Band engineering in Ti2N/Ti3C2Tx-MXene interface to 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 (Ti3C2Tx) with Ti2N interface engineering (Ti2N/Ti3C2Tx), which displayed not only superior capacitance and rate capability but also a cycling stability than pristine Ti3C2Tx. Ex-situ XRD and XPS were used to study the charge storage mechanism at the interface of Ti2N/Ti3C2Tx. Furthermore, density functional theory (DFT) calculations were employed to validate the superior conductivity at the interface of the Ti2N/Ti3C2Tx (Tx = OH) electrode. Moreover, AHSC was assembled with the Ti2N/Ti3C2Tx as cathode, and activated carbon as anode possesses outstanding energy storage performance. This study not only elucidates the charge storage process of Ti2N/Ti3C2Tx but also provides new insights for designing novel cathode materials for energy storage devices.