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 (V Ti ) influence the mechanical and electrochemical behavior of Ti 3 C 2 T x MXene. A moderate level of V Ti increases the in-plane modulus of monolayer Ti 3 C 2 T x 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 V Ti improves the electrochemical performance of MXenes. DFT indicates that partial occupation of V Ti by H 2 O, H +, or Li + redistributes charge and increases lattice stiffness, while coalescence impedes electron transport and suppresses capacitance at higher V Ti . This study deepens the understanding of vacancies in MXenes and provides a route to tune their properties.