A Ti₃C₂T_x MXene-Based Energy-Harvesting Soft Actuator with Self-Powered Humidity Sensing and Real-Time Motion Tracking Capability

Abstract

A smart soft actuator with multiple capabilities of humidity-driven actuating, humidity energy harvesting, self-powered humidity sensing, and real-time motion tracking is reported. It is designed on the basis of an MXene/cellulose/polystyrene sulfonic acid (PSSA) composite membrane. This actuator is driven by asymmetric expansion under a moisture gradient during capture of the chemical potential of humidity to mechanical power. Meanwhile, the gradient moisture chemistry also induces directional proton diffusion to generate electricity with high power density and open-circuit voltage. A good linear correlation between the humidity sensitivity, electrical signal, and bending state of this actuator allows real-time tracking of motion modes with humidity change without an external power supply. This multifunctional soft actuator can be used for engineering smart switches, artificial fingers, and soft robots with trackable and distinguishable motion patterns, as well as sensitive noncontacting humidity sensor and breathing monitors.

Fabricating flexible conductive structures by printing techniques and printable conductive materials

“…This actuator can capture the humidity energy and convert it to mechanical power by the asymmetric swelling and expansion of MCPM under moisture gradient. 164 Yan et al studied the fabrication of a flexible and highly conductive MXene/reduced graphene oxide (rGO) film by electrostatically self-assembling negatively charged MXene nanosheets and positively charged rGO nanosheets. The obtained MXene/rGO composite could effectively relieve the self-capture of rGO and MXene and maintain an ultrahigh conductivity (2261 S cm À1 ) and high density (3.1 g cm À3 ).…”

Development and challenges of smart actuators based on water-responsive materials

“…2.2.3 Other synthetic material-based actuators. In addition to polymeric materials, GO, and CNTs, many other synthetic materials with nanoscale porous structures, such as silicon dioxide, 50 Ti 3 C 2 Tx (MXene), 49,132,133 carbon nitride, 134,135 titanium oxide, 137,138 and some metal-organic frameworks, 139,140 are sensitive to humidity. Fluid adsorption and condensation in nanoscale pores can deform the pore walls.…”

Self-Powered Carbon Ink/Filter Paper Flexible Humidity Sensor Based on Moisture-Induced Voltage Generation

“…However, these humidity sensors depend on an external power supply, limiting their range of applicability and leading to growing environmental pollution problems. Therefore, a series of various new technologies based on triboelectricity, − piezoelectricity, , photovoltaics, thermoelectricity, and moist-electric generation , have been developed to meet the requirements of green sustainable energy supply and to provide possible solutions for the development of self-powered sensors. Among them, the moist-electric generation, which converts the chemical energy present in moisture into electrical energy, can generate voltage continuously in humid environments.…”