MnO Nanoflowers Electrodeposited on Vertically Aligned CNTs as Binder-Free Electrodes for High-Rate Supercapacitors.

Supercapacitors are gaining attention for their ability to deliver rapid energy discharge while maintaining a high energy storage capacity, effectively bridging the gap between capacitors and batteries. In this paper, we report the performance of a high-capacity, fast-charging, and reliable supercapacitor consisting of nanoflower-like manganese dioxide (MnO) decorated on CVD-grown carbon nanotube (CNT) electrodes fabricated using a simple and efficient room-temperature electrodeposition method. The binder-free, self-supporting MnO@CNT composite electrodes formed on a flexible carbon fabric demonstrated excellent electrochemical energy storage capabilities, as confirmed by cyclic voltammetry (CV) and galvanostatic charge-discharge (GCD) experiments. The MnO loading significantly affected the electrode's capacity, with the highest specific capacitance of 219 F g achieved at low mass loading (3.37 mg cm) and the highest areal capacitance of 1.5 F cm for high mass loading (15.6 mg cm). The rectangular curve observed in CV experiments at faster scan rates (5-50 mV s) and the triangular curve observed in the GCD experiment at high current densities (0.1 to 0.5 A g) demonstrate the high-rate capability of the MnO@CNT electrode. The electrode also showed outstanding stability, retaining 88% of its initial capacity after 7000 cycles. Electrochemical impedance spectroscopy (EIS) measurement and corresponding analysis of the data indicated fast charge transfer kinetics and facile ion diffusion into the MnO electrode, which is attributed to the nanoflower-like structure of MnO formed on porous carbon nanotubes, leading to excellent rate performance. With these advancements, our MnO@CNT supercapacitors have significant potential in electric vehicles, complementing batteries by enabling fast discharge for quick acceleration.