Preparation Of Ti₃C₂T_x MXene Films And Its Humidity Actuation And Electrical Properties

MXene（Ti₃C₂T_x）film is an extremely important 2D MXene macroscopic assembly with ultra-high electrical conductivity,tunable interlayer space and excellent mechanical property,showing great commercial value in many fields,such as energy storage,electromagnetic interference shielding and actuator.However,the currently known researches on MXene film mainly focus on how to achieve the interlayer regulation and hybridization enhancement,while ignoring the essential superior properties of MXene film and its rational development as well as utilization.In fact,water molecules in the interlayer of MXene film are directly related to the physicochemical properties of MXene film.Therefore,this paper focuses on exploring the humidity-responsive capability of MXene film,the weldability of MXene film with the assistance of water,and the rapid filtration of MXene microgel for the fabrication of MXene film,and concentrates on the applications of the MXene films in the humidity actuation and electricity fields.Meanwhile,the key structure-activity mechanism between water molecules and MXene is deeply studied and explained,which lays a good theoretical foundation for the practical application of MXene films.MXene film is highly sensitive to moisture and can quickly sense moisture on palms and fingers.In addition,when the relative humidity difference is 65%,MXene film can present a bending angle of up to 155°,and has excellent humidity actuation performance and excellent cycle stability.Through in-depth analysis,the fundamental reason why MXene film has excellent humidity actuation is that it can quickly absorb and desorb the water between layers,which leads to asymmetric expansion and contraction of double-layer structure.Based on the above characteristics,MXene film can be used as humidity-responsive actuator in the fields of flexible excavator,electrical switch and so on.Based on the intercalation mechanism of water molecules in MXene,the concept of"weldability"of MXene films is proposed in this paper.Through the auxiliary excitation of external water,the interlayer water molecules of MXene films can be re-diffused and re-arranged,so that different MXene films can be re-integrated,and the effect similar to metal welding connection can be achieved.More importantly,the"welding"is sensitive to time,that is,the MXene film can be connected freely during the time-sensitive period,but does not have weldability outside the time-effective period,ensuring the practicability of the connecting materials.Using the"weldability"characteristic,MXene film can be used as base material to connect into an actuator with complex structure that can be driven by humidity gradient;it can be rolled into vertically arranged dense electrodes whose capacitance behavior is independent of thickness,which effectively overcomes the industry problem of poor rate capability faced by thick MXene films for a long time.Inspired by silt filtration,MXene dispersion can be induced by ion to turn into microgels containing water,after the vacuum assisted filtration process is performed,the rapid preparation of MXene film can be achieved.This method can reduce the preparation time of MXene film via vacuum assisted filtration from several hours to about dozens of seconds,significantly improving the preparation efficiency.In fact,the gap between MXene microgels ensures the continuous and rapid filtration of water molecules.The strong gelation and internal riveting effect inside the microgel ensure the formability of modified MXene film（MMF）.Therefore,MMF has excellent mechanical properties while maintaining outstanding electrical conductivity,which allowing it to be used as potential energy storage materials and electromagnetic interference shielding materials.For example,the volumetric capacitance of MMF can reach up to 2020 F cm^-3;at the thickness of 36.7μm,the electromagnetic interference shielding effectiveness value can reach up to 66 d B.This paper studies and explains the important relationship between water molecules and MXene film layers,which plays an important role in re-understanding MXene films and transforming MXene materials.In addition,the humidity-responsive capability of MXene films,water assisted weldability properties,rapid filtration of MXene microgels and related mechanisms are only a small part of the interaction between water molecules and MXene films.Further understanding of the relationship between water molecules and MXene films is of great significance for promoting MXene to transition from laboratory to practical application.