High-Temperature Phase Transformation and Stability of Ti₃C₂T_x and Mo₂TiC₂T_x MXenes

MXenes have been extensively investigated for a range of applications from energy storage to catalysis. However, few studies take advantage of the inherent stability of the interior M-X transition metal carbide core for use in extreme environments. This interior M-X core gives MXenes potential to be used as highly stable transition metal carbides in inert conditions such as ultra-high temperature (&gt; 3,000 C) or highly radioactive environments. In this study, we investigated the high-temperature behavior of two M₃C₂T<i>_x</i> MXenes of Ti₃C₂T<i>_x</i> and Mo₂TiC₂T<i>_x</i> from room temperature to 2,000 C using <i>in-situ </i>annealing up to 1,100 C using two-dimensional x-ray diffraction (XRD²) and <i>ex-situ </i>XRD²sintered MXenes up to 2,000 C annealed via spark plasma sintering. In the case of Ti₃C₂T<i>_x</i>, we identified the formation of nanolamellar cubic disordered carbon vacancy TiC<i>_y</i> with strong preferential (111) plane orientation formed along the original basal plane of Ti₃C₂T<i>_x</i> MXene. Our cross-sectional scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) results further confirmed the preferentially ordered phases that keep their lamellar morphology up to 2,000 C in inert environments. In the case of Mo₂TiC₂T<i>_x</i>, which is an ordered double-transition metal MXenes, our results indicated a combination of micro- and nano-scale structures of molybdenum and titanium carbides. These findings confirm that MXenes remain as carbides under inert environments at high temperatures of at least 2000 C and identify a unique capability of MXenes to synthesize MXene-derived carbides with unique morphologies that are not possible to make via the traditional carbide synthesis routes.