Effects of Intercalation on the Interlayer Electron-Transfer Process in Mo-Based Multilayered MXene Flakes

MXene, an emerging highly conductive two-dimensional (2D) material with high cation capacity, has been widely accepted as a promising choice for next-generation electrodes in energy-storage batteries. To further improve performance, more attention should be paid to the electron-transfer process across different layers when using multilayered MXene flakes as electrodes in practical applications. In this work, threshold photoemission electron microscopy is used to characterize the transfer process of photoexcited electrons from buried layers to the top surface, with selective focus on the electron states near the Fermi level. We find that the interlayer electron-transfer process is highly sensitive to the spacing distance between neighboring layers, which varies upon temperature, cation intercalation, and flake morphology. Furthermore, ultrafast time-resolved measurements indicate that the thermal-active regime is suppressed for the interlayer electron-transfer process in intercalated MXene flakes. Our findings would serve as guidelines for the intercalation engineering of Mo-based MXene flakes, which is of critical importance in the development of applications in electrodes, capacitance, and batteries.