Macroscale superlubricity and durability of in situ grown hydrogenated graphene coatings

Although macroscale superlubricity reduces the friction of graphene materials, industrial application has been limited to special environments or complex strain engineering. Herein, high-quality hydrogenated graphene coatings (0 < ID/IG < 0.21) are synthesized on industrial materials in situ by hot-filament chemical vapor deposition. The ball-on-disk friction tests demonstrate that the hydrogenated graphene coatings have superior lubricating properties and long service lifetime at a macro-load of 1 N and high sliding speed (0.6 m/s) under ambient conditions (23–25 °C, 50–55 %RH). The hydrogenated graphene coatings deposited with moderate hydrogen supplies show ultra-low friction and even localized superlubricity (∼0.009) due to the critical factor of surface defect density. Long-term stability is observed after more than 24,840 laps. Molecular dynamics simulation is performed to explain the self-passivating and self-healing effects on the atomic level. The macroscale lubrication mechanism involves H atoms capturing carbon dangling σ-bonds. The high-quality and chemically inert graphene surface facilitates the formation of a thick solid tribofilm at the sliding contact interface. The chemisorbed H atoms on the graphene layer lead to continuous healing and stabilization of the defective structure during the macroscale friction test. Our new findings provide insights into the lubrication mechanism and reveal a new approach to achieving macroscale superlubricity and high durability for hydrogenated graphene coatings.