Fabrication And Characterization Of Flexible Pressure Sensor Based On MXene/rGO

Flexible pressure sensors have received considerable attention due to their potential applications in wearable devices,health monitoring,human-computer interaction and other fields.Among them,piezoresistive pressure sensors are an important branch of flexible pressure sensors.Sensitivity and linear operating range are the main performance indicators of piezoresistive pressure sensors.However,high sensitivity and broad effective sensing range are often incompatible,which makes the preparation of high-performance flexible piezoresistive pressure sensors still a huge challenge.In order to solve this problem,it is usually considered from the selection of materials and the structural design of flexible piezoresistive pressure sensors.Due to its unique atomic structure and dimensional characteristics,two-dimensional graphene has excellent physical and chemical properties.Based on the advantages of good surface hydrophilicity and large specific surface area,it can be assembled into electrodes with a universal conductive structure.Although two-dimensional graphene-based film pressure sensors can easily realize high sensitivity and rapid response,making them suitable for detecting tiny deformations,they cannot work effectively in real time under strong pressure and large compression.As a result,there are still limitations in practical application.Similar to graphene,a new two-dimensional material of transition metal carbides,nitrides or carbonitride（MXene）,has many advantages including large specifific surface area,good mechanical property,excellent electrical conductivity and so on.Besides,MXene is generally composed of many elements,which makes its physical and chemical properties adjustable.Unfortunately,MXene is not excellently elastic and cannot withstand enormous pressure due to its inherent brittleness.According to the principle of biological similarity and compatibility,combining the advantages of both,constructing a hybrid electrode of graphene and MXene,and designing and controlling its structure are a very effective way to further improve the performance of the hybrid electrode.Based on this,the specific work of this article is as follows:（1）A novel flexible asymmetric pressure sensor has been proposed by adjusting sensing material and optimizing the structure of electrode.As a crucial piezoresistive material,MXene/reduced graphene oxide（MXene/r GO）nanocomposite with a layer by layer stacked structure is developed by an efficient and precise laser direct writing technology.Benefit from this designed layer by layer crosslinked structure of the hybrid electrode,the proposed flexible MXene/r GO asymmetric pressure sensor exhibits excellent pressure-sensing performances,such as high sensitivity of 2.35 k Pa^-1（0-250 Pa）,low detection limit of about 2.9 Pa,fast responsive recovery（0.132 s）,and long cycle durability（over 1000 cycles）.So that our flexible MXene/r GO asymmetric pressure sensor can detect subtle body physiological motions in real time,such as wrist pulse,vocal vibration,finger movement,and breath.Additionally,the as-prepared sensor array integrated by 4×4 identical MXene/r GO asymmetric pressure sensors exhibits good multi-touch function.（2）A flexible pressure sensor employing 3D porous MXene/r GO hybrid foam as piezoresistive sensing material is developed by an efficient hydrothermal synthesis and a novel reduction method of flash instantaneous irradiation.Compared to conventional reduction methods,this instantaneous reduction process can effectively maintain MXene nanoflakes tightly interconnected r GO sheets,resulting in robust mechanical elasticity and high conductivity of the proposed MXene/r GO hybrid foam.On account of the 3D porous skeleton structure of MXene/r GO hybrid foam,the proposed pressure sensor presents a high sensitivity up to 3.75 k Pa^-1,a broad sensing range from 0 to 28 k Pa,an ultra-low detectable limit down to 1.5 Pa,rapid dynamic response/recovery times with 20/40 ms,as well as a strong stability for over 2000 cycles.Notably,the flexible pressure sensor possesses superior function of precisely detecting some subtle human activities（pulse,vocalization,breathing,etc.）and large joints（knee,finger,elbow,wrist,etc.）movements in real time.Besides,a matrix pressure array of 4×4 pixels has been exploited for multi-point recognition.In this work,the flexible MXene/r GO asymmetrical pressure sensor and flexible MXene/r GO foam-based pressure sensor developed have potential application prospects in wearable electronic products,health monitoring,human-computer interaction,electronic skin and other fields.In addition,herein,the developed MXene/r GO hybrid electrode provides a new avenue for low-cost,sustainable,large-scale production of graphene composites for other micro and nano devices.