Interfacial Engineering of Ti 3 C 2 T x MXene With COOH‐Functionalized Multiwalled Carbon Nanotubes for High‐Voltage Ionic Liquid Supercapacitors

MXene‐based electrode materials for supercapacitor (SC) application have attracted significant research attention due to their unique physicochemical and tunable properties. However, their surface oxidation and interlayer restacking issue limits their practical viability. Herein, Ti 3 C 2 T x /MWCNT–COOH hybrids were synthesized to overcome the intrinsic limitation of pristine MXene. Resulting interaction coupling of COOH group of MWCNT with MXene's surface functionalities via hydrogen bonding and electrostatic interaction improves electrolyte accessibility and surface redox activity. Ti 3 C 2 T x /MWCNT–COOH hybrids are systematically optimized and evaluated in two electrode configuration for SC application using [EMIM][BF 4 ] ionic liquid (IL) electrolyte to widen voltage window (3 V) and to improve the energy density of the device. The bulky EMIM + /BF 4 − ions modulate the charge storage kinetics, as Dunn's kinetic analysis reveals a mixed charge storage mechanism with diffusion‐controlled pseudocapacitive behavior predominates at low scan rates, owing to fast ion transport and low desolvation penalty of the IL. The optimized Ti 3 C 2 T x /MWCNT–COOH hybrid‐based symmetric SC exhibits maximum specific capacitance of 69.63 Fg −1 at 0.2 Ag −1 , an energy density of 87.04 Wh·kg −1 with 93.33% of capacitance retention after 5000 cycles. These findings establish correlation between [EMIM][BF 4 ] electrolyte and Ti 3 C 2 T x /MWCNT–COOH electrode, providing valuable insights for the development of efficient electrode–electrolyte systems for high‐performance energy storage applications.