Direct Chemical Synthesis of MnO2 Nanowhiskers on Transition Metal Carbide Surfaces for Supercapacitor Applications

Transition-metal carbides (MXenes) are an emerging class of two-dimensional materials with promising electrochemical energy storage performance. Herein, for the first time, by direct chemical synthesis, nanocrystalline epsilon-MnO2 whiskers were formed on MXene nanosheet surfaces (epsilon-MnO2/Ti2CTx and epsilon-MnO2/Ti3C2Tx) to make nanocomposite electrodes for aqueous pseudocapacitors. The epsilon-MnO2 nano whiskers increase the surface area of the composite electrode and enhance the specific capacitance by nearly 3 orders of magnitude compared to that of pure MXene-based symmetric supercapacitors. Combined with enhanced pseudocapacitance, the fabricated epsilon-MnO2/MXene supercapacitors exhibited excellent cycling stability with similar to 88% of the initial specific capacitance retained after 10000 cycles which is much higher than pure epsilon-MnO2-based supercapacitors (similar to 74%). The proposed electrode structure capitalizes on the high specific capacitance of MnO2 and the ability of MXenes to improve conductivity and cycling stability.