Free-Standing Defect-Enriched Ti ₃ C ₂ T _x MXene/Carbon Nanotube Hybrid Films for High-Performance Supercapacitors

MXene (M n +1 X n T x, n = 1–3) materials have emerged as promising electrodes for electrochemical energy storage owing to their high electrical conductivity, rich surface terminations, and mechanical robustness. Among them, titanium carbide (Ti 3 C 2 T x ) MXene has gained considerable attention due to its high surface area and excellent charge storage capabilities. However, the development of flexible, scalable, and current-collector-free Ti 3 C 2 T x electrodes remains a major challenge for practical applications. Herein, we report a free-standing-functionalized carbon nanotube (FCNT) film integrated with a thin layer of Ti 3 C 2 T x MXene (FCNT-Ti 3 C 2 T x ) as a lightweight and flexible supercapacitor electrode. The self-supported CNT network provides high mechanical strength and electrical conductivity, while the Ti 3 C 2 T x nanoflakes introduce abundant electrochemically active sites. Notably, positron annihilation lifetime spectroscopy reveals the presence of multivacancy cluster defects in Ti 3 C 2 T x, which significantly enhance ion accessibility and charge storage, resulting in an eightfold improvement in specific capacitance compared to pristine FCNT electrodes. The FCNT-Ti 3 C 2 T x electrode exhibits stable and superior electrochemical performance across acidic, basic, and neutral aqueous electrolytes. A high specific capacitance of 1203 F g −1 at 3.3 A g −1 is achieved in KOH electrolyte. These results highlight the effectiveness of defect-enriched MXene-FCNT hybrid architectures with very low Mxene loading (∼75 μg/cm 2 ), demonstrating the strong potential of this free-standing, flexible, and current-collector-free electrode for next-generation aqueous supercapacitors.