Quenched Polyampholyte Hydrogels for Low-Temperature Energy Storage and Energy-Saving Smart Window Applications

Quenched polyampholyte hydrogel is a tough hydrogel with self-healing ability, strong adhesion, and mechanical flexibility. Structure studies of polymer chains and water molecules in hydrogels made of a charge-balanced polyampholyte, a random copolymer of NaSS-co-MPTC, by SAXS and WAXS, respectively, suggested a networked globule structure in the charge-balanced polyampholyte hydrogels prevented freezing of water in the hydrogel, resulting in 'slush-like' ice formation. The amorphous water was confirmed at –45 °C was by solid-state ²H NMR. We also observed high ionic conductivity at low temperatures using EIS. Utilizing the scientific investigations, a flexible and self-healing supercapacitor with high energy density in low temperature operation was fabricated using a polyampholyte hydrogel electrolyte. At -30°C, the supercapacitor exhibited an energy density of 10.5 Wh/kg at a power density of 500 W/kg. We also modulated the overall hydrophilicity/phobicity of polyampholyte chains when synthesizing the random copolymer and adjusted the upper critical solution temperature (UCST) at high precision. Finally, we developed a stretchable, high-contrast, optically tunable stretchable smart window for energy saving applications.