Understanding Electrochemical Processes in MXenes Using in-Situ Raman and FTIR Spectroscopies

A comprehensive understanding of electrochemical interactions is essential for optimizing the performance of supercapacitors and batteries. This study introduces a novel approach for the in-situ characterization of MXenes during electrochemical processes in aqueous electrolytes. MXenes, a large family of two-dimensional materials, follow the general formula M n+1 X n T x (where M represents a transition metal, X — carbon and/or nitrogen, and T — surface terminations) and have attracted a lot of interest due to their large chemistry space and diverse properties. In particular, their metallic conductivities and redox-active surfaces make them attractive for electrochemical energy storage. In this work, real-time monitoring of vibrational modes across complementary spectral ranges was achieved by combining Raman spectroscopy (near-infrared excitation) with Fourier Transform Infrared (FTIR) spectroscopy in the mid-infrared (MIR) range. Given that the charge storage mechanisms of many emerging 2D nanomaterial systems remain unclear, the combination of these two vibrational techniques facilitates the decoupling of processes occurring within electrochemical cells. FTIR spectroscopy provides insights into contributions from confined and solvated water, while Raman spectroscopy, which is less sensitive to water, captures changes in MXene surface terminations. Density functional theory (DFT) calculations were employed to assign vibrational spectral features. The dynamic interplay between charge storage and the adsorption of active species was investigated using representative electrolytes (H 2 SO 4 , LiCl, KOH) and comparing mixed-termination Ti 3 C 2 T x with chlorine-terminated Ti 3 C 2 Cl 2 MXene electrodes. Changes in the vibrational spectra were attributed to ion intercalation and deintercalation, as well as the formation and breaking of chemical bonds. By elucidating the mechanisms underlying electrochemical processes, this study paves the way for expanded applications of MXenes in energy storage devices. Figure 1