Actuation performance of MXenes in response to moisture gradients: A systematic investigation

Humidity-responsive actuators (HRA) have garnered significant interest across various domains. Since 2020, MXene have been extensively studied for their potential in HRA, demonstrating remarkable performance. Thus far, more than 70 MXene materials have been found. However, no systematic research regarding the distinctions in their applications in the field of HRA has been carried out, limiting the exploration of their broader potential. Herein, a systematic investigation of the HRA performance within the MXene (Nb₂CT_x, V₂CT_x, Ti₃C₂T_x, and Nb₄C₃T_x) family has been conducted. The influences of atomic layer number, oxygen content, transition metal elements, film thickness, and moisture gradient on the actuation performance are thoroughly examined. It is demonstrated that the number of atomic layers plays an indispensably critical role in both the bending angle and the response/recovery time. Nb₂CT_x and V₂CT_x with fewer atomic layers show excellent performance. At 50 % relative humidity, their maximum bending angles reach 210° and 202° respectively. The HRA are exemplified by the creation of a bionic butterfly and an intelligent switch, showcasing its broad application potential.