A hydrogel electrolyte is an ideal material for flexible energy storage equipment owing to its mechanical flexibility similar to solids and its ion transport ability analogous to liquids. However, a traditional hydrogel electrolyte cannot be remolded after forming and cannot be reused after dehydration. In addition, the traditional hydrogel electrolyte cannot work in a subzero environment. Here, the poly(vinyl alcohol)/sodium alginate/poly(ethylene glycol) (PVA/SA/PEG) organohydrogel electrolyte was successfully fabricated by a freezing−thawing process followed by soaking in a saturated NaCl aqueous solution. PEG could improve the mechanical property and endowed the organohydrogel with an excellent recyclability and healing ability. Meanwhile, PEG and NaCl in the organohydrogel also endowed the gel with lowtemperature resistance. A new solution was provided to store and transport hydrogels by virtue of the good rehydration properties after the drying process. The flexible all-solid-state supercapacitor was fabricated by using activated carbon as the electrode and PVA/SA/PEG as the gel electrolyte. The flexible supercapacitors presented high areal capacitances of 103.6 mF cm −2 at 2 mA cm −2 at room temperature and 91.5 mF cm −2 at −15 °C. It is believed that the PVA/SA/PEG organohydrogel electrolyte with outstanding flexibility, freezing resistance, recyclability, and high ionic conductivity is a promising candidate for the next-generation flexible energy storage devices.

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Thermochromic smart windows are considered to be promising energy-saving devices for reducing energy consumption in buildings. The ideal materials for thermochromic smart windows should have high transmittance, high solar modulation, low phase-transition temperature, and excellent high-temperature thermal stability, which are difficult to achieve simultaneously. This work reports a simple one-step low-temperature polymerization method to prepare a thermo-responsive poly(N-isopropylacrylamide)/hydroxypropylmethyl cellulose (PNIPAM/HPMC) hydrogel achieving the above performances simultaneously. The low-temperature polymerization environment endowed the hydrogel with a high luminous transmittance (T lum) of 90.82%. HPMC as a functional material effectively enhanced the mechanical properties and thermal stability of the hydrogel. Meanwhile, the PNIPAM/HPMC hydrogel showed a low phase-transition temperature (∼32 °C) and high solar modulation (ΔT sol = 81.52%), which proved that it is an ideal material for thermochromic smart windows. Moreover, a PNIPAM/HPMC smart window exhibited high light transmittance (T 380–760 = 86.27%), excellent light modulation (ΔT 365 = 74.27%, ΔT 380–760 = 86.17%, and ΔT 940 = 63.93%), good indoor temperature regulation ability and stability, which indicated that it was an attractive candidate for application in reducing energy consumption in buildings. This work also provides an option and direction for modifying PNIPAM-based thermochromic smart windows.

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