Role of Surface Terminations for Charge Storage of TiCT MXene Electrodes in Aqueous Acidic Electrolyte.

In this study, we used 2-Dimmensionnal TiC MXene as model materials to understand how the surface groups affect their electrochemical performance. By adjusting the nature of the surface terminations (Cl-, N/O-, and O-) of TiC MXene through a molten salt approach, we could change the spacing between MXene layers and the level of water confinement, resulting in significant modifications of the electrochemical performance in acidic electrolyte. Using a combination of techniques including in-operando X-ray diffraction and electrochemical quartz crystal microbalance (EQCM) techniques, we found that the presence of confined water results in a drastic transition from an almost electrochemically inactive behavior for Cl-terminated TiC to an ideally fast pseudocapacitive signature for N,O-terminated TiC MXene.