Recent advances in state-of-the-art 2D MXenes: Synthesis, mechanical and tribological properties

Two-dimensional transition metal carbides, nitrides, and carbonitrides, collectively known as MXenes, have attracted significant attention in various fields, such as electromagnetic shielding, sensor technology, and energy storage, owing to their unique layered structure, excellent electrical conductivity, and tunable surface chemistry. Although several recent reviews have covered the mechanical and tribological properties of MXenes, the relationship among their structural characteristics, mechanical performance, and tribological behavior requires further systematic exploration. This review aims to comprehensively summarize the methodologies for MXene synthesis, elucidate their mechanical properties, and explore the mechanisms underlying their tribological behaviors. By integrating theoretical calculations with experimental investigations, we elucidate the nanomechanical characteristics of MXenes and clarify the superlubricious behavior resulting from their low shear strength. Moreover, we explore their applications as lubricant additives, solid lubricant coatings, and reinforcing phases in composites. To address the dispersion challenges of MXenes in base oils, we propose innovative strategies, including covalent functionalization and the development of hybrid materials, which can significantly improve interfacial compatibility and wear resistance. Additionally, this review deliberates on the latest progress in the applications of MXenes in triboelectric nanogenerators, biotribology, and nanotribology, highlighting their potential as self-powered sensors for flexible wearable devices and as lubricating agents for artificial joints. Finally, we propose some challenges and future perspectives relevant to the continuous development of MXenes in the rapidly growing field of tribology.