Evaluation of Oxidation Processes in Ti₃C₂T_x MXene using In Situ Electrochemical Raman Spectroscopy

MXenes, a large family of two-dimensional materials, have attracted a lot of interest due to their large chemistry space and diverse chemical, electrical, mechanical, and optical properties. MXenes follow the general formula M_n+1X_nT<i>_x</i> (n = 1, 2, 3, or 4) with M representing an early transition metal, X - carbon and/or nitrogen, and T - surface terminations (=O, –OH, and –F). In particular, MXenes’ metallic conductivities and redox-active surfaces make them attractive for electrochemical energy storage. Recently, we demonstrated that partial oxidization of Ti₃C₂T_<i>x</i> MXene by cycling the material at 1.2 V vs. Ag wire led to enhanced pseudocapacitance in water-in-salt electrolytes. However, there is a fine line between partial oxidation of Ti₃C₂T<i>_x</i> MXene and complete oxidation that leads to the formation of titania and carbon. The extent of oxidation is difficult to measure with conventional X-ray and electron-based techniques. This work focuses on using in situ electrochemical Raman spectroscopy to analyze the oxidation processes in Ti₃C₂T<i>_x</i>MXenes at the high anodic potential. Raman spectroscopy has proven to be a powerful technique for detecting the natural oxidation of Ti₃C₂T<i>_x</i> MXenes. The ability to perform Raman spectroscopy in situ during electrochemical reactions will allow us to expand our knowledge of MXene electrochemistry and its partial oxidation. The findings will help achieve higher energy density in MXene-based energy storage devices.