Hierarchical flower-like MnO2@nitrogen-doped porous carbon composite for symmetric supercapacitor: Constructing a 9.0 V symmetric supercapacitor cell

In this study, we fabricated a symmetric supercapacitor using a composite composed of manganese dioxide (MnO2)/porous carbon doped with nitrogen (N-PC). The N-PC was prepared from a covalent organic framework. Transmission electron microscopy proved that the hierarchical flower-like MnO2 nanoparticles were decorated on the N-PC surface. In a three-electrode set-up, the MnO2@N-PC (10%) composite delivered a specific capacitance of 269 F g−1 at the current density 0.5 A g−1. An aqueous symmetric system showed capacitance of 134.5 F g−1 with a specific energy of 42.1 Wh Kg−1 and specific power of 750 W Kg−1 at 0.5 A g−1. The higher specific power of the composite may be due to the synergetic effect of MnO2 (flower-like morphology) and N-PC (high surface area, hetero-atom doping, and microporous structure). Besides, we fabricated a 9.0 V symmetric supercapacitor through a series connection of six 1.5 V cells. These results ensured that the MnO2@N-PC composite is a preferable material for energy storage applications.