Vascular bundle-inspired MXene ion-conducting microchannels enabled tough ionic hydrogels with high-sensitivity sensing and high-efficiency mechanical-electric conversion

High-sensitivity hydrogel-based sensors with self-powered functions are becoming more and more important in wearable electronics fields. However, traditional hydrogels cannot satisfy the application requirements for high-performance self-powered wearable sensors due to their low conductivity, poor sensitivity, and limited electric output performance. Inspired by the transport effect of vascular bundles in trees on inorganic salts, unique ion-conducting microchannels are assembled by MXene nanosheets as conductive materials, cellulose nanofibrils (CNFs) as cross-linking supports, and NH4HCO3 as an inducer, which exhibits high mechanical properties, excellent conductivity, and high-sensitivity sensing. The MXene microchannels contribute to the directional transport of free ions in the polyvinyl alcohol (PVA) hydrogel with poly(diallyl dimethyl ammonium chloride) (PDADMAC) as ion source, thus endowing the MXene-CNF-PDADMAC-PVA (MCPP) hydrogel with high-sensitivity sensing and high-efficiency mechanical-electric conversion performance. The MCPP hydrogel-based sensor possesses a low detection limit (200 mg) and fast response time (120 ms). The MCPP hydrogel-based triboelectric nanogenerator can generate a VOC of 159.1 V, ISC of 24.5 µA, and QSC of 32.5 nC, and the MCPP hydrogel-based piezoelectric nanogenerator can output a voltage of 1134.3 mV. Thanks to the excellent self-powered sensing performance, a self-powered sensing indicator and tiny pressure detector based on the hydrogel are developed to realize the visual sensing in an uncomfortable state of the elderly without an external power supply and detect the heartbeat and fluttering pulse. Therefore, this ionic hydrogel with high-sensitivity sensing and high-efficiency mechanical-electric conversion performance is very promising for applications in next-generation advanced wearable electronics.