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 (Mo₂CT_x) 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 Mo₂CT_x MXene contributed to the superlubricity. This work demonstrates the promising potential of Mo₂CT_x MXene in improving superlubricity properties, which could accelerate the application of superlubricity in mechanical systems.