Modified MAX Phase Synthesis for Environmentally Stable and Highly Conductive Ti 3 C 2 MXene

One of the primary factors limiting further research and commercial use of the two-dimensional (2D) titanium carbide MXene Ti 3 C 2, as well as MXenes in general, is the rate at which freshly made samples oxidize and degrade when stored as aqueous suspensions. Here, we show that including excess aluminum during synthesis of the Ti 3 AlC 2 MAX phase precursor leads to Ti 3 AlC 2 grains with improved crystallinity and carbon stoichiometry (termed Al–Ti 3 AlC 2 ). MXene nanosheets (Al–Ti 3 C 2 ) produced from this precursor are of higher quality, as evidenced by their increased resistance to oxidation and an increase in their electronic conductivity up to 20 000 S/cm. Aqueous suspensions of stoichiometric single- to few-layer Al–Ti 3 C 2 flakes produced from the modified Al–Ti 3 AlC 2 have a shelf life of over ten months, compared to 1 to 2 weeks for previously published Ti 3 C 2, even when stored in ambient conditions. Freestanding films made from Al–Ti 3 C 2 suspensions stored for ten months show minimal decreases in electrical conductivity and negligible oxidation. Furthermore, oxidation of the improved Al–Ti 3 C 2 in air initiates at temperatures that are 100–150 °C higher than that of conventional Ti 3 C 2 . The observed improvements in both the shelf life and properties of Al–Ti 3 C 2 will facilitate the widespread use of this material.