2D titanium carbide (Ti 3 C 2 T x MXene) has potential application in flexible/ transparent conductors because of its metallic conductivity and solution processability. However, solution-processed Ti 3 C 2 T x films suffer from poor hydration stability and mechanical performance that stem from the presence of intercalants, which are unavoidably introduced during the preparation of Ti 3 C 2 T x suspension. A proton acid colloidal processing approach is developed to remove the extrinsic intercalants in Ti 3 C 2 T x film materials, producing pristine Ti 3 C 2 T x films with significantly enhanced conductivity, mechanical strength, and environmental stability. Typically, pristine Ti 3 C 2 T x films show more than twofold higher conductivity (10 400 S cm −1 vs 4620 S cm −1 ) and up to 11-and 32-times higher strength and strain energy at failure (112 MPa, 1,480 kJ m −3 , vs 10 MPa, 45 kJ m −3 ) than films prepared without proton acid processing. Simultaneously, the conductivity and mechanical integrity of pristine films are also largely retained during the long-term storage in H 2 O/O 2 environment. The improvement in mechanical performance and conductivity is originated from the intrinsic strong interaction between Ti 3 C 2 T x layers, and the absence of extrinsic intercalants makes pristine Ti 3 C 2 T x films stable in humidity by blocking the intercalation of H 2 O/O 2 . This method makes the material more competitive for real-world applications such as electromagnetic interference shielding.

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