Ionically conductive hydrogels have attracted considerable attention as multifunctional materials for flexible electronics and energy storage devices. Conventional hydrogels suffer from excessive swelling in aqueous environments, which compromises the mechanical integrity and hydrogel functionality, limiting underwater applications of the devices. Additionally, freezing of water at subzero temperature leads to loss of hydrogel functions and limits the operating temperature of the device. Here, we report a physically cross-linked poly(vinyl alcohol) (PVA) hydrogel reinforced with polystyrenesulfonate (PSS) confined in the PVA network through in situ polymerization. Crystalline domains in PVA formed through repeated freeze–thaw cycles, together with strong interpolymer hydrogen bonding interactions, provide a robust network integrity without the need for toxic chemical cross-linkers. Incorporation of PSS markedly enhances the mechanical performance, yielding a 55-fold increase in strength, a 33-fold increase in stiffness, and a 60-fold increase in toughness, while maintaining flexibility (fracture strain ∼210%). The presence of abundant sulfonate groups not only promotes water retention and antifreezing capability but also facilitates efficient ion transport, achieving an ionic conductivity of 10.8 mS/cm. The strong ionic interaction with sulfonate ions prevents Na+ ions from diffusing out of the hydrogel matrix and maintains conductivity even after prolonged exposure to aqueous environment. When the composite PVA–PSS hydrogel was employed as a solid electrolyte in a flexible supercapacitor, the device exhibited a specific capacitance of 100 F/g at 0.5 A/g, with ∼87% capacitance retention after 1000 GCD cycles. The device maintained significant electrochemical performance even at −15 °C. Furthermore, leveraging its fast and efficient self-recovery properties and swelling-resistant capability, the hydrogel was integrated into resistive sensors capable of reliably detecting human motions (finger, elbow, and wrist bending) in ambient, aqueous, and subzero environments. These results demonstrate the potential of PVA–PSS hydrogels as high-performance solid-state electrolytes and functional components for next-generation wearable and low-temperature flexible electrochemical devices.
Maity et al. (Tue,) studied this question.