Two-dimensional molybdenum carbide (MXene) as an efficient nanoadditive for achieving superlubricity under ultrahigh pressure

In this study, a robust macroscale liquid superlubricity with a coefficient of friction of 0.004 was achieved by introducing molybdenum carbide (Mo2CTx) MXene nanoparticles as lubricating additives in a lithium hexafluorophosphate-based ionic liquid at Si3N4—sapphire interfaces. The maximal contact pressure in the superlubricity state could reach 1.42 GPa, which far exceeds the limit of the superlubricity regime in previous studies. The results indicate that a composite tribofilm (mainly containing molybdenum oxide and phosphorus oxide) that formed at the interface by a tribochemical reaction contributed to the excellent antiwear performance. Furthermore, the extremely low shear strength of the tribofilm and the interlayers of Mo2CTx MXene contributed to the superlubricity. This work demonstrates the promising potential of Mo2CTx MXene in improving superlubricity properties, which could accelerate the application of superlubricity in mechanical systems.