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

Abstract

Ti₃C₂T_x-MXenes have extremely promising applications in electrochemistry, but the development of Ti₃C₂T_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 Ti₃C₂T_x and PEDOT with high electronic conductivity as the co-intercalator and conductive binder of Ti₃C₂T_x to synthesize Ti₃C₂T_x/MoO_3−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 Ti₃C₂T_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.