Covalent surface grafting of Ti3C2Tx flakes for enhancement of symmetric supercapacitor performance

In this work the covalent surface modification of MXene flakes (Ti3C2Tx) was proposed for the increasing of the performance of subsequently created symmetric supercapacitor. Covalent surface modification was performed with utilization of diazonium salts (hydrophobic or hydrophilic) and plasmon-assisted photochemistry. Applied procedure allows to block the reactive (weak and/or catalytically active) sites on flakes surface and increase the flakes interplanar spacing, both enhancing the functionality of an MXene-based supercapacitor. Especially pronounced positive effect gives the surface modification with hydrophilic chemical moieties. In particular, we observed increase of supercapacitance from 197 to 284 F g−1 in acidic and from 86 to 142 F g−1 in alkaline conditions for flakes grafted with –C6H4–COOH chemical moieties at scan rate 20 mV/s. The flakes grafted with hydrophobic chemical moieties allow to achieve almost constant value of supercapacitance for different speed of charge discharge. In addition, the surface grafting prevents the supercapacitor degradation and decelerates the spontaneous discharge in open circuit mode. These results suggest strategy for further improvement of MXene-based supercapacitors as energy storage device.