Electrochemically synthesized MXenes as sustainable solid lubricants: Mechanistic insights into tribofilm formation and interfacial dynamics

The development of sustainable solid lubricants is critical for reducing energy losses and material wear in advanced mechanical systems. Two-dimensional materials such as MXenes are attractive for solid lubrication due to their weak interlayer bonding, enabling low-friction sliding. However, conventional MXene synthesis relies on hazardous chemicals like hydrofluoric acid, raising environmental and safety concerns that limit scalability. Here, we report the first use of bubble-assisted electrochemically synthesized MXenes (EC-MXene) as environmentally friendly solid lubricants. EC-MXene exhibit oxygen-rich surface terminations and significantly reduced fluorine content compared to traditional MXenes. When coated on AISI 52100 steel and tested against Si 3 N 4 , Al 2 O 3 , and steel counterbodies, EC-MXene deliver excellent tribological performance, particularly against Si 3 N 4 , achieving a low and stable coefficient of friction (COF < 0.25). Surface analyses using SEM-EDS, Raman spectroscopy, TEM (SAED and EELS), and low-energy ion scattering (LEIS) reveal a robust tribofilm and dynamic replenishment mechanism that sustains lubrication by redistributing MXene flakes from pile-up zones to the sliding interface. Density Functional Theory (DFT) calculations confirm strong interfacial adhesion of EC-MXene to ceramic surfaces, supporting the observed tribological behavior. Load-dependent studies further highlight the role of adhesion and tribofilm ordering in maintaining performance. These findings position EC-MXene as a sustainable alternative to classical MXenes, combining comparable tribological properties with safer synthesis routes. Their characteristics establish EC-MXene as a benchmark for sustainable two-dimensional solid lubricants with broad potential in advanced mechanical and biotribological applications.