MXene-substrate adhesion - Towards more efficient and durable coatings

MXenes have emerged as promising solid lubricants due to their two-dimensional (2D) nature and tunable composition. However, their usage in technological applications is often hindered by a poor adhesion to substrates and peel-off during sliding, especially under high contact stress. In this contribution, we combine density functional theory (DFT) simulations and ball-on-flat tribological experiments to elucidate how adhesion to the underlying substrate governs the performance of multi-layer Ti3C2T x coatings. The results reveal a clear correlation between the computationally predicted adhesion strength on different substrates, namely Fe, Fe2O3, Si, SiO2, and the effective tribological performance: MXene coatings on steel substrate maintaining their native oxide scale demonstrated an enhanced durability and friction reduction, while coatings on Si wafers rapidly exfoliate due to poor interfacial adhesion. Finally, we present an effective strategy to improve the adhesion of Ti3C2T x on silicon, exploring the doping of Si with boron and phosphorus. DFT calculations demonstrate that doping enhances adhesion by altering the electron distribution exposed by surface, especially in case of boron. Our findings underscore the critical role of substrate adhesion and provide design strategies to boost the applicability of MXenes in lubrication technologies.