Band engineering in Ti₂N/Ti₃C₂T_x-MXene interface enhance the performance of aqueous NH₄⁺-ion hybrid supercapacitors

The aqueous hybrid supercapacitor (AHSC) based on ammonium ion (NH₄⁺) is an interesting energy storage device with excellent properties. However, the scarcity of appropriate and effective cathode materials limited its practicality. Two-dimensional (2D) transition metal nitrides, carbides, or carbonitrides (MXenes) show potential as cathode materials, but their low capacitance limits their applicability. Here, we synthesized N-functionalized 2D MXene (Ti₃C₂T_x) with Ti₂N interface engineering (Ti₂N/Ti₃C₂T_x), which displayed not only superior capacitance and rate capability but also a cycling stability than pristine Ti₃C₂T_x. Ex-situ XRD and XPS were used to study the charge storage mechanism at the interface of Ti₂N/Ti₃C₂T_x. Furthermore, density functional theory (DFT) calculations were employed to validate the superior conductivity at the interface of the Ti₂N/Ti₃C₂T_x (T_x = OH) electrode. Moreover, AHSC was assembled with the Ti₂N/Ti₃C₂T_x as cathode, and activated carbon as anode possesses outstanding energy storage performance. This study not only elucidates the charge storage process of Ti₂N/Ti₃C₂T_x but also provides new insights for designing novel cathode materials for energy storage devices.