Additive-Free TiCT MXene Actuator with Large Deformation, Programmability, and High-Humidity Stability via Precise Interlayer Spacing Control Engineering.

Introducing external substances to intercalate MXene (TiCT) or combining MXene with other inert materials to construct bilayer/multilayer structures is the current mainstream solution for improving actuation performance of MXene-based actuators. Possible issues include the degradation in mechanical and electrical properties of MXene, or the decrease in actuation performance or even structural damage of the actuator under frequent actuation. Besides, the structural and actuation performance stability of MXene-based actuators under high humidity environment also remain challenges. These issues limit the potential multifunctional integration and sustainable applications of MXene-based actuators. Here, an additive-free TiCT MXene actuator with multistimulus response, large deformation, programmability, and excellent stability under high humidity environment is fabricated. By sequentially assembling MXene nanosheets with significant size differences, additive-free MXene film with gradient structure is obtained. An innovative cyclic low-temperature annealing-rehydration technology is proposed, which achieves precise control of interlayer d-spacing, initial shape, and actuation behavior of the actuator, and significantly improves its structural and actuation performance stability under high humidity environment. This work not only provides a new paradigm for designing high-performance MXene-based actuators, but also deepens the fundamental understanding of interlayer engineering of 2D materials, laying the foundation for the development of next-generation sustainable intelligent materials and devices.