Quantitative Defect-Property Correlations in Ti₃C₂T_x MXenes via Precursor-Controlled Defect Engineering

Defect engineering holds great promise for tailoring the multifunctional properties of MXenes. However, quantitative correlations between defect and material performance remain largely unexplored due to the lack of a reliable strategy to precisely control defect densities. Here, we demonstrate that the defect density of Ti₃C₂T_x MXenes-including titanium and carbon vacancies, substitutional oxygen defects, and the associated lattice strain-is precisely controlled by adjusting carbon stoichiometry during TiC precursor synthesis and aluminum content during Ti₃AlC₂ MAX formation. The defect densities propagate from precursors to final MXenes, enabling the fabrication of a series of Ti₃C₂T_x MXenes with systematically controlled defect densities. This allows a quantitative correlation between defect density and multifunctional properties including electrical and thermal conductivities, infrared emissivity, electromagnetic shielding effectiveness, Joule heating performance, and oxidation stability. The defect-minimized Ti₃C₂T_x MXene exhibits outstanding performance, with an electrical conductivity of 26,000 S cm^-1, thermal conductivity of 57 W m^-1 K^-1, electromagnetic shielding effectiveness of 90.5 dB at 10 µm, Joule heating performance of 263 °C at 1.5 V, ultralow infrared emissivity of 0.05, and superior oxidation resistance (activation energy of 72 kJ mol^-1). Furthermore, this work establishes a comprehensive quantitative framework linking defect structure to multifunctional performance and stability.