Ti₂NbC₂T_x MXene Nanosheets as an Ordered Double Transition Metal Electrode for High-Performance Supercapacitors

The increasing demand for advanced materials in energy storage underscores the importance of chemical diversity in nanomaterials. Ordered double transition metal (DTM) MXenes have emerged as promising atomically layered 2D materials. This study investigates the flexible Ti 2 NbC 2 T x MXene, synthesized from the ordered Ti 2 NbAlC 2 MAX phase, as a supercapacitor electrode material. Electrochemical analyses revealed specific capacitances of 322 and 642 F g –1 at a current density of 0.5 A g –1 in Na 2 SO 4 (Na) and H 2 SO 4 (H) electrolytes, respectively. Ti 2 NbC 2 T x MXene exhibited exceptional cycling stability, retaining 95% capacitance in Na 2 SO 4 and 100% in H 2 SO 4 after 10,000 charge/discharge cycles. Furthermore, an asymmetric supercapacitor (ASC) was fabricated using Ti 2 NbC 2 T x MXene as the positive electrode and overcapacitive activated carbon as the negative electrode with PVA-Na and PVA-H gel electrolytes. The ASC achieved energy densities of 31.1 and 34.0 W h kg –1 for PVA-Na and PVA-H electrolytes, respectively. These results highlight the potential of Ti 2 NbC 2 T x MXene, with its unique ordered structure and double transition metal composition, for foundational research and applications in advanced energy storage technologies.