Local Surface Chemistry of Ti₃C₂T_x MXenes in Aqueous Electrolyte Monitored by In Situ Scanning Transmission X-Ray Microscopy

The pseudocapacitive behavior of Ti₃C₂T_x MXenes promises high power and energy densities thanks to redox reactions occurring during the (de-)protonation of the MXene surface in acidic electrolyte. Nevertheless, local electrochemical processes occurring at the MXene-electrolyte interface and the associated changes of the MXene surface chemistry are currently largely unexplored. To this aim, soft X-ray spectroscopies are particularly relevant as they enable the selective characterization of either the electrolyte or the material of interest thanks to their element specificity.¹ Furthermore, the high spatial resolution (&lt;30 nm) offered by X-ray Microscopy can provide precious information about local inhomogeneities at the nanoscale,² enabling the characterization of single MXene flakes. In this talk, the chemical bonding of Ti atoms in single few-layered Ti₃C₂T_x MXene flakes was monitored in different electrolytes using synchrotron-based <i>in situ </i>Scanning Transmission X-ray Microscopy (STXM) at the Ti L-edge. Significant changes of the Ti chemical environment are observed between acidic and neutral Li⁺-containing aqueous electrolyte and sub-flake inhomogeneities in the MXene surface chemistry was evidenced. Finally, potential-induced changes of MXene local surface chemistry will be discussed. <i>In situ </i>STXM will open new perspectives on the characterization of electrochemical processes in MXenes that can be monitored down to the single flake level.<br/><br/>1. Petit, T., Lounasvuori, M., Chemin, A. & Bärmann, P. Nanointerfaces: Concepts and Strategies for Optical and X-ray Spectroscopic Characterization. <i>ACS Phys. Chem. Au</i> (2023).<br/>2. Al-Temimy, A., Anasori, B., Mazzio, K., Kronast, F., Seredych, M., Kurra, N., Mawass, M., Raoux, S., Gogotsi, Y., Petit, T. (2020) “Enhancement of Ti3C2 MXene Pseudocapacitance after Urea Intercalation Studied by Soft X-ray Absorption Spectroscopy“, <i>Journal of Physical Chemistry C, </i>124, 5079.