An N-doped TiO₂ anchored Ti₃C₂T_x MXene for high-performance supercapacitors with a coin-cell configuration

One of the most significant challenges for next-generation supercapacitors is developing high-performance electrode materials. This study presents the synthesis of N-TiO₂@MXene in situ grown on conductive MXene sheets using a cost-effective, urea-assisted, scalable one-step hydrothermal method. Furthermore, structural and spectroscopic analyses show that crystalline N-doped TiO₂ nanodomains adhere to the layered Ti₃C₂T_x MXene, forming a hierarchical composite. in situ growth effectively reduces MXene restacking, increases interlayer spacing, and creates continuous electron-transport pathways, while incorporating defect-rich heterointerfaces that accelerate charge transfer and ion diffusion. The N-TiO₂@MXene electrode achieves a specific capacitance of 212.9 F g^-1 at 1 A g^-1, representing an approximately 55% increase compared to those of the pristine MXene (137 F g^-1) and other externally mixed TiO₂ and MXenes. Electrochemical impedance analysis shows that the hybrid system has significantly lower charge-transfer resistance and faster ion-transport kinetics. Long-term stability studies show 81.7% capacitance retention after 10 000 cycles at near-unity coulombic efficiency, indicating exceptional electrochemical durability. The (N-TiO₂@MXene//N-TiO₂@MXene) configuration produces a symmetric coin-cell device exhibiting a specific capacitance of 57.9 F g^-1, an energy density of 11.58 Wh kg^-1, and consistent cycling performance. A practical demonstration utilizing five series-connected coin cells effectively powers a digital clock, confirming the device's practical application. This study outlines a straightforward in situ interfacial engineering approach for fabricating defect-rich MXene-oxide heterostructures, thereby facilitating the development of high-rate, durable, and scalable energy storage systems.