Cation-induced Ti3C2Tx MXene hydrogel for capacitive energy storage

To date, Ti3C2Tx MXene has been a promising candidate for energy storage field, however the construction of 3D MXene hydrogel with their inherent hydrophilicity and high conductivity remains a challenge. Herein, a series of Ti3C2Tx MXene hydrogel was fabricated successfully via a facile and fast cation-induced strategy. Typically, the formation of hydrogel is stem from the quick cross-linking of Ti3C2Tx nanosheets, accompanying with the intercalation of high-concentration cation between the layers. Characterization analyses have demonstrated that the cation-induced Ti3C2Tx hydrogel possesses 3D porous structure and controllable basal spacing, which could synergistically facilitate fast diffusion of electrolyte ions and accessibility of electrochemical active sites. Density functional theory (DFT) calculation shows that larger hydrated radii and more intercalated cation are favorable for the expansion of basal spacing thermodynamically. As a result, the excellent capacitance and high rate-capability are both realized in cation-induced Ti3C2Tx hydrogels. Especially, as-synthesized Al-Ti3C2Tx hydro-gel delivery a remarkable capacitance of 675F/g at 1 A/g, along with a specific energy density of 46 Wh/kg when the power density is 349 h/kg, which is superior to the previous reported Ti3C2Tx electrodes. Besides, the well-designed H-Ti3C2Tx hydrogel still achieves 206F/g capacitance when the scan rate is up to 1 V/s, and it could withstand 5000 cycles with only 8% loss of capacitance. This work not only illuminates a straightforward way to construct high-performance MXene electrode for capacitive energy storage, but also provides a new guideline over the manipulation of interlayer spacing and morphology of 2D colloid materials.