Exploring the solid lubrication potential of 2D black phosphorus

Black phosphorus (BP), a rather new 2D material, features excellent electronic, optical, and tribological properties, but its potential for solid lubrication is completely unexplored. Therefore, our paper aims at experimentally evaluating the solid lubrication performance of 2D black phosphorus (BP) in dependence of the coating thickness by performing tribological tests under ball-on-disc linear-reciprocating sliding in dry conditions. BP was spray-coated onto bearing steel discs, while the effect of the thickness was evaluated by fabricating two BP coatings, BP-thin and BP-thick. Our results demonstrate that BP coatings reduced friction compared to uncoated reference samples. However, only thicker BP coatings are capable to induce a stable, long-lasting four-fold friction reduction, which was mainly traced back to the formation of a stable tribofilm in the contact zone. Therefore, our study proves the potential of BP for solid lubrication purposes with the overall aim to kick-start and boost more research endeavours in this newly emerging field.