Research On Multifunctional Integrated Sensors Based On Mxene

A sensor is a kind of device that senses different forms of external stimuli(such as pressure,strain,temperature,humidity,gas,etc.),and then converts the stimulus signals into electrical signal outputs.In recent years,research on flexible wearable electronic devices has shown a rapid growth trend.Especially,various types of multifunctional sensors have good application prospects in sports management,health monitoring,and human-computer interaction.As a new member of the two-dimensional material family,MXene has excellent properties such as metallicity,high electron mobility,high elastic modulus when stretched on the substrate plane,resistance to electron radiation,and large specific surface area.It has become another hot material after graphene and has been studied.This paper mainly focuses on using the two-dimensional material MXene as the conductive matrix,and the polymer materials(such as polydimethylsiloxane(PDMS),etc.)as the substrate or encapsulation materials to prepare ultra-sensitive,multifunctional,and self-powered highly-integrated sensors.Their principles and performance are also studied.First,a flexible and wearable multifunctional sensor that integrates pressure and temperature sensing is proposed.To achieve a high degree of integration,we introduced a three-electrode strategy to fabricate a double-layer asymmetric sensor based on MXene-silk and leaf vein layer with fractal network structure.The sensor overcomes the shortcomings of high brittleness and poor stability of MXene film.Combined with the fractal structure of leaf veins,the sensor can effectively improve the efficiency of electron transfer and electron transport between layers.In addition,the contact area between the two layers increases as the pressure increases,forming more conductive paths,so that the pressure sensor has a higher sensitivity.Moreover,encapsulated by polyethyleneterephthalate,the sensor is hydrophobic and not easy to be contaminated.Second,a strain sensor based on MXene is proposed.The fabrication method is uniformly depositing the MXene solution on the grating stripes of the PDMS substrate and then coating polyurethane solution,which greatly increases the stretchability and stability of the strain sensor.The ultra-high sensitivity and wide measurement range of the strain sensor can fully meet the monitoring functions of the flexible wearable sensor device in several human physiological signals.At the same time,due to the large coefficient of thermal expansion of the PDMS substrate,the volume expansion occurs when heated.Then,the deposited MXene conductive network is pulled by the substrate,occurring cracking,and it exhibits an ideal temperature coefficient of resistance in the unstrained state.In addition,thermochromic powders are incorporated into the PDMS substrate,so that the substrate itself constitutes a visual temperature indicating device.Therefore,the integrated multifunctional sensor is not only a strain sensor that performs exercise management and health monitoring,but also a temperature sensor that outputs dual parameters in real-time.Third,a high-performance strain sensor based on a simple preparation process is developed.The fabrication method is attaching MXene conductive sensing layer to a stretchable,highly viscous,highly elastic tape,and then pre-stretching it to construct a quasi-scaly structure on the strain sensor.This structure allows adjacent overlapping MXene to easily change their overlapping area through reversible sliding,thereby changing their contact resistance.Then,the sensor will have ultra-high sensitivity and wide effective stretching range.Afterwards,the MXene film is used as the electrode material of the supercapacitor and the positive electrode material of the air battery,and the zinc sheet is used as the negative electrode material of the air battery to obtain the supercapacitor and the zinc-air battery.Besides,circuit integration is carried out,and a self-powered integrated device composed of sensor and supercapacitor is successfully constructed.This method simplifies the test equipments,changes the current situation that the sensor requires an external power supply,and is expected to be more widely used in flexible wearable devices.