Superhydrophobic MXene Humidity Sensor And Its Wearable Devices Applications

Humidity sensors have been extensively investigated in different fields,such as medical diagnosis,national defense technology,aerospace.Various materials including carbon materials,metal halide perovskite materials,graphene materials,and even certain p-type semiconductor materials have been exploited to fabricate humidity sensing devices.However,currently these materials and corresponding processes are usually complicated,more expensive and poorer sensing performance.In addition,failure of flexible wearable humidity sensor in water environments still a challenge.Herein,we developed a novel superhydrophobic MXene humidity sensor with a simple process,low cost,faster response speed,good superhydrophobic and flexible performance.Furthermore,the humidity sensor is applied to the human oral or nasal wearing,which could achieve immediate respiratory monitoring,sound detection and non-contact sensing in different external environment and human states.The main contents of our work are given as follows:（1）Preparation and electrical performance test of MXene humidity sensor.The raw material Ti₃Al C₂ was slowly added into the mixed solution of concentrated hydrochloric acid and lithium fluoride to etch at 35℃for 24 hours,then ultrasonic stripping and centrifugation were performed to prepare two-dimensional sensing material MXene nanosheets.The MXene humidity sensor was prepared by thermal spraying on the hybrid flexible substrate of polyethylene terephthalate（PET）and polydimethylsiloxane（PDMS）with different gradient moduli.The sensor material was coated on the surface of the cross-finger electrode by drop coating method.The fastest response/recovery times for the sensor are 0.8 s and 2.4 s.The maximum resistance response is 612%.Experimental results show that the MXene humidity sensor has good mechanical flexibility and reliable electrical stability.（2）Surface modification of MXene humidity sensor.A superhydrophobic surface was constructed by spraying Si O₂ nanoparticles on the surface of the humidity sensor.Si O₂ nanoparticles are fastened on the surface of the sensor through Van der Waals force interaction,making it gets waterproof.In this sense,the interference of external electronic sensor on the device was hindered and the working life of the sensor was prolonged.In addition,the strong super-hydrophobicity of the surface also prevents MXene from the further oxidation,which enables the sensor to accomplish the humidity sensing task more quickly and accurately in different external environment.（3）The surface modified MXene humidity sensor was used to detect human breathing behavior in different states.The sensor can still work normally when it is disturbed by water in the breath detection process.Benefiting from this,this paper studies the respiration detection under different frequencies such as normal breathing,deep breathing,fast breathing and random breathing.Secondly,the speech recognition and non-contact sensing ability of the sensor are studied,which provides strong support for the research and development of superhydrophobic humidity sensor with comprehensive capability.