In Situ Electrochemical Raman Spectroscopy of MXenes in Confined Electrolytes

MXenes, a large family of two-dimensional materials, have attracted 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 = 1-4) 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. Like with many other 2D materials, Raman spectroscopy has proven to be a crucial tool for MXene characterization. More recently, in situ Raman was used to elucidate structural changes in MXene electrodes during electrochemical cycling with a subset of aqueous electrolytes. Confined electrolytes (water-in-salt, PEG, etc.) have shown promise in various electrochemical systems, with recent results pointing to new charge storage mechanisms in MXenes. Further exploration is needed to understand the effect of the cations, anions, and concentrations of confined electrolytes on charge storage mechanisms. This work focuses on using in situ electrochemical Raman spectroscopy to analyze different confined electrolyte systems in MXene cells. The findings demonstrate the potential of using MXenes in aqueous electrochemical devices.