Hollow MXene Sphere/Reduced Graphene Aerogel Composites for Piezoresistive Sensor with Ultra‐High Sensitivity

Abstract

can effectively capture subtle changes of pressures is much needed. To date, plenty of pressure sensors have been explored, including capacitive, [2,3] piezoelectrical, [4][5][6] and piezoresistive [7,8] pressure sensors. Among them, piezoresistive sensors stand out as promising candidates due to their low-cost fabrication, stability to temperature, sensitivity to pressure, etc. Piezoresistive pressure sensors can transduce changes of mechanical strain into changes of electrical resistance, and are broadly used due to their simple work mechanism and sensitivity to pressure. [9] Conventional piezoresistive pressure sensors, however, are usually based on rigid substrates like Si, [10] which are not skin-mountable and cannot meet the needs for portability and flexibility of smart wearable electronic devices. To tackle this problem, one possible way is the combination of flexible insulating matrices with carbonaceous nanomaterials as conductive fillers, such as graphene, [11] reduced graphene oxide (rGO), [12] and carbon nanotubes (CNTs). [13] For example, Park et al. combined wrinkled CNT and PDMS to build a pressure sensor [14] and more recently, Pang et al. prepared a pressure sensor based on rGO and micro-patterned PDMS substrate. [15] However, composite flexible pressure sensors like these often suffer from a performance compromise between sensor sensitivity and linear region. [16] Apart from that, the signal stability of the sensor may be influenced by the thermal expansion of the polymer substrate. [9] Another way is the utilization of the carbonaceous nanomaterials as the building blocks for making highly elastic materials. In particular, carbon aerogels prepared by this method have demonstrated extraordinary mechanical properties, [17] good flexibility, [18] high aspect ratio, [19] and exceptional thermal stability. [20] Over the past few years, a considerable amount of reports have focused on piezoresistive pressure sensors based on reduced graphene oxide (rGO) aerogel or rGO composite aerogel. For instance, Ha et al. prepared a PAA/ rGO composite aerogel for pressure sensing, [21] and recently, Peng et al. made a piezoresistive sensor based on CNT/rGO-CNF aerogel. [22] However, it still remains a challenge to further improve the sensitivity and the detecting range of these carbon aerogel based pressure sensors.Recently, a new kind of 2D transitional metal carbide/carbonitride materials (MXenes) with metal conductivity have Pressure sensing is key to smart wearable electronics and human-machine interaction interfaces. To achieve a high-performance pressure sensor that has broad linear range and is capable of detecting subtle changes of pressure, the good choice of sensing materials and rational design of structures are both needed. A novel piezoresistive sensor based on hollow MXene spheres/ reduced graphene composite aerogel and flexible interdigital electrodes is presented. Benefiting from the unique microstructure of the composite aerogel, the prepared pressure sensor exhibits high sensitivity (609 kPa −...

MXene hydrogels: fundamentals and applications

“…Such overwhelming merits make them promising candidates for microwave absorption, electromagnetic interference shielding, flexible electronics, and solar energy conversion. Thus far, there are several methods for preparing MXene aerogels including (1) direct freeze-drying of MXene NC dispersions, 16,25,35,36 (2) calcination after freeze-drying of MXene NC dispersions, [37][38][39][40][41] and (3) freeze-drying of MXene hydrogels. 5,6,12,28,[42][43][44][45][46][47] In all these methods, the sublimation of ice crystals from frozen dispersions or hydrogels was necessary for obtaining MXene aerogels.…”

MXene-Based Nanocomposite Sensors

“…Zhu et al 10 proposed a novel fabrication method of MXene-based sensors. They used positively charged spherical polymer particles and then mixed the particles with a MXene, which inherently has a negative surface charge.…”

“…The thermal expansion of a polymer in a sensor may cause signal instability of the sensor; this is why some researchers have tried to remove polymers from their sensor structure specially when the sensor is supposed to work at high temperatures where thermal expansion is more likely. 10 To improve electrical contact and enhance conduction paths, Zhu et al 10 mixed MXene hollow spheres with rGO. They were able to fabricate sensors with improved sensitivity in a broad linear range.…”

“…They were able to fabricate sensors with improved sensitivity in a broad linear range. Their pressure sensors showed excellent durability over 6000 cycles, a low detection limit of 6 Pa, and a low response time of 230 ms. 10 …”

Flexible Pressure Sensors for Biomedical Applications: From Ex Vivo to In Vivo

“…In general, piezoresistive pressure sensors are fabricated using active materials sandwiched between two vertically aligned electrodes or deposited on a pair of parallel interdigital electrodes. [99] In recent years, various conductive materials such as carbon-based fillers (carbon black, [100] CNT, [101] graphene, [102] MXenes, [103] and reduced graphene oxide [104] ), conductive polymers(PEDOT:PSS, [105] PPy, [106] and PANI [107] ), and metal nanostructures (Ag/Au nanoparticles and nanowires [108] ) have been investigated and used as the active material of piezoresistive sensors. These sensors have been widely investigated www.advmatinterfaces.de because of their easy read-out mechanism, low cost, simple device structure, and fabrication process.…”