Flexible Free‐Standing MoO(3)/Ti(3)C(2)T(z) MXene Composite Films with High Gravimetric and Volumetric Capacities

Enhancing both the energy storage and power capabilities of electrochemical capacitors remains a challenge. Herein, Ti(3)C(2)T(z) MXene is mixed with MoO(3) nanobelts in various mass ratios and the mixture is used to vacuum filter binder free, open, flexible, and free‐standing films. The conductive Ti(3)C(2)T(z) flakes bridge the nanobelts, facilitating electron transfer; the randomly oriented, and interconnected, MoO(3) nanobelts, in turn, prevent the restacking of the Ti(3)C(2)T(z) nanosheets. Benefitting from these advantages, a MoO(3)/Ti(3)C(2)T(z) film with a 8:2 mass ratio exhibits high gravimetric/volumetric capacities with good cyclability, namely, 837 C g(−1) and 1836 C cm(−3) at 1 A g(−1) for an ≈ 10 µm thick film; and 767 C g(−1) and 1664 C cm(−3) at 1 A g(−1) for ≈ 50 µm thick film. To further increase the energy density, hybrid capacitors are fabricated with MoO(3)/Ti(3)C(2)T(z) 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(−1) and 39.2 Wh L(−1), 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.