Defect-Driven Enhancement of Mechanical and Electrochemical Properties in Ti ₃ C ₂ T _<i>x</i> MXene

Two-dimensional (2D) MXenes are synthesized by a top-down etching of MAX phases, which could generates surface metal vacancies. However, the nature and impact of these vacancies remain unclear. We combine atomic force microscopy (AFM) nanoindentation, electrochemical studies, and density functional theory (DFT) to examine how titanium vacancies (VTi) influence the mechanical and electrochemical behavior of Ti3C2Tx MXene. A moderate level of VTi increases the in-plane modulus of monolayer Ti3C2Tx from 324 ± 44 to 432 ± 53 N m–1 and enhances the fracture force by ∼60%. The calculated effective Young’s modulus of 432 ± 53 GPa is among the highest for 2D materials. Also, moderate VTi improves the electrochemical performance of MXenes. DFT indicates that partial occupation of VTi by H2O, H+, or Li+ redistributes charge and increases lattice stiffness, while coalescence impedes electron transport and suppresses capacitance at higher VTi. This study deepens the understanding of vacancies in MXenes and provides a route to tune their properties.