Anomalous Enhancement in MXene-Based Electrochemical Actuators: Pseudo-Capacitance-Induced Multi-Charge Accumulation...

Two-dimensional (2D) transition-metal carbides and nitrides (MXenes) exhibit high electronic conductivity, large volumetric capacitance, and excellent mechanical robustness, making them attractive for electrochemical actuators (ECAs). However, the fundamental link between surface chemistry, charge-storage mechanism, and macroscopic actuation remains unclear, limiting their full potential. Here, we elucidate the actuation mechanism of Ti₃C₂-based ECAs, revealing that actuation is driven by pseudocapacitive reactions rather than by simple ion intercalation. Controlled hydrothermal treatment of Ti₃C₂T_x can tailor oxygen functional groups, boosting pseudocapacitive activity and interlayer adjustability. In situ structural analysis reveals that anomalous interlayer expansion arises from multiple hydrated ions accumulating at confined Ti─O─Ti active sites during pseudocapacitive reactions. Coupled with a beneficial wave-like cross-section morphology, the oxygen-functionalized Ti₃C₂-based solid-state ECA achieves a peak-to-peak strain of ∼1% at 0.05 Hz under a ±1 V square-wave voltage, which is four times greater than the pristine Ti₃C₂T_x device, while maintaining excellent cycling stability. These findings culminate in a mechanistic framework linking atomic-scale surface chemistry to macroscopic device performance, providing critical insights for designing advanced 2D material-based actuators.