Facilitating macroscopic superlubricity through graphene oxide nanosheet additives in phosphoric acid

The field of superlubricity is garnering significant global interest amid the ongoing energy crisis. Various liquids can achieve superlubricity under ambient conditions; however, this limits their applications, such as in acidic environments. Consequently, enhancing anti-wear properties and reducing the coefficient of friction (COF) have become pressing challenges. Graphene-based materials are being extensively studied for tribological applications, attributed to their unique molecular structures and lubricating properties, often serving as lubricating additives to significantly reduce COF. In this study, graphene oxide (GO) nanosheets were utilized as lubricating additives in phosphoric acid (H3PO4; pH = 1.5) to explore lubrication enhancement in acidic environments. An ultralow COF of 0.001 was achieved, accompanied by reduced surface roughness and increased contact pressure (by 96.42 %), following the lubrication with GO-H3PO4. The reduction in COF post-lubrication with GO-H3PO4 is ascribed to three primary factors: the formation of a tribofilm via chemical reactions (comprising silica and phosphorus oxide layers), the hydrogen bond effect leading to a hydrated water layer with low shear strength, and the adsorption of GO nanosheets on the friction surface, facilitating friction transfer from Si3N4/Si3N4 to GO/GO.