Superlubricity of ionic liquids at metal interfaces induced by tribochemical reactions

Ionic liquids (ILs) have demonstrated significant potential in achieving superlubricity. However, existing studies have predominantly focused on ceramic interfaces, while the superlubricity of metal interfaces in engineering applications warrants more in-depth investigation. This study systematically explores the superlubricity of the amphiphilic IL 1-butyl-2,3-dimethylimidazolium tetrafluoroborate on three typical metal interfaces: iron (Fe), copper (Cu), and aluminum (Al). Meanwhile, we evaluate the adsorption capacity of the BF-4 anion and the changes in charge transfer at the frictional interfaces. Surface analyses and density functional theory (DFT) calculations reveal that the BF-4 anion induces an anchoring effect at the metal interfaces through friction processes, forming a chemisorbed film that effectively transfers shear forces to the liquid-solid interface. Notably, the IL-Fe interface shows the least charge transfer, leading to a weaker liquid-solid interfacial interaction and significantly reducing the Fe surface's friction force, a key factor in achieving superlubricity. This research extends the application scope of ILs in superlubricity technology and provides new insights and methods for the structural design and performance optimization of ILs.