Understanding the stability difference between MXenes and TiC bulk: Insights from DFT calculations

Abstract

MXenes are of great interest due to their unique structure and versatile properties but the instability of MXenes is the main limit for their large-scale applications. In contrast, transition metal carbides with C-M bonds are very robust. An atomistic understanding of the influence of layer thickness in MXenes on their properties in comparison to transition metal carbides by first-principle calculations could reveal scientific insights. This work employed the recently developed method for theoretically calculating exchange current density method to investigate the corrosion behavior of a series of Ti_n+1C_n MXenes and TiC (111). The surface-related properties, electrochemical properties including polarization curves of anodic dissolution and cathodic hydrogen evolution reaction (HER) of Ti_n+1C_n and TiC (111) were simulated and compared systematically. Ti₂C MXene possesses the most positive equilibrium potential, the most positive exchange current density, and the most positive corrosion current density, while TiC (111) exhibits the lowest corrosion current density. With the largest surface relaxation energy, the largest surface relaxation energy density, the lowest exchange current density, and the most positive reaction energy in comparison with MXenes, TiC (111) shows the highest stability and corrosion resistance. Moreover, a strategy of introducing N doping is proposed to increase the corrosion resistance of MXenes.