Significantly Enhanced Oxidation Resistance and Electrochemical Performance of Hydrothermal Ti3C2Tx MXene and Tannic Acid Composite for High-Performance Flexible Supercapacitors.

The electrochemical performances of Ti₃C₂T_x MXene are severely restricted by the easy oxidation and restacking. Herein, tannic acid (TA) is introduced into Ti₃C₂T_x dispersion, and the mixed dispersion is further subjected to a simple hydrothermal treatment to prepare the hydrothermal Ti₃C₂T_x and TA composite (h-Ti₃C₂T_x@h-TA). Due to the decomposition of TA into gallic acid (GA), hydrothermal TA (h-TA) is a mixture of TA and GA. The strong interaction between h-TA and MXene mainly involves chemical interaction between the hydroxyl groups in h-TA and the surface/edge Ti atoms, along with numerous hydrogen bonds. The h-TA intercalation weakens MXene restacking and increases interlayer spacing, thereby improving ion transport pathways and accessibility. The chemical interaction between the hydroxyl groups of GA and the Ti atoms significantly enhances oxidation resistance and pseudocapacitive active sites. Therefore, the h-Ti₃C₂T_x@h-TA film electrode shows significantly enhanced capacitance (848 F·g^-1 at 1 A g^-1) and cycling stability (100% retention after 20 000 cycles). Moreover, flexible sandwiched supercapacitors with symmetrical h-Ti₃C₂T_x@h-TA electrodes exhibit a high energy density of 30.1 Wh kg^-1 at a high power density of 300 W kg^-1, outperforming those of Ti₃C₂T_x-based film electrodes and sandwiched supercapacitors reported so far. The extrusion-printed microsupercapacitors with h-Ti₃C₂T_x@h-TA electrodes demonstrate high areal capacitance (135 mF cm^-2 at 5 mV s^-1) along with energy storage performance (6.74 μWh cm^-2 at 506 μW cm^-2) and cycling stability (98.8% retention after 41 460 cycles), all while maintaining excellent flexibility. These impressive results indicate the great application potential of the hydrothermal Ti₃C₂T_x MXene and tannic acid composite in flexible energy storage devices.