In this study, black phosphorus quantum dots (BPQDs) have been successfully prepared at a low cost and high yield by the liquid-based high-energy ball milling method. The obtained BPQDs with an average lateral size of 6.5 ± 3 nm and a thickness of 3.4 ± 2.6 nm dispersed stably in ethylene glycol (EG). A robust macroscale superlubricity state (μ, 0.002) was achieved under a high contact pressure of 336 MPa via the lubrication of BPQDs-EG aqueous suspension (BPQDs-EG aq ) at the Si 3 N 4 /sapphire frictional interface. The wear rate lubricated by BPQDs-EG aq suspension account for 5.96% of that lubricated by EG aqueous solution (EG aq ), demonstrating the improvement in the antiwear property with the addition of BPQDs. The rolling effect of BPQDs and the low shear stress between the BPQDs interlamination played important roles in the improvement in the antiwear property. The oxidative products of BPQDs (P x O y ) contributed to the effective realization of macroscale superlubricity. This work realized macroscale superlubricity at a high contact pressure by combining the BPQDs with special liquid molecules and provided the great potential in industrial applications.

Superlubricity has recently raised an increasing interest owing to its great potential in energy saving and environmental benefits. Yet how to obtain stable superlubricity under an ultrahigh contact pressure (>1 GPa) still remains a challenge. Here, we demonstrate that robust liquid superlubricity can be realized even under a contact pressure of 1193 MPa by lubrication with partially oxidized black phosphorus (oBP) nanosheets. The analysis indicates that the oBP nanosheets that absorb large amounts of water molecules are retained at the friction interface and transform the friction pairs interface to that between the oBP nanosheets. Molecular dynamics simulation demonstrates that water molecules could be retained at the friction interface even under the ultrahigh contact pressure owing to the abundant P=O and P–OH bonds formed on the oBP nanosheet surfaces, contributing to the achievement of stable superlubricity under the ultrahigh contact pressure. This work has the potential of introducing the liquid superlubricity concept in diverse industrial applications involving high-contact-pressure operating conditions.

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