Synthesis and loading-dependent characteristics of nitrogen-doped graphene foam/carbon nanotube/manganese oxide ternary composite electrodes for high performance supercapacitors.

The ternary composite electrodes, nitrogen-doped graphene foam/carbon nanotube/manganese dioxide (NGF/CNT/MnO2 ), have been successfully fabricated via chemical vapor deposition (CVD) and facile hydrothermal method. The morphologies of the MnO2 nanoflakes presented the loading-dependent characteristics and the nanoflake thickness could also be tuned by MnO2 mass loading in the fabrication process. The correlation between their morphology and electrochemical performance was systematically investigated by controlling MnO2 mass loading in the ternary composite electrodes. The electrochemical properties of the flexible ternary electrode (MnO2 mass loading of 70%) exhibited a high areal capacitance of 3.03F/cm2 and a high specific capacitance of 284F/g at the scan rate of 2mV/s. Moreover, it was interesting to find that the capacitance of the NGF/CNT/MnO2 composite electrodes showed a 51.6% increase after 15,000 cycles. The gradual increase in specific capacitance was due to the formation of defective regions in the MnO2 nanostructures during the electrochemical cycles of the electrodes, which further resulted in increased porosity, surface area, and consequently increased electrochemical capacity. This work demonstrates a rarely reported conclusion about loading-dependent characteristics for the NGF/CNT/MnO2 ternary composite electrodes. It will bring new perspectives on designing novel ternary or multi-structure for various energy storage applications.