High-Temperature Oxidized Mo₂CT MXene for a High-Performance Supercapacitor

Molybdenum carbide (Mo₂CT MXene) did not possess suitable properties for supercapacitors. Herein, a short oxidation method of Mo₂CT in air at moderately high temperatures is proposed for fabricating a Mo₂C/MoO₃ heterostructure. The stability of Mo₂CT in air up to 700 °C and the phase transition at higher temperatures are confirmed. Such a heterostructure is beneficial in reducing the diffusion energy barrier of H⁺. In the aqueous system, the Mo₂C/MoO₃ electrode delivers a capacitance of up to 811 F g^-1. A fully assembled symmetric solid-state supercapacitor delivers 224 F g^-1 with an excellent retention rate of 91.05% after 7500 cycles. Besides, the supercapacitor can work at the low temperature of -60°, showing good low-temperature properties. The approach presented in this work opens a promising way to turn a neglected MXene, assumed to be unsuitable for supercapacitors, into one of the top-performing supercapacitor electrodes.