Sustained Superlubricity in Mo₂TiC₂ MXenes Facilitated by Tribocatalytic Reaction at The Sliding Interfaces

The materials community has witnessed remarkable progress over recent decades in exploring various attractive properties of MXenes due to their excellent, physical, chemical, and mechanical properties. These properties encompass its outstanding physical, chemical, and mechanical attributes, all of which have demonstrated exceptional potential across diverse application domains, ranging from energy storage, and electromagnetic shielding, to advancements in biological and medical technology. Recent interest in exploring their tribological properties is rooted in their layered structure and ability to shear easily coupled with their robust mechanical properties. While numerous studies have been published showcasing MXenes' promise as an additive under lubricated conditions or as a solid lubricant in dry environments, the critical factor of long-term stability as a reliable lubricant in either scenario has remained unproven, thereby constraining its full application potential within the lubrication industry.<br/>In this current work, we study an ordered double transition metal MXene (Mo₂TiC₂) and demonstrate its exceptional tribological performance in dry nitrogen atmosphere using macro-scale pin-on-disc tribo-testing. We demonstrate sustained superlubricity, with a friction coefficient as low as 0.005, persisting over the extensive course of linear sliding, spanning an astonishing distance of 86 kilometers, with no signs of failure and minimal wear rates. We will elucidate the intricate mechanisms governing wear and friction, which underpin such extraordinary tribological performance. Additionally, we explain the pivotal role played by tribo-catalytic reactions at the sliding interface, which yield a stable, lubricious tribolayer. This milestone achievement represents a game-changer across a spectrum of tribological applications and marks a significant leap forward in the development of innovative solid lubricants based on MXene.<br/><br/><i>Work performed at the Center for Nanoscale Materials, a </i><i>U.S. Department </i><i>of Energy Office of Science User Facility, was supported by the U.S. DOE, Office of Basic Energy Sciences, under Contract No. DE-AC02-06CH11357</i><i>.</i>