Water-Induced Local Redox Reactions on Individual Ti₃C₂T_x MXene Flakes in Aqueous Environment

Water at an interface, confined in nanopores or between layers exhibits unique structural and dynamic properties that differ significantly from bulk water. In layered 2D materials such as MXenes, intercalated water is believed to affect their surface chemistry by inducing local oxidation and contribute to redox processes during electrochemical cycling. However, the chemical nature of confined water and its interaction with MXene surface chemistry remains unclear. Here, we employ scanning transmission X-ray microscopy (STXM) to investigate in situ the chemical interaction of water in individual Ti₃C₂T_x MXene flakes in humid and aqueous environments with ∼50 nm spatial resolution. At the oxygen K-edge, we uncover that water trapped in pockets and wrinkles in few-layered MXene flakes has a different hydrogen bonding compared to water confined in the MXene interlayer spacing. We also reveal water-induced local redox reactions of Ti atoms non-uniformly distributed on the MXene flake upon interaction with liquid water and alkali ion neutral electrolytes, which are partly reversible upon exposure to an acidic electrolyte.