Insights into the thermal and chemical stability of multilayered V₂CT_x MXene

We report on the thermal stability of multilayered V2CTx MXenes under different atmospheres by combining in situ Raman spectroscopy with ex situ X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and scanning electron microscopy (SEM) in order to elucidate and monitor the molecular, electronic, and structural changes of both the surface and bulk of the V2CTx MXene which has recently received much attention. The MXene samples were heated up to 600 °C in inert (N2), oxidative (CO2, air), and reductive (H2) environments under similar conditions. In situ Raman showed that the V[double bond, length as m-dash]O vibration for two-dimensional vanadia is preserved up to 600 °C under N2, while its intensity reduces under H2. When heated above 300 °C under either CO2 or air, V2CTx slightly oxidizes or transforms into V2O5, respectively. Furthermore, SEM revealed the presence of an accordion-like layered structure for the MXene under N2 and H2, while under CO2 and air the layered structure collapses and forms VO2 (V4+) and V2O5 (V5+) crystals, respectively. XPS reveals that, regardless of the gas, surface V species oxidize above 300 °C during the dehydration process. Finally, we demonstrated that the partial dehydration of V2CTx results in the partial oxidation of the material, and the total dehydration is achieved once 700 °C is reached. We believe that our methodology is a unique alternative to tune the dehydration, oxidation, and properties of V2CTx, which allows for the expansion of applications of MXenes.