Mxene hybrid conductive hydrogels with mechanical flexibility, frost-resistance, photothermoelectric conversion characteristics and their multiple applications in sensing

The utilization of conductive hydrogel-based flexible sensors has garnered significant interest in various fields such as electronic skin, human activity monitoring, and human–machine interaction. Nonetheless, the development of photothermoelectric-responsive conductive hydrogels with excellent mechanical properties, extensive sensing capabilities, and resistance to low temperatures remains a formidable challenge. Herein, a combined electronic and ionic conductive hydrogel named as KMGHCa hydrogel with robust toughness, high stretchability, and photothermoelectric-responsiveness was constructed by integrating two-dimensional MXene (Ti3C2Tx) nanosheet into a gellan gum/ poly(N-hydroxyethyl acrylate) matrix in calcium chloride solution via heating–cooling-photopolymerization. The incorporation of MXene into the hydrogel not only imparted remarkable photothermal characteristics under near-infrared (NIR) light irradiation, but also functioned as a crosslinking agent and conductive additive. The as-prepared hydrogels exhibited outstanding mechanical property (tensile stress of 1463 %, tensile strain of 1008 kPa), attractive conductivity (2.07 S/m) and anti-freezing ability simultaneously. The sensor constructed by KMGHCa hydrogel exhibited a broad sensing range spanning from 0 % to 400 %, high sensitivity with a gauge factor of 4.40, and outstanding photothermoelectric conversion characteristics (photothermal conversion efficiency of 93.6 %, thermoelectric sensitivity of −0.41 %/°C, and photoelectric responsivity of 9 mA/W), which also widely applied to various applications, including monitoring various human behaviors, self-powered triboelectric nanogenerators, and NIR light-responsive photothermoelectric detector. Therefore, this work provided a general route for generating multifunctional hydrogels toward applications in motion monitoring sensors, energy harvesting devices, photothermoelectric detection systems.