Freezing-Tolerant Hydrogel Composed of Sulfonated Chitosan and Poly(vinyl alcohol) Featuring Excellent Stretchability and High Proton Conduction

Antifreezing and highly proton-conductive hydrogels show promising applications in flexible electrochemical devices owing to their inherent stretchability and safety. In this study, we chose an ethylene glycol/water (EG/H2O) binary mixture as the solvent, sulfonated chitosan (CS-SO3H) as the proton-conducting component, and the blend of CS-SO3H and poly(vinyl alcohol) (PVA) as a gelator to prepare double-network hydrogels, CS-SO3H@PVA-X (X represents the mass ratio of CS-SO3H and PVA with a value of 0, 0.5, 1.0, and 1.5), which are characterized by different techniques, including microanalysis, IR, 1H and 13C NMR spectra, TG, PXRD, and so on. CS-SO3H@PVA-X hydrogels exhibit excellent tensile strength, toughness, and a freezing-tolerant feature. Importantly, CS-SO3H@PVA-1.5 hydrogel displays not only high proton conduction in a wide range of temperatures from -35 to 70 °C, with proton conductivities of 7.2 × 10-4 S cm-1 at -35 °C and 4.56 × 10-2 S cm-1 at 70 °C and ambient humidity, but also exceptional mechanical performance, with a tensile strength of 3.11 MPa and an elongation at break of 423%, indicative of a potential application in electrochemical devices relying on proton transport and operating at extreme conditions. It is also discovered for the first time that the double-network micelles are entangled together to form the spiral crimped texture in hydrogels CS-SO3H@PVA-X (X = 1.0 and 1.5).