<i>In Situ</i> Raman and Fourier Transform Infrared Spectroscopy Studies of MXene−Electrolyte Interfaces

A comprehensive understanding of electrochemical interfaces is essential for the optimal performance of electrocatalysts, supercapacitors, and batteries. However, understanding the electrochemical behavior of MXenes during electrochemical processes by any single technique does not provide a whole picture. We achieved real-time monitoring in the complete near-mid-infrared chemical range by utilizing Raman spectroscopy (near-infrared (NIR) excitation) and Fourier transform infrared (FTIR) spectroscopy in the mid-infrared (MIR) range. The change of intramolecular O-H vibrations of MXene-confined water was monitored in real time using FTIR, while surface terminations were monitored by using Raman spectroscopy. The dynamic interplay between charge storage and the change in MXene surface chemistry was studied by employing representative electrolytes (0.5 M H₂SO₄, 1 M LiCl, and 6 M KOH) and comparing hydrophilic Ti₃C₂T<i>_<i>x</i></i> with mixed-terminations (T = O/OH/F) with hydrophobic chlorine-terminated Ti₃C₂Cl₂ MXene electrodes. <i>Ab initio</i> molecular dynamics (MD) simulations and density functional theory (DFT) calculations were used to shed light on ion insertion with a dynamic change of ion solvation and reveal the structure of the MXene-confined water.