Understanding In-Plane Sliding of Functionalized Ti₃C₂T_x MXene by In Situ Microscale Analysis of Electrochemical Actuation

Electrochemical actuation is based on the deformation of electrodes upon applying a mild potential (usually in the range of ± 5 V in a single cell). In this work, in situ local analysis of the electrochemical actuation of Ti₃C₂T_x (T = −O, −OH, −F) MXene at the microscale is achieved by Raman spectroscopy, atomic force microscopy (AFM), and scanning electrochemical microscopy (SECM) while applying potential in an electrochemical cell. First, Raman spectra recorded at a steady state with different potentials confirm the intercalation/deintercalation of Li⁺ ions, resulting in the change of out-of-plane vibrations due to the interaction of Li⁺ with the −O and −OH surface group atoms of MXene. A methylcellulose functionalization of the MXene films results in more freedom for in-plane vibrations. Second, SECM is applied to visualize the deformation of two-end-fixed MXene films both at a steady state (0 V vs Ag/AgCl QRE) and at scanning potential. The results show buckling-type actuation, which is more pronounced for methylcellulose-functionalized samples. Electrochemical AFM provides evidence of a significant in-plane sliding of the MXene flakes. Out-of-plane changes appear to be negligible in the actuation mechanism, as supported by the AFM approach curve analysis. Overall, the methylcellulose-functionalized MXene shows better actuation performance, especially in the in-plane direction and at a high frequency. The mechanism is then discussed.