As a new type of moisture-responsive material with high conductivity and hydrophilicity, MXenes have unlimited possibilities in collecting water evaporation energy. However, the mechanical and electrical properties of MXene films are compromised by the macroscopic cavities and disordered accumulation of the flakes in their structure. Here a polydopamine-treated reduced graphene oxide/MXene film was prepared as a moisture-responsive actuator, through densification of the MXene film by stronger interlayer interactions via covalent and hydrogen bonding. The compact MXene-based actuator exhibits high conductivity (3693 S cm⁻¹), mechanical properties, and humidity sensitivity. The excellent comprehensive performance enables the actuator to detect the humidity of fingertips, as a non-contact switch to turn on the circuit, or as a robot to move cargos. More importantly, a moisture-driven generator is designed and assembled by coupling this actuator with a piezoelectric element, and it can continuously output alternating current with a peak voltage of about 1 V under the drive of the moisture gradient. This research highlights the huge application potential of this moisture-responsive actuator, and provides a template for the development of advanced multifunctional MXene-based actuators.

A flexible strain sensor for detecting human motion signals has been a research hotspot. However, it is still challenging to achieve a good balance between sensitivity, strain tolerance, and toughness. In this study, we present a piezoresistive strain sensor composed of ductile bacterial cellulose (BC) and highly conductive MXene (Ti₃C₂T_x) nanosheets by applying simple gel-casting. The hydrogel exhibits excellent mechanical properties owing to the physical crosslinking by hydrogen bonds between the rich hydroxyl groups of BC and the oxygen-containing functional groups on MXene, achieving a breaking strength of 2.52 MPa and a strain of 87%. MXene also exhibits excellent electrical conductivity and sensitivity for detecting strain-induced deformation. The hydrogel can cycle more than 200 times under tensile or compressive strain and has a superior strain detection limit of 0.05% and a response speed of 130 ms. Our sensor shows real-time stress sensing under different amplitudes of human motions, such as fingers, wrists, and elbows, and still maintains its sensing ability underwater. Overall, the hydrogel sensor does not require special instrumentation, modification, or crosslinking agents in preparation; provides high tensile strength and good biocompatibility; and retains response ability underwater. Therefore, the flexible conductive hydrogel has a good application potential in the field of wearable strain–stress sensors.