Flexible Free-Standing MoO/TiCT MXene Composite Films with High Gravimetric and Volumetric Capacities.

Enhancing both the energy storage and power capabilities of electrochemical capacitors remains a challenge. Herein, TiCT MXene is mixed with MoO nanobelts in various mass ratios and the mixture is used to vacuum filter binder free, open, flexible, and free-standing films. The conductive TiCT flakes bridge the nanobelts, facilitating electron transfer; the randomly oriented, and interconnected, MoO nanobelts, in turn, prevent the restacking of the TiCT nanosheets. Benefitting from these advantages, a MoO/TiCT film with a 8:2 mass ratio exhibits high gravimetric/volumetric capacities with good cyclability, namely, 837 C g and 1836 C cm at 1 A g for an ≈ 10 µm thick film; and 767 C g and 1664 C cm at 1 A g for ≈ 50 µm thick film. To further increase the energy density, hybrid capacitors are fabricated with MoO/TiCT films as the negative electrodes and nitrogen-doped activated carbon as the positive electrodes. This device delivers maximum gravimetric/volumetric energy densities of 31.2 Wh kg and 39.2 Wh L, respectively. The cycling stability of 94.2% retention ratio after 10 000 continuous charge/discharge cycles is also noteworthy. The high energy density achieved in this work can pave the way for practical applications of MXene-containing materials in energy storage devices.