Electrochemical in Situ Tracking of Volumetric Changes in Two-Dimensional Metal Carbides (MXenes) in Ionic Liquids.

We report the volumetric changes of MXenes in contact with different ionic liquids and the swelling/contraction during electrochemical voltage cycling by complementing electrochemical dilatometry with in situ X-ray diffraction measurements. A drastic, initial, and irreversible volume expansion of MXenes occurs during first contact to ionic liquids (wetting). Voltage cycling evidenced a highly reversible expansion and contraction of electrodes at a very large amplitude of strain (corresponding with max. 12 vol %), which may allow the use of MXene as a high-performance electrochemical actuator.