Effects of Intercalation\non ML-Ti<sub>3</sub>C<sub>2</sub>T<sub><i>z</i></sub> MXene\nProperties and Friction\nPerformance

Intercalation in two-dimensional (2D) materials can modify\ntheir\nphysical, chemical, and electronic properties. This modification enables\nthe tailoring of 2D material characteristics, enhancing their performance\nand expanding their applications in various fields. The friction performance\nof 2D materials such as MoS<sub>2</sub> and graphite has a strong\ndependence on their interlayer spacing, and they exhibit an increase\nin <i>d</i>-spacing associated with a reduction in friction\nperformance. The ability to control the interlayer spacing of Ti<sub>3</sub>C<sub>2</sub>T<sub><i>z</i></sub> MXene has proven\nbeneficial for energy storage applications such as batteries and supercapacitors,\nbut no one has utilized this control of interlayer spacing for lubrication.\nIn this study, we demonstrate that interlayer spacing of multilayer\n(ML) Ti<sub>3</sub>C<sub>2</sub>T<sub><i>z</i></sub> MXene\ncan be controlled through chemical intercalation and its direct effects\non the electrical conductivity and friction performance. We observed\na notable decrease in electrical conductivity in vacuum-filtered ML-Ti<sub>3</sub>C<sub>2</sub>T<sub><i>z</i></sub> MXene films, which\nwas attributed to an increased internal resistance resulting from\nthe expansion of the interlayer gap. We also found a significant reduction\nin the coefficient of friction for ML-Ti<sub>3</sub>C<sub>2</sub>T<sub><i>z</i></sub> MXene with an increased <i>d</i>-spacing. This reduction is attributed to a weakened attraction of\nindividual ML-Ti<sub>3</sub>C<sub>2</sub>T<sub><i>z</i></sub> MXene layers (intercalated). Under a tangential force, it becomes\neasier to slide within the larger interlayer gap with weakened van\nder Waals forces. This work provides insights into the tunability\nof MXene properties through interlayer spacing, offering potential\napplications requiring materials with specific electrical and friction\ncharacteristics.