Tailoring MXene-based films as moisture-responsive actuators for continuous energy conversion

Abstract

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.