Shear-Induced Interfacial Structural Conversion Triggers Macroscale Superlubricity: From Black Phosphorus Nanoflakes to Phosphorus Oxide.

As a new two-dimensional (2D) material, black phosphorus (BP) exhibits great potential for friction reduction. However, achieving macroscale superlubricity with a BP coating remains a great challenge. In this study, we designed a new lubrication system to achieve superlubricity with a BP coating at the macroscale, involving the formation of a BP coating with deposited BP nanoflakes, followed by water lubrication. Robust superlubricity with a coefficient of friction of 0.001 can be achieved on the BP coating in a pure water environment. The superlubricity mechanism is mainly attributed to the shear-induced interfacial structural conversion of BP to phosphorus oxide, leading to the formation of tribofilms on the friction pairs with extremely low shear strength. This finding provides a new strategy for achieving superlubricity of 2D material coatings at the macroscale, which has important implications for the development of novel superlubrication systems for industrial applications.