Pristine Titanium Carbide MXene Films with Environmentally Stable Conductivity and Superior Mechanical Strength

Abstract

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.

Scalable Manufacturing of Free‐Standing, Strong Ti3C2Tx MXene Films with Outstanding Conductivity

“…Single Ti 3 C 2 T x flake has been demonstrated to have outstanding Young's modulus (≈330 GPa) and tensile strength (≈17.3 GPa), [ 15 ] which suggests that Ti 3 C 2 T x is an excellent building block for fabricating strong films. However, tensile strength values above 120 MPa [ 16 ] and Young's moduli above 10 GPa [ 17 ] have yet to be demonstrated for assembled pure MXene films (Table S1, Supporting Information). To improve the tensile strength of pure MXene films, a wide range of materials, including poly(vinyl alcohol), [ 11,18,19 ] rubber, [ 20 ] cellulose nanofibers, [ 17,21,22 ] bacterial cellulose, [ 23 ] aramid nanofibers, [ 24,25 ] and graphene oxide [ 26 ] have been used in manufacturing of MXene‐based composite films (Table S2, Supporting Information).…”

“…Recently, Chen et al [ 16 ] found that processing of Ti 3 C 2 T x dispersions with ≈0.1 m hydrochloric acid (HCl) solution triggers the self‐assembly of MXene flakes. As a result, Ti 3 C 2 T x films displayed high electrical conductivity (up to 10 400 S cm −1 ) and improved tensile strength from ≈20 to 112 MPa after the HCl treatment.…”

“…As a result, Ti 3 C 2 T x films displayed high electrical conductivity (up to 10 400 S cm −1 ) and improved tensile strength from ≈20 to 112 MPa after the HCl treatment. [ 16 ] This approach demonstrated the potential to produce pure MXene films with high strength. The lower electrical conductivity and tensile strength values in the case of pure MXene films are partly due to a combination of factors, including small MXene flake size (lateral size of couple of hundred nanometers), defects on MXene flakes due to sonication, voids formed in film due to the imperfect and irregular staking of flakes.…”

“…As an example, we produced several meters of a continuous, 940 nm thick MXene film that exhibited the highest tensile strength (568 ± 24 MPa) and Young's modulus (20.6 ± 3.1 GPa). Notably, this tensile strength is about 30 times higher than that of pure MXene film (10–20 MPa) produced by vacuum‐assisted filtration without any treatment, [ 18 ] five times higher than that of HCl treated MXene film [ 16 ] and approximately two times higher than those of the best MXene composite films. [ 27 ] After vacuum drying at 200 °C for 6 h, the films produced using blade‐coating method reached an electrical conductivity value of ≈15 100 S cm −1 that is the highest published value to date for MXene films.…”

“…e) Typical stress–strain curves of blade‐coated and vacuum‐filtered films prepared from large MXene flakes. f) Electrical conductivity of blade‐coated large Ti 3 C 2 T x films with increasing thickness before and after drying at 200 °C for 6 h. Electrical conductivity and thicknesses of films prepared by spin coating, [ 14,43,44 ] spray coating, [ 13 ] filtration, [ 11,16,18,45 ] electrophoretic deposition, [ 46 ] and rolling compressing [ 31 ] are plotted for comparison. More references are listed in Table S1 in the Supporting Information.…”