Superlubricity via operando formation of MoS2/S8 heterojunctions on steel surface with amorphous carbon protection

Superlubricity can cancel energy loss caused by friction and wear, and holds great promise for moving machine parts and carbon neutrality. However, the superlubricity under particularly on steel surface in an open atmosphere is an essential precondition for industrial use remaining a challenge. A novel strategy was proposed in this work the hybride system of a-C:H-ammonium tetrathiomolybdate in situ decomposed into MoS2 layers and sulfur monomer (S8) via flash heating induced by the friction force. The first principles calculations with van der Waals interaction considered confirming the increase in the interlayer spacing from the value of 0.65 nm for pristine bilayer to 1.07 nm for MoS2 interfaces with S8 sandwiched, in accordance well with detailed experimental results. A reduction in the interlayer binding energy and in the energy barriers for sliding the MoS2 layers on basel planes by more than 65%. Further, a reduction in the interfacial sliding energy barrier for S8 sandwiched between MoS2 from that of MoS2 layers with H2O sandwiched. Therefore, the superlubricity in the ambient condition is attributed to the incommensurate contact of S8/MoS2/a-C:H that the presence of S8 that increases the interlayer spacing of MoS2 with low EB.