Tightly intercalated Ti 3 C 2 T x /MoO 3- x /PEDOT:PSS free-standing films with high volumetric/gravimetric performance for flexible solid-state supercapacitors.

Ti 3 C 2 T x -MXenes have extremely promising applications in electrochemistry, but the development of Ti 3 C 2 T x is limited due to severe self-stacking problem. Here, we introduced oxygen vacancy-enriched molybdenum trioxide (MoO 3- x ) with pseudocapacitive properties as the intercalator of Ti 3 C 2 T x and PEDOT with high electronic conductivity as the co-intercalator and conductive binder of Ti 3 C 2 T x to synthesize Ti 3 C 2 T x /MoO 3- x /PEDOT:PSS (TMP) free-standing films by vacuum-assisted filtration and H 2 SO 4 soaking. The tightly intercalated free-standing film structure can effectively improve the self-stacking phenomenon of Ti 3 C 2 T x , 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.