An Anti-Freezing Ionic Conductive Hydrogel for Strain Sensing and Energy Harvesting Devices.

Hydrogels with excellent flexibility and conductivity have attracted intensive attention in wearable human monitoring and energy harvesting devices. However, hydrogels containing plenty of water inevitably freeze at subzero temperatures, which deteriorates flexibility and conductivity and limits their practical applications. Herein, an anti-freezing ionic conductive hydrogel is developed by introducing Na+ into the gellan gum/hydrophobically associated polyacrylamide double network. The optimized anti-freezing hydrogel AICH3 achieves outstanding mechanical properties (fracture stress 1.1 MPa and fracture strain 1700%), remarkable conductivity (2.2 S/m), and impressive strain sensitivity (GF = 7.4) at -20 °C. Benefiting from excellent flexibility, conductivity and strain sensitivity, the assembled AICH3-based strain sensor can accurately sense the bending movement of the bionic finger at -20 °C. In addition, the AICH3 can also be used as a stretchable electrode of a triboelectric nanogenerator (TENG), and the assembled AICH3-based TENG can effectively harvest energy and power electronic devices at -20 °C. The comprehensive mechanical and conductive properties of AICH3 at subzero temperatures might be attributed to the multifunctionality of Na+, which not only promotes the fabrication of physically crosslinked gellan gum/hydrophobically associated polyacrylamide double network but also suppresses the formation of ice crystals.