Influence of In Situ and Ex Situ Incorporated Cations on the Supercapacitor Performance of Multilayer Ti₃C₂T_x MXene

The effect of the addition of monovalent and divalent cations on the electrochemical performance of multilayer MXene is investigated by their incorporation in the late etching stage. Although there have been numerous reports on cation preintercalation, the simultaneous addition of cations while etching has not been reported before. This simultaneous incorporation of cations has enhanced the morphological, functional, and structural signatures of the material. The synthesis process adopted is completely devoid of additional steps of sonication and centrifugation, usually employed to obtain delaminated MXene. The electrochemical performance of multilayered MXene modified by this technique is similar to that of delaminated MXene. The enhanced performance indicates that the cation incorporation leads to inherent delamination and enhanced etching. This, in turn, enhances the electrochemical activity of the material. Structural and functional characterizations demonstrate cation-assisted cross-linking of the negatively charged nanosheets. A specific gravimetric capacitance of 277 F/g was obtained for multilayer MXene samples incorporated by Ni 2+ cations. A 135% improvement in capacitance compared to that of pristine MXene was obtained. A symmetric supercapacitor device using the optimized Ni modified MXene as electrode and H 2 SO 4 as the electrolyte gave a specific capacitance of 55.5 F/g at a current density of 0.5 A/g, energy density of 4.9 Wh/kg, power density of 233 W/kg, and cycling stability of more than 99% at a scan rate as high as 500 mV/s for 5000 cycles.