCo₂O₄@MnMoO₄ CSNAs//AC ASCs, conducted\nat current density of 20 mA cm^–2, remain 96.45%\nof the initial capacitance after 10,000 cycles, demonstrating its\nexcellent long-term cycle stability. Kinetically decoupled analysis\nreveals that the capacitive capacitance is dominant in the total capacitance\nof NiCo₂O₄@MnMoO₄ CSNAs electrode,\nwhich may be the reason for ultra long cycle stability of ASCs. Our\nassembled button ASC can easily light up a red LED for 30 min and\na green LED for 10 min after being charged for 30 s. The remarkable\nelectrochemical performance of NiCo₂O₄@MnMoO₄ CSNAs//AC ASCs is attributed to its enhanced surface area,\nabundant electroactive sites, facile electrolyte infiltration into\nthe 3D NiCo₂O₄@MnMnO₄ nanoarrays\nand fast electron and ion transport path.