Tightly intercalated Ti3C2Tx/MoO3-x/PEDOT:PSS free-standing films with high volumetric/gravimetric performance for flexible solid-state supercapacitors.

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Ti3C2Tx-MXenes have extremely promising applications in electrochemistry, but the development of Ti3C2Tx is limited due to severe self-stacking problem. Here, we introduced oxygen vacancy-enriched molybdenum trioxide (MoO3-x) with pseudocapacitive properties as the intercalator of Ti3C2Tx and PEDOT with high electronic conductivity as the co-intercalator and conductive binder of Ti3C2Tx to synthesize Ti3C2Tx/MoO3-x/PEDOT:PSS (TMP) free-standing films by vacuum-assisted filtration and H2SO4 soaking. The tightly intercalated free-standing film structure can effectively improve the self-stacking phenomenon of Ti3C2Tx, expose more active sites and facilitate electron/ion transport, thus making TMP show excellent electrochemical performance. The volumetric and gravimetric capacitance of optimized TMP-2 can reach 1898.5 F cm-3 and 523.0 F g-1 at 1 A g-1 with a rate performance of 90.5% at the current density from 1 A g-1 to 20 A g-1, which is significantly better than those of MXene-based composites reported in the literature. The directly-assembled TMP-2//TMP-2 flexible solid-state supercapacitor displays high energy/power output performances (25.1 W h L-1 at 6383.1 W L-1, 6.9 W h kg-1 at 1758.4 W kg-1) and there is no obvious change after 100 cycles at a bending angle of 180°. As a result, the tightly intercalated TMP-2 free-standing film with high volumetric/gravimetric capacitances is a promising material for flexible energy storage devices.