Abstract
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 Ti(3)C(2)T(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 Ti(3)AlC(2) MAX formation. The defect densities propagate from precursors to final MXenes, enabling the fabrication of a series of Ti(3)C(2)T(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 Ti(3)C(2)T(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.