MnO2 nanoflakes grown on 3D graphite network for enhanced electrocapacitive performance

Abstract

Free-standing 3D graphite (3DG) with an interconnected porous network and a highly conductive backbone was prepared by a chemical vapor deposition technique with Ni foam as the sacrificial template and styrene as the carbon precursor. The 3D graphite network serves as an excellent scaffold to grow MnO₂ nanoflakes through a hydrothermal reaction between 3DG and KMnO₄ aqueous solution. The interconnected and conductive 3D graphite network offers a pathway for fast electron and ion transport, while the MnO₂ nanoflakes that emanate from the backbone surface of 3DG minimize the interfacial contact resistance between 3DG and MnO₂, favoring the effective electron transport from the 3DG skeleton to MnO₂ nanoflakes. As a result, the 3DG–MnO₂ composite electrode with 13% MnO₂ nanoflakes exhibited a specific capacitance of 210 F g⁻¹ at a constant discharge current density of 2.0 A g⁻¹, which still remained at 202 F g⁻¹ at a high current density of 15 A g⁻¹. Moreover, a good capacitance retention of 75% and an outstanding coulombic efficiency of 97.8% were achieved after 4000 cycles of galvanostatic charge–discharge. These superior capacitive properties make the 3DG–MnO₂ composite one of the promising electrodes for electrochemical energy storage.