Innovative 2D materials for reducing friction in tribological systems: ab initio simulations coupled with experiments

Tribology, the science of friction, wear, and lubrication, plays a crucial role in improving energy efficiency across industrial and everyday applications. Controlling friction can lead to significant energy savings, as friction and wear contribute to nearly 20% of global energy consumption. Advances in tribology, particularly through innovative materials, offer substantial economic and environmental benefits, making it essential for technological progress and sustainability. Lubrication technologies rely on both liquid and solid lubricants. While liquid lubricants, such as synthetic oils, form protective films to reduce friction, they may fail under extreme conditions like high temperatures or vacuum. In such cases, solid lubricants, including graphite, diamond-like carbon (DLC), and transition metal dichalcogenides (TMDs) like MoS2 and WSe2, provide a more effective solution. These layered materials facilitate low-shear interlayer sliding, making them ideal for aerospace and precision engineering. Emerging 2D materials, such as MXenes and Transition Metal Carbo-Chalcogenides (TMCCs), combine mechanical strength with self-lubrication, representing a promising frontier in tribology. Computational simulations, particularly quantum mechanical approaches, play a pivotal role in understanding tribological phenomena at the atomic level. These methods allow for the study of interlayer sliding, adhesion, oxidation, and tribochemical reactions, guiding the design of new lubricant materials while reducing experimental costs. This thesis explores the tribological properties of advanced 2D materials through a combination of simulations and experiments. It investigates (i) the frictional behavior of titanium-based MXenes via density functional theory (DFT), (ii) the synergy between MXene-MoS2 composite coatings, (iii) the in-operando formation of MoSe2 and WSe2 lubricious layers from selenium nanoparticles, and (iv) the promising tribological performance of TMCCs (Nb2S2C and Ta2S2C). These findings contribute to the development of next-generation solid lubricants for demanding applications.